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Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 469 Management of scour and other hydraulic actions at highway structures. (formerly BD 97/12) Version 1.0.0 Summary This document provides requirements and advice for the management of scour and other hydraulic actions at structures. This document provides processes, to determine the level of risk associated with structural damage, caused by scour and other hydraulic actions on structures in severe weather events. This document includes allowances for climate change. This document provides advice on mitigating actions which could potentially reduce risks, caused by scour and other hydraulic actions on structures. National Variation This document has associated National Application Annexes providing alternative or supplementary content to that given in the core document, which is relevant to specific Overseeing Organisations. National Application Annexes are adjoined at the end of this document. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated National Highways team. The online feedback form for all enquiries and feedback can be accessed at: www.standardsforhighways.co.uk/feedback. This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Contents Release notes 4 Foreword 5 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Introduction 6 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Bridges over rivers - structural failure and collapse mechanism . . . . . . . . . . . . . . . . . . . . . . 6 Climate change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Structural consequences due to scour and other hydraulic actions . . . . . . . . . . . . . . . . . . . . 6 Resilience of the road network to flood-induced bridge failures . . . . . . . . . . . . . . . . . . . . . . 6 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Abbreviations and symbols 8 Terms and definitions 13 1. Scope 37 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Aspects covered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Aspects not covered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Use of GG 101 and GG 104 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Competent persons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2. Inspection and assessment process 40 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Scour susceptible structures Type 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Scour inspection process - scour susceptible structures Type 1 . . . . . . . . . . . . . . . . . . . . . . 52 Scour Level 1 assessment process - scour susceptible structures Type 1 . . . . . . . . . . . . . . . . 54 Scour Level 2 assessment process - scour susceptible structures Type 1 . . . . . . . . . . . . . . . . 54 Scour susceptible structures Type 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Scour inspection process - scour susceptible structures Type 2 . . . . . . . . . . . . . . . . . . . . . . 55 Scour evaluation process - scour susceptible structures Type 2 . . . . . . . . . . . . . . . . . . . . . . 57 Immediate risk scour susceptible structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3. Inspection of scour susceptible structures 58 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Data updating for scour susceptible structures Type 1 - scour Level 1 assessment . . . . . . . . . . . . . . 59 Inspection and data gathering for scour susceptible structures Type 1 - scour Level 2 assessment . . . . . 60 Inspection and data gathering for scour susceptible structures type 2 . . . . . . . . . . . . . . . . . . . . . . 62 4. Level 1 assessment of scour susceptible structures Type 1 64 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Scour Level 1 assessment process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 Scour Level 1 assessment process - assessment of the risk of woody debris accumulations . . . . . . 71 Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 5. Level 2 assessment of scour susceptible structures Type 1 74 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Scour Level 2 assessment process Type 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Priority factor Type 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Calculation of assessment flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Fluvial component of the assessment flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 1 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Contents Tidal component of the assessment flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Calculation of depth of flow and velocity of flow upstream of structure . . . . . . . . . . . . . . . . . . . . . 83 Calculation of the flood plain factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Calculation of depth of flow and velocity of flow through structure opening . . . . . . . . . . . . . . . . . . . 96 Calculation of maximum depth of flow at upstream face of structure . . . . . . . . . . . . . . . . . . . . . . 101 Calculation of scour depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Calculation of constriction scour depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Calculation of mean threshold velocity of flow through the bridge opening, due to constriction scour . . 102 Calculation of the additional area of flow through the bridge opening, due to constriction scour . . . . 107 Calculation of maximum depth of constriction scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Calculation of local scour depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Calculation of total scour depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Comparison of total scour depth with foundation depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Determination of scour risk rating and scour risk score . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 Assessment of stability and lateral movement of stream or river channel . . . . . . . . . . . . . . . . . . . . 123 Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 6. Assessment of vulnerability of structures to other hydraulic actions 127 Vulnerability assessment process - scour Level 2 assessment . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 7. Evaluation of scour susceptible structures Type 2 129 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Scour priority ranking process Type 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Priority ranking Type 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Priority ranking and scour risk rating Type 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 Scour evaluation and scour risk rating updating process Type 2 . . . . . . . . . . . . . . . . . . . . . . . . . 132 Scour evaluation - evaluation of the risk of structural damage . . . . . . . . . . . . . . . . . . . . . . . 132 Scour risk rating updating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 8. Risk management of scour and other hydraulic actions at structures 134 Site-specific scour risk assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Scour risk register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Scour risks management plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Severe weather event management plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Routine maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Protection of structures against scour and other hydraulic actions . . . . . . . . . . . . . . . . . . . . . . . . 137 9. Document management for scour susceptible structures 139 10. Normative references 141 11. Informative references 142 Appendix A. Woody debris accumulations - rigorous method for estimation of debris factor 143 A1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 A2 Estimation of debris accumulation size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 A2.1 Design debris length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 A2.2 Debris Froude number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 A2.3 Debris accumulation size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 A3 Calculation of debris factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 A3.1 Debris blockage area ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 A3.2 Relative flow depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 A3.3 Cross-section of debris accumulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 2 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Contents Appendix B. Woody debris accumulations - estimation of debris factor worked examples 147 B1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 B2 Case study No. 1 on Steps Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 B2.1 Case study No. 1 - simplified method for Steps Bridge . . . . . . . . . . . . . . . . . . . . . . . . 147 B2.2 Case study No. 1 - rigorous method for Steps Bridge . . . . . . . . . . . . . . . . . . . . . . . . . 153 B3 Case study No. 2 on Abbey Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 B3.1 Case study No. 2 - simplified method for Abbey Bridge . . . . . . . . . . . . . . . . . . . . . . . . 153 B3.2 Case study No. 2 - rigorous method for Abbey Bridge . . . . . . . . . . . . . . . . . . . . . . . . 159 3 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 469 1.0.0 April 2024 Core document, England NAA, Northern Ireland NAA, Scotland NAA, Wales NAA Change to policy, major revision, new document development CS 469 replaces BD 97/12. This document has been rewritten to make it compliant with the new National Highways drafting rules. The major technical updates in this document include: (1) the definition of scour susceptible structure has been amended to also include: (a) structures on the floodplain but not over or adjacent to water; and (b) structures at a location [not over or adjacent to water] where significant surface water flooding has occurred; (2) the scope has been clarified for scour and other hydraulic actions on structures, including: (a) scour in non-tidal rivers, tidal rivers and estuaries; (b) horizontal and vertical forces on structures due to hydraulic actions; (c) debris accumulations at structures; and (d) flood flows caused by rapidly melting snow; (3) the scour Level 1 assessment process has been updated; (4) the scour Level 2 assessment process has been updated; (5) the method for calculating the peak flow rate at a structure has been updated, including the fluvial component and tidal component of the assessment flow and the catchment response time; (6) the climate change allowances have been updated, so they are in accordance with UKCP18 climate change allowances published for the UK; (7) a requirement to assess the consequences on stream or river flow rates due to very rapid melting of snow (in the catchment upstream of a structure) after severe winter weather, has been introduced; (8) the method for estimation of scour depth now also includes implementation of the results from University of Southampton and University of Exeter research projects on scour caused by woody debris accumulations close to a structure in a stream or river; (9) the assessment of vulnerability of the structure to other hydraulic actions has been updated; (10) the assessment of channel stability has been updated; (11) management of risk due to scour and other hydraulic actions on a structure has been updated; and (12) a requirement for a scour assessment certificate to be completed, for a scour Level 2 assessment, has been introduced. Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change 4 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Foreword Foreword Publishing information This document is published by National Highways. This document supersedes BD 97/12 and IAN 173/13, which are withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 5 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Introduction Introduction Background Scour and other hydraulic actions are the main causes of bridge failures and collapses in the UK and internationally. With storms in the UK expected to become both more severe and more frequent as a consequence of climate change, there is a need to provide updated requirements and advice, so that there is an enhanced understanding of the potentially increased structural risks to bridges and other structures, due to severe weather events. Extreme scour and other hydraulic actions could potentially occur at a structure during a severe weather event and cause structural damage and loss of life. The aim is to avoid failure and collapse of structures, due to scour and other hydraulic actions. Bridges over rivers - structural failure and collapse mechanism A bridge failure and collapse, due to hydraulic actions during a severe weather event, can be caused by a combination of factors, which include (but are not limited to): 1) very high flow rate – large horizontal forces (very much larger forces than in normal flow conditions) on the bridge piers, abutments, retaining walls and deck; 2) scour of the river bed – undermining the structure foundations; and, 3) flotation of the bridge deck – causing uplift on the bridge piers. Climate change Climate change can significantly increase the risk of structural failure and collapse, especially with regard to scour and other hydraulic actions on structures during severe weather events. Structural consequences due to scour and other hydraulic actions Potential structural consequences due to scour and other hydraulic actions include (but are not limited to): 1) collapse of a structure such as a bridge can result in fatalities; 2) failure or collapse of a structure such as a bridge over a river can result in community severance issues and severe traffic disruption on emergency diversion routes over a period of weeks or months; 3) failure or collapse of a structure such as a bridge over a river can cause loss of utilities such as electricity supply, potentially resulting in severe disruption to residents and businesses over a period of weeks or months; 4) structure whole-life costs can be significantly increased; and, 5) the life of the structure can be reduced. Resilience of the road network to flood-induced bridge failures After the November 2009 flood event, the Cumbria region in England incurred significant cost for reconstructing its infrastructure (including replacement of collapsed bridges and major repairs to structural damage at bridges). However, the economic costs to local communities were also very significant (such as the increased travel time due to collapsed bridges, or bridges that were closed due to severe structural damage). There is a need to better understand the risks associated with the failure or limited serviceability of bridges, following a severe weather event. Whilst inspection, assessment, monitoring, hydraulic analysis and structural analysis can help identify structures that are potentially susceptible to failure due to hydraulic actions, it is also necessary to understand the implications of their failure on the wider transport network. Therefore, there is a need to enhance: 6 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Introduction 1) risk-based decision making and prioritisation of funding for inspection, assessment, monitoring, maintenance and upgrading works on scour susceptible structures; and, 2) the resilience of the motorway and all purpose trunk road network to severe weather events, especially with regard to scour and other hydraulic actions on all types of structures. Safety There is a continuing need to ensure that scour and hydraulic actions safety concerns, risks and issues are reduced to a level "so far as is reasonably practicable" (SFAIRP) [Health & Safety at Work etc Act 1974 Part 1 Sections 2 and 3 (1) UKPGA 1974/37 (HSWA) [Ref 6.N]; Highways Act 1980 Part IV Section 41 [ref. UKPGA 1980/66 [Ref 7.N]]; and Infrastructure Act 2015, Part 1 Section 5 UKPGA 2015/07 [Ref 8.N]. Purpose There is a need to quantify and manage risks due to scour, and other hydraulic actions on structures, in an effective, timely and consistent manner, then to prioritise and implement mitigating actions to reduce risks to a level "so far as is reasonably practicable" (SFAIRP). Therefore, the purpose of this document is to provide: 1) requirements and advice for the inspection, assessment and monitoring of scour at scour-susceptible structures; 2) the process to determine the scour risk rating and scour risk score for scour-susceptible structures; 3) advice on mitigating actions which, when implemented, can potentially reduce risks to affected populations caused by scour and other hydraulic actions in severe weather events; 4) advice on mitigating actions which, when implemented, can potentially reduce risks to structures caused by scour and other hydraulic actions in severe weather events; and, 5) climate change allowances, to be used in the assessment of the effect of scour and other hydraulic actions on structures in severe weather events. More detailed guidance on scour at structures is provided in CIRIA C742 [Ref 11.I]and CIRIA SP171 [Ref 12.I] Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 10.N] and GG 104 [Ref 15.N] apply to this document. 7 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Abbreviations and symbols Abbreviations and symbols Abbreviations Abbreviation Meaning AEP Annual exceedance probability SFAIRP So far as is reasonably practicable AMAX Annual maximum SWE IWWL Severe weather event, intervention warning water level. Refer to clause 8.11.2. QMED The index flood Symbols Symbol Meaning A Cross-sectional area of flow AB Cross-sectional area of the bridge opening. For example, this is the cross-sectional area from the soffit of the opening down to the channel bed, between two bridge piers. ABy Cross-sectional area of flow through the bridge opening without constriction scour, based on yB, but no greater than AB. AD Debris frontal area An Cross-sectional area of flow corresponding to the normal depth Au Cross-sectional area of flow upstream of the bridge NOTE: this is before the start of the afflux. Auf Cross-sectional area of flow at upstream face of the bridge B Average width of the channel. Refer to Figure 3.9. BB Average width of the channel at the bridge opening Bu Average width of the channel upstream of the bridge. Refer to Figure 5.33.2. C Communities importance factor CAF Communities additional factor D Debris accumulation factor DAV Average depth of the channel; that is the vertical distance between the average bank level and the average bed level. Refer to Figure 3.9. Dc Maximum constriction scour depth Dc,abutment Maximum constriction scour depth adjacent to an abutment Dc,ave Average depth of constriction scour below the original channel bed level Dc,pier Maximum constriction scour depth adjacent to a pier 8 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Abbreviations and symbols Symbols (continued) Symbol Meaning Dc,rwall Maximum constriction scour depth adjacent to a retaining wall DF Distance below average bed level to the underside of the spread footing foundation, or to or to the underside of the pile cap in the case of a piled foundation. Refer to Figure 3.9. NOTE: DF can be different at each bridge pier, abutment and retaining wall. Dl Maximum local scour depth Dl,abutment Maximum local scour depth adjacent to an abutment Dl,pier Maximum local scour depth adjacent to a pier Dl,rwall Maximum local scour depth adjacent to a retaining wall DMAX Maximum depth of the channel, relative to the lowest bank level. Refer to Figure 3.9. DR Relative scour depth DT Total scour depth dmgs Stream or river channel bed median grain size. Refer to Table 5.45.2. dsr Debris size ratio E Specific energy of open channel flow. Refer to Equation 5.34.3. e Euler's number is a mathematical constant, approximately equal to 2.71828. Euler's number is an irrational number, because it cannot be represented as a ratio of integers. F Foundation type factor Fp Flood plain factor Fr Froude number F rD Debris Froude number Fs Constriction scour distribution factor fP A Pier angle of attack factor, depending on the angle of attack of the flow on the pier fP S Pier shape factor, depending on the shape of the pier fy Depth of flow factor, depending on the relative depth of the approach flow to the pier width fd Debris factor, depending on the debris accumulation at the structure GL Land gradient factor g Acceleration due to gravity (9.81 m/s2 ) HD Height of debris accumulation 9 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Abbreviations and symbols Symbols (continued) Symbol Meaning HS History of scour occurrence factor hd Flow depth underneath the debris accumulation he Loss of energy Hsoff Height of the structure soffit above the river bed, at the upstream face of the structure KD Upstream length of debris accumulation K1, K2, K3 Debris equation factors, defined in Appendix A L Bridge pier length LD Design debris length M Ground material factor n Manning's coefficient P Length of the wetted perimeter of the flow cross-section PF-T1 Priority factor Type 1 PR-T2 Priority ranking Type 2 Q Flood flow QA Assessment flow for a severe weather event with a stated AEP calculated using: 1) the latest available weather event data, flood event data, historical data and tidal data; and, 2) the climate change allowances for the structure location. NOTE: Refer to the relevant National Application Annex. QF Fluvial component of the assessment flow. NOTE: Refer to the relevant National Application Annex. QT Tidal component of the assessment flow at a specific time of day QTide Peak tidal flow, based on the average tidal range. NOTE: Refer to the relevant National Application Annex. QTide,max Maximum tidal flow, based on the maximum tidal range. NOTE: Refer to the relevant National Application Annex. s Stream or river bed gradient. NOTE: Refer to the "Terms and definitions" table for the definition of "Stream or river bed gradient". sc Critical longitudinal slope of the channel sL The average gradient of land within 100 m of a scour susceptible structure Type 2 10 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Abbreviations and symbols Symbols (continued) Symbol Meaning TR Type of river factor TTide Tidal period VTide Volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the tidal range (in m), in m3 VTide,av The volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the average tidal range (in m), in m3 /s. NOTE: Refer to the relevant National Application Annex. VTide,max The volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the maximum tidal range (in m), in m3 /s. NOTE: Refer to the relevant National Application Annex. v Mean velocity of flow vB Mean velocity of flow through the bridge opening vB,c Mean threshold velocity of flow through the bridge opening, below which scour does not occur vc Critical velocity of flow for minimum energy conditions vcomp Competent mean velocity of flow vn Mean normal velocity of flow for uniform flow conditions vu Mean velocity of flow upstream of the bridge NOTE: This is before the start of the afflux. W Flood plain width; this is the anticipated extent of flooding following a 0.5% AEP weather event. WD Width of debris accumulation Weff Effective flood plain width Weff,L Effective width of the left flood plain Weff,R Effective width of the right flood plain WL Flood plain width on left side of river (when looking downstream), that is the anticipated extent of flooding upstream of bridge following a 0.5% AEP weather event WP Bridge pier width WR Flood plain width on right side of river (when looking downstream), i.e. the anticipated extent of flooding upstream of bridge following a 0.5% AEP weather event y Depth of flow 11 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Abbreviations and symbols Symbols (continued) Symbol Meaning yB Depth of flow through the bridge opening yB,sub Depth of flow through the bridge opening, for sub-critical flow conditions yB,sup Depth of flow through the bridge opening, for super-critical flow conditions yc Critical depth of flow for minimum energy conditions yn Normal depth of flow for uniform flow conditions yp Height of normal flow above flood plain level ysp Depth of flow at the pier including constriction scour yu Depth of flow upstream of the bridge NOTE: This is before the start of the afflux yuf Depth of flow at upstream face of the bridge z Height of river channel bed above datum α y Coefficient for flood plain effect on depth of flow α v Coefficient for flood plain effect on velocity of flow α Angle between the direction of flow and the bridge pier longitudinal centre-line, angle of attack. Refer to Figure 5.49.1b. β Internal angle of triangular shaped bridge pier. Refer to Figure 5.49.1a. ∆A Increase in cross-sectional area of flow through the bridge opening, due to constriction scour ∆A% Debris blockage area ratio 12 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions Terms and definitions Term Definition Affected populations Affected populations include: 1) road users; 2) road workers; 3) any other persons on, or close to, the highway; and, 4) any persons on, or close to, Overseeing Organisation land. Afflux Afflux is the maximum difference in water level, at a location upstream of the structure, if the structure were removed. Annual exceedance probability (AEP) The annual exceedance probability (AEP) is the inverse of the annual maximum (AMAX) flood return period of a weather event, based upon statistical records. NOTE 1: The return period of a flood on the AMAX scale is the average interval between AMAX floods of that magnitude. NOTE 2: QMED is the index flood, which is the median of the set of the AMAX flood data. It is the flow that has an AEP of 50%, or a return period of two years. Refer to the method for calculating the fluvial component of the assessment flow QF . Assessment flow The assessment flow QA is the peak flow rate at the structure to be used for the assessment, calculated for the 0.5% annual exceedance probability (AEP) weather event, using the latest available weather event data, flood event data, historical data and tidal data, including: 1) river flow (fluvial) component; 2) overland flow (pluvial) component; 3) tidal component (if appropriate); and 4) climate change allowances (for the structure location). 13 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Average tidal range The average of the mean spring tidal range and mean neap tidal range, at a specific location. In this document, the average tidal range is the sum of two components: 1) the present day average tidal range; and, 2) the climate change allowance for total potential increase in sea level, determined in accordance with the relevant National Application Annex. Catchment response time The length of time between a severe weather event occurrence in the catchment upstream of a structure and flood water arriving at the structure, which depends upon the catchment characteristics upstream of the structure. NOTE 1: A table defining the time period for very short, short, medium and long catchment response times, is provided in the relevant National Application Annex. Channel stability risk rating As part of a scour Level 2 assessment, the stability and lateral movement of a stream or river channel is assessed and the channel stability risk rating is determined, as either low, medium, or high risk. Chart datum Chart datum is a reference level for use in tidal tables, and can be approximately the lowest sea water level at a specific location, due to astronomical effects and excluding meteorological effects. The chart datum at a specific location is a reference level relative to the country specific datum. NOTE 1: The height of chart datum (CD) at a specific location in the UK relative to a country specific datum, can be negative, indicating that the chart datum is below the country specific datum. NOTE 2: The country specific datum is provided in the appropriate National Application Annex for CS 469. 14 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Climate change allowances The predictions by the responsible government body for each nation, of anticipated change at a specific location, due to climate change, for: 1) peak river flow (fluvial flow); 2) peak rainfall intensity (causes pluvial flow/surface water flow); 3) sea level rise; and, 4) offshore wind speed and extreme wave height. For each of these four categories, the climate change allowances vary according to the location in the UK. NOTE: Refer to the appropriate National Application Annex for CS 469, for information on location- specific climate change allowances. Competent civil engineer or structural engineer The competent civil engineer or structural engineer is a named person, in a defined region or area, or a scheme area, as described in clauses 1.14 and 1.15. Constriction scour Scour associated with the increased flow velocity at a horizontal constriction in the channel. Country specific datum A vertical datum, or height datum, used as the basis for deriving altitudes on maps. NOTE: The country specific datum is provided in the appropriate National Application Annex for CS 469. Critical flow Critical flow occurs when the actual flow depth is equal to the critical flow depth, y = yc . Critical flow has a Froude number FR = 1 . The critical flow corresponds to the minimum energy a flow can possess for a given discharge. Debris accumulation A complex, dynamic and irregular accumulation of material in water, ranging in size from very small to very large items, which can result in a partial or total blockage to water flow. NOTE 1: In this document, it is assumed that in a stream or river in the UK: 1) woody debris accumulations are the most frequently occurring type of debris accumulation: and, 2) other debris accumulations are not a frequently occurring type of debris accumulation. 15 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Defined distance from the structure The defined distance from the structure is measured in all directions from the extremities of the structure, not measured from the centre of the structure. Refer to Table 3.12 (scour susceptible structure Type 1) and Table 3.15 (scour susceptible structure Type 2). Ebb tide The ebb tide is the tidal phase during which: 1) the tidal current is flowing seaward, or towards the sea (ebb current); and, 2) the water level is falling. Emergency structural inspection An emergency structural inspection of the structure, above and below water level, including an underwater inspection, is described in clause 1.11. NOTE: The frequency of emergency structural inspections of the structure is provided: 1) in Table 2.8 for scour susceptible structures Type 1; and 2) in Table 2.20 for scour susceptible structures Type 2. Emergency structural inspection report A report prepared after an emergency structural inspection of a structure, immediately after a severe weather event, to investigate structural damage due to one or more of the following situations occurring: 1) other debris accumulation; 2) tidal action, including storm tides; 3) storm surges (including water flowing in a river in an upstream direction); 4) ocean or sea scour; 5) propagating ocean or sea storm surges; 6) coastal wave action; or, 7) coastal flooding. Flash flooding Flash flooding is surface water flow/overland flow, occurring during a severe weather event with a stated AEP. The flash flooding flow rate, velocity of flow and depth of flow are defined by the severe weather event with a stated AEP. 16 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Flood event An overflow of water onto an area of land which is usually dry. A flood event includes any situation where land not normally covered by water becomes covered by water. A flood event at a structure includes any situation where a rising water level, or fast flowing water, can cause undesirable consequences to occur. A flood event in a structure includes any situation where water flowing into the structure, or water overflowing in the structure, can cause undesirable consequences to occur. Flood plain The areas of land identified by the responsible government body for each nation as at risk of flooding from streams, rivers, rainfall and groundwater. The limits of the flood plain are defined by the peak water level occurring during a severe weather event with a 0.5% AEP. NOTE 1: Refer to the appropriate National Application Annex for CS 469, for information on country-specific flood risk maps. NOTE 2: A flood plain can be large flat areas of land that a river floods onto, when the flow rate in the river exceeds bank-full capacity. Flood risk map A map prepared by one of the responsible bodies for each nation, which shows the areas of land at risk of flooding, for a 0.5% AEP flood risk, due to specified sources of flooding: 1) rivers and sea; 2) reservoirs; or, 3) surface water. NOTE: Refer to the appropriate National Application Annex for CS 469, for information on country-specific flood risk maps. Flood risk vulnerability classification A classification system by the responsible government body for each nation, that categorises different types of development according to its flood vulnerability. NOTE: Refer to the appropriate National Application Annex for CS 469, for information on flood risk vulnerability classification. 17 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Flood tide The flood tide is the tidal phase during which: 1) the tidal current is flowing inland, or towards the land (flood current); and, 2) the water level is rising. Flow control structure A structure which controls the flow of water, which can affect the flow rate, or water level, upstream or downstream of the flow control structure, including (but not limited to): 1) a reservoir outflow structure; 2) a flood control structure; and, 3) a flood defence structure. A flow control structure can be operated: 1) automatically by remote control; 2) manually by remote control; 3) automatically by electrical and mechanical equipment at the flow control structure location; or, 4) manually by an operative visiting the flow control structure. Froude number F r = √v gy where: F r is the Froude number v is the velocity of flow, in m/s g is the acceleration due to gravity (9.81 m/s 2 ) y is the depth of flow, in m Geotechnical asset The man-made or natural earthworks and geotechnical structures below the road pavement layers, highway structures and the adjacent land, within the Overseeing Organisation land boundary. NOTE 1: A geotechnical asset includes, but is not limited to: 1) an embankment; 2) a cutting; or, 3) a bund. NOTE 2: Refer to DMRB CD 622 [Ref 12.N] and CS 641 [Ref 13.N]. 18 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Hydraulic actions Hydraulic actions on a structure can occur due to one or more of the following situations occurring: 1) flowing water causing the formation of scour holes near to, or under, the structure; 2) flowing water causing horizontal forces on the structure; 3) water level rising to the soffit of a bridge, or above the soffit of a bridge, causing uplift on the bridge deck; 4) static water causing horizontal forces on the structure; 5) a storm surge causing very high horizontal forces on the structure; or, 6) wave action on the structure. Immediate risk scour susceptible structure An immediate risk scour susceptible structure is a structure that is assessed to be at immediate risk of failure or collapse, based on any combination of: 1) qualitative observations of changes to the stream, river, canal, lake, pond, reservoir, or coast, or changes to the structure; 2) the occurrence of scour or other hydraulic actions likely to affect the stability or integrity of the structure; 3) significant debris accumulation at the structure; 4) damage to the structure, or significant distress at the structure; 5) assessment calculations; and, 6) monitoring of the structure. An immediate risk scour susceptible structure is an unacceptable safety risk to affected populations. An immediate risk scour susceptible structure in this document has a scour risk score of 100. Large catchment The catchment area upstream of the structure is more than 1,000 km2 . Local scour Scour due to effects of the structure on the local flow patterns, disturbing the flow and causing vortices that erode the bed locally. Low-lying catchment An area of land where the altitude of the land in the catchment is no greater than 20 m above the country-specific datum. NOTE: Refer to the appropriate National Application Annex for CS 469, for details of the country specific datum. 19 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Maintaining organisation The organisation appointed by the Overseeing Organisation to manage and operate infrastructure assets on its behalf. Maximum tidal range The tidal range between the highest and lowest astronomical tides that can occur at a specific location. In this document, the maximum tidal range is the sum of two components, each determined in accordance with the relevant National Application Annex: 1) the present day maximum tidal range; and, 2) the climate change allowance for total potential increase in sea level. NOTE 1: The largest tidal range during a 12-month period can be expected around the time of the equinox, in March and in September, if it coincides with a Spring tide. Moderate bend in a stream or river channel A stream or river channel where the change of direction of the stream or river channel is between 10 degrees and 45 degrees. Normal stream or river level The normal stream or river level is the annual average stream or river water level at the upstream face of the structure. Water level records (date, time and depth of water at the upstream face of the structure) are to be kept in the Overseeing Organisation's structures asset management information system. Other debris accumulation A type of debris accumulation in water, formed by a combination of items, where woody debris is not a major part of the debris accumulation. Other debris accumulation can include rocks or boulders carried by the flow of water, or items dumped in the water. Overseeing Organisation land Land which is owned by the Overseeing Organisation, or leased to the Overseeing Organisation. NOTE 1: Overseeing Organisation land can be remote from the motorway or all purpose trunk road network (for example land containing a depot, warehouse building, office building, or lorry parking area). NOTE 2: Overseeing Organisation land can be near to the motorway or all purpose trunk road network (for example land containing a maintenance vehicle access road (that is not public highway), services area, layby or drainage balancing pond. 20 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Principal inspection A type of inspection for highway structures, in accordance with CS 450 [Ref 9.N]. Principal of the assessing organisation A senior representative of the assessor, checker, contractor, or works examiner, having authority to sign certificates on its behalf. Propagating ocean storm surges Propagating ocean storm surges comprise a series of storm surges during a severe weather event, usually accompanied by high coastal waves and severe scour on beaches, or along estuary river banks, or along sea walls. 21 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Scour Scour is the erosion of soil or rock around or below the foundations of a structure, or near to a structure, due to hydraulic action. NOTE 1: Scour can occur in a stream or river bed, or in the sea bed, near a structure such as a bridge, when fast flowing water removes soil or rock from around or below the structure foundation, resulting in scour holes in the stream or river or sea bed. NOTE 2: Scour holes can compromise structural integrity and result in structural failure or collapse. NOTE 3: Scour holes in a stream or river bed, or in the sea bed, can gradually develop over a long period of time, then rapidly increase in depth during a severe weather event, causing sudden structural failure or collapse. NOTE 4: Scour-susceptible structures with shallow underwater foundations (such as a masonry arch bridge over a stream or river) can be at high risk of structural failure or collapse during a severe weather event. NOTE 5: There are several situations that very greatly increase the risk of severe scour near a bridge: 1) dredging or sand/gravel extraction upstream or downstream of bridge; 2) removal of a weir near a bridge; 3) influence of a reservoir, or flood defence structure, or flood control structure; 4) debris accumulation in the water, such as tree branches in the water near to a bridge pier, or boulders & rocks being carried in fast-flowing water. Static debris in the water just below the water surface can cause severe scour depth near a bridge pier, or abutment, or retaining wall, during high flow rate; or, 5) tipping crushed rock into a scour hole. Scour Assessment Certificate A certificate to be prepared, following completion of a scour Level 2 assessment of a scour susceptible structure Type 1, in accordance with clause 5.59. NOTE: refer to the appropriate National Application Annex for CS 469, for details of the country specific Scour Assessment Certificate. Scour assessment record A report prepared as part of a scour Level 1 assessment (scour susceptible structure Type 1) 22 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Scour assessment report A report prepared as part of a scour Level 2 assessment (scour susceptible structure Type 1) Scour emergency inspection A scour emergency inspection of the structure is described in clauses 3.1 to 3.8. NOTE: The frequency of scour emergency inspections of the structure is provided: 1) in Table 2.8 for scour susceptible structures Type 1; and 2) in Table 2.20 for scour susceptible structures Type 2. Scour emergency inspection report A report prepared after a scour emergency inspection of a structure, immediately after a significant flood event. Scour evaluation report A report prepared as part of a scour evaluation (scour susceptible structure Type 2) Scour inspection A scour inspection of the structure is described in clauses 3.1 to 3.8. NOTE: The frequency of scour inspections of the structure is provided: 1) in Table 2.8 for scour susceptible structures Type 1; and 2) in Table 2.20 for scour susceptible structures Type 2. Scour inspection report A report prepared as part of a scour inspection. The scour inspection report provides updated information and data, to be used: 1) in a scour assessment (scour susceptible structure Type 1); 2) in a scour evaluation (scour susceptible structure Type 2); and, 3) for comparison with survey information and data in previous inspection reports. 23 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Scour protection Protection of a scour susceptible structure Type 1 against scour and other hydraulic actions includes civil engineering works permanently installed upstream, alongside and downstream of the structure, within the defined distance from the structure (as provided in Table 3.12, or Table 3.15), which: 1) ensures the scour risk rating is low risk, in a scour Level 2 assessment; and, 2) ensures the channel stability risk rating is low risk, in a scour Level 2 assessment. Scour risk assessment A site-specific risk assessment for a scour susceptible structure, which includes: 1) risks to affected populations, due to scour and other hydraulic actions; 2) recommended immediate actions needed to reduce the risks to a level so far as is reasonably practicable (SFAIRP); 3) recommended actions needed to monitor the risks; 4) recommended interim actions needed to further reduce the risks to a level SFAIRP; and, 5) recommended actions needed to maintain risks at a level SFAIRP. Scour risk rating A designation for the structure, either low, medium, or high risk, determined in accordance with: 1) Table 2.3 and Section 4 or 5 (for scour susceptible structures Type 1) of this document; and 2) Section 7 of this document (for scour susceptible structures Type 2). Scour risk register A risk management tool to enable effective, timely and consistent risk management of scour and other hydraulic actions at structures. Scour risk score A whole number in the range 10 to 100 determined in accordance with Table 2.3 and Section 4 or 5, for a scour susceptible structure Type 1. Scour risks management plan A strategy for an area or a linear route, for scour susceptible structures on the scour risk register, to: 1) ensure that risks are reduced; and, 2) prevent an increase in risks. 24 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Scour susceptible structure Type 1 A structure located over or adjacent to water, including (but not be limited to) structures located over or adjacent to: 1) non-tidal streams, rivers, canals, ponds, lakes and reservoirs; 2) tidal streams, rivers and estuaries; and, 3) the coast and the sea. NOTE 1: Flooding at a structure over or adjacent to water can occur due to one or more of the following situations occurring: 1) a river overtopping the river bank; 2) water flowing through a geotechnical asset, such as a canal bank failure; 3) tidal action; 4) storm surges (including water flowing in a river in an upstream direction); 5) propagating ocean storm surges; 6) coastal wave action; or, 7) sea water flooding on land at, or near to, the coast. NOTE 2: A structure with a scour risk rating 'low risk' remains a scour susceptible structure, in accordance with this document. NOTE 3: The defined distance from the structure is provided in Table 3.12 of this document. 25 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Scour susceptible structure Type 2 A structure: 1) located on the flood plain, but not over or adjacent to water; or, 2) at a location where significant surface water flooding has occurred and there is evidence of ground erosion within the defined distance from the structure. NOTE 1: Flood plain flooding can occur due to one or more of the following situations occurring: 1) a river overtopping the river bank; 2) groundwater rising above ground level; or, 3) rainfall causing surface water overland flow, also known as flash flooding. NOTE 2: Significant surface water flooding can occur due to one or more of the following situations occurring: 1) groundwater rising above ground level; and, 2) rainfall causing surface water overland flow, also known as flash flooding. NOTE 3: a structure with a scour risk rating of 'low risk' remains a scour susceptible structure, in accordance with this document. NOTE 4: the defined distance from the structure is provided in Table 3.15 of this document. Severe weather event A weather event that has the potential to cause one or more of the following situations to occur: 1) harm to affected populations; 2) damage to a structure; 3) damage to other infrastructure assets, including (but not limited to) geotechnical assets and drainage assets; 4) damage to utilities; 5) damage to property; 6) operational issues, such as blocked drains on a road bridge, or blocked drains on a road below a bridge, or blocked drains in an underpass or tunnel, or a blocked watercourse at the top of a cutting; 7) customer service issues, such as delays to traffic, or community severance issues, or loss of utilities in a bridge deck; or, 8) construction and maintenance issues, such as delays to construction and maintenance work. 26 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Severe weather event intervention warning water level (SWE IWWL) A pre-determined water level at the upstream face of a scour susceptible structure, to provide the intervention warning, as part of the severe weather event management plan for the structure. Severe weather event management plan A strategy for a specific scour susceptible structure: 1) to safeguard affected populations and the structure, at all times; 2) to ensure a process is in place for the provision of advance warning to the Maintaining Organisation of severe weather events for the structure location; 3) to ensure emergency actions are planned in advance and can be implemented rapidly if needed during a severe weather event, such as closure of a bridge (to all traffic including pedestrians) and diversion of traffic onto an emergency diversion route; and, 4) to ensure potential emergency works, such as to protect pedestrians from fractured electricity cables or gas pipes in the bridge deck (caused by structural failure), are planned in advance and can be implemented rapidly if needed during a severe weather event. Sharp bend in a stream or river channel A stream or river channel: 1) with a radius of curvature of less than 3 times the top width of the stream or river channel; and, 2) where the change of direction of the stream or river channel is more than 45 degrees. NOTE: The top width of the stream or river channel is the width of the channel between opposite banks, at top of river bank level. 27 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) 28 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions Term Definition Significant flood event An overflow of water onto an area of land which is usually dry and can cause undesirable consequences to occur, including one or more of the following situations occurring: 1) harm to affected populations; 2) damage to a structure; 3) damage to other infrastructure assets, such as drainage assets, or geotechnical assets; 4) damage to utilities; 5) damage to property; or 6) operational issues, such as blocked drains on a road bridge, or blocked drains on a road below a bridge, or blocked drains in an underpass or tunnel, or a blocked watercourse at the top of a cutting. NOTE 1: A significant flood event can result in flooding at a structure. NOTE 2: A significant flood event can result in damage to a structure, with or without flooding occurring at the structure. NOTE 3: a significant flood event can include one or more of the following situations: 1) the water level has risen to within 600 mm of the soffit of a structure where the span is 3 m or more; 2) the water level has risen to the soffit of a structure where the span is up to 3 m; 3) the water level has risen to within 600 mm of the top of a retaining wall, or to within 600 mm of the top of a bridge abutment; 4) flood water has arrived at a structure, with the potential for structural damage to occur; 5) structural damage has occurred at the structure; or 6) a geotechnical asset has been damaged, with the potential for structural damage to occur. NOTE 4: for a scour susceptible structure Type 1, a significant flood event can include one or more of the following situations: 1) the water level has risen to the river bank level on one side of the river, or on both sides of the river; or 2) water has flowed over the river bank on one side of the river, or on both sides of the river. NOTE 5: for a scour susceptible structure Type 2, a significant flood event can include one or more of the following situations: 1) water has flowed over the river bank on one side of the river, or on both sides of the river and has flooded land at the structure; 2) water has overflowed and flooded land at the structure; or 29 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions Significant surface water flooding A type of significant flood event, where one or more of the following situations has occurred at a structure: 1) groundwater rising above ground level; or, 2) rainfall causing surface water overland flow, also known as flash flooding. Sinuosity The sinuosity of a watercourse is the ratio of the length of the channel to the straight line down-valley distance. Small catchment The catchment area upstream of the structure is less than 25 km2 . Specific energy of open channel flow The sum of the static pressure head, the dynamic pressure head and loss of energy, at a specific location in an open channel, such as a stream or river channel. Spring tide A Spring tide occurs at the following times: 1) at, or up to four days after, the time of the new moon, or the full moon, when the Earth, the Moon and the Sun are approximately aligned; and, 2) approximately once every 14 days throughout the year. The tidal range during a Spring tide can be expected to be larger than at other times, at a specific location. Spring tide period The period of time when a Spring tide occurs (a low Spring tide followed by a high Spring tide, or a high Spring tide followed by a low Spring tide), at a specific location. 30 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Storm surge A storm surge is the abnormal rise in sea water level during a storm over the sea, measured as the height of the seawater above the normal predicted astronomical tide. The storm surge is caused primarily by a storm's very strong winds blowing over the surface of the sea, pushing sea water towards the coastline. The height of the storm surge at any given location depends on: 1) the angle of storm impact on the coast; 2) the intensity, size, and speed of the storm; and, 3) the local sea bed profile. High intensity storm – a weather system characterised by low atmospheric pressure at the centre, high average wind speed and high wind speed gusts. Size of the storm – the radius of outermost closed isobar (ROCI). Speed of the storm – the speed at which the weather system moves. Storm tide When a storm surge and a high tide occur at the same time at the same location, the resulting storm surge is often called a storm tide. Due to the much higher sea level, a storm tide has much more devastating consequences for structures at the coast and at areas inland from the coast, than a storm surge occurring with a low tide. Straight reach in a stream or river channel A stream or river channel where the change of direction of the stream or river channel is less than 10 degrees. 31 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Stream or river bed gradient The stream or river channel bed average longitudinal gradient s measured on the channel centre line over an upstream distance of 100 m from the upstream face of the structure is designated in one of the following gradient categories: Very steep. The gradient is steeper than 1 in 10. s > 0.100 s > 10% Steep. The gradient is between 1 in 25 and 1 in 10. 0.040 ≤ s ≤ 0.100 4% ≤ s ≤ 10% Moderate. The gradient is between 1 in 50 and approx 1 in 25.1. 0.020 ≤ s < 0.040 2% ≤ s < 4% Low. The gradient is between 1 in 200 and approx 1 in 50.1. 0.005 ≤ s < 0.020 0.5% ≤ s < 2% Very low. The gradient is not as steep as 1 in 200. s < 0.005 s < 0.5% NOTE 1: These definitions of stream or river bed gradient s are used in the scour Level 1 assessment and scour Level 2 assessment for scour susceptible structures Type 1. NOTE 2: The stream or river bed gradient s can also be stated as being greater than, or less than, the critical longitudinal slope of the channel sc . Structure Any temporary or permanent structure, in accordance with CG 300 [Ref 16.N]. Sub-critical flow Sub-critical flow occurs when the actual flow depth is greater than the critical flow depth, y > yc . Sub-critical flow has a Froude number FR < 1 . Super-critical flow Super-critical flow occurs when the actual flow depth is less than the critical flow depth, y < yc . Super-critical flow has a Froude number FR > 1 . 32 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Team Leader of the assessing organisation The person responsible for overseeing and co-coordinating the work of the scour assessment, or check, team and having authority to sign certificates on behalf of the team. The Team Leader is a competent civil engineer or structural engineer. Third party A third party is: 1) a person who is not working for the Overseeing Organisation; or 2) an organisation that is not working on behalf of the Overseeing Organisation. Note: A third party can be a government department, government-owned company, developer, local authority, statutory undertaker, transport infrastructure owner (such as Network Rail or a ferry operator to an island, or a port authority), private individual, private organisation, or other legal entity which is separate from the Overseeing Organisation. Third party structure A structure that is not owned by the Overseeing Organisation, or leased to the Overseeing Organisation. NOTE 1: A third party structure can be on Overseeing Organisation land (such as a statutory undertaker's telecommunications mast). Tidal location A specific location where the water level varies in accordance with the tidal period and tidal range. Tidal period The period of time between low tide and high tide, or between high tide and low tide, at a specific location. The tidal period is not constant at a specific location. The tidal period at a specific location changes from day to day, depending on the alignment of the Earth, the Moon and the Sun. Tidal range Tidal range is the height difference (change in sea level) between high tide and low tide, at a specific location. The tidal range is not constant at a specific location. The tidal range at a specific location changes from day to day, depending on the alignment of the Earth, the Moon and the Sun. Tide Tide is the rise and fall of sea level caused by gravitational forces exerted by the Moon and the Sun and the rotation of the Earth. 33 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Underwater Inspection An inspection below water level, to determine: 1) the location of scour holes within the defined distance from the structure, for example by a multi-beam echo sounder sonar survey of the river bed, or sea bed; 2) the length, width and depth of a scour hole; 3) the distance from the nearest edge of a scour hole to the structure foundation; 4) any debris in the water within 30m of the structure; 5) any structural damage that has occurred below water level, for example due to scour or other hydraulic actions; and 6) the type and dimensions of an object on the river bed, or sea bed, for example by a side scan sonar survey at the known object location only, as identified during a multi-beam echo sounder sonar survey of the river bed, or sea bed. NOTE: The defined distance from the structure is provided: 1) in Table 3.12 (for scour susceptible structures Type 1 ): and 2) in Table 3.15 (for scour susceptible structures Type 2 ). Vulnerability assessment report A report prepared where required, as part of a scour Level 2 assessment, for a scour susceptible structure Type 1. Water depth marker sign A type of retroreflective sign used to indicate the depth of water, installed on, or no more than 1m from, the upstream face of the structure: 1) at a non-tidal location, use the type D50 design to BS EN ISO 4373; 2) at a tidal location, use the type D53 design to BS EN ISO 4373. The retroreflective grade of material on the sign face is in accordance with BS EN 12899‑1:2015 Class RA2. NOTE: Water depth marker signs are also known as "water level depth gauge boards". 34 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Weir A dam or barrier across the width of a stream or river that alters the flow characteristics of water and usually results in: 1) a change in the height of the stream or river water level; or 2) diversion of the stream or river flow. There are many different designs of weir, but usually water flows freely over the top of the weir crest before cascading down to a lower level. Woody debris Woody debris can include any of the following items: 1) tree branches; 2) tree trunks; 3) tree root boles; 4) entire tree that has fallen into the water; 5) logs; and 6) shrubs or any other type of vegetation. 35 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Terms and definitions (continued) Term Definition Woody debris accumulation A type of debris accumulation in water, formed by a combination of woody debris and other floating objects, usually with woody debris providing a frame that traps other floating objects, where woody debris is a major part of the debris accumulation. NOTE 1: A woody debris accumulation can cause undesirable consequences to occur, including one or more of the following situations occurring: 1) an increase in water level upstream of the debris accumulation; 2) an increased risk of a flood event; 3) scour resulting in severe damage to a structure, or other type of infrastructure asset; and 4) a hazard to navigation on a navigable river. NOTE 2: Woody debris accumulations can adversely affect sediment storage and routing, stream or river bed and bank structure, velocity of flow, and sinuosity of a stream or river. NOTE 3: Scour caused by a woody debris accumulation can occur at any of the following situations: 1) bridge pier in a river; 2) bridge abutment at the river bank; 3) bridge abutment partly in the river; 4) masonry arch bridge (e.g. where debris is unable to pass under the bridge due to insufficient width of arch or insufficient headroom under arch); 5) in a river at the upstream end of a pipe or culvert; 6) retaining wall supporting a river bank; 7) weir; 8) bifurcation of a river; 9) flood control structure; and, 10) flood defence structure. NOTE 4: Woody debris is a recognised form of natural flood management in some streams and rivers. There are potential scour risks at a structure located any distance downstream of purposely placed woody debris in a stream or river [D = 1.1 or 1.3 depending upon the distance along the stream or river from the purposely placed woody debris and the structure location]. 36 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 1. Scope 1. Scope General 1.1 The requirements of this document shall apply to: 1) structures in accordance with DMRB CG 300 [Ref 16.N]; 2) structural temporary works and structural permanent works; and, 3) scour of geotechnical assets, which affect, or can affect, a structure. NOTE 1 The management of risks at a third party structure is normally the responsibility of the third party. NOTE 2 For existing drainage structures, only those within the scope of CG 300 [Ref 16.N] are within the scope of this document. 1.2 This document shall be applicable to: 1) scour susceptible structures Type 1; and, 2) scour susceptible structures Type 2. 1.3 A list of structures within the scope of this document shall be prepared and updated annually for: 1) scour susceptible structures Type 1; and, 2) scour susceptible structures Type 2. 1.4 Where a multi-span bridge is partly over or adjacent to water and partly over the flood plain, the structure shall be designated a scour susceptible structure Type 1. 1.5 The inspection, assessment and risk management of scour and other hydraulic actions at scour-susceptible structures Type 1 and Type 2 shall be carried out, including: 1) scour upstream, alongside/under and downstream of a structure; 2) horizontal forces on structures such as bridge abutments, bridge piers, bridge parapets, retaining walls and uplift on bridge decks, caused by hydraulic actions; and, 3) other hydraulic actions which can occur at the structure, such as woody debris accumulations, and river flood flow caused by rapidly melting snow. Aspects covered 1.6 For all scour-susceptible structures, risks to affected populations must be reduced to a level SFAIRP and maintained at a level SFAIRP, in compliance with legal requirements [Health & Safety at Work etc Act 1974 Part 1 Sections 2 and 3 (1) UKPGA 1974/37 (HSWA) [Ref 6.N]; Highways Act 1980 Part IV Section 41 UKPGA 1980/66 [Ref 7.N]; and Infrastructure Act 2015, Part 1 Section 5 UKPGA 2015/07 [Ref 8.N]. 1.7 Each structure assessed in accordance with this document shall be allocated: 1) scour susceptible structures Type 1 - a scour risk rating (low, medium, or high risk) and a scour risk score; and, 2) scour susceptible structures Type 2 - a scour risk rating (low, medium, or high risk). 1.8 For all scour susceptible structures, mitigating actions shall be determined that can potentially: 1) reduce scour and other hydraulic action risks to a level SFAIRP; and, 2) maintain scour and other hydraulic action risks at a level SFAIRP. 37 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 1. Scope Aspects not covered 1.9 For any scour or other hydraulic actions on a structure, where requirements and advice for the analysis of scour and hydraulic actions on a structure are not provided in this document, the proposed methodology for the hydraulic analysis and structural analysis shall be discussed and agreed with the Overseeing Organisation for the structure, prior to commencement of a scour inspection or scour assessment. 1.9.1 Where either of the following situations is known to occur at a structure, the risks of scour and structural damage can potentially increase, therefore specialist advice should be obtained and any amended method agreed by the Overseeing Organisation prior to commencement of a scour assessment: 1) the water level rises to, or above, the soffit (submerged orifice); or 2) the water level rises above the structure (overtopping of the structure). NOTE At a structure located over or adjacent to water, if the structural opening is of insufficient width and height for the flow, severe turbulence can occur, potentially resulting in increased risks of scour and structural damage when the water level is either: 1) at, or above, the soffit; or 2) at the top of, or above, the structure. 1.10 The methodology for the hydraulic analysis and structural analysis of scour on a structure caused by other debris accumulations, tidal action, and river flood flow caused by rapidly melting snow, is not provided in this document and shall be discussed and agreed with the Overseeing Organisation for the structure, prior to commencement of a scour inspection, or scour assessment, or vulnerability assessment. 1.11 Following a severe weather event where a structure has been subjected to one or more of the actions shown below, potentially resulting in scour or structural damage, an emergency structural inspection shall be carried out and the report sent to the Overseeing Organisation: 1) other debris accumulation; 2) tidal action, including storm tides; 3) storm surges (including water flowing in a river in an upstream direction); 4) ocean or sea scour; 5) propagating ocean or sea storm surges; 6) coastal wave action; or 7) coastal flooding. NOTE 1 The three different types of inspection of scour susceptible structures are shown in Table 2.8 (for Type 1 structures) and Table 2.20 (for Type 2 structures). NOTE 2 Tidal action occurring each day at a structure, without occurrence of a severe weather event, does not necessitate an emergency structural inspection to be carried out. Implementation 1.12 This document shall be implemented forthwith on all scour susceptible structures and on schemes involving scour susceptible structures on the Overseeing Organisation motorway and all-purpose trunk roads and on Overseeing Organisation land, according to the implementation requirements of GG 101 [Ref 10.N]. Use of GG 101 and GG 104 1.13 The requirements contained in GG 101 [Ref 10.N] and GG 104 [Ref 15.N] shall be followed in respect of activities covered by this document. 38 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 1. Scope Competent persons 1.14 Unless otherwise stated in this document, all work carried out in accordance with this document shall be overseen by a competent civil engineer or structural engineer. 1.15 A competent civil engineer or structural engineer shall be a Chartered Civil Engineer or Chartered Structural Engineer (or possess an equivalent non-UK qualification approved by the Engineering Council in the UK, or approved in accordance with the European Union (Recognition of Professional Qualifications) Regulations 2015 UKSI 2015/2059 [Ref 3.N], as amended by the European Union (Withdrawal Agreement) Act 2020 UKPGA 2020/01 [Ref 4.N], with the necessary and relevant skills, knowledge and experience in design and construction, or demolition, or maintenance and operation, of structures. NOTE 1 The competent civil engineer or structural engineer can have specialist support from a competent hydrologist and/or hydraulic engineer, with the necessary and relevant qualifications, skills, knowledge and experience. NOTE 2 The competent civil engineer or structural engineer can have specialist support from one or more competent staff, with the necessary and relevant qualifications, skills, knowledge and experience, in the management of scour and other hydraulic actions at structures. 39 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process 2. Inspection and assessment process General 2.1 For scour susceptible structures Type 1, a programme of regular scour inspections and scour assessments shall be carried out, in accordance with clauses 2.7 to 2.19. 2.2 For scour susceptible structures Type 2, a programme of regular scour inspections and scour assessments shall be carried out, in accordance with clauses 2.20 to 2.25. 2.3 For scour susceptible structures Type 1, the scour risk rating and scour risk score for the structure shall be determined, in accordance with Table 2.3 and Section 4 or 5. 40 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Table 2.3 Scour risk rating and scour risk scores, for scour susceptible structures Type 1. Scour and other hydraulic actions risks Scour risk rating: low risk Scour risk rating: medium risk Scour risk rating: high risk No evidence of scour. Woody debris accumulation is not likely to occur. Evidence of scour, or calculated risk of scour. Woody debris accumulation is likely to occur. Evidence of significant scour, or calculated risk of significant scour. Woody debris accumulation is very likely to occur. Implementation of any actions required to prevent an increase in scour and other hydraulic actions risks. Implementation of: 1) interim actions required to reduce scour and other hydraulic actions risks; and, 2) any actions required to prevent an increase in scour and other hydraulic actions risks. Implementation of: 1) immediate actions required to reduce scour and other hydraulic actions risks; and, 2) any actions required to prevent an increase in scour and other hydraulic actions risks. Scour risk score 10 Scour risk score 40 Scour risk score 60 Scour risk score 80 Scour risk score 100. Immediate risk scour susceptible structure Green status Amber status Red status Priority 3: low priority Priority 2: medium priority Priority 1: high priority, safety critical 41 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process NOTE 1 The evaluation of the risk of woody debris accumulation at a structure is carried out as part of a scour Level 1 assessment in clause 4.7 and as part of the priority ranking process in clause 5.15. NOTE 2 The calculation of the local scour depth due to woody debris accumulation at a structure is carried out as part of a scour Level 2 assessment in clause 5.49.4. 2.4 For scour susceptible structures Type 2, the scour risk rating for the structure shall be determined, in accordance with Section 7. 2.5 A programme to manage risks due to scour and other hydraulic actions at structures shall be prepared and implemented, in accordance with Section 8. 2.6 Documents shall be uploaded to the Overseeing Organisation structures asset management information system, in accordance with Section 9. Scour susceptible structures Type 1 General 2.7 The scour inspection, assessment and risk management process shall be implemented, as shown in the flow chart in Figure 2.7 (Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheets 1 to 9). 42 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7a Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 1 of 9. 43 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7b Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 2 of 9. 44 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7c Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 3 of 9. 45 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7d Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 4 of 9. 46 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7e Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 5 of 9. 47 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7f Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 6 of 9. 48 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7g Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 7 of 9. 49 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7h Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 8 of 9. 50 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Figure 2.7i Scour inspection, assessment and risk management process for scour susceptible structures Type 1, sheet 9 of 9. 51 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Scour inspection process - scour susceptible structures Type 1 2.8 A scour inspection of scour susceptible structures Type 1 shall be carried out as described in Table 2.8, in accordance with Section 3 and CS 450 [Ref 9.N]. 52 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Table 2.8 Inspection frequency of scour susceptible structures Type 1. Scour risk rating Regular scour inspections Scour emergency inspection, after a significant flood event Emergency structural inspection, after an event described in clause 1.11 High Scour emergency inspection to be carried out. Underwater inspection to be included as part of a scour emergency inspection. Medium Scour inspection at every principal inspection. Underwater inspection to be included with principal inspection, if there are visible scour or hydraulic action issues, or previous history of scour within 30 m of the structure, or previous history of debris accumulation within 30 m of the structure, unless a scour emergency inspection has been carried out within the past 2 years. Scour emergency inspection to be carried out. No underwater inspection needed during a scour emergency inspection, unless visible scour or hydraulic action issues, or previous history of scour within 30 m of the structure, or previous history of debris accumulation within 30 metres of the structure. Low Scour inspection at every principal inspection. Scour emergency inspection to be carried out. No underwater inspection needed during a scour emergency inspection, unless visible scour or hydraulic action issues, or previous history of scour within 30 m of the structure, or previous history of debris accumulation within 30 m of the structure. Carry out an emergency structural inspection, above and below water level, including an underwater inspection, appropriate for the structural risks following the event that has occurred. NOTE An event described in Clause 1.11 can be a less frequent occurrence potentially resulting in more severe structural damage, compared to other types of flood event that can occur at the structure location. 53 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process NOTE Refer to the "Terms and definitions" table for the definition of "underwater inspection". 2.9 The scour inspection report shall be submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. 2.10 Immediately after a significant flood event has occurred, when the flood water level has significantly reduced to a safe level, a scour emergency inspection shall be carried out, as described in Table 2.8, as a special inspection in accordance with Section 3 and CS 450 [Ref 9.N], to determine if one or more of the following have occurred: 1) there are changes to the stability, shape or direction (sinuosity) of the watercourse; 2) there are changes to the ground levels, stream or river bed levels near to the structure; or 3) if damage to the structure has occurred. NOTE Each of the three items listed in this clause can affect the stability of the structure, or affect the integrity of the structure and its vulnerability to hydraulic actions. 2.11 The scour emergency inspection report shall be submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. Scour Level 1 assessment process - scour susceptible structures Type 1 2.12 A scour Level 1 assessment of scour susceptible structures Type 1 shall be carried out in accordance with Section 4, to determine if the scour risk score is 10 (the structure is low risk), or more than 10 (the structure is medium or high risk). NOTE The scour Level 1 assessment comprises simple methods, to identify scour susceptible structures: 1) that are at lowest risk from scour or other hydraulic actions; and, 2) those for which a more detailed scour Level 2 assessment is required. 2.13 Where a scour Level 1 assessment determines that the scour risk score is more than 10 (the structure is medium or high risk), the scour assessment shall progress to Level 2. 2.14 The scour Level 1 assessment record shall be submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. Scour Level 2 assessment process - scour susceptible structures Type 1 2.15 When needed following completion of a scour Level 1 assessment, a scour Level 2 assessment of scour susceptible structures Type 1 shall be carried out in accordance with Section 5, to determine the scour risk score. NOTE The scour Level 2 assessment is a detailed method to identify those structures for which the risk of structural damage due to scour and other hydraulic actions is high risk, or medium risk. 2.16 The Technical Approval Authority shall be advised in advance of a proposal to carry out a scour Level 2 assessment. 2.17 As part of a scour Level 2 assessment of a scour susceptible structure Type 1, other hydraulic actions at the structure shall be evaluated, discussed and agreed with the Overseeing Organisation and if needed a vulnerability assessment for other hydraulic actions is to be carried out in accordance with Section 6. 2.18 The vulnerability assessment report shall be submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. 2.19 The scour Level 2 assessment report shall be submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. 54 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Scour susceptible structures Type 2 Scour inspection process - scour susceptible structures Type 2 2.20 A scour inspection of scour susceptible structures Type 2 shall be carried out as described in Table 2.20, in accordance with Section 3 and CS 450 [Ref 9.N]. Refer to the "Terms and definitions" table for the definition of "underwater inspection" . 55 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process Table 2.20 Inspection frequency of scour susceptible structures Type 2. Scour risk rating Regular scour inspections Scour emergency inspection, after a significant flood event Emergency structural inspection, after an event described in clause 1.11 High, medium, or low. Scour inspection at every principal inspection. Scour emergency inspection to be carried out. Carry out an emergency structural inspection, above and below water level, including an underwater inspection, appropriate for the structural risks following the event that has occurred. NOTE: An event described in Clause 1.11 can be a less frequent occurrence potentially resulting in more severe structural damage, compared to other types of flood event that can occur at the structure location. 56 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 2. Inspection and assessment process 2.21 The scour inspection report shall be submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. 2.22 Immediately after a significant flood event has occurred, when the flood water level has significantly reduced to a safe level, a scour emergency inspection shall be carried out, as a special inspection in accordance with Section 3 and CS 450 [Ref 9.N], to determine if one or more of the following have occurred: 1) there are changes to the stability, shape or direction (sinuosity) of the watercourse; 2) there are changes to the ground levels, stream or river bed levels near to the structure; or 3) if damage to the structure has occurred. NOTE Each of the three items listed in this clause can affect the stability of the structure, or affect the integrity of the structure and its vulnerability to hydraulic actions. 2.23 The scour emergency inspection report shall be submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. Scour evaluation process - scour susceptible structures Type 2 2.24 A scour evaluation of scour susceptible structures Type 2 shall be carried out in accordance with Section 7, to determine the scour risk rating. 2.25 The scour evaluation report shall be submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. Immediate risk scour susceptible structures 2.26 Where, at any stage of a process shown below, a scour susceptible structure is considered to be at immediate risk of failure, or collapse, the structure shall be designated as an immediate risk scour susceptible structure with a scour risk score of 100: 1) scour inspection; 2) scour emergency inspection; 3) emergency structural inspection; 4) scour assessment; 5) scour evaluation; or 6) monitoring. 2.27 Where a structure has been designated as an immediate risk scour susceptible structure, the risks and issues shall be notified to the Overseeing Organisation. NOTE Refer to the "Terms and definitions" table for the definition of "immediate risk scour susceptible structure". 2.28 Immediate risk scour susceptible structures shall be managed in accordance with CS 470 [Ref 11.N]. NOTE For details of requirements for the updating of the Overseeing Organisation structures asset management information system structure record, refer to Section 9. 57 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 3. Inspection of scour susceptible structures 3. Inspection of scour susceptible structures General 3.1 Scour inspections and scour emergency inspections shall be carried out on scour susceptible structures by an Inspector, or Senior Inspector, as defined in DMRB CS 450 [Ref 9.N]. 3.2 The scour inspection, or scour emergency inspection, shall include a site inspection, site survey, office-based data gathering, and reports on scour and other hydraulic actions on the structure. 3.2.1 When carrying out a scour inspection, or scour emergency inspection, of a structure it should be undertaken in accordance with the Inspection Manual for Highway Structures Volume 1 Reference Manual IMHS V1 [Ref 9.I] and Volume 2 Inspectors Handbook IMHS V2 [Ref 10.I]. 3.3 Prior to carrying out a scour inspection, or a scour emergency inspection, a site-specific risk assessment and method statement in accordance with DMRB GG 104 [Ref 15.N] and CS 450 [Ref 9.N] shall be prepared and agreed before commencement of the site inspection and site survey. 3.4 The scour inspection report shall include information, where available, about: 1) the form of the structure, including the foundations and the ground conditions; 2) the stream, river, canal, pond, lake, reservoir, and/or estuary; 3) the condition of scour protection; 4) flow control structures; 5) evidence of changes to the stream, river, canal, pond, lake, reservoir, estuary, or coast; 6) evidence of debris accumulation; 7) evidence of scour or erosion; 8) evidence of other hydraulic actions; 9) evidence of structural issues which can potentially be made worse by scour or other hydraulic actions; and, 10) inspection history (including general inspections, principal inspections, scour inspections, scour emergency inspections) and severe weather event data history at the structure (from office-based data gathering). 3.4.1 The list of severe weather events should note, for each severe weather event, whether the structure was able to withstand the severe weather event without structural damage, where historical records are available. 3.5 The scour emergency inspection report shall include information, where available, on: 1) details of the severe weather event and any damage to the structure; 2) weather data at the time of the severe weather event; 3) at the upstream face of the structure, the peak flow rate and peak flow depth at the time of the severe weather event; 4) details of how flood relief measures and flow control measures (for example a flow control structure, or a weir) performed during the severe weather event, and whether this adversely affected the structure; 5) evidence of changes to the stream, river, canal, pond, lake, reservoir, estuary, or coast; 6) evidence of debris accumulation; 7) evidence of scour or erosion; 8) evidence of other hydraulic actions; 9) evidence of structural issues which can potentially be made worse by scour or other hydraulic actions; and, 10) updated inspection history and updated weather data history. 58 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 3. Inspection of scour susceptible structures 3.6 The scour inspection report, or scour emergency inspection report, shall: 1) indicate if there are any changes since the previous scour inspection of the structure; 2) provide details of the changes; 3) describe the consequences that have occurred, due to the changes; and, 4) describe the likely consequences that can occur, due to the changes. 3.7 The scour inspection report, or scour emergency inspection report, shall indicate where: 1) the condition of the structure has changed; 2) there is evidence of scour development, or other hydraulic actions, which have adversely affected the structure; 3) there is evidence of scour development, or other hydraulic actions, which can adversely affect the structure; and, 4) there are any defects, for example caused by scour or other hydraulic actions, which can lead to structural failure or collapse. 3.8 In the scour inspection report, or scour emergency inspection report, the date and time noted for each photograph shall be shown in the photograph description. Data updating for scour susceptible structures Type 1 - scour Level 1 assessment 3.9 Prior to carrying out a scour Level 1 assessment, for a scour susceptible structure Type 1, existing sources of data shall be reviewed and updated as follows: 1) stream or river bed profile; 2) stream or river bed gradient s ; 3) stream or river bed material; 4) the average channel depth, DAV (refer to Figure 3.9); 5) maximum channel depth, DMAX (refer to Figure 3.9); 6) length, width and thickness of foundations, for each element of the structure (such as bridge abutments, piers and retaining walls); 7) at each element of the structure, the vertical distance below the average river bed level to the underside of the spread footing foundation, or to the underside of the pile cap in the case of a piled foundation, DF (refer to Figure 3.9). If site survey data for the structure foundation is not available, a default value for DF can be used, as provided in Table 3.9.1; 8) total width of all elements of the structure in the stream or river channel (such as bridge abutments, piers and retaining walls). This dimension is measured at 900 to the direction of flow, at the structure, at water level; 9) average channel width, B (refer to Figure 3.9); and, 10) height of the structure soffit above the river bed, at the upstream face of the structure, Hsoff . 59 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 3. Inspection of scour susceptible structures Figure 3.9 Characterisation of stream or river channel geometry from site survey data. NOTE Refer to the "Terms and definitions" table for the definition of "stream or river bed gradient". 3.9.1 Where structure foundation information is not immediately available for each element of the structure, then a default value of the distance below average bed level to the underside of the spread footing foundation, or to or to the underside of the pile cap in the case of a piled foundation, DF1 or DF2 , may be used, as provided in Table 3.9.1, for each element of the structure. Table 3.9.1 Default values of the distance below average bed level to the underside of the spread footing foundation, or to the underside of the pile cap in the case of a piled foundation. Default values for the distance below average bed level to the underside of the spread footing foundation, or to the underside of the pile cap in the case of a piled foundation, DF Concrete substructure Masonry substructure DF1 1.0 m 0.3 m DF2 3.0 m 1.0 m Inspection and data gathering for scour susceptible structures Type 1 - scour Level 2 assessment 3.10 Prior to carrying out a scour Level 2 assessment, for a scour susceptible structure Type 1, the following actions shall be carried out: 1) review and updating of existing sources of data; 2) a site inspection; and, 3) a site survey, where needed, to update previous site survey data. 3.10.1 Levels should be taken at both banks and within the stream or river channel to allow the channel dimensions to be determined, as illustrated in Figure 3.9 and shown below: 1) the average channel depth, DAV ; 2) measurements of the channel width should be taken to characterise the bank-to-bank dimension. The average width of the channel, B , is the dimension between points of half average channel depth; 3) the cross-sectional area of flow, A ; 4) the maximum channel depth, DMAX ; and, 60 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 3. Inspection of scour susceptible structures 5) the distance below average bed level to the underside of the spread footing foundation, or to the underside of the pile cap in the case of a piled foundation, DF . 3.10.2 Measurements should be taken across the channel at six or more locations, within the defined distance from the structure, to characterise the channel geometry for the conditions upstream of the structure, at the structure and downstream of the structure. 3.10.3 The distance below average bed level to the underside of the spread footing foundation, or to the underside of the pile cap in the case of a piled foundation, DF , is a key parameter for determining the bed resistance to scour and the risk of scour-related failure or collapse. At all scour susceptible structures Type 1, information on the type, width, length and thickness of foundations and DF should be determined from a site investigation, if not already shown on as-built drawings, for each element of the structure (such as bridge abutments, piers and retaining walls). 3.11 Photographs shall be taken, with the date and time noted, during a scour inspection, or a scour emergency inspection, for reference in the scour assessment report and to provide a comparative reference for future inspections. 3.11.1 Photographs of relevant features should be taken, including, as examples: 1) watercourse bends, particularly where there are signs of erosion to the outer banks; 2) evidence of bank erosion or channel instability; 3) evidence of coastal erosion or instability; 4) upstream structures, such as other bridges, or weirs, or flow control structures, that can affect the flow at the structure site, or control the potential lateral movement (sinuosity) of the river channel; 5) downstream structures such as other bridges, weirs or flow control structures, that can affect the river level at the structure site, or control the potential lateral movement (sinuosity) of the river channel; and, 6) evidence of any debris accumulation upstream of, alongside, or downstream of the structure. 3.12 Following completion of the actions described in clauses 3.10 to 3.11.1, the scour inspection report, for scour susceptible structures Type 1, shall include the information, where available, shown in Table 3.12. 61 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 3. Inspection of scour susceptible structures Table 3.12 Scour inspection report - prior to carrying out a scour Level 2 assessment of a scour susceptible structure Type 1. Scour susceptible structures Type 1 - low, medium and high risk Information in the scour inspection report: 1) the non-tidal stream or river bed profile, within the defined distance upstream of the structure, alongside/inside the structure and within the defined distance downstream of the structure; or, 2) the canal or pond or lake or reservoir bed profile, within the defined distance from the structure; or, 3) the tidal stream, river or estuary profile within the defined distance from the structure. Information in the scour inspection report: 1) a ground profile survey, within the defined distance from the structure; 2) survey of underwater parts of structure including levels, within the defined distance from the structure; and, 3) survey of accumulation of debris, within the defined distance from the structure. Information in the scour inspection report: 1) evidence showing that the as-built general arrangement structural records are accurate and up to date; 2) other relevant site survey work to ensure structural integrity has not been compromised; 3) existing records (e.g. dated photographs not included in previous inspection reports, records of severe weather events, records of scour or other hydraulic actions on the structure, records of debris accumulation); 4) photographs (time and date to be recorded) taken at the time of the inspection; 5) borehole records, showing ground conditions and underwater bed conditions, within the defined distance from the structure; and, 6) historical flooding information to inform likelihood of scour history. For non-tidal streams and rivers, canals, ponds, lakes and reservoirs, the defined distance from the structure is: 1) 30 metres minimum; or, 2) 100 metres maximum in each direction. For tidal streams, rivers and estuaries, the defined distance from the structure is: 1) 50 metres minimum; or, 2) 150 metres maximum in each direction. NOTE Refer to the "Terms and definitions" table for the definition of "defined distance from the structure". Inspection and data gathering for scour susceptible structures type 2 3.13 Prior to carrying out a scour evaluation, for a scour susceptible structure Type 2 designated as scour risk rating 'high risk' in accordance with clauses 7.18 to 7.22, the following actions shall be carried out: 1) review and updating of existing sources of data; 2) a site inspection; and, 62 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 3. Inspection of scour susceptible structures 3) a site survey, where needed, to update previous site survey data. 3.14 Photographs shall be taken, with the date and time noted, during a scour inspection, or a scour emergency inspection, for reference in the scour evaluation report and to provide a comparative reference for future inspections. 3.14.1 Photographs of particularly relevant features should be taken, for example: 1) flood plain characteristics; 2) evidence of land erosion or instability, that can have been caused by scour or other hydraulic actions; 3) lack of maintenance of flow control structures or flood defences, that can cause flood water to not be contained as designed; 4) flow control structures, if not operated in a timely manner, that can cause flood water to reach the structure site; and, 5) other flow control structures. 3.15 Following completion of the actions described in clauses 3.13 to 3.14.1, the scour inspection report, for high risk scour susceptible structures Type 2, shall include the information, where available, shown in Table 3.15. Table 3.15 Scour inspection report - prior to carrying out a scour evaluation of a high risk scour susceptible structure Type 2. Scour susceptible structures Type 2 - high risk only Information in the scour inspection report: 1) photographs (time and date to be recorded) taken at the time of the inspection; 2) a level survey from the structure to the defined distance from the structure; 3) distance from water that could cause flooding or scour; 4) levels at the source of water that could cause flooding (e.g. river water level at the time of the inspection and river bank level); and, 5) likely scour or other hydraulic actions which could occur at the structure during a severe weather event. The defined distance from the structure is 100 metres. 63 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... 4. Level 1 assessment of scour susceptible structures Type 1 General 4.1 The scour Level 1 assessment shall identify and assess scour on a scour susceptible structure Type 1. 4.2 The structure shall be assessed to determine if a scour Level 2 assessment is needed. 4.2.1 The scour Level 1 assessment should not involve calculations and numerical analysis. 4.3 The scour Level 1 assessment shall evaluate the information for the structure location in: 1) the scour inspection reports; 2) scour emergency inspection reports; 3) emergency structural inspection reports; 4) the latest available flood event data; 5) the latest available tidal event data; and, 6) the latest available 0.5% AEP flood risk maps, in accordance with the relevant DMRB CS 469 National Application Annex. 4.3.1 The scour Level 1 assessment should include a list of significant flood events and severe weather events that have occurred at the structure location and note whether the structure was able to withstand the event without structural damage, where historical records are available. 4.3.2 The scour Level 1 assessment should include a list of tidal events that have occurred at the structure location and caused structural damage, where historical records are available. 4.4 The outcome of the scour Level 1 assessment shall be either: 1) the scour Level 1 assessment is to proceed to a scour Level 2 assessment; or, 2) the structure is to be designated with a scour risk rating of low risk and an associated scour risk score in accordance with Table 2.3, and clauses 5.52 and 5.53. Scour Level 1 assessment process 4.5 The following aspects shall be identified and assessed in the scour Level 1 assessment, to determine how they could potentially affect the safety, stability, or integrity, of the structure: 1) scour developing below water level and undermining the structure foundations; 2) scour developing at abutments; 3) erosion of the ground or channel banks and movement of the stream or river channel, causing greater risk of scour damage to the structure, or causing damage to geotechnical assets close to the structure; 4) debris accumulation, restricting or blocking the flow; and, 5) damage to the structure. 4.6 The scour Level 1 assessment shall be carried out in accordance with the process shown in the flow chart in Figures 4.6a, 4.6b, 4.6c, 4.6d, 4.6e, 4.6f, & 4.6g, scour Level 1 assessment process, for scour susceptible structures Type 1, sheets 1 to 7. 64 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... Figure 4.6a Scour Level 1 assessment process, for scour susceptible structures Type 1, sheet 1 of 7. 65 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... Figure 4.6b Scour Level 1 assessment process, for scour susceptible structures Type 1, sheet 2 of 7. 66 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... Figure 4.6c Scour Level 1 assessment process, for scour susceptible structures Type 1, sheet 3 of 7. 67 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... Figure 4.6d Scour Level 1 assessment process, for scour susceptible structures Type 1, sheet 4 of 7. 68 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... Figure 4.6e Scour Level 1 assessment process, for scour susceptible structures Type 1, sheet 5 of 7. 69 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... Figure 4.6f Scour Level 1 assessment process, for scour susceptible structures Type 1, sheet 6 of 7. 70 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... Figure 4.6g Scour Level 1 assessment process, for scour susceptible structures Type 1, sheet 7 of 7. Scour Level 1 assessment process - assessment of the risk of woody debris accumulations 4.7 The scour Level 1 assessment shall assess whether the risk of woody debris accumulations in a stream or river channel is high risk, or medium risk, in accordance with Table 4.7. 71 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... Table 4.7 Scour Level 1 assessment process, for scour susceptible structures Type 1, assessment of the risk of woody debris accumulations in a stream or river channel. Assessment of the risk of woody debris accumulations Woody debris accumulations risk rating Evidence of a debris accumulation within 30 m of a structure. Evidence that any of the following works have been carried out along the stream or river bank, upstream of the structure, or at the structure: 1) tree removal or pruning works; or, 2) vegetation removal or pruning works. High risk. The structure is located downstream of sources of woody debris, for example: 1) an upstream structure with evidence of debris accumulation history; 2) one or both stream or river banks with tree branches, or vegetation, overhanging the stream or river; or, 3) a catchment where there are woodland or forest areas. Medium risk. Debris accumulation is not likely to occur. Low risk. NOTE 1 The accumulation of debris can occur at bridge piers, abutments and retaining walls, as well as at other structural elements exposed to the flow. NOTE 2 There is evidence that accumulation of debris can cause a complete or partial blockage of flow at a single span bridge, or at a multi-span bridge, resulting in debris-induced severe scour and structural failure or collapse. An example is the railway bridge over the River Crane in Feltham, Middlesex RDG1 [Ref 5.I]. NOTE 3 When assessing the risk of the accumulation of debris at, or close to, a structure: 1) evidence of debris trapped at, or close to, a structure is a clear indication of potential for future debris accumulations and increased risk of scour; 2) evidence of accumulated debris at other structures located upstream of the structure is an indication that formation of debris accumulations is likely to occur at the structure; and, 3) there is potential for future debris accumulations located downstream of a catchment where there are woodland or forest areas, even if there are no records available showing a history of debris accumulations, at the structure. NOTE 4 A debris screen at a structure is very likely to significantly increase the risk of accumulation of woody debris at the structure, which can potentially result in scour, or severe scour, developing. Therefore, the presence of a debris screen at a structure indicates that the woody debris accumulations risk rating can be high risk or medium risk. Reporting 4.8 The scour Level 1 assessment record, for a scour susceptible structure Type 1, shall include: 1) the consequences, or potential consequences, of severe weather events, using the latest available flood event data, tidal event data and flood risk maps for the structure location; 2) the scour risk rating and scour risk score in accordance with clause 4.6; 72 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 4. Level 1 assessment of scour susceptible struc... 3) the consequences, or potential consequences, resulting from scour and other hydraulic actions; 4) the consequences following partial or total structural failure or collapse; and, 5) the recommendations of the scour Level 1 assessment in accordance with clause 4.4. 73 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 5. Level 2 assessment of scour susceptible structures Type 1 General 5.1 The scour Level 2 assessment shall be a detailed assessment of scour on a scour susceptible structure Type 1. 5.2 The structure shall be assessed to determine if the structure is able to withstand a severe weather event with a 0.5% AEP using the information for the structure location in: 1) the latest available weather event data; 2) the latest available flood event data; 3) historical data; 4) the latest available tidal data; and, 5) the climate change allowances defined in the relevant National Application Annex. NOTE Details of the different types of climate change allowances for each government body are provided in the relevant National Application Annex. 5.2.1 The scour Level 2 assessment should involve calculations and numerical analysis. 5.3 The scour Level 2 assessment shall evaluate the information for the structure location in: 1) the scour inspection reports; 2) scour Level 1 assessment record; 3) vulnerability assessment report; 4) scour emergency inspection reports; and, 5) emergency structural inspection reports. 5.4 The outcome of the scour Level 2 assessment shall be that the structure is to be designated with a scour risk score and an associated scour risk rating of high risk, medium risk or low risk, in accordance with Table 2.3, and clauses 5.52 and 5.53. Scour Level 2 assessment process Type 1 5.5 The scour Level 2 assessment shall be carried out in accordance with the process shown in the flow chart in Figure 5.5, sheets 1 to 3. 74 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.5a Scour Level 2 assessment process, for scour susceptible structures Type 1, sheet 1 of 3. 75 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.5b Scour Level 2 assessment process, for scour susceptible structures Type 1, sheet 2 of 3. 76 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.5c Scour Level 2 assessment process, for scour susceptible structures Type 1, sheet 3 of 3. Priority factor Type 1 5.6 For scour susceptible structures Type 1 in need of a scour Level 2 assessment, a priority factor Type 1 PF-T1 shall be calculated for each scour susceptible structure Type 1. NOTE The higher the value of priority factor Type 1 PF-T1 , the higher the priority for carrying out the scour Level 2 assessment or reassessment. 5.7 The priority factor Type 1, PF-T1 , shall be calculated using Equation 5.7: 77 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.7 Priority factor Type 1. PF-T1 = F · M · HS · TR · C · CAF · D where: PF-T1 priority factor Type 1 F foundation type factor (structure foundation) M ground material factor (e.g. the stream or river bed material at the structure) HS history of scour occurrence factor TR type of river factor C communities importance factor CAF communities additional factor D debris accumulation factor NOTE When PF-T1 is greater than 2.5, refer to clause 5.53. 5.8 The foundation type factor, F , provided in Table 5.8 shall be used in Equation 5.7. Table 5.8 Foundation type factor F. For a masonry arch structure - any foundation type F = 1.25 For a spread footing (excluding masonry arch structures) F = 1.0 For a steel or concrete piled foundation F = 0.75 5.8.1 Where the structure foundations include timber piles, or where any part of the structure contains structural timber, the Overseeing Organisation Technical Approval Authority should be consulted to discuss and agree the value of Foundation type factor, F , prior to commencement of the scour Level 2 assessment. 5.8.2 Where the structure is not a masonry arch structure, if the foundation type is unknown the foundation type factor F should be 1.0. 5.9 The ground material factor, M , provided in Table 5.9 shall be used in Equation 5.7. Table 5.9 Ground material factor M. Where there is no information on the ground material, or the ground material is granular (e.g. silt, sand, gravel). M = 1.0 Where there is some evidence that the ground material is clay. M = 0.75 Where there is geotechnical evidence that the ground material is clay, or there is some evidence that the ground material is partly rock. M = 0.5 5.10 The history of scour occurrence factor, HS , provided in Table 5.10 shall be used in Equation 5.7. Table 5.10 History of scour occurrence factor. There is evidence of scour occurrence within the defined distance from the structure. HS = 1.5 There is no evidence of scour occurrence within the defined distance from the structure. HS = 1.0 NOTE The defined distance from the structure is provided in Table 3.12. 78 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 5.11 The potential for stream or river channel instability and associated scour risk depends upon the stream or river bed bed gradient s . The type of river factor, TR , provided in Table 5.11 shall be used in Equation 5.7. Table 5.11 Type of river factor. The stream or river bed gradient s measured on the channel centre line over an upstream distance of 100 m from the upstream face of the structure Type of river factor Very steep s > 10% TR = 1.5 Steep 4% ≤ s ≤ 10% TR = 1.3 Moderate 2% ≤ s < 4% TR = 1.2 Low 0.5% ≤ s < 2% TR = 1.1 Very low s < 0.5% TR = 1.0 NOTE Refer to the "Terms and definitions" table for the definition of "stream or river bed gradient". 5.12 The consequences to road users and nearby communities following the failure or collapse of a structure such as a bridge, shall be identified and assessed as part of the scour Level 2 assessment. If a bridge failure or collapse occurs, due to scour or other hydraulic actions, the potential consequences to be assessed, in determining the communities importance factor, C , are to include: 1) traffic disruption on emergency diversion routes; 2) community severance; and, 3) loss of utilities to a nearby community (such as loss of electricity supply). 5.13 The communities importance factor, C , provided in Table 5.13 shall be used in Equation 5.7. Table 5.13 Communities importance factor C. Use of bridge or other structure Communities importance factor C Motorway, or dual carriageway A road. C = 1.0 Single carriageway A road. C = 0.9 B road. C = 0.8 C road, or unclassified road, or footbridge, or accommodation bridge, or other type of structure. C = 0.7 5.14 Where the situations described in Table 5.13 do not fully reflect the importance of a bridge or other type of structure, the value for the communities importance factor, C , given in Table 5.13, shall be multiplied by a communities additional factor, CAF as shown in Table 5.14, and used in Equation 5.7. 79 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Table 5.14 Communities additional factor. Community severance or disruption issue Communities additional factor CAF A bridge on a road to an essential industry or transport facility where there is no diversion route and loss of the bridge can result in community severance. CAF = 1.3 A bridge that provides a link within a community where loss of the bridge can result in community severance. CAF = 1.2 A bridge, or footbridge, or other type of structure, that provides utilities to a community, where loss of the structure can result in community disruption (such as loss of electricity supply). CAF = 1.2 A footbridge that provides a link within a community where loss of the footbridge can result in community severance. CAF = 1.1 All other structures. CAF = 1.0 NOTE Further information on community severance issues can be found in DMRB LA 112 [Ref 14.N]. 5.15 The accumulation of debris in the water increases the risk of scour and damage to the structure. The process shown in Table 5.15 shall be used to determine the debris accumulation factor, D . Table 5.15 Debris accumulation factor. The likelihood of woody debris accumulations in a stream or river channel Debris accumulation factor, D There is a high risk of a woody debris accumulation at the structure. Evidence of a debris accumulation within 30 m of a structure. Evidence that any of the following works have been carried out along the stream or river bank, upstream of the structure, or at the structure: 1) tree removal or pruning works; or, 2) vegetation removal or pruning works. D = 1.3 There is a medium risk of a woody debris accumulation at the structure. The structure is located downstream of sources of woody debris, e.g.: 1) an upstream structure with evidence of debris accumulation history; 2) one or both stream or river banks with tree branches, or vegetation, overhanging the stream or river; or, 3) a catchment where there are woodland or forest areas. D = 1.1 There is a low risk of a woody debris accumulation at the structure. Debris accumulation is not likely to occur. D = 1.0 5.16 The debris accumulation factor, D , shall be used in Equation 5.7. 80 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Calculation of assessment flow 5.17 The assessment flow, QA , for a severe weather event with a 0.5% AEP, including for climate change allowances, shall be calculated for the structure location, in accordance with the following: 1) the calculations are to be based on a statistical analysis of the latest available weather event data, flood event data, historical data and tidal data; 2) the climate change allowances for the structure location provided in the relevant National Application Annex; and, 3) any assessment flow, QA , calculated more than one year prior to the date of the scour Level 2 assessment, is not to be used and is to be recalculated in accordance with this document, using the latest available weather event data, flood event data, historical data, tidal data and the climate change allowances. 5.18 The consequences shall be analysed for different combinations of weather event, flood event and tidal event, occurring at the same time. 5.19 The methodology used to determine the assessment flow, QA , shall be appropriate for: 1) the catchment characteristics upstream of the structure; 2) the catchment size upstream of the structure; 3) characteristics of the stream or river downstream of the structure, which can affect the water level at the structure; and, 4) the structure location. 5.20 Where there is an upstream or downstream flow control structure, the method for determining the assessment flow, QA , shall be agreed with the Technical Approval Authority for the structure location, prior to commencement of the scour Level 2 assessment. NOTE At some structure locations, the assessment flow, QA , can be controlled by one or more upstream or downstream flow control structures, such as a reservoir outflow structure, or a flood control structure, or a flood defence structure. 5.21 The organisation responsible for operating an upstream or downstream flow control structure, such as a reservoir outflow structure, or flood control structure, or flood defence structure, shall be consulted. NOTE A flow control structure can affect the peak flow rate at the structure. 5.22 The scour Level 2 assessment report shall describe the methodology used to determine the assessment flow, QA , and is to include: 1) method used and the justification for using the method; 2) software used; 3) assumptions made; and, 4) results. 5.22.1 At non-tidal locations, the assessment flow, QA , should be determined using the fluvial component, QF . 5.22.2 At tidal locations, the assessment flow, QA , should be determined using two components: 1) the fluvial component, QF ; and, 2) the tidal component. Fluvial component of the assessment flow 5.23 The fluvial component of the assessment flow, QF , shall be the peak fluvial flow rate occurring at the structure location, during a severe weather event with a 0.5% AEP, including for climate change allowances for the structure location. 81 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 5.24 The fluvial component of the assessment flow, QF , and the catchment response time shall be determined in accordance with the methods described in the relevant National Application Annex. Tidal component of the assessment flow 5.25 At a tidal location, the tidal component of the assessment flow, QT , at a specific time of day, shall be the tidal flow rate due to the tidal period and tidal range, including for climate change allowances for the structure location. NOTE 1 Tidal periods and tidal ranges at standard and secondary ports in the UK are published in the Admiralty Tide Tables [Ref 8.I]. Values for other locations can be interpolated as appropriate. Other locally prepared tide tables can be available for a local area, or port, or harbour; for example River Thames tidal predictions [Ref 14.I]. NOTE 2 Low tide and high tide levels (tidal levels) in published tide tables can be shown as a height above Chart Datum (CD). NOTE 3 Chart Datum can be approximately the lowest sea water level at a specific location, due to astronomical effects and excluding meteorological effects. For example, the height of CD at a specific location in the UK relative to Ordnance Datum at Newlyn, Cornwall, in England, OD(N), can be negative, indicating that the Chart Datum is below Ordnance Datum. NOTE 4 Within estuaries and on tidal rivers, funnelling and storm surges can affect the tidal flows. 5.26 The tidal component of the assessment flow shall be determined for different tidal situations at the structure location in accordance with the simplified methods described in clauses 5.28 to 5.30.1. 5.27 Where there is any doubt about the suitability of the simplified methods for calculating the tidal flows detailed in clauses 5.28 to 5.30.1 in this document, specialist advice shall be obtained and agreed by the Overseeing Organisation prior to commencement of the scour Level 2 assessment. 5.28 A simplified method for estimating the peak tidal flow, QTide , shown in Equation 5.28a and the maximum tidal flow, QTide,max , shown in Equation 5.28b, shall be used: Equation 5.28a Peak tidal flow. QTide = π · VTide,av TTide where: QTide is peak tidal flow, based on the average tidal range, in m3 /s VTide,av is the volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the average tidal range (in m), in m3 TTide is the tidal period, in s 82 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.28b Maximum tidal flow. QTide,max = π · VTide,max TTide where: QTide,max maximum tidal flow, based on the maximum tidal range, in m3 /s VTide,max the volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the maximum tidal range (in m), in m3 TTide the tidal period, in s NOTE The relevant National Application Annex provides: 1) the method for calculating the average tidal range; and 2) the method for calculating the maximum tidal range. 5.29 An adjustment shall be made to QTide and QTide,max for the climate change allowance projected rise in sea level, for the structure location, defined in the relevant National Application Annex. 5.29.1 Where the peak tidal flow QTide calculated using Equation 5.28a is less than 0.5 · QF , the assessment flow QA should be calculated using Equation 5.29.1. Equation 5.29.1 Assessment flow when the peak tidal flow is less than half the fluvial component of the assessment flow. QA = QF + QTide 5.29.2 Where the peak tidal flow QTide calculated using Equation 5.28a is greater than 0.5 · QF , the assessment flow QA should be taken as the greater of QA calculated using Equation 5.29.1 and QA calculated using Equation 5.29.2. Equation 5.29.2 Assessment flow when the peak tidal flow is greater than half the fluvial component of the assessment flow. QA = QF 3 + QTide,max 5.30 The tidal rise during the flood tide can be much more rapid than the tidal fall during the ebb tide. Where the seaward face of the piers, or abutments, or retaining walls, appears to be vulnerable to scour during reverse flows on the flood tide, this shall be assessed as part of the scour Level 2 assessment. NOTE A reverse flow can only occur during a flood tide. 5.30.1 Reverse flows may be allowed for by taking the assessment flow QA as no less than the value derived from Equation 5.30.1. Equation 5.30.1 Minimum assessment flow for reverse flows. QA > 4.5 π × QTide,max Calculation of depth of flow and velocity of flow upstream of structure 5.31 Where the approximate shape of the stream or river channel cross section is one of the three options shown in Figure 5.31.8, the depth of flow yu and velocity of flow vu upstream of the structure shall be calculated by the simplified methods given in clauses 5.31.1 to 5.31.14 in this document. 83 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... NOTE Where the approximate shape of the stream or river channel cross section is not one of the three options shown in Figure 5.31.8, refer to clause 5.32. 5.31.1 The depth of flow yu and velocity of flow vu upstream of the structure should be calculated from a hydraulic analysis based on the assessment flow QA and the characteristics of the waterway and the flood plains. 5.31.2 For waterways with flood embankments on both sides of the river, unless it can be shown that these could not be over-topped by the assessment flow QA : 1) the depth of flow upstream of the bridge yu should be determined, assuming the maximum flood level upstream of the bridge is 300 mm above the top of the flood embankments; and, 2) the velocity of flow upstream of the bridge, vu , should be calculated using Equation 5.31.2b. Equation 5.31.2a Cross-sectional area of flow upstream of the bridge, with flood embankments on both sides of the river. Au = Bu · yu where: Au is the cross-sectional area of flow upstream of the bridge, in m2 . Bu is the average width of the channel upstream of the bridge, in m. Refer to Figure 3.9.1. yu depth of flow upstream of the bridge, in m, i.e. assuming maximum flood level upstream of the bridge with water level 300 mm above the top of flood embankments. Equation 5.31.2b Velocity of flow upstream of the bridge, with flood embankments on both sides of the river. νu = QA Bu · yu where: νu is velocity of flow upstream of the bridge, in m/s. QA is assessment flow, in m3 /s. Bu is the average width of the channel upstream of the bridge, in m. Refer to Figure 3.9.1. yu is depth of flow upstream of the bridge, in m, i.e. assuming maximum flood level upstream of the bridge with water level 300 mm above the top of flood embankments. 5.31.3 Where flood embankments are not present on both sides of the river, the depth of flow yu and velocity of flow vu upstream of the bridge should be calculated assuming uniform flow conditions, where the energy lost to drag at the boundary layer is equal to the change in potential energy and the depth of flow is uniform with a value, yn , defined in Equation 5.31.4a. NOTE The simplified approach described in clause 5.31.3 neglects the afflux effect on water surface profile caused by the bridge and provides a conservative estimate of the flow velocity for the calculation of scour depth. 5.31.4 The normal depth of flow, yn and normal velocity of flow, vn upstream of the bridge, based on uniform flow conditions, may be calculated based on a simplification of Manning's equation for wide channels, as shown in Equations 5.31.4a and 5.31.4b. 84 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.31.4a Manning's equation for a wide channel, to calculate the normal depth of flow. yn = ( QA · n B · s 1 2 )3 5 where: yn is normal depth of flow for uniform flow conditions, in m QA is assessment flow, in m3 /s n is Manning's coefficient, defined in clause 5.31.11 B is the average width of the channel, in m s is the longitudinal slope of the channel, defined in clause 5.31.10 Equation 5.31.4b Manning's equation for a wide channel, to calculate the normal velocity of flow. νn = QA B · yn where: νn normal velocity of flow corresponding to the normal depth of flow yn, in m/s QA assessment flow, in m3 /s B average width of the channel, in m yn normal depth of flow for uniform flow conditions, in m 5.31.5 Where the level of the normal depth of flow, yn calculated using Equation 5.31.4a exceeds the river bank levels, and flood embankments are not present, then an adjustment should be made to account for the effect of some of the water flowing onto the flood plains, as described in clauses 5.31.13 and 5.31.14. NOTE After using Equation 5.31.4a to calculate yn , if the calculated value of yn > B 10 , then the value of yn can be conservative. 5.31.6 Where Equation 5.31.4a has been used to calculate yn and the calculated value of yn > B 10 , then the method provided in clauses 5.31.7 to 5.31.8 may be used to calculate a more realistic value of yn and the method provided in clause 5.31.9 may be used to calculate vn . 5.31.7 The normal depth of flow, yn , may be determined using: 1) the value of An calculated using Manning's equation shown in Equation 5.31.7; and 2) the approximate shape of the stream or river channel cross section, refer to clause 5.31.8. 85 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.31.7 Area of the flow corresponding to the normal depth of flow. An = ( QA · P 2 3 · n s 1 2 )3 5 where: An cross-sectional area of the flow corresponding to the normal depth of flow yn , in m2 QA assessment flow, in m3 /s P length of the wetted perimeter of the flow cross section, in m n Manning's coefficient as defined in clause 5.31.11. s stream or river bed gradient as calculated in clause 5.31.10. 5.31.8 One of the three options for the approximate shape of the stream or river channel cross section, as illustrated in Figure 5.31.8, may be used: 1) Figure 5.31.8 Diagram (a), rectangular channel cross-section. Where the normal depth of flow yn is not sufficient to over-top the banks, then P = B + 2 · yn and An = B · yn when using Equation 5.31.7 to calculate yn ; 2) Figure 5.31 8 Diagram (b), trapezoidal channel cross-section. Where the normal depth of flow yn is not sufficient to over-top the banks, then P and An both depend on the normal depth of flow yn and an iterative approach is needed when using Equation 5.31.7 to calculate yn ; or, 3) Figure 5.31.8 Diagram (c) trapezoidal channel cross-section, for over-bank flow conditions, where flood embankments are not present. Where the normal depth of flow yn exceeds the bank level, then it is to be assumed that the cross-sectional area of flow boundary extends vertically above the banks when using Equation 5.31.7 to calculate yn . 86 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.31.8 Definition of parameters for determining the normal depth of flow for uniform flow conditions. NOTE 1 Figure 5.31.8 Diagram (a) is a rectangular channel cross-section, based on the average width of the channel B, with no over bank flow conditions. The method for calculating the average width of the channel B is shown in Figure 3.9. NOTE 2 Figure 5.31.8 Diagram (b) is a trapezoidal channel cross-section, with no over-bank flow conditions. NOTE 3 Figure 5.31.8 Diagram (c) is a trapezoidal channel cross-section, for over=bank flow conditions, where flood embankments are not present. 5.31.9 The normal velocity of flow, vn , corresponding to the normal depth of flow, yn , may be calculated using 87 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.31.9: Equation 5.31.9 Normal velocity of flow corresponding to normal depth of flow. νn = QA An where: νn is the normal velocity of flow corresponding to the normal depth of flow yn , in m/s QA is assessment flow, in m3 /s An is the cross-sectional area of the flow corresponding to the normal depth of flow yn , in m2 5.31.10 Unless more detailed survey data is available, the stream or river bed gradient , s , should be determined using the height of contours on maps and the total length along the channel between the contour positions: 1) at least two contours are to be used on either side of the bridge; 2) where there is not a change of channel slope close to and upstream of the bridge, an average channel slope is to be calculated; and, 3) where there is a change of channel slope close to and upstream of the bridge, the channel slope is to be calculated as the channel slope of the stream or river reach immediately upstream of the bridge. NOTE Refer to the "Terms and definitions" table for the definition of "stream or river bed gradient". 5.31.11 Values of Manning's coefficient, n , should be assumed to be as follows: 1) n = 0.035 for a straight reach in a stream or river channel, clear of obstructions and with only light bank vegetation; 2) n = 0.060 for a stream or river channel with irregular banks or heavy brush and trees on the banks; or 3) intermediate values may be adopted for stream or river channels between these two extremes. Further guidance is given in Open Channel Hydraulics Chow 1959 1959 [Ref 13.I]. 5.31.12 Where the level of the normal depth of flow yn calculated using Equation 5.31.5a does not exceed the river bank levels, the depth of flow upstream of the bridge, yu and velocity of flow upstream of the bridge, vu should be calculated using Equation 5.31.12a and Equation 5.31.12b: Equation 5.31.12a Depth of flow upstream of the bridge. yu = yn where: yu is the depth of flow upstream of the bridge, in m yn is the normal depth of flow for uniform flow conditions, in m/s 88 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.31.12b Velocity of flow upstream of the bridge. vu = vn where: vu is the velocity of flow upstream of the bridge, in m/s vn is the normal velocity of flow corresponding to the normal depth of flow for uniform flow conditions, in m/s yn 5.31.13 Where the level of the normal depth of flow yn calculated using Equation 5.31.5a exceeds the river bank levels, and flood embankments are not present, the simplified method provided in clause 5.31.14 should be used to calculate yu and vu , to account for the effect of some of the water flowing onto the flood plains. 5.31.14 In accordance with clause 5.31.13, the depth of flow upstream of the bridge, yu and velocity of flow upstream of the bridge, vu , should be calculated using Equation 5.31.14a and Equation 5.31.14b. Equation 5.31.14a Depth of flow upstream of the bridge, when banks are exceeded. yu = yn − αy · yp where: yu is depth of flow upstream of the bridge, when the level of the river bank is exceeded, or when the levels of both river banks are exceeded, in m yn is the normal depth of flow for uniform flow conditions in the channel alone, assuming vertical boundaries to the channel cross section, as shown in Figure 5.31.8 Diagram (a), in m αy is the coefficient for flood plain effect on depth of flow, given in Table 5.31.14, that depends on the flood plain factor, Fp , as defined in clause 5.33. yp is height of normal flow above flood plain level, i.e. the difference between the level of the normal depth of flow for uniform flow conditions in the channel alone and the flood plain level, as shown in Figure 5.31.8 Diagram (c), in m Equation 5.31.14b Velocity of flow upstream of the bridge, when banks are exceeded. νu = αv · νn where: νu is the velocity of flow upstream of the bridge, when the level of the river bank is exceeded, or when the levels of both river banks are exceeded, in m/s. αv is the coefficient for flood plain effect on velocity of flow, given in Table 5.31.14, that depends on the flood plain factor, Fp , as defined in clause 5.33. νn is normal velocity of flow corresponding to the normal depth of flow yn, in m/s. 89 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Table 5.31.14 Values of coefficients to account for flood plain flow. Flood plain factor Fp Coefficient for flood plain effect on depth of flow αy Coefficient for flood plain effect on velocity of flow αv Fp ≤ 1 0.25 1.00 1 < Fp ≤ 4 0.50 0.95 Fp > 4 0.70 0.90 5.32 Where the approximate shape of the stream or river channel cross section is not one of the three options shown in Figure 5.31.8, the depth of flow, yu and velocity of flow, vu , upstream of the bridge shall be calculated by a method to be proposed to the Technical Approval Authority, for approval prior to commencement of the scour Level 2 assessment. Calculation of the flood plain factor 5.33 For situations where flood water flows over the river bank during the 0.5% AEP weather event, the flood plain factor, Fp , shall be determined based on the characteristics of the flood plain areas and the river banks immediately upstream of the bridge in accordance with clauses 5.33.1 to 5.33.10. 5.33.1 The area of land upstream of the bridge, on each side of the river, should be sub-divided into eight areas as shown on Figure 5.33.1, in accordance with clause 5.33.2 and: 1) the left flood plain sectors L1, L2 and L3; 2) left river bank immediately upstream of the bridge; 3) the right flood plain sectors R1, R2 and R3; and, 4) right river bank immediately upstream of the bridge. 90 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.33.1 Illustration of idealised flood plain sectors. 5.33.2 Each of the six flood plain sectors L1, L2, L3, R1, R2 and R3, should be defined on a plan by the extent of flooding following a severe weather event with a 0.5% AEP and: 91 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 1) the length of each flood plain sector parallel to the river calculated as ten channel widths, 10 · Bu ; and, 2) the width of each flood plain sector perpendicular to the river, WL or WR , determined in accordance with the extent of flooding shown on flood risk maps for the 0.5% AEP severe weather event. 5.33.3 Each of the six flood plain sectors, L1, L2, L3, R1, R2 and R3, as defined in clauses 5.33.1 and 5.33.2, should be assessed in turn to determine the most severe obstruction it presents to any potential flood flow across it, using the following factors: 1) the density and height of vegetation; 2) seasonal variations of vegetation; 3) the presence of any raised ground; and, 4) the existence of any man-made obstructions. 5.33.4 The classification of typical flood plain situations is illustrated pictorially in Figure 5.33.4. Each of the six flood plain sectors, L1, L2, L3, R1, R2 and R3, should be individually classified, using the most severe obstruction to flood flow determined in accordance with clause 5.33.3, as one of the following: 1) very obstructed; or 2) partially obstructed; or 3) open. 92 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.33.4 Classification of floodplain sectors. NOTE The three flood plain sectors on one side of the river can each have a different classification, in accordance with this clause. 93 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 5.33.5 The left flood plain should be classified according to the worst classification assigned to any of the three left flood plain sectors L1, L2 and L3, determined in accordance with clause 5.33.4. NOTE 1 The worst classification is "very obstructed", as this situation provides the most severe obstruction to flood flow. NOTE 2 The least onerous classification is "open", as this situation provides the least obstruction to flood flow. NOTE 3 Example 1: if any of the three left flood plain sectors L1, L2 and L3 are classified as "very obstructed", then the left flood plain is to be classified as very obstructed. NOTE 4 Example 2: a flood plain is only to be classified as "open" if all three sectors on the same side of the river are classified as "open". 5.33.6 In addition to the six flood plain sectors, the left and right river banks adjacent to the bridge on its upstream side, as shown in Figure 5.33.1, should also be assessed, in order to characterise the difficulty that any flood plain flow would have when re-entering the stream or river channel upstream of the bridge. 5.33.7 The left river bank adjacent to the bridge should be classified as: 1) very obstructed; 2) partially obstructed; or, 3) open. 5.33.8 After a classification has been obtained for the whole of the left flood plain (in accordance with clause 5.33.5), this should be compared with the classification for the left river bank adjacent to the bridge (in accordance with clause 5.33.7), to determine the overall effective width of the left flood plain, Weff,L in accordance with Table 5.33.8. 94 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Table 5.33.8 Effective widths of flood plains. River bank adjacent to the bridge classification Open Partially obstructed Very obstructed Effective width of each flood plain (W = full width of respective flood plain) Effective width of each flood plain (W = full width of respective flood plain) Effective width of each flood plain (W = full width of respective flood plain) Open Weff = W Weff = 0.5W Weff = 0.5W Partially obstructed Weff = 0.5W Weff = 0.5W Weff = 0 Flood plain classifica- tion Very obstructed Weff = 0 Weff = 0 Weff = 0 95 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 5.33.9 The process described in clauses 5.33.3 to 5.33.8 for the areas of land on the left side of the river should be repeated for the areas of land on the right side of the river, to determine the overall effective width of the right flood plain, Weff,R . 5.33.10 The flood plain factor, Fp , should be determined using Equation 5.33.10. Equation 5.33.10 Flood plain factor. Fp = Weff,L + Weff,R Bu where: Fp is the flood plain factor. Weff,L is the effective width of the left flood plain, obtained from Table 5.33.8. Weff,R is the effective width of the right flood plain, obtained from Table 5.33.8. Bu is the average width of channel upstream of the bridge. Calculation of depth of flow and velocity of flow through structure opening 5.34 The depth of flow and velocity of flow through the structure opening, whatever the structure type, shall be determined for the assessment flow, QA , based on an analysis of the flow as it transitions from its upstream flow characteristics to flow characteristics through the structure opening. NOTE 1 Where the flow through the bridge opening is governed by minimum energy considerations, the depth of flow and velocity of flow through the bridge opening can be determined using clauses 5.34 to 5.38. NOTE 2 The analysis of flow through a bridge opening depends on the energy available in the upstream flow and the characteristics of the bridge opening. NOTE 3 Where there is a reduction in the width of the channel, B , caused by the bridge: 1) the depth of flow through the bridge opening, yB , can be significantly less than the depth of flow upstream of the bridge, yu ; and, 2) the velocity of flow through the bridge opening vB can be significantly greater than the velocity of flow upstream of the bridge, vu . 5.34.1 For the calculation of the velocity of flow through the bridge opening, vB , it should be conservatively assumed that: 1) the total assessment flow, QA , passes through the bridge opening; and, 2) any flow over, or around, the structure is neglected. NOTE Referring to clauses 5.40 and 5.41. It can undesirable for: 1) flood water flowing over the top of the bridge; or, 2) flood water flowing around the ends / sides of the bridge. 5.34.2 Bernoulli's equations, Equations 5.34.2a and 5.34.2b, should be used to determine the relationship between the flow upstream of the bridge and the flow through the bridge opening, assuming that there is no loss in energy, as illustrated in Figure 5.34.2. 96 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.34.2a Relationship between the depth and velocity of flow upstream of the bridge, and the depth and velocity of flow through bridge opening, for rectangular openings. yu + ν 2 u 2g − yB − ( QA yB·BB )2 2g = 0 where: yu is depth of flow upstream of the bridge, in m νu is velocity of flow upstream of the bridge, in m/s g is acceleration due to gravity, 9.81 m/s2 . yB is depth of flow through the bridge opening, in m QA is assessment flow, in m3 /s BB is average width of the channel at the bridge opening, in m Equation 5.34.2b Relationship between the depth and velocity of flow upstream of the bridge, and the depth and velocity of flow through bridge opening, for non-rectangular openings. yu + ν 2 u 2g − yB − ( QA ABy)2 2g = 0 where: yu is depth of flow upstream of the bridge, in m νu is velocity of flow upstream of the bridge, in m/s g is acceleration due to gravity, 9.81 m/s2 yB is depth of flow through the bridge opening, in m QA is assessment flow, in m3 /s ABy is the cross-sectional area of flow through the bridge opening, without constriction scour, based on yB , but no greater than AB, in m2 . AB is the cross-sectional area of the bridge opening, in m2 . For example, this is the area from the soffit of the opening down to the channel bed, between two bridge piers. 97 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.34.2 Illustration of Bernoulli's equation, based on the conservation of energy, assuming a level river channel bed. 98 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... NOTE When using Equation 5.34.2a or 5.34.2b, there are three potential solutions for yB , only two of which are positive. Of the two positive solutions, the smaller value, yB,sup represents super-critical flow (where the velocity is faster than the wave speed) and the larger value, yB,sub represents sub-critical flow (where the velocity is slower than the wave speed). Either of these conditions is possible, depending on the channel bed slope, the flow rate and the characteristics of the bridge opening. 5.34.3 In open channel flow, the specific energy is the sum of the static pressure head, the dynamic pressure head and the loss of energy, as shown in Equation 5.34.3. The loss of energy, he , is to be neglected. Where there is a channel bed slope between the two channel locations, Equation 5.34.3 should be used to determine the relationship between the depth of flow upstream of the bridge and the depth of flow through the bridge opening. Equation 5.34.3 Specific energy of open channel flow. E = y + ν 2 2g + z + he where: E is the specific energy of open channel flow, in m y is depth of flow, in m v is velocity of flow, in m/s g is acceleration due to gravity, 9.81 m/s2 z is the height of river channel bed above datum, in m he is loss of energy, in m 5.35 The situations when super-critical flow can occur through the bridge opening shall be determined and the consequences analysed, at different flow rates, up to and including the assessment flow, QA . NOTE This clause is to determine if a situation can occur, which could potentially massively increase scour risk, at a flow rate significantly less than the assessment flow. 5.35.1 The critical longitudinal slope of the channel, sc , should be calculated, using Equation 5.35.1. Equation 5.35.1 Critical longitudinal slope of the channel. sc = n 2 ( B2 B · g 10 Q2 A )1 9 where: sc is the critical longitudinal slope of the channel n is Manning's coefficient, defined in clause 5.31.11 BB is the average width of the channel at the bridge opening, in m g is acceleration due to gravity, 9.81 m/s2 QA is assessment flow, in m3 /s 5.35.2 The critical longitudinal slope of the channel, sc , calculated using Equation 5.35.1 should be compared with the channel slope, s , calculated in accordance with clause 5.31.10. 5.35.3 Where s > 0.9 · sc , or where the channel slope at the bridge s exceeds sc , or if there is another particular reason that the flow could be supercritical where the river flows through the bridge opening, then the supercritical solution should be selected with yB = yB,sup based on the smaller of the two positive solutions of Bernoulli's equation, as provided in clauses 5.34.2 and 5.34.3. 99 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 5.35.4 Where s ≤ 0.9 · sc it should be assumed that the flow will be subcritical. However, it is likely that there is energy loss at the bridge constriction, which for subcritical flow upstream of the bridge can result in a reduced depth of flow and a faster velocity of flow through the bridge opening. Therefore, the depth of flow through the bridge opening, yB , can be assumed to be no greater than the critical depth of flow for minimum energy, yc , calculated using Equation 5.35.4. Equation 5.35.4 Depth of flow and critical depth of flow for minimum energy through the bridge opening. yB ≤ yc = ( Q2 A B2 B · g )1 3 where: yB is the depth of flow through the bridge opening, in m yc is the critical depth of flow for minimum energy conditions, in m QA is assessment flow, in m3 /s BB is the average width of the channel at the bridge opening, in m g is acceleration due to gravity, 9.81 m/s2 5.36 The cross-sectional area of flow through the bridge opening, ABy , shall be calculated based on the depth of flow through the bridge opening, yB . 5.37 The cross-sectional area of flow through the bridge opening, ABy , shall be taken as no greater than the cross-sectional area of the bridge opening, AB . NOTE In clauses 5.36, 5.37 and 5.38, it is assumed that, as part of the process to determine scour depth: 1) all of the assessment flow, QA , passes through the bridge opening; and, 2) the depth of flow at the upstream face of the structure is less than the height of the soffit of the bridge opening. 5.38 The mean velocity through the bridge opening, vB, shall be calculated using Equation 5.38. Equation 5.38 Mean velocity of flow through the bridge opening. νB = QA ABy where: vB is mean velocity of flow through the bridge opening, in m/s QA is assessment flow, in m3 /s ABy is the cross-sectional area of flow through the bridge opening without constriction scour, based on yB , but no greater than AB , in m2 AB is the cross-sectional area of the bridge opening, in m2 . For example, this is the area from the soffit of the opening down to the channel bed, between two bridge piers. NOTE Refer to clauses 5.40, 5.41 and 8.12.1. There is a need to ensure that the methods used are appropriate to determine all of the following at the structure: 1) the percentage of the assessment flow QA that will pass through the structure opening; 2) the percentage of the assessment flow QA that will flow over the structure; and, 100 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 3) the percentage of the assessment flow QA that will flow around the sides/ends of the structure. Calculation of maximum depth of flow at upstream face of structure 5.39 The maximum depth of flow at the upstream face of the structure, yuf , shall be determined for the assessment flow, QA . NOTE Due to the afflux, the depth of flow at the upstream face of a structure, yuf , can be greater than the depth of flow upstream of the structure, yu . 5.39.1 The maximum depth of flow at the upstream face of a bridge, yuf , may be determined in accordance with one of the three methods provided in clauses 5.39.2 to 5.39.4, if the criteria are met. 5.39.2 Method 1. The depth of flow upstream of the bridge, yu , provides a lower bound to the depth of flow just upstream of the bridge, yuf . If yu calculated using the method provided in clause 5.31.12 or 5.31.14 exceeds the height of the bridge soffit above the river bed at the upstream face of the bridge Hsoff , then it may be assumed that the water level just upstream of the structure exceeds the soffit of the bridge, i.e. if yu > Hsoff then yuf > Hsoff ; 5.39.3 Method 2. It may be assumed that the water level does not reach the soffit of the bridge if the specific energy line for the flow through the bridge opening does not exceed the soffit level, i.e. yB + ν 2 B 2g < Hsoff . NOTE An example of a specific energy line is shown in Figure 5.34.2. 5.39.4 Method 3. Where the criteria provided in clause 5.39.2 (Method 1) or clause 5.39.3 (Method 2) are not satisfied, then the depth of flow at the upstream face of the structure, yuf may be determined iteratively using Equation 5.39.4. Where there is no positive solution for yuf greater than Hsoff , then it can be assumed that the water level cannot reach the soffit of the bridge at the assessment flow, QA . Equation 5.39.4 Depth of flow at upstream face of the bridge. 2g ( yuf − Hsoff 2 ) + ( QA Auf )2 − ( 2 · QA AB )2 = 0 where: g is acceleration due to gravity, 9.81 m/s2 yuf is the depth of flow at the upstream face of the bridge, in m Hsoff is the height of the bridge soffit above the river bed, at the upstream face of the bridge, in m QA is assessment flow, in m3 /s Auf is the cross-sectional area of flow just upstream of the bridge, in m2 AB is the cross-sectional area of the bridge opening, in m2 . For example, this is the area from the soffit of the opening down to the channel bed, between two bridge piers. NOTE The method provided in clause 5.39.4 (Method 3) is based on a sluice gate approach, which initially assumes that the depth of flow at the upstream face of the bridge yuf does exceed the height of the bridge soffit above the river bed, Hsoff . 5.40 For a structure where the depth of flow at the upstream face of the structure yuf is expected to exceed the height of the structure soffit above the river bed, Hsoff , the stability and robustness of the structure shall be assessed in accordance with clause 6.2. 5.41 For a structure where yB + ν 2 B 2g ≥ Hsoff − 0.6 , debris impact on the structure shall be assessed in accordance with clause 6.3. 101 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Calculation of scour depth 5.42 The depth of scour shall be determined, using the flow parameters previously calculated. 5.43 For each part of the the structure that can be affected by scour, the maximum constriction scour depth, Dc and maximum local scour depth, Dl shall be calculated. NOTE 1 Constriction scour is associated with the erosion of channel bed material caused by increased flow velocity through a constriction in the channel at the structure location. NOTE 2 Local scour is associated with the additional effects of piers, or abutments, or retaining walls, disturbing the flow and causing vortices that erode the channel bed locally. 5.43.1 The scour depth at each bridge pier should be calculated. 5.43.2 Where the abutment is not within 10 m of the river bank, the possibility of over-bank flood flow conditions (in the 0.5% AEP weather event) should be taken into account, to determine whether the scour depth at the abutment should be calculated. 5.43.3 Where the abutment is in the river channel, or where part of the abutment protrudes into the river channel, or where the abutment is within 10 m of the river bank, the scour depth at the abutment should be calculated. 5.43.4 Where the retaining wall is not within 10 m of the river bank, the possibility of over-bank flood flow conditions (in the 0.5% AEP weather event) should be taken into account, to determine whether the scour depth at the retaining wall should be calculated. 5.43.5 Where a retaining wall supports the river channel bank, or is in the river channel, or where part of a retaining wall protrudes in to the river channel, or where the retaining wall is within 10 m of the river bank, the scour depth at the retaining wall should be calculated. NOTE Examples of retaining walls in a stream or river channel are: 1) the head wall at the upstream end of a pipe or culvert; and, 2) the head wall at the downstream end of a pipe or culvert. Calculation of constriction scour depth 5.44 The average depth of constriction scour below the original channel bed level, Dc,ave , shall be calculated for each section of the stream or river channel at a structure, including: 1) channel between a bridge abutment and a bridge pier; 2) channel between two bridge abutments; 3) channel between two bridge piers; and, 4) channel between two retaining walls. NOTE 1 When this constriction scour depth occurs, this can result in the mean velocity of flow through the bridge opening, vB dropping to a threshold value, vB,c with no further scouring of the channel bed. NOTE 2 As constriction scour depth increases, flow velocity decreases. In such a situation, when the constriction scour depth is so great, no further scouring of the channel bed is likely, as the velocity of flow has reduced, so that the flow does not have sufficient energy to scour the channel bed any deeper. Calculation of mean threshold velocity of flow through the bridge opening, due to constriction scour 5.45 The mean threshold velocity of flow through the bridge opening, below which scour does not occur, νB,c , shall be determined. 5.45.1 The mean threshold velocity of flow through the bridge opening, below which scour does not occur, νB,c , should be assumed to be equal to the competent mean velocity of flow, vcomp . 102 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... NOTE The competent mean velocity of flow, vcomp , depends on the depth of flow, y and the stream or river channel bed material grain size. 5.45.2 If there is no stream or river bed borehole information, or insufficient site survey data of the channel bed material, the stream or river channel bed median grain size, dmgs , should be estimated using one of the default values provided in Table 5.45.2, based on the Guide to Bridge Hydraulics [Ref 5.N]. Table 5.45.2 Typical stream or river channel bed material characteristics (based on the Guide to Bridge Hydraulics ). The stream or river bed gradient, s , measured on the channel centre line over an upstream distance of 100 m from the upstream face of the structure Typical stream or river channel bed material Typical stream or river channel bed median grain size dmgs default value Very steep s > 10% Boulders, cobbles, gravels, sands 10 mm Steep 4% ≤ s ≤ 10% Cobbles, gravels, sands 5 mm Moderate 2% ≤ s < 4% Gravels, sands 2 mm Low 0.5% ≤ s < 2% Sands, silts and clays 0.5 mm Very low s < 0.5% Sands and silts 0.1 mm NOTE 1 Refer to the "Terms and definitions" table for the definition of "stream or river bed gradient". NOTE 2 A site investigation including one or more boreholes in the stream or river channel bed within the defined distance from the structure can be carried out to confirm the stream or river channel bed median grain size, dmgs . NOTE 3 The defined distance from the structure is provided in Table 3.12. 5.45.3 Where the channel bed is granular materials at the bridge opening, using the channel bed median grain size, dmgs , and the depth of flow through the bridge opening, yB , the competent mean velocity of flow, vcomp , should be estimated using Figure 5.45.3, based on the Guide to Bridge Hydraulics [Ref 5.N]. In Figure 5.45.3 "Depth" refers to the depth of flow through the bridge opening yB . 103 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.45.3 Competent mean velocities for granular materials (based on the Guide to Bridge Hydraulics). 104 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 5.45.4 Where the channel bed is cohesive materials at the bridge opening, using the channel bed material description and the depth of flow through the bridge opening, yB , the competent mean velocity of flow, vcomp , should be estimated using Table 5.45.4, based on the Guide to Bridge Hydraulics [Ref 5.N]. 105 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Table 5.45.4 Competent mean velocities for cohesive materials (based on the Guide to Bridge Hydraulics). Channel bed material description Easily erodible cohesive material Average cohesive material Resistant to erosion cohesive material Depth of flow through the bridge opening y B (in m) Competent mean velocity of flow vcomp (in m/s) Competent mean velocity of flow vcomp (in m/s) Competent mean velocity of flow vcomp (in m/s) 1.5 0.6 1.0 1.8 3 0.65 1.2 2.0 6 0.7 1.3 2.3 15 0.8 1.5 2.6 106 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Calculation of the additional area of flow through the bridge opening, due to constriction scour 5.46 The additional area of the flow through the bridge opening due to constriction scour, ∆A , shall be calculated using Equation 5.46. Equation 5.46 Additional area of flow through the bridge opening, due to constriction scour. ∆A = QA νB,c − ABy where: ∆A is the increase in cross-sectional area of flow through the bridge opening, due to constriction scour, in m2 . Refer to Figure 5.46.1. QA is assessment flow, in m3 /s νB.c is the mean threshold velocity of flow through the bridge opening, below which scour does not occur, as calculated in accordance with clauses 5.45.3 and 5.45.4, in m/s ABy is the cross-sectional area of flow through the bridge opening without constriction scour, based on yB , but no greater than AB , in m2 yB is depth of flow through the bridge opening, in m AB is the cross-sectional area of the bridge opening, in m2 . For example, this is the area from the soffit of the opening down to the channel bed level, between two bridge piers. 5.46.1 Using the increase in cross-sectional area of flow through the bridge opening due to constriction scour, ∆A , the average depth of constriction scour below the original channel bed level, Dc,ave , should be calculated, as illustrated in Figure 5.46.1. Figure 5.46.1 Average depth of constriction scour below the original channel bed level. Calculation of maximum depth of constriction scour 5.47 The maximum constriction scour depth, Dc , adjacent to each part of the structure, shall be calculated based on the average depth of constriction scour below the original channel bed level, Dc,ave and the expected variation of constriction scour across the channel, using Equation 5.47. 107 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.47 Maximum constriction scour depth. Dc = Fs · Dc,ave where: Dc is the maximum constriction scour depth, in m. Fs is constriction scour distribution factor, which should be taken from Table 5.47. Dc,ave is the average depth of constriction scour, below the original channel bed level, in m. Table 5.47 Constriction scour distribution factor. Location Outside of bend Centre of channel Inside of bend On, or downstream of, a sharp bend in a river channel 2.0 1.25 1 On, or downstream of, a moderate bend in a river channel 1.5 1.25 1 On a straight reach in a river channel 1.25 1.25 1.25 NOTE The terms "sharp bend in a river channel", "moderate bend in a river channel" and "straight reach in a river channel" are defined in the "Terms and definitions" table. 5.47.1 The maximum constriction scour depth, Dc , should be calculated adjacent to each abutment, Dc, abutment , bridge pier, Dc, pier , retaining wall, Dc, rwall and other structures. Calculation of local scour depth 5.48 The maximum local scour depth, Dl , adjacent to each part of the structure, shall be determined. 5.48.1 Where the depth of constriction scour is sufficient to expose an enlarged footing or pile cap, then the calculation of local scour depth using Equation 5.49 should be based on the geometry of the enlarged section. 5.48.2 The type of pier foundation should be assessed to determine whether the foundation has a beneficial or adverse effect on the development of local scour. For example, refer to Figure 5.48.2, which is based on the Guide to Bridge Hydraulics [Ref 5.N]. Any beneficial effects of footings on the development of local scour are to be neglected. 108 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.48.2 Effect of pier footings on local scour (based on the Guide to Bridge Hydraulics). 109 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... NOTE The effects of enlarged footings on development of local scour can be beneficial or adverse, depending on whether the footing is exposed by the constriction scour. 5.48.3 The maximum local scour depth adjacent to an abutment, Dl, abutment , or a retaining wall Dl, rwall , may be calculated based on the following: 1) the methods provided in CIRIA C742 [Ref 11.I] and CIRIA SP171 [Ref 12.I]; or 2) the methods provided in HEC 18 - FHWA-HIF-12-003 [Ref 7.I]. NOTE Further guidance on calculating local scour depth is provided in CIRIA C742 [Ref 11.I]. 5.49 The maximum local scour depth adjacent to a bridge pier, Dl,pier , shall be calculated using Equation 5.49 and depends primarily on the geometry of the pier CIRIA SP171 [Ref 12.I]. Equation 5.49 Maximum local scour depth adjacent to bridge pier. Dl,pier = 1.5 · WP · fPS·fPA·fy·fd where: Dl,pier is the maximum local scour depth adjacent to a bridge pier, in m. WP is bridge pier width, in m. Refer to Figure 5.49.1a. fPS is the pier shape factor, depending on the shape of the pier and the angle of attack of the flow on the pier. Refer to clause 5.49.1. fPA is the pier angle of attack factor, depending on the angle of attack of the flow on the pier. Refer to clause 5.49.2. fy is the depth of flow factor, depending on the relative depth of the approach flow to the pier width. Refer to clause 5.49.3. fd is the debris factor, depending on the debris accumulation at the structure. Refer to clause 5.49.4. 5.49.1 The pier shape factor, fPS , should be taken as: 1) fPS =1.0 where the angle of attack α > 10o ; or, 2) fPS should be taken from Figure 5.49.1a, where the angle of attack α ≤ 10o . The angle of attack α is defined in Figure 5.49.1.b. 110 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.49.1a Pier shape factor. 111 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.49.1b Angle of attack at a bridge pier in a river. 112 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... NOTE 1 α is the angle between the direction of flow and the bridge pier longitudinal centre-line, i.e. the angle of attack. NOTE 2 Where the direction of flow is parallel to the bridge pier longitudinal centre line, α = 0 . 5.49.2 The pier angle of attack factor, fPA should be calculated using Equation 5.49.2. Equation 5.49.2 Pier angle of attack factor. fPA = ( cos α + L WP sin α )0.65 where: fPA is the pier angle of attack factor. α is angle of attack, angle between the direction of flow and the bridge pier longitudinal centre-line, in degrees. The angle of attack is defined in Figure 5.49.1.b. L is bridge pier length, in m. WP is bridge pier width, in m. 5.49.3 The depth of flow factor, fy , should be taken as: 1) fy =1.0 , when the depth of flow at the pier including constriction scour, ysp > 2.6 · WP , where ysp is calculated using Equation 5.49.3a; or, 2) in other cases, fy should be calculated using Equation 5.49.3b. Equation 5.49.3a Depth of flow at the pier including constriction scour. ysp = yB + Dc where: ysp is depth of flow at the pier, including constriction scour, in m yB is depth of flow through bridge opening, in m Dc is the maximum depth of constriction scour, in m Equation 5.49.3b Depth of flow factor. fy =0.78( ysp WP )0.255 where: fy is the depth of flow factor. ysp is depth of flow at the pier including constriction scour, in m WP is the bridge pier width, in m 5.49.4 The debris factor, fd , for woody debris accumulations, should be determined in accordance with Table 5.49.4. Both the simplified method and the rigorous method are derived from University of Southampton and University of Exeter research Panici, Kripakaran, & Dentith [Ref 3.I], JHE 144 (12) [Ref 4.I] and WRR 54 [Ref 6.I]. Further information is provided in Panici et al 2019 [Ref 2.I]. 113 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Table 5.49.4 Debris factor. Debris accumulation factor, D , determined in accordance with Table 4.7 and Table 5.15. Debris factor, fd D = 1.0 fd = 1.0 D > 1.0 Method 1: use the simplified method described in clause 5.49.5 to determine fd . Method 2: if there is a likelihood that use of the rigorous method described in Appendix A to determine fd will reduce the structure scour risk rating obtained from Figure 5.52, request Technical Approval Authority approval for use of the rigorous method described in Appendix A to recalculate fd . NOTE 1 Refer to the "Terms and definitions" table for the definition of "woody debris accumulation", "other debris accumulation" and "defined distance from the structure". NOTE 2 Refer to clause 5.49.6, for situations where other debris accumulations are likely to occur in the stream or river channel within the defined distance from the structure. NOTE 3 The defined distance from the structure is provided in Table 3.12. 5.49.5 The simplified method for calculating the debris factor, fd , for woody debris accumulations, should be in accordance with the two steps described below: 1) the size of the debris accumulation is needed to estimate the debris factor, fd . The debris frontal area, AD (assumed to be triangular) and the upstream length of debris accumulation, KD , are estimated using Figure 5.49.5a and Figure 5.49.5b, interpolating the average width of the channel upstream of the bridge, Bu and the velocity of flow upstream of the bridge, vu ; and 2) the debris size ratio, dsr (to be calculated using Equation 5.49.5a) and the debris blockage area ratio, ∆A% (to be calculated using Equation 5.49.5b) define the debris factor fd , estimated using Figure 5.49.5c. 114 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.49.5a Graph to estimate the debris frontal area. 115 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.49.5b Graph to estimate the upstream length of debris accumulation. 116 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.49.5a Debris size ratio. dsr = KD WP where: dsr is the debris size ratio. KD is the upstream length of debris accumulation, in m WP is bridge pier width, in m Equation 5.49.5b Debris blockage area ratio. ∆A% = AD · 100 A where: ∆A% is the debris blockage area ratio. AD is the debris frontal area, in m2 A is the cross-sectional area of flow upstream of the structure, in m2 117 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.49.5c Graph to estimate the debris factor. 118 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... NOTE 1 The simplified method for estimating the debris factor, fd , can in some situations overestimate the scour depth caused by woody debris accumulation, resulting in the scour risk rating of the structure being higher. In Appendix A, the rigorous method for estimating the debris factor, fd , is provided, which can determine a more accurate estimate of the scour depth caused by woody debris accumulation. NOTE 2 Worked examples for both the simplified and rigorous methods for estimating the debris factor, fd , for woody debris accumulations, are provided in Appendix B. 5.49.6 If, after following the process described in clauses 4.6 and 5.49.4, it is determined that other debris accumulations are likely to occur at the structure, e.g. rocks and boulders being carried by stream or river water during a severe weather event, then the Technical Approval Authority should be consulted, to agree the method of determining the debris factor, fd . NOTE Refer to the "Terms and definitions" table for the definition of "other debris accumulation". 5.49.7 For piers comprising a line of columns, the maximum local scour depth, Dl,pier , may be calculated based on one of the following: 1) if the columns are in line with the flow, then the local scour is to be based on 1.15 times the depth for a single column; 2) if the columns are not in line with the flow and the spacing exceeds 5 column diameters, then the local scour is to be based on 1.2 times the depth for a single column; or, 3) otherwise, the line of columns can be approximated as a solid rectangular pier. Calculation of total scour depth 5.50 The total scour depth, DT , shall be calculated at each abutment, bridge pier, retaining wall and other structures, using Equation 5.50a, Equation 5.50b, and Equation 5.50c. Equation 5.50a Total scour depth adjacent to a pier. DT = Dc, pier + Dl, pier where: DT is the total scour depth, in m Dc, pier is the maximum constriction scour depth adjacent to a pier, in m Dl, pier is the maximum local scour depth adjacent to a pier, in m Equation 5.50b Total scour depth adjacent to an abutment. DT = Dc, abutment + Dl, abutment where: DT is total scour depth, in m Dc, abutment is the maximum constriction scour depth adjacent to an abutment, in m Dl, abutment is the maximum local scour depth adjacent to an abutment, in m 119 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Equation 5.50c Total scour depth adjacent to a retaining wall. DT = Dc, rwall + Dl, rwall where: DT is total scour depth, in m Dc, rwall is the maximum constriction scour depth adjacent to a retaining wall, in m Dl, rwall is the maximum local scour depth adjacent to a retaining wall, in m Comparison of total scour depth with foundation depth 5.51 The relative scour depth, DR , shall be calculated at each abutment, bridge pier, retaining wall and other structures, using Equation 5.51. Equation 5.51 Relative scour depth. DR = DT DF where: DR is the relative scour depth DT is total scour depth, in m DF is the distance below average bed level to the underside of the spread footing foundation, or to the underside of the pile cap in the case of a piled foundation, in m. Refer to Figure 3 .9. NOTE 1 The distance below average bed level to the underside of the pile cap DF makes no allowance for the depth of any piles. NOTE 2 It is important to recognise that the calculated total scour depth is a theoretical estimate of the potential scour depth at a specific location in the stream or river channel. The calculation methods used to calculate scour depth are considered conservative. If the calculated total scour depth shows that the scour depth can potentially extend below the underside of the foundation, it does not necessarily imply that the structure is at high risk of failure or collapse. NOTE 3 There can be specific reasons why the actual scour depth at a structure is not as great as the calculated scour depth, including (but not limited to) one or more of the following reasons: 1) the presence of an enlargement of the foundation that is not exposed by the constriction scour and hence is likely to restrict the depth of the local scour; 2) the location of the maximum depth of constriction scour does not coincide with the location of the maximum depth of local scour; 3) local scour development below a pile cap is less than that calculated on the basis of the pile cap width; 4) the presence of earlier unrecorded protection works, or the presence of more erosion resistant layers of material below the stream or river channel bed, can inhibit the development of scour; 5) the presence below the stream or river channel bed of the original cofferdam, or other sheet piling works installed during construction of the works and left in place after completion of the structure, can act as an enlargement to the pier and suppress the horseshoe vortex and resulting scour hole; 6) the hydraulic calculation is based on several conservative assumptions; 7) the foundations have been constructed on hard sound rock, or on piles, that have not been recorded; or, 120 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 8) the 0.5% AEP weather event, or greater, flood flow has not yet occurred at the structure location. Determination of scour risk rating and scour risk score 5.52 Using the calculated value of the priority factor Type 1, PF-T1 and the highest calculated value of the relative scour depth, DR , for the scour susceptible structure Type 1, the scour risk rating and scour risk score for the structure shall be determined in accordance with Table 2.3, Figure 5.52 and clause 5.53. 121 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Figure 5.52 Scour risk ratings and scour risk scores, for scour susceptible structures Type 1. 5.53 When the priority factor Type 1, PF-T1 , calculated using Equation 5.7 is greater than 2.5 and the relative scour depth, DR , calculated using Equation 5.51 is greater than 1, the scour risk score shall be rated 122 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... as either 80 or 100. Assessment of stability and lateral movement of stream or river channel 5.54 Following a site inspection and reviewing evidence recorded in inspection reports, maintenance records, or other evidence, the stream or river channel shall be assessed to determine: 1) if there is evidence of stream or river channel instability, or lateral movement, i.e. sinuosity; 2) the consequences of instability or lateral movement of the stream or river channel, that have occurred; 3) the potential for future instability or lateral movement of the stream or river channel; 4) the likely consequences of future instability or lateral movement of the stream or river channel; and, 5) the channel stability risk rating, either low, or medium, or high risk, in accordance with Table 5.54. 123 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... Table 5.54 Channel stability risk rating. Assessment of stability and lateral movement of stream or river channel Channel stability risk rating Where three or more of the following apply: 1) the stream or river bed gradient is steep, or very steep; 2) there is a moderate or sharp bend in the stream or river channel within 30 m of the structure, either upstream or downstream of the structure; 3) there is a tributary in the stream or river channel within 200 m of the structure, either upstream or downstream of the structure; 4) there is history or evidence of major channel instability or lateral movement, or stream or river bank or bed erosion, with no bank or bed protection works installed within the defined distance from the structure; 5) there is evidence stream or river bank protection works have been installed, upstream or downstream of the structure, that can have been necessitated by erosion in the past, and these works are in poor condition, i.e they show signs of major distress, or instability, or damage; 6) there is evidence stream or river bed protection works have been installed, upstream or downstream of the structure, that can have been necessitated by erosion in the past, and these works are in poor condition, i.e they show signs of major distress, or instability, or damage; and, 7) there are no mature trees along both banks, upstream and downstream of the structure, within the defined distance from the structure. High risk. Where the assessment of stability and lateral movement of a stream or river channel is not designated high risk, or low risk: Medium risk. Where three or more of the following apply: 1) the stream or river is confined within a valley, with little or no flood plain and the stream or river bed gradient is low, or very low; 2) there is a straight reach at least 200 m in length from the structure in both directions upstream and downstream of the structure (total length of straight reach is at least 400 m); 3) there are no tributaries in the stream or river channel within 200 m of the structure, either upstream or downstream of the structure; 4) there is no history or evidence of channel instability, or lateral movement, or stream or river bank or bed erosion; 5) there is evidence stream or river bank protection works have been installed on both banks, from the structure to the defined distance from the structure upstream and downstream and these works are in good condition, as recorded in inspection reports, or maintenance records; 6) there is evidence stream or river bed protection works have been installed, from the structure to the defined distance from the structure upstream and downstream and these works are in good condition, as recorded in inspection reports, or maintenance records; and 7) there are mature trees along both banks, upstream and downstream of the structure, within the defined distance from the structure. Low risk. NOTE 1 The prediction of future instability or lateral movement of a stream or river channel can involve 124 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... significant uncertainty, due to many different situations which can cause channel instability or lateral movement to occur, either gradually over a long period, or rapidly during a severe weather event. NOTE 2 Bank erosion can be most severe on the outside bank of a bend and the bend can become more pronounced over time. NOTE 3 Refer to the "Terms and definitions" table for the definition of "stream or river bed gradient", "moderate bend in a stream or river channel", "sharp bend in a stream or river channel" and "straight reach in a stream or river channel". NOTE 4 The defined distance from the structure is provided in Table 3.12. 5.54.1 The length of time that the channel has been stable (evidence is needed) should be recorded in the scour Level 2 assessment report and reviewed in future scour reassessments of the structure. 5.55 The existing scour protection measures, for the channel banks or channel bed, shall be assessed as to their current effectiveness, including for the climate change allowances for the structure location defined in the relevant National Application Annex. 5.56 Where the channel stability risk rating is high risk, or medium risk, recommended actions shall be determined, which, if implemented, could reduce the channel stability risk rating to low risk. 5.57 The stream or river channel assessment results, in accordance with clauses 5.54 to 5.56, shall be included as part of the scour Level 2 assessment report. Reporting 5.58 The scour Level 2 assessment report, for a scour susceptible structure Type 1, shall include: 1) the priority factor Type 1, PF-T1 (refer to clauses 5.6 to 5.16); 2) the assessment flow, QA (refer to clauses 5.17 to 5.30.1) and how this has been determined (fluvial component, tidal component and climate change allowances), including the affects of all flow control structures that can affect the flow rate or water level at the structure; 3) the catchment response time (refer to clause 5.24); 4) the consequences, or potential consequences, of severe weather events, using the latest available data for the structure location; 5) the depth of flow, yu and velocity of flow, vu upstream of the structure (refer to clauses 5.31 to 5.33.10); 6) the depth of flow, yB and velocity of flow, vB through the structure opening (refer to clauses 5.34 to 5.38); 7) the depth of flow at the upstream face of the structure, yuf and height of the structure soffit above the river bed, Hsoff (refer to clauses 5.39 to 5.41); 8) for each abutment, pier, retaining wall and other structures, the calculated total scour depth, DT , and the distance below average bed level to the underside of the spread footing foundation, or to the underside of the pile cap in the case of a piled foundation, DF (refer to clauses 5.42 to 5.50); 9) for each abutment, pier, retaining wall and other structures, the calculated relative scour depth, DR (refer to clauses 5.51); 10) the scour risk rating and scour risk score, in accordance with clauses 5.4, 5.52 to 5.53; 11) the channel stability assessment findings and channel stability risk rating, in accordance with clauses 5.54 to 5.57; 12) the consequences, or potential consequences, resulting from scour and other hydraulic actions; 13) the consequences following partial or total structural failure or collapse; and, 14) recommended actions. 5.58.1 Where a further investigation could potentially lead to a lower assessed scour risk rating, or a lower assessed scour risk risk score, additional work may be proposed, including: 125 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 5. Level 2 assessment of scour susceptible struc... 1) further survey work; 2) further investigation work; and, 3) refined scour assessment calculations. 5.59 A Scour Assessment Certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 shall be prepared and submitted to the Technical Approval Authority, in accordance with the relevant National Application Annex. 126 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 6. Assessment of vulnerability of structures to ... 6. Assessment of vulnerability of structures to other hydraulic actions Vulnerability assessment process - scour Level 2 assessment 6.1 For scour susceptible structures Type 1, hydraulic actions other than scour shall be identified as part of a scour Level 2 assessment, for a severe weather event with a 0.5% AEP, including the climate change allowances for the structure location defined in the relevant National Application Annex. NOTE Although scour is the most common hydraulic action that causes failure and collapse of structures, the other hydraulic actions also need to be assessed. Refer to the "Terms and definitions" table for the definition of "hydraulic actions". 6.2 For a structure where the criteria described in clause 5.40 are met, the stability and robustness of the structure shall be assessed as part of the vulnerability assessment. 6.3 For a structure where the criteria described in clause 5.41 are met, the stability and robustness of the structure shall be assessed as part of the vulnerability assessment. 6.4 After the other hydraulic actions have been identified for the structure, the following actions shall be discussed and agreed with the Technical Approval Authority for the structure, prior to commencement of a vulnerability assessment: 1) the need for a vulnerability assessment; and, 2) the methodologies to be used in the vulnerability assessment for the hydraulic analysis and structural analysis of hydraulic actions on structural components, such as bridge abutments, bridge piers, bridge decks, parapets and retaining walls. NOTE 1 The Technical Approval Authority can provide advice on the methodologies to be used in the vulnerability assessment, for the hydraulic analysis and structural analysis of hydraulic actions on structural components, such as bridge abutments, bridge piers, bridge decks, parapets and retaining walls. NOTE 2 For structures where the flood water is predicted to reach or exceed the bridge deck soffit level, the following aspects can be included in the vulnerability assessment: 1) whether uplift on the bridge soffit could lead to a reduction in stability or load carrying capacity (e.g. masonry arches); 2) whether the bridge deck or parapets could be dislodged or destroyed by hydrodynamic actions on the bridge; and, 3) identification of utilities in the bridge deck which could be damaged or destroyed by flood water. NOTE 3 For structures where the flood water is predicted to reach within 0.6 m of the structure soffit level, the possibility of the structure becoming dislodged or destroyed by actions related to debris, carried by flood water to the structure location, can be included in the vulnerability assessment. 6.5 Where, at any stage of the vulnerability assessment, the structure is considered to be at immediate risk of failure, or collapse, the structure shall be designated as an immediate risk scour susceptible structure with a scour risk score of 100. 6.6 Where a structure has been designated as an immediate risk scour susceptible structure, the risks and issues shall be notified to the Overseeing Organisation. 6.7 Immediate risk structures shall be managed in accordance with DMRB CS 470 [Ref 11.N]. NOTE Refer to clauses 2.26 to 2.28. Reporting 6.8 The vulnerability assessment report shall include: 1) the methodology for hydraulic actions analysis used in the vulnerability assessment; 127 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 6. Assessment of vulnerability of structures to ... 2) the scour risk score; 3) a statement of the findings; 4) the likely consequences of the hydraulic actions on the structure; and, 5) recommended actions. 128 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 7. Evaluation of scour susceptible structures Ty... 7. Evaluation of scour susceptible structures Type 2 General 7.1 A scour evaluation shall be carried out on a scour susceptible structure Type 2. 7.2 The scour evaluation shall identify and determine the potential consequences of scour on a structure, during a severe weather event, including: 1) scour priority ranking process Type 2; and, 2) scour evaluation and scour risk rating updating process Type 2. 7.2.1 The priority ranking and scour evaluation should not involve detailed calculations and numerical analysis. 7.3 The scour evaluation shall evaluate the information for the structure location in: 1) the scour inspection reports; 2) scour emergency inspection reports; 3) emergency structural inspection reports; 4) the latest available weather event data; and, 5) the latest available flood event data. 7.4 The outcome of the scour evaluation shall be that the structure is to be designated with a scour risk rating of high risk, medium risk or low risk. Scour priority ranking process Type 2 7.5 For scour susceptible structures Type 2, the scour evaluation programme shall be prioritised, in accordance with the process described in clauses 7.6 to 7.16. Priority ranking Type 2 7.6 A priority ranking Type 2 PR-T2 shall be calculated for each scour susceptible structure Type 2. NOTE The higher the value of priority ranking Type 2 PR-T2 , the higher the priority for carrying out the scour evaluation, or re-evaluation. 7.7 The priority ranking Type 2, PR-T2 , shall be calculated using Equation 7.7: Equation 7.7 Priority ranking Type 2. PR-T2 = F · M · HS · GL · C · CAF where: PR-T2 is priority ranking Type 2. F is the foundation type factor (structure foundation). M is the ground material factor (ground material at the structure). HS is the history of scour factor (scour occurrence at the structure). GL is the land gradient factor (as indicated by the land gradient at the structure). C is the communities importance factor. CAF is the communities additional factor. 7.8 The foundation type factor, F , provided in Table 7.8 shall be used in Equation 7.7. 129 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 7. Evaluation of scour susceptible structures Ty... Table 7.8 Foundation type factor F. For a masonry arch structure - any foundation type F = 1.25 For a spread footing (excluding masonry arch structures) F = 1.0 For a steel or concrete piled foundation F = 0.75 7.8.1 Where the structure foundations include timber piles, or where any part of the structure contains structural timber, the Overseeing Organisation Technical Approval Authority should be consulted to discuss and agree the value of foundation type factor, F , prior to commencement of the scour Level 2 assessment. 7.8.2 Where the structure is not a masonry arch structure, if the foundation type is unknown the foundation type factor F should be 1.0. 7.9 The ground material factor, M , provided in Table 7.9 shall be used in Equation 7.7. Table 7.9 Ground material factor M. Where there is no information on the ground material, or the ground material is granular (e.g. silt, sand, gravel). M = 1.0 Where there is some evidence that the ground material is clay. M = 0.75 Where there is geotechnical evidence that the ground material is clay, or there is some evidence that the ground material is partly rock. M = 0.5 7.10 The history of scour occurrence factor, HS , provided in Table 7.10 shall be used in Equation 7.7. Table 7.10 History of scour factor. There is evidence of scour occurrence at the structure. HS = 1.5 There is no evidence of scour occurrence at the structure. HS = 1.0 7.11 The potential for fast flowing water on land and associated scour risk depends upon the land gradient at the structure location. The land gradient factor, GL , provided in Table 7.11 shall be used in Equation 7.7. Table 7.11 Land gradient factor. The average gradient of land within 100 m of the scour susceptible structure Type 2 Land gradient factor Very steep 1 in 10 or steeper GL = 1.5 Steep Between 1 in 25 and 1 in 10.1 approx. GL = 1.3 Moderate Between 1 in 50 and 1 in 25.1 approx. GL = 1.2 Low Between 1 in 200 and 1 in 50.1 approx. GL = 1.1 Very low Less than 1 in 200 GL = 1.0 7.12 The consequences to road users and nearby communities following the failure or collapse of a structure such as a bridge shall be identified and assessed as part of the scour assessment. If a bridge failure or collapse occurs, due to scour or other hydraulic actions, the potential consequences to be assessed, in determining the communities importance factor C , are to include: 1) traffic disruption on emergency diversion routes; 130 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 7. Evaluation of scour susceptible structures Ty... 2) community severance; and, 3) loss of utilities to a nearby community (such as loss of electricity supply). 7.13 The communities importance factor, C , provided in Table 7.13 shall be used in Equation 7.7. Table 7.13 Communities importance factor. Use of bridge or other structure Communities importance factor C Motorway, or dual carriageway A road C = 1.0 Single carriageway A road C = 0.9 B road C = 0.8 C road, or unclassified road, or footbridge, or accommodation bridge, or other type of structure C = 0.7 7.14 Where the situations described in Table 7.13 do not fully reflect the importance of a bridge or other type of structure, the value for the communities importance factor, C , provided in Table 7.13, shall be multiplied by a communities additional factor CAF provided in Table 7.14, and used in Equation 7.7. Table 7.14 Communities additional factor. Community severance or disruption issue Communities additional factor CAF A bridge on a road to an essential industry or transport facility where there is no diversion route and loss of the bridge can result in community severance CAF = 1.3 A bridge that provides a link within a community where loss of the bridge can result in community severance CAF = 1.2 A bridge, or footbridge, or other type of structure, that provides utilities to a community, where loss of the structure can result in community disruption (such as loss of electricity supply) CAF = 1.2 A footbridge that provides a link within a community where loss of the footbridge can result in community severance CAF = 1.1 All other structures CAF = 1.0 NOTE Further information on community severance issues can be found in DMRB LA 112 [Ref 14.N]. Priority ranking and scour risk rating Type 2 7.15 All scour susceptible structures Type 2 shall be priority ranked in a list according to the priority ranking Type 2 PR-T2 for the structure. 7.16 The priority ranking list for scour susceptible structures Type 2 shall be subdivided in to three parts, to determine the scour risk rating for each scour susceptible structure Type 2, in accordance with Table 7.16. 131 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 7. Evaluation of scour susceptible structures Ty... Table 7.16 Determining the scour risk rating for a scour susceptible structure Type 2. Priority ranking Type 2 PR-T2 Scour risk rating Type 2 PR-T2 ≥ 2.0 High risk 2.0 > PR-T2 ≥ 1.0 Medium risk PR-T2 < 1.0 Low risk Scour evaluation and scour risk rating updating process Type 2 7.17 For scour susceptible structures Type 2, the scour evaluation and scour risk rating updating shall be carried out in accordance with the process described in clauses 7.18 to 7.21.1. Scour evaluation - evaluation of the risk of structural damage 7.18 The scour evaluation shall use the information shown below: 1) priority ranking Type 2 PR-T2 calculated for the structure, in accordance with clause 7.15; 2) the latest available 0.5% AEP flood risk maps for the structure location, in accordance with the relevant CS 469 National Application Annex; and, 3) data for the structure, in accordance with clauses 3.13 to 3.15. 7.19 For all scour susceptible structures Type 2 that have already been designated as high risk, or medium risk, the 0.5% AEP flood risk maps for the structure location shall be reviewed in accordance with the relevant CS 469 National Application Annex, to determine if flood water is likely to be at, or above, the soffit level of the structure during a 0.5% AEP flood event. 7.20 Following the review of flood risk maps in accordance with clause 7.19, if during a 0.5% AEP flood event, the water level is likely to be at, or above, the soffit level of the scour susceptible structure Type 2, the structure shall be designated high risk. 7.21 The scour susceptible structure Type 2 with a scour risk rating high risk, shall be qualitatively evaluated to determine the risk of structural damage due to scour occurring at the structure. 7.21.1 The qualitative evaluation should include: 1) condition of the structure; 2) depth of foundations; 3) distance from the structure to a stream or river; 4) significant structural damage that has occurred; 5) evidence of significant flood event occurrence at the structure; 6) the possibility of scour developing below flood water level and undermining the structure foundations, e.g. at piers, or abutments, or retaining walls; 7) the possibility of damage to the structure, or causing damage to geotechnical assets close to the structure; and, 8) evidence of debris or other stored materials that can obstruct flood flow, e.g. hay bales stored under a bridge. 7.22 The evaluation shall determine whether all the parts of the structure, such as abutments, piers, or retaining walls, could potentially be damaged by scour caused by flood water (calculations are not needed). Scour risk rating updating 7.23 The updated scour risk rating for a scour susceptible structure Type 2 shall be determined, at the time of a Principal Inspection or scour emergency inspection for the structure, using: 132 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 7. Evaluation of scour susceptible structures Ty... 1) the initial scour risk rating determined in accordance with clause 7.16, or updated in accordance with clause 7.20, in this document; 2) the findings of the scour evaluation in accordance with clauses 7.21 to 7.22 in this document, where the structure has already been designated high risk; and, 3) the findings from Principal Inspection reports and scour emergency inspection reports for the structure. 7.23.1 Following a significant flood event which causes scour, or increases the risk of scour, at a scour susceptible structure Type 2, the scour risk rating should be reviewed and updated. Reporting 7.24 The scour evaluation report, for a scour susceptible structure Type 2 shall include: 1) the findings in accordance with clauses 7.4 to 7.23.1; 2) for high risk structures, the consequences, or potential consequences, of severe weather events, using the latest available data; 3) for high risk structures, the consequences, or potential consequences, resulting from scour and other hydraulic actions; 4) for high risk structures, the consequences following partial or total structural failure or collapse; and, 5) for high risk structures, recommended actions. 133 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 8. Risk management of scour and other hydraulic ... 8. Risk management of scour and other hydraulic actions at structures Site-specific scour risk assessment 8.1 A site-specific scour risk assessment shall be carried out in accordance with DMRB GG 104 [Ref 15.N] for a scour susceptible structure that has been designated with a scour risk rating of: 1) scour susceptible structure Type 1 high risk and medium risk; and, 2) scour susceptible structure Type 2 high risk. 8.2 The site-specific scour risk assessment shall include: 1) risks to affected populations, due to scour and other hydraulic actions; 2) recommended immediate actions needed to reduce the risks; 3) recommended actions needed to monitor the risks; 4) recommended interim actions needed to further reduce the risks; and, 5) recommended actions needed to prevent an increase in risks. 8.3 The site-specific scour risk assessment for a scour susceptible structure shall be updated: 1) as part of the emergency scour inspection immediately following a significant flood event; 2) at the time of a principal inspection of the structure; and, 3) when there are changes to the risk profile for the structure. Scour risk register 8.4 A scour risk register shall be created and updated by the Overseeing Organisation to enable effective, timely and consistent risk management. 8.5 The scour risk register shall include scour susceptible structures which have been designated with a scour risk rating of: 1) scour susceptible structure Type 1 high risk and medium risk; and 2) scour susceptible structure Type 2 high risk. Scour risks management plan 8.6 A scour risks management plan shall be prepared for each area or linear route, for scour susceptible structures on the scour risk register, including the recommended actions from: 1) scour Level 1 assessment for scour susceptible structures Type 1; 2) scour Level 2 assessment for scour susceptible structures Type 1; 3) vulnerability assessment reports; 4) scour evaluation for scour susceptible structures Type 2; and, 5) site-specific scour risk assessments. 8.7 The scour risks management plan shall be prepared in accordance with Table 8.7a and Table 8.7b and is to include: 1) maintenance of scour risks (including routine maintenance actions, refer to clause 8.16); 2) further site survey, investigation and assessment work for scour susceptible structures Type 1 (refer to clause 5.58.1); 3) monitoring of scour risks at a frequency according to the scour risks (refer to clause 8.17 to 8.19); 4) reduction of scour risks (including civil engineering works to reduce the scour risk rating); and 5) recommended scour protection works (refer to clauses 8.20 to 8.21.1). 134 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 8. Risk management of scour and other hydraulic ... Table 8.7a Scour susceptible structures Type 1 - actions in response to scour risk rating. Scour risk rating Possible actions Prepare and implement a scour risks reduction plan and reduce risks. Carry out further investigations and further assessment. Implement appropriate regular monitoring and scour protection measures (civil engineering works) as a high priority. High Immediate risk scour susceptible structures are to be managed in accordance with DMRB CS 470 [Ref 11.N]. Prepare and implement a scour risks reduction plan and reduce risks. Medium Carry out further investigations and further assessment. Implement appropriate regular monitoring. Table 8.7b Scour susceptible structures Type 2 - actions in response to scour risk rating. Scour risk rating Possible actions Prepare and implement a scour risks reduction plan and reduce risks. Implement appropriate regular monitoring and scour protection measures (civil High engineering works) as a high priority. Immediate risk scour susceptible structures are to be managed in accordance with CS 470 [Ref 11.N]. NOTE The scour risk management strategy can vary according to the structure type, structure location and structure scour risk rating. 8.8 The scour risks management plan shall be submitted to the Overseeing Organisation. 8.9 The scour risks management plan for an area or linear route shall be reviewed at least once every five years and updated whenever structure risks change. Severe weather event management plan 8.10 A severe weather event management plan shall be prepared for scour susceptible structures that have been designated with a scour risk rating of high risk and is to be structure specific: 1) to safeguard affected populations and the structure, at all times; 2) to ensure a process is in place for the provision of advance warning to the Maintaining Organisation of severe weather events for the structure location; 3) to ensure emergency actions are planned in advance and can be implemented rapidly if needed during a severe weather event, such as closure of a bridge (to all traffic including pedestrians) and diversion of traffic on to an emergency diversion route; and, 4) to ensure potential emergency works, e.g. to protect pedestrians from fractured electricity cables or gas pipes in the bridge deck [caused by structural failure], are planned in advance and can be implemented rapidly if needed during a severe weather event. 8.11 The severe weather event management plan for a structure shall include: 1) the process for notification of severe weather events, or flood events, to the Maintaining Organisation, e.g. forecast peak water level, forecast time of peak water level, forecast peak flow rate at the structure, in addition to a regional or area weather forecast; 135 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 8. Risk management of scour and other hydraulic ... 2) the process at the Maintaining Organisation, for receiving and acting upon severe weather event warnings, or flood warnings, for the structure. Refer to the relevant National Application Annex; 3) actions needed after a severe weather event warning, or flood warning, for the structure location that has been notified to the Maintaining Organisation; 4) the pre-determined severe weather event intervention warning water level [SWE IWWL] at the upstream face of a structure. For example, the river water rises to a pre-determined higher level, which indicates that emergency actions are to be implemented; 5) emergency actions that are to be implemented when water level rises to the SWE IWWL, to safeguard affected populations and the structure; 6) pre-planned emergency diversion route; and, 7) decision making process for the Maintaining Organisation. 8.11.1 After bridge closure during a severe weather event, the decision making process for the Maintaining Organisation should include: 1) works which need to be completed for safety reasons, prior to reopening of the bridge; and, 2) when it is safe to reopen the bridge. 8.11.2 After the end of the severe weather event, where the water level was at the SWE IWWL or higher, a lessons-learned report should be prepared and submitted to the Overseeing Organisation separately from a principal inspection report or a general inspection report. 8.11.3 A lessons-learned report should be a structure-specific document and describe: 1) what actually occurred during the severe weather event, including the peak flow rate and maximum depth of flow at the upstream face of the structure; 2) a list of actions that were taken by the Maintaining Organisation during, or immediately after, the severe weather event; 3) how actions at a similar severe weather event could be improved in future, to ensure risks are reduced; 4) list any structural damage, damage to utilities, or other damage that has occurred at the structure during the severe weather event; and, 5) list proposed changes to the severe weather event management plan for the structure. 8.12 The severe weather event intervention warning water level [SWE IWWL] shall be determined according to key criteria, including: 1) the type of structure; 2) the vertical distance between the bridge soffit and the bridge deck road surface; 3) the vertical distance between the river banks and the bridge soffit; 4) the depth of flow in the river that would be likely to cause structural damage, for the type of structure; and, 5) any obstructions to flood flows. 8.12.1 For scour susceptible structures Type 1, the effect of any obstructions to flood flows onto land on either side of the structure should be evaluated using the scour Level 2 assessment work, to indicate: 1) the percentage of the assessment flow QA that will pass through the structure opening; 2) the percentage of the assessment flow QA that will flow over the structure; and, 3) the percentage of the assessment flow QA that will flow to each side of the structure. 8.13 The severe weather event intervention warning water level [SWE IWWL] shall be a clearly identifiable and accessible feature of, or mark on, the upstream face of the structure. 8.14 The severe weather event management plan, including an updated severe weather management plan, for a structure shall be submitted to the Overseeing Organisation and is to be separate from a Principal Inspection report or a general inspection report. 136 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 8. Risk management of scour and other hydraulic ... 8.15 The severe weather event management plan for a structure shall be reviewed at the Principal Inspection and updated whenever structure risks change. Routine maintenance 8.16 Routine maintenance actions for scour susceptible structures shall include: 1) maintenance of scour protection; 2) maintenance of monitoring and measuring equipment; and, 3) removal of any debris accumulations from the water within the defined distance from the structure. NOTE 1 The term "any debris accumulations" includes "woody debris accumulations" and "other debris accumulations", which are defined in the "Terms and definitions" table. NOTE 2 The defined distance from the structure is provided in Table 3.12, or Table 3.15. Monitoring 8.17 The need for and frequency of monitoring of high risk and medium risk scour susceptible structures shall be determined according to the scour risk assessment for the structure. 8.17.1 Where a scour susceptible structure is being monitored, the monitoring should include all of the following: 1) identify changes to the structure; 2) identify changes to the watercourse; 3) identify any debris accumulations within the defined distance from the structure; 4) measure the development of scour over time; and, 5) the condition of scour protection. NOTE Refer to the "Terms and definitions" table for the definition of "scour protection" . 8.18 Structure-specific recommendations for monitoring shall be notified to the Overseeing Organisation prior to commencement of monitoring of a structure. NOTE Monitoring techniques for scour and other hydraulic actions on structures fall into the following categories: 1) those that seek to measure the maximum scour levels that have occurred at the bridge site; 2) those that seek to measure the development of scour adjacent to the structure as it develops during a flood; 3) systems based on monitoring analogues (conditions that can correlate with the development of scour) such as flow velocities, water level, or weather warnings; 4) those that measure structural movement to ascertain whether scour is affecting the structure; and, 5) those that seek to measure the development of scour at a structure over time (real time monitoring by in-river instrumentation) to better understand the process of scour. 8.19 Where the monitoring indicates an unacceptable risk, the structure shall be designated as an immediate risk scour susceptible structure. Refer to clauses 2.26 to 2.28. Protection of structures against scour and other hydraulic actions 8.20 Proposals for protection of a high risk scour susceptible structure against scour and other hydraulic actions shall be determined according to the scour risk assessment for the structure. 8.21 Proposals for temporary or permanent works to protect a structure against scour and other hydraulic actions shall be submitted to the Technical Approval Authority, for approval prior to implementation in accordance with CG 300 [Ref 16.N] and CD 356 [Ref 2.N]. 137 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 8. Risk management of scour and other hydraulic ... 8.21.1 Protection of a structure against scour and other hydraulic actions should include civil engineering works permanently installed upstream, alongside and downstream of the structure, within the defined distance from the structure (as provided in Table 3.12 or Table 3.15). NOTE 1 Construction works in a watercourse can constrict the flow and have the potential to exacerbate scour issues at a structure. Design of scour protection or remediation measures needs to ensure that neither the permanent nor temporary works adversely affect flow around the structure, or flow through the structural opening.' NOTE 2 For further information on design of temporary or permanent works, for example to protect a structure against scour and other hydraulic actions, such as works on the river bed and at the river banks, refer to CD 356 [Ref 2.N]. 138 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 9. Document management for scour susceptible str... 9. Document management for scour susceptible structures 9.1 For each scour susceptible structure, records shall be uploaded to the Overseeing Organisation structures asset management information system and updated and maintained, in accordance with Table 9.1, to enable audit of actions. Table 9.1 Uploading information to the Overseeing Organisation structures asset management information system. Scour susceptible structures Type 1 Scour susceptible structures Type 2 List of scour susceptible structures Type 1, in an area, or on a linear route. List of scour susceptible structures Type 2, in an area, or on a linear route. Scour priority factor list, showing PF-T1 for each scour susceptible structure Type 1, in an area, or on a linear route. Scour priority ranking list, showing PR-T2 for each scour susceptible structure Type 2, in an area, or on a linear route. Scour inspection reports. Scour emergency inspection reports. Emergency structural inspection reports. Scour Level 1 assessment records. Scour Level 2 assessment reports, where needed. Scour Level 2 Assessment Certificate. Scour evaluation reports. Scour risk rating and scour risk score. Channel stability risk rating. Vulnerability assessment reports, where needed. Programme of survey work and further investigation work, with the aim of reducing the scour risk rating for the structure, where needed. Scour risk rating. Scour risk assessments, for high risk and medium risk structures. Scour risk assessments, for high risk structures. Scour risk registers, for high risk and medium risk structures. Scour risk registers, for high risk structures. Scour risks management plans, for high risk and medium risk structures. Scour risks management plans, for high risk structures. Severe weather event management plans, for high risk structures. Severe weather event lessons learned reports, for high risk structures. Programme of scour routine maintenance work to be carried out on a regular basis. Programme of monitoring work to be carried out on a regular basis, where needed. 139 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 9. Document management for scour susceptible str... Table 9.1 Uploading information to the Overseeing Organisation structures asset management information system. (continued) Water level records at the structure: during scour inspection, scour emergency inspection, emergency structural inspection, Principal Inspection and monitoring of the structure. Water level records at the structure, when a significant flood event occurs at the structure. Programme of scour protection works to be carried out, where needed. Details of routine maintenance work carried out, or actions implemented, to prevent an increase in risks. Details of works carried out, or actions implemented, to reduce risks. Documentation on the Maintaining Organisation management and actions for the structure. 9.2 For each scour susceptible structure, records shall be in accordance with the requirements for 'As-built, Operational and Maintenance Records for Highway Structures CG 302 [Ref 1.N]. 140 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 10. Normative references 10. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref. Document Ref 1.N National Highways. CG 302, 'As-built, operational and maintenance records for highway structures' Ref 2.N National Highways. CD 356, 'Design of highway structures for hydraulic action' Ref 3.N National Archives. UKSI 2015/2059, 'European Union (Recognition of Professional Qualifications) Regulations' Ref 4.N National Archives. UKPGA 2020/01, 'European Union (Withdrawal Agreement) Act' Ref 5.N Transport Association of Canada. Guide to Bridge Hydraulics, 'Guide to Bridge Hydraulics' Ref 6.N National Archives. UKPGA 1974/37 (HSWA), 'Health and Safety at Work etc. Act' Ref 7.N National Archives. UKPGA 1980/66, 'Highways Act' Ref 8.N National Archives. UKPGA 2015/07, 'Infrastructure Act' Ref 9.N National Highways. CS 450, 'Inspection of highway structures' Ref 10.N National Highways. GG 101, 'Introduction to the Design Manual for Roads and Bridges' Ref 11.N National Highways. CS 470, 'Management of sub-standard highway structures' Ref 12.N National Highways. CD 622, 'Managing geotechnical risk' Ref 13.N National Highways. CS 641, 'Managing the maintenance of highway geotechnical assets' Ref 14.N National Highways. LA 112, 'Population and human health' Ref 15.N National Highways. GG 104, 'Requirements for safety risk assessment' Ref 16.N National Highways. CG 300, 'Technical approval of highway structures' 141 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 11. Informative references 11. Informative references The following documents are informative references for this document and provide supporting information. Ref. Document Ref 1.I ICE Publishing; Proc of the Instn of Civil Engineers - Bridge Engineering. Ebrahimi M, Djordjevic S, Panici D, Tabor G, Kripakaran P.. Ebrahimi et al, 'A method for evaluating local scour depth at bridge piers due to debris accumulation.' Ref 2.I Elsevier, Science of The Total Environment Volume 728, 138575. Diego Panici, Prakash Kripakaran, Slobodan Djordjevića & Kevin Dentith. Panici et al 2019, 'Assessing Debris-induced Scour at Bridge Piers in Real-world Practice: A Case Study, in 38th IAHR World Congress: Water connecting the world, 1-6 September 2019, Panama City, Panama' Ref 3.I 38th IAHR World Congress: Water connecting the world, 1-6 September 2019, Panama City, Panama. Panici, D., Kripakaran, P., and Dentith, K. Panici, Kripakaran, & Dentith, 'Assessing Debris-induced Scour at Bridge Piers in Real-world Practice: A Case Study, in 38th IAHR World Congress: Water connecting the world, 1-6 September 2019, Panama City, Panama' Ref 4.I Journal of Hydraulic Engineering. Ebrahimi M, Kripakaran P, Prodanović DM, Kahraman R, Riella M, Gavin T, Arthur S, and Djordjević S.. JHE 144 (12), 'Experimental Study on Scour at a Sharp-nose Bridge Pier with Debris Blockage' Ref 5.I Rail Accident Investigation Branch, DfT. RDG1, 'Failure of Bridge RDG1 48 (River Crane) between Whitton and Feltham 14 November 2009' Ref 6.I Water Resources Research. Panici D, and de Almeida GAM. WRR 54, 'Formation, growth and failure of woody debris jams at bridge piers.' Ref 7.I US Department of Transportation, Federal Highways Administration. Arneson, LA et al. HEC 18 - FHWA-HIF-12-003, 'HEC (Hydraulic Engineering Circular) No. 18 'Evaluating Scour at Bridges' 5th edition, 2012' Ref 8.I UK Hydrographic Office. Admiralty Tide Tables, 'https://www.admiralty.co.uk/publications/publications-and-reference-guides/admiralty-tide-tables' Ref 9.I TSO. IMHS V1, 'Inspection Manual for Highway Structures. Volume 1: Reference Manual' Ref 10.I TSO. IMHS V2, 'Inspection Manual for Highway Structures. Volume 2: Inspector's Handbook' Ref 11.I Construction Industries Research and Information Association, London. Kirby, Roca, Kitchen et al. CIRIA C742, 'Manual on scour at bridges and other hydraulic structures' Ref 12.I Construction Industries Research and Information Association, London. CIRIA SP171, 'Manual on scour at bridges and other hydraulic structures – supplementary guide.' Ref 13.I Ven Te Chow. Chow 1959, 'Open Channel Hydraulics' , 1959 Ref 14.I Port of London Authority. https://tidepredictions.pla.co.uk/. River Thames tidal predictions, 'Port of London Authority Tide Tables.' Ref 15.I Federal Highway Administration, U.S. Department of Transport. Diehl, TH, 'Potential Drift Accumulation at Bridges' 142 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix A. Woody debris accumulations - rigorous method ... Appendix A. Woody debris accumulations - rigorous method for estimation of debris factor A1 General The rigorous method described in this Appendix is an alternative to the simplified method for estimation of the debris factor fd provided in Clauses 5.49.4 and 5.49.5. The rigorous method is based on the estimation of the debris factor, fd , using equations derived from regressions of experimental tests at the University of Exeter, as described in Panici, Kripakaran, & Dentith [Ref 3.I] and JHE 144 (12) [Ref 4.I]. This rigorous method requires the estimation of the woody debris accumulation size that can be expected at a structure, and then the debris factor, fd , resulting from such debris accumulation is determined Ebrahimi et al [Ref 1.I]. A2 Estimation of debris accumulation size The debris accumulation size can be estimated using the methods described in Diehl, TH [Ref 15.I] and WRR 54 [Ref 6.I] based on both field and experimental analyses. The debris accumulation size is calculated using the design debris length, LD , and the debris Froude number, F rD . A2.1 Design debris length The design debris length, LD , defines the size of the debris accumulation, based on regressions of experimental tests at the University of Southampton as described in WRR 54 [Ref 6.I]. The design debris length, LD , can be determined using Table A.1 from Diehl, TH [Ref 15.I]: Table A.1 Design debris length. Design debris length Condition LD = Bu when Bu < 12m LD = Bu 4 + 9 when 12m ≤ Bu ≤ 60m LD = 24m when Bu > 60m where: LD = design debris length, in m Bu = average width of the channel upstream of the bridge, in m A2.2 Debris Froude number The debris Froude number, F rD , can be determined using Equation A.1: Equation A.1 Debris Froude number F rD = vu √ g · LD where: F rD is the debris Froude number vu is the velocity of flow upstream of the bridge, in m/s g is the acceleration due to gravity 9.81 m/s2 LD is the design debris length, determined from Table A.1, in m 143 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix A. Woody debris accumulations - rigorous method ... A2.3 Debris accumulation size The debris accumulation size is illustrated in Figure A.1. Figure A.1 Illustration showing debris accumulation size The debris accumulation size can be determined using Table A.2, based on the work from WRR 54 [Ref 6.I]: Table A.2 Debris accumulation size. Debris accumulation dimension Equation Width of debris accumulation, WD WD = LD ( 0.774 + 0.939e −6.139F rD ) Height of debris accumulation, HD HD = LD ( 0.394 − 0.458e −5.770F rD ) Upstream length of debris accumulation, KD KD = LD ( 0.246 + 1.178e −15.039F rD ) where LD = design debris length, determined from Table A.1. e = Euler's number, which is a mathematical constant = 2.71828. F rD = debris Froude number, determined from Equation A.1. The rigorous method can only be used to calculate the debris factor fd when both of the qualifying criteria for the rigorous method are met, which are: 1) WD Bu < 0.88 ; and, 2) HD yu < 0.83 . The rigorous method, provided in this Appendix, is based on outputs from University of Southampton and University of Exeter research projects. 144 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix A. Woody debris accumulations - rigorous method ... A3 Calculation of debris factor The debris factor fd is determined using Equation A.2: Equation A.2 Debris factor. fd =K0.24 1 · K0.60 2 · K0.25 3 where: K1 = 1.33( KDWP )2 −2 ( KDWP ) +6 ( KDWP )2 −3 ( KDWP ) +6 K2 = 1 + 0.002 · ∆A1.5 % K3 = −0.76( hd yu )3 + 0.60( hd yu )2 + 0.28( hd yu ) + 0.88 KD is the upstream length of debris accumulation, determined from Table A.2. WP is the bridge pier width. KD WP is the relative debris length. ∆A% is the debris blockage area ratio, it is a percentage, determined from Table A.3. hd yu is the relative flow depth, determined from Table A.4. A3.1 Debris blockage area ratio The debris blockage area ratio, ∆A% , can be determined from Table A.3. Table A.3 Debris blockage area ratio. WD.HD 2.Au .100 for HD ≤ yu The debris accumulation cross section shape is triangular. ∆A% = WD.yu 2.Au · ( 2 − yu HD ) .100 for HD > yu The debris accumulation cross section shape is trapezoidal. where: ∆A% = debris blockage area ratio, determined from Table A.3. WD = width of debris accumulation, determined from Table A.2. HD = height of debris accumulation, determined from Table A.2. Au = cross-sectional area of flow upstream of the bridge.. yu = depth of flow upstream of the bridge. A3.2 Relative flow depth The relative flow depth, hd yu , can be determined from Table A.4. 145 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix A. Woody debris accumulations - rigorous method ... Table A.4 Relative flow depth. yu−HD yu for HD ≤ yu The debris accumulation cross section shape is triangular. hd yu = 0 for HD > yu The debris accumulation cross section shape is trapezoidal. where: hd = flow depth underneath the debris accumulation. yu = depth of flow upstream of the bridge. HD = height of debris accumulation, determined from Table A.2. A3.3 Cross-section of debris accumulation The debris frontal area, AD , is assumed to be a triangular cross-section if the height of debris accumulation HD is smaller than the depth of flow upstream of the bridge yu . Where the debris accumulation reaches the river bed, the debris frontal area AD is assumed to be a trapezoidal cross-section. The debris frontal area AD is never larger than the cross-sectional area of flow upstream of the bridge, Au . The shape of the debris frontal area AD determines whether the debris factor, fd , can be reduced, as shown in Table A.5. Table A.5 Debris accumulation cross section shape. Debris accumulation cross section shape Debris factor fd reduction Triangular, i.e. where HD ≤ yu 16%, but limited to fd ≥1.0 Trapezoidal, i.e. where HD > yu There is no permitted reduction. Note: The calculated scour depth should not be reduced by the debris factor fd . Therefore any reduction applied to the debris factor fd is limited, so that fd ≥1.0 . 146 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Appendix B. Woody debris accumulations - estimation of debris factor worked examples B1 General The two methods for the estimation of the debris factor, fd , as provided in clauses 5.49.4, 5.49.5 and Appendix A, are applied to the four case studies as worked examples in this Appendix. Normally, when calculating the debris factor, fd , if both of the qualifying criteria for the rigorous method are met, as described in Clause A2.3, then the rigorous method provides a more realistic result for the estimation of the scour depth. If the debris factor, fd , estimated from the simplified method increases the scour risk rating (compared to the no-debris case, i.e. fd =1.0 ), then the rigorous method can be used to determine a potentially more realistic estimation of scour depth, but only if both of the qualifying criteria for the rigorous method are met. B2 Case study No. 1 on Steps Bridge The following shows the case study on Steps Bridge on the River Teign, property of Devon County Council. The input data is shown in Table B.1. Table B.1 Input data for debris factor estimation at Steps Bridge. Input variable Value Bu , average width of the channel upstream of the bridge. 20.15 m vu , mean velocity of flow upstream of the bridge. 2.73 m/s Au , cross-sectional area of flow upstream of the bridge. 72.56 m2 yu , depth of flow upstream of the bridge. 2.53 m WP , bridge pier width. 2.428 m B2.1 Case study No. 1 - simplified method for Steps Bridge The simplified method applied to the Steps Bridge employed the use of Figure 5.49.5a graph to estimate the debris frontal area AD , Figure 5.49.5b Graph to estimate the upstream length of debris accumulation KD , Equation 5.49.5a to calculate the debris size ratio dsr , Equation 5.49.5b to calculate the debris blockage area ratio ∆A% and Figure 5.49.5c Graph to estimate the debris factor fd . Figure B.1 shows the estimation of the debris frontal area AD = 27m2 . 147 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Figure B.1 Estimation of debris frontal area for Steps Bridge. 148 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Figure B.2 shows the estimation of the upstream length of debris accumulation KD = 4m . 149 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Figure B.2 Estimation of upstream length of debris accumulation for Steps Bridge. 150 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... The debris accumulation size obtained above is used to calculate the debris blockage area ratio ∆A% and the debris size ratio dsr : ∆A% = AD·100 Au = 27·100 72.56 = 37.21% dsr = KD WP = 4 2.428 = 1.65 . Figure B.3 shows the estimation of the debris factor, fd =1.48 . 151 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Figure B.3 Estimation of the debris factor for Steps Bridge. 152 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... B2.2 Case study No. 1 - rigorous method for Steps Bridge The rigorous method applied to the Steps Bridge employed the equations in Appendix A. The qualifying criteria are calculated in accordance with Clauses A2.1, A2.2, A2.3: LD = Bu 4 + 9 = 20.15 4 + 9 = 14.04 F rD = √ vu g·LD = √ 2.73 9.81·14.04 = 0.23 WD = LD · ( 0.774 + 0.939 · e −6.139F rD ) = 14.03 WD Bu = 14.03 20.15 = 0.70 The qualifying criteria is met. HD = LD · ( 0.394 − 0.458 · e −5.770F rD ) = 3.85 HD yu = 3.85 2.53 = 1.52 The qualifying criteria is not met. One of the two qualifying criteria described in clause A2.3 is not met, so the calculation of fd using the rigorous method is not permitted in Case Study No.1. B3 Case study No. 2 on Abbey Bridge The following shows the case study on Abbey Bridge on the River Tavy, property of Devon County Council. The input data is shown in Table B.2. Table B.2 Input data for debris factor estimation at Abbey Bridge. Input variable Value Bu , average width of the channel upstream of the bridge. 21.26 m vu , mean velocity of flow upstream of the bridge. 2.21 m/s Au , cross-sectional area of flow upstream of the bridge. 110.6 m2 yu , depth of flow upstream of the bridge. 4.49 m WP , bridge pier width. 2.32 m B3.1 Case study No. 2 - simplified method for Abbey Bridge The simplified method applied to the Abbey Bridge employed the use of Figure 5.49.5a graph to estimate the debris frontal area AD , Figure 5.49.5b graph to estimate the upstream length of debris accumulation KD , Equation 5.49.5a to calculate the debris size ratio dsr , Equation 5.49.5b to calculate the debris blockage area ratio ∆A% and Figure 5.49.5c graph to estimate the debris factor fd . Figure B.4 shows the estimation of the debris frontal area AD = 25.0m2 . 153 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Figure B.4 Estimation of debris frontal area for Abbey Bridge. 154 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Figure B.5 shows the estimation of the upstream length of debris accumulation KD = 4.80m . 155 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Figure B.5 Estimation of upstream length of debris accumulation for Abbey Bridge. 156 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... The debris accumulation size obtained above is used to calculate the debris blockage area ratio ∆A% and the debris size ratio dsr : ∆A% = AD·100 Au = 25.0·100 110.6 = 22.60% dsr = KD WP = 4.80 2.32 = 2.07 . Figure B.6 shows the estimation of the debris factor, fd =1.32 . 157 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Figure B.6 Estimation of the debris factor for Abbey Bridge. 158 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... B3.2 Case study No. 2 - rigorous method for Abbey Bridge The rigorous method applied to the Abbey Bridge employed the equations in Appendix A. The qualifying criteria are calculated in accordance with clauses A2.1, A2.2, A2.3: LD = Bu 4 + 9 = 21.26 4 + 9 = 14.32 F rD = √ vu g·LD = √ 2.21 9.81·14.32 = 0.19 WD = LD ( 0.774 + 0.939e −6.139F rD ) = 15.36 WD Bu = 15.36 21.26 = 0.72 The qualifying criteria is met. HD = LD ( 0.394 − 0.458e −5.770F rD ) = 3.40 HD yu = 3.40 4.49 = 0.76 The qualifying criteria is met. Both of the two qualifying criteria described in Clause A2.3 are met, so the calculation of fd using the rigorous method is permitted. The size of the debris accumulation is calculated in accordance with Appendix A. The results are summarised in Table B.3. 159 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Table B.3 Calculations of the size of debris accumulation at Abbey Bridge. Output Numerical value Formula L D , design debris length 14.32 m L D = Bu 4 + 9 for 12 m < Bu < 60 m F r D , debris Froude number 0.19 F r D = √ vu g·L D WD , width of debris accumulation 15.36 m WD = L D · ( 0.774 + 0.939e −6.139F r D ) H D , height of debris accumulation 3.40 m HD = L D ( 0.394 − 0.458e −5.770F r D ) K D , upstream length of debris accumulation 4.54 m K D = L D ( 0.246 + 1.178e −15.039F r D ) 160 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... The debris factor fd is then calculated in accordance with Appendix A. Since HD ≤ yu , the cross-section of the debris accumulation is calculated as a triangle. All calculations are summarised in Table B.4. 161 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Table B.4 Calculations of the debris factor for Abbey Bridge. Output Numerical value Formula ∆A% , debris blockage area ratio 23.64 % HD = 3.40 and yu = 4.49 Therefore HD ≤ yu . ∆A% = WD·HD 2·Au · 100 KD WP , debris size ratio 1.96 KD WP hd yu , relative depth ratio 0.24 hd yu = yu−HD yu for HD ≤ yu K1 1.81 K1 = 1.33( KDWp )2−2( KDWP )+6 ( KDWP )2−3( KDWP )+6 K2 1.23 K2 = 1 + 0.002 · ∆A1.5 % = 1 + 0.002 · 0.30491.5 K3 0.97 K3 = −0.76( hd yu )3 + 0.60( hd yu )2 + 0.28( hd yu ) + 0.88 fd , debris factor 1.30 fd =K0.24 1 · K0.60 2 · K0.25 3 162 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 Version 1.0.0 Appendix B. Woody debris accumulations - estimation of de... Since HD ≤ yu , the calculated debris factor fd should be reduced by 16 %, which results in fd =1.09 . 163 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 © Crown copyright 2024. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 469 - ENAA England National Application Annex for Management of scour and other hydraulic actions at highway structures. (formerly BD 97/12) Version 1.0.0 Summary This National Application Annex sets out the National Highways-specific requirements and related advice for the inspection, assessment and risk management of scour and other hydraulic actions at highway structures. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated National Highways team. The online feedback form for all enquiries and feedback can be accessed at: www.standardsforhighways.co.uk/feedback. This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Contents Release notes 2 Foreword 3 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction 4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abbreviations and symbols 5 Terms and definitions 6 E/1. Scope 21 Aspects covered (additional to CS 469 clauses 1.1 to 1.6 , 1.8 and 1.9 to 1.17) . . . . . . . . . . . . . . . . 21 Competent persons (additional to CS 469 clauses 1.14 and 1.15) . . . . . . . . . . . . . . . . . . . . . . . . 21 E/2. Identification of scour susceptible structures Type 1 and Type 2 (additional to CS 469, Sections 1 and 9) 22 Scour susceptible structures Type 1 (additional to CS 469 clauses 1.2, 1.3, 1.4 and 9.1) . . . . . . . . . . . 22 Scour susceptible structures Type 2 (additional to CS 469 clauses 1.2, 1.3 and 9.1) . . . . . . . . . . . . . 22 E/3. Review of 0.5% AEP flood risk maps (additional to CS 469, Sections 4 and 7) 23 Scour susceptible structures Type 1 (additional to CS 469 clauses 4.3 and 4.6) . . . . . . . . . . . . . . . . 23 Scour susceptible structures Type 2 (additional to CS 469 clauses 7.18 to 7.20) . . . . . . . . . . . . . . . . 23 E/4. Climate change allowances (additional to CS 469, Sections 5 and 6) 24 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Climate change allowances for structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Peak river flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Peak rainfall intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Sea level rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 E/5. Scour Level 2 assessment (additional to CS 469, Sections 5 and 9) 27 E/6. Risk management of scour and other hydraulic actions at structures (additional to CS 469, Section 8) 28 E/7. Normative references 29 E/8. Informative references 30 Appendix E/A. Model form of scour assessment certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 (additional to CS 469, Sections 5 and 9) 31 E/A1 Scour assessment certificate - Section 1 - scour susceptible structure Type 1 details . . . . . . . . . . 31 E/A1.1 Certificate Section 1 - Notes (see clauses 5.59 & 9.1, and ENAA clauses E/5.3, E/5.4) . . . . . 31 E/A2 Scour assessment certificate - Section 2 - signatures . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 E/A2.1 Certificate Section 2 - Notes (see clauses 5.59 & 9.1, and ENAA clauses E/5.3, E/5.4) . . . . . 32 1 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 469 - ENAA 1.0.0 April 2024 England NAA Change to policy, major revision, new document development England National Application Annex to CS 469. The major technical updates in this document: (1) the scope has been clarified for scour and other hydraulic actions on structures; (2) the requirements for the identification of scour susceptible structures have been updated; (3) the requirements and advice on the use of flood risk maps have been updated; (4) the climate change allowances have been updated, so they are in accordance with UKCP18 climate change allowances published for the UK; (5) the requirements and advice on calculation of the assessment flow and the catchment response time have been updated; (6) the management of risk due to scour and other hydraulic actions on a structure has been updated; and (7) a requirement for a scour assessment certificate to be completed, for a scour Level 2 assessment, has been introduced. [Publication: April 2024] Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change 2 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Foreword Foreword Publishing information This document is published by National Highways. This document supersedes BD 97/12 "The assessment of scour and other hydraulic actions at highway structures" and Interim Advice Note 173/13 "Implementation of BD 97/12 "The assessment of scour and other hydraulic actions at highway structures", which are withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 3 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Introduction Introduction Background This National Application Annex gives the National Highways-specific requirements and advice for management of scour and other hydraulic actions at highway structures and is supplementary to DMRB CS 469 [Ref 13.N]. This National Application Annex replaces the existing National Highways-specific requirements and advice for the inspection, assessment and risk management of scour and other hydraulic actions at highway structures, previously described in BD 97/12 and IAN 173/13, which are withdrawn. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 12.N] and GG 104 [Ref 16.N] apply to this document. 4 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Abbreviations and symbols Abbreviations and symbols Abbreviations Abbreviation Definition AEP Annual exceedance probability SFAIRP So far as is reasonably practicable AMAX Annual maximum QMED The index flood Symbols Symbol Definition QA Assessment flow for a severe weather event with a stated AEP calculated using: 1) the latest available weather event data, flood event data, historical data and tidal data; and, 2) the climate change allowances for the structure location. QF Fluvial component of the assessment flow. VTide,av The volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the average tidal range (in m), in m3 VTide,max The volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the maximum tidal range (in m), in m3 5 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions Terms and definitions Term Definition Affected populations Affected populations include: 1) road users; 2) road workers; 3) any other persons on, or close to, the highway; and, 4) any persons on, or close to, Overseeing Organisation land. Annual exceedance probability (AEP) The annual exceedance probability (AEP) is the inverse of the annual maximum (AMAX) flood return period of a weather event, based upon statistical records. NOTE 1: The return period of a flood on the AMAX scale is the average interval between AMAX floods of that magnitude. NOTE 2: QMED is the index flood, which is the median of the set of the AMAX flood data. It is the flow that has an AEP of 50%, or a return period of two years. Refer to clause E/5.1 for the method for calculating the fluvial component of the assessment flow QF . Assessment flow The assessment flow QA is the peak flow rate at the structure to be used for the assessment, calculated for the 0.5% annual exceedance probability (AEP) weather event, using the latest available weather event data, flood event data, historical data and tidal data, including: 1) river flow (fluvial) component; 2) over land flow (pluvial) component; 3) tidal component (if appropriate); and, 4) climate change allowances (for the structure location). Average tidal range The average of the mean spring tidal range and mean neap tidal range, at a specific location. In this document, the average tidal range is the sum of two components: 1) the present day average tidal range; and, 2) the climate change allowance for total potential increase in sea level, determined in accordance with clause E/4.7. 6 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Catchment response time in England The length of time between a severe weather event occurrence in the catchment upstream of a structure and flood water arriving at the structure, which depends upon the catchment characteristics upstream of the structure. Refer to clause E/5.2. Channel stability risk rating As part of a scour Level 2 assessment, the stability and lateral movement of a stream or river channel is assessed and the channel stability risk rating is determined, as either low, medium, or high risk. Chart Datum in England Chart Datum is a reference level, for use in tidal tables and can be approximately the lowest sea water level at a specific location, due to astronomical effects and excluding meteorological effects. In England, the Chart Datum at a specific location is a reference level relative to Ordnance Datum (Newlyn). NOTE 1: The height of Chart Datum (CD) at a specific location in England relative to Ordnance Datum (Newlyn), can be negative, indicating that the Chart Datum is below the country specific Datum for England. Climate change allowances in England The predictions by the Environment Agency of anticipated change at a specific location in England, due to climate change, for: 1) peak river flow (fluvial flow); 2) peak rainfall intensity (causes pluvial flow / surface water flow); 3) sea level rise; and, 4) offshore wind speed and extreme wave height. For each of these four categories, the climate change allowances vary according to the location in England. NOTE 1: for England, the climate change allowances are provided in Section E/4. Competent civil engineer or structural engineer The competent civil engineer or structural engineer is a named person, in a defined region or area, or a scheme area, as described in Clause E/1.4. 7 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Country specific Datum for England A vertical datum, or height datum, used as the basis for deriving altitudes on maps. The country specific Datum for England is Ordnance Datum, located in Newlyn, Cornwall, referred to as Ordnance Datum (Newlyn), or OD (N). Ordnance Datum (Newlyn) is mean sea level, as recorded by the Ordnance Survey tidal gauge at Newlyn, Cornwall, between 1915 and 1921. Defined distance from the structure The defined distance from the structure is measured in all directions from the extremities of the structure, not measured from the centre of the structure. Refer to Table 3 .12 (scour susceptible structure Type 1) in DMRB CS 469 [Ref 13.N] and Table 3.15 (scour susceptible structure Type 2) in CS 469 [Ref 13.N]. Flash flooding Flash flooding is surface water flow / overland flow, occurring during a severe weather event with a stated AEP. The flash flooding flow rate, velocity of flow and depth of flow are defined by the severe weather event with a stated AEP. Flood event An overflow of water onto an area of land which is usually dry. A flood event includes any situation where land not normally covered by water becomes covered by water. A flood event at a structure includes any situation where a rising water level, or fast flowing water, can cause undesirable consequences to occur. A flood event in a structure includes any situation where water flowing into the structure, or water overflowing in the structure, can cause undesirable consequences to occur. 8 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Flood plain in England The areas of land identified by the Environment Agency in England, as at risk of flooding from streams, rivers, rainfall and ground water. (See England flood risk [Ref 4.I]). The limits of the flood plain are defined by the peak water level occurring during a severe weather event with a 0.5% AEP. NOTE 1: For England, information on flood risk maps is provided in Section E/3. NOTE 2: a flood plain can be large flat areas of land that a river floods onto, when the flow rate in the river exceeds bank-full capacity. Flood risk maps in England A map prepared by one of the responsible bodies in England, which shows the areas of land at risk of flooding, for a 0.5% AEP flood risk, due to specified sources of flooding: 1) rivers and sea (Environment Agency); 2) reservoirs (Environment Agency); or, 3) surface water (lead local flood authority). Flood risk vulnerability classification in England A classification system by the Environment Agency in England, that categorises different types of development according to its flood vulnerability. Structures referred to in this document, which are located in England, are in the flood risk vulnerability classification "essential infrastructure". Flow control structure A structure that controls the flow of water, and which can affect the flow rate, or water level, upstream or downstream of the flow control structure, including (but not limited to): 1) a reservoir outflow structure; 2) a flood control structure; and, 3) a flood defence structure. A flow control structure can be operated: 1) automatically by remote control; 2) manually by remote control; 3) automatically by electrical and mechanical equipment at the flow control structure location; or, 4) manually by an operative visiting the flow control structure. 9 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Geotechnical asset The man-made or natural earthworks and geotechnical structures below the road pavement layers, highway structures and the adjacent land, within the Overseeing Organisation land boundary. NOTE 1: a geotechnical asset includes, but is not limited to: 1) an embankment; 2) a cutting; or, 3) a bund. NOTE 2: refer to CD 622 [Ref 14.N] and CS 641 [Ref 15.N]. Hydraulic actions Hydraulic actions on a structure can occur due to one or more of the following situations occurring: 1) flowing water causing the formation of scour holes near to, or under, the structure; 2) flowing water causing horizontal forces on the structure; 3) water level rising to the soffit of a bridge, or above the soffit of a bridge, causing uplift on the bridge deck; 4) static water causing horizontal forces on the structure; 5) a storm surge causing very high horizontal forces on the structure; or, 6) wave action on the structure. Large catchment The catchment area upstream of the structure is more than 1,000 km2 . Lead local flood authority The lead local flood authority in relation to an area in England means (see UKPGA 2010/29 [Ref 6.N]): 1) the unitary authority for the area; or, 2) if there is no unitary authority, the county council for the area. NOTE: lead local flood authorities are responsible for developing, maintaining and applying a strategy for local flood risk management in their areas and for maintaining a register of flood risk assets. They also have lead responsibility for managing the risk of flooding from surface water, groundwater and watercourses. Low-lying catchment in England An area of land where the altitude of the land in the catchment is no greater than 20 m above Ordnance Datum (Newlyn). 10 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Maximum tidal range The tidal range between the highest and lowest astronomical tides that can occur at a specific location. In this document, the maximum tidal range is the sum of two components: 1) the present day maximum tidal range, determined in accordance with the Clause E/4.10 in this document; and, 2) the climate change allowance for total potential increase in sea level, determined in accordance with Cluase E/4.7 in this document. NOTE 1: the largest tidal range during a 12-month period can be expected around the time of the equinox, in March and in September, if it coincides with a Spring tide. Normal stream or river level The normal stream or river level is the annual average stream or river water level at the upstream face of the structure. Water level records (date, time and depth of water at the upstream face of the structure) are to be kept in the Overseeing Organisation's structures asset management information system. Overseeing Organisation land Land which is owned by the Overseeing Organisation, or leased to the Overseeing Organisation. NOTE 1: Overseeing Organisation land can be remote from the motorway or all purpose trunk road network; for example land containing a depot, or warehouse building, or office building, or lorry parking area. NOTE 2: Overseeing Organisation land can be near to the motorway or all purpose trunk road network, for example land containing a maintenance vehicle access road (which is not public highway), services area, layby or drainage balancing pond. Principal of the assessing organisation A senior representative of the assessor, checker, contractor, or works examiner, having authority to sign certificates on its behalf. Propagating ocean storm surges Propagating ocean storm surges comprise a series of storm surges during a severe weather event, usually accompanied by high coastal waves and severe scour on beaches, or along estuary river banks, or along sea walls. 11 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Scour Scour is the erosion of soil or rock around or below the foundations of a structure, or near to a structure, due to hydraulic action. NOTE 1: Scour can occur in a stream or river bed, or in the sea bed, near a structure such as a bridge, when fast flowing water removes soil or rock from around or below the structure foundation, resulting in scour holes in the stream or river or sea bed. NOTE 2: Scour holes can compromise structural integrity and result in structural failure or collapse. NOTE 3: Scour holes in a stream or river bed, or in the sea bed, can gradually develop over a long period of time, then rapidly increase in depth during a severe weather event, causing sudden structural failure or collapse. NOTE 4: Scour susceptible structures with shallow underwater foundations (such as a masonry arch bridge over a stream or river) can be at high risk of structural failure or collapse during a severe weather event. NOTE 5: There are several situations that very greatly increase the risk of severe scour near a bridge: 1) dredging or sand/gravel extraction upstream or downstream of bridge; 2) removal of a weir near a bridge; 3) influence of a reservoir, or flood defence structure, or flood control structure; 4) debris accumulation in the water, e.g. tree branches in the water near to a bridge pier, or boulders & rocks being carried in fast flowing water. Static debris in the water just below the water surface can cause severe scour depth near a bridge pier, or abutment, or retaining wall, during high flow rate; or, 5) tipping crushed rock in to a scour hole. Scour Assessment Certificate for England A certificate to be prepared, following completion of a scour Level 2 assessment of a scour susceptible structure Type 1 in England, as described in Appendix E/A in this document. Scour risk rating A designation for the structure, either low, medium, or high risk, determined in accordance with: 1) Table 2.3 and Section 4 or 5 (for scour susceptible structures Type 1) of CS 469 [Ref 13.N]; and 2) Section 7 of CS 469 [Ref 13.N] (for scour susceptible structures Type 2). 12 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Scour risk score A whole number in the range 10 to 100 determined in accordance with Table 2.3 and Section 4 or 5 of CS 469 [Ref 13.N], for a scour susceptible structure Type 1. Scour susceptible structure Type 1 A structure located over or adjacent to water, including (but not be limited to) structures located over or adjacent to: 1) non-tidal streams, rivers, canals, ponds, lakes and reservoirs; 2) tidal streams, rivers and estuaries; and, 3) the coast and the sea. NOTE 1: flooding at a structure over or adjacent to water can occur due to one or more of the following situations occurring: 1) a river over topping the river bank; 2) water flowing through a geotechnical asset, such as a canal bank failure; 3) tidal action; 4) storm surges (including water flowing in a river in an upstream direction); 5) propagating ocean storm surges; 6) coastal wave action; or 7) sea water flooding on land at, or near to, the coast. NOTE 2: a structure with a scour risk rating low risk remains a scour susceptible structure, in accordance with this document. NOTE 3: the defined distance from the structure is provided in Table 3.12 in CS 469 [Ref 13.N]. 13 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Scour susceptible structure Type 2 A structure: 1) located on the flood plain, but not over or adjacent to water; or, 2) at a location where significant surface water flooding has occurred and there is evidence of ground erosion within the defined distance from the structure. NOTE 1: flood plain flooding can occur due to one or more of the following situations occurring: 1) a river overtopping the river bank; 2) ground water rising above ground level; or, 3) rainfall causing surface water overland flow, also known as flash flooding. NOTE 2: significant surface water flooding can occur due to one or more of the following situations occurring: 1) groundwater rising above ground level; and, 2) rainfall causing surface water overland flow, also known as flash flooding. NOTE 3: a structure with a scour risk rating of 'low risk' remains a scour susceptible structure, in accordance with this document. NOTE 4: the defined distance from the structure is provided in Table 3.15 in CS 469 [Ref 13.N]. Severe weather event A weather event that has the potential to cause one or more of the following situations to occur: 1) harm to affected populations; 2) damage to a structure; 3) damage to other infrastructure assets, including (but not limited to) geotechnical assets and drainage assets; 4) damage to utilities; 5) damage to property; 6) operational issues, such as blocked drains on a road bridge, or blocked drains on a road below a bridge, or blocked drains in an underpass or tunnel, or a blocked watercourse at the top of a cutting; 7) customer service issues, such as delays to traffic, or community severance issues; or, 8) construction and maintenance issues, such as delays to construction and maintenance work. 14 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) 15 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions Term Definition Significant flood event An overflow of water on to an area of land which is usually dry and can cause undesirable consequences to occur, including one or more of the following situations occurring: 1) harm to affected populations; 2) damage to a structure; 3) damage to other infrastructure asset, such as drainage assets or geotechnical assets; 4) damage to utilities; 5) damage to property; or, 6) operational issues, such as blocked drains on a road bridge, or blocked drains on a road below a bridge, or blocked drains in an underpass or tunnel, or a blocked watercourse at the top of a cutting. NOTE 1: a significant flood event can result in flooding at a structure. NOTE 2: a significant flood event can result in damage to a structure, with or without flooding occurring at the structure. NOTE 3: a significant flood event can include one or more of the following situations: 1) the water level has risen to within 600 mm of the soffit of a structure where the span is 3 m or more; 2) the water level has risen to the soffit of a structure where the span is up to 3 m; 3) the water level has risen to within 600 mm of the top of a retaining wall, or to within 600 mm of the top of a bridge abutment; 4) flood water has arrived at a structure, with the potential for structural damage to occur; 5) structural damage has occurred at the structure; or, 6) a geotechnical asset has been damaged, with the potential for structural damage to occur. NOTE 4: for a scour susceptible structure Type 1, a significant flood event can include one or more of the following situations: 1) the water level has risen to the river bank level on one side of the river, or on both sides of the river; or, 2) water has flowed over the river bank on one side of the river, or on both sides of the river. NOTE 5: for a scour susceptible structure Type 2, a significant flood event can include one or more of the following situations: 1) water has flowed over the river bank on one side of the river, or on both sides of the river and has flooded land at the structure; 2) water has overflowed and flooded land at the structure; or, 3) significant surface water flooding has occurred at the structure16 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions Significant surface water flooding A type of significant flood event, where one or more of the following situations has occurred at a structure: 1) groundwater rising above ground level; or, 2) rainfall causing surface water overland flow, also known as flash flooding. Small catchment The catchment area is less than 25 km2 . Small and urban catchment The catchment includes urban development and the catchment area is no more than 5 km2 . Spring tide A Spring tide occurs at the following times: 1) at, or up to four days after, the time of the new moon, or the full moon, when the Earth, the Moon and the Sun are approximately aligned; and 2) approximately once every 14 days throughout the year. The tidal range during a Spring tide can be expected to be larger than at other times, at a specific location. Spring tide period The period of time when a Spring tide occurs (a low Spring tide followed by a high Spring tide, or a high Spring tide followed by a low Spring tide), at a specific location. Refer to Clause E/6.1. Storm surge A storm surge is the abnormal rise in sea water level during a storm over the sea, measured as the height of the sea water above the normal predicted astronomical tide. The storm surge is caused primarily by a storm's very strong winds blowing over the surface of the sea, pushing sea water towards the coastline. The height of the storm surge at any given location depends on: 1) the angle of storm impact on the coast; 2) the intensity, size, and speed of the storm; and, 3) the local sea bed profile. High intensity storm – a weather system characterised by low atmospheric pressure at the centre, high average wind speed and high wind speed gusts. Size of the storm – the radius of outermost closed isobar (ROCI). Speed of the storm – the speed at which the weather system moves. 17 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Storm tide When a storm surge and a high tide occur at the same time at the same location, the resulting storm surge is often called a storm tide. Due to the much higher sea level, a storm tide has much more devastating consequences for structures at the coast and at areas inland from the coast, than a storm surge occurring with a low tide. Structural collapse An event that causes failure of one or more components of a structure, causing the structure or part of the structure to break up, or fall apart, or deform excessively, or fall to a lower level. NOTE 1: structural collapse can occur at the time of structural failure, or later. NOTE 2: following a structural collapse being reported: 1) there can be a need for monitoring; and, 2) there can be a need to prepare and implement a programme for mitigating actions. NOTE 3: structural collapse, or partial collapse, includes, but is not limited to: 1) any structural debris falling from a structure to a lower level, e.g. on to land, or railway, or road below the structure, caused by gradual decline of the structure; or, 2) major structural debris, falling from a structure to a lower level, as a result of an overheight vehicle collision with a bridge, or as a result of a vehicle collision with a parapet. 18 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Structural failure An event that causes: 1) the loss or severe reduction of load carrying capacity of one or more components of a structure, or of the whole structure; 2) the loss or severe reduction of vehicle restraint of a parapet, or part of a parapet; 3) a component of a structure to become detached, or partially detached, from the structure; or, 4) a component of a structure to no longer perform as intended. NOTE 1: structural failure can occur without structural collapse. NOTE 2: following a structural failure being reported: 1) there can be a need for monitoring; and, 2) there can be a need to prepare and implement a programme for mitigating actions. NOTE 3: Structural failure includes, but is not limited to: 1) fixings failure, as fixings are components of a structure; 2) structural component failure, for example expansion joint failure; 3) parapet failure caused by a vehicle collision with the parapet; 4) structural failure caused by a vehicle collision with the structure, such as an overheight vehicle colliding with a bridge; or, 5) structural failure caused by a vehicle collision with a nearby vehicle restraint system. Structure Any temporary or permanent structure, in accordance with CG 300 [Ref 17.N]. Team Leader of the assessing organisation The person responsible for overseeing and co-coordinating the work of the scour assessment, or check, team and having authority to sign certificates on behalf of the team. The Team Leader is a competent civil engineer or structural engineer. Tidal location A specific location where the water level varies in accordance with the tidal period and tidal range. 19 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Terms and definitions (continued) Term Definition Tidal period The period of time between low tide and high tide, or between high tide and low tide, at a specific location. The tidal period is not constant at a specific location. The tidal period at a specific location changes from day to day, depending on the alignment of the Earth, the Moon and the Sun. Tidal range Tidal range is the height difference (change in sea level) between high tide and low tide, at a specific location. The tidal range is not constant at a specific location. The tidal range at a specific location changes from day to day, depending on the alignment of the Earth, the Moon and the Sun. Tide Tide is the rise and fall of sea level caused by gravitational forces exerted by the Moon and the Sun and the rotation of the Earth. Weir A dam or barrier across the width of a stream or river that alters the flow characteristics of water and usually results in: 1) a change in the height of the stream or river water level; or, 2) diversion of the stream or river flow. There are many different designs of weir, but usually water flows freely over the top of the weir crest before cascading down to a lower level. 20 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/1. Scope E/1. Scope Aspects covered (additional to CS 469 clauses 1.1 to 1.6 , 1.8 and 1.9 to 1.17) E/1.1 The management of scour and other hydraulic actions at highway structures shall be operated at National Highways in accordance with this document and DMRB CS 469 [Ref 13.N] (see CS 469 [Ref 13.N]clauses 1.1 to 1.5, and clauses 1.9 to 1.17). E/1.2 For all scour susceptible structures, risks to affected populations must be reduced to a level SFAIRP and maintained at a level SFAIRP, in compliance with legal requirements [Health & Safety at Work etc Act 1974 Part 1 Sections 2 and 3 (1) UKPGA 1974/37 (HSWA) [Ref 5.I]; Highways Act 1980 Part IV Section 41 Act UKPGA 1980/66 [Ref 10.N]; and Infrastructure Act 2015, Part 1 Section 5 UKPGA 2015/07 [Ref 11.N] (see CS 469 [Ref 13.N] clause 1.6). E/1.3 For all scour susceptible structures, mitigating actions shall be determined that can potentially: 1) reduce scour and other hydraulic action risks to a level SFAIRP; and, 2) maintain scour and other hydraulic action risks at a level SFAIRP (see CS 469 [Ref 13.N] clause 1.8). Competent persons (additional to CS 469 clauses 1.14 and 1.15) E/1.4 Unless otherwise stated in this document, all work carried out in accordance with this document shall be overseen by a competent civil engineer or structural engineer (see CS 469 [Ref 13.N] clauses 1.14, 1.15). NOTE Refer to the "Terms and definitions" table for the definition of "Team Leader of the assessing organisation". 21 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/2. Identification of scour susceptible structure... E/2. Identification of scour susceptible structures Type 1 and Type 2 (additional to CS 469, Sections 1 and 9) Scour susceptible structures Type 1 (additional to CS 469 clauses 1.2, 1.3, 1.4 and 9.1) E/2.1 A list of scour susceptible structures Type 1 shall be maintained and updated, e.g. when new structures are constructed, upgraded, or demolished (see CS 469 [Ref 13.N] clauses 1.2, 1.3, 1.4, and 9.1). Scour susceptible structures Type 2 (additional to CS 469 clauses 1.2, 1.3 and 9.1) E/2.2 A list of scour susceptible structures Type 2 shall be prepared and updated , e.g. when new structures are constructed, upgraded, or demolished (see CS 469 [Ref 13.N] clauses 1.2, 1.3, and 9.1). NOTE 1 The Environment Agency can provide 0.5% AEP flood event flood risk maps, on request, to be used for the designation of scour susceptible structures Type 2. These are available from: 1) the Environment Agency national modelling and mapping team; and, 2) the Environment Agency Partnership and Strategic Overview area team, for the structure location. NOTE 2 The Environment Agency can be contacted at Environment Agency, National Customer Contact Centre. NOTE 3 The lead local flood authority can provide access to surface water flood risk risk maps, on request, to be used for the designation of scour susceptible structures Type 2. NOTE 4 Refer to the "Terms and definitions" table for the definition of "lead local flood authority". 22 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/3. Review of 0.5% AEP flood risk maps (additiona... E/3. Review of 0.5% AEP flood risk maps (additional to CS 469, Sections 4 and 7) Scour susceptible structures Type 1 (additional to CS 469 clauses 4.3 and 4.6) E/3.1 The most recently prepared 0.5% AEP flood risk maps, of the types shown below, for the structure location shall be reviewed: 1) the Environment Agency rivers and sea flood risk maps; 2) the Environment Agency reservoirs flood risk maps; and, 3) lead local flood authority surface water flood risk maps (see CS 469 [Ref 13.N] clauses 4.3 and 4.6). NOTE The Environment Agency can be contacted at Environment Agency, National Customer Contact Centre. Scour susceptible structures Type 2 (additional to CS 469 clauses 7.18 to 7.20) E/3.2 The most recently prepared 0.5% AEP flood risk maps, of the types shown below, for the structure location shall be reviewed: 1) the Environment Agency rivers and sea flood risk maps; 2) the Environment Agency reservoirs flood risk maps; and 3) lead local flood authority surface water flood risk maps (see CS 469 [Ref 13.N] clauses 7.18 to 7.20). 23 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/4. Climate change allowances (additional to CS 4... E/4. Climate change allowances (additional to CS 469, Sections 5 and 6) General E/4.1 The climate change allowances for England shall be used in an assessment for scour and other hydraulic actions on a structure (see CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1). NOTE The climate change allowances are based on the UK climate change projections 2018 UKCP 18 (CCOL) [Ref 8.I], UKCP 18 [Ref 6.I]. Climate change allowances for structures E/4.2 The climate change allowances for England shall be used to assess immediate and short term risk to the structure, in the scour Level 2 assessment (see CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1). E/4.3 The climate change allowances for the structure location shall be determined in accordance with the Environment Agency criteria described in CCA(E) [Ref 1.I]. See CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1). Peak river flow E/4.4 When calculating the component of the assessment flow, QA , from river (fluvial) flooding, QF , the climate change allowance for peak river flow shall be used, determined for the structure location using the relevant Environment Agency documents and the criteria provided in clause E/4.5 (See CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1). NOTE The Environment Agency published flood risk maps for England England flood risk [Ref 4.I] show Flood Zone 1, Flood Zone 2, Flood Zone 3a and Flood Zone 3b areas in England. However, many of the Environment Agency Flood Zone areas shown on published flood risk maps England flood risk [Ref 4.I] are not the flooded area for a 0.5% AEP weather event. Refer to clause E/3.1 for information on how to access the 0.5% AEP flood risk maps: 1) the Environment Agency flood risk maps; and 2) the lead local flood authority flood risk maps, including maps showing areas where significant surface water flooding has occurred. E/4.5 The criteria for determining the climate change allowance for peak river flow shall include: 1) flood risk vulnerability classification - National Highways structures are "essential infrastructure"; 2) Environment Agency "river basin district", e.g. Anglian CCA(E) PRF [Ref 2.I]; 3) Environment Agency "management catchment", e.g. Broadland Rivers CCA(E) PRF [Ref 2.I]; and 4) Environment Agency climate change allowance category "2020's upper end" - total percentage increase in QF anticipated for the period 2015 to 2039 CCA(E) PRFMC [Ref 2.N]. Peak rainfall intensity E/4.6 When calculating the component of the assessment flow, QA , from surface water (pluvial) flooding in small and urban catchments, where the area of the catchment upstream of the structure is up to 5 km2 , the climate change allowance for peak rainfall intensity shall be used, determined for the structure location using the relevant Environment Agency documents and the criteria provided in clause E/4.7 (see See CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1). E/4.7 The criteria for determining the climate change allowance for peak rainfall intensity shall include: 1) Environment Agency "river basin district", e.g. Anglian CCA(E) PRI [Ref 1.N] ; 2) Environment Agency "management catchment", e.g. Broadland Rivers CCA(E) PRI [Ref 1.N] ; 24 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/4. Climate change allowances (additional to CS 4... 3) Environment Agency climate change allowance category "1% annual exceedance rainfall event" CCA(E) PRI [Ref 1.N]; and 4) Environment Agency climate change allowance category "2050's central" CCA(E) PRI [Ref 1.N] . Sea level rise E/4.8 When calculating the component of the assessment flow, QA , from tidal or coastal flooding, the average tidal range shall be determined for the structure location using two components added together (see CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, 6.1): 1) the present day average tidal range; and 2) the climate change allowance for total potential increase in sea level, determined in accordance with clause E/4.9. E/4.9 The climate change allowance for total potential increase in sea level for the structure location shall be determined from Table E/4.9 (see CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1). Table E/4.9 Determine the climate change allowance: total potential increase in sea level. Areas of England Climate change allowance for the structure: total potential increase in sea level anticipated for the period 2000 to 2039 Anglia 0.290 metres South East Thames river basin district 0.287 metres South West Severn river basin district 0.291 metres Northumbria Parts of Solway Tweed river basin district on the east coast that are in England 0.243 metres Humber 0.279 metres North West Parts of Solway Tweed river basin district on the west coast and Dee river basin district that are in England 0.240 metres E/4.10 When calculating the volume of the tidal prism, VTide,av (see CS 469 [Ref 13.N] clauses 5.28, 5.29), the average tidal range determined in accordance with clause E/4.8 shall be used. E/4.11 When calculating the component of the assessment flow QA from tidal or coastal flooding, the maximum tidal range shall be determined for the structure location using two components added together (see CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, 6.1): 1) the present day maximum tidal range, determined in accordance with clause E/4.12 ; and, 2) the climate change allowance for total potential increase in sea level, determined in accordance with clause E/4.9. E/4.12 The present day maximum tidal range for the structure location shall be determined using two components (see CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, 6.1): 25 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/4. Climate change allowances (additional to CS 4... 1) low tide level, this is the lowest astronomical tide which can occur at the structure location; and, 2) high tide level, this is either the present day extreme sea level determined in accordance with clause E/4.13, or the highest astronomical tide which can occur at the structure location, whichever is the highest level. E/4.13 The present day extreme sea level for the structure location for a 0.5% AEP event, shall be determined in accordance with CCA(E) ESL Data [Ref 3.N], CCA(E) ESL Report [Ref 4.N] and CCA(E) ESL Guide [Ref 5.N] (see CS 469 [Ref 13.N] clauses 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, 6.1). NOTE The present day extreme sea level is for still water level only CCA(E) ESL Guide [Ref 5.N] and does not include the effects of propagating ocean storm surges. E/4.14 When calculating the volume of the tidal prism, VTide,max (see CS 469 [Ref 13.N] clauses 5.28, 5.29) the maximum tidal range determined in accordance with clause E/4.11 shall be used. 26 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/5. Scour Level 2 assessment (additional to CS 46... E/5. Scour Level 2 assessment (additional to CS 469, Sections 5 and 9) E/5.1 The fluvial component of the assessment flow, QF , shall be determined in accordance with the latest version of the Environment Agency Flood Estimation Guidelines Guidance LIT 11832 [Ref 7.N] (see CS 469 [Ref 13.N] clauses 5.17 to 5.24). NOTE 1 The Environment Agency can provide their technical documents, on request. The Environment Agency can be contacted at Environment Agency, National Customer Contact Centre. NOTE 2 The fluvial component of the assessment flow, QF , can be influenced by many factors, including: 1) the catchment includes urban development and the catchment area is no more than 5 km2 , referred to as a "small and urban catchment"; 2) the catchment area is less than 25 km2 , referred to as a "small catchment"; 3) the catchment area is more than 1,000 km2 , referred to as a "large catchment"; 4) the catchment, or part of the catchment, is low-lying; 5) the catchment, or part of the catchment, has pumped drainage; 6) the catchment includes a catchment to catchment water transfer, or catchment to catchment diversion; 7) there is an extensive flood plain in the catchment, which can temporarily store flood water during a severe weather event, without any flow control structures; 8) there are one or more flow control structures in the catchment; 9) there are one or more flow control structures downstream of the structure, that can affect the flow rate, or water level at the structure; 10) the catchment, or part of the catchment, is highly permeable, e.g. underlain by fissured aquifers; 11) the catchment includes one or more sub-catchments with widely differing flood response times; and 12) there are complex interactions of flood volume and peak flow, or contributions to the peak flow from different tributaries, or other complex factors, affecting the peak flow rate at the structure location. E/5.2 The catchment response time, for the catchment upstream of the structure, shall be determined in accordance with Table E/5.2 (see CS 469 [Ref 13.N] clause 5.24). Table E/5.2 Catchment response time. Catchment response time The length of time between a severe weather event occurrence in the catchment upstream of a structure and flood water arriving at the structure Very short No more than 30 minutes. Short Between 30 minutes and 2 hours. Medium Between 2 hours and 24 hours. Long More than 24 hours. E/5.3 A Scour Assessment Certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 shall be completed and signed by the Team Leader and the Principal of the assessing organisation, in accordance with Appendix E/A in this document (see CS 469 [Ref 13.N] clauses 5.59 and 9.1). E/5.4 The Scour Assessment Certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 shall be sent to the Technical Approval Authority, for acceptance (see CS 469 [Ref 13.N] clauses 5.59 and 9.1). 27 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/6. Risk management of scour and other hydraulic ... E/6. Risk management of scour and other hydraulic actions at structures (additional to CS 469, Section 8) E/6.1 The process for providing flood guidance in England (on a national / regional / area basis) to National Highways shall include the Flood Forecasting Centre [FFC] documents (see CS 469 [Ref 13.N] clauses 8.10 and 8.11): 1) "Flood Outlook", issued twice per month FFC (FO) [Ref 9.N]; and 2) "Flood Guidance Statement", issued daily FFC (FGS) [Ref 8.N]. NOTE 1 Severe weather warnings are issued by the Met Office UKWW [Ref 7.I]. NOTE 2 The Flood Forecasting Centre is a working partnership between the Met Office and the Environment Agency, to combine their meteorology and hydrology expertise into a specialised hydrometeorology service FFC (Website) [Ref 3.I]. The FFC provides national scale forecasts for all natural forms of flooding, due to: 1) rivers; 2) surface water; 3) groundwater; and 4) tidal & coastal. NOTE 3 The FFC is fully operational 24 hours a day, 7 days a week. NOTE 4 The "Flood Outlook" FFC (FO) [Ref 9.N]provides a fortnightly general look ahead for flood risk for all natural forms of flooding (referred to in Note 2 above), including: 1) a summary (not detailed) of flooding risk for the next four weeks; 2) a seasonal weather briefing; and 3) spring tide dates. NOTE 5 The "Flood Guidance Statement" FFC (FGS) [Ref 8.N]provides a daily summary of flood risk from all natural sources, including: 1) a flooding forecast with flood risk risk categories, for the next five days; and 2) a look ahead for the following six to ten days, when there is a heightened flood risk, or an ongoing flood event. E/6.2 The process at National Highways for acting upon the "Flood Outlook" FFC (FO) [Ref 9.N]shall include (see CS 469 [Ref 13.N] clauses 8.10 to 8.15): 1) advance preparations for actions needed prior to significant flood events at structures; and, 2) advance preparations for actions needed to safeguard affected populations and structures. E/6.3 The process at National Highways for acting upon the "Flood Guidance Statement" FFC (FGS) [Ref 8.N]shall include (see CS 469 [Ref 13.N] clauses 8.10 to 8.15): 1) preparations for actions needed in response to forecast of significant flood events at high risk scour susceptible structures; 2) implementation of actions needed to safeguard affected populations and structures; and, 3) implementing operational procedures at structures which are linked to the risk levels in the Flood Guidance Statement. 28 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/7. Normative references E/7. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref. Document Ref 1.N https://environment.data.gov.uk/hydrology/climate-change-allowances/rainfall. Environment Agency.. CCA(E) PRI, 'Climate Change Allowances - Peak Rainfall Intensity (Map)' Ref 2.N Environment Agency. https://www.gov.uk/government/publications/peak-river-flowclimate-change-allowances-by-management-catchment. CCA(E) PRFMC, 'Climate change allowances - Peak river flow climate change allowances by management catchment' Ref 3.N Environment Agency. https://data.gov.uk/dataset/73834283-7dc4-488a-9583-a920072d9a9d/coastaldesign-sea-levels-coastal-flood-boundary-extreme-sea-levels-2018. CCA(E) ESL Data, 'Climate change allowances - Present day extreme sea levels (Data)' Ref 4.N Environment Agency. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_- data/file/827778/Coastal_flood_boundary_conditions_for_the_UK_2018_update_-_technical_report.pdf. CCA(E) ESL Report, 'Climate change allowances - Present day extreme sea levels (technical summary report)' Ref 5.N Environment Agency . https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_- data/file/827779/Coastal_flood_boundary_conditions_for_the_UK_2018_update_-_user_guide.pdf. CCA(E) ESL Guide, 'Climate change allowances - Present day extreme sea levels (user guide)' Ref 6.N National Archives. UKPGA 2010/29, 'Flood and Water Management Act' Ref 7.N Environment Agency. Guidance LIT 11832, 'Flood Estimation Guidelines' Ref 8.N https://www.gov.uk/government/organisations/flood-forecasting-centre/about-ourservices. Flood Forecasting Centre. FFC (FGS), 'Flood Guidance Statement' Ref 9.N https://www.gov.uk/government/news/flood-forecasting-centre-the-flood-outlook-ischanging. Flood Forecasting Centre.. FFC (FO), 'Flood Outlook.' Ref 10.N National Archives. UKPGA 1980/66, 'Highways Act' Ref 11.N National Archives. UKPGA 2015/07, 'Infrastructure Act' Ref 12.N National Highways. GG 101, 'Introduction to the Design Manual for Roads and Bridges' Ref 13.N National Highways. CS 469, 'Management of scour and other hydraulic actions at highway structures' Ref 14.N National Highways. CD 622, 'Managing geotechnical risk' Ref 15.N National Highways. CS 641, 'Managing the maintenance of highway geotechnical assets' Ref 16.N National Highways. GG 104, 'Requirements for safety risk assessment' Ref 17.N National Highways. CG 300, 'Technical approval of highway structures' 29 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 E/8. Informative references E/8. Informative references The following documents are informative references for this document and provide supporting information. Ref. Document Ref 1.I https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances. Environment Agency.. CCA(E), 'Climate change allowances for England' Ref 2.I Environment Agency. https://environment.maps.arcgis.com/apps/webappviewer/index.html?id=363522b846b842a4a90CCA(E) PRF, 'Climate change allowances for peak river flows in England (map)' Ref 3.I Meteorological Office and Environment Agency.. https://www.gov.uk/government/organisations/flood-forecasting-centre. FFC (Website), 'Flood Forecasting Centre' Ref 4.I https://www.gov.uk/government/publications/flood-risk-maps-2019. Environment Agency.. England flood risk, 'Flood risk maps, England.' Ref 5.I National Archives. UKPGA 1974/37 (HSWA), 'Health and Safety at Work etc. Act' Ref 6.I https://www.metoffice.gov.uk/research/approach/collaboration/ukcp. The Met Office, UK. UKCP 18, 'UK Climate Projections 2018' Ref 7.I https://www.metoffice.gov.uk/weather/warnings-and-advice/uk-warnings. Met Office.. UKWW, 'UK Weather Warnings.' Ref 8.I https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/research/ukcp/ukcp18- infographic-headline-findings-land.pdf. The Met Office, UK. UKCP 18 (CCOL), 'UKCP18 Climate Change Over Land.' 30 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Appendix E/A. Model form of scour assessment certificate fo... Appendix E/A. Model form of scour assessment certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 (additional to CS 469, Sections 5 and 9) E/A1 Scour assessment certificate - Section 1 - scour susceptible structure Type 1 details Name of structure 1 : Structure reference number 1 : Structure key 1 : E/A1.1 Certificate Section 1 - Notes (see CS 469 [Ref 13.N] clauses 5.59 & 9.1, and ENAA clauses E/5.3, E/5.4) 1) Note: The name of the structure, structure reference number and structure key are as shown on the Overseeing Organisation's structures asset management system. E/A2 Scour assessment certificate - Section 2 - signatures We certify that reasonable professional skill and care has been used in the preparation of the scour Level 2 assessment of (name of structure and structure reference number) with a view to securing that: 1) This structure has been assessed in accordance with: (a) CS 469 'Management of scour and other hydraulic actions at highway structures'; and, (b) England National Application Annex for DMRB CS 469 'Management of scour and other hydraulic actions at highway structures' 2 . 2) The results of the scour Level 2 assessment for this structure are: (a) the scour risk score is 10 / 40 / 60 / 80 / 100 3, 4; (b) the scour risk rating is high risk / medium risk / low risk 3, 4; and, (c) the channel stability risk rating is high risk / medium risk / low risk 3, 4 . Signed _____________________________________________ Team Leader of the assessing organisation Name ______________________________________________ Engineering Qualifications ______________________________ 5 Position held _________________________________________6 Name of Organisation __________________________________ Date ________________________________________________ Signed _______________________________________________ Principal of the assessing organisation Name _______________________________________________ Engineering Qualifications _______________________________ 5 Position held __________________________________________7 31 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - ENAA Version 1.0.0 Appendix E/A. Model form of scour assessment certificate fo... Name of Organisation ___________________________________ Date ________________________________________________ The departures and additional methods or processes given in the Schedule to this Certificate are agreed 1 . This Certificate is accepted by the Technical Approval Authority [TAA]. Signed _______________________________________________ Name ________________________________________________ Engineering Qualifications ________________________________ 5 Position held __________________________________________ TAA ________________________________________________ Date ________________________________________________ E/A2.1 Certificate Section 2 - Notes (see CS 469 [Ref 13.N] clauses 5.59 & 9.1, and ENAA clauses E/5.3, E/5.4) 2 List in a Schedule to this Certificate any departures, additional methods or processes agreed by the Overseeing Organisation and the date of the Overseeing Organisation agreement on DAS. 3 Delete as appropriate. 4 The scour risk score, scour risk rating and channel stability risk rating are to be recorded in the Overseeing Organisation structures asset management information system. Refer to CS 469 clause 9.1. 5 CEng MICE, or CEng MIStructE, or equivalent. 6 The Team Leader of the assessing organisation responsible for the whole of the scour Level 2 assessment of a scour susceptible structure Type 1. Refer to the "Terms and definitions table" for the definition of "Team Leader of the assessing organisation". 7 A Principal of the assessing organisation responsible for the whole of the scour Level 2 assessment of a scour susceptible structure Type 1. Refer to the "Terms and definitions table" for the definition of "Principal of the assessing organisation". 32 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 © Crown copyright 2024. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 469 - NINAA Northern Ireland National Application Annex for Management of scour and other hydraulic actions at highway structures. (formerly BD 97/12) Version 1.0.0 Summary This National Application Annex sets out the Department for Infrastructure, Northern Ireland's requirements and advice on the inspection, assessment and monitoring of scour and other hydraulic actions at structures over or adjacent to water and at structures on the flood plain but not over or adjacent to water. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated team in the Department for Infrastructure, Northern Ireland. The email address for all enquiries and feedback is: dcu@infrastructure-ni.gov.uk This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 Contents Release notes 2 Foreword 3 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction 4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abbreviations and symbols 5 Terms and definitions 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 NI/1. Scope 9 Aspects covered ([CS 459] 1.6 etc.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 NI/2. Climate change allowances 10 General ([CS 469] Section 5 & clause 6.1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Climate change allowances for structures located in Northern Ireland . . . . . . . . . . . . . . . . . . . . . . 10 For structures with a design life beyond 2080 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 NI/3. Normative references 12 NI/4. Informative references 13 1 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 469 - NINAA 1.0.0 April 2024 Northern Ireland NAA Change to policy, major revision, new document development Department for Infrastructure National Application Annex to CS 469. The technical updates in this document: (1) The definition of scour susceptible structure has been amended to also include structures on the floodplain but not over or adjacent to water. (2) The scope has been clarified for scour and other hydraulic actions on structures, including scour in non-tidal rivers, tidal rivers and estuaries, ocean scour, propagating ocean storm surges, coastal wave action and coastal flooding. (3) The method for estimation of scour depth now also includes implementation of the results from University of Exeter research projects on scour caused by woody debris close to a structure in a river. (4) The climate change allowances have been updated, so they are in accordance with UKCP09 climate change allowances published for the UK. (5) Management of risk due to scour and other hydraulic actions on a structure have been updated. [Publication: TBC] Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change 2 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 Foreword Foreword Publishing information This document is published by National Highways on behalf of the Department for Infrastructure, Northern Ireland. The document DMRB CS 469 [Ref 4.N] supersedes BD 97/12 "The assessment of scour and other hydraulic actions at highway structures" which is withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 3 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 Introduction Introduction Background This National Application Annex gives the Department for Infrastructure, Northern Ireland-specific requirements and advice related to management of scour and other hydraulic actions at structures and is supplementary to DMRB CS 469 [Ref 4.N]. Safety In Northern Ireland, the relevant legislation is the Health and Safety at Work (Northern Ireland) Order 1978 NIOC 1978/1039 [Ref 2.N] and Roads (Northern Ireland) Order 1993 Part II Article 8 NISI 1993/3160 [Ref 8.N]. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 3.N] and GG 104 [Ref 6.N] apply to this document. However, this document also applies to all types of structures, as defined in this document. 4 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 Abbreviations and symbols Abbreviations and symbols Abbreviations Abbreviation Definition AEP Annual exceedance probability SFAIRP So far as is reasonably practicable Symbols Symbol Definition QA Assessment flow 5 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 Terms and definitions Terms and definitions Terms Term Definition Annual exceedance probability (AEP) The annual exceedance probability (AEP) is the inverse of the annual maximum (AMAX) flood return period of a weather event, based upon statistical records. Note 1: The return period of a flood on the AMAX scale is the average interval between AMAX floods of that magnitude. Note 2: QMED is the index flood, which is the median of the set of the AMAX flood data. It is the flow that has an AEP of 50%, or a return period of two years. Refer to the method for calculating the fluvial component of the assessment flow QF . Assessment flow The flow rate to be used for the assessment, calculated for the annual exceedance probability weather event, including: 1) river flow (fluvial) component; 2) overland flow (pluvial) component (if appropriate); 3) tidal component (if appropriate); 4) ocean storm surge component (if appropriate); and, 5) climate change allowances (for the structure location). Climate change allowances The climate change allowances are predictions of anticipated change for: 1) peak river flow (fluvial flow); 2) peak rainfall intensity (causes pluvial flow / surface water flow); 3) sea level rise; and, 4) offshore wind speed and extreme wave height. Note: for each of these four categories, the climate change allowances vary according to the location in the UK. See Section NI/ 2. Flood plain The areas of land: 1) identified by Department for Infrastructure in Northern Ireland, as the generally flat areas adjacent to a watercourse or the sea where water flows in time of flood or can flow but for the presence of flood defences. The limits of the floodplain are defined by the peak water level occurring during a severe weather event with a stated AEP; 2) any other location where flash flooding is known to have caused scour within 30 metres of a structure; and, 3) any other location where flash flooding can potentially cause scour within 30 metres of a structure. 6 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 Terms and definitions Terms (continued) Term Definition Flood risk vulnerability classification, Northern Ireland Structures referred to in this document, which are located in Northern Ireland, are in the flood risk vulnerability classification "essential infrastructure". Overseeing Organisation land Land which is owned by the Overseeing Organisation, or leased to the Overseeing Organisation. Note 1: Overseeing Organisation land can be remote from the motorway or all purpose trunk road network, for example land containing a depot, or warehouse building, or office building, or lorry parking area. Note 2: Overseeing Organisation land can be near to the motorway or all purpose trunk road network, for example land containing a maintenance vehicle access road (that is not public highway), services area, layby or drainage balancing pond. Scour susceptible structure Type 1 Scour susceptible structures Type 1 are located over or adjacent to water, including (but not be limited to) structures located over or adjacent to: 1) non-tidal streams, rivers, canals, ponds, lakes and reservoirs; 2) tidal streams, rivers and estuaries; and, 3) the coast and the sea. Scour susceptible structure Type 2 Scour susceptible structures Type 2 are located: 1) on the flood plain but not over or adjacent to water; and, 2) on land where flash flooding can cause structural damage. Note: this type of structure can be located a considerable distance from a stream, river, canal, pond, lake, reservoir, an estuary, or the coast. Significant flood event, for a scour susceptible structure Type 1 For a scour susceptible structure Type 1, a significant flood event is where 50% of the stream or river capacity is reached or exceeded, e.g. during a period of heavy rainfall, or during coastal flooding. Note 1: examples include (but are not limited to): 1) river level rises to 50% of the internal depth of a culvert; 2) river level rises from normal river level to 50% of the distance between normal river level and the soffit of a bridge; and, 3) river level rises to the top of the river bank (where the soffit of the bridge is higher than the river bank level). Note 2: normal river level is to be the annual average river water level at the upstream face of the bridge. 7 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 Terms and definitions Terms (continued) Term Definition Significant flood event, for a scour susceptible structure Type 2 For a scour susceptible structure Type 2, a significant flood event is where: 1) 100% of the stream or river capacity is reached or exceeded, e.g. during a period of heavy rainfall; 2) surface water (from surface water, stream or river water, or sea water) flows over land designated as river floodplain, or sea (coastal) floodplain or surface water flooding areas, by Department for Infrastructure, Northern Ireland, e.g. during a period of heavy rainfall, or during coastal flooding. Note: examples include (but are not limited to): 1) river level rises to the top of the river bank, or flows over the top of the river bank and floods nearby land; 2) river level rises to the soffit of the culvert; 3) river level rises to the soffit of the bridge; or, 4) surface water flows over land and flows adjacent to, or under, the scour susceptible structure Type 2. Structure Any temporary or permanent structure built on, over, under, or adjacent to, any part of the Overseeing Organisations' motorway or all purpose trunk roads, or on Overseeing Organisation land. Note: This includes (but is not limited to) a bridge, tunnel, underpass, wall, subway, gantry, mast, lighting column, building, salt barn, salt storage area push wall, noise barrier and drainage structures (such as a pipe, culvert, open channel, pumping station, chamber, drainage inlet structure, or drainage outfall structure). 8 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 NI/1. Scope NI/1. Scope Aspects covered ([CS 459] 1.6 etc.) NI/1.1 DMRB CS 469 [1.1 to 1.5 and 1.9 to 1.15] is not applicable. In Northern Ireland, the process for inspection and assessment of scour and other hydraulic actions at structures shall be in accordance with Department for Infrastructure Policy in relation to the Interim Scour Management Strategy DEM 152/14 [Ref 5.N]. NI/1.2 CS 469 [1.7 & 1.8] is not applicable. For all scour susceptible structures, risks to affected populations shall be reduced to a level SFAIRP, in compliance with legal requirements. For Northern Ireland, the relevant legislation is the Health and Safety at Work (Northern Ireland) Order 1978 NIOC 1978/1039 [Ref 2.N] and Roads (Northern Ireland) Order 1993 Part II Article 8 NISI 1993/3160 [Ref 8.N]. NI/1.3 Where reference is made to Technical Approval Authority throughout CS 469 [Ref 4.N], the Department for Infrastructure Roads Division responsible for the structure being considered shall be referred to and not the Technical Approval Authority. [See CS 469 clauses 2.16, 5.8.1, 5.20, 5.32, Table 5.49.4, 5.49.6, 5.59, 6.4, 6.4 NOTE 1 and 7.8.1.] NI/1.4 The Technical Approval Authority shall be referred to as required under DMRB CG 300 [Ref 7.N]and CD 356 [Ref 1.N] as stated in clause 8.21 of CS 469 [Ref 4.N]. 9 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 NI/2. Climate change allowances NI/2. Climate change allowances General ([CS 469] Section 5 & clause 6.1) NI/2.1 The climate change allowances provided by the appropriate government body shown in Table NI/2.1 shall be used in an assessment for scour and other hydraulic actions on a structure. This refers to CS 469 [Ref 4.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1. Table NI/2.1 Government bodies responsible for publishing climate change allowances Country where the structure is located Government body responsible for publishing climate change allowances Climate change allowances to be used in a Level 1 assessment and a Level 2 assessment Northern Ireland Department for Infrastructure Refer to Tables NI/2.3, NI/2.4 and NI/2.5 NOTE 1 The climate change allowances requirement is based on the UK climate change projections 2009 (UKCP09) UKCP 09 [Ref 2.I]. These are being remodelled and updated to provide UK climate change projections 2018 UKCP 18 [Ref 3.I]), so the climate change allowances shown in this document are likely to be amended in the near future. NOTE 2 The published climate change allowances for Northern Ireland are shown in the informative reference in Table NI/2.1N2: Table NI/2.1N2 Climate change allowances for Northern Ireland - informative reference Country where the structure is located Climate change allowances informative reference Northern Ireland CCA(NI) [Ref 1.I] NI/2.2 The vulnerability classification for structures defined in this document shall be "essential infrastructure". Climate change allowances for structures located in Northern Ireland NI/2.3 For a structure located in Northern Ireland, when calculating the assessment flow QA from river (fluvial) flooding, the climate change allowance for river (fluvial) flooding shall be used, determined for the structure location from Table NI/2.3. This applies to CS 469 [Ref 4.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1. Table NI/2.3 Determine the climate change allowance: percentage increase in stream or river (fluvial) assessment flow River basin district Allowance category Climate change allowance for the structure: total potential increase in QA anticipated for the period to 2080 Applies across all of Northern Ireland Central 20% NI/2.4 For a structure located in Northern Ireland, when calculating the assessment flow QA from surface water (pluvial) flooding in small and urban catchments, where the catchment upstream of the structure is up to 5 km2 , the climate change allowance for peak rainfall intensity in small and urban catchments shall be used, determined for the structure location from Table NI/2.4. This applies to CS 469 [Ref 4.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1. 10 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 NI/2. Climate change allowances Table NI/2.4 Determine the climate change allowance: percentage increase in peak rainfall intensity in small and urban catchments River basin district Allowance category Climate change allowance for the structure: total potential increase in QA anticipated for the period to 2080 Applies across all of Northern Ireland Central 20% NI/2.5 For a structure located in Northern Ireland, when calculating the assessment flow QA from coastal flooding, the rise in sea level climate change allowance to be used is determined for the structure location from Table NI/2.5. This applies to CS 469 [Ref 4.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1. Table NI/2.5 Determine the climate change allowance: total potential increase in sea level River basin district Climate change allowance for the structure: total potential increase in sea level anticipated for the period to 2080 All of Northern Ireland coastline The climate change allowance to be used for the period to 2080 shall be obtained from the Department for Infrastructure, Northern Ireland NOTE The climate change allowance for potential increase in sea level is specific to the geographical location. For structures with a design life beyond 2080 NI/2.6 For structures located in Northern Ireland with a design life beyond 2080, the longer term risks to the structure, for the period 2081 to 2115, shall also be separately assessed in the Level 1 assessment and in the Level 2 assessment. This applies to CS 469 [Ref 4.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55 and 6.1]. NI/2.7 The climate change allowances to be used in Northern Ireland for the period 2081 to 2115 shall be obtained from the Department for Infrastructure, Northern Ireland. CS 469 [Ref 4.N] 11 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 NI/3. Normative references NI/3. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref. Document Ref 1.N National Highways. CD 356, 'Design of highway structures for hydraulic action' Ref 2.N National Archive. NIOC 1978/1039, 'Health and Safety at Work (Northern Ireland) Order 1978' Ref 3.N National Highways. GG 101, 'Introduction to the Design Manual for Roads and Bridges' Ref 4.N National Highways. CS 469, 'Management of scour and other hydraulic actions at highway structures' Ref 5.N Department for Infrastructure, Northern Ireland.. https://www.infrastructure-ni.gov.uk/- publications/interim-scour-management-strategy-dem-15214. DEM 152/14, 'Northern Ireland Interim Scour Management Strategy.' Ref 6.N National Highways. GG 104, 'Requirements for safety risk assessment' Ref 7.N National Highways. CG 300, 'Technical approval of highway structures' Ref 8.N National Archives. NISI 1993/3160, 'The Roads (Northern Ireland) Order' 12 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - NINAA Version 1.0.0 NI/4. Informative references NI/4. Informative references The following documents are informative references for this document and provide supporting information. Ref. Document Ref 1.I https://www.infrastructure-ni.gov.uk/sites/default/files/publications/infrastructure/technical-flood-risk-guidance-in-allowances-for-climate-change-6feb19.PDF. Department for Infrastructure, Northern Ireland. CCA(NI), 'Technical Flood Risk Guidance in relation to Allowances for Climate Change in Northern Ireland' Ref 2.I Centre for Environmental Data Analysis (CEDA). UK Met Office . UKCP 09, 'UK Climate Change Projections 2009' Ref 3.I https://www.metoffice.gov.uk/research/approach/collaboration/ukcp. The Met Office, UK. UKCP 18, 'UK Climate Projections 2018' 13 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 © Crown copyright 2024. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 469 - SNAA Scotland National Application Annex for Management of scour and other hydraulic actions at highway structures. (formerly BD 97/12) Version 1.0.0 Summary This National Application Annex sets out Transport Scotland's specific requirements and related advice for the inspection, assessment and monitoring of scour and other hydraulic actions at structures over or adjacent to water and at structures on the flood plain but not over or adjacent to water. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated Transport Scotland team. The email address for all enquiries and feedback is: TSStandardsBranch@transport.gov.scot This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Contents Release notes 2 Foreword 3 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction 4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abbreviations and symbols 5 Terms and Definitions 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 S/1. Scope 21 Aspects covered (additional to CS 469 clauses 1.1 to 1.6, 1.8 and 1.9 to 1.17) . . . . . . . . . . . . . . . . 21 S/2. Identification of scour susceptible structures Type 1 and Type 2 (additional to CS 469, Sections 1 and 9) 22 Scour susceptible structures Type 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Scour susceptible structures Type 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 S/3. Review of 0.5% AEP flood risk maps (additional to CS 469, Sections 4 and 7) 23 Scour susceptible structures Type 1 (additional to CS 469 clauses 4.3 and 4.6) . . . . . . . . . . . . . . . . 23 Scour susceptible structures Type 2 (additional to CS 469 clauses 7.18 to 7.20) . . . . . . . . . . . . . . . . 23 S/4. Climate change allowances (additional to CS 469, Sections 5 and 6) 24 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Climate change allowances for structures located in Scotland . . . . . . . . . . . . . . . . . . . . . . . . . . 25 S/5. Scour Level 2 assessment (additional to CS 469, Sections 5 and 9) 29 S/6. Risk management of scour and other hydraulic actions at structures (additional to [CS 469, Section 8]) 30 S/7. Normative references 31 S/8. Informative references 32 Appendix S/A. Model form of scour assessment certificate for a scour Level 2 assessment or a scour susceptible structure Type 1 (additional to CS 469, Sections 5 and 9) 33 S/A1 Scour assessment certificate - Section 1 - scour susceptible structure Type 1 details . . . . . . . . . . 33 S/A1.1 Certificate Section 1 - Notes (relevant to clauses 5.59 & 9.1] . . . . . . . . . . . . . . . . . . . 33 S/A2 Scour assessment certificate - Section 2 - signatures . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 S/A2.1 Certificate Section 2 - Notes (relevant to clauses 5.59 & 9.1] . . . . . . . . . . . . . . . . . . . 34 1 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 469 - SNAA 1.0.0 April 2024 Scotland NAA Change to policy, major revision, new document development Scotland National Application Annex to CS 469. The technical updates in this document: (1) The definition of scour susceptible structure has been amended to also include structures on the floodplain. (2) The scope has been clarified for scour and other hydraulic actions on structures, including scour in non-tidal rivers, tidal rivers and estuaries, ocean scour, propagating ocean storm surges, coastal wave action and coastal flooding. (3) The method for estimation of scour depth now also includes implementation of the results from University of Exeter research projects on scour caused by woody debris close to a structure in a river. (4) The climate change allowances have been updated, so they are in accordance with UKCP09 climate change allowances published for the UK. (5) Management of risk due to scour and other hydraulic actions on a structure have been updated. [Published: April 2024] Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change 2 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Foreword Foreword Publishing information This document is published by National Highways on behalf of Transport Scotland. The document DMRB CS 469 [Ref 5.N] supersedes BD 97/12 "The assessment of scour and other hydraulic actions at highway structures", and Interim Advice Note 173/13 "Implementation of BD 97/12", which are withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 3 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Introduction Introduction Background This National Application Annex gives the Transport Scotland-specific requirements and advice for the management of scour and other hydraulic actions at structures and is supplementary to DMRB CS 469 [Ref 5.N]. This National Application Annex replaces the existing specific requirements and advice for the inspection, assessment and risk management of scour and other hydraulic actions at highway structures which are previously described in BD 97/12 and IAN 173/13 which are withdrawn. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 4.N] and GG 104 [Ref 6.N] apply to this document. However, this document also applies to all types of structures, as defined in this document. 4 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Abbreviations and symbols Abbreviations and symbols Abbreviations Abbreviation Definition AEP Annual exceedence probability SFAIRP So far as is reasonably practicable AMAX Annual maximum QMED The index flood Symbols Symbol Definition QA Assessment flow for a severe weather event with a stated AEP calculated using: 1) the latest weather event data, flood event data, historical data and tidal data; and 2) the climate change allowances for the structures location. QF Fluvial component of the assessment flow. VTide,av The volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the average tidal range (in m), in m3 . VTide,max The volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the maximum tidal range (in m), in m3 . 5 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions Terms and Definitions Term Definition Affected populations Affected populations include: 1) road users; 2) road workers; 3) any other persons on, or close to, the highway; and, 4) any persons on, or close to, Overseeing Organisation land. 6 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Annual exceedance probability (AEP) The annual exceedance probability (AEP) is the inverse of the annual maximum (AMAX) flood return period of a weather event, based upon statistical records. NOTE 1: The return period of a flood on the AMAX scale is the average interval between AMAX floods of that magnitude. NOTE 2: QMED is the index flood which is the median of the set of the AMAX flood data. It is the flow that has an AEP of 50%, or a return period of two years. Refer to clause S/5.1 for the method of calculating the fluvial component of the assessment flow Q F . NOTE 3: A 200-year event return period is not referring to a regular event occurrence (the event only occurring once every 200 years). A 200-year event return period is an average recurrence interval for the event. This means that a 200-year event can occur in two consecutive years, then not occur again for 398 years, based upon statistical records. NOTE 4: Examples of weather event return periods, using the AMAX scale, are provided below: 1) 1 in 1000 year event is 0.1% AEP (new structure design event – structure not to fail or collapse during this event). This event has a 0.1% chance of being exceeded in any year; 2) 1 in 500 year event is 0.2% AEP. This event has a 0.2 % chance of being exceeded in any year; 3) 1 in 200 year event is 0.5% AEP (existing structure check event in this document – structure not to fail or collapse during this event). This event has a 0.5% chance of being exceeded in any year; 4) 1 in 100 year event is 1% AEP. This event has a 1% chance of being exceeded in any year; and 5) 1 in 2 year event is 50% AEP. This event has a 50% chance of being exceeded in any year. 7 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Assessment flow The assessment flow QA is the peak flow rate at the structures used for the assessment, calculated for the 0.5% annual exceedance probability (AEP) weather event, using the latest available weather event data, historical data and tidal data, including: 1) the river flow (fluvial) component; 2) overland flow (pluvial) component; 3) tidal component (if appropriate); and 4) the climate change allowances (for the structure location). Average tidal range The average of the mean spring tidal range and mean neep tidal range, at a specific location. In this document, the average tidal range is the sum of two components: 1) the present day tidal range; and, 2) the climate change allowance for total potential increase in sea level, determined in accordance with clause S/4.7. Catchment response time The length of time between a severe weather event occurrence in the catchment upstream of a structure and flood water arriving at the structure, which depends upon the catchment characteristics upstream of the structure. Refer to clause S/5.2. Channel stability risk rating As part of the scour Level 2 assessment, the stability and lateral movement of a stream or river channel assessed and the channel stability risk rating determined as either low, medium, or high risk. Chart Datum Chart Datum is a reference level, for use in tidal tables and can be approximately the lowest sea water level at a specific location, due to astronomical effects and excluding meteorological effects. In the UK, the Chart Datum at a specific location is a reference level relative to Ordnance Datum (Newlyn). NOTE: As Ordnance Datum is generally above Chart Datum, the numbers on a tide table, when given to Ordnance Datum are usually lower than when given to Chart Datum. 8 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Climate change allowances The climate change allowances are predictions of anticipated change for: 1) peak river flow (fluvial flow); 2) peak rainfall intensity (causes pluvial flow / surface water flow); 3) sea level rise; and, 4) offshore wind speed and extreme wave height. NOTE: For each of these four categories, the climate change allowances vary according to the location in the UK. See Section S/2. Competent civil engineer or structural engineer The competent civil or structural engineer is a named person, in a defined region or area, or a scheme area, as described in clause S/1.4. Defined distance from the structure The defined distance from the structure is measured in all directions from the extremities of the structure, not measured from the centre of the structure. Refer to CS 469 [Ref 5.N] Table 3.12 (scour susceptible structure Type 1), and Table 3.15 (scour susceptible structure Type 2). Flash flooding Flash flooding is surface water/ overland flow, occurring during a severe weather event with a stated AEP. The flash flooding flow rate, velocity of flow and depth of flow are defined by the severe weather event with a stated AEP. Flood event An overflow of water onto an area of land which is usually dry. A flood event includes any situation where land not normally covered by water becomes covered by water. A flood event at a structure includes any situation where a rising water level, or fast flowing water, can cause undesirable consequences to occur. A flood event at a structure can also include any situation where water flowing into the structure, or water overflowing in the structure, can cause undesirable consequences to occur. Flood plain The areas of land identified by the Scottish Environment Protection Agency, as at risk of flooding from rivers and the sea.The limits of the floodplain are defined by the peak water level occurring during a severe weather event with a 0.5% AEP. 9 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Flood risk maps in Scotland A map prepared by the Scottish Environmental Protection Agency SEPA Flood risk maps [Ref 2.I] and lead local authorities, which shows the areas of land at risk from flooding, for a 0.5% AEP flood risk, due to specified sources of flooding: 1) rivers and sea; 2) reservoirs; and, 3) surface water. Flood risk vulnerability classification, Scotland Structures referred to in this document, which are located in Scotland, are in the flood risk vulnerability classification "essential infrastructure". Flow control structure A structure which controls the flow of water, which can affect the flow rate, or water level, upstream or downstream of the flow control structure, including (but not limited to): 1) a reservoir outflow structure; 2) a flood control structure; and, 3) a flood defence structure. A flow control structure can be operated: 1) automatically by remote control; 2) manually by remote control; or, 3) manually by an operative at the flow control structure. Hydraulic actions Hydraulic actions on a structure can occur due to one or more of the following situations occurring: 1) flowing water causing the formation of scour holes near to, or under, the structure; 2) flowing water causing horizontal forces on the structure; 3) water level rising to the soffit of a bridge, or above the soffit of a bridge, causing uplift on the bridge deck; 4) static water causing horizontal forces on the structure; 5) a storm surge causing very high horizontal forces on a structure; or, 6) wave action on a structure. Large catchment The catchment area upstream of the structure is more than 1,000 km2 . 10 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Lead local flood authority The lead local flood authority in relation to an area in Scotland means: 1) the unitary authority for the area; or, 2) if there is no unitary authority, the council for the area. NOTE: Lead local flood authorities are responsible for developing, maintaining and applying a strategy for local flood risk management in their areas and for maintaining a register of flood risk assets. They also have lead responsibility for managing the risk of flooding from surface water, groundwater and water courses. Maximum tidal range The tidal range between the highest and lowest astronomical tides that can occur at a specific location. In this document, the maximum tidal range is the sum of two components: 1) the present day maximum tidal range, determined in accordance with clause S/4.10 in this document; and, 2) the climate change allowance for total potential increase in sea level, determined in accordance with clause S/4.7 in this document. NOTE: The largest tidal range during a 12-month period can be expected around the time of the equinox, in March and in September, if it coincides with a Spring tide. Normal stream or river level The normal stream or river level is the annual average stream or river water level at the upstream face of the structure. Water level records (date, time and depth of water at the upstream face of the structure) are to be kept in the structures management system. Overseeing Organisation land Land which is owned by the Overseeing Organisation, or leased to the Overseeing Organisation. NOTE 1: Overseeing Organisation land can be remote from the motorway or all purpose trunk road network; for example land containing a depot, or warehouse building, or office building, or lorry parking area. NOTE 2: Overseeing Organisation land can be near to the motorway or all purpose trunk road network, for example land containing a maintenance vehicle access road (which is not a public highway), services area, lay-by or drainage balancing pond. Principal of the assessing organisation A senior representative of the assessor, checker, contractor, or works examiner, having authority to sign certificates on its behalf. 11 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Propagating ocean storm surges Propagating ocean storm surges comprise a series of storm surges during a severe weather event, usually accompanied by high coastal waves and severe scour on beaches, along estuary river banks, or along sea walls. Scour Scour is the erosion of soil or rock around or below the foundations of a structure, or near to a structure, due to hydraulic action. Scour can occur in a stream or river bed, or in the sea bed, near a structure such as a bridge, when fast flowing water removes soil or rock from around or below the structure foundation, resulting in scour holes in the stream, or river, or sea bed. Scour holes can compromise structural integrity and result in structural failure or collapse. Scour holes in a stream or river bed, or in the sea bed, can gradually develop over a long period of time, then rapidly increase in depth during a severe weather event, causing sudden structural failure or collapse. Scour susceptible structures with shallow underwater foundations (such as a masonry arch bridge over a stream or river) can be at high risk of structural failure or collapse during a severe weather event. There are several situations which very greatly increase the risk of severe scour near a bridge: 1) dredging or sand/gravel extraction upstream or downstream of bridge; 2) removal of a weir near a bridge; 3) influence of a reservoir, or flood defence structure, or flood control structure; 4) debris accumulation in the water, e.g. tree branches in the water near to a bridge pier, or boulders & rocks being carried in fast flowing water. Static debris in the water just below the water surface can cause severe scour depth near a bridge pier, or abutment, or retaining wall, during high flow rate; or 5) tipping crushed rock into a scour hole. Scour Assessment Certificate for Scotland A certificate to be prepared, following completion of a scour Level 2 assessment of a scour susceptible structure Type 1 in Scotland, as described in Appendix S/A in this document. 12 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Scour risk rating A designation for the structure, either low, medium, or high risk, determined in accordance with: 1) Table 2.3 and Section 4 or 5 of CS 469 [Ref 5.N](for scour susceptible structures Type 1); and, 2) Section 7 of CS 469 [Ref 5.N] (for scour susceptible structures Type 2). Scour risk score A whole number in the range 10 to 100 determined in accordance with Table 2.3 and Section 4 or 5 of CS 469 [Ref 5.N], for a scour susceptible structure Type 1. Scour susceptible structure Type 1 A structure located over or adjacent to water, including (but not be limited to) structures located over or adjacent to: 1) non-tidal streams, rivers, canals, ponds, lakes and reservoirs; 2) tidal streams, rivers and estuaries; and, 3) the coast and the sea. NOTE 1: Flooding at a structure over or adjacent to water can occur due to one or more of the following situations occurring: 1) a river overtopping the river bank; 2) water flowing through a geotechnical asset, such as a canal bank failure; 3) tidal action; 4) storm surges (including water flowing in a river in an upstream direction); 5) propagating ocean storm surges; 6) coastal wave action; or, 7) sea water flooding on land at, or near to, the coast. NOTE 2: A structure with a scour risk rating low risk remains a scour susceptible structure, in accordance with this document. NOTE 3: The defined distance from the structure is provided in Table 3.12 in CS 469 [Ref 5.N]. 13 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Scour susceptible structure Type 2 A structure: 1) located on the flood plain, but not over or adjacent to water; or, 2) at a location where significant surface water flooding has occurred and there is evidence of ground erosion within the defined distance from the structure. NOTE 1: Flood plain flooding can occur due to one or more of the following situations occurring: 1) a river overtopping the river bank; 2) groundwater rising above ground level; or, 3) rainfall causing surface water overland flow, also known as flash flooding. NOTE 2: Significant surface water flooding can occur due to one or more of the following situations occurring: 1) groundwater rising above ground level; and, 2) rainfall causing surface water overland flow, also known as flash flooding. NOTE 3: A structure with a scour risk rating of 'low risk' remains a scour susceptible structure, in accordance with this document. NOTE 4: The defined distance from the structure is provided in Table 3.15 in CS 469 [Ref 5.N]. Severe weather event A weather event that has the potential to cause one or more of the following situations to occur: 1) harm to affected populations; 2) damage to a structure; 3) damage to other infrastructure assets, including (but not limited to) geotechnical assets and drainage assets; 4) damage to utilities; 5) damage to property; 6) operational issues, such as blocked drains on a road bridge, or blocked drains on a road below a bridge, or blocked drains in an underpass or tunnel, or a blocked watercourse at the top of a cutting; 7) customer service issues, such as delays to traffic, or community severance issues; or, 8) construction and maintenance issues, such as delays to construction and maintenance work. 14 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) 15 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions Term Definition Significant flood event An overflow of water onto an area of land which is usually dry and can cause undesirable consequences to occur, including one or more of the following situations occurring: 1) harm to affected populations; 2) damage to a structure; 3) damage to other infrastructure asset, such as drainage assets, or geotechnical assets; 4) damage to utilities; 5) damage to property; or 6) operational issues, such as blocked drains on a road bridge, or blocked drains on a road below a bridge, or blocked drains in an underpass or tunnel, or a blocked watercourse at the top of a cutting. NOTE 1: A significant flood event can result in flooding at a structure. NOTE 2: A significant flood event can result in damage to a structure, with or without flooding occurring at the structure. NOTE 3: A significant flood event can include one or more of the following situations: 1) the water level has risen to within 600 mm of the soffit of a structure where the span is 3 m or more; 2) the water level has risen to the soffit of a structure where the span is up to 3 m; 3) the water level has risen to within 600 mm of the top of a retaining wall, or to within 600 mm of the top of a bridge abutment; 4) flood water has arrived at a structure, with the potential for structural damage to occur; 5) structural damage has occurred at the structure; or 6) a geotechnical asset has been damaged, with the potential for structural damage to occur. NOTE 4: For a scour susceptible structure Type 1, a significant flood event can include one or more of the following situations: 1) the water level has risen to the river bank level on one side of the river, or on both sides of the river; or, 2) water has flowed over the river bank on one side of the river, or on both sides of the river. NOTE 5: For a scour susceptible structure Type 2, a significant flood event can include one or more of the following situations: 1) water has flowed over the river bank on one side of the river, or on both sides of the river and has flooded land at the structure; 2) water has overflowed and flooded land at the structure; or, 3) significant surface water flooding has occurred at the structure. 16 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions Significant surface water flooding A type of significant flood event, where one or more of the following situations has occurred at a structure: 1) groundwater rising above ground level; or, 2) rainfall causing surface water overland flow, also known as flash flooding. Small catchment The catchment area is less than 25 km2 . Small and urban catchment The catchment includes urban development and the catchment area is no more than 5 km2 . Spring tide A Spring tide occurs at the following times: 1) at, or up to four days after, the time of the new moon, or the full moon, when the Earth, the Moon and the Sun are approximately aligned; and, 2) approximately once every 14 days throughout the year. The tidal range during a Spring tide can be expected to be larger than at other times, at a specific location. Spring tide period The period of time when a Spring tide occurs (a low Spring tide followed by a high Spring tide, or a high Spring tide followed by a low Spring tide), at a specific location. Refer to clause S/6.1. Storm surge A storm surge is the abnormal rise in sea water level during a storm over the sea, measured as the height of the sea water above the normal predicted astronomical tide. The storm surge is caused primarily by a storm's very strong winds blowing over the surface of the sea, pushing sea water towards the coastline. The height of the storm surge at any given location depends on: 1) the angle of storm impact on the coast; 2) the intensity, size, and speed of the storm; and, 3) the local sea bed profile. High intensity storm – a weather system characterised by low atmospheric pressure at the centre, high average wind speed and high wind speed gusts. Size of the storm – the radius of outermost closed isobar (ROCI). Speed of the storm – the speed at which the weather system moves. 17 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Storm tide When a storm surge and a high tide occur at the same time at the same location, the resulting storm surge is often called a storm tide. Due to the much higher sea level, a storm tide has much more devastating consequences for structures at the coast and at areas inland from the coast, than a storm surge occurring with a low tide. Structural collapse An event that causes failure of one or more components of a structure, causing the structure or part of the structure to break up, or fall apart, or deform excessively, or fall to a lower level. NOTE 1: Structural collapse can occur at the time of structural failure, or later. NOTE 2: Following a structural collapse being reported: 1) there can be a need for monitoring; and, 2) there can be a need to prepare and implement a programme for mitigating actions. NOTE 3: Structural collapse, or partial collapse, includes, but is not limited to: 1) any structural debris falling from a structure to a lower level, e.g. onto land, or railway, or road below the structure, caused by gradual decline of the structure; or, 2) major structural debris, falling from a structure to a lower level, as a result of an overheight vehicle collision with a bridge, or as a result of a vehicle collision with a parapet. 18 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Structural failure An event that causes: 1) the loss or severe reduction of load carrying capacity of one or more components of a structure, or of the whole structure; 2) the loss or severe reduction of vehicle restraint of a parapet, or part of a parapet; 3) a component of a structure to become detached, or partially detached, from the structure; or, 4) a component of a structure to no longer perform as intended. NOTE 1: structural failure can occur without structural collapse. NOTE 2: following a structural failure being reported: 1) there can be a need for monitoring; and, 2) there can be a need to prepare and implement a programme for mitigating actions. NOTE 3: Structural failure includes, but is not limited to: 1) fixings failure, as fixings are components of a structure; 2) structural component failure, for example expansion joint failure; 3) parapet failure caused by a vehicle collision with the parapet; 4) structural failure caused by a vehicle collision with the structure, such as an overheight vehicle colliding with a bridge; or, 5) structural failure caused by a vehicle collision with a nearby vehicle restraint system. Structure Any temporary or permanent structure built on, over, under, or adjacent to, any part of the Overseeing Organisations' motorway or all purpose trunk roads, or on Overseeing Organisation land. NOTE: This includes (but is not limited to) a bridge, tunnel, underpass, wall, subway, gantry, mast, lighting column, building, salt barn, salt storage area push wall, noise barrier and drainage structures (such as a pipe, culvert, open channel, pumping station, chamber, drainage inlet structure, or drainage outfall structure). Team Leader of the assessing organisation The person responsible for overseeing and co-coordinating the work of the scour assessment, or check, team and having authority to sign certificates on behalf of the team. The Team Leader is a competent civil engineer or structural engineer. Tidal location A specific location where the water level varies in accordance with the tidal period and tidal range. 19 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Terms and Definitions (continued) Term Definition Tidal period The period of time between low tide and high tide, or between high tide and low tide, at a specific location. The tidal period is not constant at a specific location. The tidal period at a specific location changes from day to day, depending on the alignment of the Earth, the Moon and the Sun. Tidal range Tidal range is the height difference (change in sea level) between high tide and low tide, at a specific location. The tidal range is not constant at a specific location. The tidal range at a specific location changes from day to day, depending on the alignment of the Earth, the Moon and the Sun. Tide Tide is the rise and fall of sea level caused by gravitational forces exerted by the Moon and the Sun and the rotation of the Earth. Weir A dam or barrier across the width of a stream or river that alters the flow characteristics of water and usually results in: 1) a change in the height of the stream or river water level; or, 2) diversion of the stream or river flow. There are many different designs of weir, but usually water flows freely over the top of the weir crest before cascading down to a lower level. 20 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/1. Scope S/1. Scope Aspects covered (additional to CS 469 clauses 1.1 to 1.6, 1.8 and 1.9 to 1.17) S/1.1 The management of scour and other hydraulic actions at highway structures shall be operated at Transport Scotland in accordance with this document and DMRB CS 469 [Ref 5.N] (see CS 469 clauses 1.1 to 1.5, and clauses1.9 to 1.17). S/1.2 For all scour-susceptible structures, risks to affected populations shall be reduced to and maintained at a level that is SFAIRP in compliance with legal requirements [Health & Safety at Work etc Act 1974 Part 1 Sections 2 and 3 (1) UKPGA 1974/37 (HSWA) [Ref 1.N]; Highways Act 1980 Part IV Section 41 Act Highways Act 1980 c66 UKPGA 1980/66 [Ref 2.N]; and Infrastructure Act 2015, Part 1 Section 5 c.7 Part 1 UKPGA 2015/07 [Ref 3.N]. S/1.3 For all scour-susceptible structures, mitigating actions shall be determined that will potentially reduce scour and other hydraulic action risks to a level that is SFAIRP; and maintain scour and other hydraulic action risks at a level that is SFAIRP. See CS 469 [Ref 5.N]clause 1.8. S/1.4 Unless otherwise stated in this document, all work carried out in accordance with this document shall be carried out by a competent civil engineer or structural engineer. 21 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/2. Identification of scour susceptible structure... S/2. Identification of scour susceptible structures Type 1 and Type 2 (additional to CS 469, Sections 1 and 9) Scour susceptible structures Type 1 S/2.1 A list of scour susceptible structures Type 1 shall be maintained and updated, e.g. when new structures are constructed, upgraded, or demolished. (see CS 469 [Ref 5.N]clauses 1.2, 1.3, 1.4, and 9.1]. Scour susceptible structures Type 2 S/2.2 A list of scour susceptible structures Type 2 shall be prepared and updated , e.g. when new structures are constructed, upgraded, or demolished. (see CS 469 [Ref 5.N]clauses 1.2, 1.3, and 9.1]. NOTE 1 The Scottish Environmental Protection Agency can provide 0.5% AEP flood event flood risk maps, on request, to be used for the designation of scour susceptible structures Type 2. These are available from the Scottish Environmental Protection Agency Strategic Flood Risk Team (ref. SEPA Flood risk maps [Ref 2.I]). NOTE 2 The lead local flood authority can provide access to surface water flood risk risk maps, to be used for the designation of scour susceptible structures Type 2. NOTE 3 Refer to the 'Terms and definitions' table for the definition of "lead local flood authority". 22 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/3. Review of 0.5% AEP flood risk maps (additiona... S/3. Review of 0.5% AEP flood risk maps (additional to CS 469, Sections 4 and 7) Scour susceptible structures Type 1 (additional to CS 469 clauses 4.3 and 4.6) S/3.1 The most recently prepared 0.5% AEP flood risk maps, of the types shown below, for the structure location shall be reviewed: 1) the Scottish Environment Protection Agency rivers and sea flood risk maps; 2) the Scottish Environment Protection Agency reservoirs flood risk maps; and, 3) lead local flood authority surface water flood risk maps. [Applicable to CS 469, clauses 4.3 and 4.6.] Scour susceptible structures Type 2 (additional to CS 469 clauses 7.18 to 7.20) S/3.2 The most recently prepared 0.5% AEP flood risk maps, of the types shown below, for the structure location shall be reviewed: 1) the Scottish Environment Protection Agency rivers and sea flood risk maps; 2) the Scottish Environment Protection Agency reservoirs flood risk maps; and 3) lead local flood authority surface water flood risk maps. [Applicable to CS 469, clauses 7.18 to 7.20]. 23 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/4. Climate change allowances (additional to CS 4... S/4. Climate change allowances (additional to CS 469, Sections 5 and 6) General S/4.1 The climate change allowances provided by the appropriate government body shown in Table S/4.1 shall be used in an assessment for scour and other hydraulic actions on a structure. (Relevant to CS 469 [Ref 5.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1). Table S/4.1 Government bodies responsible for publishing climate change allowances Country where the structure is located Government body responsible for publishing climate change allowances Climate change allowances to be used in a Level 1 assessment and a Level 2 assessment Scotland Scottish Environment Protection Agency Refer to Tables S/2.4, S/2.6 and S/2.7. NOTE The climate change allowances are based on the UK climate change projections 2018 UKCP 18 (CCOL) [Ref 6.I], UKCP 18 [Ref 5.I]. Table S/4.1N Climate change allowances for Scotland - informative reference Country where the structure is located Climate change allowances informative reference Scotland CCA(S) [Ref 1.I] 24 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/4. Climate change allowances (additional to CS 4... Figure S/4.1N Use of climate change allowances in Scotland 25 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/4. Climate change allowances (additional to CS 4... Climate change allowances for structures located in Scotland S/4.2 For a structure located in Scotland, the climate change allowances shall be used in accordance with Figure S/4.3. (Applicable to CS 469 [Ref 5.N]clause 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1). S/4.3 For a structure located in Scotland, when calculating the assessment flow QA from river (fluvial) flooding, where the catchment upstream of the structure is greater than 50 km2 , the peak river flow climate change allowance shall be used, determined for the structure location from Table S/4.4. (Applicable to CS 469 [Ref 5.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1]). Table S/4.3 Determine the climate change allowance: percentage increase in stream or river (fluvial) assessment flow River basin region Climate change allowance for the structure: total potential increase in QA anticipated for the period to 2100 Argyll 56% Clyde 44% Forth 40% North East 24% North Highland 37% Orkney 41% Shetland 41% Solway 44% Tay 35% Tweed 33% Western Islands 56% West Highland 56% S/4.4 For a structure located in Scotland, when calculating the assessment flow QA from river (fluvial) flooding, where the catchment upstream of the structure is between 30 and 50 km2 , the highest of peak river flow or peak rainfall intensity climate change allowance shall be used, determined for the structure location from Tables S/4.4 and S/4.6. (Applicable to CS 469 [Ref 5.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1]). S/4.5 For a structure located in Scotland, when calculating the assessment flow QA from river (fluvial) flooding, where the catchment upstream of the structure is less than 30 km2 , the peak rainfall intensity climate change allowance shall be used, determined for the structure location from Table S/4.6. (Applicable to CS 469 [Ref 5.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1]). 26 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/4. Climate change allowances (additional to CS 4... Table S/4.5 Determine the climate change allowance: percentage increase in peak rainfall intensity River basin region Climate change allowance for the structure: total potential increase in QA anticipated for the period to 2100 West rainfall uplift region: Argyll, Clyde, Solway, Western Highland, Western Islands 55% East rainfall uplift region: Forth, North East Scotland, North Highland, Orkney, Shetland,Tay, Tweed 35% S/4.6 For a structure located in Scotland, when calculating the assessment flow QA from coastal flooding, the rise in sea level climate change allowance shall be used, determined for the structure location from Table S/4.7. (Applicable to CS 469 [Ref 5.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1). Table S/4.6 Determine the climate change allowance: total potential increase in sea level River basin region Climate change allowance for the structure: total potential increase in sea level anticipated for the period 2017 to 21 00 Argyll 0.86 metres Clyde 0.85 metres Forth 0.86 metres North East 0.87 metres North Highland 0.89 metres Orkney 0.93 metres Shetland 1.02 metres Solway 0.88 metres Tay 0.85 metres Tweed 0.89 metres Western Isles 0.93 metres West Highland 0.89 metres S/4.7 When calculating the volume of the tidal prism, VTide,av [see CS 469 [Ref 5.N] clauses 5.28, 5.29], the average tidal range determined in accordance with Section S/4.6 shall be used. S/4.8 When calculating the component of the assessment flow QA from tidal or coastal flooding, the maximum tidal range shall be determined for the structure location using two components added together, as (applicable to CS 469 [Ref 5.N] [CS 469 Sections 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, 6.1]): 1) the present day maximum tidal range, determined in accordance with Section S/4.10 ; and, 2) the climate change allowance for total potential increase in sea level, determined in accordance with Section S/4.7. 27 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/4. Climate change allowances (additional to CS 4... S/4.9 The present day maximum tidal range for the structure location shall be determined using two components CS 469 [Ref 5.N] [CS 469 clauses 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, 6.1]: 1) low tide level is the lowest astronomical tide which can occur at the structure location; and 2) high tide level is either the present day extreme sea level determined in accordance with Section S/4.11, or the highest astronomical tide which can occur at the structure location, whichever is the highest level. S/4.10 When calculating the volume of the tidal prism, VTide,max CS 469 [Ref 5.N] [CS 469 clauses 5.28, 5.29], the maximum tidal range determined in accordance with Section S/4.9 shall be used. 28 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/5. Scour Level 2 assessment (additional to CS 46... S/5. Scour Level 2 assessment (additional to CS 469, Sections 5 and 9) S/5.1 The fluvial component of the assessment flow QF shall be determined in accordance with the latest version of the Scottish Environmental Protection Agency Technical Flood Risk Guidance for Stakeholders SEPA Technical Guidance [Ref 4.I]. [Applicable to CS 469 [Ref 5.N]clauses 5.17 to 5.24]. NOTE 1 The Scottish Environment Protection Agency can provide their technical documents, on request. NOTE 2 The fluvial component of the assessment flow QF can be influenced by many factors, including: 1) the catchment includes urban development and the catchment area is no more than 5 km2 , referred to as a "small and urban catchment"; 2) the catchment area is less than 25 km2 , referred to as a "small catchment"; 3) the catchment area is more than 1,000 km2 , referred to as a "large catchment"; 4) the catchment, or part of the catchment, is low-lying; 5) the catchment, or part of the catchment, has pumped drainage; 6) the catchment includes a catchment to catchment water transfer, or catchment to catchment diversion; 7) there is an extensive flood plain in the catchment, which can temporarily store flood water during a severe weather event, without any flow control structures; 8) there are one or more flow control structures in the catchment; 9) there are one or more flow control structures downstream of the structure, that can affect the flow rate, or water level at the structure; 10) the catchment, or part of the catchment, is highly permeable, e.g. underlain by fissured aquifers; 11) the catchment includes one or more sub-catchments with widely differing flood response times; and, 12) there are complex interactions of flood volume and peak flow, or contributions to the peak flow from different tributaries, or other complex factors affecting the peak flow rate at the structure location. S/5.2 The catchment response time, for the catchment upstream of the structure, shall be determined in accordance with Table S/5.2. (Applicable to CS 469 [Ref 5.N] clause 5.24.) Table S/5.2 Catchment response time. Catchment response time The length of time between a severe weather event occurrence in the catchment upstream of a structure and flood water arriving at the structure Very short No more than 30 minutes. Short Between 30 minutes and 2 hours. Medium Between 2 hours and 24 hours. Long More than 24 hours. S/5.3 A Scour Assessment Certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 shall be completed and signed by the Team Leader and the Principal of the assessing organisation in accordance with Appendix S/A in this document. (Applicable to CS 469 [Ref 5.N] clauses 5.59 and 9.1.) S/5.4 The Scour Assessment Certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 shall be sent to the Technical Approval Authority, for acceptance. See CS 469 [Ref 5.N] clauses 5.59 and 9.1. 29 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/6. Risk management of scour and other hydraulic ... S/6. Risk management of scour and other hydraulic actions at structures (additional to [CS 469, Section 8]) S/6.1 The process for advance notification of forecast flood events at structures (on a national / regional / area basis) to Transport Scotland shall include the Scottish Flood Forecasting Service [SFFS] documents including the 'Scottish Flood Guidance Statement' issued daily by Met Office & SEPA [Ref 3.I]. (Applicable to CS 469 [Ref 5.N] clause 8.11.) NOTE 1 Severe weather warnings are issued by the Meteorological Office. NOTE 2 The SFFS is a working partnership between the Meteorological Office and the Scottish Environment Protection Agency, to combine their meteorology and hydrology expertise into a specialised hydrometeorology service SFFS . The SFFS provides forecasts for all natural forms of flooding, due to: 1) rivers; 2) surface water; 3) groundwater; and, 4) tidal & coastal. NOTE 3 The SFFS is fully operational 24 hours a day, 7 days a week. NOTE 4 The "Scottish Flood Guidance Statement" provides a daily summary of flood risk from all natural sources, including a flooding forecast with flood risk risk categories for the next five days. [ Met Office & SEPA [Ref 3.I]] S/6.2 The process at Transport Scotland, for acting upon the "Scottish Flood Guidance Statement" shall include (relevant to CS 469 [Ref 5.N] clauses 8.11 to 8.15): 1) preparations for actions needed for forecast of significant flood events at high risk scour susceptible structures; 2) implementation of actions needed to safeguard affected populations and structures; and, 3) implementing operational procedures at structures which are linked to the risk levels in the Scottish Flood Guidance Statement. 30 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/7. Normative references S/7. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref. Document Ref 1.N National Archives. UKPGA 1974/37 (HSWA), 'Health and Safety at Work etc. Act' Ref 2.N National Archives. UKPGA 1980/66, 'Highways Act' Ref 3.N National Archives. UKPGA 2015/07, 'Infrastructure Act' Ref 4.N National Highways. GG 101, 'Introduction to the Design Manual for Roads and Bridges' Ref 5.N National Highways. CS 469, 'Management of scour and other hydraulic actions at highway structures' Ref 6.N National Highways. GG 104, 'Requirements for safety risk assessment' 31 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 S/8. Informative references S/8. Informative references The following documents are informative references for this document and provide supporting information. Ref. Document Ref 1.I https://www.sepa.org.uk/media/426913/lups_cc1.pdf. Scottish Environment Protection Agency. CCA(S), 'Climate change allowances for Scotland' Ref 2.I Scottish Environment Protection Agency.. The maps show areas which are likely to flood from rivers, the sea and surface water.. SEPA Flood risk maps, 'Flood risk maps, Scotland.' Ref 3.I https://www.sepa.org.uk/media/149570/sffs_fgs_user_guide_2015.pdf. Scottish Flood Forecasting Service.. Met Office & SEPA, 'Scottish Flood Guidance Statement.' Ref 4.I Scottish Environment Protection Agency.. SEPA requirements for undertaking a Flood Risk Assessment.. SEPA Technical Guidance, 'Technical Flood Risk Guidance for Stakeholders.' Ref 5.I https://www.metoffice.gov.uk/research/approach/collaboration/ukcp. The Met Office, UK. UKCP 18, 'UK Climate Projections 2018' Ref 6.I https://www.metoffice.gov.uk/binaries/content/assets/metofficegovuk/pdf/research/ukcp/ukcp18- infographic-headline-findings-land.pdf. The Met Office, UK. UKCP 18 (CCOL), 'UKCP18 Climate Change Over Land.' 32 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Appendix S/A. Model form of scour assessment certificate f... Appendix S/A. Model form of scour assessment certificate for a scour Level 2 assessment or a scour susceptible structure Type 1 (additional to CS 469, Sections 5 and 9) S/A1 Scour assessment certificate - Section 1 - scour susceptible structure Type 1 details Name of structure 1 : Structure reference number 1 : Structure key 1 : S/A1.1 Certificate Section 1 - Notes (relevant to CS 469 [Ref 5.N]clauses 5.59 & 9.1] 1) The name of the structure, structure reference number and structure key are as shown on the Overseeing Organisation structures asset management system. S/A2 Scour assessment certificate - Section 2 - signatures We certify that reasonable professional skill and care has been used in the preparation of the scour Level 2 assessment of (name of structure and structure reference number) with a view to securing that: 1) This structure has been assessed in accordance with: CS 469 'Management of scour and other hydraulic actions at highway structures'; and Scotland National Application Annex to CS 469 'Management of scour and other hydraulic actions at highway structures'. 2) The results of the scour Level 2 assessment for this structure are: a) the scour risk score is 10 / 40 / 60 / 80 / 100; b) the scour risk rating is high risk / medium risk / low risk; and, c) the channel stability risk rating is high risk / medium risk / low risk. Signed _____________________________________________ Team Leader of the assessing organisation Name ______________________________________________ Engineering qualifications ______________________________ 5 Position held _________________________________________6 Name of Organisation __________________________________ Date ________________________________________________ Signed _______________________________________________ Principal of the assessing organisation Name _______________________________________________ Engineering Qualifications _______________________________ 5 Position held __________________________________________7 Name of Organisation ___________________________________ Date ________________________________________________ The departures and additional methods or processes given in the Schedule to this Certificate are agreed. This Certificate is accepted by the Technical Approval Authority [TAA]. Signed _______________________________________________ 33 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - SNAA Version 1.0.0 Appendix S/A. Model form of scour assessment certificate f... Name ________________________________________________ Engineering Qualifications ________________________________ 5 Position held __________________________________________ TAA ________________________________________________ Date ________________________________________________ S/A2.1 Certificate Section 2 - Notes (relevant to CS 469 [Ref 5.N] clauses 5.59 & 9.1] 2 ) List in a Schedule to this Certificate any departures, additional methods or processes agreed by the Overseeing Organisation and the date of the Overseeing Organisation agreement. 3 ) Delete as appropriate. 4 ) The scour risk score, scour risk rating and channel stability risk rating are to be recorded in the Overseeing Organisation structures asset management information system. Refer to CS 469 Section 9.1. 5 ) CEng MICE, or CEng MIStructE, or equivalent. 6 ) The Team Leader of the assessing organisation responsible for the whole of the scour Level 2 assessment of a scour susceptible structure Type 1. 7 ) A Principal of the assessing organisation responsible for the whole of the scour Level 2 assessment of a scour susceptible structure Type 1. 34 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 © Crown copyright 2024. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 469 - WNAA Wales National Application Annex for Management of scour and other hydraulic actions at highway structures. (formerly BD 97/12) Version 1.0.0 Summary This National Application Annex sets out Welsh Government's specific requirements and related advice for the inspection, assessment and monitoring of scour and other hydraulic actions at structures over or adjacent to water and at structures on the flood plain but not over or adjacent to water. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated Welsh Government team. The email address for all enquiries and feedback is: Standards_Feedback_and_Enquiries@gov.wales This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Contents Release notes 2 Foreword 3 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction 4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abbreviations and symbols 5 Terms and definitions 6 W/1. Scope 12 Aspects covered (additional to CS 469 clauses 1.1 to 1.6 , 1.8 and 1.9 to 1.17) . . . . . . . . . . . . . . . . 12 Senior Responsible Officer and Responsible Officer (CS 469 clauses 1.16 and 1.17 shall not apply) . . . . 12 W/2. Identification of scour susceptible structures Type 1 and Type 2 (additional to CS 469, Sections 1 and 9) 13 Scour susceptible structures Type 1 (additional to CS 469 clauses 1.2, 1.3, 1.4 and 9.1) . . . . . . . . . . . 13 Scour susceptible structures Type 2 (additional to CS 469 clauses 1.2, 1.3, 1.4 and 9.1) . . . . . . . . . . . 13 W/3. Inspection and assessment process (additional to CS 469, Section 2) 14 W/4. Review of 0.5% AEP flood risk maps (additional to CS 469, Sections 4 and 7) 15 Scour susceptible structures Type 1 (additional to CS 469 clauses 4.3 and 4.6) . . . . . . . . . . . . . . . . 15 Scour susceptible structures Type 2 (additional to CS 469 clauses 7.18 to 7.20) . . . . . . . . . . . . . . . . 15 W/5. Climate change allowances (additional to CS 469, Sections 5 and 6) 16 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Climate change allowances for structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Peak river flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Peak rainfall intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Sea level rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 W/6. Scour Level 2 assessment (additional to CS 469 Sections 5 and 9) 19 W/7. Risk management of scour and other hydraulic actions at structures (additional to CS 469, Section 8) 20 W/8. Normative references 21 W/9. Informative references 22 Appendix W/A. Model form of scour assessment certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 (additional to CS 469, Sections 5 and 9) 23 W/A1 Scour Assessment Certificate – Section 1 – Scour Susceptible Structure Type 1 Details . . . . . . . 23 W/A1.1 Certificate Section 1 - Notes (see clauses 5.3 & 9.1, and WNAA clauses W/5.3, W/5.4) . . . . 23 W/A2 Scour assessment certificate - Section 2 - signatures . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 W/A2.1 Certificate Section 2 - Notes (see clauses 5.59 & 9.1, and WNAA clauses W/5.3, W/5.4) . . . 24 1 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 469 - WNAA 1.0.0 April 2024 Wales NAA Change to policy, major revision, new document development Welsh Government National Application Annex to CS 469. The technical updates in this document: (1) The definition of scour susceptible structure has been amended to also include structures on the floodplain but not over or adjacent to water. (2) The scope has been clarified for scour and other hydraulic actions on structures, including scour in non-tidal rivers, tidal rivers and estuaries, ocean scour, propagating ocean storm surges, coastal wave action and coastal flooding. (3) The method for estimation of scour depth now also includes implementation of the results from University of Exeter research projects on scour caused by woody debris close to a structure in a river. (4) The climate change allowances have been updated, so they are in accordance with UKCP09 climate change allowances published for the UK. (5) Management of risk due to scour and other hydraulic actions on a structure have been updated. [Publication: April 2024] Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change 2 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Foreword Foreword Publishing information This document is published by National Highways on behalf of Welsh Government. The document CS 469 [Ref 8.N] supersedes BD 97/12 "The assessment of scour and other hydraulic actions at highway structures", as well as Interim Advice Note 173/13 "Implementation of BD 97/12", which are withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 3 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Introduction Introduction Background This National Application Annex gives the Welsh Government-specific requirements and advice for management of scour and other hydraulic actions at highway structures, and is supplementary to DMRB CS 469 [Ref 8.N]. This National Application Annex replaces the existing specific requirements and advice for the inspection, assessment and risk management of scour and other hydraulic actions at highway structures, previously described in BD 97/12 and IAN 173/13, which are withdrawn. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 7.N] and GG 104 [Ref 9.N] apply to this document. However, this document also applies to all types of structures, as defined in this document. 4 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Abbreviations and symbols Abbreviations and symbols Abbreviations Abbreviation Definition CCE Competent civil engineer FFC Flood Forecasting Centre FGS Flood guidance statement FRAW Flood Risk Assessment Wales HASAWA Health and Safety at Work Act LLFA Lead local flood authority ROCI Radius of outermost closed isobar TAN Technical advice note UKCP09 United Kingdom Climate Projections 2009 UKCP18 United Kingdom Climate Projections 2018 Symbols Symbol Definition QA Assessment flow for a severe weather event with a stated AEP, calculated using: 1) the latest available weather event data, flood event data, historical data and tidal data; and, 2) the climate change allowances for the structure location. QF Fluvial component of the assessment flow VT ide,av The volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the average tidal range (in m), in m3 . VT ide,max The volume of the tidal prism, calculated from the channel bed area upstream of the bridge that is subject to inundation at high tide (in m2 ) multiplied by the maximum tidal range (in m), in m3 . 5 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Terms and definitions Terms and definitions Term Definition Annual exceedance probability (AEP) The annual exceedance probability (AEP) is the inverse of the annual maximum return period of a weather event, based upon statistical records. NOTE 1: A weather event return period is defined in this document according to the AEP for the weather event. NOTE 2: A 200-year event return period is not referring to a regular event occurrence (the event only occurring once every 2 00 years). A 200-year event return period is an average recurrence interval for the event. This means that a 200-year event can occur in two consecutive years, then not occur again for 398 years, based upon statistical records. NOTE 3: Examples of weather event return periods are provided below: 1) 1 in 1000 year event is 0.1% AEP (new structure design event – structure not to fail or collapse during this event). This event has a 0.1% chance of being exceeded in any year; 2) 1 in 500 year event is 0.2% AEP. This event has a 0.2% chance of being exceeded in any year; 3) 1 in 200 year event is 0.5% AEP (existing structure check event in this document – structure not to fail or collapse during this event). This event has a 0.5% chance of being exceeded in any year; 4) 1 in 100 year event is 1% AEP. This event has a 1% chance of being exceeded in any year. Assessment flow The flow rate to be used for the assessment, calculated for the annual exceedance probability weather event, including: 1) river flow (fluvial) component; 2) overland flow (pluvial) component (if appropriate); 3) tidal component (if appropriate); 4) ocean storm surge component (if appropriate); and, 5) climate change allowances (for the structure location). 6 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Terms and definitions (continued) Term Definition Average tidal range The average of the mean spring tidal range and mean neap tidal range, at a specific location. In this document, the average tidal range is the sum of two components: 1) the present day average tidal range; and 2) the climate change allowance for total potential increase in sea level, determined in accordance with clause W/4.7. Catchment response time The length of time between a severe weather event occurrence in the catchment, upstream of a structure, and flood water arriving at the structure, which depends upon the catchment characteristics upstream of the structure. Refer to clause W/5.2. Channel stability risk rating As part of a scour Level 2 assessment, the stability and lateral movement of a stream or river channel is assessed and the channel stability risk rating is determined, as either low, medium, or high risk. Chart datum in Wales Chart Datum is a reference level, for use in tidal tables and can be approximately the lowest sea water level at a specific location, due to astronomical effects and excluding meteorological effects. In Wales, the Chart Datum at a specific location is a reference level relative to Ordnance Datum (Newlyn). NOTE: the height of chart datum (CD) at a specific location in Wales relative to Ordnance Datum (Newlyn), can be negative, indicating that the chart datum is below the specific datum for Wales. Climate change allowances in Wales The climate change allowances are predictions of anticipated change for: 1) peak river flow (fluvial flow); 2) peak rainfall intensity (causes pluvial flow / surface water flow); 3) sea level rise; and, 4) offshore wind speed and extreme wave height. For each of these four categories, the climate change allowances vary according to the location in Wales. NOTE: For Wales, the climate change allowance for peak fluvial flow varies for each major river basin district. See Section W/4. 7 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Terms and definitions (continued) Term Definition Flood plain in Wales The areas of land: 1) identified by the Natural Resources Wales, as at risk of flooding from rivers and the sea (see DataMapWales [Ref 8.I]). The limits of the flood plain are defined by the peak water level occurring during a severe weather event with a stated AEP; 2) at any other location where flash flooding is known to have caused scour within 30 metres of a structure; and, 3) at any other location where flash flooding can potentially cause scour within 30 metres of a structure. NOTE: For Wales, information on flood risk maps is provided in Section W/4. Flood risk maps in Wales Flood risk maps are prepared by one of the responsible bodies in Wales, identifying the areas of land at risk of flooding from: 1) river and sea (Natural Resources Wales); 2) reservoir (Natural Resources Wales); or 3) surface water (Natural Resources Wales, lead local flood authority). Flood risk vulnerability classification in Wales The Welsh Government Technical Advice Note 15 identifies the vulnerability of different land uses to flooding ( TAN 15 [Ref 9.I]). Structures referred to in this document, which are located in Wales, are in the flood risk vulnerability classification "essential infrastructure". Lead local flood authority The lead local flood authority (LLFA) in relation to an area in Wales means UKPGA 2010/29 [Ref 1.N]: 1) the unitary authority for the area; or 2) if there is no unitary authority, the county council for the area. NOTE: LLFAs are responsible for developing, maintaining and applying a strategy for the local flood risk management in their areas and for maintaining a register of flood risk assets. They also have lead responsibility for managing the risk of flooding from surface water, groundwater and ordinary watercourses. Low-lying catchment in Wales An area of land where the altitude of the land in the catchment is no greater than 20 m above Ordnance Datum (Newlyn). 8 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Terms and definitions (continued) Term Definition Maximum tidal range The tidal range between the highest and lowest astronomical tides, which can occur at a specific location. In this document, the maximum tidal range is the sum of two components: 1) the present day maximum tidal range, determined in accordance with the clause W/4.10 in this document; and 2) the climate change allowance for total potential increase in sea level, determined in accordance with clause W/4.7 in this document. NOTE: the largest tidal range during a 12 month period can be expected around the time of the Spring and Autumn equinox, in March and in September, if it coincides with a Spring tide. Neap tide Neap tides occur: 1) at, or up to 11 days after, the time of the new moon, or the full moon, when the Earth, the Moon and the Sun are at 90 degrees to one another; and 2) approximately once every 14 days throughout the year. The tidal range during a neap tide can be expected to be smaller than at other times, at a specific location. 0pt Responsible Officer (RO) The Responsible Officer is a named employee at the trunk road agent who has a delegation letter from the Senior Responsible Officer, stating that the named employee is responsible, in a defined region or area, or a scheme, for the implementation of this document, as described in clause W/1.4. Scour assessment certificate in Wales A certificate to be prepared, following completion of a Level 2 scour assessment of a Type 1 scour susceptible structure, as described in Appendix W/A in this document. Scour susceptible structure Type 1 Scour susceptible structures Type 1 are located over or adjacent to water, including (but not be limited to) structures located over or adjacent to: 1) non-tidal streams, rivers, canals, ponds, lakes and reservoirs; 2) tidal streams, rivers and estuaries; and, 3) the coast and the sea. 9 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Terms and definitions (continued) Term Definition Scour susceptible structure Type 2 Scour susceptible structures Type 2 are located: 1) on the flood plain but not over or adjacent to water; and, 2) on land where flash flooding can cause structural damage. NOTE: this type of structure can be located a considerable distance from a stream, river, canal, pond, lake, reservoir, an estuary, or the coast. Significant flood event, for a scour susceptible structure Type 1 For a scour susceptible structure Type 1, a significant flood event is where 50% of the stream or river capacity is reached or exceeded, e.g. during a period of heavy rainfall, or during coastal flooding. NOTE 1: examples include (but are not limited to): 1) river level rises to 50% of the internal depth of a culvert; 2) river level rises from normal river level to 50% of the distance between normal river level and the soffit of a bridge; or, 3) river level rises to the top of the river bank (where the soffit of the bridge is higher than the river bank level). NOTE 2: normal river level is to be the annual average river water level at the upstream face of the bridge. Significant flood event, for a scour susceptible structure Type 2 For a scour susceptible structure Type 2, a significant flood event is where: 1) 100% of the stream or river capacity is reached or exceeded, e.g. during a period of heavy rainfall; or, 2) surface water (from surface water, stream or river water, or sea water) flows over land designated as river floodplain, or sea (coastal) floodplain or surface water flooding areas, by Natural Resources Wales (see DataMapWales [Ref 8.I]), e.g. during a period of heavy rainfall, or during coastal flooding. NOTE: examples include (but are not limited to): 1) river level rises to the top of the river bank, or flows over the top of the river bank and floods nearby land; 2) river level rises to the soffit of the culvert; 3) river level rises to the soffit of the bridge; or, 4) surface water flows over land and flows adjacent to, or under, the scour susceptible structure Type 2. Small and urban catchment The catchment includes urban development, and the catchment area is no more than 5 km2 . 10 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Terms and definitions (continued) Term Definition Structure Any temporary or permanent structure built on, over, under, or adjacent to, any part of the Overseeing Organisations' motorway or all purpose trunk roads, or on Overseeing Organisation land. NOTE: This includes (but is not limited to) a bridge, tunnel, underpass, wall, subway, gantry, mast, lighting column, building, salt barn, salt storage area push wall, noise barrier and drainage structures (such as a pipe, culvert, open channel, pumping station, chamber, drainage inlet structure, or drainage outfall structure). Trunk road agent The party appointed by Welsh Government to manage highway assets on their behalf. Where the Overseeing Organisation manages the highway assets within their own organisation, the agent is to be the branch or section to which the duties have been delegated 11 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/1. Scope W/1. Scope Aspects covered (additional to CS 469 clauses 1.1 to 1.6 , 1.8 and 1.9 to 1.17) W/1.1 The management of scour and other hydraulic actions at highway structures shall be operated at Welsh Government and its trunk road agents in accordance with this document and CS 469 [Ref 8.N] clauses 1.1 to 1.6, and clauses 1.9 to 1.17. W/1.2 For all scour susceptible structures, risks to affected populations must be reduced to a level that is ALARP and maintained at a level that is ALARP, in compliance with legal requirements [Health & Safety at Work etc. Act 1974 Part 1 Sections 2 and 3 (1) UKPGA 1974/37 (HSWA) [Ref 4.N]; Highways Act 1980 Part IV Section 41 Act Highways Act 1980 c66 [ UKPGA 1980/66 [Ref 5.N]; and Infrastructure Act 2015, Part 1 Section 5 c.7 Part 1 UKPGA 2015/07 [Ref 6.N](See CS 469 [Ref 8.N]clause 1.6). W/1.3 For all scour susceptible structures, mitigating actions shall be determined that can potentially: 1) reduce scour and other hydraulic action risks to a level that is "as low as reasonably practicable" (ALARP); and 2) maintain scour and other hydraulic action risks at a level that is ALARP [ CS 469 [Ref 8.N]] [clause 1.8]. Senior Responsible Officer and Responsible Officer (CS 469 clauses 1.16 and 1.17 shall not apply) W/1.4 Clause 1.17 shall be amended to "The Responsible Officer shall be a named employee at the trunk road agent who has a delegation letter from the Senior Responsible Officer, stating that the named employee is responsible, in a defined region or area, or a scheme area, for the implementation of this document, including: 1) implementation of the management of scour and other hydraulic actions at highway structures, as described in this document; 2) following a scour inspection report, or a scour emergency inspection report, or emergency structural inspection report, or scour assessment report, or scour evaluation report, being submitted, implementation of actions needed to reduce risks and actions needed to prevent an increase in risks; 3) preparation, updating and implementation of the scour risk assessment and scour risk register, for scour susceptible structures Type 1 that have been designated with a scour risk rating of high risk and medium risk; 4) preparation, updating and implementation of the scour risk assessment and scour risk register, for scour susceptible structures Type 2 that have been designated with a scour risk rating of high risk; 5) preparation, updating and implementation of the scour risks management plan including actions needed to reduce risks and actions needed to prevent an increase in risks, for all scour susceptible structures on the scour risk register; 6) preparation, updating and implementation of the severe weather event management plan, for all scour susceptible structures that have been designated with a scour risk rating of high risk; 7) preparation, updating and implementation of the routine maintenance actions needed on a regular basis to reduce risks and to prevent an increase in risks, for all scour susceptible structures; and 8) following a structure being designated as an immediate risk scour susceptible structure, implementation of actions needed to reduce risks and actions needed to prevent an increase in risks." NOTE 1 There can be more than one Responsible Officer at the Trunk Road Agent. NOTE 2 There can be more than one Senior Responsible Officer at the Welsh Government. 12 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/2. Identification of scour susceptible structure... W/2. Identification of scour susceptible structures Type 1 and Type 2 (additional to CS 469, Sections 1 and 9) Scour susceptible structures Type 1 (additional to CS 469 clauses 1.2, 1.3, 1.4 and 9.1) W/2.1 A list of scour susceptible structures Type 1 shall be maintained and updated, e.g. when new structures are constructed, upgraded, or demolished. Scour susceptible structures Type 2 (additional to CS 469 clauses 1.2, 1.3, 1.4 and 9.1) W/2.2 A list of scour susceptible structures Type 2 shall be prepared and updated, e.g., when new structures are constructed, upgraded, or demolished. NOTE 1 Natural Resources Wales can provide FRAW maps for areas where detailed flood modelling has been undertaken. These are available on and are to be used for the designation of scour susceptible structures Type 2. DataMapWales [Ref 8.I] NOTE 2 Surface water flood risk maps are also available on DataMapWales [Ref 8.I], to be used for the designation of scour susceptible structures Type 2. NOTE 3 Refer to the "Terms and definitions" table for the definition of "lead local flood authority". 13 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/3. Inspection and assessment process (additional... W/3. Inspection and assessment process (additional to CS 469, Section 2) W/3.1 Where a Level 2 scour assessment for Type 1 structures (Section 5) has been carried out, the scour risk score shall be taken as the calculated value in accordance with Section 5. NOTE For structures with a Level 2 scour assessment, Table 2.3 shows an indicative summary of the likely conditions at the structure that lead to the calculated scour risk score. W/3.2 CS 469 2.8 shall not apply. A risk-based approach shall be taken to decide when scour inspections are carried out. NOTE 1 Table 2.8 of CS 469 [Ref 8.N] can be used a guide in deciding when scour inspections are carried out. NOTE 2 For example, low risk structures could be subject to an emergency scour inspection when a flood event is considered to put them at particular risk. 14 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/4. Review of 0.5% AEP flood risk maps (additiona... W/4. Review of 0.5% AEP flood risk maps (additional to CS 469, Sections 4 and 7) Scour susceptible structures Type 1 (additional to CS 469 clauses 4.3 and 4.6) W/4.1 The most recently prepared 0.5% AEP flood risk maps (FRAW maps found on DataMapWales [Ref 8.I]), of the types shown below, for the structure location shall be reviewed: 1) Natural Resources Wales flood event flood risk maps; and, 2) Natural Resources Wales or lead local flood authority surface water flood risk maps. (Relevant to CS 469 [Ref 8.N]clauses 4.3 and 4.6.) Scour susceptible structures Type 2 (additional to CS 469 clauses 7.18 to 7.20) W/4.2 The most recently prepared 0.5% AEP flood risk maps (FRAW maps found on DataMapWales [Ref 8.I]), of the types shown below, for the structure location shall be reviewed: 1) Natural Resources Wales flood event flood risk maps; and, 2) Natural Resources Wales and lead local flood authority surface water flood risk maps. (Relevant to CS 469 [Ref 8.N]clauses 7.18 to 7.20]. 15 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/5. Climate change allowances (additional to CS 4... W/5. Climate change allowances (additional to CS 469, Sections 5 and 6) General W/5.1 The climate change allowances for Wales shall be used in an assessment for scour and other hydraulic actions on a structure. (Relevant to CS 469 [Ref 8.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1]. NOTE The climate change allowances for sea level rise are based on the UK climate change projections 2018 UKCP 18 [Ref 10.I]. All other climate change allowances are based on the previous projections. Climate change allowances for structures W/5.2 The climate change allowances for Wales shall be used to assess immediate and short term risk (up to 2029) to the structure, in the scour Level 2 assessment. (Relevant to CS 469 [Ref 8.N] clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1]. W/5.3 The climate change allowances for the structure location shall be determined in accordance with the Natural Resources Wales criteria described in CCA(E) [Ref 5.I](Relevant to CS 469 [Ref 8.N] clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1.) Peak river flow W/5.4 When calculating the component of the assessment flow QA from river (fluvial) flooding QF , the climate change allowance for river (fluvial) flooding shall be used, determined for the structure location from Table W/4.4. Alternatively, QA could be determined by rerunning existing models with revised hydrology accounting for climate change. (Relevant to CS 469 [Ref 8.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1.): Table W/5.4 Determine the climate change allowance: percentage increase in stream or river (fluvial) assessment flow Climate change allowance for the structure: total potential increase in QF anticipated for the 2020s River basin district Central / change factor Upper Severn 10% 25% West Wales 15% 25% Dee 10% 20% W/5.4.1 The projected peak river flow change is a range, with the highest estimate equally likely to occur as the lowest estimate. For this reason the central estimate, or change factor, should be used to assess the potential impact of climate change. W/5.4.2 In addition to the change factor, an assessment of risk should be made using the upper end estimate. W/5.4.3 The information derived from this assessment should be used to inform mitigation measures. NOTE Natural Resources Wales published flood risk maps for Wales flood risk ( DataMapWales [Ref 8.I]) show Low, Medium and High Risk areas in Wales. However, many of the Natural Resources Wales Flood Zone areas shown on published flood risk maps are not the flooded area for a 0.5% AEP. Refer to W/3.1 for information on how to access: 1) Natural Resources Wales flood risk maps for a 0.1% AEP ; and 2) Natural Resources Wales or lead local flood authority flood risk maps showing areas where significant surface water flooding has occurred. 16 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/5. Climate change allowances (additional to CS 4... Peak rainfall intensity W/5.5 When calculating the component of the assessment flow QA from surface water (pluvial) flooding in small and urban catchments, where the area of the catchment upstream of the structure is up to 5 km², the climate change allowance for peak rainfall intensity of +10% shall be used. NOTE This is the total potential increase in peak rainfall intensity, resulting in surface water (pluvial) flooding anticipated for the period 2015 to 2039. This "upper end" climate change allowance applies across all of Wales CCA(W) [Ref 4.I]. (Relevant to CS 469 [Ref 8.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1). W/5.5.1 For river catchments over 5 km2 the values in Table W/4.4 should be used. Sea level rise W/5.6 When calculating the component of the assessment flow QA from coastal flooding, the rise in sea level climate change allowance shall be used, determined for the structure location from Table W/4.7 CCA(W) [Ref 4.I] and CS 469 [Ref 8.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, & 6.1. W/5.7 The climate change allowance for total potential increase in sea level for the structure location shall be determined from Table W/4.7 CCA(W) [Ref 4.I] and CS 469 [Ref 8.N]clauses 5.2, 5.17, 5.23, 5.25, 5.29, 5.55, 6.1]. Table W/5.7 Determine the climate change allowance: total potential increase in sea level Local Authority Area Climate change allowance for the structure total potential increase in mean sea level by 2100* Flintshire 0.76 metres Denbighshire Conwy 0.75 metres Anglesey 0.74 metres Gwynedd 0.76 metres Powys 0.79 metres Ceredigion 0.80 metres Pembrokeshire Carmarthenshire 0.83 metres Swansea Neath Port Talbot Bridgend Vale of Glamorgan 0.84 metres Cardiff Newport Monmouthshire 0.85 metres *Higher central allowance (70th percentile). The allowances are derived using the UKCP 18 [Ref 10.I] 2100 dataset. 17 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/5. Climate change allowances (additional to CS 4... W/5.8 When calculating the volume of the tidal prism, VTide,av (see CS 469 [Ref 8.N] clauses 5.28, 5.29), the average tidal range determined in accordance with Section W/4.6 shall be used. W/5.9 When calculating the component of the assessment flow QA from tidal or coastal flooding, the maximum tidal range shall be determined for the structure location using two components added together (relevant to CS 469 [Ref 8.N]clauses 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, 6.1) as: 1) the present day maximum tidal range, determined in accordance with clause W/4.10; and, 2) the climate change allowance for total potential increase in sea level, determined in accordance with clause W/4.7. W/5.10 The present day maximum tidal range for the structure location shall be determined using two components (see CS 469 [Ref 8.N]clauses 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, and 6.1) as: 1) low tide level is the lowest astronomical tide that can occur at the structure location; and, 2) high tide level is either the present day extreme sea level determined in accordance with clause W/4.11, or the highest astronomical tide that can occur at the structure location, whichever is the highest level. W/5.11 The present day extreme sea level for the structure location for a 0.5% AEP event, shall be determined in accordance with CCA(E) ESL Data [Ref 1.I], CCA(E) ESL Report [Ref 2.I] and CCA(E) ESL Guide [Ref 3.I] (applicable to CS 469 clauses 5.2, 5.17, 5.23, 5.25, 5.28, 5.29, 5.55, and 6.1). NOTE The present day extreme sea level is for still water level only (see CCA(E) ESL Guide [Ref 3.I]) and does not include the effects of propagating ocean storm surges. W/5.12 When calculating the volume of the tidal prism, VTide,max (see CS 469, clauses 5.28, 5.29), the maximum tidal range determined in accordance with clause W/4.9 shall be used. 18 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/6. Scour Level 2 assessment (additional to CS 46... W/6. Scour Level 2 assessment (additional to CS 469 Sections 5 and 9) W/6.1 The fluvial component of the assessment flow, QF , shall be determined in accordance with the Natural Resources Wales Flood estimation technical guidance note: GN008 [Ref 6.I] (applicable to CS 469 [Ref 8.N] clauses 5.17 to 5.24). NOTE 1 Natural Resources Wales can provide their technical documents, on request. Natural Resources Wales can be contacted at Natural Resources Wales, general enquiries. NOTE 2 The fluvial component of the assessment flow, QF , can be influenced by many factors, including: 1) the catchment includes urban development, and the catchment area is no more than 5 km², referred to as a "small and urban catchment"; 2) the catchment area is less than 25 km², referred to as a "small catchment"; 3) the catchment area is more than 1,000 km², referred to as a "large catchment"; 4) the catchment, or part of the catchment, is low-lying; 5) the catchment, or part of the catchment, has pumped drainage; 6) the catchment includes a catchment-to‑catchment water transfer, or catchment-to-catchment diversion; 7) there is an extensive flood plain in the catchment, which can temporarily store flood water during a severe weather event, without any flow control structures; 8) there are one or more flow control structures in the catchment; 9) there are one or more flow control structures downstream of the structure, that can affect the flow rate, or water level at the structure; 10) the catchment, or part of the catchment, is highly permeable, e.g. underlain by fissured aquifers; 11) the catchment includes one or more sub-catchments with widely differing flood response times; and 12) there are complex interactions of flood volume and peak flow, or contributions to the peak flow from different tributaries, or other complex factors, affecting the peak flow rate at the structure location. W/6.2 The catchment response time, for the catchment upstream of the structure, shall be determined in accordance with Table W/5.2 (applicable to CS 469 [Ref 8.N], clause 5.24). Table W/6.2 Catchment response time Catchment response time The length of time between a severe weather event occurrence in the catchment upstream of a structure and flood water arriving at the structure Very short No more than 30 minutes. Short Between 30 minutes and 2 hours. Medium Between 2 hours and 24 hours. Long More than 24 hours. W/6.3 A Scour Assessment Certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 shall be completed and signed by the Team Leader and the Principal of the assessing organisation, in accordance with Appendix W/A in this document (applicable to CS 469 [Ref 8.N], clauses 5.59 and 9.1). W/6.4 The Scour Assessment Certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 shall be sent to the Technical Approval Authority, for acceptance (applicable to CS 469 [Ref 8.N], clauses 5.59 and 9.1). 19 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/7. Risk management of scour and other hydraulic ... W/7. Risk management of scour and other hydraulic actions at structures (additional to CS 469, Section 8) W/7.1 The process for advance notification of forecast flood events at structures (on a national / regional / area basis) to the Welsh Government shall include the Flood Forecasting Centre (FFC) documents (applicable to CS 469 [Ref 8.N], clause 8.11): 1) "Flood Outlook", issued twice per month FFC (FO) [Ref 3.N]; and 2) "Flood Guidance Statement", issued daily FFC (FGS) [Ref 2.N]. NOTE 1 Severe weather warnings are issued by the Met Office UKWW [Ref 11.I]. NOTE 2 The FFC is a working partnership between the Met Office and the Environment Agency, combining their meteorology and hydrology expertise into a specialised hydrometeorology service FFC (Website) [Ref 7.I]. The FFC provides national scale forecasts for all natural forms of flooding, due to: 1) rivers; 2) surface water; 3) groundwater; and, 4) tidal & coastal. NOTE 3 The FFC is fully operational 24 hours a day, 7 days a week. NOTE 4 The "Flood Outlook" provides a fortnightly general look ahead for flood risk for all natural forms of flooding (referred to in Note 2 above), including: 1) a summary (not detailed) of flooding risk for the next four weeks; 2) a seasonal weather briefing; and 3) spring tide dates. NOTE 5 The "Flood Guidance Statement" provides a daily summary of flood risk from all natural sources, including: 1) a flooding forecast with flood risk risk categories, for the next five days; and 2) a look ahead for the following six to ten days, when there is a heightened flood risk, or an ongoing flood event. W/7.2 The process at the Welsh Government, for acting upon the "Flood Outlook" shall include [applicable to CS 469, clauses 8.11 to 8.15]: 1) advance preparations for actions needed prior to forecast of significant flood events at structures; and 2) advance preparations for actions needed to safeguard affected populations and structures. W/7.3 The process at the Welsh Government, for acting upon the "Flood Guidance Statement" shall include [applicable to CS 469, clauses 8.11 to 8.15]: 1) preparations for actions needed for forecast of significant flood events at high risk scour susceptible structures; 2) implementation of actions needed to safeguard affected populations and structures; and 3) implementing operational procedures at structures which are linked to the risk levels in the Flood Guidance Statement. 20 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/8. Normative references W/8. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref. Document Ref 1.N National Archives. UKPGA 2010/29, 'Flood and Water Management Act' Ref 2.N https://www.gov.uk/government/organisations/flood-forecasting-centre/about-ourservices. Flood Forecasting Centre. FFC (FGS), 'Flood Guidance Statement' Ref 3.N https://www.gov.uk/government/news/flood-forecasting-centre-the-flood-outlook-ischanging. Flood Forecasting Centre.. FFC (FO), 'Flood Outlook.' Ref 4.N National Archives. UKPGA 1974/37 (HSWA), 'Health and Safety at Work etc. Act' Ref 5.N National Archives. UKPGA 1980/66, 'Highways Act' Ref 6.N National Archives. UKPGA 2015/07, 'Infrastructure Act' Ref 7.N National Highways. GG 101, 'Introduction to the Design Manual for Roads and Bridges' Ref 8.N National Highways. CS 469, 'Management of scour and other hydraulic actions at highway structures' Ref 9.N National Highways. GG 104, 'Requirements for safety risk assessment' 21 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 W/9. Informative references W/9. Informative references The following documents are informative references for this document and provide supporting information. Ref. Document Ref 1.I Environment Agency. https://data.gov.uk/dataset/73834283-7dc4-488a-9583-a920072d9a9d/coastaldesign-sea-levels-coastal-flood-boundary-extreme-sea-levels-2018. CCA(E) ESL Data, 'Climate change allowances - Present day extreme sea levels (Data)' Ref 2.I Environment Agency. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_- data/file/827778/Coastal_flood_boundary_conditions_for_the_UK_2018_update_-_technical_report.pdf. CCA(E) ESL Report, 'Climate change allowances - Present day extreme sea levels (technical summary report)' Ref 3.I Environment Agency . https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_- data/file/827779/Coastal_flood_boundary_conditions_for_the_UK_2018_update_-_user_guide.pdf. CCA(E) ESL Guide, 'Climate change allowances - Present day extreme sea levels (user guide)' Ref 4.I Welsh Government. CCA(W), 'Climate change allowances and flood consequence assessments' Ref 5.I https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances. Environment Agency.. CCA(E), 'Climate change allowances for England' Ref 6.I Natural Resources Wales. GN008, 'Flood estimation technical guidance' Ref 7.I Meteorological Office and Environment Agency.. https://www.gov.uk/government/organisations/flood-forecasting-centre. FFC (Website), 'Flood Forecasting Centre' Ref 8.I https://datamap.gov.wales/layergroups/inspire-nrw:FloodRiskAssessmentWales. Welsh Government. DataMapWales, 'Flood Risk Assessment Wales' Ref 9.I Welsh Government. TAN 15, 'Technical Advice Note 15: Development, flooding and coastal erosion' Ref 10.I https://www.metoffice.gov.uk/research/approach/collaboration/ukcp. The Met Office, UK. UKCP 18, 'UK Climate Projections 2018' Ref 11.I https://www.metoffice.gov.uk/weather/warnings-and-advice/uk-warnings. Met Office.. UKWW, 'UK Weather Warnings.' 22 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Appendix W/A. Model form of scour assessment certificate fo... Appendix W/A. Model form of scour assessment certificate for a scour Level 2 assessment of a scour susceptible structure Type 1 (additional to CS 469, Sections 5 and 9) W/A1 Scour Assessment Certificate – Section 1 – Scour Susceptible Structure Type 1 Details Name of structure 1 : Structure reference number 1 : Structure key 1 : W/A1.1 Certificate Section 1 - Notes (see CS 469 [Ref 8.N] clauses 5.3 & 9.1, and WNAA clauses W/5.3, W/5.4) 1) Note: The name of the structure, structure reference number and structure key are as shown on the Overseeing Organisation's structures asset management system. W/A2 Scour assessment certificate - Section 2 - signatures We certify that reasonable professional skill and care has been used in the preparation of the scour Level 2 assessment of (name of structure and structure reference number) with a view to securing that: 1) This structure has been assessed in accordance with: (a) CS 469 'Management of scour and other hydraulic actions at highway structures; and, (b) Wales National Application Annex for DMRB CS 469 'Management of scour and other hydraulic actions at highway structures 2 . 2) The results of the scour Level 2 assessment for this structure are: (a) the scour risk score is 10 / 40 / 60 / 80 / 100 3, 4; (b) the scour risk rating is high risk / medium risk / low risk 3, 4; and, (c) the channel stability risk rating is high risk / medium risk / low risk 3, 4 . Signed _____________________________________________ Team Leader of the assessing organisation Name ______________________________________________ Engineering Qualifications ______________________________ 5 Position held _________________________________________6 Name of Organisation __________________________________ Date ________________________________________________ Signed _______________________________________________ Principal of the assessing organisation Name _______________________________________________ Engineering Qualifications _______________________________ 5 Position held __________________________________________7 23 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 CS 469 - WNAA Version 1.0.0 Appendix W/A. Model form of scour assessment certificate fo... Name of Organisation ___________________________________ Date ________________________________________________ The departures and additional methods or processes given in the Schedule to this Certificate are agreed 1 . This Certificate is accepted by the Technical Approval Authority [TAA]. Signed _______________________________________________ Name ________________________________________________ Engineering Qualifications ________________________________ 5 Position held __________________________________________ TAA ________________________________________________ Date ________________________________________________ W/A2.1 Certificate Section 2 - Notes (see CS 469 [Ref 8.N] clauses 5.59 & 9.1, and WNAA clauses W/5.3, W/5.4) 2) List in a Schedule to this Certificate any departures, additional methods or processes agreed by the Overseeing Organisation and the date of the Overseeing Organisation agreement on DAS. 3) Delete as appropriate. 4) The scour risk score, scour risk rating and channel stability risk rating are to be recorded in the Overseeing Organisation structures asset management information system. Refer to CS 469 clause 9.1. 5) CEng MICE, or CEng MIStructE, or equivalent. 6) The Team Leader of the assessing organisation responsible for the whole of the scour Level 2 assessment of a scour susceptible structure Type 1. Refer to the "Terms and definitions table" for the definition of "Team Leader of the assessing organisation". 7) A Principal of the assessing organisation responsible for the whole of the scour Level 2 assessment of a scour susceptible structure Type 1. Refer to the "Terms and definitions table" for the definition of "Principal of the assessing organisation". 24 Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024 © Crown copyright 2024. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 22-Jun-2025, CS 469 Version 1.0.0, published: 30-Apr-2024

Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 450 Inspection of highway structures (formerly BD 63/17) Version 0.1.0 Summary This document gives the Overseeing Organisation's requirements for inspection of its highway structures. Application by Overseeing Organisations Any specific requirements for Overseeing Organisations alternative or supplementary to those given in this document are given in National Application Annexes to this document. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated Highways England team. The email address for all enquiries and feedback is: Standards_Enquiries@highwaysengland.co.uk This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Contents Contents Release notes 4 Foreword 5 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Introduction 6 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Abbreviations 7 Terms and definitions 8 1. Scope 10 Aspects covered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Use of GG 101 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Quality assurance and audits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2. General requirements 11 Extent of inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Health and safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Competence of inspection staff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Management and reporting of risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Immediate risks to public safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Resulting actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Fire risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3. Maintenance inspections 17 Inspection types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Safety inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Call out inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 General inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Principal inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Special inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Agreement and reviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Suitable situations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Underwater inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Inspection for assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Headroom measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 4. Management and planning of maintenance inspections 23 Inspection programmes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Inspection frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Scheduling inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Preparation of inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Notification of incomplete inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Notification of late inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Contents 5. Records of maintenance inspections 27 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Uploading and authorising . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Records for safety inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Records for general inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Records for principal inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Records for special inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Records for inspection for assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Records for access gantries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Photographic and video records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Records of immediate risks to public safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6. Acceptance inspections and records 31 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Inspection type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Efficient use of inspection resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Pre-opening inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Defects liability inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Transfer inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Handback inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Acceptance inspection records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 7. Alternative means of access 37 Approval of alternative means of access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Management and planning for the use of unmanned aerial vehicles (UAVs) . . . . . . . . . . . . . . . . . . 37 Selection of unmanned aerial vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 8. Risk-based principal inspection intervals 39 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Inspection intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Risk assessment procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Risk rating procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Risk assessment forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Roles and responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Record management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 9. Structures inspectors' competencies and certification 42 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Inspection personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Trainee inspectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 10. Health and safety 44 Inspection hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Where the role of the inspection organisation is carried out by other parties . . . . . . . . . . . . . . . 44 Operation and maintenance of access gantries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Health and safety plans and records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 11. Normative references 47 12. Informative references 48 Appendix A. Risk-based principal inspection intervals 49 A1 Risk-based principal inspection intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 A1.1 Risk assessment procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 A1.2 Risk score evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 2 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Contents Appendix B. Details of inspector core competencies 77 B1 Core competence requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 B1.1 Level of competency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 B1.2 Introduction to inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 B1.3 Structures types and elements / behaviour of structures . . . . . . . . . . . . . . . . . . . . . . . 78 B1.4 Inspection process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 B1.5 Defects descriptions and causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 B1.6 Investigation and testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 B1.7 Repair techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 B1.8 General aptitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 3 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0.1.0 April 2021 Core document, Wales NAA Incremental change to requirements Text alignment with CG 300 and CD 354 for clarity. No technical changes. Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0 March 2020 4 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Foreword Foreword Publishing information This document is published by Highways England. This document supersedes BD 63/17, which is withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 5 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Introduction Introduction Background This document describes the inspection and reporting requirements for highway structures on motorway and all purpose trunk roads as defined in GG 101 [Ref 12.N]. This document covers the use of the Inspection Manual for Highway Structures and should be read in conjunction with CG 302 [Ref 1.N]. It should be read in conjunction with CS 452 [Ref 5.I] when dealing with tunnels. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 12.N] apply to this document. The inspection requirements described in this document are based on the following overarching principles. 1) To detect in good time any defect that may cause an unacceptable safety or serviceability risk or a serious maintenance requirement, in order to safeguard the public, the structure and the environment and to enable appropriate remedial action to be taken. 2) To provide information that enables the management and maintenance of a stock of structures to be planned on a rational basis in a systematic manner, in order to support the achievement of the objectives of the Overseeing Organisation. 3) To ensure that inspections are undertaken by suitably experienced and competent staff. These overarching principles align with Management of Highway Structures: A Code of Practice. MHS CoP [Ref 7.I] 6 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Abbreviations Abbreviations Abbreviations Abbreviation Definition MEWP Mobile elevated working platform NHSS 31 National Highway Sector Scheme 31 TAA Technical Approval Authority TSM The Traffic Signs Manual 7 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Terms and definitions Terms and definitions Term Definition Parties and organisations Agent The party appointed by the Overseeing Organisation to manage highway assets on their behalf, e.g. maintaining agent, managing agent, managing agent contractor, trunk road agent, concessionaire, service provider or operating company. Where the Overseeing Organisation manages the highway assets within their own organisation, the agent is to be the branch or section to which the duties have been delegated. Constructor The organisation contracted by the Overseeing Organisation or the agent to undertake construction works on its behalf. Can also be termed the Contractor. Designer The organisation responsible for the overall design including proprietary components. Inspection Organisation The organisation contracted by the Overseeing Organisation or the Agent to undertake inspections on its behalf. Where the Overseeing Organisation inspects the highway assets within their own organisation, the Inspection Organisation is to be the branch or section to which the duties have been delegated. Technical Approval Authority (TAA) As defined in CG 300 [Ref 17.N]. Positions and roles Authorising Engineer The engineer appointed by the Supervising Engineer who authorises inspection reports Inspector A person appointed by the Supervising Engineer with the competence and qualifications to inspect highway structures. Senior Inspector A person appointed by the Supervising Engineer with the competence and qualifications to inspect highway structures, able to demonstrate broader experience and proficiency of the relevant areas and has evidence of having advised others. Supervising Engineer The engineer appointed by the Agent who supervises the inspection programme and is ultimately responsible for inspections of highway structures. Dates and periods Date of inspection the date an inspection was undertaken and completed, where evidence and observations are gathered at the structure. In the case where an inspection takes more than one day, the date an inspection was completed. 8 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Terms and definitions (continued) Term Definition Defects liability period the period, as specified in the contract, following completion of the project during which the Contractor can be liable for defects in its work. This may also be referred to as the defects correction period, period of maintenance or prescriptive period. In general, and in the absence of an express provision to the contrary, the defects liability period provisions are in addition to, and not in substitution for, the common law rights. Due date for inspection The due date for inspection is set from construction and repeats at the relevant inspection interval. It is not affected by variations in the date of inspection. Scheduled date for inspection The date an inspection is scheduled to occur on. Types of structure Complex structure The following criteria are used to define complex structures where one or more apply; 1) skews greater than 25°; 2) unconventional or novel design aspects; 3) unusual elements or load paths; 4) half-joints, hinge-joints or post-tensioning; 5) any individual span exceeding 50 m; 6) history of unresolved foundation problems, significant structural defects, or significant safety issues; 7) structures subject to interim measures in CS 470 [Ref 9.I]; 8) scour susceptibility (risk rating 1-4) to BD 97 [Ref 18.N]; and, 9) retaining walls greater than 7.0 m in height. Special structure The following criteria are used to define special structures where one or more apply: 1) any individual span exceeding 100 m; 2) moveable bridges; 3) moveable inspection access gantries, gantry rail and gantry support systems; 4) large viaducts and crossings with unresolved structural issues and or weight restrictions, subject to continuous monitoring and inspection, 5) structures with suspension systems, (e.g. cable stayed, or suspension bridges, but not footbridges); and, 6) tunnels. Types of inspection Acceptance Inspections inspections which are undertaken at a specific point in the lifecycle of a structure (pre-opening inspection, defects liability inspection) or at transfer of ownership (transfer inspection, handback inspection). Maintenance Inspections inspections which are undertaken on a routine basis (safety inspection, general inspection, principal inspection), or in response to a specific issue (special inspection, inspection for assessment) 9 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 1. Scope 1. Scope Aspects covered 1.1 This document shall apply to highway structures over, under or alongside roads under the responsibility of the Overseeing Organisation as defined in accordance with GG 101 [Ref 12.N]. NOTE Additional technical advice on the inspection methods for highway structures is provided in the Inspection Manual for Highway Structures IMHS [Ref 6.I]. 1.2 The scope of highway structures which require inspection shall be as defined in Table 2.1. 1.3 For any structures that are identified as requiring different inspection management arrangements to those described in this document, the Agent shall propose an appropriate inspection management arrangement for the agreement of the Overseeing Organisation. NOTE Advice on alternative inspection management arrangements is provided in the National Application Annexes. 1.3.1 Some special types of structures, for example cable stayed bridges, may require different inspection management arrangements to those described in this document. 1.3.2 The Overseeing Organisation may inform the Agent of structures that require alternative inspection management arrangements. Implementation 1.4 This document shall be implemented forthwith on all schemes involving the inspection of highway structures on the Overseeing Organisations' motorway and all-purpose trunk roads according to the implementation requirements of GG 101 [Ref 12.N]. Use of GG 101 1.5 The requirements contained in GG 101 [Ref 12.N] shall be followed in respect of activities covered by this document. Quality assurance and audits 1.6 The Agent's quality management system shall be amended to reflect the requirements of this document if necessary, in accordance with GG 102 [Ref 14.N]. 1.7 The Agent shall be prepared for audits against this document at any time, including but not restricted to: 1) achievement of required quality of inspections and the associated reports; 2) inspector competence and training; 3) inspection management; and, 4) health and safety arrangements. 10 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 2. General requirements 2. General requirements Extent of inspection 2.1 Inspections shall be carried out for each structure type according to the requirements shown in table 2.1 11 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 2. General requirements Table 2.1 Extent of inspection according to structure type Structure type8 NAA exceptions1 Definition Extent of inspection2 Bridge, buried structure, subway underpass, culvert and any other similar structure S, NI A structure with a clear span or internal diameter greater than 0.9 m supporting the highway as it crosses an obstacle (e.g. river, valley or flood plain) or a service (e.g. local road, railway or canal), or, a structure with a clear span or internal diameter greater than 0.9 m supporting the passage of a service (e.g. local road, railway, canal) over the highway. All structural elements and adjacent structural and non-structural elements relevant to the behaviour, stability and safety of the structure Earth retaining structure S, NI A structure associated with the highway with an effective retained height of 1.5 m or greater, where the dominant function is to retain earth3 All structural elements and adjacent structural and non-structural elements relevant to the behaviour, stability and safety of the structure Reinforced/strengthened soil/fill structure with hard facings S, NI A structure associated with the highway with an effective retained height of 1.5 m or greater where the dominant function is to stabilise the slope and/or retain earth All structural elements and adjacent structural and non-structural elements relevant to the behaviour, stability and safety of the structure. Sign gantry and signal gantry S Portal and cantilever gantries that support signs and/or signals Structural aspects of all sign/signal gantries Cantilever mast for traffic signal Structural aspects of all cantilever masts High mast for lighting with a vertical distance from top of post to bottom of flange of 20 m or more Structural aspects of masts Masts for monitoring equipment. i.e. camera, radio, speed camera and telecommunication transmission equipment. Structural aspects of masts Catenary lighting support system Structural aspects of all catenary support systems Lighting columns, masts, and posts4,5 Posts for traffic signs or signals where any post is greater than 7m in height6 Structural aspects of sign/signal posts where any one post has a vertical distance of more than 7m from the top of the post to he bottom of the flange plate or top of foundation 12 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 2. General requirements Table 2.1 Extent of inspection according to structure type (continued) Access gantry A movable structure providing access to a highway asset, typically for bridge inspection and maintenance Structural aspects of all movable access gantries Road tunnel7 A subsurface highway structure enclosed for a length of 150 m or more Structural aspects of all road tunnels Other structures that are within the footprint of the highway, e.g. service/utility crossings. All structural elements and adjacent structural and non-structural elements relevant to the behaviour, stability and safety of the structure Other structures Any other structures not in above subgroup as agreed with Overseeing Organisation defined as requiring technical approval in accordance with CG 300 [Ref 17.N] or any agreed with the Overseeing Organisation All structural elements and adjacent structural and non-structural elements relevant to the behaviour, stability and safety of the structure Third party structures NI Any of the above categories but owned by others, e.g. private owners or utility companies As agreed with the Overseeing Organisation Note 1 Variations to this table are provided in the respective National Application Annexes where highlighted in this column. Note 2 All structure types include any adjacent or integral road restraint systems and any approach/departure transitions, connections and terminations. Note 3 Retained height of earth retaining structures is the level of fill at the back of the structure above the finished ground level at the front of the structure. Note 4 For the inspection of lighting columns less than 20 m in height see TS 501 [Ref 13.I]. Note 5 For the inspection of masts and columns which have lifting hoists, winches and cables see SI 1998/2306 [Ref 4.I] and manufacturer's recommendations. Note 6 For the inspection of traffic sign posts less than 7 m in height see CS 125 [Ref 11.N]. Note 7 For the inspection of mechanical and electrical equipment and other specific features of road tunnels see CS 452 [Ref 5.I] . Note 8 The structure types may not align with those used in the asset management systems used by Overseeing Organisations. 13 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 2. General requirements 2.1.1 Highway structures which are marginally outside the dimensions stated in table 2.1, especially those which are subject to hydraulic action, may be included within the scope of this document by agreement with the Overseeing Organisation. 2.2 Structural aspects of sign and signal gantries and masts shall include foundations, columns, beams, arms, structural connections and components and the structural performance of any significant attachments (e.g. fixed signs and variable message signs) and their connections. 2.3 Access gantries which are either attached to the structure on a permanent basis, or are moved into position from storage, shall be managed and inspected in accordance with the Institution of Structural Engineers publication 'The Operation and Maintenance of Bridge Access Gantries and Runways' IStructE Gantries & Runways [Ref 20.N]. 2.4 Where an inspection organisation becomes aware of any visible potential risks from structures which are not owned by the Overseeing Organisation but are within the footprint of the Overseeing Organisation's highway, the Overseeing Organisation and the owner of the structure shall be be immediately informed by the Agent. NOTE 1 This can include structures or features outside the boundary of the highway, but which have the potential to affect the integrity of the Overseeing Organisation's structure or highway. NOTE 2 The Overseeing Organisation, or their agent if instructed, can liaise with the other owner, to confirm how the risk can be resolved and whether there is an adequate regime of inspections and maintenance. NOTE 3 This does not negate the responsibility of the agent to check all structures within the footprint of the highway during safety inspections. Health and safety 2.5 Inspections of highway structures, including any testing, must be managed to comply with general statutory and other relevant health and safety requirements and any associated regulations and approved codes of practice and guidance documents that amplify these requirements. 2.6 General statutory and other relevant health and safety requirements, and the Overseeing Organisation's internal safety procedures, must be complied with by agents when planning and undertaking inspections of highway structures. NOTE Specific requirements for health and safety are provided in Section 10. Competence of inspection staff 2.7 All inspections shall be undertaken by personnel that satisfy the health, experience and, where appropriate, qualification and certification requirements for the particular inspection type. 2.8 Measures for the management and monitoring of physical fitness of all inspection staff shall be carried out in accordance with the procedures of the inspection organisation. 2.9 Competence of all inspection staff shall be managed in accordance with the competence management system of the inspection organisation, developed under the general provisions of GG 102 [Ref 14.N] and BS EN ISO 9001 [Ref 12.I]. NOTE Specific requirements for inspector competencies are provided in Section 9. 2.10 The Supervising Engineer shall be a chartered civil or structural engineer (or possess an equivalent EU qualification) with experience in inspection, design, construction or maintenance of highway structures. 2.10.1 An incorporated civil or structural engineer may be appointed for this position subject to the agreement of the Technical Approval Authority (TAA) including a review of their experience. 2.10.2 A chartered highways and transportation engineer may be appointed for this position subject to the agreement of the TAA including a review of their experience. 2.11 Any Authorising Engineers shall be appointed and supervised by the Supervising Engineer. 14 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 2. General requirements 2.11.1 The Supervising Engineer may act as an authorising engineer. 2.12 An Authorising Engineer shall be an incorporated or chartered civil or structural engineer (or possess an equivalent EU qualification) with experience in inspection, design, construction or maintenance of highway structures. 2.12.1 A chartered or incorporated highways and transportation engineer may be appointed for the position of Authorising Engineer subject to the agreement of the TAA including a review of their experience. 2.12.2 Personnel with other qualifications or experience may be appointed for the position of Authorising Engineer, with restrictions on the scope of structures they may authorise, (for example, Category 0 and 1 structures as defined in CG 300 [Ref 17.N]), subject to the agreement of the TAA including a review of their experience. 2.13 The Agent shall maintain records of the qualifications, background and any TAA agreements of staff appointed to be a Supervising Engineer or Authorising Engineer and make them available for audit and review by the Overseeing Organisation. Management and reporting of risks Immediate risks to public safety 2.14 A procedure, common to all maintenance inspections, shall be established by the Agent, whereby inspection staff have a clearly defined duty to inform the Supervising Engineer or designated staff, at the earliest possible opportunity, of any defect or hazard that represents or has the potential to represent an immediate risk to public safety and/or structural stability. NOTE For guidance on the factors that contribute to an immediate risk see CS 470 [Ref 9.I]. 2.15 Staff undertaking a structural inspection shall note any deficiencies at or near the structure which, in their opinion, represents or has the potential to represent a significant safety hazard and report them as an immediate risk to public safety. NOTE The scope described in table 2.1 does not affect the inspector's duty of care under health and safety legislation to report any safety hazards they encounter that are outside the scope of their inspection. 2.16 Staff undertaking a structural inspection shall report any suspected defects of a non-structural nature that represents or has the potential to represent an immediate risk to public safety. NOTE Suspected defects can include any structure that has electrical and/or mechanical equipment attached or adjacent to it. Examples of such risks can include bare wires or loose mechanical fixtures. 2.17 Where the defects or risks posed by the Overseeing Organisation's structure or highway could affect adjacent property, this shall be reported in accordance with procedures for the management and reporting of risks. Resulting actions 2.18 The Overseeing Organisation, and any other owner of the structure, shall be immediately informed by the Agent, and any other owner of the structure, of any possible defect or risk; 1) requiring urgent attention; or, 2) representing or having the potential to represent a hazard to road, rail and other users. NOTE Additional reporting requirements are provided in the National Application Annexes. 2.19 Action shall be immediately taken by the Agent to safeguard the public and/or sustain structural functionality. 2.19.1 Suitable safeguarding actions may include: 1) undertaking a special inspection; 2) undertaking detailed testing; 15 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 2. General requirements 3) scheduling remedial works; or, 4) restricting or closing the structure to traffic. Fire risks 2.20 The following fire hazards and factors shall be reported during any maintenance inspection. 1) any significant or potential fire hazards such as the open air storage of combustible materials, industrial buildings, scrap yards, agricultural storage of combustible materials, or other potential fire safety hazards or any other perceived high level of risk such as the storage of fuel tanks, gas bottles, chemicals, agricultural materials, a significant number of vehicle tyres, other combustible materials; and, 2) any significant factors to indicate any history of fires, such as evidence of vandalism, burnt vehicles, or other incidents underneath or adjacent to the structure. 2.21 Any significant fire hazards or factors reported during the inspection shall be immediately notified to the Overseeing Organisation and recorded on the asset information management system of the Overseeing Organisation. 2.22 Any significant fire damage shall be recorded and made subject of a risk assessment, including options for recommendation of immediate closure of the structure or further investigation, e.g. special inspection, testing or assessment, in light of the damage. 16 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 3. Maintenance inspections 3. Maintenance inspections Inspection types 3.1 The five types of maintenance inspection that shall be used for highway structures are: 1) safety inspection; 2) general inspection; 3) principal inspection; 4) special inspection; and, 5) inspection for assessment. NOTE Variations to the five types of maintenance inspection are provided in the National Application Annexes. Safety inspection Definition 3.2 Safety inspections for highway structures shall be carried out to ensure the safe and efficient identification of safety related defects. NOTE 1 A safety inspection provides a check of those parts of a highway structure that are visible from the highway and are usually undertaken as part of the highway safety inspection regime. NOTE 2 The purpose of a safety inspection is to identify significant deficiencies or signs of damage which represent, or can lead to, a danger to the public or high maintenance costs and therefore require immediate or urgent attention. For example collision damage to superstructure or bridge supports, damage to parapets, spalling concrete or insecure expansion joint plates. NOTE 3 Safety inspections are not specific to highway structures and generally cover all fixed assets on the highway network, including carriageways, footways, structures, drainage, verges and lighting. NOTE 4 Variations to safety inspections for highway structures are provided in the National Application Annexes. 3.2.1 Safety inspections for highway structures should be scheduled at a frequency according to the risks and significance of a particular route or asset. 3.2.2 Safety inspections should be carried out by trained highway maintenance staff. 3.2.3 Safety inspections should be carried out from a slow moving vehicle. 3.2.4 Alternative methods for carrying out the safety inspection may be agreed with the Overseeing Organisation. NOTE In certain circumstances, it is necessary for staff to proceed on foot either to confirm suspected defects or to complete the inspection. For example, some bridges require a weekly or monthly walkover. Frequency 3.3 Safety inspections of all fixed assets shall be carried out at frequencies not less than the requirements set down by the Overseeing Organisation. NOTE Variations to safety inspections of all fixed assets are provided in the National Application Annexes. 3.3.1 The frequency of safety inspections should give due regard to any special considerations, for example, does the structure form, material, usage or location influence the required frequency and reflect the importance of a particular route or asset. 3.3.2 Safety inspections may be necessary as a result of notification of a defect by a third party, e.g. police or public. 17 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 3. Maintenance inspections Call out inspection 3.4 Maintenance staff carrying out a safety inspection shall inform a member of the inspection organisation of any defects which they consider to require a subsequent call out inspection. 3.5 The need for a call out inspection in response to a concern raised by a safety inspection shall be assessed by a member of the inspection organisation. 3.6 Where the need for a call out inspection is confirmed it shall be undertaken by the inspection organisation with the appropriate priority according to the nature of the concern. NOTE A call out inspection is not categorised as a special inspection and as such the Agent is not required to agree this activity with the Overseeing Organisation. 3.7 Any resulting actions from the call out inspection shall be dealt with as an immediate risk to public safety or prioritised for action in accordance with asset management procedures. General inspection Definition 3.8 A general inspection shall comprise a visual inspection of all parts of the structure that can be inspected without the need for additional access equipment, using safe, ground level viewing positions around the structure. NOTE 1 The purpose of a general inspection is to provide information on the physical condition of all visible elements of a highway structure. NOTE 2 Variations to general inspections are provided in the National Application Annexes. 3.8.1 Visual aids may be used to assist identification of defects over a distance, e.g: 1) binoculars; or, 2) cameras with telephoto lenses and a tripod. 3.8.2 The inspection should include adjacent earthworks and waterways where they can affect the behaviour or stability of the structure. NOTE For example, riverbanks in the vicinity of a bridge examined for evidence of scour or flooding or for conditions, such as the deposition of debris or blockages to the waterway, which can lead to scour of bridge supports or flooding. 3.8.3 Traffic management arrangements should reflect the class of road, traffic volumes, presence of hard shoulder and means of access from off-highway that exist at a structure. NOTE Guidance is provided in TSM Chapter 8 [Ref 21.N], the DfT publication 'Safety at Street Works and Road Works' ' Streetworks CoP [Ref 15.N] and DMRB GD 301 [Ref 16.N]. 3.8.4 The inspection should be undertaken in daylight, enabling the whole structure to be inspected from a number of safe viewing points or through the use of fixed access facilities, e.g. inspection galleries and steps. NOTE Other planned daytime operations, e.g. litter clearance, can afford sufficient daytime traffic management opportunities to provide safe viewing positions for inspection. 3.8.5 The inspection may take place under street lighting if there is a sufficient level of lighting: 1) to show all parts of the structure; and, 2) to allow any defects to be identified from the viewing positions. 3.8.6 External task lighting may be used subject to suitable controls to prevent dazzling of road users. NOTE Guidance on the use of external task lighting used adjacent to live traffic is available in TSM Chapter 8 [Ref 21.N]. 18 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 3. Maintenance inspections Frequency 3.9 General inspections shall be undertaken at intervals of 24 months. 3.9.1 Tolerance on the due date for inspection may be permitted for the determination of the scheduled date for inspection in accordance with Section 4. Principal inspection Definition 3.10 A principal inspection shall comprise a close examination, within touching distance, of all accessible parts of a structure. NOTE 1 The purpose of a principal inspection is to provide information on the physical condition of all accessible parts of a highway structure. NOTE 2 A principal inspection is more comprehensive and provides more detailed information than a general inspection. NOTE 3 Variations to principal inspections are provided in the National Application Annexes. 3.10.1 The inspection should include adjacent earthworks and waterways where they could affect the behaviour or stability of the structure. NOTE For example, riverbanks in the vicinity of a bridge examined for evidence of scour or flooding or for conditions, such as the deposition of debris or blockages to the waterway, which could lead to scour of bridge supports or flooding. 3.10.2 The inspection should include removal of inspection covers and opening of hatches and enclosures to access hidden components. NOTE See Section 10 for further advice on confined spaces. 3.11 A principal inspection shall utilise suitable means of safe access and/or traffic management works where required. NOTE The agent can propose, for the agreement of the TAA, the use of alternative means of access for areas of difficult or dangerous access in accordance with Section 7, e.g. obscured parts of a structure and/or confined spaces . 3.12 A principal inspection shall utilise suitable inspection techniques including hammer tapping to detect loose concrete cover and repeated thickness measurements of weathering steel in accordance with CD 361 [Ref 22.N]. NOTE Intrusive testing is not a requirement for a principal inspection, but can be recommended for further investigation, e.g. during a special inspection, or incorporated into the principal inspection under agreement with the agent as a result of previously identified defects. 3.13 A principal inspection shall include the measurement of minimum headroom for the following areas, where present, at the down-chain and up-chain edges of the structure for: 1) each structure free zone (verge); 2) the paved width including separate measurements for: a) each running lane; and, b) each hard strip or hard shoulder. Frequency 3.14 A principal inspection shall be a replacement of a due general inspection. 3.15 Principal inspections shall be undertaken at intervals of 72 months, unless a longer interval has been agreed by the Overseeing Organisation. 19 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 3. Maintenance inspections 3.15.1 Tolerance on the due date for inspection may be permitted for the determination of the scheduled date for inspection in accordance with Section 4. 3.15.2 A longer interval between principal inspections may be agreed with the Overseeing Organisation providing the proposal is supported by a risk assessment in accordance with Section 8. Special inspection Definition 3.16 A special inspection shall provide detailed information on a particular element, part, area or defect that is causing concern, or inspection of which is beyond the requirements of the general and principal inspection regime. Agreement and reviews 3.17 All special inspections shall be agreed by the TAA before being implemented by the Agent, and their justification recorded on the asset information management system of the Overseeing Organisation. NOTE Variations to special inspections are provided in the National Application Annexes. 3.18 Where a series of special inspections is proposed at a particular frequency over a period of time the total number and frequency shall be subject to initial agreement with the TAA. 3.19 A review of the justification and frequency of a series of special inspections shall be subject to regular agreement with the TAA, in light of information gathered during the course of the special inspections, at intervals no greater than: 1) 12 months; or, 2) after six special inspections since the last review. Suitable situations 3.20 Once agreed, special inspections shall be tailored to a specific need to gather information on the condition or details of the structure. NOTE A special inspection can be a suitable response to: 1) the specific characteristics of the structure, for examples the material or structural form; 2) a recommendation identified by a maintenance inspection; 3) certain events, such as the transit of a significant abnormal load, or a flood; or, 4) a recommendation to consider parts of the structure more closely or at a more frequent interval than the normal general and principal inspection regime. 3.20.1 Special inspections may be suitable for the following situations: 1) a structure known or suspected to be subject to a rapid change in condition or circumstance; 2) a general inspection is not sufficient to provide the access or information required; 3) visible defects not explained by a single cause or where the extent of a defect needs to be ascertained; 4) periodic or continuous monitoring to check against a specific problem from worsening, e.g. crack growth and deformations; 5) cast iron structures, at intervals not exceeding six months; 6) structures strengthened by the use of bonded plates, at intervals of six months for the first two years and thereafter in accordance with the intervals prescribed in the maintenance records; 7) structures that have weight restrictions, or other forms of restriction to reduce traffic loading, at intervals not exceeding six months or as agreed by the Overseeing Organisation; 8) structures that have to carry an abnormal heavy load are to be inspected before, during and after the passage of the load if either: 20 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 3. Maintenance inspections a) an assessment has indicated that the margin of safety is below that which could be provided for a design to current standards; or, b) similar loads are not known to have been carried. 9) structures in areas of mineral extraction, when subsidence occurs; 10) structures where settlement is observed greater than that allowed for in the design. The cause is to be identified and steps taken to monitor the rate of settlement and to assess the urgency of remedial measures; 11) to investigate the damage to structures involved in a major incident, chemical spillage or fire; 12) bridge piers situated in a fast flowing river; probing of river bridge foundations after flooding. Where probing indicates the possibility of scour, further underwater inspection is to be carried out in accordance with BD 97 [Ref 18.N]; 13) permanent access gantries prior to use and at intervals in accordance with The Institution of Structural Engineers report on The Operation and Maintenance of Bridge Access Gantries and Runways IStructE Gantries & Runways [Ref 20.N]; 14) hoists, winches and associated cables are to be inspected in accordance with the relevant chapters of the Factories Act; 15) post-tensioned concrete bridges as described in CS 465 [Ref 8.I]. NOTE Further examples of when special inspections are recommended are given in the Inspection Manual for Highway Structures IMHS [Ref 6.I]. 3.20.2 A special inspection may comprise the following in any combination: 1) a close visual inspection; 2) testing and measurements; or, 3) monitoring. 3.20.3 Special inspections may be planned as: 1) a one-off inspection; 2) a discrete series of inspections; or, 3) an ongoing programme of inspections. NOTE 1 Refer to CS 470 [Ref 9.I] for further guidance associated with the monitoring and management of substandard structures. NOTE 2 Guidance on limited site testing that can be undertaken as part of a special inspection for concrete structures, i.e. half-cell potential, chloride level, cover meter and depth of carbonation, is provided in CD 359 [Ref 3.I]. NOTE 3 The wall thickness of steel hollow sections can diminish through internal corrosion and can go unnoticed. The non-destructive measurement of uncorroded thickness of sections at critical areas, e.g. base of parapet posts, rails near ends or joints, is recommended for elements: 1) which exceed or are approaching the end of their design life; or 2) where poor detailing for durability is evident; or, 3) where there are visible signs of distress or deterioration. NOTE 4 See also NAA's for exceptions to Note 3 where some items are included in PI coverage. Underwater inspection 3.21 A programme of underwater inspections shall be implemented for structures where the foundations and parts of the structure are below water. NOTE An underwater inspection is a specific type of special inspection concerned with parts of highway structures that are below water level. 21 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 3. Maintenance inspections 3.22 An underwater inspection shall record the condition of the structure below water level, the existing stream bed profiles and any evidence of scour in accordance with BD 97 [Ref 18.N]. 3.23 Photographic records provided by remotely operated vehicles or unmanned underwater vehicles shall be in accordance with the requirements of photographic or video records given in Section 5. Inspection for assessment 3.24 An inspection for assessment shall provide the information required to undertake a structural assessment. 3.25 Inspection for assessment shall be undertaken following the requirements given in CS 454 [Ref 3.N]. Headroom measurements 3.26 The equipment and method used for headroom measurement shall have a tolerance of not greater than +/- 10 mm. 3.27 Any headroom deficiencies shall be managed and notified to the Overseeing Organisation in accordance with CD 127 [Ref 4.N]. 3.27.1 Where there is any evidence of collision by road vehicles or waterborne vessels these should be documented including dimensioned sketches and photographs to show the extent and location of the damage and the members affected. 3.28 Any safety concerns as a result of collisions, e.g. significant deformations or damaged concrete or reinforcement, shall be reported immediately in accordance with the procedure for an immediate risk to public safety. 3.29 The condition of any low headroom warning signs attached to the structure shall be recorded, in accordance with CS 125 [Ref 11.N]. 22 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 4. Management and planning of maintenance inspec... 4. Management and planning of maintenance inspections Inspection programmes Inspection frequency 4.1 Inspections shall be carried out and repeated at the frequencies given in Table 4.1. 23 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 4. Management and planning of maintenance inspec... Table 4.1 Schedule of inspections Structure type NAA Exceptions1 First PI2 First GI Subsequent PI's W For spans between 0.9 m and 1.8 m, principal inspections are not required except for corrugated steel culverts For spans between 0.9 m and 1.8 m, principal inspections are not required except for corrugated steel culverts Bridge, buried structure, subway underpass, culvert and any other similar structure Year 6 Year 2 6-year interval3 Earth retaining structure Year 6 Ye- ar 2 6-year interval3 Reinforced/strengthened soil/fill structure with hard facings Year 6 Ye- ar 2 6-year interval3 Sign gantry and signal gantry E Year 6 Ye- ar 2 6-year interval3 Mast E Year 6 Ye- ar 2 6-year interval3 Access gantry Inspection prior to use in accordance with the Institution of Structural Engineers publication 'The Operation and Maintenance of Bridge Access gantries and Runways' IStructE Gantries & Runways [Ref 20.N]. Road tunnel Year 6 Ye- ar 2 6-year interval Other structures None4 Ye- ar 2 None4 Third party structures None4 Ye- ar 2 None4 24 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 4. Management and planning of maintenance inspec... NOTE 1 ( 1 ) Variations to table 4.1 are provided in the respective National Application Annexes where highlighted in this column. NOTE 2 ( 2 ) Table 4.1 does not include pre-opening inspection. NOTE 3 ( 3 ) Intervals between inspections can be varied up to a maximum of 12 years subject to a risk assessment, where allowed (see Section 8). NOTE 4 ( 4 ) Where structures are close to the carriageway and/or pose a particular risk to users if failure were to occur then principal inspections can be appropriate. Scheduling inspections 4.2 Upon the start of a contract or commission and every 12 months thereafter, a 12-month programme of all maintenance inspections to be undertaken shall be developed and submitted by the agent for the agreement of the Overseeing Organisation. NOTE Variations to a programme of maintenance inspections are provided in the National Application Annexes. 4.3 Inspections shall be scheduled and undertaken on the due date for inspection. NOTE Variations to inspection scheduling are provided in the National Application Annexes. 4.3.1 The scheduled date for inspection may be varied by up to ± 6 months subject to the approval of the Supervising Engineer that any such changes to the inspection interval are acceptable. NOTE The ± 6 month variation is intended to allow the flexibility for inspection operations, e.g. to allow inspections to be combined during traffic management opportunities for efficiency, or to avoid severe weather events during the winter. 4.3.2 Where access is required to the property of third parties, land owners and authorities, in order to undertake an inspection then the programme should be prepared with allowance for the time required to gain access. 4.3.3 Any third parties, land owners and authorities should be contacted to establish procedures and lead in times to gain access. NOTE For example, access to the main railway network can require up to 32 weeks notice. 4.3.4 Where access to the highway network is restricted by application and approval, e.g. by a system of road space bookings, the programme should be prepared with allowance for the time required to gain access. 4.4 The due date for inspection of a subsequent general or principal inspection shall remain as per the original schedule, and not be changed to accommodate any variations in the date of inspection. NOTE The due date for inspection is set from construction and repeats at the intervals in Section 3. It is not affected by variations in the date of inspection. 4.5 Inspections shall be scheduled to minimise disturbance to the public and make the most efficient use of resources. NOTE For example, schedule inspections to take advantage of traffic management measures planned for other reasons or combine special inspection activities with a principal inspection. 4.5.1 In developing inspection plans and groups of structures for combined activity, agents and supervising engineers should take account of local factors (e.g. the route, geography, junction layouts and common structure types) to provide the most efficient use of temporary traffic management and inspection resources over the whole inspection cycle. 4.6 For structures which require multiple visits to undertake an inspection, the date of inspection recorded shall be the date of completion of the inspection. 25 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 4. Management and planning of maintenance inspec... Preparation of inspections 4.7 Prior to undertaking an inspection, inspectors shall review the structure records to familiarise themselves with: 1) the characteristics of the structure; 2) any hazards; 3) the condition at the time of the last inspection; 4) any worsening of defects over time; 5) any significant maintenance or modifications since the last inspection; 6) any hidden or enclosed structural features that are to be accessed during the inspection; 7) any buried structural features to which can inform reasons for any visible defects. NOTE Additional preparation requirements for maintenance inspections are provided in the National Application Annexes. 4.8 A risk assessment and method statement shall be prepared by the inspection team and agreed by the Supervising Engineer, or a designated deputy, before undertaking the inspection. NOTE The Inspection Manual for Highway Structures IMHS [Ref 6.I] provides details of a suitable review and method statement for maintenance inspections. Notification of incomplete inspections 4.9 The inspection organisation shall immediately inform the TAA , including a justification, when they become aware of any incomplete inspections. NOTE 1 An incomplete inspection is where any of the inspection coverage or proximity requirements for the type of inspection undertaken have not been met. NOTE 2 Variations to notifications to incomplete inspections are provided in the National Application Annexes. 4.9.1 When it is known in advance that the scope of inspection is to be affected, that is the proposed omission of elements or exceptions to the required inspection proximity, the TAA should be informed, including a justification, for discussion prior to the inspection. NOTE This can avoid the need to revisit the structure. 4.10 Where a justification to accept an incomplete inspection is not accepted by the TAA the requirement to inspect those elements shall remain unaffected. 4.11 Any visible elements which have not been inspected shall be recorded. NOTE Variations to inspections of visible elements are provided in the National Application Annexes. 4.12 Where it becomes evident from an inspection report that the inspection is incomplete, this shall immediately be brought to the attention of the TAA, with proposals for remedial action. NOTE Variations to reporting of incomplete inspections are provided in the National Application Annexes. 4.13 The proposals for remedial action to resolve incomplete inspections shall address any immediate risks and options to complete the inspection and the associated time scales for revisiting the structure. NOTE Variations to addressing incomplete inspections are provided in the National Application Annexes. Notification of late inspections 4.14 When an inspection is late, or when it becomes apparent a programmed inspection cannot be achieved, the inspection organisation shall immediately notify the Overseeing Organisation. 4.15 Any notification shall address the implications of the delayed inspection, any immediate structural risks and the associated time scales for completing the inspection of the structure. 26 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 5. Records of maintenance inspections 5. Records of maintenance inspections Introduction 5.1 Inspection records shall provide information for identifying, assessing, quantifying and prioritising maintenance in a systematic manner. 5.2 In addition to the requirements for each type of maintenance inspection, all inspection records shall contain: 1) the date and time of inspection; 2) those responsible for undertaking the inspection (including their certification numbers if applicable); 3) general information about the structure (e.g. name, reference and location); 4) details of the prevailing weather conditions at the time of the inspection; 5) details of the access arrangements used to approach the structure e.g. parking and walking route; 6) details of any access equipment used and proximity gained, 7) details of any visual aids used such as binoculars or telephoto lenses; 8) details of any traffic management used, including lane closures and durations; and, 9) any difficulties in the above which prevented a thorough inspection of all elements and features. NOTE Variations to inspection records are provided in the National Application Annexes. 5.3 Inspection information shall be recorded in the format and/or asset information management system of the Overseeing Organisation. NOTE 1 Variations to how inspection information is recorded are provided in the National Application Annexes. NOTE 2 Inspections records include access gantries. Uploading and authorising 5.4 Inspection records shall be checked and uploaded onto the asset information management system of the Overseeing Organisation within six weeks of the date of inspection. NOTE 1 'Checking' is defined as reading through the inspection record and making corrections to ensure it is accurate and complete. NOTE 2 Variations to timescales and how inspection records are checked and uploaded onto an asset information management system are provided in the National Application Annexes. 5.5 Inspection records shall be reviewed and authorised on the asset information management system of the Overseeing Organisation by the Authorising Engineer within six weeks of uploading. NOTE 1 'Reviewing' is defined as reading through the inspection record to ensure it is accurate and complete, noting and prioritising any recommendations or risks. 'Authorising' is defined as confirmation that the report is accurate and all relevant procedures have been followed. NOTE 2 Variations to reviewing and authorising inspection records are provided in the National Application Annexes. 5.6 Authorising Engineers shall not authorise their own inspection records. Records for safety inspection 5.7 The Agent shall record any anomalies, defects and/or actions taken on the asset information management system of the Overseeing Organisation. NOTE Variations to recording anomalies, defects and/or actions taken are provided in the National Application Annexes. 27 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 5. Records of maintenance inspections Records for general inspection 5.8 The records created during a general inspection shall include: 1) the condition of all of the elements inspected; and, 2) the viewing locations and walking route any observations were made from. NOTE Variations to general inspection records are provided in the National Application Annexes. 5.9 Elements not inspected during the inspection shall be recorded on the asset information management system of the Overseeing Organisation. 5.10 Defects shall have their location, severity, extent and type of defect recorded in a manner compatible with the asset information management system of the Overseeing Organisation. Records for principal inspection 5.11 The records created or updated during a principal inspection shall include the condition of all of the elements inspected and: 1) the location, severity, extent and type of all defects on the structure, including, where appropriate, detailed descriptions, photographs and sketches of the defects that clearly identify their location and illustrate the severity/extent of damage; 2) for bridges over roads, the headroom information based on measurements taken during the inspection; 3) any significant change (e.g. works carried out or deterioration) since the last principal inspection; 4) any information relevant to the integrity and stability of the structure; 5) the scope and timing of any remedial or other actions recommended before the next inspection; 6) the need for a special inspection, additional investigations and/or monitoring; 7) a description of any testing that was undertaken, details of the information collected and an interpretation of the information; and, 8) a list of visible elements or regions that have not been inspected. NOTE Variations to principal inspection records are provided in the National Application Annexes. 5.12 A principal inspection shall include a review of the completeness and accuracy of the inventory records. 5.12.1 A statement confirming the records reviewed should form part of the report. 5.12.2 Any deficiencies in the records should be corrected during the principal inspection. NOTE Variations to deficiencies in principal inspection records are provided in the National Application Annexes. Records for special inspection 5.13 The records created by a special inspection shall include the following. 1) background and reasons for the special inspection; 2) a detailed description of the condition of those parts of the structure that have been inspected including, where appropriate, photographs and sketches; 3) for a strike on a bridge deck, the headroom at the impact point(s) and a measurement of the height and photographs of the vehicle/s involved in the collision, if present at the scene; 4) any significant change (e.g. works carried out or deterioration) since the last maintenance inspection to those parts of the structure that have been inspected; 5) a description of any testing that was undertaken, details of the information collected and an interpretation of the information; 6) any information relevant to the integrity and stability of the structure. 28 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 5. Records of maintenance inspections 7) the scope and timing of any remedial or other actions recommended before the next inspection; 8) the need for any additional investigations and/or monitoring; and, 9) all aspects identified and/or required by the monitoring specification for structures managed in accordance with CS 470 [Ref 9.I]. Records for inspection for assessment 5.14 The information from an inspection for assessment shall be recorded as part of the assessment report. NOTE Guidance on the information required from an inspection for assessment is provided in CS 454 [Ref 3.N]. 5.15 The time requirements for uploading and authorising shall not apply to records for inspection for assessment. 5.15.1 The inspection for assessment report should be made available to the assessment team/s at the start of the assessment. NOTE Inspection for assessment records can be issued within a specific instruction and time frame. Records for access gantries 5.16 The records created by an inspection of an access gantry shall include the condition of all of the elements inspected. 5.17 Agents shall record the access gantry inspection report, along with any operational certificates or service records on the asset information management system of the Overseeing Organisation. Photographic and video records 5.18 All photographic and video records shall include: 1) a description of the scene and any components and defects shown, and its precise location on the structure; 2) an accompanying schedule and/or key drawing indicating the coverage of the relevant parts and elements of the structure; and, 3) details of any deterioration or change in status of existing defects recorded in previous photographic or video records. 5.19 The location of the viewed elements and their defects shall be capable of being identified by anyone reviewing the inspection report, photographic or video record and schedule. 5.19.1 Close up photographs should be accompanied by a wider view to assist location of the defect and feature being shown. 5.20 The photographic or video electronic files shall be uniquely referenced according to the schedule. 5.21 The accompanying inspector's report shall discuss the findings of the photographic record and be referenced according to the schedule. 5.22 Each video clip file shall be referenced by a unique identifier. 5.23 Time specific elements and defects that are in view in video clips shall be noted in the schedule if multiple elements are included in the video clip. 5.24 The photographic or video record shall be of such quality and resolution that allows all visible defects in the materials to be readily identified and then subsequently reviewed and the condition of the element to be scored by the inspector. NOTE For example, being able to identify and record cracks in concrete of 0.2 mm width. 5.24.1 A ruler to indicate the scale of the defect or element should be included in close-up photographs . 29 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 5. Records of maintenance inspections Records of immediate risks to public safety 5.25 The procedure for reporting immediate risks to public safety shall result in a record of the defect identified and/or safety concern raised, including times and dates, and the subsequent action planned/taken. 30 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 6. Acceptance inspections and records 6. Acceptance inspections and records Introduction 6.1 The four types of acceptance inspection shall be used for highway structures: 1) pre-opening inspection; 2) defects liability inspection; 3) transfer inspection; and, 4) handback inspection. 31 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 6. Acceptance inspections and records Table 6.1 Summary of acceptance inspections Event Carried out by Parties notified Outcomes Time Pre-opening inspection Overseeing Organisations representative and/or Agent Constructor, Technical Approval Authority, Overseeing Organisation (or their representative) and/or local authority, rail and waterways authorities etc as appropriate. Inspection records including any additions to the defects/snagging list, and facilitation of the identification and transfer of information and acceptance inspection records. About one month before the issue of completion documentation or the opening/re-opening of the structure to the public Defects liability inspection Overseeing Organisations representative and/or Agent Constructor, Overseeing Organisation (or their representative) and/or local authority, rail and waterways authorities etc as appropriate. Confirmation of all defects rectified and any latent defects and developing problems that were not previously reported. Just prior to end of the defects liability period – timing is to be sufficient to allow any agreed outstanding work to be undertaken before the end of the defects liability period and, if necessary, enforcement of contractual obligations. Transfer inspection Party taking over responsibility Current owner and Agent and/or local authority, rail and waterways authorities etc as appropriate. Principal or general inspection records (identify and agree any defects to be rectified before transfer). Facilitate the identification and transfer of information and acceptance inspection records. Prior to transfer – timing is to be sufficient to allow any agreed work to be undertaken by the current owner/occupier before transfer. Handback inspection Party taking over responsibility Current maintainer/owner and Agent and/or local authority, rail and waterways authorities etc as appropriate. Principal inspection records (identify and agree any defects to be rectified before handback). Facilitate the identification and transfer of information and acceptance inspection records. Prior to handback – timing is to be sufficient to allow any agreed outstanding work to be undertaken by the current owner before the end of the concession period, in order to allow completion of any outstanding contractual obligations. 32 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 6. Acceptance inspections and records 6.1.1 The need for an acceptance inspection may be determined by the TAA. NOTE 1 The purpose of an acceptance inspection is to provide a formal mechanism for exchanging information and documenting and agreeing the current status of, and outstanding work on, a structure prior to changeover of responsibility for operation, maintenance and safety from one party to another. This includes an inspection after changeover, e.g. at the end of the defects liability period. NOTE 2 The format, content and timing of an acceptance inspection depends on its specific purpose. NOTE 3 An acceptance inspection is mainly for the benefit of the party taking over responsibility for the structure. NOTE 4 By their nature an acceptance inspection can only ascertain the finished quality of any visible elements. NOTE 5 Further guidance is provided in the National Application Annexes. 6.2 The acceptance inspection shall be carried out at a time suitable for all relevant parties to attend. 6.2.1 The inspection should be organised and carried out by the party taking over responsibility and accompanied by representatives of the current owner/occupier to facilitate agreement, together with any other party considered appropriate. NOTE A successful acceptance inspection requires liaison and cooperation between the Overseeing Organisation, the current occupier and/or owner, Agent and Constructor, as well as within the Overseeing Organisation to agree inspection organisation and arrangements. 6.3 The party carrying out the inspection shall notify the relevant parties in table 6.1. NOTE It is at the discretion of the notified party as to whether they attend the inspection, unless any contractual obligations apply. 6.4 Approval of the party responsible for the site shall be obtained before undertaking the inspection . 6.4.1 The party responsible for the site should facilitate the inspection with the provision of access equipment. 6.5 The safe systems of work in place for the site shall be followed. 6.5.1 Where the safe systems of work in place on site restrict the intended extent of the inspection the details should be recorded with an agreement as to how the condition of uninspected elements are to be determined. 6.6 The whole structure shall be inspected during an acceptance inspection. Inspection type 6.7 All acceptance inspections shall take the form of a principal inspection. 6.7.1 In certain circumstances the form of acceptance inspections may be relaxed to a general inspection, subject to the agreement of the TAA. NOTE The form of acceptance inspections depends on the type of structure and whether reducing the scope affects the coverage of the inspection at the appropriate proximity. For example if all structural elements are accessible without the need for access equipment. 6.7.2 For transfer and handback inspections; where the results of a recent principal inspection are agreed to be relevant and sufficient with the TAA, then a separate acceptance inspection may be omitted. NOTE Agreement to omit an acceptance inspection can depend on factors such as time passed, the quality and coverage of the principal inspection report, the size of the structure, any rapid deterioration of defects or ongoing structural issues subject to interim measures. Efficient use of inspection resources 6.8 An acceptance inspection shall be planned to minimise disruption to road users and overall cost of traffic management and access equipment. 6.8.1 An acceptance inspection should make use of existing traffic management and access arrangements and/or combine the pre-opening inspection with inspections/checks scheduled under the contract. 33 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 6. Acceptance inspections and records Outcomes 6.9 The outcome of the acceptance inspection shall be communicated to the Overseeing Organisation. 6.10 Any outstanding responsibilities the existing owner retains after transfer shall be made clear to the existing owner and the party taking over responsibility. Pre-opening inspection 6.11 A pre-opening inspection shall be undertaken for new structures, reconstructions and major modifications prior to changeover of responsibility. NOTE The term "major modification" includes any bridge widening, strengthening, replacement of structural members and/or major refurbishments. 6.12 A pre-opening inspection shall not be undertaken as the principal means to check a structure for defects. 6.12.1 Effective supervision and records should be in place throughout the construction phase for acceptance inspections to provide the necessary confidence in the performance of the structure and to ensure that hidden elements have been constructed in accordance with the requirements. NOTE 1 Where a pre-opening inspection is relied on as the principal means to check the structure, there is a significant risk that major defects do not become apparent before the most cost effective opportunity to correct them, e.g. whilst relevant specialist teams are on site and a means of access such as scaffolding is in place. NOTE 2 Failure as a result of erroneous construction e.g. too widely spaced or incorrectly positioned or located or under-specified components which were not identified during construction, might not be detected during acceptance or routine maintenance inspections, hence the emphasis on effective quality management and supervision during construction. 6.13 Prior to the pre-opening inspection the following shall be provided to the agent: 1) all records of defects identified and addressed during the construction period, e.g. snagging lists; 2) a written recommendation that the works are substantially complete, that the structure meets all the performance requirements and any exceptions have been identified alongside a plan to address them. 6.14 The inspection shall be carried out prior to issue of the completion documentation and prior to the opening/re-opening of the structure to the public. NOTE It is good practice to programme the pre-opening inspection one month before opening of the structure to the public, to allow time for the necessary reports to be developed and accepted. 6.15 Any proposed interim arrangements, e.g. where traffic is allowed to use the structure in a staged sequence, shall be subject to agreement with the TAA. 6.15.1 The Agent should be aware that the responsibility for checking and accepting the works on any structure and what this entails depends on the form of contract and the wording included therein. NOTE Under normal contractual arrangements and existing standards, it is the responsibility of the Constructor and/or Designer to carry out checks/inspections during construction and, in collaboration with the Overseeing Organisation, or other party designated by the Overseeing Organisation, produce a snagging list prior to completion. These inspections/checks facilitate the issue of completion documentation (e.g.. certification). 6.16 The pre-opening inspection shall record any defects or work outstanding under the contract and any works to be completed prior to the agent taking responsibility for the operation and maintenance of the structure. 6.17 Following the pre-opening inspection, the Agent, or other party designated by the Overseeing Organisation, shall produce a pre-opening inspection report informing the Overseeing Organisation of all defects and work outstanding identified during the inspection. 34 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 6. Acceptance inspections and records 6.18 The Constructor shall be informed by the Agent of any defects that have been identified during the pre-opening inspection. 6.19 Any defects and work outstanding that need to be completed shall be agreed between the Agent and Constructor. 6.20 A time for the work in clause 6.19 is to be achieved within shall also be agreed between the Agent and Constructor. NOTE Handover procedures for construction compliance certificates are given in CG 300 [Ref 17.N]. Defects liability inspection 6.21 A defects liability inspection shall be undertaken for new structures, reconstructions and major modifications at the end of the defects liability period. NOTE 1 Variations to defects liability inspections are provided in the National Application Annexes. NOTE 2 A defects liability inspection allows confirmation that all defects have been rectified and the identification of any latent defects and developing problems that were not previously identified in the pre-opening inspection. 6.21.1 The timing of the inspection should allow for any agreed work to be undertaken before the end of the defects liability period and for any possible notices to be raised. NOTE 1 It is normal for a construction contract to include a defects liability period during which the Constructor can be liable for defects in their work. NOTE 2 The defects liability period usually commences upon practical completion of the works and runs for the period specified in the contract. 6.22 The Agent, or other party designated by the Overseeing Organisation, shall undertake maintenance inspections in accordance with this document, or as agreed with the Overseeing Organisation, during the defects liability period. 6.23 Where latent defects/developing problems are identified during the defects liability inspection, which were not previously identified, then these shall be reported to the Overseeing Organisation without delay. 6.24 Any latent defects/developing problems identified shall be set down in the report in a manor which allows agreement with each party to achieve an agreed remedy. NOTE 1 The scope of defects for which each party is liable can be set out in the contract. NOTE 2 The Constructor's liability can include the responsibility for making good any latent defects or developing problems that appear. Transfer inspections 6.25 A transfer inspection shall be undertaken on existing structures prior to transfer of ownership of the structure, between two different owners. NOTE 1 A transfer inspection is undertaken in circumstances where the ownership, and therefore responsibility for, an existing structure changes from one party to another. For example trunking and detrunking. NOTE 2 Transfers of responsibility for operation and maintenance between agents during or at the start/end of their contract does not require a transfer inspection unless agreed by the Overseeing Organisation. 6.26 The timing of the transfer inspection shall allow for any agreed work to be undertaken by the current owner/occupier before transfer. Handback inspections 6.27 A handback inspection shall be undertaken on existing structures prior to handback of the structure at the end of a concession period where responsibilities for operation and maintenance are transferred. 35 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 6. Acceptance inspections and records NOTE A handback inspection is undertaken in circumstances where the responsibility for an existing structure changes from one party to another but the overall asset owner remains the the same. For example after a Private Finance Initiative, Public Private Partnership, or Design Build Finance and Operate concession period. 6.27.1 The handback inspection should enable the comparison of the current condition and performance of the structure against the measures specified in the contract. 6.27.2 The outstanding work to be completed should be based on the measures specified in the contract. 6.28 The timing of the handback inspection shall allow for any agreed outstanding work to be undertaken before the end of the concession period and enforcement of any outstanding contractual obligations. Acceptance inspection records 6.29 Records shall comply with the relevant requirements set down in this document for the nominated type of inspection, in addition to the requirements of this section. NOTE See maintenance inspections and records for maintenance inspections for provisions on access proximity, reporting and review/authorisation requirements etc. 6.29.1 The information and records created and/or transferred as part of an acceptance inspection should be consistent with the circumstances and scope of the inspection. 6.30 All acceptance inspection records shall include the identification, documentation and agreement of the following: 1) any defects to be rectified before changeover including the identification of developing problems and work outstanding and securing agreement on any works to be completed before changeover; 2) any permanent access provisions and features affecting general safety and security of the structure with agreement reached before changeover; 3) any special inspection requirements; 4) the date on which the changeover of responsibility occurs; and, 5) to confirm the accuracy and coverage of "as-built" records. 6.30.1 Acceptance inspection records should be supplemented with any other information considered relevant to the current and future management of the structure. 6.31 Agreed acceptance inspection reports shall be recorded on the asset information management system of the Overseeing Organisation. NOTE 1 Details of appropriate records for highway structures are provided in CG 302 [Ref 1.N]. NOTE 2 For details of appropriate records for structures and other assets outside the scope of this document contact the Overseeing Organisation. 36 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 7. Alternative means of access 7. Alternative means of access Approval of alternative means of access 7.1 Alternative means of access for close examination for structural inspections on specific structures shall only be used with prior agreement of the TAA. NOTE 1 The use of alternative means of access is an area worthy of much consideration and can be approved by the TAA subject to acceptance of evidence submitted. NOTE 2 For TAA applications, a similar level of qualifications in application, checking and review can be followed according to the category of structure and significance of the proposal or features as would be administered under CG 300 [Ref 17.N]. 7.1.1 The use of alternative means of access may be used to: 1) supplement a principal inspection, but may not replace a principal inspection; 2) supplement a general inspection; 3) replace a general inspection, provided the scope of the inspection is not reduced. 7.1.2 Alternative equipment, methods or systems, may be acceptable alternatives to close inspection, provided they have been designed, developed and are suitable for the proposed use. NOTE Alternative systems can include: 1) cameras on long reach poles; 2) high resolution and telephoto photography from ground level; 3) thermal imaging; 4) remote controlled vehicles (or propelled by winch) with mounted video equipment; 5) unmanned underwater vehicles; or, 6) unmanned aerial vehicles. 7.1.3 The use of alternative means of access for structural inspections should be limited to viewing small areas of particularly difficult access or small span low risk structures. 7.1.4 Alternative means of access and inspection should not be proposed to replace close up inspections carried out under a principal inspection unless it eliminates a significant safety hazard, while avoiding or mitigating the shortfalls of remote inspection. 7.1.5 Any proposed system should be compared to the benefits of an inspection from touching distance afforded by a principal inspection. NOTE The use of alternative systems can enhance and improve the quality of an inspection and the data available to identify defects, but can be subject to constraints on their performance which possibly would not be apparent during consultations with providers. 7.1.6 Any proposals should resolve where the resulting data can be stored and how it can be accessed by the inspection organisation and the Overseeing Organisation. 7.2 Any alternative systems equipped with cameras shall be able to gather the necessary information to undertake the inspection in accordance with the requirements for photographic and video records given in Section 5. Management and planning for the use of unmanned aerial vehicles (UAVs) 7.3 When proposing or planning the use of a UAVs for undertaking inspection or survey work the inspecting organisation shall confirm and apply the limitations on their use that are imposed by the Civil Aviation Authority (CAA). NOTE The potential benefits of using unmanned aerial vehicles to view structures are widely recognised. However they can be subject to constraints on their performance, such as working under a bridge deck or confined space with reduced ability to create downdraft or counter sudden changes in wind direction. 37 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 7. Alternative means of access 7.4 The use of unmanned aerial vehicles for inspections or surveys in open air or public space is a commercial operation and the operator shall have all necessary permissions issued by the Civil Aviation Authority prior to undertaking the work. NOTE Exceptions can apply to enclosed spaces such as buildings or internal box structures. Consultation with the CAA is recommended in these circumstances. 7.5 The requirements and regulations that are in effect at the time of the inspection or survey must be obtained from the Civil Aviation Authority and applied. 7.6 Prior to each flight a specific risk assessment and flight plan shall be prepared. 7.6.1 A flight risk assessment may include: 1) possible distraction to road users, and others likely to be affected; 2) presence of overhead power lines or similar; 3) location of controlled air space; 4) adverse weather conditions; 5) any permissions required for flying over privately owned land adjacent to the network. 7.7 The risk assessment and flight plan shall include any ground level aspects which need to be under the control of the operator. 7.8 The privacy of any persons or their vehicles which are incidentally recorded during the flight must be protected in accordance with relevant UK laws. 7.9 The inspection organisation and operator shall be insured for each flight to the appropriate level indicated in terms of their contract and commensurate with the potential risk to cause damage. Selection of unmanned aerial vehicles 7.10 The operator shall select an unmanned aerial vehicle which satisfies the requirements of the Civil Aviation Authority and suit the physical constraints of each proposed location. 7.10.1 Potential issues that should be considered are: 1) payload and overall weight; 2) battery life; 3) collision damage protection (sense and avoid); 4) wind speed in which it can operate; 5) size of small unmanned aircraft and the spaces to be accessed, e.g. between bridge beams; 6) the need for ground control or other reference points; and, 7) the ability of the camera to view above and below the aircraft. 38 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 8. Risk-based principal inspection intervals 8. Risk-based principal inspection intervals Introduction 8.1 Agents shall prepare risk assessments to ascertain the interval between principal inspections (PIs) for structures they deem worthwhile. NOTE 1 Specific requirements and exclusions on the use of risk-based principal inspection (PI) intervals are given in the National Application Annexes. NOTE 2 Assessments are based on principles of risk analysis to support decisions as to whether increased inspection intervals can be used. It is assumed that engineering judgement can be used throughout any assessment. NOTE 3 It is not the intention of this methodology to be used as a cost saving exercise; rather any reductions in principal inspection activity for lower risk structures can be reinvested into other inspection activities where the flexibility allows a greater focus on another set of higher risks. NOTE 4 There are potential reductions in exposure to inspector safety risk that can result from a well managed risk assessment exercise. NOTE 5 It is intended that by using the qualitative scoring system, structures can be ranked or grouped in terms of relative risk to determine an increased interval between principal inspections. 8.2 The following structures shall not be subject to risk assessment to increase the interval between principal inspections. 1) special structures; 2) complex structures, excluding retaining walls with a retained height greater than 7 m; 3) structures adjacent to or over a waterway where there is a medium or high risk of damage due to flooding in accordance with BD 97 [Ref 18.N]; 4) bridges with severe (marine environment) exposure; 5) structures which could affect an operational railway if a failure occurred; nor, 6) structures which have a current inspectors condition rating as 'Poor', or 'Average' or 'Critical' condition scores of 0-40. Inspection intervals 8.3 Principal inspection intervals determined through risk assessment shall not exceed twelve years. 8.3.1 Subject to the risk assessment and agreement by the TAA, principal inspections may be held at intervals of 6, 8, 10 or 12 years. 8.3.2 Inspection schedules should be updated to reflect any changes made to the frequency. NOTE 1 Scheduling of inspections remains in accordance with Sections 3 and 4. NOTE 2 Updating of inspection schedules can require assistance of the Overseeing Organisation to make any changes. 8.4 Where a structure has been subject to a risk assessment process resulting in an increased interval between principal inspections, a review of the factors determined during the risk assessment shall be carried out following each subsequent general inspection. NOTE A review of the factors determined during the risk assessment is undertaken to ensure that the assumptions on the risk levels remain valid, e.g. unexpected deterioration of defects or other risks which become apparent. Risk assessment procedure 8.5 The procedure for determining risk-based inspection intervals shall be as shown in Figure 8.5. 39 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 8. Risk-based principal inspection intervals Figure 8.5 Risk assessment procedure 8.6 The risk score shall be calculated based on certain parameters, representing the likelihood of an event (defect occurring, structural failure), its potential consequences, the ability to detect a failure and the ability to control the outcome. 40 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 8. Risk-based principal inspection intervals NOTE 1 Risk assessment considers the risk of failure for prioritisation as essentially: Equation 8.6N1 Risk definition Risk = f(P, S, D, C) where: P = probability or likelihood of event S = severity or consequence of event D = ability to detect a hazard or failure C = ability to control, respond or intervene NOTE 2 Probability, P, can be separated into various factors, e.g. the probability of actual strength being less than the required strength, or the probability of the actual loading exceeding the specified or allowed loading. NOTE 3 Severity, S relates to the severity or consequence of an event or incident and can relate to safety and potential threat to life, or the functionality of the structure above and below or other types of consequence, such as environmental or financial costs. NOTE 4 Ability to detect, D, can relate to hidden or buried critical components which are subject to existing design and construction errors, failure or deterioration without detection. such as over-stressed or corroding hidden components, can be evident by visible signs of failure in adjacent components or they can be too deep to be detected. Brittle failure modes in some components can show no signs of stress or overuse until they fail. NOTE 5 Ability to control, C, can include a number of factors such as, availability of measures to correct or support an identified component failure prior to collapse, obsolete components, propensity for rapid deterioration, brittle (instantaneous) failure modes, low structural redundancy. Risk rating procedure 8.7 The risk score shall be developed in order to determine risk rating and the inspection interval. NOTE Suitable risk assessment parameters and scoring procedure are provided in Appendix A. Risk assessment forms 8.8 Structures shall be assessed using the Overseeing Organisation's risk assessment forms. NOTE 1 The location of the relevant risk assessment form is provided in the National Application Annexes. NOTE 2 The risk assessment form has been developed to assist and inform engineering judgement. Roles and responsibilities 8.9 The risk assessments shall be undertaken by personnel approved by the Supervising Engineer. 8.10 The completed risk assessments shall be authorised by the Supervising Engineer. 8.11 Risk assessment forms shall be subject to agreement with the Technical Approval Authority (TAA). 8.11.1 Only structures determined to have an increased inspection interval should be submitted for agreement. Record management 8.12 Signed and authorised risk assessments and agreed inspection interval shall be uploaded to the Overseeing Organisation's record management system. 41 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 9. Structures inspectors' competencies and certi... 9. Structures inspectors' competencies and certification Introduction 9.1 Personnel undertaking inspections of highway structures shall demonstrate the required level of competency for the role of either Inspector (I) or Senior Inspector (SI) as detailed in the tables in Appendix B. NOTE 1 Separate competence requirements are provided in the National Application Annexes. NOTE 2 The primary differences between the two competence levels are that a senior inspector is able to demonstrate broader experience and proficiency of the relevant areas and has evidence of having advised others when compared to an inspector. See Terms and Definitions. NOTE 3 A registered scheme entitled Bridge Inspector Certification Scheme has been developed in accordance with National Highway Sector Scheme 31 ( NHSS 31 [Ref 13.N] ). NOTE 4 While presently there is a single scheme to establish the competence of bridge inspectors, this does not prevent other providers from establishing a similar training scheme in accordance with NHSS 31 [Ref 13.N]. 9.2 A candidate for inspector or senior inspector shall develop and submit evidence for review to the scheme administrator. NOTE 1 The scheme administrator assigns candidates an assessor who reviews the evidence and provides either approval or comments to the candidate, in accordance with the scheme. NOTE 2 Where the evidence submitted to the assessor for review is accepted, the assessor can invite the candidate to attend an interview to confirm whether the candidate has met the requirements to become a certified inspector or senior inspector. NOTE 3 Training courses are available to assist candidates with their submissions and applications. 9.3 A certified Inspector or Senior Inspector shall renew their registration and certification at the defined intervals given in the scheme. 9.3.1 Subsequent submissions should be made with the aim that continuous certification is achieved. 9.4 Prior to certification as either an inspector or senior inspector role being achieved, inspection staff shall be regarded as a 'trainee inspector'. Inspection personnel 9.5 The Supervising Engineer shall assess the suitability of the level of certification and experience of prospective inspectors before engaging them for particular structures inspections. 9.5.1 Both inspector roles should have the necessary competencies to undertake principal inspections, general inspections and acceptance inspections. 9.5.2 Inspections for assessment, special inspections and monitoring inspections should be undertaken by personnel with the specialist expertise and experience relevant to the purpose of the inspection. NOTE It is expected that personnel with the specialist expertise and experience relevant to the purpose of the inspection can be accompanied by a certified Inspector or certified Senior Inspector. Trainee inspectors 9.6 Trainee inspectors shall not undertake an inspection on their own. 9.6.1 For structures which need a one or two person inspection team to complete the inspection, a trainee inspector may accompany a certified Inspector or Senior Inspector. 9.6.2 For complex or special structures the certified inspectors and senior inspectors may be supplemented by trainee inspectors who can make up to 25% of the team which are on site throughout the inspection. 42 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 9. Structures inspectors' competencies and certi... NOTE Conditions on using trainee inspectors are intended to balance the requirement for experienced personnel and requirements for training. 9.7 For complex and special structures a certified senior inspector shall lead and undertake the inspection, and produce or oversee the report. NOTE Complex and special structures are defined in the Terms and Definitions. 9.8 For structures which incorporate uncommon materials, such as laminated timber or fibre composite materials, inspection personnel shall either be: 1) a certified inspector with knowledge and experience of the particular material and the mechanisms of deterioration; or, 2) a joint inspection team where a certified inspector is accompanied by a person with knowledge and experience of those materials and the mechanisms of deterioration, who provides their written advice to the Inspector. 43 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 10. Health and safety 10. Health and safety Inspection hazards 10.1 A site specific risk assessment shall be prepared, and agreed by the Supervising Engineer, before commissioning and undertaking inspections which feature the following safety hazards: 1) work at height; 2) work over water; 3) diving; 4) confined spaces; 5) asbestos; 6) traffic management; 7) work near/on railway or underground property; 8) work near/on electrical cables or lines; 9) work near/on services such as gas, water or sewerage supplies; 10) lone working; or, 11) other occupational hazards covered by specific legislation. NOTE These hazards are defined in accordance with the health and safety legislation and approved codes of practice. 10.1.1 For hazards associated with asbestos and lone working, generic or task-based risk assessments may be suitable, provided any site specific risk assessments are carried out if required by legislation. 10.1.2 Within the context of a confined spaces safety hazard, wherever mould growth is encountered, e.g. in a box girder or other confined space, it should be regarded as toxic. 10.1.3 Relevant personal protective equipment should be available to allow an inspection to continue if mould is encountered. NOTE 1 A review of previous reports can alert the inspector or supervising engineer of the presence of any mould growth. NOTE 2 For further advice see HSE website for 'Construction hazardous substances: Harmful micro-organisms' https://hse.gov.uk/construction/ [Ref 2.I]. 10.1.4 In areas where the structure cannot be accessed from off the main highway network and there is no hard shoulder, verge, refuge area or maintenance area in the vicinity of a structure then traffic management may be required in order to provide a safe working area to access and view the structure. 10.1.5 Guidance on the requirements for short duration stops is available in The Traffic Signs Manual TSM Chapter 8 [Ref 21.N] however these may not be used for planned situations. 10.2 The inspection organisation shall follow GG 105 [Ref 2.N] for Overseeing Organisation requirements covering the management of asbestos. 10.3 Inspections which involve working near or on railways shall be arranged with, and carried out in full accordance with, the requirements of the relevant railway body. 10.4 While the hazards in clause 10.1 have been identified as occurring most frequently, other hazards shall also be subject to appropriate management and risk assessment, and be managed appropriately. 10.5 Any risk assessment shall evaluate whether the hazard can be eliminated, e.g. by an alternative access route, use of remotely operated vehicles or unmanned underwater vehicles. Where the role of the inspection organisation is carried out by other parties 10.6 Where the role of the inspection organisation is carried out by other parties, the Agent shall prepare an outline risk assessment, agreed by the Supervising Engineer, and provide this to the inspection organisation, before commissioning the inspection. 44 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 10. Health and safety 10.7 Where the role of the inspection organisation is carried out by other parties, the inspection organisation shall prepare an operational risk assessment and method statement and submit this to the agent prior to any inspection operation. Operation and maintenance of access gantries 10.8 Prior to using any access gantries which form a permanent part of the structure, the Agent shall check the existence and validity of the operational certificate(s) for access gantries and confirm they cover the proposed inspection activity. 10.9 Inspection and certification of access gantries shall be carried out and issued in accordance with The Institution of Structural Engineers publication The Operation and Maintenance of Bridge Access Gantries and Runways ( IStructE Gantries & Runways [Ref 20.N]). 10.10 Where during the course of an inspection of an access gantry, or at any other time, any defects become apparent, the Agent shall: 1) take any necessary immediate action to secure the safety of workforce and the structure; and, 2) make the defects known to the Overseeing Organisation, with a recommended course of action. Health and safety plans and records 10.11 Agents shall develop written plans and retain records in order to demonstrate compliance with health and safety legislation while planning and carrying out inspections of highway structures. NOTE 1 The following is a rudimentary list of legislation and official guidance that covers some activities and hazards likely to be encountered during the inspection of highway structures at the time of publication. It is not exhaustive nor is it intended to cover every situation: 1) Health and Safety at Work Act 1974 HASAWA 1974 c.37 [Ref 8.N] lays down provisions for employers and employees to control hazards encountered during the course of activities undertaken at work; 2) The Management of Health and Safety at Work Regulations 1999 SI 1999/3242 [Ref 5.N] for the management of health and safety at work. See also 'Working alone, health and safety guidance on the risks of lone working' HSE INDG73 [Ref 17.I]; 3) Workplace (Health, Safety and Welfare) Regulations 1992 (WHSWR 1992) SI 1992/3004 [Ref 7.N]. See also 'Workplace health, safety and welfare, approved code of practice and guidance (HSE L24)' HSE L24 [Ref 19.I]; 4) The Construction (Design and Management) CDM Regulations 2015 ( SI 2015 No. 51 [Ref 9.N]) apply to the whole construction process on all construction projects, from concept to completion. See also 'Managing health and safety in construction. Guidance on Regulations' HSE L153 [Ref 11.I]; 5) Working At Height Regulations 2005 (WAHR 2005) SI 2005/735 [Ref 6.N]. See also 'Working at height. A brief guide (HSE INDG401)' HSE INDG401 [Ref 18.I] and the 'Work at Height, Access and Information Toolkit (WAIT)' https://www.ppe.org [Ref 16.I] that provides guidance to eliminate and control work at height including the selection of appropriate access equipment; 6) The Confined Spaces Regulations 1997 SI 1997/1713 [Ref 10.N]. See also 'Safe work in confined spaces - Approved code of practice and guidance' HSE L101 [Ref 14.I] that provides guidance on how to assess the risk of working within a particular confined space and put precautions in place for work to be carried out safely; 7) The Diving at Work Regulations 1997 SI 1997/2776 [Ref 19.N] – see also 'Commercial diving projects inland/inshore - Approved Code of Practice and Guidance' HSE L104 [Ref 1.I] that provides practical advice and guidance on how to comply with the requirements of the Diving at Work Regulations 1997 and applies to all diving projects conducted in support of civil engineering or marine-related projects inland in Great Britain; 8) The Control of Asbestos Regulations 2012 SI 2012/632 [Ref 15.I]. See also 'Managing and working with asbestos - Control of Asbestos Regulations 2012 - Approved code of practice and guidance' HSE L143 [Ref 10.I] and GG 105 [Ref 2.N]; 45 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 10. Health and safety 9) The Traffic Signs Manual TSM Chapter 8 [Ref 21.N] provides good practice for the signing and marking of obstructions as well as for the temporary traffic control necessitated by such obstructions of the highway; 10) The DfT publication 'Safety at Street Works and Road Works' ( Streetworks CoP [Ref 15.N]) is a concise guide for traffic management arrangements on single carriageways or dual carriageways where the traffic speed is below 50 mph. NOTE 2 This section provides a minimum set of safety requirements for frequently occurring residual risks and hazards associated with inspection activities and their location, proximity and frequency. 46 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 11. Normative references 11. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref 1.N Highways England. CG 302, 'As-built, operational and maintenance records for highway structures' Ref 2.N Highways England. GG 105, 'Asbestos management' Ref 3.N Highways England. CS 454, 'Assessment of highway bridges and structures' Ref 4.N Highways England. CD 127, 'Cross-sections and headrooms' Ref 5.N The National Archives. legislation.gov.uk. SI 1999/3242, 'HEALTH AND SAFETY - The Management of Health and Safety at Work Regulations 1999' Ref 6.N The National Archives. legislation.gov.uk. SI 2005/735, 'HEALTH AND SAFETY - The Work At Height Regulations 2005' Ref 7.N The National Archives. legislation.gov.uk. SI 1992/3004, 'HEALTH AND SAFETY - The Workplace (Health, Safety and Welfare) Regulations 1992' Ref 8.N The National Archives. legislation.co.uk. HASAWA 1974 c.37, 'Health and Safety at Work etc. Act 1974' Ref 9.N The National Archives. legislation.gov.uk. SI 2015 No. 51, 'HEALTH AND SAFETY The Construction (Design and Management) Regulations 2015' Ref 10.N The National Archives. legislation.gov.uk. SI 1997/1713, 'HEALTH AND SAFETY. The Confined Spaces Regulations 1997' Ref 11.N Highways England. CS 125, 'Inspection of traffic signs' Ref 12.N Highways England. GG 101, 'Introduction to the Design Manual for Roads and Bridges' Ref 13.N NHSS 31, 'National Highway Sector Scheme 31 - Bridge Inspector Certification Scheme' Ref 14.N Highways England. GG 102, 'Quality management systems for highway works' Ref 15.N TSO. Streetworks CoP, 'Safety at Street Works and Road Works: A Code of Practice' Ref 16.N Highways England. GD 301, 'Smart motorways' Ref 17.N Highways England. CG 300, 'Technical approval of highway structures' Ref 18.N Highways England. BD 97, 'The Assessment of Scour and Other Hydraulic Actions at Highway Structures' Ref 19.N SI 1997/2776, 'The Diving at Work Regulations 1997' Ref 20.N IStructE. IStructE Task Group. IStructE Gantries & Runways, 'The operation and maintenance of bridge access gantries and runways' Ref 21.N TSO. TSM Chapter 8, 'Traffic Signs Manual Chapter 8 - Traffic Safety Measures and Signs for Road Works and Temporary Situations' Ref 22.N Highways England. CD 361, 'Weathering steel for highway structures' 47 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 12. Informative references 12. Informative references The following documents are informative references for this document and provide supporting information. Ref 1.I HSE. HSE L104, 'Commercial diving projects inland/inshore - Diving at Work Regulations 1997 - Approved Code of Practice and guidance' Ref 2.I HSE. https://hse.gov.uk/construction/, 'Construction hazardous substances: Harmful micro-organisms. ' Ref 3.I Highways England. CD 359, 'Design requirements for permanent soffit formwork' Ref 4.I The National Archives. legislation.gov.uk. SI 1998/2306, 'HEALTH AND SAFETY. The Provision and Use of Work Equipment Regulations (PUWER) 1998' Ref 5.I Highways England. CS 452, 'Inspection and records for road tunnel systems' Ref 6.I TSO. IMHS, 'Inspection Manual for Highway Structures ' Ref 7.I Department for Transport. UK Roads Liaison Group. MHS CoP, 'Management of Highway Structures - Code of Practice' Ref 8.I Highways England. CS 465, 'Management of post-tensioned concrete bridges' Ref 9.I Highways England. CS 470, 'Management of sub-standard highway structures' Ref 10.I HSE. HSE L143, 'Managing and working with asbestos - Control of Asbestos Regulations 2012 - Approved Code of Practice and Guidance' Ref 11.I HSE. HSE L153, 'Managing health and safety in construction. Construction (Design and Management) Regulations 2015. Guidance on Regulations' Ref 12.I BSI. BS EN ISO 9001, 'Quality management systems. Requirements' Ref 13.I Highways England. TS 501, 'Road lighting inspection' Ref 14.I HSE. HSE L101, 'Safe work in confined spaces - Confined Spaces Regulations 1997 - Approved code of practice and guidance' Ref 15.I The National Archives. Legislation.gov.uk. SI 2012/632, 'The Control of Asbestos Regulations' Ref 16.I PPE Media. https://www.ppe.org, 'Work at Height Access and Information Toolkit' Ref 17.I HSE. HSE INDG73, 'Working alone, health and safety guidance on the risks of lone working' Ref 18.I HSE. HSE INDG401, 'Working at height. A brief guide' Ref 19.I HSE. HSE L24, 'Workplace health, safety and welfare. Approved code of practice and guidance' 48 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Appendix A. Risk-based principal inspection intervals A1 Risk-based principal inspection intervals A1.1 Risk assessment procedure This procedure outlines a suitable basis for the risk assessment of intervals between principal inspections as described in Section 8. A1.1.1 Risk assessment parameters The risk assessment uses five categories to cover the parameters used to ascertain the risk score. These categories are: 1) structure type; 2) environment; 3) inspection/assessment; 4) condition; and, 5) consequences. Within each category are the specific assessment criteria which vary depending on the structure type and situation. Table A.1 describes these criteria and gives the assumptions and the principles behind their selection and how they affect the scoring. Whilst it is accepted that these assumptions may not fit every situation, they should nevertheless produce a good indication of the overall level of risk exposure. Engineering judgement should then be used to determine an acceptable interval between principal inspections. A1.1.2 Source of information The risk assessment has been designed such that all the input data to complete the risk assessment is readily available and accessible within the Overseeing Organisation's records management system. Table A.1 suggests sources of information. 49 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.1 Sources of information Assessment parameter Risk factor(s) affected Commentary Source of information Structure type Form P, S, D, C Different structural forms can be expected to experience varying degrees of deterioration and have each been rated accordingly to consider this. (a) Inventory (b) Structure File Material P, S, D, C The primary constituent material will have an impact on the likelihood of deterioration. Historical performance has been evaluated for different construction materials and is reflected in the scoring. (a) Inventory (b) Structure File Age P, C The age of a structure will usually affect the likelihood and rate of deterioration. In general, it would be expected that an older structure approaching the end of its design life will encounter more maintenance issues and hence be more prone to deterioration. Newer structures may encounter initial teething problems before they are considered to be performing optimally. Propensity for obsolescence of components and reduced understanding of some materials and structural forms also increases with age. (a) Inventory (b) Structure File Span / height / headroom / length P, S, C Although every structure has different design requirements, probabilistic analysis shows that bridges with longer spans and retaining walls with greater retained heights, tend to be at a higher risk of failure. Not only is the likelihood increased but also the associated consequence of failure. (a) Inventory (b) Structure File Environment Flooding P, S, C Structures in areas susceptible to flooding should be assessed as having increased risk. (a) Qualitative assessment of the available information that would inform the likelihood of flooding (b) Environment Agency records Inspection / Assessment 50 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.1 Sources of information (continued) Assessment parameter Risk factor(s) affected Commentary Source of information Visual access D Limited visual accessibility to critical elements will reduce the reliability of the general inspections undertaken between principal inspections. (a) Qualitative assessment of the available information on visual accessibility. Latent defects P, D, C Some structure types are more susceptible to containing defects that are not evident during a Principal Inspection for example, post-tensioned concrete bridges with internal grouted tendons. (a) Inventory (b) Structure File Assessments P, S, D, C Where an assessment has been carried out on a structure, a greater degree of confidence can be achieved with regard to the structure's ability to carry load. The findings of the assessment report should give a clear indication of any current load restrictions and any recommended condition factors. Any current load restrictions in place indicate that the current condition of the bridge is below design standard, resulting in a higher potential risk of deterioration. Where definitive records are not available engineering judgement is to be used considering the age of the structure and its performance under current loading regimes. (a) Load Management Records (b) Assessment reports (c) Interim Measures Records Condition Inspector's condition rating P Condition is to be assessed using two criteria. The first is the inspector's subjective condition rating of the structure (ie. good, fair or poor), which should give a good overview of the condition of the structure. (a) Inspection records 51 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.1 Sources of information (continued) Assessment parameter Risk factor(s) affected Commentary Source of information Condition Performance Indicators P Secondly, condition performance indicators, where available, are to be taken into account. These are an objective measure of the physical condition of the highway structures stock, calculated using the severity/extent condition rating system. They are reported for each structure on a scale of 0 to 100, where 0 represents the worst possible condition and 100 represents the best possible condition. 1) Average Condition PI Score, PIav (based on all elements) 2) Critical Condition PI Score, PIcrit (based on the most critical elements only) (a) Condition Performance Indicator Reports Concrete deterioration P Any deterioration of concrete including that due to thaumasite sulphate attack, alkali aggregate reaction, alkali silica reaction and alkali carbonate reaction should be scored (a) Inventory (b) Structure File (c) Inspection records Consequences Load type P, S, C Load type may not have an impact on the likelihood of general deterioration but increased stress ranges in materials during repeated loading cycles increase the probability of fatigue failure. Load type will also have a bearing on the overall consequence of any potential collapse. (a) Load Management Records (b) Assessment reports (c) Interim Measures Records (d) Inspection Records Route supported and obstacle crossed P, S, C These attributes are intended to reflect the importance of the structure within the overall road network in the event of a structural collapse. Inventory Failure mode D, C Brittle failure modes can result in collapse without warning and high consequences whereas ductile modes typically give warning of structural distress. (a) Inventory (b) Assessment reports 52 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals A1.1.3 Scoring system The scoring system is used to determine an indicator of relative risk to support decisions on appropriate intervals between principal inspections. The risk assessment scoring tables consist of the five categories, each containing a number of criteria for which there are several attribute options with an associated score based on the level of risk. A lower score indicates higher risk, whilst a higher score indicates lower risk. The attribute risk scores for each category are summed together to return the actual risk score for a category. In all cases where data are unknown or unobtainable, a conservative approach should be taken by applying the lowest score available. Hence, for a structure with many unknown variables, it is likely that the recommended principal inspection interval will remain at 6 years. In all cases where the attribute returns to a risk score of 'Inspection to remain at 6 years' this means that, irrespective of the final adjusted risk score, the nature of the attribute requires the interval between principal inspections to be 6 years. 53 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.2 Risk scoring for bridges and large culverts Category Criteria Attribute Risk score Uniform box or tubular culvert 4 Framed span - bridges 3 Simply supported 2 Arched 1 Structural form Other or not known 0 In situ reinforced concrete 4 Precast prestressed concrete 4 Steel 3 Brick/masonry/stone 2 In situ mass concrete 2 In situ prestressed concrete 2 Corrugated rolled steel 1 FRP (fibre-reinforce plastics) 1 Timber 1 Constituent material Other 0 0-10 years 2 10-25 years 1 25 years + 0 Age of the structure Not known 0 Greater than minimum maintained headroom 1 Headroom Less than minimum maintained headroom requirement 0 Not known 0 10 m or less 2 10 m to 25 m 1 Structure type Span Greater than 25 m 0 54 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.2 Risk scoring for bridges and large culverts (continued) Category Criteria Attribute Risk score Mild i.e. no exposure to de-icing salts 3 Exposure Moderate i.e. routes with de-icing salts 1 Not known 0 No risk i.e. structure not near or adjacent to waterway 4 Scour Very low risk of scour damage i.e. scour risk rating of 5 2 Not known 0 No risk i.e structure not near or adjacent to waterway 4 Low risk i.e structure is adjacent to / over waterway with low likelihood of flood damage 2 Environment Flooding Not known 0 Full access to all parts of the structure 5 An enhanced general inspection has been completed in the last 6 years and will be undertaken between principal inspections. 4 All parts of the structure visible from a distance (including the use of binoculars) 3 Limited access / view of structure 0 Certain parts of the structure not visible from a distance (including the use of binoculars) 0 Level of visual accessibility during a general inspection Not known 0 Low possibility of latent defects 3 Medium likelihood of latent defects occurring and remaining unnoticed 2 High likelihood of latent defects occurring without any visible secondary effects 0 Inspection and assessment Likelihood of latent defects going unnoticed during a principal inspection Not known 0 55 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.2 Risk scoring for bridges and large culverts (continued) Category Criteria Attribute Risk score Load management, design or assessment give no concerns over capacity of the structure to carry current loading 4 Structural review recommends assessment as low or lesser priority 2 Structural review recommends assessment as medium or higher priority 0 Inspection and assessment (Continued) Assessment No indication of design or assessment capacity of structure 0 Good 3 Fair 2 Condition - inspector's opinion Not known Inspection to remain at 6 years Very good (90-100) 4 Good (80-90) 3 Fair (65-80) 2 Poor (40-65) 0 Condition performance indicator (average score) Not known Inspection to remain at 6 years Very good (90-100) 6 Good (80-90) 4 Fair (65-80) 2 Poor (40-65) 0 Condition performance indicator (critical element score) Not known Inspection to remain at 6 years No 3 Yes Inspection to remain at 6 years Condition Signs of concrete deterioration including TSA, AAR, ASR and ACR Not known 0 56 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.2 Risk scoring for bridges and large culverts (continued) Category Criteria Attribute Risk score Full highway loading and heavy load route 0 Full highway loading 1 Footway/cycleway loading 3 Applied loading Other or not known 0 Motorway 0 A road 2 B road 3 Access / minor route 4 Footway/cycleway 4 River / canal 2 Route supported Other or not known 0 Motorway 0 A road 2 B road 3 Access/minor route 4 Footway/cycleway 4 Disused/natural ground 5 River/canal 2 Obstacle crossed Other or not known 0 Brittle failure 0 Ductile failure 2 Consequences Potential failure mode Other or not known 0 57 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.3 Risk scoring for small-span structures Category Criteria Attribute Risk score Arched 1 Simply supported 2 Uniform box or tubular culvert 4 Walls/invert/roof structurally continuous 2 Structural form Other or not known 0 In situ reinforced concrete 4 Precast reinforced concrete 4 Brick/masonry/stone 3 In situ mass concrete 3 In situ prestressed concrete 3 Corrugated rolled steel 2 Steel 2 FRP/GRP (reinforced plastics) 1 Constituent material Other or not known 0 0-10 years 2 10-25 years 1 25 years + 0 Age of the structure Not known 0 Greater than 3 m deep 3 Between 0.6 m and 3 m 1 Less than 0.6 m deep 0 Approximate cover Not known 0 10 m or less 2 10 m to 50 m 1 Greater than 50 m 0 Structure type Structure length Not known 0 58 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.3 Risk scoring for small-span structures (continued) Category Criteria Attribute Risk score Dry 2 Environment Wet 0 Not known 0 No risk i.e. structure not near or adjacent to waterway 4 Scour Very low risk of scour damage i.e. scour risk rating of 5 2 Not known 0 No risk i.e. structure not near or adjacent to waterway 4 Low risk i.e structure is adjacent to/over waterway with low likelihood of flood damage 2 Moderate/high risk i.e structure is adjacent to/over waterway with medium/high likelihood of flood damage Inspection to remain at 6 years Environment Flooding Not known 0 Full access to all parts of the structure 5 An enhanced general inspection has been completed in the last 6 years and will be undertaken between principal inspections. 4 All parts of the structure visible from a distance (including the use of binoculars) 3 Limited access/view of structure 0 Certain parts of the structure not visible from a distance (including the use of binoculars) 0 Level of visual accessibility during a general inspection Not known 0 Load management, design or assessment gives no concerns over capacity of the structure to carry current loading 4 Structural review recommends assessment as low or lesser priority 2 Structural review recommends assessment as medium or higher priority 0 Inspection and Assessment Assessment No indication of design or assessment capacity of structure 0 59 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.3 Risk scoring for small-span structures (continued) Category Criteria Attribute Risk score Good 3 Fair 2 Condition - inspector's opinion Not known Inspection to remain at 6 years Very good (90-100) 4 Good (80-90) 3 Fair (65-80) 2 Poor (40-65) 0 Condition performance indicator (average score) Not known Inspection to remain at 6 years Very good (90-100) 6 Good (80-90) 4 Fair (65-80) 2 Poor (40-65) 0 Condition performance indicator (critical element score) Not known Inspection to remain at 6 years No 3 Yes Inspection to remain at 6 years Condition Signs of concrete deterioration including TSA, AAR, ASR and ACR Not known Inspection to remain at 6 years Full highway loading and heavy load route 0 Full highway loading 1 Footway/cycleway loading 3 Consequences Applied loading Other or not known 0 60 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.3 Risk scoring for small-span structures (continued) Category Criteria Attribute Risk score A road 2 B road 3 Motorway 0 Other road 3 River / canal 2 Consequences (Continued) Feature affected by collapse Not known 0 61 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.4 Risk scoring for retaining walls Category Criteria Attribute Risk score Cantilever 3 Crib wall 3 Diaphragm wall 2 Gabion wall 3 Gravity 4 Reinforced soil 2 Secant piled 2 Sheet pile 2 Contiguous piled 2 Structural form Other or not known 0 Masonry/brick/blockwork 2 In situ mass concrete 3 In situ prestressed concrete 4 In situ reinforced concrete 4 Precast plain concrete 4 Precast prestressed concrete 4 Precast reinforced concrete 4 Steel 3 Constituent material Other or not known 0 0-10 years 2 10-25 years 1 25 years + 0 Structure type Age of the structure Not known 0 62 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.4 Risk scoring for retaining walls (continued) Category Criteria Attribute Risk score Less than 3 m 4 Between 3 m and 4.5 m 2 Between 4.5 m and 6 m 1 Over 6 m 0 Maximum retained height Not known 0 10 m or less 2 10 m to 50 m 1 Greater than 50 m 0 Structure type (Continued) Length of the retaining wall Not known 0 Mild i.e. no exposure to de-icing salts 3 Moderate i.e. routes with de-icing salts 1 Severe i.e. marine environment Inspection to remain at 6 years Exposure Not known 0 No risk i.e. structure not near or adjacent to waterway 4 Scour Very low risk of scour damage i.e. scour risk rating of 5 2 Not known 0 No risk i.e. structure not near or adjacent to waterway 4 Low risk i.e. structure is adjacent to/over waterway with low likelihood of flood damage 2 Environment Flooding Not known 0 63 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.4 Risk scoring for retaining walls (continued) Category Criteria Attribute Risk score Yes 0 No 2 Signs of deterioration since the last inspection Not known 0 Full access to all parts of the structure 5 An enhanced general inspection has been completed in the last 6 years and will be undertaken between principal inspections. 4 All parts of the structure visible from a distance (including the use of binoculars) 3 Level of visual accessibility during a general inspection Limited access/view of structure 0 Load management, design or assessment gives no concerns over capacity of the structure to carry current loading 4 No indication of design or assessment capacity of structure 0 Assessment needed but no assessment has been undertaken. 0 Inspection and Assessment Assessment Not known 0 Good 3 Fair 2 Condition - inspector's opinion Not known Inspection to remain at 6 years Very good (90-100) 4 Good (80-90) 3 Fair (65-80) 2 Poor (40-65) 0 Condition Condition performance indicator (average score) Not known Inspection to remain at 6 years 64 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.4 Risk scoring for retaining walls (continued) Category Criteria Attribute Risk score Very good (90-100) 6 Good (80-90) 4 Fair (65-80) 2 Poor (40-65) 0 Condition performance indicator (critical element score) Not known Inspection to remain at 6 years No 3 Yes Inspection to remain at 6 years Condition (Continued) Signs of concrete deterioration including TSA, AAR, ASR and ACR Not known 0 Full highway loading and heavy load route 0 Full highway loading 1 Footway/cycleway loading 3 No live load surcharge 4 Applied loading Other or not known 0 A road 2 B road 3 Motorway 0 Other road 3 River/canal 2 Consequences Feature affected by collapse Not known 0 65 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.5 Risk scoring for masts Category Criteria Attribute Risk score Structure Steel 3 Primary material FRP/GRP (reinforced plastics) 1 Other or not known 0 0-5 years 3 5-10 years 2 10-20 years 1 20 years + 0 Age of the mast Not known 0 10 m or less 3 10 m to 15 m 2 Greater than 15 m 1 Height of the mast Not known 0 Mild i.e. no exposure to de-icing salts 3 Environment Exposure Moderate i.e. routes with de-icing salts 1 Not known 0 Yes 0 No 2 Signs of deterioration since the last inspection Not known 0 Yes 0 No 2 Inspection Defects that could affect the structural integrity of the mast Not known 0 66 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.5 Risk scoring for masts (continued) Category Criteria Attribute Risk score Full access to all parts of the structure 5 An enhanced general inspection has been completed in the last 6 years and will be undertaken between principal inspections. 4 All parts of the structure visible from a distance (including the use of binoculars) 3 Limited access/view of structure 0 Not known 0 Inspection (Continued) Level of visual accessibility during a general inspection Certain parts of the structure not visible from a distance (including the use of binoculars) 0 Good 3 Fair 2 Condition - inspector's opinion Not known Inspection to remain at 6 years Very good (90-100) 4 Good (80-90) 3 Fair (65-80) 2 Poor (40-65) 0 Condition performance indicator (average score) Not known Inspection to remain at 6 years Very good (90-100) 6 Good (80-90) 4 Fair (65-80) 2 Poor (40-65) 0 Condition Condition performance indicator (critical element score) Not known Inspection to remain at 6 years 67 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.5 Risk scoring for masts (continued) Category Criteria Attribute Risk score A road 2 B road 3 Motorway 0 Other road 3 River/canal 2 Consequences Feature affected by collapse Not known 0 68 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.6 Risk scoring for sign and signal gantries Category Criteria Attribute Risk score Cantilever gantry 1 Mast arm 1 Portal gantry 2 Structural form Other or not known 0 Steel 2 Concrete 1 FRP (fibre-reinforced plastics) 1 Primary material Other or not known 0 0-5 years 1 5-20 years 1 20-80 years 0 80 years + 0 Age of the gantry Not known 0 Less than 5.7 m 0 Minimum headroom Greater than 5.7 m 1 Not known 0 10 m or less 2 10 m to 20 m 1 Greater than 20 m 0 Structure type Span Not known 0 Mild i.e. no exposure to de-icing salts 3 Moderate i.e. routes with de-icing salts 1 Severe i.e. marine environment 0 Environment Exposure Not known 0 69 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.6 Risk scoring for sign and signal gantries (continued) Category Criteria Attribute Risk score Yes 0 No 2 Signs of deterioration since the last inspection Not known 0 Yes 0 No 2 Defects which could affect the structural integrity of the gantry Not known 0 Full access to all parts of the structure 5 An enhanced general inspection has been completed in the last 6 years and will be undertaken between principal inspections. 4 All parts of the structure visible from a distance (including the use of binoculars) 2 Limited access / view of structure 0 Not known 0 Inspection Level of visual accessibility during a general inspection Certain parts of the structure not visible from a distance (including the use of binoculars) 0 Good 3 Fair 2 Condition - inspector's opinion Not known Inspection to remain at 6 years Very good (90-100) 4 Good (80-90) 3 Fair (65-80) 2 Poor (40-65) 0 Condition Condition performance indicator (average score) Not known Inspection to remain at 6 years 70 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.6 Risk scoring for sign and signal gantries (continued) Category Criteria Attribute Risk score Very good (90-100) 6 Good (80-90) 4 Fair (65-80) 2 Poor (40-65) 0 Condition (Continued) Condition performance indicator (critical element score) Not known Inspection to remain at 6 years Yes 0 No 1 Does the gantry have any electronic displays, e.g. VMS, FMS? Not known 0 Railway 0 Motorway 0 A road 1 B road 2 Importance Feature affected by collapse Not known 0 71 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.7 Risk scoring for service crossings and other structures Category Criteria Attribute Risk score Environmental barrier 3 Soakaway 3 Service tunnel 1 Structure type Other or not known 0 0-5 years 3 5-10 years 2 10-20 years 1 20 years + 0 Structure Age of the structure Not known 0 Mild i.e. no exposure to deicing salts 3 Moderate i.e. routes with deicing salts 1 Severe i.e. marine environment 0 Exposure Not known 0 No risk i.e. structure not near or adjacent to waterway 3 Very low risk of scour damage i.e scour risk rating of 5 2 Scour susceptible i.e.. scour risk rating of 1-4 0 Scour Not known 0 No risk i.e. structure not near or adjacent to waterway 3 Low risk i.e. structure is adjacent to/over waterway with low likelihood of flood damage 2 Moderate/high risk i.e. structure is adjacent to/over waterway with medium/high likelihood of flood damage 0 Environment Flooding Not known 0 72 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.7 Risk scoring for service crossings and other structures (continued) Category Criteria Attribute Risk score Yes 0 No 2 Signs of deterioration since the last inspection Not known 0 Yes 0 No 2 Defects which could affect the structural integrity of the structure Not known 0 Full access to all parts of the structure 3 All parts of the structure visible from a distance (including the use of binoculars) 2 Limited access/view of structure 0 Not known 0 Inspection Level of visual accessibility during a general inspection Certain parts of the structure not visible from a distance (including the use of binoculars) 0 Good 3 Fair 1 Poor 0 Condition Condition - inspector's opinion Not known 0 Railway 0 Motorway 0 A road 1 B road 2 No affect on road/rail network 3 Consequences Feature affected by collapse Not known 0 73 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals A1.2 Risk score evaluation The actual risk score (A) for each category is then analysed against the maximum possible risk score (M) for the category and weighting (W) to produce the adjusted risk score (S) for the particular category. Each of the categories are weighted according to their relative importance. S = A M · W The sum of the adjusted risk scores forms the total risk score (T) of between 0 and 100. T = ∑(S) Table A.8 Risk score evaluation for bridges and large culverts Category Maximum risk score (M) Weighting % (W) Structure type 13 20 Environment 11 17 Inspection and assessment 12 25 Condition 16 20 Consequences 14 18 Table A.9 Risk score evaluation for small span structures Category Maximum risk score (M) Weighting % (W) Structure type 15 25 Environment 10 15 Inspection and assessment 9 20 Condition 16 20 Consequences 6 20 Table A.10 Risk score evaluation for retaining walls Category Maximum risk score (M) Weighting % (W) Structure type 16 20 Environment 11 15 Inspection and assessment 11 25 Condition 16 25 Consequences 7 15 Table A.11 Risk score evaluation for masts Category Maximum risk score (M) Weighting % (W) Structure 9 20 Environment 3 15 Inspection 9 25 Condition 13 25 Consequences 3 15 74 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.12 Risk score evaluation for gantries Category Maximum risk score (M) Weighting % (W) Structure type 8 25 Environment 3 10 Inspection 7 25 Condition 13 25 Importance 3 15 Table A.13 Risk score evaluation for service crossings and other structures Category Maximum risk score (M) Weighting % (W) Structure 6 20 Environment 9 15 Inspection 7 25 Condition 3 25 Consequences 3 15 A1.2.1 Risk rating Once the total risk score has been derived, it can be used to determine the risk rating for the structure (high, medium, low or very low). The risk rating is then used to determine a recommended principal inspection interval in accordance with Tables A.14 to A.19. Table A.14 Risk rating and recommended principal inspection interval for bridges and large culverts Total risk score Risk rating Recommended principal inspection interval 0 ≤ T < 65 High 6 years 65 ≤ T < 75 Medium 8 years 75 ≤ T < 85 Low 10 years 85 ≤ T ≤ 100 Very low 12 years Table A.15 Risk rating and recommended principal inspection interval for small span structures Total risk score Risk rating Recommended principal inspection interval 0 ≤ T < 50 High 6 years 50 ≤ T < 60 Medium 8 years 60 ≤ T < 70 Low 10 years 70 ≤ T ≤ 100 Very low 12 years Table A.16 Risk rating and recommended principal inspection interval for retaining walls Total risk score Risk rating Recommended principal inspection interval 0 ≤ T < 55 High 6 years 55 ≤ T < 65 Medium 8 years 65 ≤ T < 75 Low 10 years 75 ≤ T ≤ 100 Very low 12 years 75 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix A. Risk-based principal inspection intervals Table A.17 Risk rating and recommended principal inspection interval for masts and mast schemes Total risk score Risk rating Recommended principal inspection interval 0 ≤ T < 50 High 6 years 50 ≤ T < 60 Medium 8 years 60 ≤ T < 70 Low 10 years 70 ≤ T ≤ 100 Very low 12 years Table A.18 Risk rating and recommended principal inspection interval for sign/signal gantries Total risk score Risk rating Recommended principal inspection interval 0 ≤ T < 50 High 6 years 50 ≤ T < 60 Medium 8 years 60 ≤ T < 70 Low 10 years 70 ≤ T ≤ 100 Very low 12 years Table A.19 Risk rating and recommended principal inspection interval for service crossings and other structures Total risk score Risk rating Recommended principal inspection interval 0 ≤ T < 50 High 6 years 50 ≤ T < 60 Medium 8 years 60 ≤ T < 70 Low 10 years 70 ≤ T ≤ 100 Very low 12 years A1.2.2 Final assessment and decision The recommended principal inspection interval is used to assist the informed decision on the most appropriate inspection interval, based on all the information available. It does not replace engineering judgement. The final decision on the most appropriate principal Inspection interval is recorded on the risk assessment spreadsheet form which should be signed by the person responsible for preparing the risk assessment, and the supervising engineer. 76 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Appendix B. Details of inspector core competencies B1 Core competence requirements B1.1 Level of competency Competency is assessed in terms of awareness (A), knowledge (K), experience (E) and proficiency (P) against seven headline competencies and their associated sub-competencies. Table B.1 Level of competency Achievement rating Description A Awareness General understanding of the competence, including an appreciation of its relevance. K Knowledge Knowledge and understanding of the competence with an ability to demonstrate its relevance/application. These apply to theory only E Experience Knowledge, understanding and experience of undertaking the competence. P Proficiency Knowledge, understanding and experience of undertaking the competence and competent to advise others. These apply to practical application, as well as theory Note: Core competence requirements C1-C7 for Inspector (I) and Senior Inspector (SI) roles are detailed in tables B.2 to B.8 B1.2 Introduction to inspections Certified inspectors are expected to demonstrate the following competencies. 77 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.2 Introduction to inspections Ref. Outcome/Skill I SI Purpose of inspections Be able to outline the importance of undertaking inspections. K K C1.1 Be able to explain the terms 'safe for use' and 'fit for purpose'. K K Inspector roles, responsibilities and competencies Be able to describe the two inspector roles and their associated responsibilities. K K C1.2 Demonstrate appropriate level of knowledge of the competencies for the different roles. K K Inspection types Be able to explain the different inspection types. K K Demonstrate the importance of having an appropriate inspection regime. K K C1.3 Demonstrate awareness of the range of different special inspections, their function and which factors typically initiate their use. K K C1.4 Codes of practice and guidance Demonstrate appropriate knowledge and use of the relevant structure inspection codes of practice and guidance, e.g. Inspection Manual for Highway Structures. E P B1.3 Structures types and elements / behaviour of structures Certified inspectors are expected to demonstrate competency of common types of structures, their key elements and materials. The competency includes background information and guidance on the fundamentals of structural behaviour, the basic principles of structural mechanics and material properties. Table B.3 Structure types / behaviour of structures Ref. Outcome/Skill I SI Bridges Demonstrate knowledge of the major bridge elements: 1) Superstructure; 2) Substructure; 3) Safety elements; 4) Durability elements; and, 5) Ancillary elements E P Demonstrate knowledge of typical primary and secondary deck element types. E P Demonstrate knowledge of bridge types using span form, construction form and construction material. E P Demonstrate knowledge of water management systems, their function and importance. E P C2.1 Demonstrate knowledge of utilities, private services, signs and lighting. E P 78 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.3 Structure types / behaviour of structures (continued) Ref. Outcome/Skill I SI Other structure types Demonstrate knowledge of the definition of a culvert and the different types. E P Demonstrate knowledge of the definition of a subway and the different types. E P Demonstrate knowledge of the definition of a retaining wall and the different forms. E P Demonstrate knowledge of sign/signal gantries and the different types. E P Demonstrate knowledge of the different mast types and functions. K E C2.2 Demonstrate knowledge of ancillary structures, function and type. K E Structural mechanics Be able to describe the loadings to which bridges are subjected. K E Be able to demonstrate knowledge/experience of the load path for a structure. K E Be able to demonstrate knowledge of modes of failure. K E Demonstrate an understanding of a materials responses to loading. K E C2.3 Demonstrate an understanding of a structures responses to loading. K E Properties of common construction materials Demonstrate an understanding of the properties of the following common primary materials and how they influence the safety, durability and functionality of a specific component and the whole structure. 1) concrete; 2) reinforced concrete; 3) pre-stressed concrete (pre-tensioned and post-tensioned); 4) steel; 5) masonry; and, 6) timber. K E C2.4 Demonstrate an understanding of the following secondary materials: 1) asphalt; and, 2) asbestos. K E C2.5 Properties of specialist construction materials Demonstrate an understanding of the properties of the following materials and how they influence the safety, durability and functionality of a specific component and the whole structure: 1) wrought iron; 2) cast iron; 3) aluminium and its alloys; and, 4) advanced composites. A K 79 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies B1.4 Inspection process Certified inspectors are expected to demonstrate competency of the fundamentals of the inspection process, including scheduling, planning, undertaking, reviewing and interpreting the results. The competency includes consideration of environmental impacts, selection of appropriate access equipment and safe working practices. In addition, it highlights the importance of accurate, reliable data capture and storage post the inspection. Table B.4 Inspection process Ref. Outcome/Skill I SI Scheduling groups of inspections Demonstrate knowledge of relevant documentation which outlines details regarding the frequency of inspections. E P Demonstrate understanding of criteria which can constrain or influence a schedule, for example, confined spaces, use of MEWPs, etc. E P Explain the objectives of each cyclical inspection type. E P Demonstrate ability to monitor progress of inspections against schedules. E P C3.1 Demonstrate experience of access requirements, for example, road space booking, track possessions, waterways access, major events, etc. E P C3.1 (Cont) Demonstrate knowledge of the ability to vary frequency of inspections based on a risk based approach, including special inspections. A K 80 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.4 Inspection process (continued) Ref. Outcome/Skill I SI Planning and preparing for an inspection Explain the function and importance of existing records. E P Demonstrate ability to challenge validity of existing structures records. E P Demonstrate awareness of the importance of the structures current assessed capacity. E P Explain what further information might need to be determined from a pre-inspection visit. E P Demonstrate experience of and an appreciation of the importance of method statements, health and safety considerations and risk assessments in undertaking inspections. E P Demonstrate understanding of aspects to be considered in deciding method of access. This can include: 1) consideration of types of access equipment; 2) restrictions/obstructions caused by equipment; 3) lone working; 4) traffic management requirements; and, 5) routes to be used to and from the site. E P Explain the types of notifications which can be required prior to gaining access. E P Demonstrate an understanding of the range of equipment that can be utilised to undertake an inspection. Range to include: 1) access equipment; 2) personal protective equipment; 3) data recording equipment; and, 4) measuring or inspection equipment. E P Demonstrate an understanding of the environmental considerations to be taken into account, for examples asbestos, bats, badgers. E P Explain the process for planning any testing which may be required as part of an inspection. E P Outline the key aspects for an inspection method statement. E P C3.2 Demonstrate knowledge of how to cost undertaking inspections, the procurement of third party support and budgetary constraints. E P 81 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.4 Inspection process (continued) Ref. Outcome/Skill I SI Performing inspections Describe a practical approach of undertaking an inspection, highlighting the key aspects. E P Explain the reasons and implications of restricted working hours on the process of undertaking an inspection. E P Explain the reasons why good housekeeping whilst on site is imperative and what does it involve. E P Demonstrate an understanding of the need to escalate potential safety critical defects. E P Demonstrate an understanding of substandard parapets and road restraint systems. E P C3.3 Demonstrate an understanding of communication protocols (for example, who is the Principal Contractor etc) and how to set one up. E P Recording inspection findings Demonstrate understanding of the importance of recording defects accurately in terms of type, location, extent, severity and cause. E P Outline different methods used for recording defects. E P Demonstrate knowledge of the prerequisites of a data capture and inspection pro forma. E P Be able to explain the importance of signing off an inspection. E P Demonstrate knowledge of the principals of an element condition rating process. E P Explain the level of detail to be recorded depending upon the type of inspection. E P C3.4 Understand how the accuracy of reporting can affect overall structure condition performance indicators, as well as element condition rating. K E Interpreting inspection findings Demonstrate knowledge of factors which affect whether a structure is safe for use and/or fit for purpose. K E Be able to identify possible safety critical defects and report them within the prescribed timescales. K E Understanding of the need to utilise existing records to help interpret defects E E Demonstrate knowledge of the range of maintenance works which are commonly recommended following an inspection. E E C3.5 Demonstrate an awareness of how defects are managed to identify future maintenance works, based on priority and cost. K E 82 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.4 Inspection process (continued) Ref. Outcome/Skill I SI Maintenance planning process Demonstrate understanding of how the data captured from inspections complements other information held for a structure. K E Explain the importance of up-to-date and comprehensive data on the condition of a structure with respect to its input to maintenance planning. K E Demonstrate an overview of the process for obtaining funding for future maintenance works and how it is value managed. K E C3.6 Demonstrate knowledge of a bridge management system. K E Obligations of current health, safety and environment legislation Demonstrate understanding of the need to minimise health and safety risks to the public and others who may be affected by the work activities. E P Demonstrate understanding of the need to minimise health and safety risks to those actually carrying out the works. E P Demonstrate understanding of the need and breadth of personal protective equipment utilised for undertaking inspections for safe working. E P Demonstrate understanding and practical experience of managing and applying safe systems of work. E P Demonstrate knowledge of relevant legislation and sources of guidance. E P Demonstrate understanding of the need to minimise the impact on the environment, seeking expert advice if necessary to identify and implement appropriate working practices and/or mitigation measures. E P C3.7 Experience of having dealt with: 1) utilising access equipment; 2) moving on foot alongside live carriageways; 3) accessing and exiting from traffic management; 4) working at height; 5) working in, on or adjacent to water, railways etc.; 6) toxic substances, e.g. lead in paint; 7) lone working; 8) night work; and, 9) confined spaces. E P C3.8 Other skills Demonstrate basic knowledge of traffic management practices and relevant reference material, such as Chapter 8 of the Traffic Signs Manual. K K B1.5 Defects descriptions and causes Certified inspectors are expected to demonstrate competency of the importance and requirements for describing and categorising defects. Emphasis is placed on principal defects that are likely to be encountered in concrete structures, steel and steel/concrete composite structures, masonry structures 83 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies and structures built of other materials. Table B.5 Defect descriptions and causes Ref. Outcome/Skill I SI Understanding principal defects Demonstrate understanding of the principal causes of defects including: 1) inadequate structural capacity; 2) substandard clearance; 3) naturally occurring damage, e.g. scour; 4) accidental or deliberate damage; 5) structural materials deterioration; 6) structural elements functionality, e.g. bearings, drainage, expansion joints; 7) failure of water management systems; 8) adequacy and function of parapets and vehicle restraint systems. E P Demonstrate understanding of the implications of deterioration. E P Demonstrate understanding of issues that cause collapses or structure closures, for example, erosion, scour, bridge strikes. K K Demonstrate knowledge of bridge specific defects. E P Demonstrate knowledge of culvert specific defects. E P Demonstrate knowledge of retaining wall specific defects. E P C4.1 Demonstrate knowledge of sign/signal gantry and mast specific defects. K E Concrete defects Demonstrate knowledge of defects caused by structural distress. E P Demonstrate knowledge of defects arising due to material nature. E P Demonstrate knowledge of defects caused by external agents, e.g. reinforcement corrosion, thaumasite sulphate attack. E P Demonstrate knowledge of defects caused by accidental or deliberate damage. E P Demonstrate knowledge of defects due to construction or detailing errors. E P Demonstrate knowledge of defects associated with protective coatings and repair systems. E P Demonstrate knowledge of minor defects, e.g. defects which generally only affect the visual appearance of the concrete. E P Demonstrate knowledge of defects that can occur in pre-stressed concrete. E P C4.2 Demonstrate knowledge of defects that can occur in post-tensioning systems. K E 84 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.5 Defect descriptions and causes (continued) Ref. Outcome/Skill I SI Steel defects Demonstrate knowledge of defects caused by structural distress. E P Demonstrate knowledge of defects arising due to material nature. E P Demonstrate knowledge of defects instigated by external agents, e.g. bimetallic corrosion. E P Demonstrate knowledge of defects caused by accidental or deliberate damage. E P Demonstrate knowledge of defects arising due to fabrication errors, e.g. poor welds. E P Demonstrate knowledge of defects associated with protective systems. E P Demonstrate knowledge of defects associated with closed members. E P Demonstrate knowledge of defects associated with corrugated steel buried structures. E P C4.3 Demonstrate knowledge of defects which affect the whole system, e.g. beams with jack arches. E P Masonry defects Demonstrate knowledge of defects caused by structural distress. E P Demonstrate knowledge of defects arising due to material nature. E P Demonstrate knowledge of defects instigated by external agents, e.g. frost, vegetation. E P Demonstrate knowledge of defects caused by accidental or deliberate damage. E P C4.4 Demonstrate knowledge of defects arising due to alterations to masonry structures, e.g. concrete saddle etc. E P C4.5 Defects in miscellaneous materials Demonstrate appropriate level of awareness of defects which can occur in other materials, including: 1) cast iron; 2) wrought iron; 3) aluminium; 4) timber; 5) advanced composites; and, 6) wire rope. K K B1.6 Investigation and testing Certified inspectors are expected to demonstrate competency of the range of different testing techniques available. A candidate is required to understand the purpose of undertaking testing, what it involves, the outputs and any other relevant considerations. 85 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.6 Investigation and testing Ref. Outcome/Skill I SI The testing process Demonstrate an understanding of the need and purpose of testing, and when it is appropriate. K K Demonstrate an understanding of the different investigations and testing to examine: 1) structural arrangement and hidden defects; 2) distortion and movement; 3) material properties; 4) deterioration activity; 5) deterioration rate; 6) deterioration cause or potential. K K Explain what is required in developing an effective testing programme. 1) Setting objectives of testing. 2) Identification of testing options. 3) Appraisal of testing options. 4) Monitor and supervise testing. 5) Evaluate results. 6) Recommendations for corrective action. A K Demonstrate knowledge of investigation processes, e.g. trial holes. K K C5.1 Demonstrate awareness of the procurement processes for engaging specialist services. A K Common testing techniques Demonstrate knowledge of common testing techniques, such as: 1) decontamination survey; 2) cover surveys; 3) half-cell potential surveys; 4) strain gauges; 5) carbonation test; 6) chloride/sulfate/alkali content; 7) ultrasonic testing; 8) coring; and, 9) paint film thickness measurements. K K C5.2 Demonstrate knowledge of limitations of investigations and tests. A K B1.7 Repair techniques Certified inspectors are expected to demonstrate competency of the importance of understanding the range of repair techniques available. 86 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.7 Repair techniques Ref. Outcome/Skill I SI C6.1 Repair techniques for concrete structures Demonstrate knowledge of the principal repair techniques for concrete structures. Knowledge to include (but not limited to): 1) materials used for repairs (e.g. sprayed concrete, hand-applied cementitious mortars, epoxy resins); 2) methods for inhibiting corrosion (e.g. cathodic protection, impregnation, surface treatments); 3) strengthening methods (e.g. plate bonding, composite column wrapping). K K C6.2 Repair techniques for metal structures Demonstrate knowledge of the principal repair techniques for metal structures. Knowledge to include (but not limited to): 1) repairs by plating; 2) member replacement; 3) protective coatings and paints, such as epoxy resins and polyurethane; and, 4) heat straightening. K K C6.3 Repair techniques for masonry structures Demonstrate knowledge of the principal repair techniques for masonry structures. Knowledge to include (but not limited to): 1) repointing/brickwork repairs; 2) sprayed concrete; 3) retrofitting of reinforcement; 4) anchors; 5) concrete saddle/relieving slabs; and, 6) stitching. K K C6.4 Repair techniques for other structures, e.g. timber Demonstrate knowledge of the principal repair techniques for other materials. K K Importance of routine maintenance Demonstrate knowledge of the importance of undertaking routine maintenance. K K C6.5 Demonstrate an understanding of the importance of balancing essential preventative maintenance works. K K 87 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.7 Repair techniques (continued) Ref. Outcome/Skill I SI C6.6 Recommending appropriate repairs Demonstrate experience of recommending repairs appropriate to the identified defects. E P B1.8 General aptitude Certified inspectors are expected to demonstrate competency of the general aptitude skills required by an inspector. Table B.8 General aptitude Ref. Outcome/Skill I SI Practical aptitude Be able to demonstrate ability to make sound and prudent judgements. P P Demonstrate excellent attention to detail. P P Be able to work to deadlines. P P C7.1 Be able to appreciate one's own capability and scope of knowledge. P P Working with people Demonstrate experience of having worked successfully in a team. P P C7.2 Demonstrate experience of having engaged successfully with third parties and public. P P Communication skills Be able to interpret drawings and reports. P P Be able to draw clear sketches. P P Be able to write reports. P P Be able to communicate verbally in a clear and comprehensive way. P P Be able to demonstrate proficiency in communicating findings from an inspection. P P C7.3 Demonstrate range of IT skills. E P Personal skills Demonstrate self-motivation. P P Be able to decide and set priorities. P P Be able to take decisions and have confidence to challenge a situation/decision if necessary. P P C7.4 Demonstrate understanding of knowing one's limitations. P P 88 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Appendix B. Details of inspector core competencies Table B.8 General aptitude (continued) Ref. Outcome/Skill I SI Obligations of current health and safety legislation Demonstrate knowledge and understanding of current health and safety legislation obligations. P P Demonstrate a positive attitude towards health and safety. P P Demonstrate ability to develop working practices that promote safety and secure the compliance of subordinates. P P C7.5 Demonstrate knowledge and understanding of the importance of method statements and risk assessments. P P Management/supervision Demonstrate ability to manage and motivate teams. K P Demonstrate ability to advise and present recommendations to others. K P Identify resources required for an inspection. E P C7.6 Ensure that inspection activity complies with the appropriate contractual and legal requirements. K P 89 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 © Crown copyright 2021. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 450 England National Application Annex to CS 450 Inspection of highway structures (formerly BD 63/17) Version 0.0.1 Summary This National Application Annex sets out the Highways England-specific requirements for inspection of its highway structures. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated Highways England team. The email address for all enquiries and feedback is: Standards_Enquiries@highwaysengland.co.uk This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Contents Contents Release notes 2 Foreword 3 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction 4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abbreviations 5 Terms and definitions 6 E/1. General 7 General requirements (CS 450, 2.2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Extent of inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Management and planning of maintenance inspections (CS 450, 4.1 and 4.2) . . . . . . . . . . . . . . . . . 7 Inspection frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Scheduling inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Records of maintenance inspections (CS 450, 5.3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Risk-based principal inspection intervals (CS 450, 8.1 and 8.8) . . . . . . . . . . . . . . . . . . . . . . . . . 7 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Risk assessment forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Structures inspectors competencies and certification (CS 450, 9.1) . . . . . . . . . . . . . . . . . . . . . . . 8 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 E/2. Inspection of sign gantries and signal gantries 9 General requirements (CS 450, 2.2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Gantries with handrails less than 1100 mm high . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 E/3. Normative references 11 1 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0.0.1 April 2021 England NAA Incremental change to notes and editorial updates (April 2021) Minor editorial changes only. Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0 March 2020 2 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Foreword Foreword Publishing information This document is published by Highways England This document supersedes BD 63/17, which is withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 3 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Introduction Introduction Background This National Application Annex gives Highways England-specific requirements for the management of the inspection of its highways structures. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 2.N] apply to this document. 4 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Abbreviations Abbreviations Abbreviation Definition IAMIS Integrated asset management information system SMIS Structures management information system TAA Technical Approval Authority 5 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Terms and definitions Terms and definitions Term Definition Asset information management system of the Overseeing Organisation In England this is the Integrated Asset Management Information System (IAM IS) 6 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 E/1. General E/1. General General requirements (CS 450, 2.2) Extent of inspection E/1.1 All parts of sign and signal gantries including significant attachments and gantry equipment shall be inspected in accordance with Section E/2. Management and planning of maintenance inspections (CS 450, 4.1 and 4.2) Inspection frequency E/1.2 Inspection schedules shall be varied as detailed in Table E/1.2. Table E/1.2 Variations to schedule of inspection in Table 4.1 Structure type First PI First GI Subsequent PIs Sign gantry and signal gantry Year 2 Year 4 6 year interval Mast Year 2 Tear 4 6 year interval Scheduling inspections E/1.3 The programme shall also show all inspections involving access to railway property for 24 months ahead. Records of maintenance inspections (CS 450, 5.3) Introduction E/1.4 Inspection records shall be recorded on the Integrated Asset Management Information System (IAM IS) in accordance with the guidance for the system. NOTE Guidance on the the format of inspection records in IAM IS is given in the supporting documents and training material for the system. Risk-based principal inspection intervals (CS 450, 8.1 and 8.8) Introduction E/1.5 Section 8 of CS 450 [Ref 1.N] shall be used to determine risk based principal inspection intervals. Risk assessment forms E/1.6 The risk assessment spreadsheet forms for England shall be used. E/1.6.1 The methodology in Appendix A of CS 450 [Ref 1.N], on which the spreadsheet is based, may be incorporated into other systems provided the following provisions are met: 1) the alternative system is certified by the provider for accuracy, such that the same results are achieved; 2) the Supervising Engineer recommends relevant procedures have been followed and that the alternative system is suitable; and, 3) the alternative system is subject to overall agreement with the TAA. NOTE 1 The spreadsheet and forms are available at the same web page as this standard. NOTE 2 Separate risk assessment forms have been developed for each of the following structure types: 1) bridges and large culverts; 2) small-span structures; 7 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 E/1. General 3) retaining walls; 4) masts and mast schemes; 5) sign/signal gantries; and, 6) service crossings and other structures. E/1.6.2 For multi-span bridges a single risk assessment may be carried out using a combination of the worst criteria across all spans. This, however, is likely to result in a conservative score. Alternatively, each individual span may be assessed separately, with the lowest scoring span (most conservative) being used to determine the most appropriate principal inspection interval for the structure. Structures inspectors competencies and certification (CS 450, 9.1) Introduction E/1.7 Section 9 shall be used to define the structure inspectors competencies and certification requirements. 8 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 E/2. Inspection of sign gantries and signal gantri... E/2. Inspection of sign gantries and signal gantries General requirements (CS 450, 2.2) E/2.1 All parts of sign and signal gantries including significant attachments and gantry equipment shall be inspected for defects. NOTE 1 Typical significant attachments and gantry equipment include: 1) signs; 2) automatic signals and variable message signs; 3) CCTV cameras; 4) speed cameras; 5) control equipment boxes; and, 6) wiring and cable trays. NOTE 2 Common problems on gantries constructed between 2009 and 2016 include: 1) weld failures to the upper aluminium pivot trunnion on matrix lane signs giving rise to extensive remedial work including the installation of some secondary restraints; 2) failure of gantry equipment fixings when combined with lack of structural redundancy in remaining fixings, resulting in equipment falling onto the carriageway; 3) non-access gantries with sign support frames suffering failure of the supporting frame structure causing it to fall onto the carriageway; 4) structural bolted connections found to have loose or missing bolts; 5) loosening of the fixings, possibly due to vibration; 6) defects to joints can include evidence of movement, bolt distortion and structure distortion; 7) plastic cable ties locating aluminium mesh to walkways on lattice type gantries degrading and failing, resulting in the mesh being lost or damaged and needing to be replaced. Some of these ties have been known to have a life as short as two years.; 8) aluminium pop rivets used to attach small signs to gantries and in contact with steel corroding and failing, allowing a sign to fall. Locations of pop rivets can include fixing signs, cover plates or cladding to the gantry.; 9) structural bolts to many cantilever gantries were masked by tape and were incorrectly installed with large slotted holes without suitable structural washers, and have had to be replaced; and, 10) insecure cable trays and cables. E/2.1.1 Any protective covering to structural members or connections should be removed and replaced to allow inspection of all components and joints, if this can be safely achieved, or otherwise be noted for appropriate action. E/2.1.2 Insecure cable trays and cables should be secured during the inspection, if this can be safely achieved, or otherwise be noted for appropriate action. E/2.2 All fixings shall be inspected for corrosion, security and, if plastic, for UV degradation. E/2.2.1 Where plastic cable ties have not been replaced by a hook type metal mechanical fixing then the ties should be recorded and reported for remedial works. E/2.3 Frames to any matrix lane signs over each lane shall be inspected for defects. NOTE Defects can include evidence of any excess play, weld fracture or other problems with the pivot mechanism and associated components. E/2.4 Aluminium pop rivets shall be inspected for corrosion, particularly bi-metallic corrosion at the interface of dissimilar metals. 9 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 E/2. Inspection of sign gantries and signal gantri... E/2.4.1 Any recommendations to provide replacement fastenings should be of a type that do not cause bi-metallic corrosion at the fastening, for example nickel copper alloy rivets that are non-reactive with steel or aluminium. E/2.5 Access walkways shall be inspected for trip hazards and be subject to appropriate reporting and management. NOTE Appropriate management can include removal of the object or risk if this can be safely achieved during the inspection. E/2.6 Signs, electrical equipment and any cover screens shall be inspected for any apparent or possible defects. E/2.7 During the inspection of a sign or signal gantry, where items which could fall or be dislodged from the gantry are identified, appropriate measures shall be taken as an immediate risk to public safety. NOTE Appropriate measures in E/2.7 can include removal of the object or risk if this can be safely achieved during the inspection. Gantries with handrails less than 1100 mm high E/2.8 Where the handrail on a sign or signal gantry is less than 1100 mm the inspector shall: 1) record the height in the inspection report and the register of constraints for the structure; and, 2) recommend appropriate actions to bring the handrail up to standard or to install suitable safety provisions. NOTE Sign and signal gantries have been built to varying standards and consequently not all gantries have handrails to the current standard height of 1100 mm. E/2.8.1 Any recommended maintenance actions should be subject to a risk assessment and be subject to incorporation within other programmed activities. NOTE Raising the height of handrails can obscure the view of a sign. 10 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 E/3. Normative references E/3. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref 1.N Highways England. CS 450, 'Inspection of highway structures' Ref 2.N Highways England. GG 101, 'Introduction to the Design Manual for Roads and Bridges' 11 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 © Crown copyright 2021. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 450 Northern Ireland National Application Annex to CS 450 Inspection of highway structures (formerly BD 63/17) Version 0.0.1 Summary This National Application Annex contains the Department for Infrastructure, Northern Ireland-specific requirements for inspection of its highway structures. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated team in the Department for Infrastructure, Northern Ireland. The email address for all enquiries and feedback is: dcu@infrastructure-ni.gov.uk This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Contents Contents Release notes 2 Foreword 3 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction 4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abbreviations 5 Terms and definitions 6 NI/1. Northern Ireland National Application Annex 7 General requirements [CS 450, 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Extent of inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Management and reporting of risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Resulting actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Maintenance inspections [CS 450, 3] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Inspection types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Safety inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 General inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Special inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Management and planning of maintenance inspections [CS 450, 4] . . . . . . . . . . . . . . . . . . . . . . . 8 Preparation of inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Records of maintenance inspections [CS 450, 5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Records for principal inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Acceptance inspections and records [CS 450, 6] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Alternative means of access [CS 450, 7] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Risk-based principal inspection intervals [CS 450, 8] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Record management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Structures inspectors' competencies and certification [CS 450, 9] . . . . . . . . . . . . . . . . . . . . . . . . 9 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 NI/2. Normative references 10 1 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0.0.1 April 2021 Northern Ireland NAA Incremental change to notes and editorial updates Minor editorial amendments only. Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0 March 2020 2 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Foreword Foreword Publishing information This document is published by Highways England on behalf of the Department for Infrastructure, Northern Ireland This document supersedes BD 63/17, which is withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 3 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Introduction Introduction Background This National Application Annex gives Department for Infrastructure, Northern Ireland, specific requirements related to the management of the inspection of its structures and applies to all roads in Northern Ireland. References in this document to organisations, and legislation etc. is deemed to refer to the Northern Ireland equivalent where appropriate. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 3.N] apply to this document. 4 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Abbreviations Abbreviations Abbreviation Definition SMS-R The Department's Structures Management System-Roads TAA Technical Approval Authority 5 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Terms and definitions Terms and definitions Term Definition Structures Management System-Roads (SMS-R) Asset information management system of the Overseeing Organisation 6 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 NI/1. Northern Ireland National Application Annex NI/1. Northern Ireland National Application Annex General requirements [CS 450, 2] Extent of inspection NI/1.1 The following exceptions given in Table NI/1.1 shall apply. Table NI/1.1 Extent of inspection according to the structure type Structure type Definition Extent of inspection Bridge, buried structure, subway underpass, culvert and any other similar structure As per Table 2.1 except: 1) all structures of span 3 m and greater; 2) bridges/culverts 1.8 m to 3 m span if cover to road surface is less than 1 m; 3) multi-span bridges/culverts where the cumulative span is greater than or equal to 5m, if cover to road surface is less than 1 m; 4) corrugated metal culverts 0.9 m or more in span; and, 5) pedestrian subways. As per Table 2.1 Earth-retaining structure As per Table 2.1, but greater than 1.5 m As per Table 2.1 Reinforced/strengthened soil/fill structure with hard facings As per Table 2.1, but greater than 1.5 m As per Table 2.1 Third party structures As per Table 2.1, but add third party masts for camera, radio, speed camera and telecommunication transmission equipment etc As per Table 2.1 NOTE: For third party masts for camera, radio, speed camera and telecommunication transmission equipment etc. refer to third party structures. 7 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 NI/1. Northern Ireland National Application Annex Management and reporting of risks Resulting actions NI/1.2 Any instances of structural deterioration or behaviours likely to indicate a reduction in carrying capacity or safety shall be reported immediately to the Department's Divisional Office. Formal documentation is not required. Maintenance inspections [CS 450, 3] Inspection types NI/1.3 The inspection procedures defined in this National Application Annex and the Inspection Manual for Highway Structures IMHS [Ref 2.N] shall be used. Safety inspection NI/1.4 Safety inspections shall be undertaken as part of the highway safety inspection regime. General inspection NI/1.5 General inspections shall include approach/departure safety fences and connections. Special inspection NI/1.6 All special inspections shall be agreed with the Overseeing Organisation before being implemented by the Agent. Management and planning of maintenance inspections [CS 450, 4] Preparation of inspections NI/1.7 Previous general and principal inspection records shall be reviewed before the forthcoming inspection to identify any long standing issues. NI/1.8 Where they exist for a structure, the records described in the structure/maintenance manual or as described in CG 302 [Ref 1.N] shall be referred to prior to carrying out a principal inspection. NI/1.9 Notification of incomplete inspections and discussions around this shall be with the Overseeing Organisation and not the Technical Approval Authority (TAA). Records of maintenance inspections [CS 450, 5] Introduction NI/1.10 Inspections shall be recorded in accordance with procedures described in the Inspection Manual for Highway Structures IMHS [Ref 2.N]. NI/1.11 Inspection records shall be recorded on the Structures Management System-Roads (SMS-R) in accordance with the guidance for the system. NOTE The current reporting format for general and principal inspections can be obtained from the Overseeing Organisation. NI/1.11.1 Formal documentation should not be provided for safety inspections. Records for principal inspection NI/1.12 The Agent shall: 1) check the information held in the Structures Management System-Roads (SMS-R); 2) update SMS-R if errors and/or missing data is identified; and, 3) record any significant change or deterioration since the last principal inspection. 8 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 NI/1. Northern Ireland National Application Annex Acceptance inspections and records [CS 450, 6] Introduction NI/1.13 Issues relating to acceptance inspections shall be referred to the Overseeing Organisation. NI/1.14 Where any approval or discussion is required with Technical Approval Authority (TAA) this shall be with the Overseeing Organisation. Alternative means of access [CS 450, 7] NI/1.15 Where any approval or discussion is required with TAA this shall be with the Overseeing Organisation. Risk-based principal inspection intervals [CS 450, 8] Introduction NI/1.16 Risk-based principal inspection intervals shall not apply in Northern Ireland. NI/1.17 The Overseeing Organisation's policy shall be used to alter the interval between principal inspections. NOTE The policy can be obtained from the Overseeing Organisation. Record management NI/1.18 Where a longer principal inspection interval has been agreed the relevant information shall be recorded on the Structures Management System-Roads (SMS-R). Structures inspectors' competencies and certification [CS 450, 9] Introduction NI/1.19 The competence and certification requirements shall apply in full to all inspectors except those department staff who have otherwise been deemed competent in accordance with department policy. 9 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 NI/2. Normative references NI/2. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref 1.N Highways England. CG 302, 'As-built, operational and maintenance records for highway structures' Ref 2.N TSO. IMHS, 'Inspection Manual for Highway Structures ' Ref 3.N Highways England. GG 101, 'Introduction to the Design Manual for Roads and Bridges' 10 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 © Crown copyright 2021. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 450 Scotland National Application Annex to CS 450 Inspection of highway structures (formerly BD 63/17) Version 0.0.1 Summary This National Application Annex contains the Transport Scotland-specific requirements for inspection of its highway structures. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated Transport Scotland team. The email address for all enquiries and feedback is: TSStandardsBranch@transport.gov.scot This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Contents Contents Release notes 2 Foreword 3 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction 4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abbreviations 5 Terms and definitions 6 S/1. Scotland National Application Annex 7 Scope [CS 450, 1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Aspects covered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 General requirements [CS 450, 2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Extent of inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Maintenance inspections [CS 450, 3] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Safety inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Principal inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Special Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Agreement and reviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Management and planning of maintenance inspections [CS 450, 4] . . . . . . . . . . . . . . . . . . . . . . . 8 Inspection programmes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Scheduling inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Preparation of inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Notification of incomplete inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Records of maintenance inspections [CS 450, 5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Records for safety inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Records for general inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Records for principal inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Acceptance inspections and records [CS 450, 6] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Defects liability inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Risk-based principal inspection intervals [CS 450, 8] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Structures inspectors competencies and certification [CS 450, 9] . . . . . . . . . . . . . . . . . . . . . . . . 9 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 S/2. Normative references 10 S/3. Informative references 11 1 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0.0.1 April 2021 Scotland NAA Incremental change to notes and editorial updates Minor editorial changes only. Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0 March 2020 2 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Foreword Foreword Publishing information This document is published by Highways England on behalf of Transport Scotland. This document supersedes BD 63/17, which is withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 3 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Introduction Introduction Background This National Application Annex gives Transport Scotland, specific requirements related to the management of the inspection of its structures. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 2.N] apply to this document. 4 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Abbreviations Abbreviations Abbreviation Definition SMS Transport Scotland Structures Management System TM Traffic management 5 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 Terms and definitions Terms and definitions Term Definition Bridges section he part of the organisation responsible for highway structures in Transport Scotland Transport Scotland Structures Management System (SMS) the asset information management system of the Overseeing Organisation 6 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 S/1. Scotland National Application Annex S/1. Scotland National Application Annex Scope [CS 450, 1] Aspects covered S/1.1 For structures with particular requirements the inspection regime is defined in the operation and maintenance manuals. Otherwise the Agent shall agree the appropriate inspection regime with Bridges Section. General requirements [CS 450, 2] Extent of inspection S/1.2 The following exceptions given in Table SI/1.7 shall apply. Table S/1.2 Variations to extent of inspection according to structure type Structure type Definition Extent of inspection Bridge, buried structure, subway underpass, culvert and any other similar structure As per Table 2.1, but greater than or equal to 0.9 m As per Table 2.1 for: all structures greater than or equal to 3-m span, culverts 2-m to 3-m span, or multi-cell culverts where the cumulative span is greater than or equal to 5 m, corrugated metal culverts 0.9 m or more in span, pedestrian subways. Earth retaining structure As per Table 2.1, but greater than 1.5 m As per Table 2.1 Reinforced/strengthened soil/fill structure with hard facings As per Table 2.1, but greater than 1.5 m As per Table 2.1 Sign gantry and signal gantry As per Table 2.1, but including large variable matrix signs Structural aspects of large sign/signal gantries and large variable matrix signs Maintenance inspections [CS 450, 3] Safety inspection Definition S/1.3 Safety inspections shall include reactive scour inspections. Frequency S/1.4 Safety inspections shall be carried out in accordance with contract requirements. Principal inspection Definition S/1.5 Principal inspections shall be carried out in accordance with the Transport Scotland Structures Manual TS SM [Ref 3.N]. S/1.6 The following tasks shall be undertaken at each principal inspection: 1) thickness testing of metal parapets at representative sample locations (e.g. post bases and rail connections) at a rate not less than one per parapet. A drawing indicating test locations is to be included in the principal inspection report.; 7 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 S/1. Scotland National Application Annex 2) probing for scour, in accordance with the scour management strategy and flood risk management plan; and, 3) concrete investigations where this is recommended by the Agent and agreed with the Overseeing Organisation. S/1.6.1 Where results from thickness testing of metal parapets show they have significantly deteriorated, testing should be undertaken for each post and alternate rail connection with each post. Special Inspection Agreement and reviews S/1.7 The extent of the detailed investigations, the methods to be used and reporting requirements shall be agreed with bridges section. Management and planning of maintenance inspections [CS 450, 4] Inspection programmes Scheduling inspections S/1.8 The Agent shall enter the proposed and actual date of the general and principal inspections on the Transport Scotland Structures Management System (SMS). NOTE 1 The SMS provides reports on annual programmes, showing any backlog from previous years. NOTE 2 The 2-year and 6-year cyclic programme for general and principal inspections are held in the SMS. Preparation of inspections S/1.9 Where records exist for a structure, the records described in CG 302 [Ref 1.N] shall be referred to prior to carrying out a principal inspection. Notification of incomplete inspections S/1.10 The Agent shall record any hidden features or areas which cannot be inspected and state why they cannot be inspected. S/1.11 The Agent shall provide details of the work required to access the hidden features/areas and the associated costs. Records of maintenance inspections [CS 450, 5] Introduction S/1.12 The Agent shall: 1) record the date of the previous general or principal inspection in the SMS; 2) include comments on defects reported in the previous general or principal inspection report and any works carried out since the last inspection; 3) include photographs showing a scale for all defects with a maintenance priority of 3 and above; 4) cost estimates are to be provided for all defects with a maintenance priority ranking of 3 and above, including access method and TM requirements; and, 5) prioritise defects for inclusion in a maintenance programme. NOTE Refer to Transport Scotland Structures Manual TS SM [Ref 3.N] for further guidance. The manual sets out which priority defect records require 'work required' and 'costs' to be entered. S/1.13 Inspection records shall be recorded on the Transport Scotland Structures Management System (SMS). 8 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 S/1. Scotland National Application Annex Records for safety inspection S/1.14 Safety inspections shall be recorded in accordance with contract requirements. Records for general inspection S/1.15 General inspections shall be recorded on forms generated in the SMS. Records for principal inspection S/1.16 In addition to the requirements for records of maintenance inspections Agents shall also provide: 1) a current general arrangement drawing showing the location of the photographs; 2) headroom measurements and the date the headroom was measured; and, 3) the findings of concrete investigations when the principal inspections are carried out. Including the year of an initial concrete investigation or the year of the most recent concrete monitoring investigation. S/1.16.1 The general arrangement drawing should include a plan, elevation and cross section. S/1.16.2 The findings of concrete investigations should be submitted with principal inspection records to Bridges Section. S/1.17 When carrying out a principal inspection, the Agent shall check, amend and update the information held in the SMS. S/1.17.1 A full inventory report should be called up on the SMS and studied prior to and during principal inspections to identify and correct any errors and omissions. S/1.18 Input of missing data and correction of errors in the SMS shall be carried out as per contractual timescales. Acceptance inspections and records [CS 450, 6] Introduction S/1.19 Issues relating to acceptance inspections shall be referred to bridges section. Defects liability inspection S/1.20 The joint inspection at the end of the defect liability period (or any such defect rectification period as defined in the contract) constitutes the equivalent of an initial principal inspection and shall be reported using the SMS principal inspection form. Risk-based principal inspection intervals [CS 450, 8] Introduction S/1.21 Section 8 shall not be used for inspections for Transport Scotland. S/1.22 Principal inspection intervals for Transport Scotland shall not be increased. Structures inspectors competencies and certification [CS 450, 9] Introduction S/1.23 Section 9 shall not be applicable to work for Transport Scotland, unless specifically applied by contract. NOTE Transport Scotland inspector competence requirements are given in TS IA 46/16 [Ref 1.I]. 9 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 S/2. Normative references S/2. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref 1.N Highways England. CG 302, 'As-built, operational and maintenance records for highway structures' Ref 2.N Highways England. GG 101, 'Introduction to the Design Manual for Roads and Bridges' Ref 3.N Transport Scotland. TS SM, 'Transport Scotland Structures Manual' 10 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.0.1 S/3. Informative references S/3. Informative references The following documents are informative references for this document and provide supporting information. Ref 1.I Transport Scotland. TS IA 46/16, 'Structures Inspector Competencies and Certification (Interim Amendment)' 11 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 © Crown copyright 2021. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 Design Manual for Roads and Bridges Highway Structures & Bridges Inspection & Assessment CS 450 Wales National Application Annex to CS 450 Inspection of highway structures (formerly BD 63/17) Version 0.1.0 Summary This National Application Annex gives the Welsh Government-specific requirements for inspection of its highway structures. Feedback and Enquiries Users of this document are encouraged to raise any enquiries and/or provide feedback on the content and usage of this document to the dedicated Welsh Government team. The email address for all enquiries and feedback is: Standards_Feedback_and_Enquiries@gov.wales This is a controlled document. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Contents Contents Release notes 2 Foreword 3 Publishing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Contractual and legal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction 4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Assumptions made in the preparation of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abbreviations 5 Terms and definitions 6 W/1. Wales National Application Annex 7 General requirements [CS 450, 2.1] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Extent of inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Management and planning of maintenance inspections [CS450, 4.1] . . . . . . . . . . . . . . . . . . . . . . 7 Inspection Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Management and reporting of risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Records of maintenance inspections [CS 450, 5.2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Acceptance inspections and records [CS 450, 6.1, 6.2.1, 6.3, 6.16, 6.19] . . . . . . . . . . . . . . . . . . . . 7 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Pre-opening inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Defects liability inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Risk-based principal inspection intervals [CS 450, 8.1, 8.2, 8.4, 8.6] . . . . . . . . . . . . . . . . . . . . . . 7 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Structures inspectors' competencies and certification [CS 450, 9.1] . . . . . . . . . . . . . . . . . . . . . . . 8 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 W/2. Normative references 9 1 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Release notes Latest release notes Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0.1.0 April 2021 Wales NAA Incremental change to requirements New requirement and Note inserted at W/1.2. Previous versions Document code Version number Date of publication of relevant change Changes made to Type of change CS 450 0 March 2020 2 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Foreword Foreword Publishing information This document is published by Highways England on behalf of the Welsh Government. This document supersedes BD 63/17, which is withdrawn. Contractual and legal considerations This document forms part of the works specification. It does not purport to include all the necessary provisions of a contract. Users are responsible for applying all appropriate documents applicable to their contract. 3 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Introduction Introduction Background This National Application Annex gives the Welsh Government, specific requirements related to the management of the inspection of its structures. The specific requirements for highway structures on motorways and trunk roads in Wales with respect to this standard are set down in the Welsh Government Structures Inspection Manual. These requirements are in addition to those contained in this Annex and in the main body of this standard. The Welsh government's principal inspection risk assessment guidance and risk assessment form can also be obtained using the contact details provided above. Assumptions made in the preparation of this document The assumptions made in GG 101 [Ref 2.N] apply to this document. 4 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Abbreviations Abbreviations Abbreviation Definition DLI Defects liability inspections EDDMS Electronic drawing and document management system NHSS 31 National Highway Sector Scheme 31 POI Pre-opening inspections WG Welsh government 5 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 Terms and definitions Terms and definitions Term Definition Agent The party appointed by the Overseeing Organisation to manage highway assets on their behalf, e.g. maintaining agent, managing agent, managing agent contractor, trunk road agent, concessionaire, service provider or operating company. Where the Overseeing Organisation manages the highway assets within their own organisation, the agent is to be the branch or section to which the duties have been delegated. Constructor The organisation contracted by the Overseeing Organisation or the agent to undertake construction works on its behalf. Can also be termed the Contractor. Designer The organisation responsible for the overall design including proprietary components. 6 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 W/1. Wales National Application Annex W/1. Wales National Application Annex General requirements [CS 450, 2.1] Extent of inspection W/1.1 Welsh Government Structures Inspection Manual SIM(W) [Ref 3.N] shall be followed for all inspections. NOTE The specific requirements for highway structures on motorways and trunk roads in Wales with respect to this standard are set down in the Welsh Government Structures Inspection Manual, available on the Electronic Drawing and Document Management System (EDDMS). These requirements are in addition to those contained in this National Application Annex and CS 450 [Ref 1.N]. Management and planning of maintenance inspections [CS450, 4.1] Inspection Frequency W/1.2 Welsh Government Structures Inspection Manual SIM(W) [Ref 3.N] shall be followed for all inspections. NOTE The specific requirements for highway structures on motorways and trunk roads in Wales with respect to this standard are set down in the Welsh Government Structures Inspection Manual, available on the Electronic Drawing and Document Management System (EDDMS). These requirements are in addition to those contained in this National Application Annex and CS 450 [Ref 1.N]. Management and reporting of risks Records of maintenance inspections [CS 450, 5.2] Introduction W/1.3 Welsh Government (WG) maintenance inspection records shall be entered in the structures management system with a copy of the report also stored within the respective structure folder on the Electronic Drawing and Document Management System (EDDMS). NOTE Further guidance on recording inspection records is contained within the WG Structures Inspection Manual. Acceptance inspections and records [CS 450, 6.1, 6.2.1, 6.3, 6.16, 6.19] Introduction W/1.4 All forms of acceptance inspection shall be carried out by representatives of each respective organisation to ensure that all parties are in agreement with the outcome of the inspection. W/1.5 Pre-opening inspections (POI) and defects liability inspections (DLI) shall be organised in agreement with the Overseeing Organisation. W/1.6 All relevant parties shall be notified of the outcome of the inspections. Pre-opening inspection W/1.7 Following the pre-opening inspection, the party designated by the Overseeing Organisation shall produce a Pre-opening Inspection Report informing the Overseeing Organisation of all defects and work outstanding identified during the inspection. Defects liability inspection W/1.8 Any agreed works identified during the Defects Liability Inspection shall be recorded in a brief report. W/1.8.1 The report should include confirmation that any defects identified at the time of the Pre-Opening Inspection have been rectified. 7 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 W/1. Wales National Application Annex Risk-based principal inspection intervals [CS 450, 8.1, 8.2, 8.4, 8.6] Introduction W/1.9 The Welsh Government's policy shall be used to determine the interval between principal inspections for individual structures. See the Welsh Government Inspection Manual SIM(W) [Ref 3.N] W/1.10 All structures forming the inspection programme shall be subject to preparation of risk assessments by the Agent. The procedure for determining risk based inspection intervals is as shown in CS 450 [Ref 1.N]. W/1.11 All structures forming the Inspection Programme shall be subject to the risk-based assessment process. Individual risk assessment forms have been developed for each of the following structure types; 1) culverts; 2) single span bridges; 3) multi span bridges; 4) gantries / footbridges; 5) retaining walls; and, 6) technology structures. NOTE Further information to assist Agents in completion of risk assessments is available in the guidance note and user manual documents held on the Electronic Drawing and Document Management System (EDDMS). W/1.12 All structures forming the inspection programme shall be subject to the risk assessment process. W/1.13 The principal inspection frequency shall not increase for the following structure types; 1) complex structures, including hinge joint, half joint and PTSI bridges; 2) rail structures. W/1.14 The risk-based inspection interval for all structures shall be subject to review following each subsequent general inspection. NOTE The WG risk assessment considers the likelihood of deterioration and consequence of failure. Structures inspectors' competencies and certification [CS 450, 9.1] Introduction W/1.15 All personnel carrying out inspections on WG owned structures shall be certified (or working towards certification) in accordance with the BICS, which has been developed in accordance with National Highway Sector Scheme 31 (NHSS 31). 8 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 CS 450 Version 0.1.0 W/2. Normative references W/2. Normative references The following documents, in whole or in part, are normative references for this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. Ref 1.N Highways England. CS 450, 'Inspection of highway structures' Ref 2.N Highways England. GG 101, 'Introduction to the Design Manual for Roads and Bridges' Ref 3.N Welsh Government. SIM(W), 'Welsh Government Structures Inspection Manual' 9 Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021 © Crown copyright 2021. You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence. To view this licence: visit www.nationalarchives.gov.uk/doc/open-government-licence/, write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email psi@nationalarchives.gsi.gov.uk. Downloaded from https://www.standardsforhighways.co.uk on 17-Jun-2025, CS 450 Version 0.1.0, published: 29-Apr-2021

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