New UK guidance on hydraulic actions on highway structures and bridges

This paper outlines key technical changes introduced to two documents in Highways England Design Manual for Roads and Bridges that cover hydraulic actions on structures: CD 356 and CS 469. CD356 provides practical requirements and guidance for designers to determine hydraulic actions that are either not covered or are covered in insufficient detail in the Eurocodes and UK national annexes, and incorporates provisions for climate change. These include design processes, scour assessment, scour protection design, methods for deriving input parameters, and site investigation. CS 469 provides practical requirements and guidance for the inspectors, assessors and asset managers of structures. Its new extended scope includes structures over or adjacent to water, on floodplains and located where significant surface water flooding has occurred. The document includes requirements and advice on scour caused by floating or submerged debris, other hydraulic actions, scour emergency inspections and scour management of risk, with amendments to scour risk scores and ratings. Climate change allowances are updated. It clarifies where the advice of the overseeing organisation is needed, roles and responsibilities of key stakeholders in the scour inspection, assessment and risk management process, the definition of a competent civil or structural engineer and many of the technical definitions.