Scour & Engineering Design

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For Highway Authorities, Local Authorities, Network Rail and Rivers' Trusts

Scour, Erosion and Geomorphological Change

Scour at bridge structures is a real and significant problem in the UK. During the Storm Desmonds floods of 2010, 26 bridges collapsed and many more were deemed to be at risk of failure. Edenvale Young Associates has considerable experience in assessing geomorphological change and the risk of scour to structures. In the past three years we have undertaken:

Level 1 and 2 scour assessments in accordance with the design manual for roads and bridges DB97/ 12
Assessed the scour and erosion for bridges and wharf structures using hydraulic modelling techniques
Designed scour protection to a range of bridge types in the temporary and permanent works condition
Designed emergency works to mitigate the risk of collapse to historic structures subject to scour.
Evaluated toe scour for the design of a breakwater toe subject to wave action.
Geomorphological assessment, modelling and design of river restoration works and fish passes
Monitoring and provision of advice of coastal cliff failures using drone technology

Holistic Approach

How we assess scour risk

A risk-based approach to bridge design, maintenance and structural assessment is increasingly understood to be best practice. Assessing the risk of scour and undercutting of foundations, and the geotechnical or structural failure of a structure requires careful consideration of a range of factors which may affect the response of a bridge in exceptional flow conditions. Edenvale Young has extensive experience in this type of work.

Site Investigation – Preparation of appropriate site investigation for use in scour and geotechnical analysis.
Hydrological Analysis – Estimation of extreme flood flows using the Flood Estimation Handbook.
River Hydraulic Modelling – 1D-2D hydraulic modelling to evaluate the regional fluvial conditions.
Geomorphological Modelling – 2D-3D hydraulic modelling with a coupled sediment transport/bed shear stress model to evaluate downstream scour and changes to the river channel.
Geotechnical Analysis – Assessment of abutment and pier instability due to sliding, bearing, slope stability and other modes of failure.
Protection – Advice and design of bridge pier impact mitigation and scour protection.

Hydraulic modelling for the assessment of scour and erosion

Level 1 and 2 scour assessments (DB97/ 12) are rapid evaluation techniques to identify where there are potential problems associated with scour at a bridge structure. They are based on empirical techniques developed in the 1950. However, they are limited to a range of bridge types and forms. Hydraulic modelling using 2D and 3D software facilitates a step change in the evaluation of scour to bridges and other structural forms. Location adjacent to bridge piers and abutment where there are high velocities and bed shear stresses can readily identified and this gives more reliable assessment of scour.

Edenvale Young is experienced in the use of Three-Dimensional modelling with OpenFOAM/interFoam which has a number of significant advantages in terms of evaluating scour and the response of a bridge structures in extreme fluvial events. This includes improved understanding of flow velocities and bed shear stresses adjacent to a pier, abutment or caisson. Bridge Geometry including the configuration of cut waters, bridge piers, arches, foundations and abutments influence flow velocities around and through the structure and are critical to the process of scouring for individual bridges. The use of OpenFOAM modelling allows the configuration of the structure to be adjusted rapidly.

Scour and Channel Movement

When do I need to think about scour and erosion?

Any structure within the river and coastal environment will be subject to erosive pressures in extreme weather events. The need to undertake an evaluation of scour and erosion will depend on individual requirements but this could include:

Regular inspections and assessment of structures subject to hydraulic loading
Monitoring of coastal failure.
Identification of critical assets and specialist assessment including 2d and 3d hydraulic modelling techniques
Evaluation and monitoring of ongoing erosion or scour
Design of new bridges and other hydraulic structures such as fish passes

If you need a scour assessment or want to discuss whether an existing or proposed structure might be susceptible to scour contact us to discuss your requirements.