Scour protection design at Network Rail structures in South Wales

Our ongoing involvement in the Network Rail scour assessment programme has seen several high-priority Network Rail structures over water assessed for their scour risk, resulting in the protection of important assets. This project requires a unique collaboration between our environmental and engineering teams to design the right solution for our client.


We were to complete the scour protection design at several structures in the Bridgend area of North Wales that fell within the high-priority rating category. The design of scour protection is based on several factors, primarily around hydraulic velocities, flows at the structure as well as bed levels and foundation depths. 

As part of any works with a watercourse, a Flood Risk Activity Permit must be submitted to the relevant consenting body. We had initial discussions with Natural Resource Wales (NRW) and concerns were raised with the type of protection and the levels at which it was to be installed, stating that the concrete mattress levels were too shallow and would potentially cause velocities to increase through the structure and disturb the migration of fish and other aquatic animals.


Based on our designs, NRW recommended that the mattress would be buried approximately 1m below existing bed levels, to allow the natural deposition of gravels, over time limiting the impact on the natural ecological cycle of the watercourse. However, after considering several different options, this was found not to be possible.

Our environmental team modelled the protection hydraulically and assessed the impact of the mattress on the wider water body environment at various depths in the channel. By doing this, we could assess at what depth the mattress could be installed to meet both the NRW concerns and those outlined through the Water Framework Directive (WFD).

Through a detailed WFD assessment report, it was found that at a depth of 600mm below existing bed levels the impact of the mattress on the wider watercourse, both ecologically and hydraulically, would be negligible.

We presented the data, in the form of flood water levels, channel velocities and gravel migration heat maps, to NRW in pre-works and post-works tabulated results which showed that at 600mm below bed level, the mattress did not increase any of the parameters above and as such was agreed and consented to by NRW.


By working collaboratively with our client, stakeholders, and our engineering and environmental experts, our solution was consented to by NRW and allowed Network Rail to protect important assets from scour. The 600mm depth meant that the mattress could be installed safely and within the client’s budget.

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Want to know more?

For more information on this project please contact Scott Riddlestone.


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