Introducing SCOUR, a tool developed by APEM to assess the risk of scour releases upon watercourses downstream of reservoirs in England and Wales. This innovative tool provides high level information that addresses new impact assessment guidance for the Environment Agency.

To reduce flood risk, water companies and reservoir owners must prove that they can quickly reduce (or draw down) the water levels in the reservoir. Testing reservoir drawdown, or scour testing, can involve a short “dry” test or fully opening and closing an outlet valve, releasing large volumes of water into the watercourse.

Scour testing requires consent from the Environment Agency, as it can have a range of environmental impacts, from displacing fish to affecting water quality downstream.

Changing requirements mean that there are more full tests, so the Environment Agency have asked water companies and owners of large reservoirs to assess risk specifically in the following areas:

  • Increase in downstream flow rates, to assess whether their reservoir will cause scour of valuable river gravels, which can be important spawning habitat for salmonids and lampreys
  • Discharge of fine sediment from the reservoir bottom, which may suffocate the river bed downstream
  • Discharge of polluted sediment, to consider if pollutants may be present in significant amounts in reservoir sediment
  • Discharge of water from the reservoir bottom, which may have low dissolved oxygen or be substantially warmer or cooler than the river water downstream
  • Release of fish from the reservoir, which may be very different from the fish living downstream

Using the scour assessment tool to provide a high level risk assessment, reservoir owners can submit a request to the Environment Agency to continue to make scour releases every 6 months, which are required by law for reservoir safety.

This innovative tool also helps reservoir owners prioritise mitigation action or further investigation, where needed.

An Image of an unnamed reservoir

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