Risk assessment of existing flood detention (storage) reservoirs

The Environment Agency is carrying out a portfolio risk assessment of their portfolio of around 200 large flood detention reservoirs (FDRs), to inform their reservoir safety management and operation. The ‘Guide to risk assessment for reservoir safety management’ (RARS) was published in 2013 and provides a methodology for risk assessing existing reservoirs in the United Kingdom. It was intended primarily for reservoirs which are normally full, where indicators of poor condition can be observed. It was therefore necessary to extend RARS to cover FDRs, and this paper describes the key elements of the extension to the RARS Tier 1 methodology. It is anticipated similar extensions could be applicable to FDRs owned and operated by other agencies. The next step is to extend RARS for Tier 2 and 3. Washland flood detention reservoirs are in effect partially bunded reservoirs, so some aspects of the approaches adopted here will also be applicable to non-impounding reservoirs.