Eller Beck Flood Storage Reservoir – the challenges of low impact flood storage design

The proposed Skipton Flood Alleviation Scheme comprises two flood storage reservoirs and in-town flood defence works. The scheme is to provide a 1 in 100 year standard of protection to Skipton, North Yorkshire.

One flood storage reservoir, on Eller Beck, is located within a golf course and a national park. To ensure that the 14m high earth embankment dam is sympathetic to its surrounding landscape the preferred spillway solution for the Category A dam was a reinforced grass channel.

However, the A65 road embankment immediately downstream of the dam has the potential to create a range of tailwater levels, the greatest of which is only 1m from the spillway crest. This could result in a hydraulic jump forming anywhere on the downstream face of the embankment. Consequently, the design team investigated the performance and restrictions in the use of reinforced grass systems under hydraulic jump conditions.

The proposed site is constrained by transport infrastructure on both abutments as well as significant geological features, which have required detailed investigation and analysis to confirm their likely impact on the earth embankment dam.

This paper explores the decision-making process which led the design team to the adopted solution and discusses the design challenges encountered.