Upstream Passage of Adult Salmonids: Blocking off Cul-De-Sacs with Graduated-Field Fish Barriers

The hydrology of watercourses in the vicinity of hydropower installations is often complex.  It varies with cascade catchment area inflows, generation and spill regimes, and statutory compensation flows in the residual basin area.  Depending on discharge regimes from draft tubes, spillways, tailraces, fish passes and residual channels, ascending adult salmonids can be attracted into hydrological cul-de-sacs where their upstream migration is delayed. This paper reviews hydropower installations in Europe where graduated-field fish barriers (GFFBs) have been installed to exclude ascending adult salmonids from tailrace and draft tube environments.  Case histories include Rygene on the Nidelva River (Norway), Vessy on the Arve (Switzerland) and Beeston on River Trent (England).  Our paper also reviews other hydropower installations in Europe where installation of GFFBs is being considered as an option to exclude ascending adult salmonids from draft tubes, tailraces and spillway channels. This approach is being driven by a combination of biological, economic and safety goals. Based on a review of the literature on fish guidance using electric fields, GFFBs have been quite successful in achieving results — especially for upstream fish-guidance needs where river flows and water velocity can be leveraged with the graduated nature of the technology to yield positive results.