Rygenefossen Hydroelectric Outlet Tunnel

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Project description

Smith-Root commissioned the installation of an electric fish barrier in the tailrace of Rygenefossen (Rygene Hydroelectric Power Plant) located near Arendal, Norway. The hydropower dam at Rygenefossen impounds the Nid River (Nidelva) and utilizes a hydraulic head of 11.5 m. Water exits the turbine into a tunnel and travels 3.2 km downstream before release back into Nidelva near the township of Helle. The system operates with a maximum generating flow of 170 cumecs) and maximum velocity of about 3.0 m/s.

Atlantic salmon migrate upstream in Nidelva, and previously a significant number of migrating fish entered the outlet tunnel instead of continuing upstream to the fish pass at the dam. Agder Energi commissioned Smith-Root to design an electrical barrier at the confluence of the tunnel and Nidelva with the purpose of deterring fish from entering the tunnel.

After initial construction, Agder Energi and Smith-Root calibrated the electrode configuration and determined a more effective electrode alignment. The new alignment was operated and tested during the 2014 migration period. An independent consulting firm found that more than 99% of migrating fish avoided the outlet tunnel and continued upstream in the residual channel of Nidelva to the fish ladder, confirming the barrier is operating as intended.