Adding auxiliary discharge into the entrance pool of a fishway: influence of pool design on fish passage

Theatrette

The German Federal Institute of Hydrology (BfG) and the German Federal Waterways Engineering and Research Institute (BAW) are working on restoring connectivity for fish in large German rivers with focus on constructing efficient fishways. In large rivers a sufficient attraction flow is needed to guide fish into the entrance. It can be produced by adding auxiliary discharge into the lowermost (entrance) pool of the fishway. This however may distract fish from their passage. To minimize this risk we investigated different solutions for adding auxiliary discharge through a horizontal bar screen into the entrance pool. Passage times of five different fish species volitionally swimming through different set-ups in an open flume were compared to identify the influence of screen design and flow fields on fish passage and to develop recommendations for a functional pool design.