Guiding Efficiency of Bar Racks and Louvers for Selected European Fish Species during Downstream Migration at Hydropower Facilities

Swiss rivers are used intensively for hydropower production, which contributes 60% to the electricity supply. The new national water law and fisheries legislation require the re-establishment of fish migration. To provide an upstream migration corridor, many fish ladders have been constructed in recent decades. However, almost no downstream migration facilities yet exist.
A few European countries have used technological solutions to facilitate downstream migration (such as horizontal screens) at small hydropower plants. However, no analogous solutions exist for larger European hydropower plants. In an artificial flume we tested the guiding efficiency for selected European fish species of bar racks and louvers angled at 15 and 30 degrees to the flow. Three fish species (barbel, spirling, grayling) were caught from wild river populations for testing. The clear spacings tested for bar racks and louvers were 5 and 11 cm and related water velocities of 30 cm/s and 60 cm/s. A total of 10 different configurations were evaluated. Louvers did not generally show sufficient guiding efficiency, and fish often swam in the direction of the turbines. However, some bar rack configurations (5 cm clear spacing) produced good results, guiding fishes efficiently away from the turbine entrance and into the secure bypass.