Author(s): Jean-Marc Ribi; Kathrina Steffen; Jean-Louis Boillat; Armin Peter; Anton J. Schleiss
Linked Author(s): Jean-Marc Ribi, Anton J. Schleiss
Keywords: Keywords: Hydropeaking; Fish shelter; Juvenile wild brown trout; Fish trajectories; UVP
Abstract: A systematic ecohydraulic study was performed with the purpose to find optimum refuge configurations which the fishes can find to take shelter during hydropeaking. In a 12m long and 1.2m wide artificial channel, a lateral rectangular fish refuge of 1.2 m depth and 2 m length was installed. The system was continuously fed with fresh river water from the reservoir of Maigrauge dam. Velocity patterns were measured throughout the vertical section, that is between the shelter and the main channel. A transverse wall element was installed in the middle of the refuge in order to favour the water exchange between the main channel and the refuge and to create attractive velocity currents for the fish. By changing the angle of this wall towards the upstream and the downstream directions, water exchange and velocity distribution between main channel and refuge could be varied in a wide range. All configurations were tested with the juvenile wild brown trout (0+ and 1+) caught by electrofishing. These trout were released at the upstream end of the main channel under normal flow conditions. The discharge was then increased during 3 hours to a hydropeaking factor of 10. The movement of the fish was continuously video recorded and then digitalized. Every configuration was tested with a new sample of 20 wild trout. Attractiveness of 5 different configurations of fish refuges could be analyzed comparing the velocity patterns to the fish trajectories for the best refuge configuration, more than 80% of the fish found the refuge either by swimming from the upstream or from the downstream during the first 20 minutes after the beginning of hydropeaking.
Year: 2009