Session C8: Requirements for the Traceability of Bypasses for Downstream Migrating Fish - Ethohydraulic Insights

Abstract: There is a strong demand to build new fish ways due to amended regulations in conservation and restauration regarding the longitudinal passableness of rivers. The upstream migration of anadromous species, like Salmon is well investigated and technical standards for efficient fish passes exist. However, for the downstream movement of diadromous and potamodromous species little knowledge is available. Therefore it is necessary to enhance our understanding for the orientation and behavioural pattern of fish, facing migration barriers, to determine the requirements for a traceable bypass. Prerequisite for a proper efficiency is a good traceability, which means that the fish do not loose time to find the entrance and accept the bypass as an alternative migration corridor. This is a complicated task because the specific species behaviour has to be taken in account. To investigate the downstream migrating behaviour of fish, a reproducible set up is needed in which the fish can be observed directly, the installed bypasses and peripheral components can be changed easily, while important operating values, like discharge and velocities can be controlled. Nevertheless such a laboratory set up has to have a situational similarity with the real situation in the field (in front of a hydropower plant), so that the results are transferable and applicable. This specific field of Ethology in a through-flow model flume is called Ethohydraulic. The used model flume is completely glazed, 30 m long, 2 m wide, 1 m deep and has the capacity for up to 1 m3/s process water. The study investigates the effect of different bypass shapes, sizes and positions on the traceability and acceptance for fish. Additionally the different alignments of screens and the approach velocity in front of a bypass in competition to a water outlet are tested with salmon smolts, silver eel and potamodromous fish so far