Beitrag zur Hydraulik von Einlauföffnungen an Fischabstiegen

It's a well-known fact, that downstream migrating fish show an avoidance behaviour at inflow sections and orifices to bypasses. This causes a delay in migration, exhaustion and a larger risk of predation. From laboratory tests it was found that the velocity gradient (increase of velocity along e definite way of flow) is the major parameter that guides this avoidance. For the smolts of the Chinook salmon (Oncorhynchus tshawytscha) a critical value is known. Due to the fact that the flow to an orifice can be regarded as a potential flow the velocity field and thus the acceleration field can be calculated for a given geometry of the inflow reach. The formulas for the calculation of velocity field and velocity gradient are presented for some common geometries. For the case of a partly opened door with a gap from bottom to surface the application of this new method is shown. The example shows how this approach can help to prove the velocity gradient being below a critical value.