Author(s): Ismail Albayrak; C. Robert Kriewitz; Claudia Beck; Robert M. Boes
Keywords: Downstream fish migration; Fish behavior; Fish guidance efficiency; Flow field; Fish guidance structure
Abstract: Downstream fish passage through turbines or over spillways may significantly increase fish mortality during migration periods. Therefore the implementation of protection systems stopping fish from entering turbine intak es has a high priority in regard to ecologically upgrading hydro power plants (HPPs) .For that reason VAW of ETH Zurich conducts research on louvers and angled bar racks, so-called fish guidance structures (FGS) ,to adapt and advance them in regard to safe fish passage and a successful economical implementation. This paper presents the results of an experimental investigation on louver and modified angled bar rack with and without a bottom overlay (BO) angled at 15°to the approach flow. For the former, the bars were angled 90°to the flow direction while for the latter they were angled 45°. The instantaneous flow velocities around the FGSs and in the bypass were measured in a laboratory open channel flume using ADV-probes (Acoustic Doppler velocimetry) .The water depth was always 0. 90 m with a mean flow velocity of 0. 6 m/s. The longitudinal velocity near the bypass entrance in terms of approach velocity increased to 2. 4, 1. 6 and 1. 4 for the louver, modified angled bar rack without BO and with BO, respectively. The highest traverse velocity towards the structure was found for the louver whereas low and no traverse velocities occurred for the modified angled bar rack without BO and with BO, respectively. Primary results of the live-fish experiments showed that fish guidance efficiency (FGE) e. g. for Barbel and Spirlin was the highest for the modified angled bar rack with BO, meaning that this structure creates a more favorable flow field than the others. To summarize, the findings of the present study provide an important foundation to continue development of the FGSs designed to guide central European target fish species to a downstream-bypass.