Influence of operation modes and fish behavior on fish passage through turbines

Abstract

Abstract The assessment of fish passage through turbines is important to develop cost-efficient environmental solutions and strategies that avoid individual fish injuries and, therefore, enhance the fish population development in a catchment. As part of the FIThydro project, fish passage analysis were performed for the bulb turbine in Bannwil, the S-turbine in Guma and the bulb unit at the test facility in Obernach. Numerical modelling in principle provides the most comprehensive information on hydrodynamic conditions in the turbine passage. Many details of the main relevant stressors on fishes can be derived. The information of different stressors like pressure, strike, shear and turbulence can be extracted with high accuracy assuming that a fish pathway follows a streamline through the turbine. The accurate prediction of the stressors and the validation with measurements enables the designer to develop a turbine that reduces the stress on the fish and, hence, increase the fish survival rate. The survival rate also strongly depends on biological aspects of a fish species. Besides the reaction of the fish on the different stressors, complex parameters like swim behavior or preferred swim elevations are of high importance on the survival rate. However, these parameters vary among different fish species. CFD simulations of different turbines are performed and simulation results were compared to measurements with the Barotrauma Detection System (BDS) sensors at the test cases in Guma and Bannwil, as well as live fish tests at the test facility in Obernach. The fish behavior was modeled in the CFD based evaluation method. Studies related to swimming speed, fish orientation and especially the actual passage location demonstrate the sensitivity of these parameters on the fish survival rate. Another aspect was the influence of operating conditions on fish passage. A wide spectrum of operating conditions was analyzed and fish passage hill-charts for different stressors were generated. This knowledge enables an adapted power plant operation related to migration movements of certain fish species. The CFD based analysis method shows to be a powerful tool to improve fish passage through a turbine by changing hydraulic design and by adapting operational modes. Relative improvements to conventional designs and operation can be quantified.