Simulation-driven design with computational fluid dynamics has been used to evaluate the flow downstream of a hydropower plant with regards to upstream migrating fish. Field measurements with an Acoustic Doppler Current Profiler were performed, and the measurements were used to validate the simulations. The measurements indicate a more unstable flow than the simulations, and the tailrace jet from the turbines is stronger in the simulations. A fishway entrance was included in the simulations, and the subsequent attraction water was evaluated for two positions and two angles of the entrance at different turbine discharges. Results show that both positions are viable and that a position where the flow from the fishway does not have to compete with the flow from the power plant will generate superior attraction water. Simulations were also performed for further downstream where the flow from the turbines meets the old river bed which is the current fish passage for upstream migrating fish. A modification of the old river bed was made in the model as one scenario to generate better attraction water. This considerably increases the attraction water although it cannot compete with the flow from the tailrace tunnel.
We constructed a model that predicted path selection of Atlantic salmon. Our basic assumption for the model was that Atlantic salmon optimize migration by selecting a path that minimizes water resistance. The model prediction was compared with observations in a fishway, and the results were within expectations. It appeared like the fishway design and flow configuration at our study site caused some problems for the fish to discover both of the available paths. Therefore, only 53% of female fish and 67% of male fish selected the optimal path in the beginning of the fishway, but 92% of female fish and 97% of male fish selected the optimal path at the end of the fishway. Velocity over ground was very low, which is likely because every weir in the fishway was an obstacle for the fish. This knowledge can be used to improve future fishway design, or improve flow configuration for existing fishways.
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