Optimizing attraction flow for upstream fish passage at a hydropower dam employing 3D Detached-Eddy Simulation

•A 3D CFD simulation of a hydropower dam tailrace was calibrated successfully.•Hydraulic results were linked to fish performance through fish-size-speed relations.•Fishway attraction flow results agree with general literature recommendations.

Restoration of upstream fish passage requires construction of efficient fishways. Selection of attraction flow rates and entrance velocities is one of the fundamental research tasks on medium-sized German rivers as general recommendations are ambiguous.We used a transient 3D Computational Fluid Dynamics model of a hydropower dam tailrace calibrated with Acoustic Doppler Current Profiler velocity data and Detached-Eddy Simulation turbulence modeling to produce seven flow fields. Hydraulic results were linked to fish performance by means of fish-size-speed relations (ethohydraulic scale).Resulting attraction flow relationships agree well with literature recommendations if the competing flow is defined as the adjacent turbine flow. Further, we found that entrance velocity clearly determines the downstream influence of the attraction flow plume over the attraction flow rate if no rapid mixing is present.