This work is part of a project aiming at dimensioning a fishway for a hydroelectric power plant on the Rhine River. Here we only focus on the design of the fishway entrances, for which a physical model of the draft tubes and tailrace of the powerplant was built at EPFL in 2016. As a complementary tool, a 3D numerical model was built at EDF R&D, based on the Code Saturne software. The numerical model was built first, which provided a 3D description of the site geometry and started emphasizing the predominant phenomena for the flow description. In the present case, the turbulent intensity below the turbines was identified as a key point for the model calibration. Both the physical and the numerical model were validated against field observations and ADCP measurements. The results show that good agreement is obtained with both models for several turbine exploitation configurations of the powerplant.