Maximizing the performance of hydropower plants by taking advantage of the remaining energy downstream of dams via the installation of hydrokinetic turbines is feasible. In these cases, the design of the rotor diameter and velocity are fundamental and depend on the depth and velocity of the river, respectively. In this study, the Saint-Venant model was applied and calibrated by linear regression of measured and simulated flow rates, which resulted in a correlation of 0.99. The validation was performed using measured velocities that are comparable to the simulated velocities. A power curve was generated for the measured flow rates and simulated velocities and obtained a correlation of 0.96. The curve was used to estimate the velocity, calculate the energy density, and define a design velocity of 2.35 m/s. Ten points in the study area were selected for the turbine locations, and the velocities were determined using the power curve for the measured flow rates and simulated velocities. The rotor design was performed using the blade element method (BEM), and a rotor diameter of 10 m was defined. The 10 turbines can generate 2.04 GWh/year of electricity. The results demonstrate the potential for utilising the remaining energy of hydroelectric plants.