Flow characteristics in tailrace: understanding how hydrodynamics may attract fish to hydropower plant in South America

Abstract

Hydropower plant (HPP) operation may influence downstream flow regimes, which can affect the fish movement. In South America, tailrace fisheries are often killed or injured when interacting with spillways and turbines. Hydrodynamic flow-pattern studies are essential to facilitate mitigation. We developed a computational fluid dynamics model to investigate flow downstream of Três Marias HPP (Brazil). Included in the model were the draft tubes, tailrace and a 3-km river reach. We simulated a common scenario consisting of three active turbines on the right side of the powerhouse (109.6, 108.0 and 108.0m3s–1) and three inactive turbines, by using Ansys Fluent (ver. 12). We identified a straight discharge plume from the right-most turbine that was constrained by the right-side wall. Further, there was the generation of significant plumes from Turbines 2 and 3. The maximum velocities in these plumes appears not to be a barrier for Pimelodus maculatus and Prochilodus costatus, because their prolonged swimming speeds for their maximum total length were higher than the modelled velocities. The results will support mitigation decisions such as fish passage and turbine-screen design in this particular HPP and may be a model for further studies in the South America.