Downstream alterations on hydrodynamic fields by hydropower plant operations: implications for upstream fish migration

Abstract

This study identifies hydrodynamic alterations in flow downstream of a dam that are related to hydropower plant (HPP) operation and that might attract Neotropical potamodromous fish to unsafe places in the tailrace during their reproductive migration. Our hypotheses are (1) the hydrodynamic flow in the tailrace presents conditions that are strong attractive for fish than those found in the downstream reach and (2) there are no velocity barriers preventing the upstream migrant from reaching the tailrace over a wide range of turbine discharge. Two calibrated numerical models were created for the Tres Marias HPP (Brazil), using different turbine discharges: (1) a three-dimensional (3D) model of flow in the tailrace and (2) a two-dimensional (2D) model for flow in the 3-km reach downstream of the dam. Resulting flow fields of the Tres Marias HPP tailrace have elevated hydraulic strain and velocity homogeneity by as compared to the flow field of the downstream reach. The tailrace velocities are slow for mature individuals of all study species, which may swim from downstream reach to unsafe areas in their sustainable and prolonged mode by available corridors for different turbined discharges.