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 Três 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 Três 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.

Perspectives on the environmental implications of sustainable hydro-power: comparing countries, problems and approaches

“…For example, dam tailraces can attract and congregate fish in the artificial flow field created by dam tailraces, which can lead to high mortality events during turbine start/stop procedures, particularly if fish have entered the turbine draft tubes. To investigate how turbine operations influenced the flow field downstream of a dam, Mendes et al (2021) used calibrated numerical two-and three-dimensional hydraulic models to assess flows in the dam tailrace and a 3-km downstream river reach. Model outputs were evaluated taking into consideration the swimming capacities of mature individuals from three common migratory fish species: Prochilodus costatus (Valenciennes, 1850), Pimelodus maculatus (Lacepe `de, 1803) and Leporinus reinhardti (Lutken, 1874).…”

“…The low attraction and passage efficiency of the fishway suggests current designs are ineffective, largely because they fail to account for dam hydraulic attraction effects and the behavioural cues they provide. As suggested above (Braga et al, 2021;Mendes et al, 2021), improved understanding of the interactions between river hydrology downstream of dams and fish will be key to ensuring fish encounter and react to dams in ways that will minimally disrupt their ecology and life-history.…”

“…Thus digitalization and new methods for field data collections have improved applied environmental studies and pointed to the many subtleties of fish interactions with dams (Braga et al, 2021;Hahn et al, 2021;Sundt et al, 2021). High resolution data collection systems will undoubtedly come to be more commonly deployed and will facilitate the development of detailed models (Katopodis, 2021;Mendes et al, 2021) able to better and more quickly identify trade-offs within hydropower production systems that will facilitate improving their overall environmental sustainability.…”