Hydrodynamic behavior of stilling basins with deflectors to reduce supersaturation of total dissolved gases: analysis of Yacyretá and Jorge Cepernic dams

High air entrainment to the hydraulic jump is one of the inherent aspects of this macroturbulent flow, extending its presence from the free surface to the bottom. Depending on the variety of fishes in this natural habitat, important values of supersaturation of total dissolved gases (TDG) could be reached immediately downstream of the energy dissipation structure, putting under risk the life of fishes. This article deals with the influence of deflectors designed to reduce TDG on the hydrodynamic behavior of energy dissipators of two important dams. The first one is Yacyretá dam (Paraná River, Argentina – Paraguay) where horizontal deflectors were installed after an environmental incident with important mortality of fishes due to supersaturation of TDG. The second case corresponds to Jorge Cepernic dam (Santa Cruz River, Argentina), which is currently under construction. Hydrodynamic evaluation of the stilling basins under initial design conditions and those derived from the installation of the deflectors was carried out by means of two-dimensional physical models of each of the mentioned projects. The analyses showed a decrease of the energy dissipation rate for Yacyretá energy dissipator, with a hydraulic jump length that exceeds the length of the stilling basin, aspects that demand a continuous supervision of the works. On the other hand, the evaluation carried out for Jorge Cepernic dam does not exhibit significant changes of the hydrodynamic behavior of the stilling basin, except in a region downstream of the deflectors.