Author(s): L. C. S. Oliveira; Iran E. Lima Neto

Linked Author(s): Iran Eduardo Lima Neto, Iran E. Lima Neto

Keywords: water intake operation; hydraulic transients; sediment resuspension; water quality; tropical semiarid regions; large reservoirs

Abstract: The present study investigates numerically the effects of the water intake operation of Castanhão, the largest multi-use reservoir in Latin America. First, transient hydraulic modeling was carried out using the software ALLIEVI. The results indicated that, even for the fastest closing conditions of the water intake valve (t = 1.0 min), the impact of hydraulic transients was negligible. Next, computational fluid dynamics (CFD) simulations were performed using the software ANSYS FLUENT to investigate the induced flow patterns approaching the water intake. With the turbulence values obtained, an empirical model as a function of the turbulent kinetic energy was applied to assess the thresholds for sediment resuspension. The results showed that the converging flow towards the water intake generated enough turbulence at the bottom of the reservoir to resuspend the sediment. However, the longitudinal extent of potential sediment resuspension was limited to the areas relatively close to the water intake (< 200 m). Finally, CFD simulations were carried out under well-mixed and thermally/chemically stratified conditions and for different flow rates at the outlet. For low water levels and low flow rates, which are typical conditions of tropical semiarid reservoirs, most of the flow was withdrawn from the upper water layers (epilimnion). Contrastingly, for high flow rates, a significant flow was also withdrawn from the lower water layers (hypolimnion). As a result of these different induced flow patterns, the values of water quality parameters at the outlet increased up to about 30% for stratified water conditions, as compared to well-mixed ones.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024