Author(s): Javier Patarroyo; Eric Mainville

Linked Author(s): Javier Patarroyo

Keywords: Stilling basin; Erosion; Plucking; CFD

Abstract: Hydro-Quebec’s Robert-Bourassa hydroelectric facility is part of the La Grande Rivière hydroelectric complex which generates all together 17,445 MW. It is located on La Grande river in the north of Quebec, Canada. The hydropower facility is comprised of a reservoir, a main dam, 29 dikes, a spillway and two hydroelectric power stations. The Robert-Bourassa (5,616 MW) and La Grande-2-A (2,106 MW) power plants. The design of the spillway was completed on a 1: 100 scale physical model in 1975. The spillway consists of a concrete control structure and a man-made waterfall discharging into a stilling basin below the dam. It has eight bays of 12.19 m wide with parabolic-shaped rollways and four heated gates. The discharge capacity is 16,500 m³/s under normal operating conditions. Having passed through the gates, the kinetic energy of the water is dissipated in a 135 by 122 metres basin at the foot of the spillway. It then flows down a 1,500 m long rock channel with a vertical drop of 110 m on its way back into the La Grande river. The channel has 10 steps ranging from 9.1 to 12.2 metres in height and 127 to 200 metres in length. Between 1979 and 1981 the spillway was continuously on service, after that period, damages in the basin were observed. It was concluded that the improper operation of the gates resulted in high turbulence in the basin that triggered an erosion process. In 1983, discharge tests on the prototype were carried out to establish an optimal operating mode for the spillway gates. The tests showed that the simultaneous operation of all the eight gates has beneficial effects on the phenomena of turbulence, erosion and plucking in the stilling basin. Recently, studies on the anticipated effects of climate change indicate a trend towards an increase in annual flows within the hydrographic basin of La Grande river. The latter increases the probability of carrying out spills during winter. However, only 4 heated gates are available during the winter period. In this context, a hydraulic study was necessary to understand the uncertainties related to the behaviour of the stilling basing for the spillway operation with a combination of less than 8 gates without compromising the integrity of the basin. The purpose of this paper is to describe the simulations that were conducted using computational fluid dynamics (CFD) model on the stilling basin for different operating conditions. The model shows complex flow patterns for unexpected operational situations at the spillway design.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221631

Year: 2022