Investigating the Turbidity Current Venting Operation from Multiple Outlets by Using TELEMAC-3D

Operating different reservoir outlets is a challenging decision-making process balancing the releases of turbidity currents with the maintenance of clear water circulation within the reservoir. Experimental model tests for the Shihmen Reservoir in Taiwan were conducted to investigate the venting of turbidity currents for existing outlet facilities and additional proposed sediment bypass tunnels. In this study, a three-dimensional numerical model, based on TELEMAC-3D, was validated and used to estimate the venting operation and behavior of turbidity current within the reservoir under multiple outlet conditions. A fully three-dimensional simulation analyzed various turbidity current characteristics, including the plunging location, head velocity, arrival time at each outlet, and muddy lake evolution. The results confirm that the upstream bottom outlets' operation delays the turbidity current at the dam's outlets. Moreover, the additional release of sediments further hinders the formation of the muddy lake near the water supply intake, which means more clear water could be supplied during flooding events. Therefore, a suitable venting strategy is proposed with a systematical operation to balance water storage and sediment release from the water resource availability point of view. Overall, understanding turbidity current processes and assessing venting operation could provide an excellent reference to the reservoir manager to increase the desilting rate and extend reservoir usage life.