Turbidity Currents in Reservoirs

Abstract

Turbidity currents are major transport agents in reservoirs in which high concentrations of fine sediments flow in. Reservoir sedimentation due to turbidity currents is often severe in these cases. Turbidity currents are not well understood due to their complex turbulent flow structure, the interaction between the flow with the particles and the interaction between particles themselves. In this thesis the venting efficiency was determined for three reservoir implementations that might decrease sedimentation caused by turbidity currents. The three were: an additional sediment sluice, blocking a part of the reservoir and a deepened thalweg. Computations were done by means of a Reynolds averaged Navier Stokes (RANS) model. The Shihmen Reservoir in Taiwan was taken as a case study. In this particular reservoir suspended sediment concentrations are measured during the event of a turbidity current. According to the model results the additional sediment sluicing tunnel was the most effective solution. Results indicated that the location of such a tunnel and the reservoir operation method applied are thereby important to increase the venting efficiency. It was shown that a RANS model such as presented, is able to capture the complex behaviour of turbidity currents in reservoirs and is therefore a valuable tool for reservoir managers.