Reservoir Sedimentation Management: Evaluating Sediment Size and Bottom Tunnel Effects on Sediment Flushing Efficiency

Reservoir sediment flushing, recognized as a highly effective approach for mitigating reservoir sedimentation, involves the downstream discharge of sediment-laden flows through bottom tunnels. Alongside other critical parameters in pressure flushing, the simultaneous operation of bottom tunnels significantly contributes to the efficient removal of sediments from the reservoir, and this study evaluated the effects of the number and placement of these tunnels. The primary aim of removing sediment from reservoirs is to restore the lost volume resulting from sediment accumulation. This study endeavors to pinpoint the most optimal parameters for maximizing sediment removal from reservoirs, stressing the significance of effectively eliminating sediment from the dam reservoir during pressure flushing. To achieve these objectives, the CFD solver in Fluent is employed. While simulating bed erosion around bridge piers is not feasible within the Fluent CFD solver, a morphological model was developed and integrated with Fluent to address bed erosion beyond the flow solution. This integrated model combines the flow solution with a sediment transport model to establish the morphological model. The results demonstrated that achieving efficient pressure flushing in a reservoir with a constant water level is best accomplished in a reservoir containing sediment with a smaller average diameter, higher accumulation level, and a greater number of active bottom tunnels. Key elements include maintaining consistent discharge from each tunnel, ensuring uniform tunnel elevation, and preserving a fixed distance between them.