Numerical modeling for sediment-pass-through reservoirs

Sediment accumulation in reservoirs on the North Fork Feather River will soon affect hydroelectric power generation. For sediment control, low-level outlets through the dams have been considered to allow Sediment-Pass-Through (SPT) the reservoirs. The objective of SPT is to maintain sediment balance through the reservoirs with no net erosion or deposition over an extended operating cycle. The velocity required for bed sediment to pass through a reservoir will be achieved by reservoir level drawdown during large floods. A numerical modeling study, using FLUVIAL-12, was made to evaluate the feasibility and effectiveness of SPT for the system. The study developed the following features: (1) rating curves that specify the reservoir drawdown in relation to the changing discharge; and (2) reservoir operation rules that specify the operational procedure and settings for control gates. Simulated results are presented to demonstrate that mass balance for the river/reservoir system can be achieved, without adverse siltation in the river channel to affect fish spawning. This approach for reservoir sediment control should be useful for similar problems.