Two-Dimensional Sediment Transport Modeling under Extreme Flood at Lower Cache Creek, California

Sediment transported along with extreme flooding may greatly affect flood conveyance and associated operations and management in the lower cache creek system. In this study, the relative sediment capture and transport in lower cache creek, under current bathymetric conditions and one modification alternative (2A), is evaluated. Sediment dynamics in the lower cache creek system, which includes a floodplain and settling basin, are evaluated under extreme flow events. Of particular interest is the sediment trap efficiency of the cache creek settling basin (CCSB) under different flood scenarios. The CCSB was designed as a retention basin to capture sediment and reduce sediment loading into the Yolo Bypass, therefore preserving flood conveyance of the bypass. Sediment dynamics for each flow event, under both the current condition and 2A, are simulated with the CCHE2D model, a two-dimensional depth-averaged flow and sediment transport model. The simulations allow relative comparison of the sediment trapping performance of the current condition and 2A. Preliminary simulation results are presented here.