Simulating dam removal with a ID hydraulic model: Accuracy and techniques for reservoir erosion and downstream deposition at the Chiloquin Dam removal

摘要

Hydrodynamic models are often used to reduce uncertainty regarding the outcomes of dam removal, though the accuracy of these models is not regularly evaluated post-removal. With the goal of improving understanding on the accuracy and limitations of making predictions of sediment dynamics following dam removal, we compare predicted and observed sediment erosion and deposition in the reservoir and downstream for the Chiloquin Dam removal. Results from a ID (HEC-RAS) hydraulic and sediment transport analysis (Yang equation) are compared to pre- and post-removal bathymetric and sediment surveys. Observed bathymetric changes indicate minimal response in both the reservoir and the downstream reaches to the removal, due in part to the low water year and the low volume of sediment stored in the reservoir following drawdown. Model simulations overpredicted erosion in the reservoir and downstream relative to what was observed, likely due to a combination of limited field documentation of resistant hardpan and to issues in model stability. Magnitude and potential sources of error are presented and suggestions are made regarding data needs and potential modeling approaches in future dam removal studies.