Abstract
After the Orville Dam crisis that happened in 2017, California Senate Bill 92 was enacted,requiring dam owners to develop Emergency Actions Plans and submit inundation maps to the California Department of Water Resources Division of Safety of Dam (DSOD) every ten years for evaluation and approval. The Hydrologic Engineering Center – River Analysis System (HEC- RAS) is a simulation software that is commonly used by the dam owners or the consulting companies that they hire to develop the dam breach model needed to create the inundation map. DSOD uses the Decision Support System for Water Infrastructure Security (DSS-WISE) to review the models that are submitted by the owners and compares the results of those models with its own DSS-WISE simulations. Differences between the dam breach hydrographs generated by DSS-WISE and HEC-RAS can be attributed to at least five known differences between how these models generate dam breach hydrographs. Two of the most obvious differences between DSS-WISE and HEC-RAS are the different side slope options to define breach shapes and differences in the storage-elevation curves used to represent the volume of the reservoir. The purpose of this project was to investigate the extent to which the vertical breach side slopes and use of approximated storage-elevation curve by DSS-WISE significantly impact dam breach hydrographs. This project aims to study how a dam break impacts the changes in flow at the dam using a simple dam breach model, whereas HEC-RAS models require more parameters and information to be developed. Therefore, Hydrologic Engineering Center – Hydrologic Modeling System (HEC-HMS) was chosen to develop dam breach models for 36 dams for testing these variables. The results showed the use of vertical dam breach side slopes influenced the dam breach hydrograph. The hydrograph peak flow rate was always higher when the breach was defined with a rectangle shape with vertical side slopes and averaged 10% higher even though the average width of the breach and the cross-sectional area of the breach was kept constant. The range of the percentage differences was between 1% and 22%. Based on the comparison of the storage-elevation curves, it was observed that the DSS-WISE approximated storage-elevation curves differ substantially from the measured curves in some cases. Comparing differences in dam break peak flows modeled in HEC-HMS using DSS-WISE approximated storage-elevation curves and the measured curves, the average percentage difference in the hydrograph peaks was 3%, with the percentage difference ranging between -11% and 35%. Dams where the DSS-WISE- approximated storage-elevation curve had larger differences from the measured storage-elevation curve resulted in greater differences in the dam breach hydrographs.