More than 1 million Californians live and work in the floodplains of the Sacramento-San Joaquin Valley where flood risks are among the highest in the nation. The California Department of Water Resources (DWR) launched the statewide FloodSAFE initiative to improve public safety through integrated flood management. To inform FloodSAFE decision making, DWR required updated hydrologic information.
DWR partnered with the US Army Corps of Engineers (USACE), Sacramento District to conduct the Central Valley Hydrology Study (CVHS). CVHS is a comprehensive assessment of stream flow frequencies and magnitudes in the Sacramento and San Joaquin river basins. The objective of the hydrologic analysis was to estimate peak flows and hydrographs for various annual exceedence probabilities to describe flood hazard throughout the basins.
As principal contractor for USACE, Ford Engineers designed and conducted the hydrologic analyses. Tasks included:
- Collaboration with staff from the US Geological Survey, USACE Hydrologic Engineering Center, Federal Emergency Management Agency, and members of the CVHS hydrologic advisory committee to define study objectives and methods.
- Review of Bulletin 17B and development of study procedures for a systemwide analysis.
- Compilation and review of the historical record from gages throughout the system.
- Development of HEC-HMS precipitation-runoff models for estimation of local flow from ungaged watersheds.
- Development of HEC-ResSim reservoir operation models to simulate the regulated flow condition.
- Development of HEC-RAS hydraulic models to route flow through the system.
- Development of IPAST, a software application to facilitate the extraction of model results and process those results to create the required hydrologic outputs.
- Statistical analysis to develop flow-frequency curves.
- Estimation of the effects of climate variability on the CVHS flow-frequency analysis.
- Presentation of methods and results to stakeholders throughout the multi-year study, including development of a Web forum to disseminate information and facilitate discussion.
- Preparation of method documentation, plans, and the final report.
Along with USACE, we developed the following key products, which have been applied to major studies including the Central Valley Floodplain Evaluation and Delineation Program and the Central Valley Flood Protection Plan.
- Unregulated flow time series based on the historical record.
- Unregulated flow-frequency curves at about 200 key locations.
- HEC-ResSim models of the Central Valley.
- Identification of the critical duration for 138 key locations in the Central Valley.
- Regulated flow time series (unregulated flows routed through the reservoir model).
- Products to illustrate application such as unregulated-to-regulated flow transforms and regulated flow-to-stage transforms.