Reducing the Risk of Flooding in California

More than 1 million Californians live and work in the Sacramento-San Joaquin Valley where flood risks are among the highest in the nation. The California Department of Water Resources launched the statewide FloodSAFE initiative to improve public safety through integrated flood management.

To inform FloodSAFE decision making, DWR, in partnership with the U.S. Army Corps of Engineers, Sacramento District, conducted the Central Valley Hydrology Study to obtain the required hydrologic information. The study assessed stream flow frequencies and magnitudes in the Sacramento and San Joaquin river basins. The objective was to estimate peak flows and hydrographs for various annual exceedance probabilities to describe flood hazard throughout the basins.

As principal contractor for USACE, we designed and conducted the hydrologic analyses. Our work included:

• Collaboration with U.S. Geological Survey, USACE Hydrologic Engineering Center, Federal Emergency Management Agency, and members of the CVHS hydrologic advisory committee to define study objectives and methods
• Compilation and review of  historical record from gauges throughout the system
• Development of HEC-HMS precipitation runoff models for estimation of local flow from un-gauged 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 software to facilitate extraction of model results and process those results to create the required hydrologic outputs
• Presentation of methods and results to stakeholders throughout the multiyear study, including development of an online forum to disseminate information and facilitate discussion
• Preparation of method documentation, plans, and final report 

With the 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

The Floodplain Management Association and American Society of Civil Engineers recognized CVHS with outstanding project awards.