The California Department of Water Resources (DWR) has released the third phase of a study evaluating potential options for the reoperation of the state’s existing flood protection and water supply systems to provide increased benefits. The Phase III report, titled Assessment of Reoperation Strategies, concludes that potential benefits to water supply, ecosystem, and flood management are limited, but more significant benefits could be achieved with investment in new infrastructure.

The state’s water supply systems currently are operated to meet regulatory requirements, contractual obligations, and operating rules. In 2008, the state Legislature authorized and directed DWR to identify options for the reoperation of the state’s existing flood protection and water supply systems to achieve three objectives: 1) increased water supply reliability, 2) flood protection, and 3) enhanced ecosystem.

In Phase III of the multi-phased study, DWR evaluated reoperation strategies in greater detail for Shasta Lake, Lake Oroville, and Lake McClure, in coordination with their associated groundwater basins to achieve the three objectives. Reoperation strategies included basing operations on five-day weather forecasts, managing reservoirs in closer alignment with groundwater storage (known as conjunctive use), and increasing river flows to benefit the ecosystem. The Phase III Report also describes the potential benefits of operating the State Water Project (SWP) and Central Valley Project (CVP) as a single project, sharing storage and conveyance facilities.

Following are the key findings of the study:

·Reoperating Oroville, Shasta, and McClure individually would have limited benefits, mainly because the reservoirs and their associated projects already are significantly optimized to meet existing flood and regulatory requirements and contractual commitments.

·Operating the SWP and CVP as a single project would provide incremental water supply reliability and ecosystem restoration benefits; combined average annual water deliveries could increase by 100-150 thousand acre-feet per year.

·Reoperation benefits were evaluated under existing and new Delta conveyance, and under current and projected future climate conditions. Projected benefits of reoperation under these scenarios were similar.

·Achieving additional benefits likely would require investment in new infrastructure.

For this study, DWR developed an analytical framework to guide the formulation and evaluation of various combinations of reoperation strategies. Water agencies and system owners and operators can apply this reoperation framework to formulate their own range of reservoir and system reoperation scenarios to evaluate features such as:

·Public benefits associated with proposed reservoir reoperation projects for the Proposition 1 Water Storage Investment Program.

·Surface water available for groundwater replenishment to help meet requirements of the Sustainable Groundwater Management Act.

·Additional flow releases from existing reservoirs to improve ecological conditions in the Delta and upstream watersheds to inform the Bay-Delta Water Quality Control Plan Update and Voluntary Settlement Agreements.

Following are the recommendations for the next phase of the study:

·Evaluate potential for using flood water for managed groundwater recharge on farmland and working landscapes to achieve flood protection, drought preparedness, aquifer remediation, and ecosystem restoration.

·Evaluate existing flood operating rules of reservoirs under changing hydrology.

·Assess feasibility of existing reservoir spillways and outlets to pass floodwater safely with changing hydrology.

·Identify challenges and opportunities in implementing system reoperation.

The analytical framework developed in this study will be useful for water agencies and reservoir owners and operators interested in evaluating opportunities for potential benefits through reoperation of their water systems.