Augmentation of CVP Water Supplies Through Reservoir Reoperation and Conjunctive Use With Fluvial Process Restoration
How much potential increase in water yield can be realized through water supply project reoperation with conjunctive use for the river systems in the Central Valley of California? Preliminary analyses indicate the potential for at least a 1,000,000 AF increase in water yield. Through this reoperation, can essential fluvial processes be restored that enhance fisheries? What is the combined benefit of increased water supply and aquatic habitat restoration?
Need and Benefit
Meeting growing water needs in the Central Valley of California, including water for the environment, requires new strategies for expanding the benefits derived from a fixed yield of water. It is possible that this can be accomplished through more productive operation of existing storage and delivery infrastructure with some additions to the system, particularly actively recharged groundwater banks. Initial studies by NHI indicate that at least 1,000,000 AF of additional water yield could result from this strategy.
This research seeks to define the opportunities and constraints on reservoir reoperation conjunctively managed with groundwater banks, secondary storage, and off stream storage in the Central Valley, both as stand-alone strategies and in combination. A system-wide approach has the potential to yield significant environmental benefits by augmenting water supplies through reoperation of the terminal reservoirs, and conveying pre-delivered water to secondary storage through existing river corridors in a manner that restores more natural fluvial processes and improves ecological conditions. The ecological functionality of the down-river segments will require new operating rules that simultaneously allow for the recovery and storage of pre-delivered water and the re-establishment of the magnitude, duration, and frequency of flows capable of mobilizing, transporting, and depositing sediments.
The Bureau of Reclamation has statutory obligations under the Central Valley Project Improvement Act (CVPIA) of 1992 to assess the potential for modifications in the operations of the CVP to contribute to the Act's fish and wildlife restoration mandate (Section 3406(b)), to develop a program to supplement the water available for that mandate through water management techniques including "conjunctive use" and "groundwater banking" (Section 3406(b)(3)), and to develop "least cost" plans to replace the CVP yield dedicated to that mandate (Section 34080)). Water 2025 calls for similar new strategies to increase water yield.
The primary hypothesis is that reservoirs can be reoperated to release water in a pattern that could produce the desired fluvial process benefits, while still meeting all existing obligations for water supply and environmental restoration. The "surplus" water committed to this purpose will be generated by reoperating reservoirs to allow for greater capture of the peak flows in existing on-stream reservoirs; that is, water that would otherwise be released for flood control purposes. This can be done by conveying some portion of the water released for fluvial restoration into a secondary storage facility, either a groundwater bank or an off-stream storage facility, in advance of the wet season to create additional flood retention capacity in the reservoir. The foregone flood control releases held in secondary storage will allow all water supply obligations of the reservoir to continue to be met. Any water released for fluvial process restoration that cannot be conveyed to secondary storage could be allowed to flow through the system to meet Delta inflow/outflow requirements for the entire Central Valley. Each reservoir does not need to be reoperated every year for fluvial benefits. Rather, ecosystem restoration operations could be coordinated to produce fluvial process restoration flows on rotating basis.