In over-subscribed water systems across the globe, water managers must devise ways to meet future needs in every sector out of a fixed endowment of water and its storage and delivery infrastructure. Global climate change is one driver of new water storage as runoff patterns become more intense and compressed. Conjunctive management of surface and groundwater resources is a tool that can help meet this considerable challenge.
In the immense and complicated water system of the Central Valley of California, reoperating existing reservoirs in conjunction with groundwater banks could generate surplus water to restore more natural flow patterns in the eleven regulated tributaries of the Central Valley – comprising by far the largest ecosystem restoration program ever undertaken in this geography – while also satisfying growing demand from agricultural and urban users. Because it utilizes existing infrastructure, conjunctive management is faster and less costly to implement than other water supply augmentation strategies. Indeed, it could generate more new water supply than any other current alternative, and, uniquely, do so without any governmental subsidies.
NHI is developing a system-wide roadmap that shows how to optimize the entire Central Valley system through conjunctive management of surface and groundwater to produce these results. Under the system-wide approach, the storage and release regime of the Central Valley tributaries’ eleven existing terminal reservoirs would be modified to capture a larger fraction of peak-flow events as they move through the system. Additional storage capacity would be created by moving a substantial portion of the reservoir water into groundwater banks in basins with currently unutilized storage capacity. Thus, reservoir reoperation would provide source water to actively recharge groundwater banks with water that would otherwise spill for flood control. In drier years, the banked water would be recovered and reintegrated into the existing (or enhanced) water delivery system to provide supply benefits throughout the system. Enhanced storage in the terminal reservoirs creates operational flexibility that allows the surplus peak-flow water to be released into the downstream river system in a pattern that restores more natural fluvial and geomorphic processes for aquatic habitats. This management technique will substantially improve the capacity of existing infrastructure to control flood events.
The system-wide analysis has now progressed through the “proof of concept” stage, and NHI is applying the results in regional demonstration projects. The first regional component is being developed in the Sacramento Valley in collaboration with the Glenn Colusa Irrigation District, the Northern California Water Authority and local water managers. In the context of a basin-wide integrated water management plan, we are exploring options for linking the largest federal Central Valley Project reservoir (Lake Shasta) and the State Water Project reservoir (Lake Oroville) with the local groundwater system. In this case, conjunctive management holds the promise of improving supply reliability, eliminating risk factors associated with increasing groundwater use, and restoring aquatic habitats in the Sacramento and Feather River basins.
The Central Valley of California could provide a model for conjunctive management to be used in watersheds worldwide. NHI is using our system-wide analysis as the foundation for a global initiative on dam reoperation.