This column was contributed by Jennifer Cosio Arellano, water conservation program manager with the Water Resources Association San Benito County. The opinions expressed do not necessarily represent BenitoLink or other affiliated contributors. Lea este artÃculo en español aquÃ.
On January 17, 2025, the United States Bureau of Reclamation (Reclamation) and the San Luis & Delta-Mendota Water Authority (SLDMWA) signed a cost share agreement for the B.F. Sisk Dam Raise and Reservoir Expansion Project (Sisk Dam Raise). The project would add much needed water storage to the Central Valley Project and improve water supply reliability for SLDMWA members. SLDMWA is a joint powers authority representing water and irrigation districts that together supply water for two million people, over one million acres of farmland, and 135,000 acres of wetlands and wildlife habitat, including areas of San Benito County. Â
The San Benito County Water District (District) first started receiving deliveries of imported water from the Central Valley Project in the late 1980’s to alleviate overdraft in the local groundwater basin and to improve water quality for agricultural and municipal customers. The reliability of these supplies has decreased over time, mainly due to increasingly stringent regulations to protect the environment and water quality in the Sacramento-San Joaquin Delta. The District has been participating in the planning process for the Sisk Dam Raise project to mitigate these impacts and ultimately increase the reliability of its imported supplies. It would allow the District to store water in wet years that currently goes unused and save it for droughts when it is needed more.
The Sisk Dam Raise would add approximately 130,000 acre-feet of water storage to San Luis Reservoir by raising the dam’s embankment by 10 feet. Under the terms of the cost share agreement, Reclamation would reserve 39,000 acre-feet of the new storage for its own use and provide 30% of the project funding. The remaining 91,000 acre-feet of storage, or 70% of the project, would be funded by contributions from the participating water agencies. The District has tentatively reserved a storage allocation of 5,033 acre feet, which equates to 5.5% of the non-federal contribution. A final decision on project funding is not expected until 2027.
Separately, Reclamation is also working on another project with the Department of Water Resources (DWR) to implement the B.F Sisk Safety of Dams Modification Project (Safety of Dams Project). This project, once complete, will raise the dam an additional 10 feet beyond that is needed for additional water storage, but will not increase the storage capacity of the dam. The purpose of the Safety of Dams Project is to protect San Luis Reservoir in the event of an earthquake. It entails adding stability berms, shear keys, and other safety features to the existing 3.5-mile-long dam. Alongside the work being done at the dam, there will be additional modifications to various structures around the reservoir to accommodate the increased water storage due to the Sisk Dam Raise project. There will also need to be modifications to State Route (SR) 152 where it crosses the San Luis Reservoir at Cottonwood Bay to accommodate the expanded reservoir’s increased water surface levels.
Overall, both projects will benefit the state of California in various ways. By increasing our water storage options, we will be able to improve water management, especially for municipal customers in times of severe or multi-year droughts and for critical wetland habitat. Additionally, the Sisk Dam Raise project will improve the public safety of SR 152 by reducing seismic risk and protect commuters with safer road infrastructure.
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