Deal reached to expand massive reservoir near Bay Area to increase water supplies

In a significant boost for increasing Northern California’s water supplies, eight water agencies have reached an agreement with the federal government to spend nearly $1 billion to raise the height of the dam at one of California’s largest reservoirs, San Luis Reservoir between Gilroy and Los Banos.
Already the fifth largest reservoir in the state, San Luis would expand by 130,000 acre feet — enough water for 650,000 people a year — under the deal, which calls for raising its 382-foot dam by 10 feet to store more water during wet years to use during droughts.
The agreement is set to be commemorated Wednesday at an event at the Department of Interior in Washington, D.C.
Santa Clara County residents would be the main beneficiaries of project, which requires rerouting more than 1 mile of Highway 152.
Under the deal, the Santa Clara Valley Water District, a San Jose agency that provides water to 2 million residents in Santa Clara County, would contribute $435 million of the $942 million cost of the project. It would receive the largest share of the new water, 60,000 acre-feet, or the equivalent of building three new reservoirs the size of its Lexington Reservoir in Los Gatos.
Other agencies that would receive some of the water are the massive Westlands Water District in Fresno, the Byron Bethany Water District in Contra Costa County, the city of Tracy, the San Benito County Water District and the Del Puerto, San Luis and Pacheco water districts.
“This is a really big milestone,” said Cindy Kao, imported water manager for the Santa Clara Valley Water District. “It’s an agreement in principle that takes us a big step forward to making this project a reality.”
Under the deal, the U.S. Bureau of Reclamation, which built San Luis Reservoir in the 1960s, signed an agreement with the San Luis Delta Mendota Water Authority. The authority is an influential agency of 29 water districts that purchase water from the federal government, most of them in the Central Valley, but which also includes the Santa Clara Valley Water District. All eight signatories are members of the authority.
“We’re happy it made it across the finish line,” said Cannon Michael, a Los Banos farmer and chairman of the San Luis Delta Mendota Water Authority. “It’s a project with no opposition, which is rare for California water, and a lot of benefits.”
Under the deal, the federal government will put up 30% of the funding and receive 30% of the new storage space in the reservoir, or 39,000 acre-feet. The eight water agencies will contribute 70% of the funding and receive 91,000 acre-feet. Construction would begin in 2027 and end in 2032, overseen by the Bureau of Reclamation.
The project still has hurdles to overcome, including securing permits and the eight water districts agreeing to form a legal authority to complete details such as financing and planning.
Environmental groups that have fought new dams on rivers for decades say they generally do not oppose this one, since the off-stream reservoir has been in place since the 1960s, and all of the canals, pipes and pumps associated with it are already there.
“There are other dam proposals that take out whole river canyons or flood Indian cultural sites, or violate wild and scenic river rules,” said Ron Stork, policy director at Friends of the River, a Sacramento environmental group. “This one doesn’t do those things. It just makes a larger bathtub ring around the reservoir. There are things that could go wrong but this one has a pretty good chance of being built.”
California has suffered through three severe droughts since 2007.
Scientists say that as the world continues to warm from climate change, increased temperatures are making droughts worse. They are also increasing the power of atmospheric river storms in the winter, because more moisture evaporates into such storms during warmer temperatures.
As a result of the new “weather whiplash,” the administrations of President Biden and Gov. Gavin Newsom have pushed to construct more reservoirs to capture water during wet years to reduce impacts on cities, farms and fish during the inevitable droughts.
Constructing new dams can be highly controversial. Often their costs run in the billions, and rural agricultural areas don’t have the money to fund them alone. When they are proposed to block rivers, they meet strong resistance from environmentalists.
One promising project, a $1.5 billion plan to increase the height of the dam at Los Vaqueros Reservoir in Contra Costa County, adding 115,000 acre-feet of new storage, collapsed in September when the Contra Costa Water District and other Bay Area water agencies couldn’t agree on who would shoulder the costs and risks.
San Luis Reservoir is among the most remarkable engineering projects in California’s water system. The largest off-stream reservoir in the United States, it is a vast inland sea, 7 miles long, that is visible to motorists driving past Pacheco Pass on Highway 152 between Santa Clara County and Los Banos.
Construction began when President John F. Kennedy pushed a dynamite plunger there in 1962 with former Gov. Pat Brown. Today water from the massive lake irrigates farms across the Central Valley and also provides drinking water for Silicon Valley, including San Jose.
Its huge earthen dam, named for Democratic congressman B.F. Sisk, who represented the Central Valley from 1955 to 1979, is is 3.5 miles long at its crest — twice the length of the Golden Gate Bridge.
Two years ago, the Bureau of Reclamation began a $1.1 billion project to retrofit the dam and strengthen it against earthquakes. The new agreement, if completed, would add the dam-raising project to the ongoing seismic work.
“We’re excited,” Michael said. “This is a critical project. Hopefully we can demonstrate it can get done.”