For nearly two decades, Los Vaqueros Reservoir — a sprawling lake in eastern Contra Costa County nearly 3 miles long and 170 feet deep — has been a popular spot for boating, fishing, hiking and a key source of water for local residents.
But now, after years of drought and new money available from a 2014 state bond measure to fund water projects, a long-standing idea to dramatically enlarge the reservoir to help provide drought insurance to cities all the way to San Jose is gaining momentum.
Some environmentalists say the idea, which they support, also would reduce the need for Gov. Jerry Brown’s controversial $17 billion plan to build two huge water tunnels under the Sacramento-San Joaquin River Delta.
The plan, which would cost roughly $800 million, is simple: Raise the earthen dam by 51 feet, to 269 feet high. That would make it the second tallest dam in the Bay Area, eclipsed only by Warm Springs Dam, at 319 feet tall, on Lake Sonoma near Healdsburg.
The proposal would expand the size of Los Vaqueros, located in the rolling hills near the Alameda-Contra Costa county line, from its current 160,000 acre-feet capacity to 275,000 acre-feet, enough water when full for the annual needs of 1.4 million people.
Other water agencies — including the Santa Clara Valley Water District, the East Bay Municipal Utility District and the Alameda County Water District — are in early talks with the Contra Costa Water District, which owns the reservoir, over whether they would help pay to construct the project so they could draw water from the enlarged lake, particularly during dry years.
“There’s new interest because of the drought and the project’s benefits,” said Marguerite Patil, who oversees expansion studies for the Contra Costa Water District. “And there’s some opportunity to get state matching funds. It seems like good timing.”
The idea was first floated shortly after Los Vaqueros was built in 1998 with $450 million from the 500,000 customers of the Contra Costa Water District.
It surfaced again in 2010 when the district won an advisory vote from its customers to increase Los Vaqueros’ size by raising the dam 34 feet. But at the time, the economy was struggling, and there were few state matching funds. So Contra Costa officials could not find other agencies to help foot the bill for the larger, 275,000 acre-foot option.
Now times have changed again.
Other agencies, particularly the Santa Clara Valley Water District, which provides water to 1.9 million people in Silicon Valley, are taking a fresh look.
“It’s a concept that’s worth exploring,” said Barbara Keegan, chairwoman of the district’s board. “We have to look at many options. I don’t think it’s wise to put all our eggs in one basket. It’s an interesting idea that requires additional study.”
Contra Costa officials are working on detailed environmental studies and a feasibility study with the U.S. Bureau of Reclamation. Both documents are scheduled to be finished next year.
The officials also have submitted a “concept paper” to the California Water Commission, a state panel that will decide how to hand out some of the $7.5 billion in Proposition 1 bond funding approved by voters in 2014.
“We’ll find out over the next year who is serious and who is ready to pursue it,” Patil said.
The project would require a pipeline to be built about 8 miles from Los Vaqueros to the South Bay Aqueduct, a series of pipes and canals that takes Delta water 40 miles to San Jose from Bethany Reservoir near Livermore.
Contra Costa says the benefits to Bay Area water agencies are clear. A bigger reservoir could be filled up in wet years, providing more water in dry years.
Another key issue: Los Vaqueros does not use the massive federal and state pumps near Tracy to divert water from the Delta into its storage. Those pumps are regularly slowed when endangered fish, such as salmon, smelt and steelhead, are nearby and at risk of being killed by them.
Instead, Los Vaqueros has two intakes, at Old River near Discovery Bay and on Victoria Island in the Delta. Those intakes draw water at a much slower rate than the state and federal pumps, and they have modern fish screens.
That feature could allow agencies such as the Santa Clara Valley Water District to more easily take water from the Delta, which makes up 40 percent of its supply, without as many headaches.
Supporters of Brown’s tunnels plan contend that the tunnels also would reduce reliance on the state and federal pumps by moving water through the Delta more easily. But environmental groups say that the project — which critics call a Southern California water grab — is almost certain to be tied up in court for years.
“This project could be a less expensive approach to getting greater water supplies, particularly in dry years when it is needed the most, without a decade of costly and unproductive litigation,” said Jonas Minton, a former deputy director at the state Department of Water Resources who is now with the Planning and Conservation League, a Sacramento environmental group.
Keegan said that fact isn’t lost on the Santa Clara Valley Water District.
“Development of alternative sources could help us in our decision-making process in terms of whether we support or don’t support the tunnels,” she said.