Federal officials study enlarging San Luis Reservoir

jsbranti@modbee.com and tmiller@mercedsunstar.comDecember 8, 2013 

Water levels appear frighteningly low at the San Luis Reservoir, but water officials assure that is relatively normal this time of year.

In fact, government researchers have just completed a study about expanding the reservoir, which they say would increase California’s water storage capacity and improve the reliability of water supplied by Central Valley Project canals.

The U.S. Bureau of Reclamation estimates it would cost $360 million to raise B.F. Sisk Dam by 20 feet and expand the reservoir by 130,000 acre-feet of water. The proposed project also would make the dam more earthquake safe as well as raise the dam embankment, dikes, spillway, intake towers and access bridge.

San Luis gets a spotlight each summer as west San Joaquin Valley farms and Southern Californians call for more water.

Sisk Dam and San Luis Reservoir are about 12 miles west of Los Banos in Merced County. They are key parts of the Central Valley Project and the State Water Project. The dam was completed in 1967. When the reservoir is full, currently it can hold more than 2 million acre-feet of water.

That water is stored for both agricultural irrigation and domestic needs.

Unlike reservoirs near the Sierra Nevada that hold runoff from melting snow, the San Luis Reservoir gets most of its water pumped to it from the Sacramento-San Joaquin Delta.

Drought and environmental pumping restrictions kept the reservoir level to near-record lows this past summer, much to the dismay of farmers and city users. So San Luis has been hot news this year. Though there have been a couple of dry years, an enlarged capacity would help in wet years.

Chris White, general manager for the Central California Irrigation District, said during a wet year, the reservoir will fill up in the spring. Any excess water flows on through. “In those years where they can capture a little more water, having a place to put it would be a good thing,” White said.

Dave Robinson, agriculture commissioner for Merced County, said an increased capacity would certainly be good news to west side farmers. “That reservoir is a critical part of irrigation on the west side,” he said, adding the area has struggled with drought and federal regulations. “Increased capacity, I think, would be very valuable, if you can move water into it.”

The possibility of raising the dam has been considered since 2001 as a way to increase reliability of water deliveries. Uncertain water supplies make it hard for farmers to plan their crops, obtain financing and make other decisions about their farms, the report contends.

Lack of reliable irrigation water from canals has been cited among the reasons San Joaquin Valley farms have started pumping more groundwater. Concerns about falling groundwater levels and the sinking surface levels it causes is growing.

In a different report issued last month, parts of Merced County near El Nido were found to have subsided by more than 21 inches in just two years because of overpumping aquifers.

But water supply isn’t the only reason this appraisal was done, says the U.S. Bureau of Reclamation.

The enlargement also would allow the federal government to shore up the dam and reduce earthquake risk. The Ortigalita fault crosses beneath the reservoir.

Expanding the reservoir also would help prevent algae blooms that affect water quality for city water users.

Dos Palos is no stranger to algae blooms. Clogs from algae buildup deserve much of the blame for the city’s water woes that began in September, according to city officials. The algae blocked the filtration system, which took about six weeks to fix.

Dos Palos’ system siphons water from the California Aqueduct, about 17 miles from the city limit. Some of that water comes from the reservoir.

“It’s not just agricultural, it’s residential water,” said Darrell Fonseca, Dos Palos’ city manager. “Everybody can share in it, we just need to manage it better.”

“We haven’t made a decision to expand the reservoir yet. This report is just on what it would cost, its benefits and feasibility,” said William Aley, a project manager for the Bureau of Reclamation.

The San Luis Reservoir Expansion Draft Appraisal Report determined raising the dam is technically feasible, and it recommends numerous additional studies be done on exactly how it could be done and who could fund it.

The 160-page report is posted at this link. The Bureau of Reclamation is accepting public comments about the report through Jan 17.

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