A federal leader last week mentioned a study to raise San Luis Dam and expand the nearly empty San Luis Reservoir in western Merced County, raising eyebrows all around. Why study expansion of a reservoir holding 16% of its capacity? And why now?
First, a little context. San Luis Reservoir is an important hub in California’s waterworks — supplying both west San Joaquin Valley farmers and Southern California cities. The reservoir has no natural stream to fill it, so water is pumped there from the sensitive Sacramento-San Joaquin River Delta.
San Luis Reservoir at 16% this month.
When pumping was restricted this year to protect dying fish species and water quality, California lost the opportunity to send a lot of water into the reservoir. The lost pumping and the drought have turned the reservoir into an August mud puddle.
So why look at expanding San Luis Reservoir now?
Half of the answer: It’s part of the ongoing efforts under the Central Valley Project Improvement Act, a 1992 environmental reform law that includes a section to improve water supply.
The other half: The U.S. Bureau of Reclamation is going through a dam safety study. The planning division is appraising a project to both reduce earthquake risks and improve deliveries to the federal Central Valley Project.
At the same time apparently, water customers began asking about expanding the capacity of the reservoir.
By sometime next year, the appraisal study will let federal leaders know if they should do a full-blown feasibility study.
This is all part of a bigger fight, pitting Northern California against Southern California over water. It’s a story that has played out over decades. Another chapter is about to be finished as the state prepares the Bay Delta Conservation Plan, touted as a way to fix this marathon problem. It’s a nerve-racking process.
The short-term solution makes everyone even more nervous: Hoping for a wet winter. This problem could get much worse if California gets a third year of drought.
The U.S. Bureau of Reclamation is preparing a report on raising San Luis Dam to enlarge San Luis Reservoir in western Merced County.
The 2 million acre-foot reservoir is already the key west Valley holding place for irrigation water for a broad swath of farming, including 600,000-acre Westlands Water District.
Bureau Commissioner Michael Connor on Saturday mentioned his agency is working on a draft appraisal, which roughly describes the benefits, costs and feasibility of raising the dam. Connor was a panel member at the Delta Water Summit.
He did not say why the appraisal is being done now or release other details, such as how much larger the reservoir would become. His statement about the possible enlargement of San Luis was a surprise to many water agency officials and observers.
The appraisal report should be ready in October. If it appears feasible, the bureau would complete a final feasibility study within a few years.
San Luis is one of the largest off-stream reservoirs in the country, but it is only holding 16% of its capacity right now. Drought and environmental water pumping restrictions in Northern California have left it near historic lows.
Remember those stories last week about a record-setting, scary-sounding dry spell for the combined months of January and February? You’ll forget all about them if we see a series of storms this month and next.
The record dry time is actually in the Northern Sierra, the most important watershed in the state, as my Sacramento Bee colleague Matt Weiser wrote. That snowpack melts into the state’s biggest reservoirs.
At the federal pumps near Tracy in the south delta.
But the Northern Sierra is actually in better shape than it was at this time last year. So is the Southern Sierra. The snow from the big storms in November and December is mostly still up there. It hasn’t melted.
The huge reservoirs in Northern California — Shasta, Oroville, Trinity — are all holding an above-average amount of water right now. We’re not hearing anything yet about water restrictions in the Bay Area.
The real concern is San Luis in western Merced County, where west San Joaquin Valley farmers get water.
It is not a mountain reservoir. It does not have a big, natural stream, unlike the reservoirs I’ve mentioned. It is one of the larger off-stream reservoirs you will find anywhere in the United States.
So, water must be pumped into San Luis from the Sacramento-San Joaquin River Delta, 120 miles away. The delta pumping has been limited to protect the dwindling delta smelt. So it San Luis only at 69% of average right now.
The reservoir is 2 million acre-feet — about four times bigger than Millerton Lake, though it’s not all devoted to the Central Valley Project. The state stores water there, too.
Many experts tell me they don’t think it will fill.
There are bigger questions now, because pumping for San Luis usually continues well into the warm season to provide water. To provide enough water, the reservoir needs to get continuous pumping from the delta in spring.
What if the weather stays dry? What if the pumping restrictions continue at the delta? How much water will be available in May and June when the thermometer starts to climb?
Should farmers fallow a lot of acreage? Should they drill new wells and keep pulling water from the ground?