Three reservoir projects in the Diablo Range on the westside of both the Northern San Joaquin Valley and the Delta are part of a strategy to store receive runoff during wet years to cushion California water supplies against prolonged drought.

The projects — raising San Luis Reservoir, building a Del Puerto Canyon dam and raising Los Vaqueros Reservoir — would add 245,000 acre feet of water storage capacity.

When coupled with the proposed Sites Reservoir in the Antelope Valley portion of the Coastal Range — of which the Diablo Range is a subrange — an additional 1,827,000 acre feet of off-stream storage could be created.

That — as Congressman Josh Harder has pointed out — comes close to providing capacity for 2 million acre feet of “excess” water that experts contended could have been captured during the heavy winter storms.

But that comes with a huge caveat.

The existing Delta water operations involving water capture and release would need to be altered for the most effective outcome for increased water storage.

Under a “first flush” protocol based on a biological opinion issued by the federal government in 2019 and “take permits” issued by California in 2020, if the additional capacity had been in place — at least south of the Delta at San Luis and Del Puerto — it may not have made a difference.

That’s because the first flush policy requires two weeks of reduced pumping into the California Aqueduct intake northeast of Tracy at the onset of the first big winter storm.

The idea is to send enough water through the Delta to “flush” the endangered Delta Smelt away from the pumps.

The pumps — based on the order — were running at about 50 percent capacity from Jan. 3 through Jan. 16.

That meant 84,000 feet of water that could have been pumped into the off-stream San Luis Reservoir flowed into the ocean.

That 84,000 acre feet of water would have been enough to irrigate 25,000 acres of farmland for a year or cover the needs of 150,000 households for a year.

The subsequent spring snowmelt did end up filling the 2 million acre foot San Luis Reservoir.

Elected leaders in Sacramento on both sides of the aisle criticized how more eater was diverted into storage based on the biological opinion which, ironically, could be used to justify the $16 billion Delta tunnel that most adamantly oppose.

That’s because had the tunnel been in place during the winter storms, it would have moved 180,000 more acre feet — according to the state Department of Water Resources — around the Delta to the head of the California Aqueduct to avoid the pumps.

That may have eased concerns about not capturing excess water that isn’t needed to sustain the Delta ecological  system from running into the ocean during winter storm. But having a tunnel in place with an intake on the Sacramento River before it runoff reaches the Delta would mean it could also divert water during tight water supply times such as a drought.

It is that feared diversion that would significantly upend the sustainability of water supplies for the Northern San Joaquin Valley in times of drought

That’s because other fish flow orders in place during the summer and spring would  likely force the cannibalization of existing water rights on the Merced, Tuolumne and Stanislaus rivers’ collective watersheds.

What the four dam

projects would add

The B.F. Sisk Dam’s proposed expansion in Merced County  would add 130,000 acre of feet of storage to the 2 million  acre foot capacity of the San Luis Reservoir along Highway 152 west of Los Banos and Interstate 5.

The Del Puerto Canyon reservoir project west of Patterson in Stanislaus County would add 82,000 acre feet.

 The Los Vaqueros project in Contra Cista County would add 115,000 acre feet of capacity to bring it to 275,000 acre feet of overall storage.

The 1.3 million acre foot Sites reservoir is in the Antelope Valley portion of Glenn and Colusa counties.

Together, the four projects would create almost a third of the capacity now in the State Water Project that can store 5.8 million acre feet with the most being behind Oroville Dam with 3.5 million acre feet.

The four projects are equal to almost a sixth  the storage capacity of the 12 million acre foot Central Valley Water Project. Shasta Dam with 4.5 million acre feet is its biggest component.

New Melones Reservoir, on the Stanislaus River has 2.4 million acre feet of storage or just 600,000 acre feet more of the combined storage of the four projects.

As such, the four projects combined represent a significant increase in California’s surface storage.

More importantly, they dovetail into changing climate scenarios and do so by being off-stream storage. That means they don’t’ interrupt fish flows and such.

Long before “climate change” became prevalent in modern day conversations, the concept of large dams in the Sierra and higher elevation of the foothills for water storage per se as opposed to flood control had passed.

San Luis Reservoir, completed in 1967 in the Diablo Range foothills west of Los Banos, is the largest off-stream reservoir in the United States with 2 million acre feet of storage.
Even in non-drought years, the water level can get low.

That’s because it is fed by excess stormwater as well as excess snowmelt from the Sierra.

 It’s a holding pond, if you will, for water ultimately heading farther south.

The Sites Reservoir — first proposed in the 1950s — is on target to become the state’s next major reservoir.

Nestled in foothills of western Colusa and Glenn counties, it has been inching in earnest toward groundbreaking and a 2031 target completion date for the better part of the last decade since voters approved a statewide water bond in 2014.

It is designed to add up to 1.3 million acre feet of storage that would be used to help supply water for up to 27 million Californians and 500,000 acres of Central Valley farmland. It also would provide water for fish needs in dry years

To get an idea of the impacts it will have, the storms that dropped 120,000 acre feet of water on California the first two weeks of January was enough to serve the needs of 1.3 million Californians for a year.

Most of that water — a large amount of the precipitation of that fell in the Northern Sacramento Valley — went out into the ocean.

Climate patterns, that are following patterns going back over 800 plus years and verified via the carbon dating of trees, means less precipitation in northern and central California.

That said, while there will be less overall precipitation, there will be more rain at the lower elevations and less snow at the higher elevations.

There aren’t that many sites left where the soil, rock formations, and location are all ideal for larger off-stream reservoirs on the scale of San Luis or Sites.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com