Does Drought-Prone California Need Another Reservoir?

For a century, California and the West have grappled with the job of storing water. The first half of the 20th century was the heyday of western dams; now many of them are aging; they were designed for the needs and values of another era. The benefits were clear: a 2021 article in Environment Research Letters, using data going back a century, noted, “Arid regions with access to stored water avoided the 13 percent losses in crop value experienced in areas with more limited storage during droughts.” It added, “it is unlikely that the U.S. will witness another dam bonanza like the West’s in the mid-20th century.”

“Every major river in California is dammed and some have two or more,” notes the web page of the environmental group Clean Water Action. The last big dam was completed in 1980. So, after building about 1,500 dams and more than 1,300 reservoirs that can store 43 million acre-feet of water, is California dammed out? If more storage is called for, where can it go? And if water is needed to fill it, where would that come from?

In principle, more storage is good, said Jay Lund, co-director of the Center for Watershed Sciences at the University of California, Davis. The persistence of droughts and the likelihood that climate change will exacerbate them reinforce this idea. “If you have a bigger house and an extra room is offered for free, you would always take it,” he said.

“But if you have to pay for it, you’d think about it more carefully… We have 1,500 rooms — or regulated dams — in California. That doesn’t mean the 1,501st room is not worthwhile. But you want to scrutinize it more…. 

“The best sites are already taken. Now we have more expensive sites that generally yield less water… In terms of water delivery and economics, things are not as great as they used to be — without even getting into the environmental costs,” Lund said.  

Efforts to Increase Reservoir Storage Focus on the Sites Project
The largest and most visible of the three pending reservoir projects is the proposed Sites Reservoir.  A separate plan to increase the size of Shasta Dam and its reservoir — the state’s largest, located on the upper Sacramento River —  gained steam during the Trump administration, but seems less possible now. But the push for new storage remains pressing. The discussion of Sites Reservoir, its funding, its potential benefits and potential drawbacks are a microcosm of the larger questions facing California.

These include: how much new infrastructure is worth the expense and effort, and who pays? How much will fish, rivers, and wetlands suffer from new reservoir projects? Should local water agencies also find more storage capacity in depleted aquifers? And finally, is it more important to increase supply or to reduce demand?

Such questions and a host of technical, financial, legal, ecological, hydrological, and political complications have dogged all suggestions for new storage in the eight years since California voters passed a $7.5 billion state water bond, known as Proposition 1. Some $2.7 billion of the 2014 bond is designated for storage projects. 

The financial picture of the Sites project became far more secure in recent weeks, after the California Water Commission reaffirmed its support for spending $875 million in Proposition 1 funds for the Sites project. The federal Environmental Protection Agency then announced Sites can get a $2.2 billion low-interest loan. The federal Agriculture Department already agreed to loan Sites $450 million. Federal funds from the 2016 Water Infrastructure Investment for the Nation Act (WIIN) and last year’s infrastructure act will cover some of the remaining cost of $975 million.  In April, the Metropolitan Water District of Southern California agreed to give the Sites agency $20 million for planning expenses

The Sites reservoir would not need an old-fashioned dam — a good thing, since putting new dams on any of the state’s heavily dammed rivers and creeks is surpassingly difficult. Instead of holding back a river directly, Sites will be an “off-stream” reservoir: Its water will be pumped in from a river that might have occasional excess flows. 

California’s off-steam reservoirs include Diamond Valley Lake in Riverside County, the San Luis Reservoir at the edge of the Central Valley, and Contra Costa County’s Los Vaqueros Reservoir in the Bay Area. 

In Sites’ case, the water would come from the Sacramento River, 14 miles away, when big rainfalls leave it water to spare. In dry years, Sites, designed to hold up to 1.5 million acre-feet of water, could then supply 300,000 to 450,000 acre-feet annually to farms, cities and environmental uses. (An acre-foot, or 326,000 gallons, is enough water to supply the annual indoor and outdoor use of one or two average households.)

Balancing Additional Storage with the Needs of Endangered Fish
As the economics of the Sites project look more favorable, the sharp environmental objections. which could morph into lawsuits, remain.  The overall concern in environmental groups’ and agencies’ comments on the project’s environmental impact report is Sites’ potential impact on the Sacramento River. The dam and reservoir at Lake Shasta, plus other diversions, have already altered its flow and temperature; add the burden of Sites withdrawals and the river would become less supportive of endangered runs of salmon and could push Delta smelt into extinction.

The comments of the Natural Resources Defense Council, the Sierra Club and 10 other fishery or environmental groups argue that the environmental assessments used flawed models, making their conclusions both incomplete and imprecise. The report “fails to adequately account for and assess impacts of the project in light of climate change,” the groups contended. 

The comments also argue that the proposed Sacramento River diversions to the Sites Reservoir through its new plumbing system could change the river’s water temperatures and flows, to the detriment of endangered winter-run salmon. Changes to wetlands could harm migratory birds and 14 miles of new roads could lead to roadkill of other wildlife, they added. Doug Obegi, a senior attorney for NRDC, has called Sites an “environmentally destructive dam.”

Jerry Brown, the executive director of the Sites Project Authority (no relation to the former governor of the same name), feels the most recent plans avoid real environmental harm. “I’m 100 percent confident that Sites Reservoir will be built. It must be built,” he said in an interview. In terms of protecting fish, he said, “we are definitely close to the sweet spot around what we can actually accomplish [with storage] and be protective…

“Sites is a project that would draw water off [the Sacramento River] during high flood periods, put it into the reservoir and release it generally during drier periods,” he said.

The organizational plan of the Sites project is a departure in California’s major water management systems, which are dominated by the state and federal governments. These control water deliveries from, respectively, the California State Water Project and the Central Valley project. Each is a complex network of dams, reservoirs, power plants, pumps, and canals that remade the natural plumbing of California. Sites will be connected to these networks, but will be managed differently.

“We’re trying to do something that has never really been done,” Brown said. “It’s a group of local agencies that are leading the project and will own and operate it.” The 23 agencies investing in the project, he added, would pay off the loans over time, likely spending $2.65 billion. State and federal water authorities are partners, not managers. The Sites Authority, the product of a joint powers agreement, controls everything from engineering and operations to environmental planning.

Southern California’s 1990’s Storage Investment Fends Off the Consequences of Drought
One possible inspiration for the Sites project sits 500 miles to the south, in Riverside County. Northern California water customers have eyed Diamond Valley Lake with envy for two decades. In the late 1990’s, the Metropolitan Water District of Southern California spent $1.9  billion to build it. The Met then filled the new reservoir with water from the Colorado River and the State Water Project — water pumped through the Sacramento-San Joaquin delta, the beating but sclerotic heart of California’s state and federal water systems.

When work on the 800,000-acre-foot Diamond Lake reservoir was completed in 2000, it nearly doubled Met’s storage capacity.  So when the last drought produced severe water restrictions in more northerly areas, southern Californians could use up to 15 percent of the reservoir’s water. So they got off lightly. The southern region also needs less: it has ramped up programs for water reuse and desalinating seawater.

Northern California agencies would love that kind of cushion. But though Diamond Valley Lake was a game-changer for southern California water suppliers, Sites, like most new storage proposals available to northern California water managers, offers, at best, partial solutions.  

One water expert believes that recognizing that all storage solutions now are partial should prompt engineers and water managers to think more creatively about new tools for storage.“There are a lot of possibilities” for solving water shortage problems, said Justin Fredrickson, the water and environmental policy analyst at the California Farm Bureau. “We’re not in an era where there’s a single silver bullet. [We need] buckshot.”

He added, “Just like all politics is local, all water management is local.… The space we have within which to move is increasingly local and regional.” While the 20th century dams and decisions created, he said, “a statewide system where we wheel water from one end of the state to the other. Our economy is embedded in that.” But, he added, “we need to build some flexibility back into the system that we’ve lost.”

Expansion Plans Could Add Capacity for Two Major Reservoirs
Retrofitting and expanding two off-stream reservoirs — one in the Bay Area and one at the center of the state — may increase flexibility and resilience for their customers. The Interior Department just announced it will invest $100 million from the new infrastructure law to strengthen and raise the height of the 55-year-old B.F. Sisk dam, which created the San Luis Reservoir, bordering I-5 near Pacheco Pass. An earthquake fault runs beneath the reservoir. 

The announcement of the grant was framed as enhancing protection from earthquakes; raising the dam would “reduce downstream safety concerns by reducing the likelihood of overtopping if slumping were to occur during a seismic event.”  Unmentioned was the purpose that the Trump administration advertised in its last month in office: expanding the San Luis reservoir. 

Now, both aims are being pursued in tandem. The work on constructing seismic retrofits, which begins this year, will be coordinated with ongoing efforts to further raise the dam and increase the capacity of San Luis Reservoir by 130,000 acre-feet.

That’s an incremental increase; about 6.5 percent of the reservoir’s current capacity of 2 million acre-feet. Water is pumped into the San Luis reservoir from river flows through the Sacramento-San Joaquin Delta, and is sent south to the farmlands of the San Joaquin Valley and to the cities of the Metropolitan Water District. 

Los Vaqueros Reservoir sits about 75 miles to the north, serving the residents and businesses of Contra Costa County east of San Francisco Bay as well as other Bay Area and central California water districts. It was completed in 1998, holding 100,000 acre-feet of water. Its capacity expanded to 160,000 acre-feet  in 2012; last year the state approved a grant of $470 million in Proposition 1 funds to help pay for a $1 billion expansion to 275,000 acre-feet. It also received more than $64 million in federal funds from the WIIN Act. The expansion is intended to provide more reliability and flexibility in water deliveries, particularly to wildlife refuges.

Reservoir Expansions Translate to Incremental Delivery Increases
Most accounts  of reservoir construction or expansion focus on total reservoir capacity. But the size of a reservoir means less than what it can deliver:  When complete and filled, Sites would deliver, on average, 243,000 acre-feet of water annually — and perhaps up to 450,000 acre-feet in dry years when all users are thirsty, particularly those with environmental needs.

The expanded Los Vaqueros reservoir’s annual deliveries would increase by an average of 69,000 acre-feet. Altogether, the average increase is less than one percent of annual total use of 37.5 million acre-feet of water by California’s farms, businesses, and homes.  But it will help the reservoir’s transition from having its primary focus on Contra Costa County customers to becoming more of a regional facility.

Raising the B.F. Sisk dam would increase the size of the San Luis Reservoir by 130,000 acre-feet, but there are no claims it would make new water deliveries. So with all these projects put together, the total increase in water deliveries each year will be real, but incremental.

A 2019 report on storage from the Public Policy Institute of California noted, “The average volume of new water from these facilities is small, and costs are high. Four projects [including Sites and Los Vaqueros] deemed eligible for state matching grants under Proposition 1 would expand statewide reservoir capacity by about 3.3 million acre-feet, but they would raise annual average supply by only 760,000 acre-feet, or 2 percent of annual farm and city use. Their combined cost would be nearly $10 billion.

Still, said Jay Lund of U.C. Davis, most water users want more reservoir storage anyway — preferably in the closest reservoir, or one “hydrologically adjacent,” meaning most easily accessed via California’s complex plumbing. Sites water, he said, would benefit Sacramento Valley rice farmers; it will also flow to water districts in the Central Valley.

Jerry Brown, the executive director of the Sites agency, said these Sacramento Valley farmers, some of whom got high-priority water contracts when Shasta dam was built in the 1940s, are concerned about the future. “They have some of the highest water-priority rights in the system,” Brown said. “You’d think that they’d need this least…. But what they’re seeing is changes in the management of water in California that are affecting them. They can foresee what’s coming and are taking action to ensure water for their future.”

The farmers and their water agencies will pay tens of millions of dollars for construction to get water that will benefit both them and the environment, helping streamflows and wetlands. But there may also be costs associated with lawsuits and delays, if environmental or tribal opponents, who feel that not all relevant tribal groups were consulted, take Sites to court. 

Brown thinks environmental objections can be met. “We agree we don’t want to hurt the salmon, because [then] the water project is jeopardized,” he said, adding, “Where there’s some fundamental disagreement … in the broader way water is managed and used within the state. Some wish and strive to take us back to pre-dams and pre-channelization of the water. Others are trying to take what we have and adapt to what we see coming.”

Is reservoir Storage the Best Option for the Future?
Academic experts like Lund are wary about advocating for new dams. A 2019 paper co-authored by Lund in the Journal of the American Water Resources Association, said, “On average, expanding facilities north of California’s Delta provides some benefit in 92 percent of [the] years modeled under historical conditions and in 61 percent of years modeled in a warm-dry climate.” South of California’s Delta, expanding storage capacity “provides [some benefits in 86 percent] of years modeled under historical conditions and 99 percent of years modeled with a warm-dry climate…”

The paper added, “The limited benefit of surface storage capacity expansion to statewide water supply should be considered in planning California’s water infrastructure.”

Newsha Ajami, the chief development officer for research at the Lawrence Berkeley National lab’s Earth and Environmental Sciences, doesn’t do such gentle demurrals. “I think raising any reservoir is a bad idea,” she said, adding such ideas are uninspiring and outdated. “The extreme ups and downs of the climatic era we are in don’t lend themselves to the storage model built in the 20th century… How much per acre-foot of water are we spending on these dam raises?”

She added, “I think Sites is a terrible idea. It’s off the river so people think it’s not going to have fish issues,” but “projects like Sites still deprive aquatic species of the limited water available to them.” Her recipe for decentralized storage involves everything from more groundwater storage in the Central Valley to more work by individuals and communities — which, at best, will only get a small portion of Sites water — to use, reuse, store, and conserve water more efficiently.

A 2017 paper that Ajami co-authored holds, “The water sector is going through a paradigm shift. Many communities are incorporating decentralized solutions such as water reuse and recycling, stormwater capture and demand-side management in order to address both short- and long-term water resources challenges…”  (“Demand-side management” basically means conservation.)

“You have to look at the cost estimates of different projects and the amount of [storage] capacity they are going to be generating,” Ajami said in an interview. “It’s easy when you’re talking about dams. It’s not easy when you’re talking about groundwater storage.”

California has developed incentives for farmers to send atmospheric rivers back into the depleted aquifers, but knowing how and where to recharge water is complex, as “& the West” explained in 2019.  

There are also drawbacks to storage by aquifer recharge. “Recharge is fraught because there are too many hands reaching for too little water,” said Lois Henry, founder of SJV Water, the Central Valley’s water-centric news report.

Going forward, “I would say we need a different kind of plan” for storage, said Fredrickson of the California farm bureau. “But there’s a lot of inertia. It’s difficult to think in a different way. We have two choices. We can have the imagination to build something different … or stay stuck in a place where we don’t have a lot of options and just make do.”

Felicity Barringer is the editor and lead writer for Stanford University’s Bill Lane Center for the American West’s “… & the West” online magazine on western environmental and health issues. The article was originally posted on the website of the Bill Lane Center.