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How climate change could threaten the water supply for millions of Californians

Climate change and California's water supply

A Delta water district fights salinity. The problem will worsen as ocean level rises, threatening Delta water quality and statewide water supplies.
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A Delta water district fights salinity. The problem will worsen as ocean level rises, threatening Delta water quality and statewide water supplies.

When it comes to California and climate change, the predictions are staggering: coastal airports besieged by floodwaters, entire beaches disappearing as sea levels rise.

Another disturbing scenario is brewing inland, in the sleepy backwaters of the Sacramento-San Joaquin Delta. It’s a threat to the Delta’s ecosystem that could swallow up a significant portion of California’s water supply.

Scientists from government and academia say rising sea levels caused by climate change will bring more salt water into the Delta, the hub of California’s water-delivery network. As a result, millions of gallons of fresh water will have to be flushed through the Delta, and out into the ocean, to keep salinity from inundating the massive pumping stations near Tracy. That will leave less water available for San Joaquin Valley farmers and the 19 million Southern Californians and Bay Area residents who depend on Delta water – eventually as much as 475,000 acre-feet of water each year, enough to fill Folsom Lake halfway, according to one study by the Public Policy Institute of California.

“With rising sea levels, with climate change, that creates additional pressure coming in from the ocean,” said Michael Anderson, the state’s climatologist, in a recent interview. “Sea level rise is going to become more of an influence.”

It figures to become a pocketbook issue for practically any Californian who drinks water that runs through the Delta. A 2010 study by scientists from UC Davis said rising seas, coupled with the inundation of some islands in the western Delta, will translate into higher costs for purifying water for human use. The additional cost could go as high as $1 billion a year, “making the Delta less desirable as a conventional water source,” the study said.

That cost doesn’t include the $17.1 billion Gov. Jerry Brown proposes to spend on the Delta tunnels, his controversial plan for reshaping the estuary’s plumbing system.

Brown’s administration is heralding the threat from climate change as one of the reasons for building the tunnels, which would increase water bills for urban Southern Californians and San Joaquin Valley farmers. An environmental impact statement released by state and federal officials in December said the tunnels are needed to prevent a significant cutback in water deliveries from the Delta.

Without the tunnels, the ability to pump water south “will be reduced under future climate and sea level rise conditions,” state and federal officials wrote. “Delta exports would be reduced by as much as 25 percent by the end of the century.”

Complicating the issue, climate scientists also agree a warmer climate will mean more rain and less snow. The Sierra snowpack serves as a giant reservoir that naturally releases water long after the rainy season ends. If more of California’s precipitation falls as rain instead of snow, much of that water will flow to the ocean in winter and spring, while it’s still raining. That will leave less water available in summer to satisfy human needs and to offset salinity in the Delta.

Salt water is already a problem at the Contra Costa Water District, which serves 500,000 residents in eastern and central Contra Costa County. Its location near the spot where water becomes brackish in the Delta puts Contra Costa on the front lines of the battle against salinity from the ocean. One of its four main intake pipes at the western edge of the Delta is precariously close to the point where water becomes too salty to drink without substantial treatment.

The agency has invested millions on intake pipes that are further and further away from the ocean. In 1997 it opened an intake along the Old River closer to the heart of the Delta. In 2010 it spent $80 million building another intake a few miles east of the Old River facility. It considered building a desalination plant a few years ago, but the project, estimated to cost $175 million, has been tabled.

Contra Costa’s main weapon against salinity is Los Vaqueros Reservoir, a 19-year-old man-made lake. Though it’s in the southwest Delta, it feeds off a pipeline from a San Joaquin River tributary from the east. Its purpose is to hold 160,000 acre-feet of fresh water that Contra Costa uses to dilute the supply that washes in from the Pacific.

“Things can get very salty for prolonged periods of time,” said Maureen Martin, the agency’s senior water resources specialist, during a recent tour of Los Vaqueros.

Contra Costa has spent nearly $560 million on Los Vaqueros, and it isn’t done yet. Working with 11 other Bay Area agencies, it’s developing a plan to expand Los Vaqueros’ capacity by two-thirds, an $800 million project.

Martin said her agency doesn’t consider sea-level rise “an imminent threat to Delta water quality.” But the scientific projections are influencing Contra Costa’s long-term planning on Los Vaqueros and other facilities.

Climate change “would probably cause the Delta to become saltier,” she said.

If climatologists are correct, the just-ended drought gave Delta residents a taste of things to come. In 2015, when the drought was at its worst and relatively little fresh water was trickling through the estuary, state officials worried about a surge of salt water gushing in. The Department of Water Resources built a temporary rock barrier on the West False River, near the heart of the Delta, to hold back the salty ocean water.

The price was $37 million, including the expense of removing the 150,000 tons of rocks when the rainy season started. State officials declared it a successful investment. The barrier helped the state avoid releasing 90,000 acre-feet of water from upstream reservoirs to flush out the salinity.

Over the long haul, state officials believe keeping the salt at bay will be crucial to the viability of the State Water Project and the federal government’s Central Valley Project, the delivery networks that move much of Northern California’s water through the Delta to the water agencies of Southern California and the San Joaquin Valley.

It’s a task that could become increasingly difficult as sea levels rise. Not only will higher waters bring a generally higher volume of salt into the estuary, they will put more stress on the 1,100 miles of levees protecting Delta farms and homes. A levee breach could inundate the SWP and CVP pumping stations with salt water, forcing them to shut down and reduce operations.

It represents one of the state’s arguments for the tunnels project: By diverting a portion of the Sacramento River’s flow at Courtland, at the northern fringe of the Delta, and piping it directly to the Tracy pumps, the state and federal water projects can sidestep much of the salt water and keep pumping water more reliably.

“The location of the north Delta diversion facility is further inland, making it less vulnerable to salinity intrusion,” officials wrote in the environmental report last December.

Tunnels opponents aren’t swayed by that argument.

They don’t dispute that rising seas will bring more salt to the Delta. But they say the tunnels would actually worsen the problem and make Delta water dangerously salty for farming and drinking water needs. By pulling some of the fresh water out of the Sacramento at the upstream location, opponents fear it will increase the salt concentration in the remaining water flowing through the Delta. In that respect, they’re insulted that the threat from global warming is being used to justify the project.

“Whatever the truth might be about the extent or arrival of (climate) changes, the theory is being used as one more arrow shot at us,” said John Herrick, attorney for the South Delta Water Agency.

“There isn’t a shadow of a doubt in our minds that once they’re able to take water from up north, they’d doom us,” he added.

The twin tunnels would take water from the Sacramento River and transport it under the Delta. See which islands and rivers they would cross.

Dale Kasler: 916-321-1066, @dakasler

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