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San Diego Diversifies Water Supplies, But Increases Reliance On Colorado River

Scripps Institution of Oceanography
The Colorado River stretches from the Rockies across the Southwest and supplies water to 40 million people in eight states.
San Diego Diversifies Water Supplies, Bur Increases Reliance On Colorado River

The majority of San Diego County’s water supply comes from the Colorado River. It keeps our faucets running and landscapes green and it makes quite a trek to get here.

San Diego Diversifies Water Supplies, Lessens Reliance On Imported Supplies
The majority of San Diego County’s water supply comes from the Colorado River. It keeps our faucets running and landscapes green and it makes quite a trek to get here.

"It starts as snow in the Colorado Rockies," explained Dennis Cushman, assistant general manager for the San Diego County Water Authority. "The water runoff, when it melts, goes into Lake Powell,"

Metropolitan Water District Southern California
Colorado snowpack remains above normal for this time of year at 114 percent, and runoff is currently projected to be 101 percent of normal for the water year. Still, Lake Mead and Lake Powell reservoirs are less than half of their capacity, as of March 2014.

From Lake Powell, water flows down the Colorado River to Lake Mead.

"And from Lake Mead, it travels down even farther to Lake Havasu near the Arizona border with California," Cushman said.

From there, the river water continues 242 more miles before connecting to nine San Diego reservoirs, Cushman said.


The faraway river is San Diego’s closest large body of water, and a vital supply to 40 million people and seven other western states.

San Diego County gets two sources of supply from the river: one comes via the Metropolitan Water District in Los Angeles.

"But separately, a little over 10 years ago, the Water Authority struck independent Colorado River water supply deals with the Imperial Irrigation District," Cushman said, "And we invested our ratepayer money in canal lining projects out in the Imperial Valley desert."

This year, San Diego County is getting 180,000 acre feet of Colorado River water from the independent supply.

"By 2021, it will be 280,000 acre feet of water per year under those transfers," explained Cushman.

But just like the record-dry Northern California Sierra, where up until this year San Diego got 20 percent of its supply, the Colorado River is also under sustained pressure from drought and demand.

Lake Mead and Lake Powell reservoirs are less than half their capacity. Bathtub rings of white mineral deposits provide the only evidence of the once flourishing body of water.

"I think California is right on the cusp of having a very serious water crisis with water rationing and everything else," said Tim Barnett, marine physicist emeritus at Scripps Institution of Oceanography.

Barnett's extensive studies of the Colorado River and particularly Lake Mead, led him to warn five years ago there's a 50 percent chance Lake Mead will run dry within a couple of decades if climate changes as expected and future water usage is not curtailed.

"If you don’t like the global warming explanation, you’ve got Mother Nature, and she’s offering a very harsh lesson," said Barnett, who said he came out of retirement for his grandchildren's sake.

Barnett, and his colleague Dave Pierce, found that demand, evaporation and human-induced climate change are creating a yearly deficit of nearly 1 million acre-feet from the Colorado River system.

He said water managers should reassess their drought contingency plans with a worst-case scenario approach that includes human-induced climate change.

"Because it will be really different if you know, water and rain are going to come back differently, say, in two years," said Barnett. "Your management approach would be entirely different than if you say, 'well, whatever we’ve got now is the most we’re ever going to have again.'"

Dennis Cushman assures that San Diego has little risk of shortages from its Colorado River supplies because of the region’s high priority in the water rights system.

"If shortages ever hit California, those shortages start at the lowest of the priority system," Cushman said. "And those are supply cuts that could come to Metropolitan Water district, so we could be impacted by supply cuts to Metropolitan if shortages were imposed in California, but it would take a while for those shortages to impact Imperial Irrigation District supplies.

Cushman said despite 14 years of drought, the Colorado River over the long term is a very healthy system.

"This year, the supply conditions in terms of precipitation are at about normal — a little bit above normal right now," said Cushman. "So it’s having a pretty good year this year."

Looking ahead, Cushman said San Diego County will rely less on imported water because of investments in local water supply diversification, such as the desalination plant in Carlsbad.

The San Diego County Water Authority is also increasing storage at local reservoirs, such as San Vicente in Lakeside, where the newly reconstructed dam is 117 feet higher than the old one, doubling its capacity.

Still, Cushman said, the historic dry conditions are concerning.

"We’re out there right now, given the unprecedented drought conditions in California, asking the public — thanking them for conserving the water they’ve conserved — and asking everyone to do more."

Tamara Sheldon, a researcher of environmental and energy economics at UC San Diego, said getting people to conserve more may have to come with a price tag.

"Water is a scarce resource in San Diego, but it’s not priced as if it were a scarce resource," Sheldon said. "When there’s a shortage of gasoline, then the price goes up, and when the price goes up, consumers respond by cutting back on their gasoline use to save money," Sheldon added.

San Diego County has enough water in storage to get through this year and into next without mandatory cutbacks, Cushman said. He said they’ll continue to monitor conditions and take action as needed.

Corrected: February 8, 2023 at 5:31 AM PST
The headline on this story has been updated to reflect San Diego County's lesser reliance on imported water supplies.