Giant Reservoir Built Just in Time

Faced with a shortage of water flowing south from the Sierra snowpack, Southern California officials expect to tap into a mammoth new reservoir in Riverside County by summer, before it has even been filled for the first time.

Though the reservoir may be pressed into service sooner than expected, the $2-billion project near Hemet, called Diamond Valley Lake, was planned as an insurance policy for just such a time as this, when water supplies run short, officials say.

They point to a stark contrast between 10 years ago, when a California water shortage forced mandatory conservation measures, and today, when a shortage means merely tapping into reserves.

Back then, the Metropolitan Water District of Southern California, which serves 17 million people from Ventura County to San Diego County, maintained about 600,000 acre-feet of water in storage, either in reservoirs or ground-water basins.

Today, the agency has more than 2 million acre-feet of water--thanks largely to Diamond Valley Lake. An acre-foot is about 325,900 gallons of water, enough to serve a family of four for two years.

“Without it, we wouldn’t have anything there at all,” said Eddie Rigdon, the Metropolitan Water District’s assistant group manager for water system operations. “Almost immediately, the reservoir is doing exactly what it’s designed to do--which is meet the demand during [dry] times.”

Environmental activists agree. Although tapping the reservoir now means a risk that Diamond Valley will not be able to help in the event of a more serious drought, they say it will help the state this summer, when California’s energy crisis could hit a new peak.

If Diamond Valley Lake allows Southern California to reduce the amount of water it pumps over northern mountains, an operation that requires an enormous amount of electricity, it could save the day--and keep the lights on.

“It’s not a risk-free policy,” said Tom Graff, the Oakland-based regional director of the nonprofit group Environmental Defense. “But it’s probably the way to go. This is a good thing overall.”

Construction on Diamond Valley Lake--the largest earthen dam project in the United States--began in 1995. In January 2000, the Metropolitan Water District began funneling water from Northern California and the Colorado River into the reservoir--enough water each day to fill an Olympic-sized swimming pool.

Eventually, the reservoir will hold 800,000 acre-feet of water. But it’s not full yet--even after the Metropolitan Water District moved about 150,000 acre-feet of water into Diamond Valley from another reservoir. It contains about 525,000 acre-feet of water today, said Water District spokesman Bob Muir.

It’s not full simply because of the reservoir’s remarkable size.

Eventually, its capacity will be twice as large as that of Castaic Lake, the next largest reservoir in Southern California. When full, Diamond Valley will hold an estimated 260 billion gallons of water, so much that it would take 20,000 years to fill it with a garden hose. It has increased the amount of water stored above-ground in Southern California by about 50%.

Today’s water shortage is not necessarily the major drought that Diamond Valley was designed to protect Southern California against. But it is close enough, water officials say, that it makes sense to open the reservoir’s taps.

Though the flow from the Colorado River will be close to normal this year, California’s State Water Project, which provides water to 20 million people across the state and is the other major source of water for Diamond Valley Lake, is running short.

Mostly because of a paltry snowpack in the Sierra, the basin that collects runoff from the Sierra and begins funneling it south is running at 43% of capacity, said Department of Water Resources spokesman Jeff Cohen.

Overall, the State Water Project is expected to offer its customers, including those in Southern California, just 30% of the water requested, he said. Typically, the Water Project can meet the requests in full--including last year, when statewide, the project shipped its customers 3.6 million acre-feet of water.

“This year, it’s come way down,” Cohen said. Opening the taps on the Diamond Valley Lake, he said, “just shows the need for multiple water sources. That’s what it was constructed for.”