From Mountaintop to Tap : HOW MELTED SIERRA SNOWPACK BOOSTS VALLEY WATER SUPPLY

Ebullient water officials say California does not have to worry about this year’s water supply. After the close of the rainy season, the Golden State’s reservoirs are fuller than in a normal year, and the mountain snow that feeds those reservoirs is deeper than usual, thanks to the downpours of January and March.

The State Department of Water Resources’ statewide runoff projections, which indicate how much water will end up in the reservoirs, are 152% of normal. Runoff projections from the Mono Basin/Owens Valley area, which supplies most of Los Angeles’ water, are 154% of normal.

Much of the water in state reservoirs comes from snow atop the Sierra Nevada. The snow melts in warmer weather and fills the streams that pour into the reservoirs. The state’s largest reservoirs have 978 billion more gallons of water than they do in an average year (9.45 trillion gallons this year compared to an average of 8.47 trillion--112% of normal).

Officials with the Los Angeles Department of Water and Power say the estimated amount of water the Owens Valley watershed will send into Southland reservoirs this year is about 266 billion gallons--about 1 1/2 times the annual 173 billion gallons.

Predicting Runoff

Snow is measured at more than 300 stations statewide by technicians who insert a hollow metal rod into the snowbanks. The rod measures not the depth of the snow but the amount of water it would be converted to if it melted. At the time of the most recent measurements, each 10 inches of snow would yield about 4 inches of runoff.

Snowpack Totals

The water that moves through the Los Angeles Aqueduct comes from snowpacks in the Owens Valley. The amount of snow measured at several stations as of April 1 are shown above.

1. Mammoth Pass Station:

April 1 snowpack: 61.0”

Avg. April 1 snowpack: 31.3”

2. Rock Creek Station:

April 1 snowpack: 20.4”

Avg. April 1 snowpack: 11.3”

3. Big Pine Creek Station:

April 1 snowpack: 32.9”

Avg. April 1 snowpack: 18.6”

4. Cottonwood Lakes Station:

April 1 snowpack: 25.8”

Avg. April 1 snowpack: 13.7”

Reservoir Levels

Reservoir water levels depend not only on how much rain has fallen, but also on whether the snow in the mountains has melted (usually it doesn’t all melt and run off until summer) and how much rain and runoff there was last year. Many reservoirs are now full.

The Los Banos holding station, which contains runoff from the Central Valley and holds 752 billion gallons of water, is full, as it was last year. But in drought seasons it has dipped to about 130 billion gallons.

Other reservoirs store water to be sent through the state aqueduct system into the homes of Californians. Lake Shasta, the state’s largest reservoir, has the capacity to store 1.467 trillion gallons of water.

The reservoir that is mostly devoted to the Los Angeles aqueduct system, Crowley Lake, has 40 billion gallons of water this year, slightly lower than the usual 42.3 billion gallons. But Los Angeles DWP officials point out that much of the extra-deep snowpack has yet to melt and fill Crowley.

Deep Snowpack, Heavy Runoff

Storms in January and March helped boost April 1 snowpack survey totals and runoff predictions far above the normal range.

Eastern Sierra Nevada Snowpack (Percentage of normal*) 1970: 71% 1975: 97% 1980: 158% 1985: 97% 1990: 43% 1995: 187% est. * Normal: Based on 50-year average

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Eastern Sierra Nevada Runoff (Percentage of normal*) 1970: 90% 1975: 93% 1980: 146% 1985: 100% 1990: 51% 1995: 154% est. * Normal: Based on 50-year average

Where Our Water Comes From

In years of scarce rainfall, Los Angeles purchases water from the Metropolitan Water District, the wholesaler that oversees State Water Project supplies, which are transported from the Sacramento Delta region and Colorado River.

1993-94 Projections for 1994-95 Los Angeles Aqueduct 22% 73% Metropolitan Water District 63% 15% Ground water 15% 12%

Sources: Los Angeles Department of Water and Power; state Department of Water Resources.

Researched by NICHOLAS RICCARDI / Los Angeles Times