High Sierra Topix

Sierra snowpack won't fill reservoirs

Peter Fimrite, Chronicle Staff Writer
Thursday, March 27, 2008

(03-26) 16:23 PDT SAN FRANCISCO -- The water content of the Sierra Nevada snowpack, which holds more H{-2}0 than the biggest man-made reservoir, is about equal to the long-term average, despite an extremely dry March, state hydrologists said Wednesday.

Measurements at historic Phillips Station, next to the Sierra-at-Tahoe resort, on Wednesday found 98 percent of the normal amount of water in the snow for this time of year, said Ted Thomas, the spokesman for the state Department of Water Resources.

That's almost twice as much water as last year, but Thomas said it isn't enough to fill the reservoirs when the snow melts in the spring and summer.

"Our reservoir levels are down because of last year," Thomas said. "And March has been very dry both rain-wise and snow-wise. It would take a significant rise in the snowpack to fill the reservoirs. We don't see it on the horizon."

For 63 years, the water content of the snow - the amount of water that would be on the ground if all the snow melted - has been measured every month between January and May. The measurements, which are taken in the same locations throughout the Sierra every year, are used to determine the water supply for the coming year.

This month's survey, done by water resources staff using an aluminum pole, matched electronic surveys that show the snow statewide contains 97 percent of the average amount of water in the snow dating back about three decades, Thomas said.

Last month, a sampling of four Sierra monitoring stations showed snow levels ranging between 110 and 138 percent of normal.

On Wednesday, the lowest-elevation measurement, Tamarack Flat at 6,500 feet, showed 30.4 inches of snow-water content, or 112 percent of normal for this time of year. The highest station, Alpha at 7,600 feet, registered 32.6 inches, or 98 percent of normal. Lyons Creek had 33 inches, or 106 percent of average. Phillips Station, which has served as a kind of guinea pig for measurements, had 53.4 inches of snow with a water content of 27.8 inches.

The winter snowpack in the Sierra is not only important to skiers and snowboarders, it is an essential part of the state's water supply. Up to 60 percent of the state's water is contained in the Sierra snowpack. When it melts, the water is used to irrigate 775,000 acres of farmland and help quench the thirst of California's 36 million people. About a quarter of the state's power comes from hydroelectric plants that count on heavy mountain runoff.

The northern Sierra Nevada, covering an area roughly from the Trinity River to the Feather River, is particularly crucial because it provides water for both Shasta Lake, which is used by the federal Central Valley Project to supply farmers as far away as Bakersfield, and Lake Oroville, which is primarily used by the State Water Project to deliver water to homes and businesses all the way to Southern California.

The northern Sierra is at 105 percent of normal, Thomas said.

"That's a good thing," said Thomas, "but we're not sitting pretty."

Thomas said Lake Oroville is carrying only 60 percent of what it normally has this time of year and no significant rain or snow is expected. The reservoir holds 3.5 million acre-feet, but it currently has only 1.6 million acre-feet of water in it.

Last year at this time, Lake Oroville had 3.1 million acre-feet of water despite very dry conditions. That's because the year before had been very wet.

The water content of the peak snowpack on April 1 last year was only 40 percent, leaving the state's reservoirs short. In addition, Thomas said, the state is under court order to protect the endangered delta smelt, requiring reduced pumping.

Showers are expected in the Bay Area and light snow could fall in the Sierra from Friday night through Saturday morning, with more inclement weather on Tuesday and Wednesday next week, but no serious storms are on the horizon, said Bob Benjamin, a National Weather Service forecaster.

"It's a cold front moving through with minor quantities of precipitation," Benjamin said. "It's spring showers mostly. It's nothing that will add anything of significant value to the snowpack."


E-mail Peter Fimrite at pfimrite@sfchronicle.com.