Advertisement

Science File / An exploration of issues and trends
affecting science, medicine and the environment

Frozen Assets

Yearly Survey of Snowpack in State's Mountains Predicts How Much of a Vital Resource--Water--Will Be Available

April 16, 1998|NONA YATES | TIMES STAFF WRITER

"Snow is gold out in the West."

Garry Schaefer, hydrologist, Natural Resources

Conservation Service

*

Water has always been an emotional subject in the West. From the pioneers who came in search of gold to the executives of today's corporate farms, western water has had many suitors.

In California, the water that irrigates millions of acres of agricultural land, powers hydroelectric generators and flows from nearly every faucet in the state begins its life as snow high in the state's mountains, particularly the Sierra Nevada.

Each winter and early spring, a small army of surveyors ventures into some of the most inaccessible areas of the state to measure the snowpack and forecast how much of this vital resource will be coursing down from the mountains in the spring runoff.

"Everyone's eyes are on the snow survey," said Dave Hart, snow survey field activities coordinator at the Department of Water Resources in Sacramento.

"Everyone" includes water agencies such as the Los Angeles Department of Water and Power, San Joaquin Valley farms, government agencies, utility companies and recreational users. All have a stake in how much water is available.

The state's recently completed April 1 survey shows California's water supply is well above normal, though not the record-setting numbers some might have expected with the heavy El Nino-generated storms this season.

"We did have some very decent snow-producing storms in January and February. If those had continued, we probably would have had some astonishing results, but in March we ended up with about half as much as usual," said Frank Gehrke, head of the California Cooperative Snow Survey.

Statewide, the snowpack stands at 160% of normal. In the Sierra, it ranges from 150% in the north to 185% in the south. The Eastern Sierra, where most of Los Angeles' water comes from, is at 160% of normal, he said.

That was still considerably short of 15 years ago. "We generally look to 1983 as the maximum, certainly within recent history," when the April statewide average reached 227% of normal, Gehrke said.

The state conducts monthly surveys from January through May. In many ways, however, April 1 is the most critical. Water agreements throughout the state are determined from this survey.

"We base everything on the April 1 survey," such as water purchase contracts and pumping decisions, said Steve Keef, chief hydrographer for the Los Angeles Department of Water and Power in Bishop.

Snow surveying started in the early 1900s when James Church, a professor at the University of Nevada at Reno, began studying snow on Mt. Rose near Lake Tahoe and developed a method of measuring water content by weighing the snow.

His early work established the relationship between the winter mountain snowpack and the spring rise in lake levels. Some of Church's "snow courses" are still used.

The snow course is at the heart of the survey. It typically consists of about 10 snow sampling points spaced 50 feet apart. There are approximately 300 snow courses statewide, each with distinctive orange and black markers.

Surveyors, who generally travel in teams of two or three and often in bad weather, measure the exact spot at which to take a core sample and plunge a metal tube--made up of 30-inch sections--into the snowpack. They mark the snow depth by the numbers etched on the tube, weigh the core samples in the tube and calculate the water content.

Water content is determined from weight, rather than depth, because a foot of snow can contain from as little as half an inch of water to seven inches or more. An ounce of snow is equal to about one inch of water, experts say.

"A snow course is like a giant rain gauge; we're measuring the amount of rain sitting on the ground in a frozen state," Hart said. With this year's prodigious snowpack that rain gauge can often be 15 to 20 feet deep.

Most surveyors agree that it is difficult yet rewarding work. Many sites are easily reached from mountain roads, by snowmobiles or helicopters.

A few remote locations can only be reached by snowshoe or several days of cross-country skiing. Along the way, surveyors stop in cabins that were stocked during the summer. Problems with equipment, animals and weather can all conspire to make the job a strenuous, even dangerous, one.

"You're skiing in 5 or 6 miles . . . if you have lousy snow conditions you can be breaking trail where snow is coming up over your knees every step. You're climbing up to 11,500 feet, and by the end of the day you're going to be pretty wore out," said Keef of the DWP.

"We woke a bear up one time years ago," he said. "There was no altercation . . . [but] he came into the cabin the night after we were there [and] ripped the cabin apart looking for food."

More accessible locations also can pose problems.

Advertisement
Los Angeles Times Articles
|
|
|