Rainfall Fails to Quench Drought’s Thirst : Weather: Parched ground soaks up water. Some officials are encouraged by signs of a larger storm pattern.

Three days of raining like cats and dogs in Los Angeles and across the state will save about a week’s worth of watering lawns and parks, but will not avert mandatory water rationing that began in California’s two most populous regions Friday, water officials said.

Although Los Angeles has received a welcome 3.75 inches of rain since Wednesday, the city obtains much of its water supply from watersheds in the northern half of the state, which still suffers from record low levels of runoff.

About 2 inches of rain fell in the Bay Area, while residents of Marin County, north of San Francisco, began their first day living with restrictions of a scant 50 gallons of water per day per person.

Currently, runoff is about 15% of normal and snowpack water content is less than 7% of normal, according to the most recent survey. Meanwhile, storage at more than 155 reservoirs across California is running 50% of normal--even with the storm.

“It would take a biblical 40 days and 40 nights of rain to get us out of this drought situation,” said Doug Priest, manager of the state drought center in Sacramento. “This storm will give us maybe a week of not having to water our lawns or wash our streets. That’s about it.”

What has encouraged water officials is that the storms were prompted by a larger weather pattern that means more rain to come.

A deepening low pressure system over the eastern Pacific replaced a high pressure system that typically diverts incoming storms toward Northern California, Oregon and Washington, said Stephen Burback of WeatherData Inc., which provides forecasts for The Times.

Department of Water Resources Director David Kennedy, appointed by Gov. Pete Wilson to head his drought task force, said the weather pattern is the most hopeful he has seen in years.

“We haven’t seen a pattern like this in five years,” he said. “But we won’t count it until it’s in the reservoir.”

Five years ago, a February deluge produced heavy flooding in Northern California.

Contributing to the water shortage in Los Angeles, which before the storm was suffering its driest season ever, is a lack of mechanisms to catch, clean and save rainfall, water experts said.

A preponderance of flat terrain coupled with a lack of undeveloped space makes it all but impossible to build a regional reservoir system large enough to make a difference.

Beyond that, runoff is generally too polluted with oils, chemicals and tar to make it economical to capture and cleanse appreciable amounts for human consumption.

The storm sent an unusually large amount of rainwater and partially treated sewage into Ballona Creek, which empties into the Pacific Ocean at Marina del Rey. Officials said billions of gallons of contaminated runoff traveled through storm drains and sewers into Santa Monica Bay. The rush of polluted runoff and sewage forced the closure of beaches along the Los Angeles coastline.

What little rain does fall in the city’s more than two dozen reservoirs, including the Hollywood Reservoir and Silver Lake Reservoir, is restricted for emergency storage and maintaining pressure within the distribution system.

“The existing reservoirs in the Los Angeles Basin are not supply reservoirs, they are for emergency storage only,” said Debra Sass, a spokeswoman for the Department of Water and Power. “For the most part, rain falling in Southern California percolates into the ground or goes down storm drains that flow to the sea.”

In Santa Barbara, about 85,000 people were dependent upon nearby Gibraltar Reservoir for 30% of their water supplies until the lake dried up in November, 1989. Since then, the community has been pumping ground water and sharing water drawn from Lake Cachuma, 20 miles away, with at least six other communities.

“All this storm did was drop enough rain to fill the 20-foot-deep cracks at the bottom of Gibraltar Reservoir,” said Bob Roebuck, water resources manager for Santa Barbara. “It’s not so encouraging.”

Similarly, soil and sandstone remains are so dry around San Luis Obispo and Morro Bay that accumulation has been negligible in reservoirs serving those communities.

“The latest rain just soaked right into the ground,” said Dean Thompson of the state drought center. “As it continues to rain, however, that problem will cure itself.”

In San Francisco, which ended February with about 3.25 inches of rain--half an inch more than normal--officials were more optimistic about the rainfall’s effects on reservoirs.

“We’ll get some good runoff into local reservoirs in the Bay Area from this rain,” said Mike Pechner of the private Golden West Meteorology service. “But the rainfall and snow in the Sierra is not even a drop in the bucket.”

The storms have brought brief relief to thirsty farms in Kern and Tulare counties that are trying to cope with depleted ground water supplies and dramatic cuts in water delivered by state and federal agencies.

“This rain will help considerably in keeping trees and orchards alive,” Thompson said. “But it won’t help with crops--it will take a good deal more rain than we’ve had to put the farmer back into business.”

In the all-important Sierra, forecasters said 12 to 24 inches of new snow were expected by Friday evening. State water officials said it was too little too late.

“Overall, snowpack conditions averaged 7% of normal for this time of year,” said James F. Wickser, DWP assistant general manager for water, who based his estimate on snowpack survey results released Friday.

Although the survey was taken before the current wave of storms hit California, the recent rain will only supply enough water to increase the water content of the snowpack by a few percentage points, he said.

During the last drought, in 1977, snowpack conditions measured 27% of normal.

“The state, as a whole, could recover somewhat only if we got 2 1/2 times the normal rainfall for March and April,” said Gary Hester, chief of forecasting for the state Department of Water Resources. “Right now, the most optimistic outlook would give us normal rainfall in March.”

As a caveat, he said: “The number of inches of rainfall it would take to achieve that amount has only happened once in the last 60 years.”

In the meantime, Los Angeles, which normally relies on snowpack in the the eastern Sierra for 70% of its water supply, must again this year seek supplies elsewhere.

However, the water district’s deliveries from the State Water Project are being cut 90% this year. So Los Angeles, like most of Southern California, will depend more heavily this year upon water drawn from the Colorado River.

“We are entering uncharted territory as far as water supply goes,” Wickser said. “To supplement the dwindling supply, the city may be forced to evaluate its plan for mandatory conservation requirements and increase the percentage of cutbacks.”

Mandatory water rationing in Los Angeles went into effect Friday, with a 10% required cutback from 1986 usage. The Los Angeles City Council has also approved a 15% cutback effective May 1.

“The slug of rain we’ve had will give some relief as far as water demands for sprinklers are concerned,” said Robert Gomperz of the Metropolitan Water District. “But it doesn’t change preparations for the continuation of the drought.

“To anyone who thinks these storms will alleviate the need to conserve, I say: ‘Forget it, you’re dreaming.’ ”