Warnings Are Issued About Slides, Floods

With more than an inch of rain expected in some areas Saturday, county officials warned residents of fire-ravaged communities Thursday to prepare for possible mudslides and flooding.

“There’s an extreme risk confronting some homes,” said Jean Granucci, spokeswoman for the Los Angeles County Department of Public Works. “It’s not just water that comes down off the hillsides with debris flows and presents a danger. It’s big rocks.”

A “pretty strong storm” developing in the eastern Pacific Ocean is expected to begin dumping up to 1 1/2 inches of rain on local mountains Saturday morning, with lighter rain expected along the coast and in the valleys, said James McCutcheon, a meteorologist with WeatherData Inc., which provides forecasts for The Times.

The risk of devastating mudslides is lower in fire-denuded hillsides in Topanga Canyon, Calabasas and Malibu than in Altadena and other communities near the San Gabriel Mountains, said Frank H. Weirich, a geography professor at the University of Iowa.

“Debris flows in the San Gabriels are among the highest in the world, largely because rainfall there is so intense--up to half an inch an hour--and the slopes are steeper,” Weirich said.

But mudslides similar to the one last month that closed all but one lane of Pacific Coast Highway could occur this weekend on slopes burned in the Calabasas-Malibu fire, officials said. That slide occurred during a storm that dropped only half an inch of rain.

“If it rains a lot, it’s going to cause massive problems,” said Capt. Steve Floyd of the Los Angeles County Fire Department’s Topanga station.

About 173,000 sandbags have been distributed countywide since October, when a series of firestorms destroyed more than 1,100 structures and burned vegetation on more than 20,000 acres in six counties, Granucci said.

Topanga residents have picked up more than 5,000 of those sandbags, and Floyd said firefighters hope to distribute hundreds more from the Topanga station before the storm hits Saturday.

Extra road crews will be detailed to clear debris from culverts during the storm to reduce the risk of road closures, Granucci said. And county engineers, who have advised 114 property owners in the area on how to prevent flood damage, are hoping that the advice pays off this weekend, she said.

Soil scientists, engineers and other specialists from the federal Soil Conservation Service on Thursday briefed Rep. Anthony C. Beilenson (D-Woodland Hills) on their efforts during a tour of the Calabasas-Malibu fire zone, telling him that the potential for storm-related disaster in the Santa Monica Mountains is high. About 40 specialists had poured into the area to counsel landowners, conduct damage surveys, and prepare plans for flood and erosion control projects.

The problem, officials said, is that mountain soils have lost the ability to hold moisture, due to the loss of vegetation and the burned earth becoming “hydrophobic”--the term for soil made water-repellent by burning oils and gases from melted plant matter.

As a result of these conditions, said Thomas D. Benson, a hydraulic engineer with the federal service, three inches of rainfall in a 24-hour period could do as much damage as 10 inches would ordinarily.

Staff members from the service are creating plans and letting contracts for a variety of projects, including sandbagging of storm channels, clearing trash and debris from stream beds, and building debris dams to keep boulders from burying vulnerable homes and roads. Officials said they hope to have some of the projects completed by the end of the month.

Under its Emergency Watershed Protection Program, the service pays 75% of the cost of such projects, while a local agency--in this case, usually Los Angeles County--pays the other 25%. The emergency program paid much of the cost of the aerial reseeding of 7,000 burned acres with a mixture of native and non-indigenous seeds.

The service is also counseling stream-side homeowners to be ready to evacuate at the onset of major storms, Benson said.

For property owners and those interested in learning more about mudslide hazards, the Soil Conservation Service has scheduled a free tour of the Calabasas-Malibu fire area at 9:30 a.m. Saturday. To reserve a space on the tour, call (310) 455-1030.

The National Park Service is looking for volunteers to help clean up parkland devastated in the Green Meadows fire in Ventura County on Saturday. For information, call (818) 597-1036, Exts. 243 or 244.