Reports warn of mudslides in burn areas

Newly released federal and state wildfire reports offer a grim assessment on threats to life, homes and drinking water supplies if hard rains hit steep slopes charred in last month’s wildfires.

Those most at risk appear to be residents of rural eastern Orange County, portions of Bouquet Canyon and Val Verde in Los Angeles County, and vacation homes in the Angeles and San Bernardino national forests, according to the reports and government officials.

More than $6 million in federal emergency funds have been approved in the last week to stabilize denuded forest lands, many of which sit above threatened communities.

In many cases though, residents will have to rely on their own judgment to determine if they should evacuate, as applications of sandbags or straw bales may do little to help.

The warnings come amid predictions of a dry, La Nina winter throughout most of drought-stricken Southern California. However, officials said that even a single day of pounding rains could trigger a disaster because there are no plants to hold soil, rocks and debris in place.

“La Nina? You can’t speak in those terms,” said Randy Westmoreland, a U.S. Forest Service soils scientist who led a multi-agency team that evaluated risks in the wake of the Santiago fire.

“You could get all your storm in one event, and it could be 80% above normal . . . in five minutes,” Westmoreland said. “If you get one big storm with the right intensity, it could trigger flooding and mudslides.”

Modjeska Canyon in Orange County, which sees runoff from the Cleveland National Forest, could be hardest hit. Soil and storm experts said that because of last month’s wildfires, mudslides in the canyon could measure “19 times greater” than mudslides occurring before the fires.

Also, flash floods and other runoff threaten hundreds of homes that exist between two canyon creeks, experts said.

The flooding could be four to eight times greater than in pre-fire conditions, experts said.

Westmoreland, who has done such assessments for nearly 20 years, said, “It’s some of the worst risk I’ve seen because so much vegetation burned.”

Westmoreland spent days hiking through and flying over the burn areas with other team members.

“You basically went from fully vegetated to no coverage at all, just ash and bare dirt, so now you have nothing to hold anything back,” Westmoreland said. “Worse than a flood is a debris flow through that canyon. That is my worst fear, the mud and water and ash and everything [the water] picks up along the way.”

In the Cleveland National Forest, aerial mulching via fixed-wing aircraft or helicopters will begin Monday in an effort to stabilize bare slopes.

Mulch is “that gooey, green stuff you see homeowners spray on their lawns to grow grass, but without the seeds,” U.S. Forest Service spokesman Louis Haynes said.

County officials and homeowners have begun aggressive erosion control work in areas ravaged by wildfires, including laying sandbags to protect homes, clearing culverts and repairing roads, said Ed Edahl, a public information officer for the Federal Emergency Management Agency.

More work is expected to begin next week in Orange County and be completed within a year, he said. In the meantime, Edahl said, “a real rain could create immediate problems.”

“What residents do about this is really up to them,” he added.

Nearly 100 cabin-dwellers inside the Angeles National Forest would be notified with a knock on the door by rangers if there is a serious risk, said Forest Service spokesman Stanton Florea, but local government officials are responsible for public safety in non-forest areas.

Hundreds of homes that burned in the Grass Valley and Slide fires could pose a risk to neighboring homes and to Green Valley Lake, Lake Arrowhead and other sources of drinking water, according to separate federal and state reports.

Two reports on the 28,000-acre Santiago fire -- which is believed to have been set by an arsonist Oct. 21 -- paint the most dire picture.

“The principal concern with the Santiago fire is loss of human life and property,” one report states. Danger areas include, but are not limited to, Modjeska and Williams canyons, the upper reaches of Silverado Canyon and Santiago Canyon.

The state report recommends developing emergency evacuation plans and clearing dangerous vegetation from all evacuation routes.

It also calls for the closure of all public, open space recreation areas in these zones for up to two years. The closure would allow vegetation to grow back, experts say.

Westmoreland, the federal team leader, said that although sandbagging and straw bales might help stabilize soil in smaller or slower rainfalls, they would do little to hold back water and mud in more severe storms.

He said the best thing to do in areas like Modjeska is to get out when rain starts to fall.

“When it’s raining, the safest thing is not to be there. . . . I would really like to have people be safe, and if they’re not there when it’s raining, they’re safe.”

Orange County Fire Authority Capt. Kris Concepcion, an agency spokesman, said he could not comment on the reports because he had not read them thoroughly.

He said that although the county does have fire evacuation plans in place for its rural reaches, there are currently no such plans for floods or mudslides. But he said a task force of county officials and staff has been meeting to develop an emergency contingency plan.

Concepcion would not comment on whether reverse 911 or door-to-door notification systems might be used but said all options would be explored.

Modjeska Canyon, including its firehouse, lost power and phone service during much of the Santiago wildfire.

Sheriff’s officials circled the narrow, unlit back roads issuing evacuation orders over bullhorns, and volunteer firefighters banged on doors to alert people.

All of the reports will be available on U.S. Forest Service websites in the coming days.

janet.wilson@latimes.com

jennifer.delson@latimes.com