Pounding Rains Unleash Mud, Rock Flow

La Canada Flintridge - Fast-forming storm cells unloaded intense rainfall on mountain slopes denuded by the Station Fire, triggering flows of mud, rocks and boulders early today into a hillside neighborhood in La Canada Flintridge and leaving six homes with "minor to moderate" damage, authorities said.

No injuries were reported, but residents of at least six homes self- evacuated at the height of the debris flows, which occurred near the top of Ocean View Boulevard, said Los Angeles County Fire Inspector Frederic Stowers.

The same sudden heavy rains unleashed at least one slide onto Angeles Crest Highway above La Canada Flintridge, a tour of the area showed this morning. U.S. Geological Survey scientists and Forest Service employees were not allowed past a CHP roadblock at Bay Tree Road. A contractor at the scene said the slide covered the highway with mud and rocks to a depth of four feet.

The post-fire erosion came without warning, authorities said. It sent mud flowing into hillside cul-de-sacs, partially buried some vehicles, and blocked driveways and garages.

"This was an uncharted storm and we had 1 to 2 inches of rain in less than 20 minutes," Stowers told City News Service. "This area was burned by the Station Fire. Mud let loose from the top of the mountain."

The National Weather Service issued a flood advisory for the Station Fire burn area at 11:32 p.m. Thursday, warning of heavy showers in the San Gabriel Mountains. Rain gauges in the burn area were reporting .3 inches of rain in 30 minutes and the flood advisory warned minor debris flows were likely.

But the storm cells formed so quickly that forecasters in Oxnard couldn't see them initially, and residents near the top of Ocean View Boulevard in La Canada Flintridge learned of the flows when they heard the mud and rocks moving, according to Stowers.

"It was uncharted, it developed quick and we couldn't see it," said NWS Meteorologist Curt Kaplan, speaking this morning from Oxnard. "There was a convergence line where the cells pulled together. We got the advisory out, but you can't forecast it when it happens this fast."

The flood advisory was cancelled at 12:13 a.m., but by that time mud, rocks and boulders were moving, and more than 45 firefighters were sent to Normanton Drive and other cul-de-sacs to start sand-bagging, Stowers said.

By 2 a.m. the Los Angeles County emergency flood response included more than 75 firefighters and public works employees, Stowers said.

"This area was identified as a high-risk hazard area after the Station Fire," Stowers said. "We already had K-rail up there on some of the streets. But mud came over some of the barriers. Some vehicles, the mud came over the top on one side."

Rock Castle Drive was closed due to mud flows overtopping concrete barriers, and 12 to 24 inches of mud oozed into cul-de-sacs such as Earnslow Drive and Normanton Drive, On Scene reported.

The neighborhood is one of many normally protected by engineer-designed debris basins and other permanent flood control structures and channels. But mud and rocks came down unimpeded, far outside the catchment zones of the man- made erosion control measures, according to On Scene.

The neighborhood is also one of many along the foothills where the nearest slopes were intentionally denuded during back-fire operations intended to deny fuel to the Station Fire and keep flames away from homes.

While largely successful in preventing loss of homes to fires, back- firing also removed the last barriers of vegetation between the hillside neighborhoods and the vast mountain watersheds above.