Officials Survey Valley Damage by Helicopter

A helicopter filled with city officials lifted off into bright sun and clear skies Thursday, taking them on a tour of San Fernando Valley storm damage.

Councilwoman Laura Chick could see 15 miles as the Los Angeles Fire Department aircraft hovered over endless turquoise swimming pools and palm trees on a day of 70-degree temperatures.

“It’s beach weather,” she said as the red-and-white Bell 412 flew away from five homes in West Hills damaged by a recent mudslide. “That’s one thing about Los Angeles--we bounce back fast.”

But, as Chick warned later, the good weather of the past few days is misleading. As President Clinton declared Los Angeles and other counties federal disaster areas Thursday, federal and state officials were keeping a wary eye on the mudslides that are among the costliest effects of the El Nino season’s rains.

To date, mudslides have caused the bulk of the estimated $4-million damage in Los Angeles and are expected to result in more than $1 billion in damage across the state this year, experts say.

The mudslides have also played a key role in destruction of homes, officials said. As of Thursday, building officials had declared off-limits 25 buildings and restricted entry to another 25. In Santa Clarita, two homes were red-tagged; declared unfit for habitation.

While the fastest-moving mudslides occur during heavy rains, other equally damaging mudslides can happen weeks or even months later as water works its way through the soil.

Those disasters-in-waiting were the main source of worry for the officials on Thursday’s tour, a trip that cost the Fire Department $2,500 and was designed to give Los Angeles city officials a sense of the extent of damage from the storms that have pummeled the area in recent weeks.

“Our [flood] channels can handle the storms, but now we have to worry about what’s happening under the ground,” said Fire Chief William Bamattre.

“The real troublesome issue is mudslides,” Chick agreed.

In an attempt to get a better handle on that issue, state and federal geologists have been working since the El Nino season began to develop maps to predict mudslides, especially those that break free during heavy rain. Such a slide resulted in the deaths of at least two people in Laguna Canyon in Orange County earlier this week.

But on Thursday’s tour, officials were also concerned about longer term slides, the kind that geologists call “big, slow movers” because the earth shifts slowly for weeks and even months before giving way.

Two things happen after heavy rains that determine mudslides. First, soil becomes saturated with water, loosening it. Then, the water begins to work its way to the bedrock beneath the soil, lubricating the rock layers.

On a slope, those two factors make the bedrock act like the surface of a playground slide. Any number of conditions--from an earth tremor to additional rainfall--can set the soil atop the bedrock in motion.

“It could be a beautiful, sunny day in July--you could be playing golf--all of a sudden, the sucker lets loose,” said David Howell, a geologist with the U.S. Geological Survey in Menlo Park.

Such slides are responsible for damage to five homes in West Hills as well as two other sites toured Thursday: a home in Encino in which a back wall collapsed, and a home off Mulholland Drive, where a chunk of earth shifted and left behind a 20-foot-deep gash. The home suffered no damage.

City building codes have been modified in recent years to require stronger foundations of hillside homes and prevent construction on steep slopes. Still, geologists say little can be done to stop such slides from causing damage.

The problem is especially serious in local mountain ranges, where the underlying siltstone bedrock can become soap-like when moistened.

“The Santa Monica [Mountains] are unstable under the best of circumstances,” said Doug Morton, a geologist with the USGS in Riverside. “If you’d look at a map, you’d be blown away at the extent of landslides that have occurred there. There’s just oodles of them.”

City officials urged homeowners to take precautions against mudslides. Safety measures include proper site drainage and tarps to keep water from soaking into the soil around hillside homes.

As the helicopter hovered above a gaping hole in the roof of one Woodland Hills commercial building, where the weight of undrained water broke the supports, Bamattre noted that gutters should be kept clean to allow rain to drain runoff.

“It’s when they’re not kept clean that there’s a problem,” Bamattre said.

Times correspondent Dade Hayes contributed to this story.