Rains May Worsen Coast Landslides : Portuguese Bend: Geologist says movement of earth over slickened bedrock may increase 30%. At current rate, 14 feet of rugged headlands fall into the ocean every year.

Experts fear that recent rains will worsen landslides in the Portuguese Bend area of Rancho Palos Verdes, testing the effectiveness of the city’s $7-million effort to control the shifting hillsides.

Heavy rains have soaked into the area’s undeveloped hills and canyons, and the bentonite clay coating the bedrock has become slick, experts say. When there isn’t enough friction to hold a slope, it can break loose and the mass of earth resting on the tilted bedrock can skid slowly down, city geologist Perry Ehlig explained.

“The rains will probably speed up parts of the slide, especially down along the bluffs,” said Ehlig, who predicts that the speed may increase by as much as 30%. However, he said it will be at least two weeks, maybe longer, before the full effect of the recent storms can be measured.

Even before the rains, parts of the Portuguese Bend slide had begun to speed up because of heavy wave action that is eroding the steep cliffs at the lower end of the slide zone, Ehlig said. The collapse of these cliffs releases pressures that have been holding the slide back, he explained.

The latest reports show the city is losing 14 feet a year as the rugged headlands above the Portuguese Bend cove slump and crumble into the ocean.

Scores of homes have been damaged or destroyed in the landslide area in the past 35 years. The slow-moving slides have torn out roads, sewer and water lines as they inch down the steep canyons and slopes. Little damage has been reported in recent months, but that may change if the rains speed up the earth movement, as expected.

“We’ll just have to wait and see,” said Ehlig, 64, a geology professor at Cal State Los Angeles who has studied these landslides for decades. “When it gets wet, the bentonite is as slick as grease or wax.”

The Portuguese Bend slide, which was first triggered in 1956, is one of several in a two-square-mile area on the south side of the city. The city placed a moratorium on all building in the area in 1976 after the Abalone Cove landslide, which damaged or destroyed 45 homes. The lands in the zone are privately owned and mostly undeveloped.

The city spent more than $7 million fighting the slides, most of it in Abalone Cove, the most densely populated area. Since 1986, a dozen “dewatering” wells have been drilled in Abalone Cove to remove water so that the slick clays could dry. Drains were built to carry away the surface water.

Ehlig, who directed the abatement work, said it has slowed the land movement in Abalone Cove to a creep of no more than an inch or two a year. He does not think a rainy winter will have much impact on Abalone Cove lands because of the city’s efforts there.

However, the story is different in Portuguese Bend, where only half a dozen dewatering wells have been drilled, he said. So far, very little drainage and grading work has been completed, so storm water is percolating into the underground and wetting the bentonite, he said.

The primary problem in Portuguese Bend is the lack of drainage in Portuguese Canyon, which cuts across the landslide area. Although the city plans to clean out the canyon, that work is opposed by some homeowners who do not want to see wildlife habitat destroyed, he said.

“Potentially there are some very real problems there because the city hasn’t opened up the canyon yet,” Ehlig said.

The canyon’s waterway is choked with brush and has no way to reach the ocean because of the slide. Ehlig said the runoff becomes trapped in the lower canyon and seeps into the underground, where it lubricates the slide. Clearing the channel is essential to controlling the landslides, he said.

The active portion of the Portuguese Bend slide covers nearly half a square mile and is shaped like a bowl tilted on its side. The lower third of the slide area includes Palos Verdes Drive South, a major thoroughfare.

The land between Palos Verdes Drive South and the ocean bluffs has been most affected by the erosion caused by the waves.

Recent measurements show that parts of this area are now moving toward the ocean at a relatively fast clip--14 feet a year. That’s a 25% speedup over the previous year, Ehlig said. as a result, the bluffs are breaking away and slumping into the ocean, creating a brown plume of mud in the bay.

Stopping the wave erosion would require building some kind of barrier or seawall, a proposition that could cost as much as $60 million, the U.S. Army Corps of Engineers has estimated.

Not all parts of the slide are moving at the same speed, according to Ehlig. In fact, as dramatic as the increase in movement has been, the rate of sliding is not nearly as fast as it was 15 or 20 years ago, when the slide was moving up to 35 feet a year, Ehlig said. He credits the city’s slide-abatement work for the slowdown.

In the central parts of the slide, uphill from Palos Verdes Drive South, the land is now moving about 18 inches a year, resulting in cracks and fissures large enough for Ehlig to stand nearly waist-deep.

Because it sits astride the moving landscape, nearly a mile of Palos Verdes Drive South is sinking and cracking. Over the years, a section of the road has been relocated and rebuilt several times. Portions of the old roadbed can be seen 700 feet downhill, along with culverts, house foundations and other debris that is falling to the beach below.

The original slides were triggered in 1956 by Los Angeles County road crews who were extending Crenshaw Boulevard south into the steep canyons. After homeowners filed suit, the courts ruled the county was liable for damages.

With more dewatering wells, more drainage and good management, Ehlig believes the Portuguese Bend area can be stabilized to allow some limited development in selected areas.

The city might allow private developers to build a golf course, under carefully controlled conditions, to generate much-needed tax revenues. That money could be used to finance other slide-abatement work, he said.

“We leave it like it is, it’ll just get worse,” he said.