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Rancho Palos Verdes Using Satellites to Track Landslides

August 18, 1994|JEFF KASS | SPECIAL TO THE TIMES

Rancho Palos Verdes, a bluff-top community plagued by landslides, has turned to satellite technology to measure how much the Earth's surface is moving.

On Tuesday the city began surveying 58 sites inside the 1,100-acre landslide area in which building has been restricted since 1978.

City officials are working with the Torrance office of electronics company Leica Inc. to utilized the Global Positioning System, 24 satellites that relay navigational signals to Earth.

An antenna at each of the 58 sites will provide the satellites with readouts on their latitude and longitude. By tracking changes in those coordinates over time, the city hopes to get a more accurate projection of where slides will occur and what can be done to stop them.

For $15,000 this year--the same amount Rancho Palos Verdes has paid county surveyors to annually monitor 18 sites--the city will receive quarterly readouts on the landslide area's movement, said Trent Pulliam, the city's director of public works. Movement also can be measured during and after landslide prevention measures, such as grading, to test their effectiveness.

"It's high-tech for a 100,000-year-old landslide," said Councilman Lee Byrd.

In 1956, road construction triggered the 270-acre Portuguese Bend landslide, destroying at least 102 homes. Creeping earth has damaged or destroyed nearly 100 more homes since then. In 1978, after another slide, the city created the 1,100-acre building moratorium area near Palos Verdes Drive South.

Experts say 130 acres of land in the moratorium area near upper Narcissa Drive has not moved as a result of landslides in hundreds of thousand years, and area homeowners there would like to expand or modify their homes. The area also contains about 40 vacant lots that some would like to see developed.

Orange County developer Barry Hon, who owns another 427 acres within the moratorium area, is considering developing a golf course and up to 50 homes, said spokesman Michael Mohler.

But talk of lifting parts of the moratorium met with opposition in the past. Although the satellite readings alone will not prove that swaths of land are stable enough to support homes and golf courses, Byrd said, he hopes they will inject some facts into an often emotional debate.

But Andrew Sargent, a local environmentalist, said the satellite readings will not provide city officials with any new information.

"The land is moving. We know it's moving," Sargent said. "This is going to confirm it's moving."

Sargent added that the effects of anti-landslide measures, which include wells to remove ground water and prevent the earth from become wet and slippery, may not be felt immediately. He suggested that building only be allowed on land that has not moved in at least 30 years.

County surveyors have tracked the land movement since 1956, and the city has informally tracked 18 sites over the past two years with the satellite system to test the technology's accuracy. But Byrd said this will be the city's first comprehensive use of the system, which originally was designed to help the military move troops.

Landslide readings will have a minuscule margin of error: 3 millimeters, approximately 3/25 of an inch, said Charles Abbott, president of Charles Abbott Associates, which contracts with the city for engineering services.

Rancho Palos Verdes is not the only municipality to find uses for the satellite system. The Port of Los Angeles recently purchased $104,000 worth of equipment to help select sites for piers, said Harry Yamatsuka, the acting survey supervisor. And the city of Rolling Hills is considering using the satellites to map land parcels.

Other non-military uses include tracking automobiles and buses and monitoring prime fishing spots.

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