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Ground motion examined as factor in L.A. water main breaks

October 9, 2009 | 12:00 pm

The investigation into what could be causing a sharp rise in “major blowouts” of Los Angeles water mains has expanded to examine whether tectonic activity might be playing a role.

The L.A. Department of Water and Power have asked scientists at the Jet Propulsion Laboratory for help. As it happened, JPL officials were already evaluating ground movement in the Los Angeles Basin because of a several recent minor earthquakes.

Examining the timing and location of the breaks, JPL scientists notice “some deviation from the normal range” of ground movement in L.A. in the last 100 days, said Andrea Donnellan, a geophysicist at JPL.

“We’re trying to understand,” she told The Times.

Donnellan said scientists concluded there has been a change in ground movement by using GPS data from sensors embedded in the ground across the Los Angeles Basin. 

The sensors have been in place for only a few years, however, so it’s difficult to say whether the movements of the last 100 days is really an anomaly.

The movement detected is fairly subtle and may not be directly related to any increase in the number or intensity of local earthquakes.

As a result, Donnellan said, it’s doubtful that ground movement is a primary cause of the water main breaks. Los Angeles has seen a surge in recent month in what engineers have called major blowouts in the city’s aging water system in which streets have flooded and pavement has buckled -- in some cases damaging homes and businesses.

City engineers are trying to determine what’s causing the breaks and have been taking soil samples, sending pipe pieces to labs for testing and performing a statistical analysis on each break.

While the DWP says it has not found a cause, experts have offered various theories. Some said a prime suspect should be the city’s recent decision to allow sprinklers to run only on Mondays and Thursdays.

They say that if more water flows through the system on those two days when people water their lawns and then pressure suddenly changes on other days, it could be putting added stress on already aging pipes.

The DWP said it’s too early to determine a cause. Officials confirmed that the DWP is seeking assistance from USC, JPL and Cornell University, bur declined to comment further.

As part of JPL’s effort, scientists will analyze radar data of ground movement taken from a NASA airplane.

Donnellan said it could be months before researchers have any answers. Engineers also stressed that the city’s 7,200 miles of pipe aren’t actually leaking more than usual -- in fact, the number of leaks, about 1,400 a year, is down from the past and represents a lower rate per mile of pipe than in other cities.

The problem is with bigger, more destructive leaks that send water shooting through streets. The matter came to the DWP’s attention Sept. 5, after a 5-foot-wide trunk line under Coldwater Canyon Avenue in Studio City exploded, sending a 10-foot gusher of water and mud into the air.

Homes and businesses were flooded, and the street, a major thoroughfare connecting the San Fernando Valley and the Westside, was closed for a week. That pipe was 95 years old and officials suspected that age may have been a factor in its failure.

Less than 72 hours later, another, newer main burst in Valley Village, creating a sinkhole that swallowed half of a fire truck that responded to the call.

Firefighters crawled out the window to safety. As officials analyzed those problems, they realized they had been seeing an increase in major blowouts.

-- Jessica Garrison

Photo: Coldwater Canyon Avenue is littered with broken pieces of pavement after a water main break overnight flooded the Studio City neighborhood and created a large sinkhole under the street, which then collapsed. Credit: Irfan Khan / Los Angeles Times

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