DWP workers move dirt away from 12 inch water main.
The water rationing system in the city of Los Angeles, which has limited outdoor watering to Mondays and Thursdays, contributed to a rash of water main breaks in the summer of 2009. That's the conclusion of an independent team led by a USC engineer who reported to the Environment and Energy Committee of the Los Angeles City Council. The LA Department of Water and Power says its engineers must read the report before responding to it.Updated at 12:21 a.m., April 14 | Permalink
167-page report makes recommendations, analyzes DWP strategy for managing pipes
A team of scientists from USC, Cornell University, Flow Science Incorporated, NASA's Jet Propulsion Laboratory and other engineering firms developed the recommendations after a city council request last summer.
Jean-Pierre Bardet presented the recommendations to councilmembers Tuesday afternoon. He and his team concluded that 90 percent of blowouts in the second half of last year happened in cast iron pipes that were somewhat corroded. (Cast iron pipes are about 70 percent of the total in the system.) Drops in water temperature accelerated blowouts, but not in summertime. Instead, Bardet said, major shifts in pressure catastrophically weakened pipes.
Engineers recommended a faster and more efficient pipe replacement program, and better inspections. During inspections, scientists wrote, DWP staffers should use"digital field recorders (rather than written notes) to capture field data in directly usable form" and "Increase the level of resources devoted to main replacement so as to reduce the backlog as quickly as practicable."Updated at 4:05 p.m. | Permalink
DWP contends corrosion primary cause of breaks
The DWP has released a statement about Bardet's report, indicating nobody there has yet read it. "The Department believes corrosion is the indisputable and primary factor in most of our water main breaks, including those from last September," the DWP statement says. "We believe Dr. Bardet's findings will support this position."
DWP says its own internal report blames blowouts in September 2009 on system pressures created by repairing breaks from earlier in the summer. "It is the Department’s position that the operational changes to accommodate City Trunk Line repairs resulted in ruptures on mostly cast iron mains, which accounts for the increased severity of the breaks in the weeks that followed," the report says.Earlier | Permalink
"The investigation team findings reveals a connection between the city's water rationing program and an increase in pipe breaks during the summer of 2009 especially with cast iron pipes," Jean-Pierre Bardet, who leads the Megacities project at the University of Southern California, told the committee chair, Councilwoman Jan Perry.
L.A.'s water main system includes more than 7,200 miles of pipe, Bardet said.
Cast iron pipes were the site of 90 percent of breaks in the system since 2001.
Those pipes have been exposed to corrosive materials in which they've been buried for decades, weakening the pipe walls.
Bardet said those pipes weren't able to handle large variations in pressure caused by dramatically different use Monday and Thursday as compared with the other days of the week.
To illustrate, Bardet held up a paper clip, which he began to bend in small circles. The metal can sustain the small amplifications of energy, he said; as the circles grew, the larger pulses weakened and broke the metal.
Residents from Studio City complained about the speed with which the city's settling claims related to that blowout.
A deputy city attorney told the council committee that 83 percent of claims in that area have been settled, many by insurance committees. But several homeowners who reside in Councilman Paul Koretz's district complained angrily that they've not been able to start repairs without financial settlement from the Los Angeles Department of Water and Power.
Bardet recommended that the city avoid large variations in water pressure in rationing efforts this year. He'll present his report to the full City Council within a month.
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