When a landslide violently shoved Malibu’s 30-inch water main last Thursday, it split open a joint, creating a major leak that threatened to undermine Pacific Coast Highway. Waterworks District 29, the county agency that manages the area’s water supply, immediately shut down the entire line. They then called Doty Brothers — one of three private contracting firms on call 24 hours a day, 7 days a week — to begin the repair.
Impact on the water supply to homes and businesses was not felt until the hillside storage tanks began to empty.
Malibu’s water supply is stored in 47 water tanks at 24 different sites. Those tanks can only be filled from one source, the 30-inch main that runs along the ocean side of PCH carrying water from the Metropolitan Water District plant in Culver City. MWD is the large regional agency that brings L.A., and most of Southern California, water through a series of aqueducts and reservoirs from sources in Northern California, the Owens Valley or the Colorado River.
When the main line is shut down, it takes about 24 hours before most of Malibu loses its water supply, and, even then, there are still some isolated neighborhoods with small storage tanks nearby that rarely run out.
How quickly the tanks are depleted depends on how neighborhood residents cut back on their water use, as well as on decisions made in the county’s control room at the Civic Center. The brain and the heart of the water system, the room is filled with gauges and dials that allow the hydraulic engineers to monitor water levels and pressure in each storage tank, and identify the lines in which water is still flowing.
The first homes to lose water service are usually those on hilltops, where the flow slows to a trickle as water pressure drops.
The engineers adjust what they can to keep pressure up in the lines so western Malibu, which is farthest from the source, doesn’t run out prematurely. They empty the storage tanks into the main line, but no matter how they juggle it, there still is only a one-day supply for the whole city.
The 47 storage tanks hold a little more than 11 million gallons, only one-third of what the town should have in reserve, according to water experts. The majority is held in three major storage areas: two 1 million gallon tanks at Nicholas Beach, one 1.8 million gallon tank at Point Dume and a 3 million gallon tank at Pepperdine. The 43 smaller tanks hold a cumulative 4.385 million gallons.
To increase the city’s storage capacity to a three-day level would cost an estimated $50 million to service 5,000 customers in Malibu and another $10 million for the 2,000 customers in Topanga, which would have to be paid for by a bond issue approved by voters.
A major repair on the main line generally takes about 24 hours to complete. A hole 10 feet by 10 feet is dug around the pipe, 14 feet deep to the top of the pipe and then another 3 feet to get under it. Then, they shore up the sides of the hole before they can put a worker into it, who cuts the metal pipe and puts in a new section that has to be welded. The pipe is then covered inside and out with concrete to seal it and prevent erosion. Only after the concrete sets and the section is tested can they open the valves and refill the line.
Once the repair is finished, it takes another 24 hours or so to get full pressure back in the main line. Then, they can begin to refill the storage tanks. The whole process takes a minimum of three days, and frequently longer, to complete.
Thursday’s break was reportedly the worst anyone has seen in the last 27 years. The situation was complicated by a second major break just west of the first, adding a day to the repair time.
Although major shutdowns of the line are relatively rare, Waterworks 29 records indicate there have been approximately nine lesser breaks during the last seven years in the same area, the last in April of this year. This is an indication, some experts say, of continuing land movement in the area and portends possible future disruptions.