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Climate and Environment

Oh Dam... That's A Lot of Cleanup

Water flows down a dam spillway into the San Gabriel River
The San Gabriel Dam provides flood protection and hydroelectric power to the San Gabriel Valley.
(Daryl Barker
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Following a series of winter storms, Los Angeles County officials are now tackling the clean up of five reservoirs along the south-facing San Gabriel mountain slopes.

Why it matters

A map of L.A. County shows the location of 14 dams.
(Courtesy L.A. County)

Think of dams as a giant bathtub. It works like this: We want to collect as much stormwater as possible. But we also need a way to let the water run off to replenish vegetation and natural habitats.

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And we also need a way to let water out of that big tub if it's in danger or overflowing.

If that outlet is plugged up with sediment and debris that came from wildfires and storms, then that can be a problem.

In the L.A.-area there are 14 dams. Mark Pestrella, Director of L.A. County Department of Public Works said five serve as “the backbone of our water conservation system”

  • Pacoima Dam
  • Big Tujunga Dam
  • Cogswell Dam
  • Santa Anita Dam
  • San Gabriel Dam

Why action is needed now

Even before this winter, the L.A. County Department of Public Works was preparing to clean up leftover debris from past storms and the Bobcat fire. Then we had a wave of strong storms that added much more debris, filling up the reservoirs quicker than expected.

Worst-case scenario is that the reservoirs are filled to the brim which can be a potential flood risk. That said, Pestrella assures there is no risk of overflow, even if Southern California sees another deluge of rain similar to earlier this month.

What's next

A lot of the reservoirs are overdue for restoration, like the Pacoima Dam which was built in 1929. Another example: The Santa Anita Dam is holding 600,000 cubic yards of muckand silt is blocking two of three valves that release the stormwater.

Cleaning up the reservoirs will take three years and cost (gulp) $225 million. Pestrella said getting the job done will require continuous support from the state and federal level to keep these reservoirs running smoothly.

Current reservoir levels statewide

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More on water districts

Our newsroom's public affairs show AirTalk (which airs on 89.3 FM) recently talked to Michael McNutt, of the Las Virgenes municipal water district and Craig Miller, of the Western Municipal Water District, about what's going on in their areas and water districts overall.

Was the recent wet weather a boon or bust for water districts?
What questions do you have about Southern California?