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Burn Scar Debris Basins In LA County Fill With Sediment After Storms

A yellow excavator moves mud away from a concrete vertical drain.
Crews use excavators to move mud away from a vertical drain tower to improve water drainage after the storm.
Courtesy of the Los Angeles County Dept. of Public Works)
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Crews from L.A. County Public Works are digging out debris basins after heavy rain from recent storms refilled them with sediment. The Oakglade basin in Monrovia is now about 40% full, even after crews worked to remove hundreds of cubic yards of mud before last weekend’s storm hit.

What happened during the storm? The debris basins worked like they should, according to L.A. County Public Works. Water is separated from the mud and sediment by a big concrete filter. That keeps the sediment behind a wall and prevents it from filling up much faster. Most of the water is captured and used to recharge local aquifers.

How much are we talking about? A cubic yard is the size of a washing machine, so their goal is to move the equivalent of 7,000 washing machines of debris, filling up dump trucks using excavators and bulldozers and hauling it to a sediment placement area a few miles away.

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Why it matters: This area is highly susceptible to flash flooding because it's downstream from the huge 2020 Bobcat Fire burn scar. If mud and trees plug up the basin, it could spill out onto the streets and neighborhoods below.

How much water was captured? During the most recent storm over MLK weekend, two billion gallons of stormwater were captured in the two L.A. County basins. That’s enough water to serve 48,000 residents for one year — equivalent to a community like La Mirada, Azusa or Cerritos.