Los Angeles County crews are hauling sediment out of dams and debris basins across the foothills, trying to beat the clock before El Niño storms arrive this winter. County officials estimate their teams will remove as much as 1.3 million cubic yards of sediment this year alone, work tied directly to fears that the Eaton Fire burn scar could turn heavy rain into dangerous flooding and debris flows.
The push is part of the county's annual reservoir and debris-basin cleanout, which runs every year from April 15 to Oct. 15, according to the Los Angeles Times. Los Angeles County Public Works oversees a flood-control system that includes 14 dams in the foothills and mountains and roughly 180 debris-catching basins, per the same report. “It's really critical that our dams and our debris basins have capacity to hold back water and debris,” Assistant Deputy Public Works Director Sterling Klippel told the Times.
Klippel, who oversees storm operations, engineering and the county's dams, has said the goal is to get sediment-removal projects wrapped up by Oct. 15, right as the rainy season begins, according to the Daily Bulletin. He has also said that a strong El Niño does not guarantee significant storms will hit any particular area, but it does raise the odds — a point echoed in the Times' reporting, which notes the strong El Niño this year increases the odds of drenching rainstorms across Southern California.
Eaton Wash Dam Becomes the Focal Point
Nowhere is the urgency sharper than at Eaton Wash Dam in eastern Pasadena, one of the 14 dams managed by Public Works. Crews removed sediment there on Sept. 28, part of a broader excavation effort meant to restore the dam's capacity of 956 acre-feet of water — roughly 325,851 gallons per acre-foot, according to the Daily Bulletin's reporting. Between Sept. 22 and Sept. 28 alone, the county removed 147,930 cubic yards of sediment from the dam, per the same account.
The concern dates back to a storm in February 2025, when ash and mud from the Eaton Fire scar washed down from the mountains and into the dam, as LAist reported at the time. Officials warned that if the dam's valve outlet became clogged during a subsequent storm, the structure could breach and flood communities downstream. The resulting debris-removal project was expected to cost $13 million and clear up to 500,000 cubic yards of sediment by April, LAist reported, and the county said the material removed had not been found to be hazardous. Sediment removal is expected to continue at Eaton Wash Dam, Devil's Gate Dam in Pasadena and San Gabriel Dam for a few more weeks, per the Daily Bulletin.
Why Burn Scars Raise the Stakes
Burn scars like the one left by the Eaton Fire increase the amount of rocks, boulders, sand and mud that wash downstream during major storms, and debris flows can strike suddenly in areas burned within the previous three to five years, according to the Daily Bulletin. The National Weather Service says most burn areas remain prone to flash flooding and debris-flow activity for at least two years, though the exact risk varies by burn severity, terrain steepness, the size of the burned area and proximity to population centers, per the National Weather Service.
Not everyone sees the slopes as a worst-case scenario. Tim Martinez, land manager and planning director for the Arroyos & Foothills Conservancy, has said natural regrowth — including laurel sumac and mountain buckwheat — has strengthened slopes affected by the Eaton Fire, and that conditions are not as dire as once feared after nearly two years of regrowth, according to the Daily Bulletin. Martinez plans to keep monitoring Millard Canyon, Rubio Canyon and the Chaney Trail area, which has been closed since Jan. 7, 2025, per the same reporting.
Lessons From Past El Niño Winters
County officials have reason to take the threat seriously. During the 2004-05 El Niño, storms filled Los Angeles County's dams until they spilled over, the Times reported. The 1997-98 El Niño was far worse: storms, mudslides, floods and sewage spills across California caused 17 storm-related deaths and $550 million in damage, according to the San Gabriel Valley Tribune. One of those deaths was Nathan Cook, swept away by a wall of water while riding along the Arroyo Seco in Altadena on Feb. 7, 1998. That February, Santa Barbara recorded 21.74 inches of rain, breaking monthly records dating to 1867, and 15 county dams reached their highest levels since the 1983 El Niño, with five overflowing their spillways, the Tribune reported.
A 2022 study estimated that a severe, once-in-a-century flood would threaten the homes of hundreds of thousands of people across the Los Angeles region, according to the Times. As fires become more frequent and extreme, keeping dams and stormwater-capture projects clear is an increasingly difficult and costly task, LAist has reported.
Residents and Rebuilders Watch the Sky
For families rebuilding in the Eaton Fire's footprint, the stakes are personal. Victoria Knapp, whose new home is about 85% built, has said she hopes the county will stock sandbags at fire stations and maintain K-rails along Altadena Drive; she expects to move in around early or mid-November, according to the Daily Bulletin. Virginia Kimball has said people should avoid hiking or driving near burn-scarred foothills and mountains during severe storms, per the same report.
Despite the uncertainty, rebuilding in Altadena continues. The county has approved 4,012 building plans, about 213 homes have been completed, and 2,310 homes are currently under construction, the Daily Bulletin reported. Most builders plan to proceed with construction despite the forecast El Niño winter rains, according to the same account.
