Rain Batters Los Angeles, Threatening Mudslides, Toxic Flooding after Wildfires
San Francisco Chronicle
(TNS)
Jan. 26—After a significant downpour that ended an extended dry spell — and with more rain anticipated — Los Angeles County residents were urged Sunday to prepare for potential flooding, mudslides and debris runoff in and around the footprints of the recent wildfires.
As the rain arrived, flood advisories were in effect Sunday afternoon for parts of Los Angeles County, including the eastern burn area of the Franklin Fire and the burn scars of the Palisades, Hurst and Sunset fires. The National Weather Service said minor debris flows and minor flooding in low-lying areas with poor drainage systems were possible impacts. Lightning and small hail were reported in some areas, and the advisories indicated some flooding had started to occur.
The advisories came after a flood watch — which signaled flooding was possible — took effect at 10 a.m. Sunday and was expected to last until 4 p.m. Monday for the charred areas of the Eaton and Palisades fires, as well as the Franklin, Hughes and Bridge fires.
The National Weather Service issued a flash flood warning until 11 p.m. Sunday for the Franklin burn scar and the western portion of the Palisades
burn scar. "While not immediately likely, a life threatening debris flow will be possible," the warning said.
About an inch of rain was forecast for much of the region over the next three days — the first significant precipitation of the year.
While the rain was expected to aid firefighters' efforts to contain the destructive blazes, the environmental risks loomed.
"While damaging debris flows are not the most likely outcome, there is still a lot of uncertainty with this storm," the National Weather Service said on X. "The threat is high enough to prepare for the worst-case scenario."
The weather service urged residents in and around the burn areas to protect their homes and prepare for possible evacuations. Sandbags were available at the Altadena Golf Course, Victory and Robinson parks in Pasadena, and La Costa Post Office in Malibu. Information about other locations was available at lacounty.pw/sandbags.
The rain was expected at a time when much of Southern California is in severe drought, according to the U.S. Drought Monitor. Snow was also in the forecast, with the top of Mount Wilson blanketed Sunday morning, just north of Altadena on the edge of the Eaton Fire burn scar.
Debris flows occur when water flows rapidly, accumulating mud, rocks and branches. As little as 0.16 of an inch of rain in 15 minutes translates to a 40% to 60% chance of a debris flow in Topanga Canyon along Highway 27 and up to a 40% chance of a debris flow in Eaton Canyon in northeast Altadena, scientists said. Short downpours are more likely to trigger debris flows than moderate rain over long periods.
The charred footprint of the Eaton Fire was the most worrisome, in part because of the region's topography.
Debris basins — there are 21 in the Eaton Fire burn area and two in the Palisades Fire burn area — are designed to protect against mudslides, although significant debris flows can overtop basins. In 2009, a debris flow overwhelmed infrastructure and damaged 43 homes and 25 cars in an area near the Eaton Fire's current footprint. In 2018, after a fire charred the Santa Barbara Mountains, a debris flow killed 23 people in Montecito.
Aside from debris flows, pollutants were cause for concern. Officials cautioned that ash in recent burn zones was a toxic mix of incinerated cars, electronics, batteries, building materials, paints, furniture and other household items — and contains pesticides, asbestos, plastics and lead. Residents were urged to wear protective gear during cleanup efforts.
Los Angeles Mayor Karen Bass issued an executive order last week to expedite cleanup efforts and mitigate the environmental impacts of fire-related pollutants. County supervisors also approved an emergency motion to install flood-control infrastructure and expedite and remove sediment in fire-impacted areas. County workers installed barriers and cleared drainage pipes and basins.
As of Sunday night, containment of the Palisades Fire, which charred about 23,500 acres, reached 90%, and containment of the Eaton Fire, which charred some 14,000 acres, reached 98%.
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