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As devastating wildfires continue to ravage the Los Angeles metropolitan region, local officials are warning of possible flooding, landslides and toxic debris flows in the coming weeks and months.
“Properties have been damaged beyond belief,” said Mark Pestrella, director of Public Works for Los Angeles County, a joint county and city of LA. press conference on Thursday.
“They’re full of sediment, debris, silt and hazardous materials,” Pestrella added, referring to burn scar sites around the Palisades and Eaton fires.
TheFire of Palisadesthat has destroyed the Pacific Palisades neighborhood, is now 23,713 acres and only 31 percent contained, according to Cal Fire. TheEaton Fireburning north of Pasadena, is 14,117 acres and 65 percent contained.
“Both areas suffered watershed damage, burned to such an extent that we expect massive debris-laden flows when it rains,” Pestrella said.
“Should we have significant rainfall, we expect all street areas and all communities to be affected by debris flows that could be hazardous to human health,” he warned.
To deal with this looming threat, Pestrella said he and his teams are developing plans to capture and retain as much debris as possible during a heavy rainfall event.
“We expect the window to open for rain later this month and so we are already deploying manpower to the area,” he added.
Asked at the press conference to explain why a particular point in Pacific Palisades had already suffered a slope collapse, Pestrella explained that this was due to a geophysical process called “dry ravel.”
The phrase “dry ravel” refers to the rolling or sliding of particles down a slope in steep, barren landscapes,according to scientists. During wildfires, these particles can be moved by collapsing chunks of sediment that have accumulated behind vegetation.
“It’s a landslide: debris in the streets and on properties,” Pestrella said. “Some of that material supports some of the structures that are left.”
He also noted some water flooding, due to the amount of resource that was used during firefighting efforts, as well as some destruction of water and gas lines.
“A warning to all residents, regardless of where you live in LA County, if you have slopes behind your homes or if you are located on top of a slope, those slopes have become fragile,” he said.
“The soil that supports your home has become fragile and damaged, if you will, because of the events we’ve had, wind included,” added Pestrella, who stressed that the dangers of debris flows exist “even when it’s not raining.”
Regarding the toxic nature of the debris flow, Pestrella noted that the federal Environmental Protection Agency (EPA) is working with local partners to clean the properties of hazardous substances.
Tara Fitzgerald, EPA’s on-scene coordinator, explained that the Federal Emergency Management Agency has tasked the agency with conducting a “removal of household hazardous materials in the footprint of the burnt”.
That recall, which he said began Thursday, involves removing “the most immediate risk to public health and workers.”
According to Fitzgerald, materials targeted for disposal include pesticides, lithium-ion and other batteries, fuel and other items that would normally be sent to a household hazardous waste management landfill.
“We are working quickly to ramp up and look forward to supporting this recovery effort,” he added.
As for possible flooding in the coming weeks and months, Daniel Swain, a climate scientist at the University of California, Los Angeles, expressed some concern about what could be in a webinar earlier this week.
While forecasts do not indicate that such a deluge is imminent on the horizon, Swain noted that significant rainfall is “still very possible in February or March or even April.”
And if such an event occurs, he warned, “there will be great concern about the potential for flash flooding and debris flows in and downstream of all these areas.”
