Ventura County officials warned residents Thursday that there’s very little time to install protections as homes near recent fire lines face an elevated risk of flash floods and mudslides that could follow the wildfires when it rains this winter.
"Every canyon that is within this burn zone is at risk," Ventura County Geologist Jim O'Tousa said in a video interview distributed by the Ventura County Public Works Department.
On Thursday, Ventura County flood control and public works officials toured the area of the Thomas Fire that has scorched more than 440 square miles of terrain in Ventura and Santa Barbara counties.
The amount of mud and debris in creeks and flood channels in the burn area could double in any heavy rains this winter, according to the Ventura County Watershed Protection District. The estimate is based on computer models that project potential mudflows from the burned terrain.
Areas of previous landslides, like the seaside community of La Conchita, are especially vulnerable, O'Tousa said. The area saw major landslides in 1995 and 2005.
"They should be very wary" and consider buying flood insurance, he said. "And in the worst case, they should not spend the night in those houses" during rainstorms.
Homes located on canyons or below a hillside or mountain drainage — that would be a V-shaped indentation on a slope — are at risk, as are homes that back onto a slope, he said.
Getting through the first or second rains of the season is no guarantee a property is safe from a mud flow. A third or fourth drenching could be what triggers a slide. Also, when debris basins and culverts fill up or are blocked with fire debris, they cannot hold water, forcing the flow in an unpredictable direction.
Several years of regrowth of the burned plant life will be needed before the watershed in the Thomas Fire burn area is stable, O'Tousa said.
The U.S. Natural Resources Conservation Service is working with Ventura and Santa Barbara counties and city officials to plan for mudslide protections.
Residents in vulnerable areas can expect to see concrete K-rail barriers, sandbags and hay bales. Those measures can direct mud flows off the hillsides, past homes, and onto flat areas where the debris can be hauled away.
The counties have requested financial help from the conservation service, which can pay 75 percent of the protective measures. Once the federal and local agencies agree on the scope of work, installation should take about 10 days, said Jae Lee, assistant state conservationist for field operations who oversees a territory that includes Ventura County.