Hillsides left bare by the Thomas Fire pose a mudslide threat
The steepness of the burn area increases the danger
The frightening hiss and crackle of the massive Thomas Fire in Southern California has been replaced by the loud droning of heavy equipment below the burn area.
Public work crews in Ventura and Santa Barbara counties are frantically clearing out every debris basin and storm drain possible, because the fire has left behind another threat – mudslides.
“The Thomas Fire burned all of our front country range here,” said Tom Fayram, Santa Barbara’s deputy director of public works.
“All these hills normally have a protective cover of chaparral. That’s all gone. Almost 100% gone,” he said.
What’s left is black-gray hillside that officials and residents alike fear will become ashy waves of floodwater with the first rain of a so far bone-dry season.
Dave Peterson’s two homes in the Montecito foothills were barely spared the wrath of roaring flames, but another ominous monster, in the form of a charred slope, looms less than 75 yards from his family compound.
“Underneath three, four, 10 feet of soil, it’s all rock,” Peterson explained, looking at the burn zone.
“When that soil gets wet, it just slides off the rock. It’s a treacherous situation, all right.”
Getting rid of debris
Ventura County officials predict any rain will pour twice the usual amount of water into flood channels because of the burned hills.
Work crews are cutting down dead or doomed trees and bulldozers are scooping up debris near a cement-ringed storm drain large enough for a human to walk through.
They are taking no chances in flood channels, hauling away anything that could block the drain and cause pooling, then flooding all around.
While such cleanup occurs before every rainy season, the scale of the Thomas Fire has cranked up the intensity.
“Generally we are dealing with hundreds of acres (burned), not in the thousands or hundred thousands,” said Jeff Pratt, director of public works in Ventura County.
“This is an order of magnitude or two greater than anything we’ve ever dealt with.”
The Thomas Fire is the largest wildfire in state history, having burned around 282,000 acres since it began December 4. It was 92% contained Monday; officials don’t expect full containment until later this month.
Both Santa Barbara and Ventura counties have experienced fire and then flood after rains before.
A spring 2014 brush fire above the Camarillo Springs neighborhood burned off all plant life.
When rains hit later that year, countless tons of loosened rocks cascaded onto 13 homes. Ten of them were red-tagged, ruled uninhabitable.
The National Weather Service office in Oxnard predicts lower than average rainfall for Santa Barbara and Ventura Counties for the next three months.
But forecasters say it takes only one storm with a lot of rain in a short amount of time to mush up fire-stricken hillsides and start a slide.
“A typical threshold would be about a half an inch of rain,” Robbie Monroe of the National Weather Service Oxnard office told CNN.
“About a half an inch per hour can start to produce issues, mudslides “
Praying for rain – just not too much
Planting anything on the hillsides now won’t stave off the danger. If it does rain hard, authorities would use K-rail barriers, sandbags or wooden plank fencing to keep water and debris away, and to divert the flow, said Jim O’Toussa, a geologist with the Ventura County Public Works Agency.
Other options for gentler slopes are laying down jute, wattles (encased tubes of straw) and silt fencing, he said.
“We can also, depending on site characteristics, use large rocks in a series of check dams – low mounds of large rock in channels – to reduce (floodwater) velocity, thereby reducing erosion and storing some eroded material,” O’Toussa said.
The cruel irony is that the region is suffering from several years of drought, and officials say they need the rain to regrow the plants and trees that can keep the hillsides together and flood-proof.
“We’re kind of damned if we do and if we don’t get rain,” said Fayram, “because we need the rain, but we don’t need a serious debris flow problem, either.”
To add more peril, Fayram says the steepness of the Thomas Fire burn area could quickly create high-velocity mud and rock flows.
“In these mountains, we go from 3,000 feet to sea level in sometimes just four or five miles,” Fayram said.
The residents of these communities are well aware that several miles away from the lowest edge of the Thomas Fire line, a chain-reaction flood is possible.
“It’s just too much to handle after everything that’s happened,” said Pamela Ueckert of Ventura, pushing her child in a stroller on a walk with her mother.
Her home stands, although it reeked of the Thomas Fire’s gagging calling card – oppressive smoke.
“I just feel bad for people who lost their homes,” Ueckert said. “They shouldn’t have to handle any more.”
In these two drought-battered counties, they’ll pray for rain – just not so much as to unleash the muddy beast lurking in Thomas Fire’s scorched wake.