Preparedness

In New California Disaster Era of 'Fire-Floods,' Where Will Deadly Debris Flows Strike Next?

California is entering what experts call the “fire-flood” era: a formidable one-two punch prompted by warmer temperatures, bigger wildland fires, and more intense winter rain dumps, even in drought years.

by Tony Bizjak, The Sacramento Bee / October 25, 2018
A firefighter walks among the rocks and mud left by a mudslide Wednesday, Jan. 10, 2018, in Montecito, Calif. Anxious family members awaited word on loved ones Wednesday as rescue crews searched grimy debris and ruins for more than a dozen people missing after mudslides in Southern California destroyed houses, swept cars to the beach and left more than a dozen victims dead. AP/Marcio Jose Sanchez

(TNS) - Brent Larson awoke at 4 a.m. to the shake and rumble of what felt like a freight train rolling down the hill toward his Santa Barbara County home.

He leaped from his bed and woke his two sons. In seconds, a wall of water, mud and rock slammed into his house, smashing through one window, then the next, then a third, pouring in as the trio sprinted to the safety of the chimney at the home’s far corner.

“It was like out of ‘Indiana Jones,’” he said, nine months later, still shaken.

He was lucky.

Twenty-one of his Montecito neighbors were killed that Jan. 9 night, and 400 homes damaged or destroyed. Two other people are missing, believed to be entombed somewhere in the now hardened mud that still covers parts of Montecito, an upscale village next to Santa Barbara.

Worse, that night was not a freak incident, state emergency officials say.

California is entering what experts call the “fire-flood” era: a formidable one-two punch prompted by warmer temperatures, bigger wildland fires, and more intense winter rain dumps, even in drought years.

Fall fire season sets the table by denuding millions of acres of hillsides and baking the soil surface so that it becomes non-absorbent, or, in scientific terms, hydrophobic. When heavy winter rains hit, the water cannot penetrate the burned soil, and instead rolls downhill in the form of a mud and ash soup, similar to a flash flood, carrying boulders and trees with it.

“We know where things are headed,” climate scientist Daniel Swain of UCLA said. “We are just entering this era, and it is only going to get more interesting from here.”

Interstate 5 at risk

As witnessed in Montecito, debris flows can run for miles, burying highways, ripping up gas lines, destroying homes and taking human life. A quarter-mile of Highway 101 was buried in 12 feet of mud soup that morning. Battered cars and trucks ended up dumped on the beach below town.

California’s wild-land fires were massive and destructive again this summer. SWAT teams from the state Department of Forestry and Fire Protection have been busy scouring fire-scarred hillsides across the state in recent weeks and identified areas ripe for fire-flood debris flows should heavy rains hit.

That includes areas on the western edge of Redding and around remote Whiskeytown where the Carr Fire burned in July and August, as well as charred mountain slopes above Interstate 5 north of Redding.

Debris flow conditions can last several years after a fire. Montecito and other Santa Barbara County communities remain at risk, as do areas around Santa Rosa and Napa, where destructive fires hit in 2017.

A debris flow earlier this month during a cloudburst at the Ferguson Fire site near Yosemite forced closure of Highway 140, blocking people from getting in and out of the national park.

In Southern California, where more people live in steep canyons, the risk is more acute, officials say. Riverside County has issued warnings to residents of Trabuco Canyon about debris flow potential from the Holy Fire. The state Office of Emergency Services, Cal Fire and others have sent crews there to do prep work.

It’s not a mudslide

The ‘fire-flood” debris flow phenomenon is not new. Hydrologists, geologists and others in government and academia have studied post-fire flash floods for decades and know how fast and deadly they can be. One in 2003 killed 14 people at a church camp in San Bernardino.

Debris flows are sometimes described as mudslides, but the two are not the same. Mudslides occur when a hill becomes saturated and large amounts of subsoil slump and slide. Debris flows take only the top layer of soil with them, and run more like flash floods, moving fast and sweeping up debris.

“A debris flow is a flood on steroids,” said Jason Kean, a United States Geological Survey research hydrologist. “You add rocks, boulders and other objects. That weight, it is lethal. You can’t block it with a sandbag. You can’t outrun a debris flow. You need to get out of the way.”

The January flood storm in Montecito – home to Oprah Winfrey, Ellen DeGeneres, Rob Lowe and other celebrities – offered a laboratory-like lesson for emergency operations officials around the western United States.

A somber Winfrey posted a video the next morning of her yard covered ankle deep in mud. She was lucky. Her neighbor wasn’t. “The house in back ... is ... gone,” she said.

It started in early December with the Thomas Fire, then the biggest wildfire in state history, which burned for more than a month, prompting more than 100,000 evacuations and destroying 1,000 buildings along miles of coastal mountains.

As emotionally exhausted residents returned to their homes post-fire, county and state officials were meeting in war rooms with their eyes on upcoming January storms. In December, county crews cleared out drainage basins to ready them for the flash floods.

Thirty hours before the rainstorm hit, Santa Barbara emergency operations officials issued an evacuation notice to hillside residents.

County emergency management director Rob Lewin said his team suspected the debris flows would follow creeks and watersheds, but didn’t know how far they would spread. So they drew a line across the hill in the middle of town along East Valley Road. Uphill from that line, evacuations were mandatory. Downhill, they issued a voluntary evacuation warning.

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Shock on the hillside

The storm turned out to be huge, at one point dumping more than a half-inch of water in five minutes on the fire-baked hillsides. Officials estimated that some flows racing through neighborhoods may have been 25 miles per hour and tall enough to engulf vehicles.

Lewin was taken aback by their reach and ferocity. “We knew we were going to have debris flows,” he said. “We never anticipated it would be to the degree it was.”

Resident Brent Larson, who runs a boutique gardening business, had heard the warnings and knew a flash flood could hit.

His family’s house, though, was low on the hill, below the mandatory evacuation zone, and far from the fire scars. So he stayed.

“We’d been evacuated so many times during the fire season, families were so tired of moving back and forth,” he said. “That is why we were in the house that night.”

He awoke “by the grace of God,” thanks possibly to a bright light outside the window from a nearby fire at a broken gas main. He felt a rumble and heard trees snapping moments before the flow smashed into his house. “We ran to the furthest part from where it hit. The fireplace made sense.”

At some point, he noticed his cellphone had received a warning text from officials saying: National Weather Service flash flood warning for burn areas in Santa Barbara County. Take protective action to stay safe.

County emergency operations chief Lewin said the percentage of people who evacuated was “relatively low,” partly because of fire-related “evacuation fatigue,” partly from lack of public understanding about debris flows.

Better warning systems debated

With fires, “you can smell the smoke, see the flames, you understand what a fire can do. But in public responses, they didn’t know that mud can kill,” said Mark Jackson of the National Weather Service.

Officials now are debating whether better warnings can be issued in the future, based on more precise analysis of where flows might run and how big they will be.

The U.S. Geological Survey annually publishes maps that show which fire-scarred hillsides they and state officials believe are at risk for debris flows. The problem, the USGS’ Jason Kean said, is “our maps show where the debris flows (might) begin, not where they go. That is a tool we don’t have yet. That is something that clearly needs to get done.”

UC Berkeley geologist Bill Dietrich contends the techniques are available to accomplish that, using lidar, a combination of laser and radar, to analyze topography. He said officials need to commit to using the technology more widely now.

“The Montecito case is a prime example of a failure to tell where things will go,” he said. Dietrich drove through Montecito the day officials reopened the muddied roads. The flow routes were predictable, he said.

After the Jan. 9 flood, state officials did step in and assemble maps, as Dietrich suggests, that show better guesses of where flows might run. Similar work is being done at the Holy Fire site in Riverside County.

Santa Barbara County now faces another high-risk winter. County emergency chief Lewin has begun holding public meetings with the message to be alert and prepared. Have a plan. Heed instructions. And go when told to.

An early October rainstorm “triggered a lot of emotions” on the hillside, he said. “We know the community has a level of trauma.”

Jackson of the National Weather Service also has been giving presentations about debris flows. In those talks, he warns that what happened in Santa Barbara County last January is not a solo event.

“There are other Montecitos around California.”


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