California

Floods ‘on steroids’ could bring new dangers to wildfire areas. Are Malibu, Paradise at risk?

‘I would leave.’ When rains come, here’s the risk burned California areas face

Areas in Shasta County burned by the Carr Fire in 2018 are prone to another risk when the rainy season starts. Scientists explain why wildfire-burned hillsides can't absorb as much water, and why debris flows and flooding are more likely to happen.
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Areas in Shasta County burned by the Carr Fire in 2018 are prone to another risk when the rainy season starts. Scientists explain why wildfire-burned hillsides can't absorb as much water, and why debris flows and flooding are more likely to happen.

First came fire. Now the floods?

With late-season wildfires increasingly common in California, the twinning of the two catastrophes is becoming an alarmingly regular fear. Officials in both Northern and Southern California are planning this week for the possibility of a second set of disasters while still battling the flames of the first.

Two weeks ago, emergency crews frantically knocked on doors in Paradise, warning California residents to flee as the Camp Fire, the state’s deadliest and most destructive wildfire blaze, ran uncontrolled toward the town. It has claimed 84 lives with more fatalities expected, and destroyed more than 11,000 homes since it began.

Now, less than two weeks later, state Cal Fire teams are knocking again on remaining doors in the remote Northern California canyons where the fire burned through, warning residents of a new and imminent danger:

Powerful debris-filled flash floods, fed by heavy rains, may be racing down fire-scarred hillsides in coming days.

This is the new California, where hyper-hot wildfires burn into late fall and even early winter, leaving vast hillsides impermeable to water and susceptible to suddenly flowing slurries of water, ash, surface soil, trees, rocks and other materials. In some cases, the threat zone is right above housing developments.

With rains expected in fire areas this week, six separate agencies have issued public flash flood alerts since Monday for the mountains around the still-burning Camp Fire in Butte County. Included is a stark warning from the state Department of Conservation that debris flows can be up to 50-feet deep and run at 30 miles per hour.

A dozen members of the Cal Fire Watershed Emergency Response Team (WERT) have been combing the fire-charred hillsides near Pulga and Concow since last week attempting to identify the highest-risk areas.

PARADISE DEBRIS FLOW RISK

Federal geologists have put together a preliminary map of where debris flows are most likely to occur in the Camp Fire area during intense rains. This map shows the likelihood of a debris flow in a storm with a peak 15-minute intensity of one inch per hour.
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Map: Nathaniel Levine • Source: U.S. Geological Survey

Another 21-member WERT-led team is doing the same this week at the Woolsey Fire, which has burned 1,500 homes in the coastal mountains of Los Angeles and Ventura counties.

Those crews are quickly becoming an advance guard meant to prevent a second wave of mass casualties after fires.

The crews are laboriously digging into the soil with spades and pouring water on the ground to determine the soil’s level of hydrophobia — how much it will repel water. They are being guided by satellite photos of the burn areas, as well as by crews in helicopters looking for places where the fire appears to have burned especially hot, leaving little behind to slow the roll of earth if a slide happens.

The hottest burn areas of the Camp Fire appear to be lightly populated, WERT chief Eric Huff said on Tuesday — leaving fewer people in danger. But there are a handful of residences dotted around those areas.

“We have made contact with those folks to let them know they are in that higher risk area,” he said. WERT members have warned them to be ready to leave if the rain hits hard and fast. “Folks need to be aware and keep themselves out of harm’s way.”

National Weather Service meteorologists said the first set of storms this week likely will bring some heavy rain, but they said they don’t think it will be of the intensity that typically triggers a debris flow, which is about a quarter-inch in 15 minutes.

“This first (storm) is not what we’d call a gully washer, but we are apprehensive and we are watching it closely,” said Dan Keeton of the weather service. “It remains to be seen how (soil) is going to react.”

Several geologists and hydrologists interviewed by The Bee point out that the state has long suffered from flash floods and debris floods, especially in Southern California, some of them causing fatalities. But with temperatures rising and more wildfires, the threat appears to be increasing and more widespread.

Debris flows are different from mudslides, which typically involve hillsides becoming so saturated with water that they slump and slide. Scientists describe debris flows as more akin to floods, because the flows often contain more than 50 percent water and flow quickly.

“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.”

State officials learned a stark lesson about the power of debris flows in January when a huge downpour hit the coastal Santa Barbara County city of Montecito days after the Thomas Fire had swept through on the hill above the town.

Emergency officials issued flash flood and evacuation alerts before the storm, but were taken aback by the speed and breadth of the flow that destroyed more than 400 residences and left 21 people dead and two missing.

A quarter-mile of Highway 101 in Montecito was buried for a week in twelve feet of wet mud and debris, and mangled cars and trucks were deposited on the beach below town.

Santa Barbara officials said they believe some Montecito residents stayed in their homes despite warnings because they were suffering from “evacuation fatigue,” having been told several times in the weeks before to leave because of the Thomas Fire in nearby mountains.

One of them, Brent Larson, awoke to what sounded like a freight train coming down the hill above his house. A wall of water, mud and rock slammed through one window, then a second, then a third, pouring into the house as Larson and his sons ran to the safety of a fireplace at the far end. Larson said it felt like a scene out of an Indiana Jones movie.

A voluntary evacuation order was in place for his neighborhood. He didn’t take it seriously. Next time, he says “if there is a voluntary evacuation, (I’ll) get the hell out of the there.”

Other residents who survived woke up to find their neighborhoods encased in mud. A somber Oprah Winfrey shot and posted a video of her yard covered in mud. She was lucky. Her neighbor wasn’t. “The house in back ... is ... gone,” she said in the video.

National Weather Service meteorologist Mark Jackson gives talks about debris flows. His message: There are other Montecitos in waiting around the state.

“These things really move too fast for you to escape when you are right there,” he said. “If you can see burned hills from your house, you are susceptible.”

Cal Fire WERT chief Huff says the Montecito catastrophe opened eyes among emergency first responders about the need to get a quick handle on the potential paths of post-fire debris flows. The Camp Fire was only days old when fire-fight commanders called WERT and asked them for help.

“We learned from the Thomas Fire we have to move quickly,” Huff said. Even as the fires raged last week, “incident management teams are making that call, ‘We need a WERT team out there now.’”

With rains forecast, he said, it feels like a race against time. “We’ve had moments (in the last week) where it felt the clock was ticking loudly in my head.”

Geologists at the United States Geological Survey on Monday published the first preliminary maps showing where debris flow risk is highest at the Camp and Woolsey fires. Those maps will be amended as more data comes in from WERT crews as well as from U.S. Forest Services’ Burned Area Emergency Response teams.

“If you live in one of these areas, folks have to have one eye on the hillsides and the other on the weather forecast,” UCLA climate scientist Dan Swain said. “You can’t turn your back on it.”

The good news in Northern California, Huff said, is that there appear to only a few areas at high risk for debris flows, and there are only a few homes in those areas. There are bigger swaths of hillsides at risk at Southern California’s Woolsey Fire, which swept through seaside mountains in Malibu.

Officials have warned of flash flood or debris flow potential in other fire areas as well this winter, including in the Redding area where the Carr Fire burned this summer, and the hills near Clear Lake where the Mendocino Complex Fire burned.

Even residents of Montecito are still not out of the danger zone. Officials say some burned mountainsides take several years to regain normalcy.

Crews, meanwhile, are out placing debris barriers on hillsides above the Feather River and tributaries to limit potential flows of toxic materials into fisheries, Huff said.

Jackson, the meteorologist, said officials are not alarmed at the moment. For the most part, they are welcoming rain because it will start regrowth on burned hillsides, allowing them to begin the process of returning to normal, he said.

“Not every one of these storms is a bad storm,” he said. “We are in a drought. We need rain. We just done want it to come down fast.”

This 360 video taken on Monday, Nov. 19, 2018, shows the devastation the Camp Fire caused on Berry Creek Drive in the Plantation Retirement Community in Paradise. Not compatible with iOS devices.

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