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Landslide hazards from Bolt Creek Fire loom in months ahead

A U.S. Forest Service vehicle parked on a dirt road with burnt vegetation and soil alongside it.
U.S. Forest Service
To assess the threat of the Bolt Creek Fire – which started in September approx. 60 miles outside Seattle – burn scar on the watershed for hazards such as debris flow, the U.S. Forest Service conducted a Burned Area Emergency Response (BAER) of the area.

More than six weeks after the Bolt Creek Fire was ignited in the Mt. Baker-Snoqualmie National Forest just north of Skykomish, cooler temperatures and wetting precipitation finally returned to Western Washington in late October.

The rain and snow was seen as a welcome sign for dousing the fire, which had forced evacuations along U.S. Highway 2 and produced unhealthy air quality for millions of Washingtonians throughout September and much of October.

Although the immediate threats of the smoke and flames have subsided, what comes next is worrying emergency agencies throughout Washington: an elevated risk for debris flows and landslides on the land left parched by the fire.

Debris flows are a slurry mix of mud, gravel and vegetation litter that can be quickly swept up by heavy precipitation, especially on steep terrain. These debris flows move quickly and are unpredictable, leaving people, animals and property all in harm’s way, according to Reid Wolcott, the National Weather Service warning coordination meteorologist.

“We’ve been really dry for a long time,” Wolcott said. “It will take awhile for the soils to saturate enough to where we get to true landslide threats.”

“We will, during this winter, get to that point where we have an elevated threat of landslides throughout Western Washington, and when that occurs the risk of landslides will be elevated even higher on those burn scars. But for now, the debris flow threat occurs any time you have heavy rainfall.”

The National Weather Service in Seattle issued a flash flood warning on Oct. 25 for the Bolt Creek Fire burn scar due to the risk of debris flow, and the warning certainly won’t be the last of the season.

“This is really far beyond anything we’ve seen here in Western Washington to date,” Wolcott said. “We have had fires here in Western Washington. But the fires this year burned longer, they burned more severely because of the hot, dry conditions and a few easterly wind events. It was perfect conditions for developing burn scars.”

To assess the threat of the Bolt Creek Fire burn scar on the watershed for hazards such as debris flow, the U.S. Forest Service conducted a Burned Area Emergency Response (BAER) of the area.

First, a group of scientists across multiple disciplines surveyed the area and quantified on a five-step critical value scale the threat to life and safety, natural resources and property. Then, treatment plans are recommended for the area.

Possible treatments included the removal of bridge crossings, dip construction for runoff and the horizontal falling of logs to stabilize the hillside. But because of how late into autumn the Bolt Creek Fire burned, shorter term treatment plans were needed such as hazard signage and road closures.

Burned trees and exposed soil are in the foreground with mountains, covered in evergreen trees and clouds behind.
U.S. Forest Service
The area that is at immediate risk of debris flow from the Bolt Creek Fire is U.S. Highway 2. During the winter, thousands of vehicles per day head toward Leavenworth and Stevens Pass for wintertime recreation, passing through Skykomish and other areas now in danger of a catastrophe.

“The goal is to try and get [the BAER] done before winter rainfall and snowfall, which is a challenge with this current fire process, with this late, dry fall,” said John Kelley, a U.S. Forest Service BAER coordinator.

“That makes this a unique process because this fire will not be contained until it basically gets snowed and rained on. So implementation of BAER-funded repair is challenging to get on the ground because of the way the fire is coming to an end.”

The first BAER group completed its assessment between Sept. 25 and Oct. 5, while a second BAER began surveying additional areas of the fire Oct. 27.

The second BAER team surveyed areas near the perimeter of the fire that continued to burn since the first assessment. The group also reassessed some of the higher burn severity regions.

The BAER team is responsible for assessments on U.S. Forest Service infrastructure, but will communicate findings to partners at the Washington State Department of Transportation (WSDOT) and the Department of Natural Resources.

The area that is at immediate risk of debris flow from the fire is U.S. 2, where 6,500 vehicles per day pass just beyond the fire’s southern boundary between mileposts 46 and 50 near Skykomish. During the winter, thousands of vehicles per day head toward Leavenworth and Stevens Pass for wintertime recreation, passing through Skykomish and other areas now in danger of a catastrophe.

WSDOT currently inspects the area daily for hazards, but will move to its winter operating schedule to include round-the-clock operations on the highway earlier this year due to the burn scar, according to spokesperson RB McKeon.

While connecting communities is important to WSDOT, there may be incidents this winter when the highway will close for a multi-day stretch if the burn scar poses a risk to travelers or crews.

In the case of a U.S. 2 closure, residents of Skykomish will again be faced with no alternate route on the Old Cascade Highway, after part of the highway washed out in 2011 and has not been rebuilt since.

“Safety always comes first,” McKeon said. “If it’s not safe to have the road open we’ll close it for as long of a stretch as we need to.”

McKeon said that if multiple storms in a short period create unsafe conditions, a multi-day closure may be needed to allow crews to assess and clean up a landslide or debris flow before reopening the roadway.

WSDOT has removed more than 500 trees from the area and will continue to monitor for any potential threats.

Smoke from a wildfire covers half of a tree-covered hillside.
U.S. Forest Service
The Suiattle River Fire along the border of Snohomish and Skagit counties also burned late into the season which poses new challenges for the region.

Not only does the Bolt Creek Fire pose a new challenge to agencies in Western Washington but numerous other fires burned late into the season, including the Goat Rocks Fire in Lewis County and Suiattle River Fire along the border of Snohomish and Skagit counties.

According to Wolcott, the NWS meteorologist, the hazards associated with the Bolt Creek Fire burn scar will decline over the next two to five years, but human-caused climate change is worsening fire projections, meaning more burn scars are likely to occur in the future.

“This is the first go-around, which makes it really concerning,” Wolcott said. “The people in this area are not used to dealing with this hazard.”

“Even our partners, they’re trying to plan for hazards they’ve never had to deal with before. It’s definitely a challenge across the board because this is a new threat, and something that can really happen any year. But we happened to get several this year, and one particularly bad one.”

This story was written for the University of Washington’s News Lab.

Anthony Edwards is a senior at the University of Washington double majoring in Journalism and Public Interest Communication and Meteorology. He is the president of The UW Dawgcast, the University of Washington campus forecasting team and was formerly sports editor at The Daily UW.