By Ann McCreary
Local highway crews were experiencing déjà vu this week, when mudslides came down over Highway 20 east of Loup Loup Pass, in the same area where slides closed the highway almost exactly a year ago.
Highway 20 was closed briefly around 9:30 p.m. Monday night (April 9) when mud, rocks and trees slid over the highway near milepost 222, about 7 miles east of the summit. Washington State Department of Transportation (WSDOT) crews were able to clear one lane within about 20 minutes and had both lanes open by about 12:30 a.m. said Wayne Rice, maintenance supervisor for WSDOT in Okanogan.
Like last year, the slides are a legacy of past wildfires that burned vegetation and damaged soil on slopes above the highway, setting the stage for years of erosion and slides. “It’s the gift that keeps on giving,” Rice said Tuesday.
With saturated soil in the spring and no vegetation to hold the water, the hillsides are primed to slide when rain comes, said Don Becker, WSDOT maintenance supervisor in Twisp. “They’re having a heck of a time trying to keep the hillside intact. When you have loads of trees, they drink so much water. When they’re dead, they’re not drinking water … and you’ve got 3 million trees burnt.”
Mudflows in early April last year near milepost 222 undercut the road, causing extensive damage. There were multiple debris slides and road failures along Highway 20 on both sides of the summit last spring, forcing closure of a 16-mile stretch of the highway. The road remained closed until July 10, when it opened partially with one lane through the most-damaged sections. Repairs cost more than $4 million.
The slide Monday night “wasn’t hugely deep but was spread over a good area,” Rice said. He said highway crews reported that a truck was stuck in the mudslide when they arrived, but the driver was able to leave when crews cleared a lane.
Crews were continuing to work at the site Tuesday to clear culverts and divert water into ditches, he said. “Keeping the culvert inlets open is a challenge,” Rice said.
The same area experienced a slide last weekend that brought down debris that plugged some culverts, but did not block the roadway, he said. WSDOT will keep a front-end loader parked nearby in case of future slides.
The affected section of road, sometimes referred to as the “seven devils” by local motorists, is below a north-facing slope, Rice said. “There is still snow on that slope and any time you get moisture on snow” there is a potential for runoff, he said.
Soils scientists and hydrologists evaluated the area after last year’s slides, and concluded that burn scars from the Odin Road Fire of 2009 and the Carlton Complex Fire of 2014 were largely responsible for the massive mudslides last spring.
On the other end of Highway 20 over the North Cascades, WSDOT crews began clearing the road of snow this week. Becker said crews got the Silver Star gate dug out and were bringing in equipment to begin moving snow off the roadway.