SR401 landslide

A landslide above Knappton on State Route 401 gave way on Feb. 22. The southbound lane remained open the morning of Feb. 23, but the highway was closed entirely later that day.

NASELLE — Repairing the landslide-damaged highway between Naselle and Megler is likely to keep State Route 401 “closed for an extended period of time,” a Washington State Department of Transportation spokeswoman said Feb. 26.

SR401 serves as the most direct route between Astoria-Warrenton and Naselle. Its closure means having to take U.S. Highway 101 around the edge of Willapa Bay, roughly doubling Naselle-Astoria commuting time.

The landslide, one of several in the area caused by heavy rainfall, began taking a bite out of the highway above the old Knappton Mill site on Feb. 22. Pam Shipp, a local resident who has documented the slide with her photographs, was among the first to encounter it during her evening commute. “I bottomed out and almost lost control of my car, heading over the embankment. Thought I’d run over a body! Went back and found the highway separating and sliding. Called the cops,” Shipp said on her Facebook page.

WSDOT left the southbound lane open that night, but by Tuesday, Feb. 23, the roadway had shifted significantly and had deteriorated to the point of becoming a hazard, so crews closed the entire highway to through traffic. Some sections of roadway moved three feet in less than 24 hours. The Dismal Nitch Rest Area located along SR 401 just east of the Astoria-Megler Bridge is also closed until further notice.

“The damage is significant and will require extensive repairs that will likely take months,” WSDOT said Feb. 23. Agency geotechnical engineers began an on-site analysis Feb. 26 to begin the process of designing a permanent repair, WSDOT communications consultant Celeste Dimichina said. “We need to gather information from the field, design a long-term fix, put the construction contract for the work out for competitive bid to hire a contractor, who will then do the work,” she said. “To help inform a long-term fix, we’ll need to complete some exploratory drilling, which we’ll analyze and compare to the conceptual designs we have drafted. We’re working on the timeline for this work.”

This landslide happened at a location which showed earlier signs of giving way.

“Some folks have asked why we did not do something about this stretch of highway sooner,” Dimichina said. “This section of highway is a known unstable slope, one of many that we track and manage adjacent to state highways. It was recently re-evaluated and ranked near the top of our repair list. If the slope had not suddenly failed, we were scheduled to performed slope stabilization work in 2024. As part of our proactive stabilization efforts, we continually evaluate slopes based on a number of factors and assign funding balancing hazard and risk when prioritizing slopes for funding.”

“There is never a good time to close the road,” WSDOT Project Engineer Joanna Lowrey said. “Because the roadway is actively moving and too unstable and saturated from heavy rainfall, closing the highway ensures that we keep travelers safe.”

In addition to the many who commute between Pacific and Clatsop counties for home and work, the closure will mean substantially longer travel times for delivery drivers, repairmen, Knappton-area schoolchildren and others.

For ongoing updates about the closure and repairs, see:

A more comprehensive explanation of how WSDOT sets landslide-repair priorities: https://wsdot.wa.gov/sites/default/files/2011/03/11/Unstable-Slope-Management-Program-Folio.pdf

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