On Oct. 11, a landslide buried Washington state Route 410 and dammed the Naches River in the Nile Valley, east of Mount Rainier and west of Yakima, in the Cascade Mountains.
Over the weekend of Oct. 10, a massive landslide covered a half mile of state Route 410 in Nile Valley, Wash., with rock and debris up to 30 ft. (9.1 m) deep. The slide disrupted the course of the Naches River, pushing the riverbed up the slope opposite the slide, leaving fish exposed on the rocks dozens of feet above their previous home.
The affected section of highway is between Mount Rainer National Park and SR 410’s junction with U.S. 12, about 20 mi. northwest of Yakima. The slide also damaged another main route, Nile Road, which runs parallel to SR 410. When both of those roadways were closed, the 1,500 residents of Nile Valley were faced with a 90-mi. detour.
The cause of the slide is unknown. Although Washington’s Department of Natural Resources is investigating further, right now the Washington State Department of Transportation (WSDOT) is less concerned with the “why” behind the slide and more focused on the “how” of fixing the problem.
The first step for WSDOT and contractor Selland Construction Inc., based in Wenatchee, Wash., was to build a temporary emergency route on Nile Road for local traffic. Crews spent the week following the slide bringing in rock and gravel to build up the road. They put in culverts to direct the wandering river under the temporary gravel road and put rocks and trees alongside it to keep the water from eroding the route.
The Naches River is “still trying to figure out where it wants to go, as far as a new channel,” said WSDOT spokesperson Meagan McFadden. “That was something we were up against last week: the river constantly diverting itself while we’re trying to build this temporary roadway.”
The contractor created a large pool area near the landslide to help offset the unpredictable flow of the river and to make the construction of the emergency route possible. Now, to prevent spillage from that pool, crews are constructing a channel to carry the water away from the temporary road.
“We’re building a channel that will handle the velocity of the river and water flow,” said McFadden.
Meanwhile, a design team is planning another roadway, probably also temporary but intended to last through the winter. This road will be at a higher elevation, above the 100-year floodplain, and it will be paved. It may or may not remain past spring; McFadden said designers are still determining where the new roads are going to go.
For now, the push is on keeping the emergency route from eroding until the higher elevation, interim road is built.
“We have no timeline. We’re just working as quickly as we can to get things open and fixed temporarily for wintertime. Usually the snow comes down the third week of November, so we’re trying to work against the clock here,” McFadden said.
The current estimate for the emergency response, channel construction, and building the emergency and winter roads is $7.8 million, although the numbers are far from firm at this point. CEG