Lessons from 2009 Naches slide in Yakima Valley

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by GLENN FARLEY / KING 5 News

NWCN.com

Posted on April 11, 2014 at 5:14 PM

Updated Friday, Apr 11 at 7:29 PM

YAKIMA COUNTY, Wash. – In mid October of 2009, a slide four times the volume of the slide that wiped out a neighborhood near Oso on March 22 created problems for state road engineers trying to help the area recover because of slide debris blocking a highway and a river.

Clearly, there are major differences between the 2009 Nile Valley slide and Oso -  the  least of which was in Nile Valley nobody was killed. However a number of homes were lost from being swallowed  up by the slide debris, which were red-tagged and undermined by both the slide and subsequent flooding from the Naches River. 

In Oso, at this writing, 36 people are now officially listed as deceased and a the neighborhood along Steelhead Drive - erased by mud that moved at freeway speeds.

But once the last victims from the Oso slide zone is recovered, there is the serious economic question of how to rebuild Highway 530 that connects Darrington and Arlington.  If it a key question for many residents of those communities who are wondering about the future as they confront two plus hour daily detours up and around Highway 20 in Skagit County.   

There may  be lessons learned in dealing with State Route 410, the main road between Yakima and Chinook pass.  After the 2009 slide, some 1,500 residents found themselves cut off upstream of the slide. 

The Washington State Department of Transportation and other Yakima County authorities were able to focus on getting something opened 24 hours after the slide stopped moving and after all people were accounted for, said Don Whitehouse, WSDOT’s administrator for the South Central Region.

Within two days, a temporary road was created by building up a roadbed through flood debris.  It was road opened only for residents to get in and out.   Six weeks after the slide, the county road was raised 10 feet in places and paved, but sharp curves held the speed limit to 35 miles per hour.  That “temporary 410” highway would remain the state of affairs for two and one half years before a new Highway 410 could be built around the slide.  

But there were lots of questions about what to do about a permanent road.  The massive debris piles of some 40-million cubic yards weren’t going anywhere.  Do you build over the top of the slide?  Or do you build around it.   

Once the slide was considered stable, the decision was made to build around it.  To make room, another channel was dug for the Naches River south of the slide, the original channel having been blocked. Then other measures were undertaken to both make the river resemble nature as closely as possible, while adding more rock to keep the free flowing river from meandering back against the new highway and undercutting it. 
 

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