LYNNWOOD — If the roadway seems like it’s sinking, it’s not your imagination.
The intersection of Ash Way and Maple Road in Lynnwood has settled more than 19 inches since that portion of Maple Road was built in 1983. It now is sinking an average of about an inch a year, records show.
The city of Lynnwood and Snohomish County are talking about working together on potential fixes — and the varying price tags that accompany each proposal. The county’s involved because it owns Maple Road east of Highway 525.
The roadway is built on top of roughly 37 feet of peat, according to a City Council memo. It frequently floods after significant rainfall.
As little as an inch of rain can prompt partial road closures, said Jared Bond, the city’s environmental and surface water supervisor.
“Anytime we get above two inches, there’s a high likelihood we have to close the whole roadway, and that’s two inches in 24 hours,” he said.
An estimated 34,500 cars travel the intersection each day.
Two ideas were floated to Lynnwood’s council earlier this month for consideration.
The first is to overlay the existing road with additional pavement, to add elevation. It’s the cheaper option, with the city’s bill running up to $750,000. The downside is the added weight from new pavement could increase the sinking to more than an inch a year, meaning another overlay would be required in five or so years.
“The additional weight would just exacerbate the settlement problem,” Bond said.
The second option, with a cost of up to $3.6 million, is to drive “pin-piles” — like the poles that support piers and bridges — 40 feet into the solid ground beneath the peat. Under that option, “roadway settlement would be virtually non-existent,” according to the council memo.
That option was recommended in a technical study done in 2013.
As the road settles, culverts, pipes and other drainage devices are sinking too, Bond said. Any work that’s done will have to account for drainage to ward off worsening any flooding downstream.
Rikki King: 425-339-3449; rking@heraldnet.com.
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