Unusual beaver dam removed at risk of backup and flooding

WOODINVILLE, Wash. — Washington Department of Transportation crews worked all day Thursday to remove a beaver dam lodged in an 80-foot culvert underneath state Route 9.

Staff at the Brightwater Wastewater Treatment Plant on the north side of the highway had first noticed a pond reaching unusual levels in the last week or two and contacted WSDOT about it.

A spokesperson for Bridgewater said WSDOT then found the beaver dam inside the long pipe under the highway.

Dave McCormick, the assistant regional administrator for operations at WSDOT, said the dam caused water to back up on one side. If left untouched, the dam could suddenly break, causing water to gush through the pipe and flood properties downstream.

Or, the water could back up and undermine the pavement of state Route 9 above.

“Although they haven’t completely clogged this particular culvert, they’ve made a pretty darn good effort,” McCormick said.

He said that as beaver populations are rebounding in King County, WSDOT is familiar with the problem of dams in culverts, but usually not one so large in a pipe so long.

Crews had to first put a steel plate on the north end of the culvert to stop the flow of water.

Then, they went inside to put a hook on the 20-ft. dam and used a cable to drag pieces out bit by bit.

“The rascal has built his den right in the middle of the culvert, so it’s hard for us to reach,” McCormick said.

But after a full day of seeing branches and debris pulled out slowly, WSDOT said the culvert was clear enough that the problem has been resolved.

They never saw signs of the beaver or beavers.

The northbound lane of state Route 9 near state Route 522 will remain closed on Friday, due to a different construction project.

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