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What’s Clogging Your Commute? New Culverts For Fish And Flood Mitigation

Upgrades to old infrastructure are often needed to help reduce the risk of flooding. That can lead to inconvenient road closures.

But the payoff is not just for humans. Replacing old culverts and pavement can also help endangered fish.

Backhoes and bulldozers will be working alongside SR 522 at Lake Forest Park Towne Center for the next couple of months. The city is re-plumbing the culverts beneath this roadside mall. The main motivation for the work, at least initially, was major flooding.

“We’re going from approximately six feet to 20 feet in width – all four of these culverts are twenty feet in width,” said city engineer Neil Jensen.   

The city needed to more than triple their size to accommodate the runoff that comes from all the towns and suburbs northwest of Lake Washington. Jensen says the old ones had overflowed four times over the past two decades, ruining dozens of nearby homes and causing major disrupt tions in the neighborhoods near the mall and highway.   

He says the root cause is recent development that has filled in what were once farm fields or wetlands with more and more pavement, which makes runoff more intense.

“And it tends to flow to the creeks and streams and rivers now much more rapidly, much more ‘flashy’ as they like to say,” he explained recently while peering into the pit where the new culverts were being worked in by construction crews.

 “If you get the same volume of water, you get it in a more compressed time. And that’s what causes flooding,” Jensen said.   

And so, he says the city took a leap of faith and started planning the culvert replacement project even before they knew how they would fully fund it. They began with mitigation funds from FEMA and King County. The work was more expensive than the $4-million those grants would cover. The total estimated cost for the upgrades is about $7-million.  

But then in 2013, an important decision came down, from US District court, mandating that the state has to replace culverts that block migration of fish that local tribes depend on.

“And the culvert here at 522 was determined to be only 33% passable by fish,” said April Magrane,  the lead biologist for the Northwest Region of the Washington State Department of Transportation.

She says older culverts weren’t built with fish in mind. They’re often too steep or elevated, blocking passage for endangered and threatened species.

“They are not making it up into their spawning grounds. And we’re hoping to remedy that here.”  

That’s why you’ll likely see more and more work on culverts, statewide. WSDOT expects to replace an average of 30 to 40 per year from now till 2030.

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