I-90 Lanes Near Issaquah Reopen; Months of Work to Improve Salmon Traffic

If you live in the Snoqualmie Valley and regularly commute to Issaquah, Bellevue and/or Seattle,  you may have noticed something different along I-90 the past couple weeks – no more I-90 lane closures near the Highpoint and Issaquah Highlands exits.

It took nearly $3 million, but the Washington State DOT just finished up the project that had me wondering “what are they doing under the freeway for all these months?”

Turns out it was all in the name of traffic – salmon traffic  – including the big three most Snoqualmie Valley 3rd graders study, Chinook, Sockeye and Coho.  Underneath the roadway in this area, the East Fork of the Issaquah Creek runs between eastbound and westbound I-90.

The DOT spent about 5-6 months replacing a 12-foot diameter culvert under busy I-90 with a much larger 40-foot diameter culvert.  The benefit?  Slowing down the East Fork of the Issaquah Creek and helping more salmon reach their spawning destination.

The smaller culvert had forced the creek into a narrow opening under the freeway, in essence speeding up the creek while forcing its way through the narrow opening.  There was also nearly a 2-foot drop after the culvert that was too high for salmon to jump when heading upstream.  The new culvert allows the creek to spread out and slow down, making it so more than just the strongest and hardiest of salmon can navigate the creek through the culvert and migrate to their spawning grounds.

According to the Washington State DOT website, “The 25 foot stream was shoehorned into an eight-foot stream bed. This barrier was identified in 2006 as a barrier to fish passage.”  Washington State law requires the DOT to install and maintain culverts to assist fish in their spawning passage.  Fish and Wildlife officials help the DOT identify and prioritize culvert replacement/maintainence.

Old 12-foot culvert under I-90. Courtesy of WA State DOT

Extra precautions were taken during construction as the area contains two large pipelines that transport natural gas between Canada and Utah.  With project completion, those pipelines are now supported by concrete rather than dirt and water, making the area safer.  The larger, stronger culvert also supports I-90 above, making the roadway safer during heavy rains and flooding events.

“Removing fish barriers is important to the restoration of fish habitats and salmon recovery efforts,”  according to the DOT website.  You can see a King 5 story on the project HERE.

Next October when hundreds of SVSD 3rd graders take their annual field trip to the Issaquah Fish Hatchery, maybe they’ll see the improvements in the form of even more salmon.

Two large natural gas pipes that had to be avoided while replacing the Issaquah Creek culvert that runs between East and Westbound I-90. Photo courtesy of WA State DOT

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  • Thanks for sharing. I was wondering what was going on there. I thought maybe it had something to do with the water that is frequently running across the highway near there even when it is not raining. Always wondered about that as well.

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