Tribe Looks to Replace Interstate 5 Bridge Over Nisqually River in Effort to Prevent Freeway Closure


The Nisqually Indian Tribe is working to replace the  Interstate 5 bridge over the Nisqually River and plans to place about a mile and a half of the freeway on piers, so the changing course of the river does not wash the road out in the case of a catastrophic flood.

So far, the tribe has taken several members of the Washington State Legislature and various stakeholders on tours of the river, trying to garner support for the project. The South Sound Military Communities Partnership has slated the project on its legislative agenda, according to William “Bill” Anderson, the program director.

Washington State Department of Transportation (WSDOT) completed a study in June 2020 on potential traffic congestion on I-5 going from Mounts Road to Tumwater, and the project across the Nisqually Delta falls within its scope.

The Nisqually Tribe has already received $5 million from the WSDOT for the next step in its current effort, which involves conceptual design, construction cost estimates and a National Environmental Policy Act environmental review of the alternatives for the project.

“We’re hopeful to have that work done by the 2023-25 Legislative biennial budget, and at that point, we’ll take the preferred alternative and the cost estimate and seek construction funds,” said David Troutt, natural resources director with the Nisqually Indian Tribe. “It’s a little uncertain what that may cost, but it’s somewhere between $3-5 billion.”

The Legislature will make its decision on whether to appropriate the funds by March of 2023, but Troutt said the $3 billion to $5 billion is expected to be supplemented by federal dollars.

Troutt said I-5 acts as a dam across the Nisqually Delta and constricts the flow of floodwaters out of the mouth of the Nisqually River. It also constricts the flow of Puget Sound waters into the mouth.

“There are several things going on that we’re trying to deal with the Nisqually River, relative to I-5,” Troutt said. “One of which deals with upstream flooding possibilities and potentials due to the I-5 dam across the Nisqually Delta, blocking the efficient flow of flood waters downstream. We want to relieve that pressure.”

He said the tribe noticed with the catastrophic flood of 1996 and then again with the flood of 2020 to a lesser extent, that private properties flooded for long periods of time, in large part because the water did not efficiently move through the Nisqually Valley floor due to I-5’s blockage.

“The other issue we want to resolve is the impact (I-5 is) having on the downstream habitat for fish, and that it’s affecting the salinity of our critically restored estuary,” Troutt said. “As we are seeing sea-level rise increase, the dam across the Nisqually Delta from I-5 is preventing those (Puget Sound) waters from moving upstream, so the habitat that we’ve created that the fish are dependent on is getting deeper and more saleen.”

He said the project would create a more resilient and functioning estuary that would support the recovery of Chinook, steelhead and chum salmon. It will do that by allowing the habitats to adjust to climate change to support salmon survival and recovery, he said.

“The solution is to allow for the free flow of the Nisqually River across its historic floodplain in that delta there, by moving I-5 back onto piers, allowing the floodwaters to move freely downstream and the Puget Sound to move freely upstream,” Troutt said.

Interstate 5 currently causes the Nisqually River to constrict its flow, but the river is still releasing its energy above I-5 in dynamic and potentially dangerous ways, Troutt said. The river is constantly looking to continue to move downstream and release that energy, but it’s being forced by I-5 to release the energy elsewhere, he said.

Trout said the river is eroding the sediment on its shores rapidly in the areas just above I-5, and has created an unsustainable bend in the river directly upstream from the bridges, which has caused water to flow upstream at times as the river looks to discharge its flow.

“And so it’s going to continue to dig away and try to find the quickest way to release it to Puget Sound, and there’s a distinct possibility that it could be at that bend and punch through I-5 (in a place) where there’s no structure to support it,” Troutt said. “The result would be taking out I-5 completely, north and southbound lanes, for some period of time before it can be repaired.”

That kind of outage is projected to occur about 500 yards north of the Nisqually River Bridge.

And with Joint Base Lewis-McChord being a high-profile asset to national security, an outage like the one Troutt mentioned would be catastrophic to the base, since many of its service members use I-5 to commute from Thurston County.

For the same reasons, the local economy would be affected, as well as the tribe’s treaty rights, because if salmon see further decline, the tribe has fewer days to harvest the river’s resources.

“It really is a unique project that is basically a transportation-roads project, but it has a significant connection to treaty rights, salmon, orcas, national security with JBLM, local economies and transportation,” Troutt said. “I don’t know if there’s another project like it in the country that brings all of those various elements together like this one does.”