Chehalis River Dam

Artist rendering of Flood District's proposed flood retention dam on Chehalis River.

A week after the release of the national draft Environmental Impact Statement (EIS), officials with the Lewis County Flood Control Zone District are working to figure out how to mitigate the impacts that the proposed flood-retention structure on the Chehalis River would have on the land, water and fish.

“This project won’t go forward unless it can mitigate any specific impacts in the upper upper Chehalis Basin and it won’t go forward unless there is an accompanying aquatic species restoration plan looking at the whole basin,” Chehalis Basin Board Member J. Vander Stoep said in a Sept. 23 meeting. 

The impact statement detailed how the project, which would cost more than $400 million, would have “high permanent impairment of habitat function” for fish species. The removal of 485 acres of trees would lead to increased water temperatures, which would impact Chinook and coho salmon as well as steelhead. Fish passage would be restricted and spawning habitat would be reduced. Nine endangered species are present in the project area. Additionally, about 340 acres of wetland and stream buffers would see impacts. 

Consultant and geomorphologist Shane Cherry presented a preliminary mitigation strategy to the Lewis County

commissioners acting in their role of directors of the flood control zone district, noting that final mitigation processes are negotiated during the permitting process and are enforceable as conditions of the project. In prioritizing the project area and the 20-mile strip of downstream river, Cherry said some mitigation efforts will require negotiating with private property owners. 

One major mitigation strategy would be planting trees along potentially 53 miles of the river. The new trees would provide more shade in an attempt to cool the water that would be heated by the project’s construction. 

Although many environmental impacts on aquatic species would only occur during the construction of the project, Cherry told commissioners not to dismiss them.

“It’s not trivial, because construction would last approximately five years,’ he said. 

Other strategies include hyporheic exchange enhancements, which Cherry described as manipulations in how the water flows into the ground, which can create colder pockets of water for fish. The channel could be manipulated in other ways to provide fish safe places to “hunker down” when the river is too high, Cherry added. 

Removing small natural dams could also assist fish passage upstream. 

Overall, Cherry estimated that mitigation efforts could cost up to $86 million.

“This is not an outlandish number, especially for a project that has a very heavy aquatic footprint,” he said. 

Lewis County Manager Erik Martin noted that the city of Pe Ell should be heavily involved, and that they should comment on the impact statement and mitigation efforts since the flood retention facility would be close to the city. 

According to Martin, the county is conducting polling and will conduct focus groups in order to gauge public opinion on the project. 

The public can submit comments at public meetings being held virtually on Oct. 8 and 14. Details can be found at


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