Thurston County joins Chehalis Basin long-term strategy dialogue

A study of the Chehalis Basin’s future is underway, with Thurston County reengaging as a voice in policy and public engagement. 

The Thurston County Board of County Commissioners received a briefing from the Office of Chehalis Basin (OCB) on six long-term options under study in 2025, with a final strategy expected in 2026. The briefing was delivered at a work session on Wednesday, Sept. 24. 

The basin is Washington’s second largest after Columbia, with both serving as an industrial corridor for timber and farming.

OCB Director Jeff Zenk said catastrophic floods in 2007 and 2009 spurred the current strategy. 

The 2007 flood closed Interstate 5 for four days and caused almost $1 billion in damage. In 2009, the highway closed for two days.

Then-Gov. Christine Gregoire responded by creating the Chehalis River Basin Flood Authority in 2008, then launched a basin-wide flood and habitat plan in 2012. 

The Washington Legislature later established the Office of Chehalis Basin and Chehalis Basin Board in 2016. Investments began in 2017. 

Zenk addressed the switch from a battle to cooperation. 

“For a hundred years, people have fought over fish and flooding, and now, by taking a collaborative approach, they’re able to actually get things done,” he said. 

More than 140 projects have been delivered in less than a decade, Zenk relayed, wherein more than 200 homes and businesses have been protected, as well as roughly 300 acres. 

The state has provided money, including $70 million, then $75 million, and another $75 million in 2025–27, Zenk detailed. The funding supports aquatic species restoration, floodproofing and elevation of buildings, floodplain management, erosion control and a basin-wide flood warning system. Voluntary property acquisitions produce both flood protection and fish recovery. 

Zenk estimated basin-wide habitat restoration could reach about $1 billion if all projects are completed. The board is weighing large dams and levees against lighter restoration-driven approaches. 

Board Chair Tye Menser noted Thurston County once held a seat on basin work groups, but no longer has representation on the basin board. He said county concerns should help shape the comparative review. 

“I felt like this presentation was really important … to show that there are … multiple options under consideration,” he said. 

Six long-term directions 

Zenk outlined six plans now under comparative study, and said all of the plans build on ongoing programs. 

All options extend existing programs, including the Aquatic Species Restoration Program, floodproofing, acquisitions, flood authority projects, a flood warning system, floodplain planning and erosion control. 

Option A includes a flow-through dam near Pe Ell, Local Actions Non-Dam (LAND) Alternative levees around Centralia and Chehalis, and modification of the Skookumchuck Dam for fish passage and limited flood benefit. The dam gates would stay open under normal conditions and close only in major storms, releasing water later through a trap-and-haul system for fish. 

Option B also includes a flow-through dam and LAND levees, but removes the Skookumchuck Dam entirely. Options A and B would increase aquatic species restoration. 

Option C excludes a Pe Ell dam, LAND Alternative levees and Skookumchuck changes. It would expand restoration, floodproofing and flood authority projects. 

Option D leaves out a Pe Ell dam but would apply LAND Alternative levees  spanning Skookumchuck segments, China to Salzer Creek and Centralia airport. It proposes the removal of the Skookumchuck Dam and more habitat restoration. 

Option E would also apply LAND Alternative levees, but modify the Skookumchuck Dam instead of removing it. Zenk said it would improve coho and steelhead returns, though spring Chinook gain more from full removal since much of their spawning habitat lies within the reservoir. 

Option F includes the Pe Ell flow-through dam, an airport levee, and LAND Alternative levees, while preserving the Skookumchuck Dam unchanged. 

Zenk said modeling weighs project costs, homes protected, salmon recovery potential and downstream impacts.  

Menser asked how dams compare with levees given flooding enters from multiple tributaries. 

Zenk relayed a Pe Ell dam holds flows from the Willapa Hills, but not the Skookumchuck. He added levees may shield Centralia and Chehalis, but can increase water levels downstream. 

Skookumchuck Dam 

The Skookumchuck Dam, built in 1970 for hydropower, faces a decision point, Zenk said.  

TransAlta plans to close its last coal turbine by the end of 2025. Water rights tied to the reservoir are valued at about $80 million, and off-channel storage is under study as a replacement. 

Board Vice Chair Wayne Fournier asked about liability if ownership changes. Zenk said responsibility would transfer to the new manager, citing Lake Tapps as precedent. 

Fournier also asked about public access. Zenk said most land above the reservoir belongs to Weyerhaeuser and is closed. 

On fish impacts, Zenk said spring Chinook would see the biggest gains from full removal because the reservoir covers much of their breeding habitat. Coho and steelhead would benefit more from retrofitting. 

Agriculture depends on regulated flows that could decline if the dam is taken out, he added. According to Zenk, the Department of Fish and Wildlife and the Quinault Indian Nation favor removal, while the Chehalis Tribe has raised concerns about sediment and summer flows. 

Fournier urged liability and economic costs be factored into the review. He reminded the board that TransAlta has made community investments during the coal plant shutdown and wanted to know what role the company would have if the dam’s future is altered. 

Meanwhile, in terms of public participation, the OCB encouraged the board to recommend approaches on how best to inform county communities. 

Fournier said the OCB should collaborate with county staff familiar with Skookumchuck Valley agriculture and address liability risk early. 

Zenk noted the Thurston County Conservation District is already a partner on erosion control and spotted frog research. Menser said the county may adopt a resolution supporting the process, but not a single plan until the review concludes. 

To participate in the process, the public is being invited to open houses. 

An open house is scheduled for Oct. 8 at Montesano City Hall from 5 p.m. to 7:30 p.m., with an online open house available through Oct. 31.