South of Pe Ell, the narrow Chehalis River cuts through forest land before weaving its way east toward bigger cities, widening along the way.
It’s here, though, on Weyerhauser-owned timber land, that local authorities think they can tame the flooding that has proved such a menace downstream. A cohort of officials visited the site Friday to hear the latest on a nine-figure dam proposal designed to retain much of the water that surges over the river’s banks during flood events.
“The idea is to reduce the frequency and extent of flooding downstream,” said project designer Keith Moen, of HDR Engineering. “When a high flood is anticipated, you could close the gates and temporarily retain water upstream to prevent the flood wave.”
Moen’s long-discussed project is a 254-foot tall dam with a spillway that’s 210 feet wide. While a dam has been discussed for years, the proposal currently under environmental review would not alter the river’s flow until gates are raised during flood events. The dam would be installed where what’s known as the Tin Bridge currently spans the Upper Chehalis.
The most recent estimate pegs the dam’s cost at $385 million, including land acquisition, but it may be a while before such funding needs to be provided and construction crews start work.
“The absolute, 100-percent, best-case scenario is two years of environmental review, two years of design and permitting and two years of construction,” said Erik Martin, administrator of the Chehalis Basin Flood Control Zone District. Martin is also Lewis County’s Public Works Director and will be transitioning to county manager in August. “That’s probably much more aggressive than will actually happen. … We’ve got to past the first hurdle before we can get to the second hurdle.”
The Flood Control Zone District is sponsoring the dam project, and members of its advisory committee were joined Friday by Moen and representatives from Weyerhauser and the U.S. Army Corps of Engineers. The Corps and the Washington State Department of Ecology are currently coordinating as they begin the environmental review process for the dam proposal.
“The Corps is very eager to stay on timeline,” said Janelle Leeson, a senior regulatory project manager with the agency. “Two years is a projected schedule, but we have a lot of work to do.”
If the project does get the regulatory go-ahead, stakeholders will then have to determine which entities take on the necessary roles to keep it moving. Though the Flood Control Zone District is the permit applicant for the project, plans have yet to outline further responsibilities.
“If we get through [environmental review] and it looks like this rises to the top as a preferred alternative, then we go forward with more. Who ‘we’ is is sort of the big question,” Martin said. “Who is going to own, maintain and operate this facility if it goes forward?”
Lewis County Commissioner Edna Fund, whose role also makes her a supervisor for the district, said it’s important to move the project through the regulatory phase, even if some details have not been decided.
“People ask who’s going to own this dam,” Fund said. “We haven’t determined that. But we’re moving forward with the permitting for the Flood Control Zone District.”
The project itself is designed to retain as much as 65,000 acre-feet of water during peak flooding. During the 2007 flood that devastated the area, estimates show that the dam would have cut peak flow in the Chehalis by close to 27 percent. According to the projections, the dam could reduce closures of I-5 by three days, protect 559 high-value structures and save nearly $1 billion in flood damage reduction over a century of use.
The vast majority of the time, the dam would allow water to flow through as it normally does, with five tunnels allowing fish to pass upstream. That portion of the river is home to Chinook, Coho and Steelhead.
“Most of the time it’s going to be open, so the water’s just going to flow through,” Moen said. “The gates would only be closed to retain water during flooding, which is not that frequent — for short periods of time every few years.”
When the gates are raised during flood events, a “trap and haul” facility will allow salmon to be collected and trucked to their destinations upstream. During construction of the dam, a diversion tunnel will be built to allow fish to navigate around the work site.
The dam itself would have a footprint of six acres; as water is retained, the temporary reservoir created could be as large as 720 acres. The proposal builds the dam on a large foundation that could eventually support construction of a permanent reservoir, if that option is deemed favorable decades down the road.
The funding for the project will come from the state, which has provided the money for the early steps of the process in its capital budget. Backers are hopeful that a favorable environmental review will ensure the money for construction is allocated when the time comes.
“There’s no assurances, but if things continue and it looks like a positive solution, something that is manageable both from an environmental impact view and from what the effectiveness of the dam will do for flooding, then I think most people who are involved in the process are optimistic that that funding will be there,” Martin said.
Fund noted that local Rep. Richard DeBolt, R-Chehalis, is the ranking member on the House Capital Budget Committee, and Sen. John Braun, R-Centralia, serves as ranking member on the House Ways and Means Committee. The propensity of floods to close the interstate has generated statewide buy-in as well, she said.
“We wouldn’t be building a water retention facility if we didn’t have I-5 being closed for three to four days when we have a flood event,” she said. “We’d be in a whole different situation if we didn’t. That’s why legislators from east to west support this project.”