The Chehalis Basin Board heard a presentation on Thursday, April 3, in Grand Mound, focused on plans to reduce catastrophic flooding to the Centralia and Chehalis area without the construction of a proposed flow-through dam on the Chehalis River near Pe Ell.
The board heard about proposals from the Local Actions Non-Dam (LAND) Alternative Steering Committee.
Moffat and Nichol, an engineering firm hired on as a consultant by the board, presented a preliminary report on how the construction of levees and other projects would impact flooding in the area along with simulations to test their effectiveness. The four plans shown include construction of as many as 11 projects. Most are levee improvements around parts of Centralia and Chehalis, with some protecting the Chehalis-Centralia Airport and the unincorporated community of Adna.
The Chehalis Basin Board is viewing these design proposals ahead of a June meeting where board members will pick which long-term flood solutions they want to continue working on. The board will decide on an official long-term flood solution for the Chehalis Basin Strategy in the first months of 2026.
That decision will determine whether the board plans to move forward with building a flow-through dam above Pe Ell, a collection of levees and other improvements or a combination of projects.
The Moffat and Nichol presentation focused on simulations run by the firm that show how the different project designs might affect flood waters. Maps showed potential changes in water height in and around Centralia and Chehalis. The most effective of the designs would lower flood waters primarily in parts of Centralia and the floodplains between Centralia and Chehalis — especially around Interstate 5.
“We think that this should be a suitable alternative to not increase water levels along I-5," Patrick McLaughlin, project engineer for Moffat and Nichol, said. “How we confirm that is with the next level of 2D modeling.”
The firm will now run more rigorous simulations on that model to verify their current findings. That model is also estimated to be the most cost effective design that meets project goals and could be built in piecemeal fashion as funding becomes available.
During the meeting, board members asked questions and voiced concerns about what they saw and what they hope to see from a more detailed analysis. While the projections show a reduction in water levels in and around Chehalis and Centralia and the areas around Interstate 5, they also predict small increases in water levels downstream ranging from .2 to .5 feet.
“I appreciate the effort and the detail that's actually going into it, and I actually look forward to the next when you get into the deeper modeling and not just 1D but 2D, because, you know, we are right now down stream,” said Glen Connelly, a representative for the Confederated Tribes of the Chehalis Reservation. “What does .3 feet look like? Maybe it's only 3 inches but on the reservation 3 inches can close the road that accesses the reservation, and so it can make it where the entire government operations and the casino and the hotel shuts down. Those are important factors for us.”
The Moffat Nichol team will return to present more refined findings and a draft project proposal to the Chehalis Basin Board at its June meeting to give board members the best possible idea of what the Local Action Non-Dam Alternative project could look like.
The main alternative to the a LAND proposal is a flow-through dam that would be built above Pe Ell. That installation, proposed by the Chehalis River Basin Flood Control Zone District, would be used as a flood retention facility and temporary reservoir during extreme flooding events.
According to the Office of the Chehalis Basin website, the Washington state Department of Ecology and the U.S. Army Corps of Engineers are currently reviewing that project as part of the State Environmental Policy Act and the National Environmental Policy Act. Those reports are projected to be finished in late 2025.
