The Chehalis River Basin Flood Control Zone District (Flood District) is seeking to construct a unique flood-control dam and associated temporary reservoir on the Chehalis River near Pe Ell and make improvements to the levee around the Chehalis-Centralia Airport.
Under the Flood District’s proposal, waters in the Chehalis River would flow freely through the proposed flow-through dam structure unless a major flood occurs in the upper Chehalis River Basin, triggered by rainfall in the Willapa Hills. The dam would then close its gates to temporarily hold back floodwaters to reduce flood-related damage from Pe Ell to Centralia. Water would be safely released later. (See the vicinity map.)
The proposed project also includes airport levee improvements to protect the Chehalis-Centralia Airport, local businesses, and area transportation from major flood damage. In addition to raising the existing levee around the airport, about 1,700 feet of Airport Road would also be raised. For more information about the flow-through dam, visit ChehalisRiverBasinFCZD.com.
Current status: State releases revised draft environmental impact statement
The Washington State Department of Ecology (Ecology) and U.S. Army Corps of Engineers (Corps) are conducting separate environmental reviews of the Flood District’s proposed flood-damage reduction project. Ecology is reviewing the proposal under the State Environmental Policy Act while the Corps is assessing the project under the National Environmental Policy Act.
On Nov. 20, 2025, Ecology released a revised state draft environmental impact statement for the project. The updated draft study analyzes whether the proposal would adversely impact the environment and ways these impacts might be offset or mitigated. While Ecology released its original state draft environmental study for the proposal in February 2020, the Flood District made significant design, location, construction and operational changes to their project, which were submitted to Ecology in April 2024.
Given the extent of the changes, Ecology determined a revised draft environmental study was necessary to ensure the state environmental review is accurate, complete and transparent for the new project design. The revised draft study is not a decision-making document. It does not approve or deny the proposal. Instead, it provides critical information for decision-makers, such as the Chehalis Basin Board, to consider.
View more information about the state and federal reviews.
The Chehalis Basin Board is assessing whether the proposed flow-through dam should be incorporated into the long-term Chehalis Basin Strategy to help reduce flood-related damage in the upper part of the Chehalis River Basin. The Board will use the findings in the state environmental review, as well as other information, to inform their recommendations to the Washington Legislature. Their decision is anticipated in 2026.
The Board is also considering several other options for large-scale flood damage reduction, including the “Local Actions Non-Dam Alternative.” Board members will decide which projects to move forward after the state environmental review of the proposed dam is complete.
What is the Flood District?
As result of the devastating Chehalis River floods in 2007 and 2009, the Lewis County Board of County Commissioners formed the Chehalis River Basin Flood Control Zone District (Flood District) to find solutions to reduce flood risks, protect Basin communities, and preserve the ecosystem benefits the Chehalis River system provides.
Past webinar recordings and Fact Sheets about the proposed flood-control dam:
Community Update: Proposed solutions for large-scale flood damage reduction (Oct. 2024)