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Chehalis River Basin
EIS
Revised draft environmental review of proposed Chehalis River Basin Flood Damage Reduction Project
We closed the public comment period on the revised draft environmental impact statement Feb. 4, 2026
During the comment period, Ecology held several public meetings, online and in person. You can find links to meeting recordings and transcripts below:
Dec. 11, 2025
, virtual public hearing |
recording
transcription
Jan. 6, 2026
, public hearing |
transcription
Jan. 8, 2026
, virtual public hearing |
recording
transcription
Jan. 13, 2026
, public meeting |
transcription
Jan. 21, 2026
, public meeting |
transcription
What was the Revised Draft EIS about?
We analyzed potential environmental impacts of the proposed Chehalis River Basin Flood Damage Reduction project. The project explores ways to reduce the severity and duration of major and catastrophic floods that occur in the Chehalis River basin in southwest Washington. Proposed by the
Chehalis River Basin Flood Control Zone District
(Flood District), the project recommended two actions:
Constructing a unique flow-through dam and associated temporary reservoir on the Chehalis River near the town of Pe Ell.
Make changes to the Chehalis-Centralia Airport levee.
We analyzed potential project impacts and released a revised draft environmental impact statement that outlined our findings to gather public comments. We are currently reviewing comments and will finalize the environmental impact statement this summer.
The revised draft environmental impact statement is not a decision-making document. It does not approve or deny the proposal. Instead, it provides critical information for decision-makers to consider.
I want to...
Read the full revised draft environmental impact statement
Read comments we received on the revised draft environmental review
What happens now that the comment period is over?
We will review and consider all the comments we receive and prepare a final environmental impact statement for the proposed project. We will weigh all comments equally, regardless of how they were submitted to us (verbal, written or online).
We anticipate publishing a final environmental impact statement for the project in late summer 2026. A response to comments will be attached to the final environmental impact statement.
The final study will also inform permit decisions that will be made if the project moves forward. If the project moves forward, the Flood District anticipates starting construction in 2030.
Background
Location of the proposed flood retention facility and temporary reservoir and airport levee. Click image to download full version of map.
The Flood District originally proposed the flood damage reduction project with a different design a few years ago. We conducted a
draft environmental review
of that original design and held a public comment period in 2020. However, in the five years since our first draft environmental review, the Flood District changed the location, design, and construction details for its proposal, and resubmitted an updated proposal to us in April 2024. We determined the changes were significant enough to revise our original draft environmental impact statement for the project.
The
revised
draft environmental impact statement does not compare the two designs. It only looks at the new design, its potential environmental impacts, and possible measures to mitigate or offset any environmental impacts.
What our revised draft environmental study found
We used scientific models to help understand, test and predict how the proposed project would impact the environment. We found there would be adverse environmental impacts at the site of the dam structure, in the temporary reservoir area, and in areas downstream from the proposed dam during construction and operation.
The revised draft environmental impact statement found constructing and operating the flow-through dam and temporary reservoir would significantly and negatively impact fish and wildlife as well as aquatic and land habitats, recreation, earth, water, transportation, wetlands, land use, Tribal resources, cultural resources, environmental health and safety, environmental justice, and public services and utilities.
View virtual open house in full screen
Fish impacts
Our modeling data shows the proposed flow-through dam facility would adversely impact salmon and steelhead trout populations, especially near the structure. Our modeling also predicts climate change will continue to cause salmon and steelhead trout populations in the Chehalis River basin to decline, and the proposed dam is likely to magnify these adverse impacts.
Modeling also predicts the proposed project would reduce the genetic diversity within and among spring- and fall-run Chinook salmon runs as well as coho and chum salmon populations in 3,400-square-mile Chehalis River drainage system. We would also see significant adverse impacts to steelhead trout, lamprey, mountain whitefish, freshwater mussels, amphibians and macroinvertebrates such as insects, worms, snails and crayfish.
Tribal and cultural resources impacts
Based on available information, the proposed project would significantly impact Tribal cultural and natural resources.
Wildlife impacts
The project would significantly impact on wildlife species, their habitats and associated vegetation during construction and operation. Once operational, the proposed dam structure and associated temporary reservoir would block migratory pathways for wildlife.
Earth impacts
We found landslide risks around the temporary reservoir area. The project would also change the river channel and how neighboring sediment moves.
Water impacts
We found the proposed project would reduce the amount of streamside vegetation and shade cover along the Chehalis River and streams near the project. This would degrade area water quality by raising stream temperatures and reducing dissolved oxygen levels(which impacts fish). In addition, the project would eliminate peak downstream flows that are critical for forming natural channels that help slow down flood waters and create habitat areas for fish and other aquatic life.
Finally, the project would also reduce conditions favorable for replenishing large woody debris in basin rivers and streams. Large woody debris helps slow erosion and provides habitat areas for salmon and other aquatic species. In addition, wetlands, streams, and their buffers would be significantly impacted by dam construction activities and by operating the temporary reservoir.
Federal environmental review process also underway
The
U.S. Army Corps of Engineers
is conducting a separate
federal review
of the Flood District’s proposal under the
National Environmental Policy Act
. We will continue to coordinate with the Flood District, other state agencies and the U.S. Army Corps of Engineers during the review. However, the SEPA and NEPA processes will remain separate and on different schedules.
Details about the Flood District's proposed project
The Flood District’s proposed project entails building a unique flow-through dam and associated temporary reservoir on the Chehalis River near the town of Pe Ell and making changes to the Chehalis-Centralia Airport levee.
Under the Flood District’s proposal, the Chehalis River would flow freely through the dam structure unless a catastrophic or major flood occurs in the upper Chehalis River basin, triggered by heavy precipitation in the Willapa Hills. The dam would then close its gates to temporarily hold back flood waters to reduce flood-related damage from Pe Ell to Centralia. Water would be safely released later.
The project is not intended to address flooding in all parts of the Chehalis River basin and would not stop regular annual flooding.
What changes were made to the original project proposal?
The Flood District made several key changes to its original proposal, in response to our findings in the 2020 draft environmental impact statement including:
Moving the dam structure about 1,000 feet upstream from its original location.
Revising plans so fish could pass through the site before and after construction.
Submitting a plan to manage vegetation.
Identifying new construction quarry sites and updating information about roads proposed to be used during dam construction.
Making minor updates to the proposed airport levee portion of the project.
Drafting mitigation plans that address how adverse environmental impacts from the proposal could be offset.
Does the revised draft study connect to the Chehalis Basin Strategy?
The independent Chehalis Basin Board is leading the development of the Chehalis Basin Strategy—the long-term action plan for reducing flood damage and restoring salmon and other aquatic life in the Chehalis River basin. The board is considering a combination of projects and investments and is working on recommendations to present to the Washington Legislature in 2026 to move the strategy forward. The board will consider the information in our environmental review as they make decisions about the long-term strategy.
Climate change integrated into findings
We integrated climate change in our analysis of future conditions for the location where the proposed flood retention dam would operate. Unless Washington sees significant restoration efforts, climate change will drive more frequent floods, higher flood levels, and would put native fish runs at higher risk in the future.
Revised, draft study also analyzes two other alternatives
In addition to the proposed project, our revised draft environmental impact statement also analyzed what is known as a "no action" alternative. This analysis examines what would happen if the applicant doesn’t build the flood retention facility, or if we don’t see any improvements made to the airport levee. The study also analyzed a “local actions” alternative based on localized and nonstructural actions that could help retain floodwaters and reduce flood-related damage.
Calendar
Review process
Year
Details
Revised SEPA Draft Environmental Impact Statement
2025
Detailed analysis of the revised proposal for a flow-through flood control dam and airport levee changes.
SEPA Draft Environmental Impact Statement
2020
Detailed analysis of the flood retention facility and levee changes.
NEPA Project level review
2020
Detailed analysis of the flood retention facility and levee changes.
SEPA scoping for the EIS
2018
Comment period to collect information about what to include in the EIS.
SEPA Programmatic review
2017
High-level consideration of possible flood-reduction options.
SEPA findings, administrative process questions
The Washington Legislature passed the
State Environmental Policy Act
(SEPA) in 1971. The state law is designed to help local governments and state agencies identify potential environmental impacts likely to result from projects and decisions such as building public facilities, issuing permits for private projects, or adopting regulations, policies and plans.
SEPA’s environmental review process is designed to work with other regulations to provide a comprehensive review of a proposal.
While most regulations focus on aspects of a proposal, SEPA requires the identification and evaluation of probable impacts on all elements of the environment. The SEPA review process helps agency decision-makers, project proponents and the public understand how an entire proposal will affect the environment.
The SEPA process can be used to avoid, reduce or compensate for any probable adverse environmental impacts by modifying or denying a permit. An environmental review may include an
environmental impact statement
. The process begins with scoping, which sets up participation from the public, local and Tribal governments, and other state and federal agencies to comment on a proposal’s alternatives, impacts and potential mitigation measures to be analyzed.
Our revised draft environmental review analyzed:
Probable, adverse environmental impacts from the Flood District’s proposed project — including the project’s five-year construction period and 50-year operations period
Three flood scenarios: Major, catastrophic, and recurring floods
A “no action” alternative that examines what would happen if the proposed flow-through dam, temporary reservoir and airport levee improvements were not built.
A “local actions” alternative analyzing localized and nonstructural actions that could help retain floodwaters and reduce flood-related damage.
We consider a “significant and unavoidable impact” to be a major environmental impact that cannot be offset or reduced to a lower level. The revised draft environmental study contains mitigation measures that the Flood District and state agencies have proposed to reduce the project’s environmental impacts. The revised draft study did not analyze whether these mitigation measures would be effective or feasible. Our study identifies this uncertainty. More work will be done to develop mitigation measures during permitting and later stages of project design.
The state’s draft environmental review analyzed:
Probable, adverse environmental impacts from the proposed project — including the 5-year construction period and 50-year operations period for the project.
A major flood, catastrophic flood, and recurring flood scenarios.
A No Action and a Local Actions Alternative.
Yes. We are accepting public comments on the revised draft environmental impact statement through Feb. 4, 2026. Comments can be submitted by mail, online, at an evening public hearing in Centralia on Dec. 9, 2025, and Jan. 6, 2026, or virtually on Dec. 11, 2025, and Jan. 8, 2026. There are more details under the “Providing public comments” section of this web page.
In the EIS, a significant and unavoidable impact is a major environmental impact that cannot be offset or reduced to a lower level. The EIS contains proposed mitigation for the Flood District to develop and implement. However, we don’t know if mitigation is technically feasible or economically possible. The EIS identifies this uncertainty.
We are looking for comments that provide facts and information for us to consider. Comments simply in support of or opposition to the proposed flood damage reduction project are not as helpful. Ideally, public comments address issues such as:
Likely environmental impacts and potential mitigation measures.
Degree to which various types of resources could be affected.
Project alternatives and methodologies.
New data or studies to consider.
We will consider all the comments we receive. It does not matter how many times different people make the same comment. Duplicate comments do not increase the value or weight of a comment.
Over the last century, salmon runs in the Chehalis River basin have declined dramatically and floods have become bigger, more frequent, and more dangerous. Scientists warn these trends will worsen as weather patterns become more unpredictable due to climate change. In all the future scenarios we evaluated, we included climate change predictions such as changes in rainfall frequency and intensity, sea-level rise, increased flooding frequency and intensity, and increased air and water temperatures.
The environmental review looked at three future flood scenarios:
Major flood scenario
in which stream flows in the Chehalis River reach 38,800 cubic feet per second at the Grand Mound gauge, similar conditions as the 2009 flood.
Catastrophic flood scenario
in which stream flows in the Chehalis River reach 75,100 cubic feet per second at the Grand Mound gauge, similar conditions as the 1996 flood.
Recurring flood scenario
where flooding in the Chehalis River basin happens every year for three consecutive years.
Yes. While highly unlikely, if ground shaking from a large earthquake happened while the temporary reservoir was holding water and the dam structure failed, the water would significantly affect people, buildings, roads, and the environment downstream from the facility.
The revised draft environmental impact statement for the Chehalis River Basin Flood Damage Reduction project provides critical information that will be used by the
Chehalis Basin Board
, local and Tribal governments, state agencies, the public, and other decision makers.
Translated Content
Translated content
Borrador corregido de la revisión ambiental del proyecto propuesto para la reducción de daños por inundaciones en la cuenca del Chehalis River
El período de comentarios públicos estará abierto hasta el 4 de feb. de 2026
Abrimos un
período de comentarios públicos
de 75 días para el borrador corregido de la declaración sobre el impacto ambiental. Aceptaremos comentarios hasta el 4 de feb. de 2026.
Envíe sus comentarios por correo postal o en línea, o compártalos en una de nuestras audiencias públicas:
6 de ene. de 2026, audiencia pública
8 de ene. de 2026, audiencia pública virtual
21 de ene. de 2025, audiencia pública
Para reducir la gravedad y la duración de las inundaciones importantes y catastróficas que ocurren en la cuenca del Chehalis River en el suroeste de Washington, el
Chehalis River Basin Flood Control Zone District
(distrito de inundaciones) propuso dos acciones:
Construir una presa de flujo continuo única y un embalse temporal asociado en el Chehalis River, cerca de la ciudad de Pe Ell.
Realizar cambios en el dique Chehalis-Centralia Airport.
Analizar los posibles impactos ambientales del proyecto propuesto para la reducción de daños por inundaciones en la cuenca del Chehalis River. Hemos publicado un borrador corregido de la declaración sobre el impacto ambiental que describe nuestros hallazgos.
El borrador corregido de la declaración sobre el impacto ambiental no es un documento para la toma de decisiones. No aprueba ni rechaza la propuesta. Más bien, proporciona información crítica para que los tomadores de decisiones la tengan en cuenta.
Resultados generales
Utilizamos modelos científicos para ayudar a comprender, probar y predecir cómo el proyecto propuesto impactaría el medio ambiente. Descubrimos que se producirían impactos ambientales adversos en el sitio de la estructura de la presa, en el área del embalse temporal y en áreas aguas abajo de la presa propuesta durante la construcción y el funcionamiento.
El borrador corregido de la declaración sobre el impacto ambiental concluyó que la construcción y el funcionamiento de la presa de flujo continuo y el embalse temporal afectarían de manera significativa y negativa a la fauna, específicamente a los peces, los hábitats acuáticos y terrestres, la recreación, el suelo, el agua, el transporte, los humedales, el uso del suelo, los recursos tribales y culturales, la salud y seguridad ambiental, la justicia ambiental y los servicios públicos.
¿Qué tipos de comentarios necesita Ecología?
Haga clic en este enlace para aprender cómo hacer comentarios efectivos para las revisiones ambientales requeridas bajo la SEPA. Esto incluye cuáles comentarios son útiles y cuáles no, e incluye ejemplos de textos de comentarios efectivos:
Cómo hacer comentarios públicos efectivos para revisiones ambientales de la Ley de Política Ambiental del Estado de Washington (SEPA)
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Contact our Language Access team:
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Related links
State Environmental Policy Act (SEPA)
U.S. Army Corps of Engineers
Contact information
Environmental review:
Meg Bommarito
EIS Project Manager
meg.bommarito@ecy.wa.gov
425-681-6236
Media contact:
Curt Hart
Communications Manager
curt.hart@ecy.wa.gov
564-250-2126