State environmental review of proposed Chehalis River Basin Flood Damage Reduction Project

The Chehalis River Basin Flood Control Zone District has proposed constructing a flood-retention dam and associated temporary reservoir on the Chehalis River near Pe Ell, and making changes to the Chehalis-Centralia Airport levee.

The public comment period for the draft state environmental review (EIS) of the proposed Chehalis River Basin Flood Damage Reduction Project ended May 27, 2020. The project applicant is currently considering potential project changes to construction, operation, fish passage design, and location. Ecology is awaiting the revised project description from the applicant and continues to work on the final EIS.

Draft environmental review released

Location of the flood retention facitility and temporary reservoir and airport levee. Click to download full version of map.

Our draft state Environmental Impact Statement (EIS) analyzed how the proposal is likely to affect the environment under the State Environmental Policy Act (SEPA). Our focus sheet has an overview of the findings of the draft EIS. A presentation on the draft EIS is available as slides or with audio.

We held a public comment period on the draft state EIS from Feb. 27 through May 27, 2020. Comments received are available to view and download. Comments are valued equally, and responses will be included in the final EIS.

Final environmental review

We are developing the final EIS and expect to release it in 2025. It will include revisions based on the public comments we received for the draft EIS, as well as additional modeling and impact analyses. It will include a range of potential impacts based on high and medium climate-change models from the University of Washington Climate Impacts Group. The report also will provide responses to the substantive comments we received on the draft EIS.

We have been coordinating with other state agencies, the U.S. Army Corps of Engineers, and the Flood District throughout the process. The Flood District has provided clarifications on the proposed project to be considered in the final EIS. 

Flood District's proposed project

The Flood District's proposed flood retention dam and associated temporary reservoir is intended to reduce damages from major floods from Pe Ell to Centralia triggered by rainfall in the Willapa Hills. The airport levee changes would raise and widen the Chehalis-Centralia Airport levee and nearby roads to increase levee protection level during catastrophic floods. The project is not intended to address flooding in all parts of the Chehalis River basin and would not stop regular annual flooding. 

See proposed project images:

Relationship to Chehalis Basin Strategy

Communities in the basin are working with the Chehalis Basin Board on a long-term strategy to reduce flood damage and restore aquatic species habitat in the Chehalis River basin. One part of the Chehalis Basin Strategy is to consider large-scale flood-damage reduction actions. The Flood District's project evaluated in the draft environmental review is one of the proposed actions for consideration. The Board is expected to use the information in the environmental review, along with other information, to inform their recommendations for the long-term strategy.

Study identifies significant environmental impacts

Our review studied the likely significant environmental impacts from the Flood District’s project as well as alternatives. We looked at 17 different environmental elements including impacts to air quality, cultural resources, environmental health and safety, environmental justice, fish and aquatic species, habitat and land use, recreation, transportation, tribal resources, water, wetlands, and wildlife.

Under our analysis, the project would reduce flooding to buildings and infrastructure, including U.S. Interstate 5. It would have significant adverse effects, mainly along the Chehalis River in the area above the flood retention dam and below it to the confluence with the South Fork of the Chehalis River. These include:

  • Reducing spring- and fall-run Chinook salmon, Coho salmon, and steelhead trout
  • Reducing native aquatic species such as lamprey and mussels
  • Reducing wildlife such as amphibians
  • Degrading habitat on land, and in water and wetlands
  • Degrading river and stream water quality
  • Eliminating access for recreational fishing and whitewater boating
  • Increasing greenhouse gas emissions
  • Impacting Tribal and cultural resources

Several impacts from the proposal would be unavoidable unless measures to offset them are determined to be feasible and meet regulatory requirements. This would be determined during future permitting processes including local and Tribal governments, and state and federal agencies.

Should the project move forward, it will need nearly 40 local, state, and federal authorizations, approvals, and permits.

EIS analysis integrates climate change

Climate change will drive more frequent floods, higher flood levels, and would put native fish runs at higher risk in the future, absent significant restoration efforts. We integrated climate change in our analysis of future conditions where the proposed flood retention dam would operate.

Project alternatives analyzed

In addition to the proposed project, the EIS also analyzed what is known as a "no action" alternative. This analysis examines what would happen if the flood retention facility is not built or no improvements are made to the airport levee. The study also analyzed an alternative based on localized and nonstructural actions that could help retain floodwaters and reduce flood-related damage.

Federal EIS

The U.S. Army Corps of Engineers is conducting a separate but synchronized federal review of the district's proposal under the National Environmental Policy Act.

Summary available of state EIS scoping

Scoping is the first step in the state and federal environmental review process. From Sept. 28 through Oct. 29, 2018, we and the Corps of Engineers held a joint SEPA-NEPA EIS scoping period—including two public hearings—to receive input regarding the scope of the state EIS. The SEPA EIS Scoping Summary Report provides a summary of scoping comments and outreach.

SEPA findings, administrative process questions