To reduce flood damage in the Chehalis River basin, the Chehalis River Basin Flood Control Zone District is proposing to construct a new flood retention facility and temporary reservoir near the Lewis County town of Pe Ell, and make levee improvements around the Chehalis-Centralia Airport.
We and the U.S. Army Corps of Engineers (USACE) have determined the proposal could have significant adverse environmental impacts and will require formal studies through separate state and federal Environmental Impact Statement (EIS) processes.
See our Determination of Significance for the project proposal
Our role in reviewing the District's proposed flood damage reduction project will be to:
- Conduct the state environmental review process under the State Environmental Policy Act (SEPA).
- Offer public engagement opportunities.
- Should the project proceed after the environmental review is complete, issue environmental permits consistent with state and federal laws and rule.
USACE, the lead federal environmental agency, will conduct a separate review under the National Environmental Policy Act. We and the USACE will each develop a separate Environmental Impact Statement (EIS). No permit decisions can happen until after the state and federal environmental reviews are complete.
Scoping is the first step in the environmental review process. We and the USACE held a 31-day joint SEPA and NEPA EIS scoping period from Sept. 28 through Oct. 29, 2018—including conducting two public scoping meetings. Although the EIS scoping period now is closed, the public input we received regarding the scope of the EIS will help us identify:
- A reasonable range of alternatives, including alternative sites and project designs, based on the purpose of each project.
- Potentially affected natural, cultural, or community resources and the extent of study and analysis needed to understand different potential impacts.
- Likely significant, unavoidable adverse environmental impacts.
- Measures to avoid, minimize, and offset any adverse effects.
We and the USACE received comments from citizens, local and tribal governments, state and federal agencies, and organizations. These comments will be summarized, our agencies will issue separate SEPA and NEPA scoping reports later in 2018. The scoping reports will summarize the input we received about what should be included in each draft EIS. The meeting materials presented at the EIS scoping meetings are available at the project EIS website.
Proposed project details
The EIS scoping period will help us and the USACE decide what resources and impacts to analyze for the proposed Chehalis River Basin Flood Damage Reduction Project that includes:
Open the map to see location details
- Building a new flood retention facility and temporary reservoir near the town of Pe Ell in Lewis County. The proposed structure would have an expandable foundation.
- Making levee improvements around the Chehalis-Centralia Airport.
for the proposed project.
Proposed flood retention facility would only operate during major floods
The Chehalis River Basin Flood Control Zone District's proposed project involves constructing a new floodwater retention facility and temporary reservoir on the Chehalis River near the town of Pe Ell in Lewis County.
During a major flood, the proposed facility is designed to substantially reduce flood damages in parts of the Chehalis River basin by storing up to 65,000 acre feet of water in a temporary reservoir. When it is safe to do so, retained floodwater water would be released slowly back to the river over a period of time. Most of the time, however, the Chehalis River would flow through the structure's low-level outlet works at the river's normal rate of flow and volume — allowing fish to pass upstream and downstream.
The flood retention facility is not designed to protect communities from all flooding, nor would it stop regular annual flooding from the Chehalis River.
Proposed flood retention facility details
The top of the proposed flood retention structure would be 1,220 feet long and up 254 feet high — including three to five feet of freeboard for safety and a 210 foot-wide emergency spillway. The structure would be built on a foundation that could be expanded should a permanent reservoir and additional water retention capability be needed in the future. However, any structure expansion or major operational changes would require new environmental reviews and permits.
To construct the retention facility and reservoir, trees and vegetation at the site would need to be removed. A new power line would be constructed to operate the dam’s pumps, gates, instruments, and other controls. The project also would include developing a quarry, material storage and processing sites, and setting aside areas for offices and storing equipment.
Proposed Chehalis-Centralia Airport levee improvements
To protect the Chehalis-Centralia Airport, local businesses, and area transportation from damages from 100-year floods, the district also proposes raising the existing airport levee and part of Airport Road. The project would:
- Add four to seven feet to the height of the existing 9,500 foot-long levee by adding earthen materials or flood walls.
- Raise about 1,700 feet of Airport Road along the southern extent of the airport.
- Potentially change the northwest corner of the levee to avoid interfering with the runway glide path.
- Include utility infrastructure and other transportation improvements.
Now that scoping is complete, the next environmental review step will be developing a draft and then a final EIS for the project proposal. The USACE will follow similar steps. The EIS process provides many opportunities for public involvement, guidance, and comments. Each agency will summarize the comments received during scoping into a summary document, and make the summaries available on the project website. No permit decisions can be made until after the final EIS is issued.