About the Final PEIS

A programmatic environmental impact statement (PEIS) takes a comprehensive approach to analyzing the impacts, benefits, and costs of planning-level decisions that affect a large area. It provides a road map that guides how management plans and individual projects are designed and implemented in the future.

The Lower Green River Corridor final PEIS evaluates three different approaches (called alternatives) to reducing flood risks. Key findings from the final PEIS include:

  • All three alternatives substantially reduce flooding in most areas during a major flood;

  • There is broad support for flood risk management while achieving multibenefits, although at a higher cost and with more impacts on the land uses immediately adjacent to the Lower Green River; and

  • Tribal interests and treaty rights in the Lower Green River Corridor are an important consideration.

Now that the final PEIS has been issued, the District Board of Supervisors will identify next steps that could include directing the development of a Lower Green River Corridor Flood Hazard Management Plan.

Printed copies of the final PEIS and appendices are available at city halls, libraries, and community centers in Auburn, Kent, SeaTac, Tukwila, and Renton, and additional hard copies are available upon request by calling (206) 349-6361 or emailing: lwrgreen_printrequest@parametrix.com.

Alternatives

Three alternatives, including their possible impacts on the environment and their potential to achieve additional benefits, are analyzed in the final PEIS. Each alternative takes a different approach to managing flood risk, and each describes potential impacts and ways to reduce or eliminate them.

Click each box below to read the three alternative descriptions

Impacts and Benefits

All three alternatives would substantially reduce flooding in most areas during a major flood. Because flooding is a natural process that cannot be eliminated, flooding would continue, although it would be lessened. With the proposed alternatives, the number of residents and jobs potentially impacted could be reduced by at least 50 percent – the percentage of disadvantaged populations at risk could be reduced even more substantially.

All three alternatives require some property acquisition to improve existing flood facilities. Alternative 3 would intentionally provide more benefits than Alternative 1 or 2 by increasing floodplains, habitat, and open space. Because of this, Alternative 3 would acquire more property and would have more impacts on adjacent land uses.

The key environmental issues addressed in the final PEIS involve potential impacts from new or improved flood management facilities, providing opportunities to improve habitat for salmon, understanding impacts on various land uses, and protecting agricultural areas.

  • In addition to the three alternatives, the District has modeled a No Build Scenario, showing how the Lower Green River Corridor could be affected by flooding without implementing additional flood risk reduction measures. It is shown to help demonstrate what is at risk.

    Under this scenario, the District would maintain existing facilities to meet current requirements. No additional flood hazard management actions or improvements would be made. Work would continue on facilities currently under construction, but nothing else would be built and existing levees and floodwalls would not be improved.

Timeline

The final PEIS was issued on April 30, 2024. The District Board of Supervisors will identify next steps that could include directing the development of a Lower Green River Corridor Flood Hazard Management Plan.

Under any alternative, future individual projects would have project-specific environmental reviews as part of the design and permitting process.