Click for PEIS Comment Summary Report

🚨

Click for PEIS Comment Summary Report 🚨

Protecting the Lower Green River Corridor

The King County Flood Control District (District) protects people, property, and communities from the harmful impacts of floods. Without additional measures to manage floods, large areas of the Lower Green River Corridor (corridor) are at risk of substantial inundation during an 18,800 cubic-feet-per-second (cfs) flood. The District wants to make sure the corridor is a safe place to live, fish, work, farm, and play for generations to come.

**Interactive Flood Map**

This **interactive flood map** was developed to help users see how much flooding would occur in the corridor during a 500-year flood event. Review this how-to guide before using the map.
The corridor includes approximately 21 miles of the Green River and its floodplains, including portions of Auburn, Kent, Renton, SeaTac, Tukwila, and unincorporated King County. Flooding puts at risk approximately 14,600 housing units, 42,200 jobs, warehouses, farms, parks, and natural areas that sustain threatened salmon.

Flood events are characterized in terms of their chance of occurring each year. Two common characterizations are 100-year and 500-year flood events:
A 100-year flood event has a one percent chance of occurring each year or a 26 percent chance of occurring at least once in 30 years. Local floodplain regulations are typically based on 100-year flood event.
- A 500-year flood event has a 0.2 percent chance of occurring each year or approximately a six percent chance of occurring at least once in 30 years.
- A flood event can also be defined as the volume and rate of water flowing through the river. For the Lower Green River, the median peak flow for a 500-year flood equates to 18,800 cfs of water, and a 100-year event equates to 12,000 cfs of water.

Protection Takes Planning

The District is considering developing a Lower Green River Corridor Flood Hazard Management Plan that would guide future investments to reduce flood risks over the next 30-50 years. To inform the plan, a draft programmatic environmental impact statement (PEIS) was prepared. The study analyzes three different approaches (called alternatives) to reducing flood risks in the Lower Green River Corridor while providing other important benefits:

Learn more About the DRAFT PEIS

(please click here for corrections to Draft PEIS)

Input is Important

Public input will help shape flood protection planning on the Lower Green River.

The District held a public comment period from March 20, 2023 to June 20, 2023. Tribes, jurisdictions, agencies, stakeholders, and members of the public were invited to comment on the draft PEIS and three alternative approaches for flood hazard management.

The District will respond to all comments in the final PEIS. A final PEIS could be issued by mid-2024 and would identify a preferred alternative. The Board could direct preparation of a Flood Hazard Management Plan after the final PEIS is issued.