Green River Basin

Green River Basin Map
Highlighted Area Above: Green River Basin

The King County Flood Control District invests resources in the Green River Basin to protect public safety, the regional economy, and critical infrastructure. This basin includes the Green River which flows northwest about 93 miles from its headwaters in the Cascades to its outlet in Elliott Bay via the Duwamish River. Major tributaries include Soos, Newaukum and Mill Creeks, and the Black River. The Green River flows through several cities, including Auburn, Kent, Renton, Tukwila, and Seattle.

Green River

Major flood control features along the Green River include Howard Hanson Dam, which is in the upper Green River sub-watershed, and the levee system that lines almost all riverbanks of the lower Green and Duwamish Rivers. Howard Hanson Dam and the levee system combine to reduce flooding in the lower river to a fraction of its historical magnitudes.

With major historical flooding largely controlled by a dam and levees, commercial and industrial land use in the largely flat and generally accessible lower Green and Duwamish River valleys has proliferated in what were formerly rural and agricultural communities. Agriculture endures in some parts of the lower Green River around the Cities of Auburn and Kent, and agriculture and rural residential development are the primary land uses in the middle Green River.

Residents, businesses and farms below the Howard Hanson Dam in the Green River Valley prepared for a higher risk of flooding due to damage that occurred to an earthen bank next to the dam after record high water in January 2009. While temporary improvements made by the U.S. Army Corps of Engineers successfully lowered the risk of flooding in the Green River Valley, the dam continued to operate at a limited capacity during the 2010/2011 flood season, creating a heightened risk of flooding in the lower valley.

In March 2011, the US Army Corps of Engineers announced the return of full operational capacity at Howard Hanson Dam. However, this functioning dam and levee system does not eliminate all risks of flooding. The dam was formerly thought to control water up to a 500-year flood event. Now, the US Army Corps of Engineers recognizes the dam capacity can control water up to a 140-year flood event.

Investments in the Basin

Current Basin Projects 

Black River Pump Station Improvements
This project makes a number of improvement to the Black River Pump Station to ensure that the station continues to provide flood risk reduction benefits to this economically vibrant area. Improvements will also ensure the operation is safe, reliable, efficient, and avoids or minimizes impacts to the environment. Improvements include: seismic and structural, fish passage, mechanical renovations, and high-use engine replacement.

Galli’s-Dykstra Levee Repair Project
This project completes a phase 1 repair per a request from the City of Auburn by elevating a 3500 feet levee reach to meet FEMA levee certification requirements.

Green River System-Wide Improvement Framework
The Green River System-Wide Improvement Framework outlines a prioritized strategy to address levee deficiencies in order to optimize flood risk reduction, address system-wide issues and maintain eligibility for the 17 miles of levees currently enrolled in the Corps of Engineer’s Levee Rehabilitation and Inspection Program under Public Law 84-99.

Lower Russell Levee Setback Project
This project will remove and replace the existing flood containment system of levee and revetments along the right (east) bank of the Green River between river mile 17.85 (S 212th St) and river mile 19.25 (S 228th Street/Veterans Drive) in the City of Kent in order to construct a flood prevention system that balances policy directives regarding flood risk reduction, habitat restoration, and recreational use.

Lower Green River Corridor Plan

The District is preparing a Lower Green River Corridor Flood Hazard Management Plan for approximately 21 river miles of the Lower Green River. The goal of the Plan is to provide a long-term approach to reduce flood risk and improve fish habitat while supporting the economic prosperity of the region. The District is also preparing a Programmatic Environmental Impact Statement (PEIS), which will analyze alternatives for flood protection that could be included in the Plan.

Please visit for more information on the proposed alternatives for the Lower Green River Corridor Flood Hazard Management Plan.

Completed Basin Projects

  • Reddington Levee Setback and Extension
  • Teufel Mitigation