Auburn Narrows Floodplain Reconnection Project

Project overview

This project will make the Green River within Auburn Narrows Natural Area more closely resemble natural river and floodplain habitat. Three new inlet channels will connect floodplain wetlands and an existing side channel to the Green River mainstem. Then, water from the Green River will spread out and connect to more areas for fish habitat. In addition, a buried rock revetment beneath the site access road forming the western edge of the largest wetland will be removed. This will let natural river processes occur without impediment. Large wood structures will be placed throughout the Green River and the newly constructed channels, which will create more variety in hydraulic conditions and provide better habitat for fish. Throughout the floodplain, habitat features such as snags and brush piles will be placed to provide more natural conditions for wildlife. The site will be replanted with native vegetation to provide shade to the Green River.

The challenge

The middle Green River provides spawning and rearing habitat for eight species of salmonids. These include Chinook, steelhead, coastal cutthroat trout, coho, pink, and sockeye. Salmonid habitats at the project site include both mainstem and side channel habitats. Little instream large woody material is found in this straightened section of the river, but a large logjam is present downstream.

At the project site, the river shows evidence of impacts from human influence. Those impacts include flow control, levee construction, railroad construction, road, construction and restoration. The first major action to impact geomorphology at the site was the construction of the Burlington Northern Rail Line. Other early projects include the construction of bridge crossings for Auburn-Lake Holm Road. For over 100 years, these crossings have constrained the floodplain to roughly one third of its historic width. The crossings have also held the channel along the north valley wall. The Highway 18 bridge affects the channel for approximately 1500 feet upstream and downstream.

Recreational uses, timing, intensity

The Auburn Narrows Natural Area is mostly used for informal recreation. The riverbanks are popular with anglers during the fall. The river itself is closed to boating in this reach due to the presence of a large log jam downstream at RM 32.5. Green River Community College and the Washington Department of Natural Resources own the right bank of the Green River in this reach. There is an access trail from the college to the right bank.

Project timeline

Alternative Analysis – Complete
Preliminary Design – Complete
Final Design and Permitting – 2026-2027
Construction Target – Summer 2028

Existing funders

• Washington State Recreation and Conservation Office
• Washington State Salmon Recovery Funding Board
• King County Cooperative Watershed Management Grant (King County Flood Control District)
• King County Surface Water Management Fees
• King County Parks Levy Open Space River Corridor Grant

Project documents

For reports, engineering documents, or other additional project information, please contact the project manager, Alex Hallenius, at alex.hallenius@kingcounty.gov.