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Seattle Pedestrian Master Plan
Thornton Creek Water Quality Channel
Seattle, WA
By working together, an engaged City and Northgate community helped shape the innovative project called the Thornton Creek Water Quality Channel. The result is a 2.7-acre public amenity and water quality facility, located just south of Northgate Mall in Seattle, adjacent to the I-5 corridor. As landscape architects and civil engineers, SvR designed the channel to treat runoff generated from 680 acres during small, high-frequency storms.
The channel provides habitat and functions as a bioswale, mimicking the structure of a natural stream bed and riparian zone with a central base flow channel and densely vegetated banks. The site provides water quality treatment and accommodates seasonal high flows. Channel highlights include:
- A series of cascading weirs, pools, boulders, and large woody debris
- Large-scale natural drainage treatment in a public setting
- Integration into mixed-use development by providing public open space
- Targeting up to 91% average annual runoff for water quality treatment
- Plant mix includes a blend of 18-inch to 36-inch tall reeds, rushes, sedges, and shrubs to provide year-round flow resistance and contribute to urban habitat and biodiversity
The water for treatment comes from Interstate 5, Washington’s busiest freeway, as well as the North Seattle Community College campus, Seattle’s north end public transit hub, nearby arterial streets, and the Northgate Mall.
Resource: Operations and Maintenance Manual for Thornton Creek Water Quality Channel (5.5 Mb PDF)
