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Thornton Creek Water Quality Channel

The Thornton Creek Water Quality Facility became fully operational in September 2009.

The Thornton Creek Water Quality Channel provides multiple environmental benefits in a highly urbanized environment. The Facility receives and treats runoff from 680 acres, most of which was formerly untreated before entering the South Fork of Thornton Creek and flowing to Lake Washington. In addition, the Facility design effectively uses limited space to achieve multiple community goals by integrating public open space and a highly technical water quality facility. It has catalyzed the Northgate neighborhood’s emergence as a growing urban center for the City of Seattle. View the final report (pdf).

The Thornton Creek Water Quality Channel project uses natural drainage system technology – drainage that mimics the way nature works - to clean the water, slow it down and let water flow through the channel year-round. The design includes native landscaping and pedestrian pathways that provide access throughout the site with connections to the Lorig mixed-use development, ERA Care Development, the King County Transit Center, the Northgate Mall, the new Library and Community Center just up 5th Avenue NE, NE 100th Street and 3rd Avenue NE.

Located at the headwaters of the South Branch of Thornton Creek, this site offers the last available opportunity to improve the quality of stormwater runoff before it reaches the creek. The channel design will divert stormwater from the drainage pipe under the site to a series of surface swales (or small ponds) landscaped with special soils and native plants. These swales slow down the water, allow it to seep into the soil, and remove pollution before the water reaches the creek.

The channel will have water flowing in dry weather, as well as clean stormwater from the frequent storms. The existing storm drain pipe will stay in place to carry high storm flows when the channel cannot handle all the stormwater volume.

Plan view

Thornton Creek Water Quality Channel Project plan showing connections to pedestrian pathways and the rest of the mixed-use development.

Plan view