Thornton Creek Water Quality Channel
Sunday June 21st 2009, 9:13 pm
Filed under: Water

Thornton Creek Water Quality Channel
image via Seattle Times

The recently opened Thornton Creek Water Quality Channel sits on 2.7 acres as part of Thornton Place, a transit-oriented, mixed-used development just south of Northgate Mall in Seattle and adjacent to the I-5 corridor. What was once a parking lot for overflow mall traffic, the Channel now acts as both a neighborhood amenity with pedestrian pathways and overlooks as well as a way to slow and treat runnoff from the surrounding 680 acres, while also providing much-needed habitat.

Thornton Place, February 2009
February 2009, image via Seattle Public Utilities

According to Seatle Public Utilities, the Channel works by diverting “stormwater from the drainage pipe under the site to a series of surface scales (or small ponds) landscaped with special soils and native plants. These swales slow down the water, allowing it to seep into the soil, and remove pollution before the water reaches the creek.”

Thornton Place - plan
plan, image via Seattle Public Utilities

As landscape architects and civil engineers for the Channel project, SvR Design out of Seattle worked closely with Seattle Public Utilities and the Northgate community for the design and construction of this new amenity that is targeting up to 91% average annual runnoff for water quality treatment. From their website:

“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. 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. 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.”

Thornton Creek Water Quality Channel

Thornton Creek Water Quality Channel
images via justsmartdesign

The project also acts as a model for the Northgate area and other neighborhoods lying in the watershed of a stream many people didn’t even realize existed due to years of development crowding the stream and forcing into it’s current narrow state which has caused higher water flow and more bank erosion. And with such a large amount of paved surfaces surrounding the water body, there was little area for the rainwater to seep into the ground naturally which meant contaminants would flow directly into the stream. But now, this is a first step towards fixing the problem and a sollution that sits well with many supporters for Thornton Creek’s restoration.

While the project is now open to the public, it will take another year for the vegetation to get well-established and grow into its full glory. But until then, people can enjoy the trails, the water and the sound of dragonflies buzzing in the air, a sound once uncommon to this area.

Thornton Creek Water Quality Channel

Thornton Creek Water Quality Channel
images via justsmartdesign


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[...] shopping mall and parking garage. Thanks to activists — and $6.85 million in funding — it is now a transit-oriented mixed-use development, featuring a bioswale capable of treating stormwater through natural processes before releasing it [...]

Pingback by Streetsblog San Francisco » What can SF Learn from Other Cities’ Urban Water Projects? 04.16.10 @ 1:35 pm



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