News Feature | October 19, 2016

Seattle Builds First-Of-Its-Kind Stormwater System

Sara Jerome

By Sara Jerome,

Seattle Public Utilities (SPU) is turning to a natural solution to manage its stormwater challenges, carving out space between sidewalks and curbs to create tiny marshlands within its urban landscaping.

“This voluntary retrofit of a storm system in a dense urban setting is the first of its kind in the United States,” the Daily Journal of Commerce reported in an editorial by a project backer.

The project, dubbed "the swale on Yale," has placed marshy tracts known as “biofiltration swales” along the blocks near Yale Avenue, according to SPU. The utility is working with local businesses to get the new stormwater treatment systems into its landscape.

“The project is the biggest piece of Seattle’s effort to cut back on one of the most pernicious clashes between the Emerald City and its natural surroundings: the stormwater runoff that pours into Puget Sound, dumping loads of toxic chemicals nasty enough to kill salmon and other aquatic life,” Crosscut reported.

When the project is complete, four city blocks will have stormwater treatment swales helping purify runoff before it pours into Lake Union. Backers say the approach will reduce pollution in the lake. In fact, the utility says the project will treat an average of 190 million gallons of stormwater annually.

“It does this by diverting the stormwater into a series of extra-wide planting areas between the sidewalk and the roadway. These naturalistic, biofiltration ‘swales’ are designed to slow the stormwater flow and remove pollutants before they reach the lake,” Crosscut reported.

The marshy landscaping is aesthetically pleasing, but this project contains more than the eye can see. It includes a diversion vault, which diverts the stormwater underground into the biofiltration swales, a swirl concentrator, also stored underground, which will spin the stormwater to remove large solids into a sump, and a new storm drain.

“Slowing the stormwater flow by diverting it into swales allows sediments and pollutants to settle out before the water is discharged into Lake Union. Each swale will be approximately 270-feet long by approximately 10.5, 11.5 or 16.5-feet wide,” the utility explained.

Other key ingredients: dirt and plants.

“Soils and plants actually do a really fantastic, inexpensive job of treating and filtering all those pollutants,” says Jessie Israel, Director of Puget Sound Conservation at The Nature Conservancy, per Crosscut. “It’s like the newest oldest technology.”

The project was funded and created through a public-private partnership between Seattle Public Utilities and Vulcan Real Estate, according to the Daily Journal of Commerce.

For similar stories visit Water Online’s Stormwater Management Solutions Center.