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July 2019

CityLink Seattle

Project Spotlight: Swale on Yale

For many of Seattle Public Utilities’ projects, there’s often more benefit than meets the eye. Such is the case for the Swale on Yale project, a green stormwater infrastructure (GSI) project started in 2012 and now in its second phase.

Bioswales on Yale Ave N
Bioswales on Yale Ave N

At first glance, the project’s garden-like swales, built on the 300 and 400 blocks of Yale Ave N and Pontius Ave in South Lake Union, may just look like decorative, urban planting beds. In reality, they represent a hardworking natural drainage system — one great example of how SPU uses GSI to keep local waterways clean and enhance our natural environment.

What is a swale?

When it rains in Seattle, rain runs off streets, rooftops, parking lots, and other impermeable surfaces, picking up oil, grease, metals, and other pollutants, and carrying them to nearby water bodies.  A swale, or bioswale, is a naturalistic biofiltration system designed to slow stormwater flow and remove pollutants before the stormwater enters our local waters.

Each of the four bioswales in this project are about 270 feet long and 10-16 feet wide. Altogether, these bioswales will greatly reduce the amount of pollution in Lake Union by treating an average of 190 million gallons of stormwater annually flowing down from Capitol Hill.

In addition to the four bioswales, the Swale on Yale project includes:

  • a diversion vault, or large underground tank, constructed under Yale Ave N, between Stewart and John Streets, that diverts stormwater into the biofiltration swales;
  • A swirl concentrator, also under Yale Ave N, which spins the stormwater to create a vortex. When that happens, large solids and pieces of trash separate from the water and routinely cleaned out by SPU crews;
  • and approximately 2,000 feet of new storm drain, built to move untreated stormwater into the diversion vault, then to the swirl concentrator, and then to the biofiltration swales.
Seattle Public Utilities crew cleaning out bioswales
Seattle Public Utilities crew cleaning out bioswales

Come check it out!

Want to see the project up close and personal? Head down to South Lake Union. You’ll find interpretive signage on display to teach people about water quality and the benefits of urban ecosystems like the swales. And keep an eye out for an electric pole in one of the swales, wrapped in decorative material to show the different layers of the swale, such as plants and river rock.

Swale on Yale interpretive sign
Swale on Yale interpretive sign