Seattle Public Utilities Mami Hara, General Manager/CEO

Swale on Yale – Capitol Hill Water Quality

BallardNDS

Phase 1 of the Swale on Yale project was completed in 2013.

What & Why

SPU is working with Cascade neighborhood businesses and property owners to construct a stormwater treatment system on four blocks on Yale Avenue North and Pontius Avenue North. This project will consist of four biofiltration swales, a pre-treatment swirl concentrator, and a diversion structure. The project will greatly improve the quality of stormwater runoff entering South Lake Union.

What’s happening now?

The project team is currently designing the final phase. The design will include biofiltration swales along the 300 blocks of Yale Ave N and Pontius Ave N. Private development construction is scheduled for 2016, followed by swale construction in 2017 and 2018.

Project goals and benefits

By the end of construction, four city blocks will have stormwater treatment swales that remove pollutants before the water enters Lake Union.

This project will treat an average of 190 million gallons of stormwater annually flowing from Capitol Hill into Lake Union, greatly reducing the amount of pollution flowing into the lake. 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.

This project includes:

  • Four biofiltration swales: 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; they will be built along two blocks of Yale Avenue North and Pontius Avenues North.
  • Diversion vault: A large underground tank will be constructed under Yale Avenue North, between Stewart and John Streets, to divert the stormwater into the biofiltration swales.
  • Swirl concentrator: This equipment, also to be installed under Yale Avenue North, will spin the stormwater to create a vortex. When that happens, large solids and trash separate and collect in a sump. The sump will be cleaned regularly by SPU crews.
  • New storm drain: Approximately 2,000 feet of new storm drain will be built to convey untreated stormwater into the diversion vault, swirl concentrator, then the biofiltration swales. The treated stormwater then will go back into the storm drain for discharge into Lake Union.

Connect


Jason Sharpley, project manager
jason.sharpley@seattle.gov
(206) 615-0030

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