Swale on Yale

This unique green stormwater infrastructure project was designed to treat over 400 acres of stormwater runoff (roughly 190 million gallons per year) from the Capitol Hill neighborhood of Seattle prior to discharging into Lake Union. The multi-phase project is constructed and partially operational, with full operation anticipated in 2020. When complete, the system will consist of four biofiltration swales that are designed to remove sediment and pollutants from stormwater diverted from an existing 72-inch storm drain main. Stormwater runoff from the basin previously directly discharged to Lake Union without treatment. Each swale extends the length of one full block and has been constructed as part of private developments adjacent to the swales. A major component of the project provides a naturalistic water quality treatment system in an urban setting, while creating an amenity for the adjacent developments and the neighborhood as a whole. To accommodate the swales, the design required major street revisions, construction of a 12-inch water main, over 2,000 linear feet of stormwater conveyance piping, relocation of a gas main, and undergrounding of the overhead power, telephone, and cable in the area.

KPFF was hired by Seattle Public Utilities to take a concept design for the treatment system and develop the concepts into cost-efficient and constructible Street Improvement Permit (SIP) plans. KPFF met repeatedly with SDOT to ensure the format of the information being presented was acceptable and to work through a variety of design issues related to the street and pedestrian impacts. The project ran a parallel permitting timeline with the adjacent private development, whom KPFF also prepared SIP plans for. Through extensive experience in developing SIP plans, KPFF was able to approach the complex public-private project and use project phasing to streamline the design and construction of the conveyance system and the surrounding street improvements.

The project has been awarded an “In the Works Design Excellence Award” by the Seattle Design Commission. The project has been exemplary in terms of agency and consultant teams working together