Seattle Public Utilities (SPU) is advancing work on the Holden Natural Drainage Systems (NDS) Project along SW Holden Street between 16th Avenue SW and 17th Avenue SW. The infrastructure initiative installs roadside rain gardens, also known as bioretention cells, to collect and clean polluted stormwater before it empties into Longfellow Creek and Puget Sound.

Each year, more than 12 million pounds of pollution are carried into local water bodies via stormwater runoff from neighborhood roofs, roadways, and parking areas. Left untreated, these pollutants pose significant risks to salmon, wildlife, and aquatic ecosystems. Community members interested in the environmental dynamics of the watershed can watch a Nature Conservancy video on Longfellow Creek.

The bioretention cells will be situated in the public right-of-way between the street edge and property line. These shallow depressions are engineered with deep-rooted native vegetation and specialized soil mix to filter urban runoff. Beyond water quality improvements, the project converts temporary painted curb bulbs into permanent concrete curb bulbs at 17th Avenue SW and SW Holden Street, while adding ADA accessibility ramps and revised landscape plantings.

In response to community feedback gathered during design phases, SPU incorporated key infrastructure adjustments into the final project design:

• Localized Flooding Control: Crews will construct a new underground water quality treatment facility and drainage infrastructure at the north side of 17th Avenue SW to mitigate recurring intersection flooding.
• Emergency Response Prioritization: Following coordination with Seattle Fire Department Station 11, an existing speed cushion on SW Holden Street will be removed to clear emergency transit routes.
• Affordable Housing Coordination: The project alignment is coordinated with the nearby former Dumar Substation site development, where the city selected a community partner for homeownership projects as detailed in the City of Seattle Office of Housing announcement.
• Urban Canopy Mitigation: Installing the underground treatment facility requires removing two trees; SPU will replant one tree on site and fund the Seattle Department of Transportation (SDOT) to plant five additional trees in nearby areas.

Major construction is expected to span eight to ten months. Work will generally occur Monday through Friday from 7 AM to 5 PM, with potential evening or weekend work if required. Traffic control plans maintain open westbound lanes on SW Holden Street, alongside temporary pedestrian detours, temporary parking restrictions, and a temporary relocation of the Metro bus stop at 16th Avenue SW. Property and driveway access will be preserved throughout active operations.

Following construction, SPU retains full operational responsibility for maintaining the bioretention cells and managing plant health. Residents can review earlier planning stages through the Mid Design Narrated Presentation or examine completed engineering layouts via the Final Design Narrated Presentation. Project updates are available by registering on the project email updates page, or by contacting Senior Project Manager Wan-Yee Kuo directly at Wan-Yee.Kuo@seattle.gov.