South Thornton Natural Drainage System (NDS) Project

Photo of a street with natural drainage system.
Example of a natural drainage system project a few years after installation.

Project Description

Improving Our Communities with Natural Drainage Systems
Seattle Public Utilities (SPU) will construct natural drainage systems (NDS) at 4 sites in the south Thornton Creek basin. NDS are built in the roadway shoulder (the space between the street edge and property line) and are filled with deep-rooted plants and spongy soils that temporarily hold and clean polluted stormwater from streets. These features capture and clean pollutants before they can reach Thornton Creek.

Natural drainage systems can offer multiple benefits to local neighborhoods and ecosystems, including:

  • Increased landscaping
  • Lower risk of flooding
  • Creation of habitat along streets
  • Healthier creek ecosystems
  • Traffic calming
  • More street trees
  • Pedestrian safety improvements

Check out the Project FAQ for more information.


Seattle Public Utilities (SPU) will construct natural drainage systems (NDS) at 4 sites in the south Thornton Creek basin. Selected sites can be viewed on this Thornton Creek map.


We're partnering with the Seattle Department of Transportation (SDOT) to incorporate walkways into some of the streets that do not currently have formalized sidewalks, which aligns with community requests to install pedestrian improvements as a part of this project.

We are also partnering with the City's Office of Arts and Culture for this project and will incorporate an art installation in the natural drainage system near Wedgwood Elementary School.

*To provide a comfortable and accessible walking connection to Northgate Elementary School, SDOT is planning to construct a new asphalt sidewalk on the north side of N 117th St between Meridian Ave N and 1st Ave NE. This project will be constructed in coordination with the Natural Drainage Systems on N 117th St and the redevelopment of Northgate Elementary. For more information about this project, please contact or (206) 485-8781.

What's Happening Now?

We completed our 60% design for each of the project sites and are continuing in the design phase. We will provide updates when we reach our late design milestone. In the meantime, please visit our online open house to:

  • Learn about natural drainage systems and benefits to your community
  • Review the 60% designs for each project site
  • Learn about the project background and timeline

Community Benefits

This project will reduce pollution in Thornton Creek and Lake Washington and help manage stormwater by constructing natural drainage systems in your neighborhood. It will also provide other community benefits, which include reduction of street flooding, traffic calming, trees, and added landscaping.

The project will also help the City of Seattle achieve its goal of managing 700 million gallons of stormwater runoff using green infrastructure.

Community Engagement

We completed our 60% design for each of the project sites and are continuing in the design phase. We will provide updates to the community when we reach our late design milestone. Please visit our online open house to learn more about the project.

If you're interested in learning more and finding out about upcoming community engagement events, please sign up to receive project email updates.

Public Art at Wedgwood Site

Seattle Public Utilities, in coordination with the City of Seattle Office of Arts & Culture (ARTS) is working to create an art installation for this project.

Proposed artwork to be installed in the NDS near Wedgewood Elementary School.

Artist, Leo Berk, developed an artwork to bring awareness to the ecological benefits of the natural drainage system that SPU is installing in Wedgwood. His design uses the visual metaphor of an oversized kitchen strainer perforated with pattern that illustrates the mechanism of this bioretention system. The pattern specifically highlights how these systems reduce the roadway pollutants that enter Thornton Creek and Lake Washington.

Leo Berk is a Seattle artist who has installed numerous public art projects and exhibited in galleries and museums around the Pacific Northwest. His artworks are fabricated in a wide range of materials with his preferred material being the one he hasn’t used yet.



2017 - 2018

  • Early project planning and site selection
  • Outreach to residents about potential sites

2019 - mid-2022

  • Design development for selected sites
  • Design phase outreach at key project milestones
  • Provide responses to community questions or comments, as requested


  • Finalize design
  • Advertise and award construction contract

Late-2022/Early 2023

  • Construction at one of more of the sites is tentatively scheduled to begin in late-2022/early 2023
  • SPU will provide pre-construction outreach and include information about start date, duration, and anticipated impacts prior to work starting at each of the sites.



Natural drainage systems slow stormwater and filter out pollutants before they can harm our creeks and other waterways. Keeping pollutants out of our water is important for fish, aquatic life, and people.
Building a natural drainage system in Thornton Creek basin is part of the Plan to Protect Seattle's Waterways. SPU used to call these "roadside rain gardens" but now calls them "natural drainage systems" or "NDS".
Why Thornton Creek? Thornton Creek is a salmon-bearing urban creek with degraded water quality. Stormwater picks up pollutants from streets—including oil, heavy metals, and fertilizers—and flows into the creek through ditches or pipes. This project will remove pollutants from the stormwater before it reaches the creek and reduce the quantity of stormwater going into the creek.


Project Documents

Project Overview

Project FAQ

60% design boards