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 before it reaches 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 are 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.

To provide a comfortable and accessible walking connection to Northgate Elementary School, SDOT is planning to construct a new 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.

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

What's Happening Now?

We have completed our 90% design phase for each of the project sites. We are now presenting updated street and drainage improvements to the community, answering questions, and gathering community feedback as we finalize the project design.  Please visit our 90% design online open house to:

  • Learn about natural drainage systems and the benefits to your community
  • Learn about the project background and timeline
  • Review the 90% designs for each project site

Community Benefits

Natural drainage systems will reduce pollution in Thornton Creek and Lake Washington and help manage stormwater. This project will also provide other community benefits such as  reduced street flooding, improved traffic calming, new trees, and landscaping.

Community Engagement

During the project’s design, we have engaged the community to gather input, answer questions, and incorporate feedback into the project design. Please sign up for our email list to stay informed of project updates and opportunities to engage with the project.

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


  • Finalize design
  • Advertise and award construction contract

Late-2022/Early 2023

  • Construction is tentatively scheduled to begin late 2022/early 2023
  • SPU will provide information about start date, duration, and anticipated impacts prior to beginning work 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.