South Thornton Natural Drainage System (NDS) Project

Photo of a street with natural drainage system.
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 the stormwater enters our waterways.

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

Check out the Project FAQ for more information.

Location

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.

Sites:

Note, SPU and SDOT are also balancing on-street parking and pedestrian safety priorities while designing the sites.

*To provide a comfortable and accessible walking connection to Northgate Elementary School, Seattle Department of Transportation (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 is expected to be constructed as soon as mid-2021. SPU's project team is also in coordination with the Northgate Elementary School Replacement Project.

What's Happening Now?

We completed our 30% design for each of the project sites and are continuing in the design phase. We will provide updates when we reach our 60% design milestone. In the meantime, please visit our online open house to:

  • Learn about natural drainage systems and benefits to your community
  • Review the early designs for each project site
  • Get info on the project schedule 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 30% 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 60% 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.

Schedule

2017 - 2018

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

2019 - 2021

  • Onboard design consultant
  • Design development for selected sites
  • Design phase outreach throughout 2021

2022

  • Anticipated construction

2023

  • Project closeout

 

Background

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

30% design boards