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Delridge Basin

  • Anticipated future look of the Delridge Natural Drainage Systems. June 2012 - Ballard Natural Drainage System Project.
  • Anticipated future look of the Delridge Natural Drainage Systems. November 2011 - Ballard Natural Drainage System Project.
  • Anticipated future look of the Delridge Natural Drainage Systems. December 2010 - Ballard Natural Drainage System Project.

Natural drainage prevents polluted runoff from harming the fish and other wildlife that call Longfellow Creek home.


Seattle Public Utilities (SPU) is responsible for managing stormwater throughout the city. We use a three-pronged approach to prevent sewage overflows:

  • Fix It First—retrofit existing storage tanks to control up to 100 percent of the total volume.
  • Keep the Stormwater Out—add Green Stormwater Infrastructure (GSI), such as natural drainage, to protect Longfellow Creek from polluted runoff.
  • Store What’s Left—if the retrofit and GSI projects are as successful as expected, a new storage tank would not be needed.

We are currently working on two projects in the Delridge neighborhood.

Delridge Natural Drainage System Project

SPU is planning to construct a natural drainage systems project along several blocks of 17th Ave SW in the South Delridge neighborhood. These natural drainage systems will be located within the existing planting strips and along the Seattle Department of Transportation (SDOT) proposed neighborhood greenway. By co-locating natural drainage systems projects along neighborhood greenways, the City is creating streets that manage stormwater well and provide safe and comfortable features for people of varying ages and abilities to walk, ride bikes, and get around more safely.

The project is currently in design with construction anticipated for mid-2015.

Connect With Us

Don Anderson, Project Manager
(206) 233-1086

Delridge Basin Sewer System Improvement Project

We will replace the existing control systems at two existing storage tanks in the Delridge area. The tanks — one at the corner of Delridge and Orchard (CSO 2 fact sheet (pdf)) and the other at the corner of 22nd and Henderson (CSO 3 fact sheet (pdf)) — were built in the 1980s and do not operate as designed. Fixing these facilities will:

  • improve the ability to monitor and control the amount of flow allowed into the sewer system
  • reduce the frequency and volumes of sewage overflows into Longfellow Creek
  • reduce maintenance costs

Retrofit Project Schedule

Design and pre-construction planning is happening through May 2014. Construction is expected to begin in mid-2014 and take approximately seven months to complete.

Environmental Analysis Documents

The Washington State Environmental Policy Act (SEPA) Checklist and Determination of Non-Significance were published on September 16, 2013. These documents detail the regulatory compliance efforts for the retrofit project.

Connect With Us

Tara Wong-Esteban, Project Manager
(206) 684-5903