Delridge Natural Drainage System (NDS) Project

Photo of plantings in the South Delridge neighborhood.
Natural drainage system cells and plantings in the South Delridge neighborhood.

Project Description

The Delridge natural system project reconstructed several blocks of roadway in the South Delridge neighborhood to include natural drainage systems and pedestrian improvements. Delridge is a neighborhood with a combined sewer system where the sewage and stormwater normally flow in one pipeline. When it rains, the volume of stormwater can exceed the capacity of the system, sometimes leading to sewage overflows to Longfellow Creek. These overflows not only spill sewage into our waterways, they also spill polluted stormwater runoff that flows off rooftops, streets, and other hard surfaces. The natural drainage system process slows and filters polluted runoff every time it rains. Natural drainage systems can slow and reduce polluted runoff by capturing it and cleaning it before it harms our waterways.


The project added natural drainage system cells along 17th Avenue Southwest between Southwest Henderson Street and Southwest Kenyon Street.

Project Results

By placing natural drainage systems along the best walking and bicycle routes, the project:

  • Protects our waterways from polluted stormwater runoff, which helps keep families and marine life healthy
  • Provides neighborhood improvements such as pedestrian and bicycle safety
  • Reduces demand on existing pipes and sewage treatment facilities
  • Reduces energy and operating costs because stormwater will not need to be pumped to the treatment plant


Construction was completed in winter 2016.

Public Utilities

Andrew Lee, General Manager and CEO
Address: 700 5th Avenue, Suite 4900, Seattle, WA, 98104
Mailing Address: PO Box 34018, Seattle, WA, 98124-5177
Phone: (206) 684-3000

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Seattle Public Utilities (SPU) is comprised of three major direct-service providing utilities: the Water Utility, the Drainage and Wastewater Utility, and the Solid Waste Utility.