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Project overview

Green River stormwater retrofit project area map - smallerThe project would develop best practices to manage stormwater and local drainage improvement techniques to meet future in-stream flow conditions and water quality goals in the Duwamish River Watershed or Water Resource Inventory Area 9 (WRIA 9), an administrative area.  For more information, review the detailed work plan (Acrobat PDF).


The population in this part of the Green River Watershed is projected to grow by a quarter of a million people between year 2000 and 2040.

This would result in:

  1. The conversion of additional land for urban use; and,
  2. The redevelopment of previously developed land for higher density use.

What will the project do?

  • Develop a cost estimating and retrofit prioritization plan
  • Develop tools and methodology that would be the basis for a planning-level evaluation of the most cost-effective combination of:
    • Stormwater Best Management Practices: and,
    • Low Impact Development techniques
  • The cost estimation tool and methodology may then be used as a technique for retrofitting all Puget Sound developed lands

Anticipated outputs and outcomes

Outputs from the implementation of this project would include:

  1. Flow and water quality data throughout the study area.
  2. Computer Modeled flow and water quality conditions in selected study area rivers and streams for idealized fully forested conditions, current conditions, and anticipated 2040 conditions considering population growth and climate change.
  3. Stream flow and associated water quality goals throughout WRIA 9.
  4. The magnitudes and types of stormwater retrofits needed to achieve in-stream flow and water quality goals, including their estimated costs.
  5. Planning-level cost estimate(s) and methodology to implement stormwater retrofit projects in the watershed.
  6. Planning-level cost estimate(s) and methodology to implement stormwater retrofit projects throughout the Puget Sound region.

Science, policy, and public awareness expected outcomes include:

Short term:

  1. Increase awareness of the importance of implementing stormwater retrofit projects to achieve the Puget Sound Partnership’s Action Agenda
  2. Improved coordination between stormwater managers and other interested parties.


  1. A set of monitoring and modeling tools available for future stormwater retrofit evaluations,
  2. Increase understanding and planning for establishing a systematic stormwater retrofit program for the Puget Sound region
  3. Enhanced understanding of the importance of improving stormwater controls during urban redevelopment projects.

Long term:

  1. Implementation of the most cost-effective stormwater retrofits under the auspices of a Puget Sound stormwater retrofit program, and
  2. Improve streamflow and water quality conditions throughout Puget Sound through implementation of stormwater retrofits.


Data collection, analysis & model development Data management timeline - Green River Stormwater Retrofit Planning Project
Model output & analysis Model output timeline - Green River Stormwater Retrofit Planning Project
Report development & delivery Report timeline - Green River Stormwater Retrofit Planning Project
Marketing Marketing timeline - Green River Stormwater Retrofit Planning Project
June 2010
Dec. 2013

Please see project milestones for a more detailed timeline.

Project status

  • The project administrative team has defined the basic team structure, roles, and schedule.
  • Four out five project contracts have been approved:
    • Contract Kellogg & Associates - Completed
    • Contract University of Washington - Completed
    • Contract City of Auburn - Completed
    • Contract City of Covington - Completed
    • Contract City of SeaTac - Pending
    • The Quality Assurance Project Plan (956 Kb Acrobat pdf) or QAPP is complete, approved by EPA and published.
  • Data for computer modeling analysis are being identified and collected.
  • A meeting was held with EPA on Friday, September 10th, 2010 to review grant expectations.
  • The EPA conducted a Webinar on Tuesday, October 12th, 2010 for project reporting procedures and schedules.
  • An all-project team meeting was held on November 19, 2010, February 2011, May 2011, September 2011, December 2011, March 2012, June 2012, September 2012, December 2012.
  • WRIA 9 Watershed Ecosystem Forum briefing (1.3 Mb Acrobat pdf) was held on February 10, 2011, November 2012.
  • April 12, 2011 Stakeholder Workshop #1
  • January 26, 2012 Stakeholder Workshop #2


  • U.S. Environmental Protection Agency grant
  • Local Matching Fund total
Total Project Funds $1,337,767

For more information about the Stormwater Retrofit Project, please contact Jim Simmonds, Project Manager, Science and Technical Support Section.