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Retrofit Planning for Improving Miller and Walker Creeks

Retrofit Planning for Improving Miller and Walker Creeks

When it rains in the Miller and Walker Creeks basin, streams flow high and fast, and the water is polluted.  This is because much of the area was built with the idea of getting water into the creeks as quickly as possible.  Now, we realize that this washes pollution (oil, gas, fertilizers, pesticides, metals used to waterproof wood, etc.) into the streams and causes high flows that damage habitat.

The Miller Walker Basin Partners (the cities of Burien, Normandy Park, and SeaTac; King County; and the Port of Seattle) conducted a stormwater retrofit analysis that identified potential strategies and projects to help reduce runoff into Miller and Walker Creeks.

Maps and Reports

Miller-Walker stormwater retrofit reports, maps and other products can be downloaded here:

Final Miller-Walker Stormwater Retrofit Implementation Plan, 2015 (includes Appendices A and D-H) (Large PDF file, 50MB)

    Appendix B - Infiltration Feasibility Assessment for the Miller-Walker Basin (Adobe PDF, 20MB)       

    Appendix C - Preliminary Pre-Engineering Design Reports:

         Moshier Park, Preliminary Pre-Engineering Design Report (Adobe PDF, 13MB)

         6th Ave SW, Burien, Preliminary Pre-Engineering Design Report (Adobe PDF, 47MB)

         King County Court House, Burien, Preliminary Pre-Engineering Design Report (Adobe PDF, 53MB)

    Appendix I - Public Outreach and Involvement Materials (Adobe PDF, 9MB)

Level I Stormwater Retrofit Site Evaluation Map (Adobe PDF)

Level I Stormwater Retrofit Site Evaluation Criteria (Adobe PDF)

Level I Stormwater Retrofit Site Evaluations - Matrix (Adobe PDF)

Level II Stormwater Retrofit Site Evaluation Map (Adobe PDF - 7MB)
Level II Stormwater Retrofit Site Evaluation Matrix (Adobe PDF)

Miller-Walker Infiltration Feasibility Assessment (Large PDF file - 20MB)
Public Comments and Answers, May 2014 (Adobe PDF)

Hydrologic Assessment of Stormwater Retrofit Need in the Miller-Walker Basin (Adobe PDF) 

How the Retrofit Analysis Was Done

The Basin Partners prioritized and ultimately selected four stormwater retrofit projects for developing pre-design reports. These projects could use a variety of methods to slow and purify stormwater flows, ranging from additional pipes to carry stormwater to local treatment facilities to green stormwater infrastructure, such as rain gardens and permeable pavement. All potential projects were located on public property. 

The analysis does not provide funding or authorization for construction of projects; it is a planning document that is implemented through future agreements among the agencies. For example, Burien used the pre-engineering design report for Moshier Park to win a grant from Department of Ecology for further engineering and design work in 2015.

Public Meeting Series

The stormwater analysis provided the Miller Walker Basin Partners with a list of potential strategies designed to improve water quality and reduce flooding and erosion. The Basin Partners hosted a series of public meetings to discuss the benefits of the analysis and potential stormwater retrofit opportunities in your community, starting in April, 2014 and ending in November, 2014. Meeting attendees learned more about the objectives of the analysis, the Basin Partners’ findings, and had opportunities to provide input.

Download the presentation from the October-November 2014 public meetings:
Stormwater Retrofit Public Meeting Presentation for Miller and Walker Creeks (Adobe PDF - 2MB)

Stormwater Runoff and Pollution

When it rains, stormwater collects from impervious surfaces, including roofs and pavement. The untreated water then drains into local waterways, such as Miller and Walker creeks, carrying runoff and pollutants that eventually flow into Puget Sound. Motor oil, brake fluid, weed killers, and other chemicals contaminate the creeks, negatively impacting the wildlife within these waters. As an example, a recent survey showed that over 80% of coho salmon adults in Miller and Walker creeks died before they could lay eggs. This measurement, also referred to as a stream’s pre-spawn mortality rate, demonstrates the importance of stormwater quality improvements.

Benefits of Managing Stormwater

In addition to improving water quality for wildlife and their habitat, stormwater management has benefits for our communities and neighborhoods. Controlling and absorbing stormwater can reduce erosion and flooding on roadways and private property. Traditional stormwater facilities, like detention ponds, allow stormwater to collect and slowly release back into the stormwater system for treatment. Green stormwater infrastructure uses natural features to keep stormwater runoff close to its source.

Current Stormwater Projects in Miller and Walker Basins 

Communities in the Miller-Walker Basin have already been busy improving water quality:

  • In 2007, the Port of Seattle completed significant upgrades to its stormwater management practices to prevent contaminated runoff from reaching local streams and Puget Sound. These practices range from aircraft and equipment management to detention and treatment of stormwater runoff.
  • In Burien, the city is constructing a new stormwater and trail project in the Northeast Redevelopment Area north of SR 518. The project will make improvements to treat runoff that would ordinarily flow directly into Miller Creek.

What is Green Stormwater Infrastructure?

One way to manage harmful stormwater runoff is through green stormwater infrastructure. This is a cost-effective and environmentally-friendly way to remove pollutants from our local waterways, reduce occurrences of flooding, and replenish groundwater systems.

For example, rain gardens and swales use plants and soil to absorb the water when it rains. Other types of green stormwater infrastructure, such as permeable pavement, allow water to drain through it and back into the ground.

Stewardship of the Miller/Walker Creeks basin is jointly funded by the City of Burien, City of Normandy Park, City of SeaTac, King County, and the Port of Seattle. On behalf of the partners, this page is proudly hosted by King County Department of Natural Resources and Parks - Water and Land Resources Division.

Miller and Walker Basin Stewardship Sponsoring Jurisdictions

Miller-Walker Creek Questions

  • Contact Iris Kemp with questions about Miller and Walker Creeks

Lake Burien Questions

  • Direct questions about Lake Burien, including toxic algae testing, to Chris Knutson