Stormwater Management Action Plan

It’s estimated between 1,000 and 2,000 salmon and cutthroat trout could have spawned each year under historic conditions in Miller and Walker Creeks. Today there are several fish barriers that prevent salmon and trout from reaching the upper portions of Miller Creek. Since spawning salmon monitoring began in 2010, the number of salmon in Miller Creek has dramatically declined from a high of 420 in 2011 to only 32 in 2021.

Key facts:

• 5.1 square miles, or 69%, of the total watershed is within Burien city limits.
• The lower portions of Miller Creek are considered moderately important for fish, and the upper portions are designated as low importance as compared to other streams in the Puget Sound region, according to a regional study called the Puget Sound Watershed Characterization.
• Compared to the other watersheds in Burien, the Miller Creek watershed is not as well served by stormwater management facilities.
• There are many roads considered to be highly polluting including Ambaum Blvd SW, SW 152nd St, SW 148th St, SW 128th St, 1st Ave S, and SR 509.
• In the Miller Creek watershed, the Downtown, Evansville, and Sunnydale neighborhoods have fewer parks, fewer trees, and more people who are from communities that have historically been left out of or harmed by urban planning processes, and therefore experience disproportionate environmental harms and risks.
• Learn more by downloading the receiving water conditions assessment and receiving water prioritization report.

The SMAP is being developed for the Downtown catchment of the Miller Creek basin, seen below in orange.

The SMAP will guide solutions in Downtown Burien to improve water quality in Miller Creek. In August 2022 the community was asked to provide feedback on the types of solutions proposed for the Downtown catchment. Based on the community feedback and discussions with other City departments seven solutions were developed. Each of the solutions is supported by numerous regional studies and City-wide plans.

Three of the proposed SMAP solutions are stormwater projects, as seen in the map below. These projects either upgrade existing stormwater facilities or add new facilities to manage existing development.

1. The first project will upgrade Ambaum Regional Pond, which currently holds stagnant and milky water that discharges into Miller Creek (labeled on the map as CIP-1). Nearly all stormwater in the Downtown catchment flows through Ambaum Regional Pond in the southern portion of the catchment. The project will provide enhanced water quality treatment for the polluted runoff from the Downtown catchment and allow the pond to drain more frequently.
2. The second project will construct a new in-ground planter (bioretention facility) at Dottie Harper Park (CIP-2). This facility will provide water quality treatment and restore flows for stormwater runoff from two roads.
3. The third project will add small dispersed water quality treatment facilities in the alley between SW 152^nd Street and SW 153^rd Street (CIP-3). These facilities will provide water quality treatment for stormwater runoff from roadways and commercial parking lots.

Two of the proposed SMAP solutions are land management programs. Both land management programs would be voluntarily implemented on private property. The first program, the Green Stormwater Infrastructure Program, would incentivize private property owners to replace impervious surfaces (such as parking stalls), planters, and other features with bioretention facilities, tree planters, or other vegetated stormwater facilities. The second land management program, the Impervious Surface Reduction Program, builds on an existing City program that incentivizes development and redevelopment projects to include public benefits. If the program were to be implemented, development and redevelopment projects would be incentivized to reduce the amount of impervious surface on their site by allowing additional building height. 

An improved approach to stormwater facility maintenance will be outlined in the SMAP for the City’s stormwater program based on asset management principles. Improved data management will help prioritize stormwater facilities that need the most maintenance. Updating maintenance criteria and levels of service by type of stormwater management facility will streamline maintenance.

The final proposed SMAP solution is a water quality monitoring program. The monitoring program would install a permanent water quality monitoring site in the Downtown catchment which would gather continuous data. City staff, or volunteers, would also collect regular samples throughout the year. This program would allow the City to track progress in the Downtown Tributary, ensure the City is maximizing its investments, and would inform adaptive management of Miller Creek.

The SMAP includes an implementation plan for these solutions and more. The implementation plan is divided into short-term actions (years 1-6) and long-term actions (years 7-20). The short-term recommendations are the seven preferred solutions. The long-term recommendations would be implemented as Burien’s urban center redevelops and as opportunities to partner with transportation projects, parks projects, and private landowners arise. Long-term SMAP actions would be guided by water quality monitoring and adaptive management. Adaptive management would allow the City to use resources efficiently in response to new information. Some long-term project locations have been identified and can be seen on the map below.

To learn more about the SMAP, you can review the map and video below. You can also review the results from the community survey.

The draft SMAP for Downtown Burien will be available for review and comment in February 2023.

What is stormwater?

Stormwater runoff is generated from rain and snowmelt events that flow over land or impervious surfaces, such as paved streets, parking lots, and building rooftops, and does not soak into the ground. The runoff picks up pollutants like trash, chemicals, oils, and dirt/sediment that can harm our rivers, streams, lakes, and coastal waters (also known as receiving waters).

What is a watershed?

A watershed is an area of land where all rainfall and snow melt drains to a common stream or waterbody, such as a lake or Puget Sound.

What is a catchment (also called subbasin)?

For our purposes, a catchment is a portion of a watershed and is between approximately 400 and 600 acres.    

What is stormwater management?

Stormwater management is the process of controlling stormwater runoff with the goal of detaining stormwater and removing pollutants.

What is a stormwater project?

Stormwater projects reduce stormwater runoff and prevent harmful chemicals, toxins, and wastes from coming into contact with our local bodies of water.

What is stormwater management influence?

How much of an improvement within a specific area the City can make to water quality through the projects and actions developed in this plan. For example, an area with many stormwater treatment facilities and detention ponds would have a LOWER stormwater management influence score than an area without these, since much of the stormwater is already being treated.

What is the Stormwater Management Action Plan?

SMAP is a comprehensive stormwater planning process required by the Washington State Department of Ecology. The SMAP process prioritizes stormwater investments and actions in a selected catchment to accommodate future growth in a way that minimizes impacts on receiving waters. A catchment is typically between 400 and 600 acres.

Why is the City only focusing on one stream?

The goal of this process is to identify several smaller areas (catchments) within one stream basin that would benefit most from the new stormwater management projects and activities. This will help focus our limited budget and staffing to make the best improvements possible. This will not prevent the City from completing projects in other parts of Burien, but it will allow staff to better compare the benefits of one project over another.

How did the City come up with the values and environmental goals for the projects?

The City’s Climate Action Plan, the Green Burien Urban Forest Stewardship Plan, the Comprehensive Plan, the Urban Center Plan, responses to the 2022 Community Assessment Survey, and technical information were reviewed to come up with values and environmental goals for project types that are feasible in the Downtown catchment.