What is a Structural Stormwater Control?

A Structural Stormwater Control (SSC), as defined by the Washington Department of Ecology (Ecology) Municipal General Stormwater Permit, includes municipal infrastructure projects that treat or control local stormwater pollution. SSCs include stormwater retrofits for existing development, but also projects in undeveloped areas. These investments create healthier waters and communities.

Ecology defines 11 project types that qualify as SSCs.

Click here to learn about the 11 types of Structural Stormwater Controls defined by the Washington Department of Ecology.

All eleven project types (Types #1–11) serve one (or more) of four different beneficial functions: they provide flow control, reduce toxic pollution, restore natural ecosystems, or maintain and preserve existing structures.

Nature’s Scorecard 2022 developed the following SSC Glossary of Terms to convey complex SSC project types to the public. Our glossary combines the 11 SSC project types as defined by the Municipal General Stormwater Permit into four “function types,” for ease of public consumption.

Click here to view our map of SSC function types. Are there SSCs in your neighborhood? What stormwater control functions do those projects serve?

Flow control projects capture water to slow and control the flow of stormwater, preventing flooding. Example: detention pond. Photo credit: Jessie Darland, Kitsap Sun.

This category includes: new flow control facilities (Type #1), new LID BMPs (Type #3), retrofits of existing flow control facilities (Type #4), and permanent removal of impervious surfaces (Type #10).

Toxics reduction projects filter toxic pollutants out of stormwater. Example: Point Defiance Regional Stormwater Park, Tacoma. Photo credit: Rae Lee. 

This category includes: new runoff treatment facilities (Type #2), new LID BMPs (Type #3), and retrofits of existing treatment facilities (Type #4).

Projects that restore ecosystem function are intended to mimic the natural environment and reconnect the natural water cycle system. Example: property acquisition and demolition at Cedar Grove Mobile Park to reconnect floodplain. Photo credit: King County. 

This category includes: property acquisition and permanent protection from development (Type #5), restoring riparian buffers (Type #7), restoring forest cover (Type #8), and floodplain reconnection (Type #9).

Maintaining and preserving infrastructure can prevent pollution from getting into our waterways. Example: High efficiency street sweeper. Photo Credit: Seattle. 

This category includes: maintenance with capital construction costs ≥ $25,000 (Type #6), and street sweeping and line cleaning (Type #11).