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Surface Water Design Manual (SWDM)
A technical manual detailing requirements and standards for designing storm water management systems in King County, to mitigate the impacts of new development and redevelopment on the natural environment, downstream neighbors, and existing man-made drainage systems. The SWDM is also applicable in other municipalities that have adopted it. 

  • 2021 SWDM - the most current version
  • Older versions still applicable to some vested open projects:
  • Archived versions 
    These older versions of the Surface Water Design Manual are no longer active, but are available for municipalities who have referenced them in stormwater management codes.

King County Code (KCC) Title 9 
Surface Water Management Code

Stormwater Pollution Prevention Manual
This guide describes best management practices for businesses, residents, managers, and owners of property in unincorporated King County to apply to reduce the contamination of stormwater, surface water, and groundwater.

King County stormwater scientific publications catalog
King County Science Section

2014 Post Construction Monitoring Report (1.8 Mb Acrobat pdf)
2013 Post Construction Monitoring Report (1.6 Mb Acrobat pdf)
2012 Post Construction Monitoring Report (13.1 Mb Acrobat pdf)
Reports monitoring the success of retrofits to stormwater detention and treatment facilities constructed by past subdivision development projects, a grant from the State of Washington Department of Ecology to improve stormwater facilities owned and operated by King County.

Green River Stormwater Retrofit Project documents
Results of an ongoing study working to develop best practices for improving stormwater management and reducing non-point source pollution in areas that have already been developed.

Stormwater Retrofit Analysis and Recommendations for Juanita Creek Basin in the Lake Washington Watershed
Strategies to improve flow and water quality to support aquatic life in Juanita Creek, including fish.

Wetlands and Urbanization: Implications for the Future
The Puget Sound Wetlands and Stormwater Management Research Program (PSWSMRP) was a ten-year regional research effort documenting how urbanization affects wetlands. The studies examined the impacts of stormwater on the five major structural components of wetlands: (1) hydrology, (2) water quality, (3) soils, (4) plants, and (5) animals. The fourteen papers in this monograph are divided into four sections: Program Overview, Descriptive Ecology, Assessment of Stormwater Effects, and Management Guidelines.

Characteristics of the low-elevation Sphagnum-dominated peatlands of western Washington: a community profile
Also known as "the bog book", this publication provides a compilation of data and findings about Sphagnum-dominated peatlands from existing local sources, most of which are unpublished as of November, 2001.

For questions about the stormwater website, please contact us at stormwater@kingcounty.gov