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Stormwater services

Managing stormwater and waterborne pollution

Find comprehensive services, data and information related to stormwater and non-point source pollution in King County, Washington.

To offer a suggestion or report an error on the King County stormwater services and information website, please contact Fred Bentler, webmaster.

Stormwater Services and Information for King County, Washington

King County has submitted an equivalency package, including the King County Surface Water Design Manual, to Ecology for review and approval.  Due to the PCHB ruling in 2013 Ecology was required to rewrite sections of the 2012 Western Washington Stormwater Manual and published the 2014 version of their manual on December 17th, 2015.  Ecology will be providing comments to King County based on their equivalency review to both Ecology’s 2012 and 2014 Manuals.  King County and the other Phase I jurisdictions have been meeting with Ecology to facilitate this process and are still working with Ecology to develop an equitable framework for review and approval.  No timeline has been finalized as of mid-January.  


2009 King County Surface Water Design Manual (SWDM)

Pursuant to King County Council adoption of Ordinance 16264, the Department of Natural Resources and Parks adopted a public rule revising the King County Surface Water Design Manual (SWDM). In accordance with King County Code, Chapter 2.98, Rules of County Agencies, this public rule was adopted on January 9, 2009.

The hard copy of the 2009 SWDM is available for purchase at the Water and Land Resources Division office at 201 S. Jackson Street, 6th floor reception. The manual costs $145 plus tax and can be ordered by calling 206-477-4800 and paying an additional $13 for shipping.

Need a copy of the 2005 SWDM? It is now on sale at the special discounted price of $51 plus tax and shipping. Call 206-477-4800 to order or come to 201 S Jackson Street 6th floor reception and save shipping.

Files are available for download in Adobe Acrobat PDF format.

The entire manual is available for download. One great benefit of having the SWDM as one electronic document is the search function. It is only necessary to take the time to download it once. Save it to your desktop for convenient access.

2009 King County SWDM (18 MB)

Here the SWDM is provided in sections.

This document contains the main body of the SWDM, which includes Chapters 1-6 and the Definitions Section.

2009 SWDM Main Body (7.8 MB)

This next section includes the SWDM Appendices.

Appendix A Maintenance Requirements for Flow Control, Conveyance, and WQ Facilities (140 Kb)

Appendix B Master Drainage Plan Objective, Criteria and Components, and Review Process (25 Kb)

Master Drainage Planning for Large Site Developments - Process and Requirements   details the Process and Requirements to submit  a Master Drainage Plan to the Department of Permitting and Environmental Review 

Appendix C Small Project Drainage Requirements (2.2 MB)

Appendix D Erosion and Sediment Control (ESC) Standards (2.2 MB)

The Reference section is the final part of the SWDM. Although some of the materials in this Reference section may have been adopted by administrative rule or by ordinance, the administrative rule that adopted the SWDM has not formally adopted any of the materials in this section.

References (2.3 MB)


2009 Design Manual Errata:

The printed version of the Manual does not include the errata. If you have a printed version of the Manual, you can download the errata from the page linked here.

2009 SWDM Errata

Application of the Manual's targeted protection levels is determined from the following three application maps of King County. The maps are available here to view or download. This pdf format was chosen to allow the user to zoom in and out, pan the map in any direction, and print the map at the best resolution possible. Click the icon below if you need to download Adobe Acrobat.
Get Adobe Acrobat

Other than the website listed on the maps, the content of the 2009 maps is the same as the 2005 maps.

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2009 Flow Control Applications Map, PDF file







2009 Water Quality Applications Map, PDF file







2009 Landslide Hazard Drainage Areas Map, PDF file




SWDM Summary of Changes (14 KB)

SWDM Public Rule (20 KB)

Previous versions: 2005 Design Manual and other archived documents.

2009 Design Manual Drawings:

Standard drawings from the 2009 King County Design Manual can be downloaded individually in AutoCAD DWG format. Additionally the AutoCAD DWG drawings can be downloaded as a single 9.0 Mbyte file or chapters can be downloaded individually.


Select a group of drawings to download and extract:





Standard Drawings in AutoCAD DWG format


Large ZIP file of all chapters
Download ZIP files of individual chapters:





(9.1 MB)

For questions about the stormwater services website, please contact Dale Nelson, Engineer, King County Stormwater Services Section.