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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

Surface Water Design Manual

Pursuant to King County Council adoption of Ordinance 18257, 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 March 25th, 2016.  The 2016 SWDM will become effective April 24th, 2016. 

PLEASE NOTE: The manual below is the version used for public rule adoption and is subject to errata edits to be posted prior to the effective date.

Printed copies of the 2016 SWDM are not being provided.  Interested parties can download the electronic version of the manual and then  print and bind their own manual. General printing instructions for the manual will be made available shortly. Contact David Batts at for further information.

The entire 2016 SWDM including Chapters 1-6, Appendices A through D, Definitions,  and Reference sections is available for download  in Adobe Acrobat PDF format. The electronic version of the manual is searchable and the bookmarks function within the navigation pane allows for quickly moving through document.  Note that although some of the materials in the Reference section of the 2016 SWDM  may have been adopted by administrative rule or ordinance, the administrative rule that adopted the SWDM has not formally adopted any of the materials in this section.

2016 Surface Water Design Manual Documents

Combined SWDM including all chapters, appendices, definitions, and reference sections (17,397 KB) Updated 4/18/16

SWDM Chapters

Chapter 1-Drainage Review and Requirements (904 KB) Updated 4/18/16

Chapter 2- Drainage Plan Submittal (299 KB) Updated 4/18/16

Chapter 3-Hydrologic Analysis and Design (590 KB) Updated 4/18/16

Chapter 4-Conveyance System Analysis and Design (2,079 KB) Updated 4/18/16

Chapter 5-Flow Control Design  (2,163 KB) Updated 4/18/16

Chapter 6-Water Quality Design  (3,114 KB) Updated 4/18/16

Definitions (242 KB) Updated 4/18/16


Appendix A-Maintenance Requirements for Flow Control, Conveyance, and Water Quality Facilities (352 KB) Updated 4/18/16

Appendix B-Master Drainage Plan Objective, Criteria, Components, and Review Process (30 KB) Updated 4/18/16

Appendix C-Simplified Drainage Review Requirements (2,203 KB) Updated 4/18/16

Appendix D-Construction Stormwater Pollution Prevention Standards (1,795 KB) Updated 4/18/16


Combined References, Forms and Worksheets (4,123 KB) Updated 4/18/16

2016 SWDM Cover Pages

Full Manual binder cover (18,199 KB)

Full Manual binder spine (1,662 KB)

Appendix C and D covers  (4,854 KB)

Surface Water Design Manual Application Maps

Find the most up-to-date information posted on iMap

SWDM maps in PDF format:

Flow Control Application Map (898 KB)

Water Quality Application Map (948 KB)

Landslide Hazard Drainage Areas Map (1,288 KB)

PDF Map Errata Notes:

  • Unincorporated and Incorporated boundaries have not been updated
  • On Flow Control Application Map, major receiving waters #7 should read, “Snoqualmie River downstream of confluence of the Middle fork, Snoqualmie River Middle Fork downstream of confluence with Rainey Creek.”
  • Note that the default flow control designation for Forest Production Zone Area is Conservation Flow Control.
  • Note the default water quality designation for Forest Production Zone Area is Basic water quality treatment.

SWDM signed Public Rule and Summary of Changes (2009-2016)

SWDM Public Rule PUT-8-3-5

SWDM Summary of Changes (21 KB) (19 KB)


If you have questions about the proposed changes, contact Mark Wilgus at

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