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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 is effective as of April 24th, 2016. 

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. Contact David Batts at for further information on suggested printing specifications.

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.

Important Notice about Projects Permitted under Earlier Versions of the SWDM

Per requirements in King County’s Phase 1 Municipal Stormwater Permit (effective date August 1, 2019), projects permitted under earlier versions of the SWDM that have not started construction* by  July 1, 2021 must be revised to comply with the requirements of the 2016 SWDM, or subsequent versions as directed by state regulations. Revisions will need to be approved by the Permitting Division of King County Department of Local Services (DLS-PD), or its successor agency prior to construction.

*“Started construction” means, the site work associated with, and directly related to the approved project is at a stage where rough grading is complete or utilities are installed. For rough grading to be considered complete, elevations are within 1 foot of final design elevations.

2016 Surface Water Design Manual documents

Combined SWDM including all chapters, appendices, definitions, and reference sections (17,397 KB) Errata Update 6/15/16

Note: Reference 8-F is outdated and should be disregarded when applying requirements from the 2016 SWDM. Text in the main body of the SWDM contains the relevant information on the adjustment process.

SWDM errata edits (6/15/16) 

Errata and edits log (6/15/16)

SWDM chapters

Chapter 1-Drainage Review and Requirements (904 KB) Errata Update 6/15/16

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

Chapter 3-Hydrologic Analysis and Design (590 KB) Errata Update 6/15/16

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

Chapter 5-Flow Control Design  (2,163 KB) Errata Update 6/15/16

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

2016 Design Manual Drawings:

Standard drawings from the 2016 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


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

Note: Reference 8-F is outdated and should be disregarded when applying requirements from the 2016 SWDM. Text in the main body of the SWDM contains the relevant information on the adjustment process.

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)

Blanket adjustments and Clarifications

Stormwater Management at King County International Airport (KCIA)

Optional Use of Dispersive/Infiltrative FCBMPs in Erosion Hazard Areas

Stormwater Management of Trails in Forested Areas

If you have questions about these changes, contact Mark Wilgus at

Information on Key Provisions of King County Drainage Code Title 9

Key provisions of King County Code 9.04 and 9.12

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