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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.

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.

SWDM Summary of Changes (14 KB)

SWDM Public Rule (20 KB)

2009 Design Manual Drawings:

Select a group of drawings to download and extract:

Standard Drawings in AutoCAD DWG format

2009 Surface Water Design Manual errata

The following links contain pages that are intended to be printed double-sided and to replace those pages in the manual. The user has the option of downloading individual pages for each chapter/appendix separately or all the changes for each chapter/appendix with one download for each chapter/appendix.

Chapter 1

Chapter 5

Elimination of impervious surface percentage exemption and small project review threshold

Since Washington State courts have thrown out the KCC 16.82 clearing limits, the Department of Ecology has determined that the County may no longer allow the impervious surface exemption in Core Requirement #3, Section 1.2.3, and the rural zone impervious surface limit criterion for the Small Project Review in Section This change is effective as of March 22, 2010 and we plan to revise the text of the 2009 Surface Water Manual (SWDM) in an errata this fall to include this change.

Blanket adjustments and clarifications 

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