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2009 King County Surface Water Design Manual

A technical manual detailing stormwater management requirements for parcel development in King County, WA. Also applicable in any other municipalities that have adopted this manual. At present the most current version is the 2021 Surface Water Design Manual.

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.

Complete 2009 King County SWDM (18 MB)

Separate SWDM 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 fixes from the pages linked below.

2009 Design Manual application maps

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.

SWDM Summary of Changes (14 KB)

SWDM Public Rule (20 KB)

Previous versions of the SWDM: 2005 and earlier

Map of flow control applications in King County

Map of water quality applications in King County

Map of landslide hazard drainage areas in King County

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