Skip to main content

2016 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.

Important Notice about Projects Permitting 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.

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 25, 2016. The 2016 SWDM is effective as of April 24, 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 as a downloadable file. The manual is searchable and the bookmarks within the navigation pane allow 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 the References section.

2016 Surface Water Design Manual documents

Combined SWDM including all chapters, appendices, definitions, and reference sections (1.8 MB) 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Note: Reference 8-F is outdated and should be disregarded when applying requirements from the 2016 SWDM.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 (12.1 KB) (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 (2.1 MB) Updated 4/18/16

Chapter 5 - Flow Control Design (2.2 MB) Errata Update 6/15/16

Chapter 6 - Water Quality Design (3.1 MB) 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 (2.2 MB) Updated 4/18/16

Appendix D - Construction Stormwater Pollution Prevention Standards (1.8 MB) 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 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 (4.1 MB) 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 (18.2 MB)

Full Manual binder spine (1.7 MB)

Appendix C and D covers (4.9 MB)

Surface Water Design Manual application maps

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

SWDM maps in PDF format:

Flow Control Application Map (898 KB)

Water Quality Application Map (948 KB)

Landslide Hazard Drainage Areas Map (1.3 MB)

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 (238 KB)

SWDM Summary of Changes (686 KB)

Blanket adjustments and clarifications

Stormwater Management at King County International Airport (KCIA) (387 KB)

Optional Use of Dispersive/Infiltrative FCBMPs in Erosion Hazard Areas (265 KB)

Stormwater Management of Trails in Forested Areas (380 KB)

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 (140 KB)