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2009 Thurston County Drainage Design and Erosion Control Manual

The Thurston County Drainage Design and Erosion Control Manual sets standards for reducing and managing stormwater runoff on new development and redevelopment projects in the unincorporated areas of Thurston County. The manual also applies to projects within incorporated and urban growth areas that adopt the Thurston County manual.

red arrowThe drainage manual you see on this page was approved by Thurston County commissioners on August 17, 2009 and took effect November 16, 2009.  To view the adopting ordinance, click here. To see the previous, 1994 version, click here.

manual coverThe new manual is consistent with the 2005 Department of Ecology Stormwater Manual for Western Washington. The updates were required under Thurston County's NPDES Phase II permit.

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2016 Drainage Design and Erosion Control Manual Revision for Thurston County

The FINAL DRAFT of the Thurston County Drainage Design and Erosion Control Manual is available for review.  There will be a public hearing on the DDECM and the LID Code Revisions on Tuesday, September 27, 2016, at 5:30 p.m., in Room 280, Building 1 of the Thurston County Courthouse Complex, 2000 Lakeridge Dr. SW, Olympia, WA 98502. Verbal and written comments will be accepted at the public hearing. You can also send written comments as outlined below. The Final Draft includes revisions based on comments received during the first public comment period. Please see the Comment Resolution document below for a summary of the changes.  

A comment form is provided below as a MS Word document. Please use this document when submitting comments. If you choose not to use this document, please include the following with your comments to aid in comment resolution:

• Volume number

• Chapter, section, and page

• Specific text that pertains to your comment and suggested change. If your comment is a general comment, please explain your concerns and suggested remedies.

• Name and contact information (so we can follow up if we have questions about your comment)

Please send your comments to Mark Maurer at maurerm@co.thurston.wa.us by close of business September 27, 2016. Electronic copies are preferred, but hard copies can be sent to Mark Maurer, 2000 Lakeridge Drive SW, MS: B4-1WR, Olympia, WA, 98502.

Final Draft Drainage Design and Erosion Control Manual September 2016

Comment Resolution

Comment Form (downloadable)

Preface and Table of Contents

Volume I

Volume II

Volume III

Volume IV

Volume V

Per the Phase II NPDES Permit, Thurston County is required to revise the Drainage Design and Erosion Control Manual to be equivalent to the Stormwater Management Manual for Western Washington (SWMMWW) by December 31, 2016. The volumes below were revised based on the 2015 Pierce County Stormwater Management & Site Development Manual which is equivalent to the SWMMWW. There are two copies of each Volume. The “Clean” copy shows only the additions with a vertical line that indicates where the changes are and the “Redline” copy shows the full markup all the additions and deletions. Both copies are provided to aid in your review.



Summary of Changes

Comment Form (downloadable)




2009 Drainage Design and Erosion Control Manual for Thurston County


Administrator Memo's


Modeling Information

  • The 2009 Drainage Design and Erosion Control Manual for Thurston County requires the use of the Western Washington Hydrologic Model, Version 3 (WWHM3) with Thurston County enhancements for BMP design. The Thurston County enhancements include the use of additional rain gage stations and 15-minute time steps and also include a recharge calculator to demonstrate minimum infiltration requirements for projects. The program is available for download by clicking here.
  • Guidance for Using the Recharge Calculation in WWHM3 with Thurston County Enhancements (PDF)
  • Department of Ecology memo approving Western Washington Hydrologic Model with Thurston County Enhancements (PDF)

Design Guides for 2009 Drainage Manual Best Management Practices

Fact Sheets

Related Items

Contact Us

 Staff contact: Pat Allen (360) 867-2078.  E-mail: AllenP@co.thurston.wa.us


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