Thurston County Storm and Surface Water Utility

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.

The 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.

The 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.

2009 Drainage Design and Erosion Control Manual for Thurston County

• Cover page and master table of contents, with links to the following PDFs.
• Volume 1 (1.6 MB), Minimum Technical Requirements and Site Planning
• Volume 2 (2.9 MB), Construction Stormwater Pollution Prevention
• Volume 3 (2.7 MB), Hydrologic Analysis and Stormwater Conveyance
• Volume 4 (2.3), Source Control
• Volume 5 (4 MB), Stormwater BMPs

Policies

• Alternative Paving Surfaces
• Closed-Circuit Television Inspection
• Subdivision Land Area Calculations

Administrator Memo's

• Rural Large Lots
• Mechanical Equipment
• Salmon Creek Basin

Errata

• Errata No. 1. August 2012

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

• Design Guide for Detention Ponds (PDF)
• Design Guide for Wet Ponds (PDF)
• Design Guide for Post-Construction Soils Quality and Depth (PDF)
• Design Guide for Roof Downspout Runoff Controls (PDF)
• Design Guide for Bioretention (PDF)

Fact Sheets

• What You Need to Know About Abbreviated Drainage Plans (PDF)
• How to Determine Whether You Can Submit An Abbreviated Drainage Plan (PDF)
• Sample Abbreviated Drainage Plan (PDF)
• What is in the 2009 Drainage Manual? (PDF)
• What is the Difference Between the 1994 Drainage Manual and the 2009 Drainage Manual? (PDF)
• Stormwater Problems and Impacts: Why the Fuss? (PDF)
• How is the 2009 Drainage Manual Different from Ecology's 2005 Stormwater Management Manual for Western Washington? (PDF)
• What Are the 12 Minimum Requirements? When do They Apply? (PDF)
• Single Family Residential Projects -- On a Single Lot (PDF)
• The Drainage Scoping Report -- A New Requirement (PDF)

Related Items

• Commercial Stormwater Agreement to Maintain Template Microsoft Word version
• Commercial Stormwater Pollution Prevention Source Control Plan Template (PDF) (For a Microsoft Word version, click here)
• Stormwater Pollution Prevention Source Control Plan BMPs (Microsoft Word)
• Residential Subdivision Agreement to Maintain Template Microsoft Word version
• Single Family Residential Agreement to Maintain Template Microsoft Word version
• Stormwater Pollution Prevention Source Control Manual -- Residential (PDF)
• Maintenance Check Lists for Agreement to Maintain (PDF)
• Checklist for items required at Final Acceptance and prior to release of Financial Guarantees (PDF)
• Operation & Maintenance Cost Estimate Template (PDF)
• Bond Quantities Worksheet Microsoft Excel version
• Closed Circuit TV Inspection Policy (PDF)
• Stormwater Conveyance Connection Application Form (PDF)

Contact Us

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