2010 Highway Runoff Manual
WSDOT revised the Highway Runoff Manual, M 31-16 in May of 2010 response to the settlement of the appeal of the NPDES permit filed in April 2009. The revision includes:
- New language (i.e., Section 3-4.2) on stormwater retrofit requirements for projects that occur within the Puget Sound Basin and receive Design Approval after July 1, 2010.
- Slight changes to Figures 3.1, 3.2, and 3.3 to clarify the Minimum Requirement applicability at the project and TDA level.
- Additional information on meeting project retrofit obligations off-site.
WSDOT revised the Highway Runoff Manual, M 31-16 in June of 2008. In an August 20, 2008 letter, the Washington State Department of Ecology (Ecology) informed WSDOT that it reviewed the June 2008 HRM and deemed the manual equivalent to Ecology’s current Stormwater Management Manuals. All projects going to Ad on or after March 6, 2010 must comply with the requirements and guidelines contained in the June 2008 HRM. All projects that require a Section 401 Water Quality Certification have to meet (as they have since 7/1/2007) the applicable requirements and guidelines contained in Ecology’s 2005 Stormwater Management Manual for Western Washington or 2004 Stormwater Management Manual for Eastern Washington OR those contained in the June 2008 HRM.
The 2008 HRM revision improves content clarity and reflects advancements in stormwater management and improvement in design tools. Significant changes in the 2008 HRM revision are described in the manual’s Publications Transmittal (pdf 48 kb). The current version of the Stormwater Design Documentation Spreadsheet is version 3.0.
The spring 2006 HRM revision included improvements to clarity and reflected advancements in stormwater management and improvements in design tools. Significant changes included the following:
- A major reorganization and rewrite of the 2004 HRM's Chapter 3 – Stormwater Planning and Design Guidance, including changing the chapter title to Stormwater Planning and Design Integration, and moving it into the Chapter 2 position (the 2004 HRM's Chapter 2 – Minimum Requirements, now appears as Chapter 3)
- Greater uniformity in applying the manual's minimum requirement thresholds for eastern and western Washington
- An expanded list of flow control exempt surface waters
- Clarifications to retrofit guidance
- Improvements to the Endangered Species Act Stormwater Design Checklist
- Applying the Threshold Discharge Area approach to eastern Washington
- Refinements and additions related to infiltration guidance
- Refinements related to MGS Flood enhancements
- Refinements/additions to flow control modeling credits for several BMPs and modeling Low Impact Development (LID) approaches
- Elimination of Appendix 4C – Downstream Analysis, whose content was incorporated into the Hydraulics Manual update
- Refined design criteria for several best management practices (BMPs)
- Additional figures and photos to enhance BMP design descriptions
- Fully integrating LID approaches into Chapter 5, thereby eliminating the need for Appendix 5A – Low Impact Development Land Use Practices
- A process for seeking approval to use BMPs not currently in the HRM (emerging technologies and high operations and maintenance BMPs), thereby eliminating the need for Appendix 5B – Experimental BMPs Under Development
- Glossary enhancements
- Expanded document hyperlink capabilities