The Highway Runoff Manual is the guidance that WSDOT, engineering consultants, and many local agencies use to design stormwater systems for transportation projects. Together with WSDOT's Hydraulics Manual, (pdf 11.06 mb) the HRM provides tools for designing effective stormwater collection, conveyance, and treatment systems for highways, ferry terminals, park and ride lots, and other transportation-related facilities.
The Highway Runoff Manual represents years of extensive research, collaboration, and negotiation by an interdisciplinary technical team of water quality, stormwater, and erosion control specialists; designers; hydrologists; geotechnical and hydraulics engineers; landscape architects; and maintenance staff. The technical team also includes several county representatives and benefits from a close working relationship with Washington State Department of Ecology (Ecology) staff, with work also contributed by consultants and outside reviewers. The technical team recognized that it is inefficient, and in some instances ineffective, to try to emulate how local jurisdictions manage runoff from residential, commercial, and industrial land uses. Consequently, their approach to developing the HRM takes into consideration that WSDOT:
- Needs a statewide approach for managing stormwater that recognizes the differences in climate, soils, and land uses.
- Has limited control of pollutants entering its right of way (including pollutants generated from atmospheric deposition, vehicle operation, litter, organic debris, and surrounding land uses).
- Highway projects are linear in nature and, as such, are faced with practical limitations in terms of locating and maintaining stormwater treatment facilities within state-owned right of way.
- Lacks funding mechanisms (such as stormwater utility fees) and land use controls (zoning and land use ordinances) available to local governments.
- Must be accountable to taxpayers to provide cost-effective stormwater facilities.
The HRM receives periodic updates to enhance content clarity as well as reflect changes in the regulatory landscape, advancements in stormwater management, and improvements in design tools. To receive e-mail announcements of postpublication updates, send a blank e-mail to
subscribe-stormwater_list@lists.wsdot.wa.gov. Comments and suggestions for improving the HRM should be e-mailed to
schaffl@wsdot.wa.gov or mailed to:
Highway Runoff Manual
Attention: Stormwater Team Lead
WSDOT
PO Box 47332
Olympia, WA 98504-7332
2008 Revision
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 must comply with the requirements and guidelines contained in the June 2008 HRM one year from the effective date of the WSDOT NPDES Municipal Stormwater Permit, which is projected by Ecology to occur in fall 2008. 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.
Post-publication Updates
- No postpublication updates exist at this time.
2006 Revision
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
2006 Highway Runoff Manual
Training
Training on the analysis methods used to design stormwater runoff treatment and flow control facilities has been incorporated into the HQ Hydraulics Section's curriculum. Training on guidance and procedures for temporary construction-related erosion and sediment control facilities has been incorporated into the Environmental Services' erosion and sediment control program curriculum. Training for applying other elements of the HRM is under development.
Highway Runoff Manual Electronic Mailing List
To receive e-mails announcing updates, training opportunities, and improvements in design tools, send a blank e-mail to: subscribe-stormwater_list@lists.wsdot.wa.gov. You will then receive an e-mail asking you to confirm your subscription. To unsubscribe, send a blank e-mail to: unsubscribe-stormwater_list@lists.wsdot.wa.gov.
Frequently Asked Questions (FAQs)
The HRM FAQs page answers a variety of questions about the Highway Runoff Manual.