The Highway Runoff Manual (HRM) 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 13.5 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 hydraulic engineers; landscape architects; and maintenance staff. The technical team also includes several county representatives and benefites from a close working relationship with 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 (e.g., 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 (e.g., stormwater utility fees) and land use controls (i.e., zoning and land use ordinances) available to local governments.
- Must be accountable to taxpayers to provide cost-effective stormwater facilities.
The HRM reflects the best available science
in stormwater management to ensure that WSDOT projects adequately protect the functions and values of critical environmental areas. Best available science includes information presented in Washington State Department of Ecology’s stormwater manuals, research findings and successful stormwater management strategies from other areas of the country, and results of WSDOT’s own testing of innovative stormwater management practices. WSDOT considers this manual to include
All
Known,
Available, and
Reasonable methods of prevention and
Treatment (AKART) for stormwater runoff discharges consistent with state and federal law.
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 emails announcements of post-publication updates, send a blank email 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
2006 Revision
WSDOT revised the Highway Runoff Manual M 31-16 effective May 16, 2006 for projects going to Ad after July 1, 2007.
Application of the revised guidance in the May 2006 HRM is optional, but encouraged for projects going to Ad during the 2005-2007 biennium since the revised guidance provides additional flexibility in stormwater designs over the March 2004 manual.
The spring 2006 HRM revision includes improvements to improve clarity and reflect advancements in stormwater management and improvement in design tools. Significant changes include:
- 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 (i.e., 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 flow control exempt surface waters list
- 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 MGSFlood 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 (i.e., 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
Download a copy of the 2006 Highway Runoff Manual (pdf 12 mb)
Post-publication Updates
2004 Revision
WSDOT completely revised the HRM in March 2004. The 2004 HRM revision represents over two years of extensive research, collaboration, and negotiation by an interdisciplinary technical team.
The March 2004 HRM provides:
- More options for runoff treatment and flow control.
- Stormwater management approaches that can take advantage of the project site's terrain, vegetation, and soil features to promote infiltration.
- Guidance in choosing solutions that consider the watershed context of the project.
- A process for analyzing offsite options in instances where it may not be practicable to provide treatment and/or flow control from project site areas.
- Retrofit guidance for determining whether it is cost-effective to provide stormwater treatment and flow control beyond what is required.
- Guidance for integrating stormwater planning and design into the context of the WSDOT overall project development process.
In a letter to WSDOT, Ecology conditionally approved the revised HRM for use as an equivalent approach to the Stormwater Management Manual for Western Washington (2001) and for compliance with Ecology permits.
Training
Training on the analysis methods used to design stormwater runoff treatment and flow control facilities has been incorporated into the Hydraulics Branch'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 emails announcing updates, training opportunities, and improvements in design tools send a blank email to subscribe-stormwater_list@lists.wsdot.wa.gov. You will then receive an email asking you to confirm your subscription. To unsubscribe, send a blank email to unsubscribe-stormwater_list@lists.wsdot.wa.gov.
Frequently Asked Questions
The HRM FAQ page answers a variety of questions about the Highway Runoff Manual.