Volume Reduction of Highway Runoff in Urban Areas: Final Report and NCHRP Report 802 Appendices C through F (2015) / Chapter Skim
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Pages 20-27
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C H A P T E R 3 Findings and Applications Summary of Findings The purpose of this project was to develop guidelines for transportation agencies on implementing volume reduction practices that are specific to limited access urban highways and specific to the conditions encountered as part of each project. As such, it was not the intent of this project to reach categorical conclusions about volume reduction or define a single preferred approach for achieving volume reduction.
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Key Factors for Volume Reduction Volume reduction of highway runoff refers to reduction of the amount of highway and right-of-way runoff that discharges directly either via overland flow or channelized flow or subsurface pipe flow to streams, rivers, lakes, the ocean or other water bodies. Therefore, to achieve volume reduction, water must be discharged to other hydrologic pathways.
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The definition of these highway types for the Guidance Manual was intended to help the user identify the constraints and opportunities for volume reduction that are specific to the standard highway types that are most similar to the conditions on a given project. More information about these highway types and their attributes in relation to volume reduction is provided in Section 3.3 of the Guidance Manual.
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Menu of Volume Reduction Approaches Section 4.1 of the Guidance Manual provides a summary of existing stormwater control measures (SCMs) in use in the highway environment, including an evaluation of which of these SCMs provide significant volume reduction potential.
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• Relative potential risk of groundwater quality impacts by VRA • Safety considerations by VRA • Maintenance activities by VRA Additionally, Section 4.4 of the Guidance Manual provides additional references for VRA design and maintenance information, including selected nationwide guidance and selected state-specific DOT guidance. Framework for Selecting and Applying VRAs The Guidance Manual (Section 5.1)
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would infiltration in excess of natural conditions potentially cause geotechnical issues or downgradient habitat concerns? • Does the cost required to construct the VRA and/or mitigate potential risks posed by the VRA outweigh the volume control benefits it would achieve?
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a function of project type (i.e., new vs. redevelopment vs.
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a mutual understanding amongst the design team regarding volume reduction goals and the way that volume reduction considerations will be incorporated into the project development process. Similarly, the Guidance Manual can be used to help scope the additional or alternative analyses that may be needed in the design process as part of achieving volume reduction or demonstrating its infeasibility.
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