Research on Design for Prevention of Ditch Erosion on Virginia Highways

Roadside ditch erosion has been problematic on Virginia highways. VDOT, through the Virginia Transportation Research Council, requested that roadside ditch erosion be investigated by means of a research project. Virginia Tech was selected to conduct this study. In support of this research, design guidance documents were surveyed to learn the current established policy and procedures for soil data collection and reporting, and the design practice for hydrologic and hydraulic analyses of roadside ditches. Site visits to each of Virginia's nine construction districts were made to interview district personnel about their personal experience with roadside ditch design, performance, and erosion failures. Current ditch design practices in nine other states were investigated through the collection and survey of state drainage manuals, and phone interviews with DOT personnel. Finally, an extensive review of current literature was performed with the intent of investigating current research on ditch erosion and erosion control. Results of the research indicate that three major factors are contributing to the occurrence of erosion in roadside ditches. They include, 1) insufficient soil information collected on road projects and reported in unusable formats for the hydraulic designers, 2) overuse of default values and criteria in hydraulic design, and 3) geographical and management issues not currently encompassed by current VDOT ditch design policies and procedures. Recommendations directed at these factors are provided, along with tables presenting updated correlations between site-specific conditions and hydraulic parameters for design.