Better Back Roads Management Evaluation

Jun. 26th 2014

Vermont has an extensive network of unpaved roads throughout the state. These roads can be damaged and degraded over time due to seasonal snow melt and rain storms as well as due to large storm and flood events. The damage is not only costly to repair, but transportation can be inhibited in rural areas. The runoff from the unpaved roads also causes non-point source pollution as sediment and excess nutrients runoff into the surface water. The Vermont Better Backroads program has been providing funds for towns and organizations to implement recommended Best Management Practices (BMPs) since 1997. A total of 414 sites have received funding from the program between 1997-2011. As part of a two-year study to assess efficacy of BMPs in reducing erosion and water quality degradation on Vermont’s back roads, Dr. Beverly Wemple and graduate student Joanne Garton, of the University of Vermont, assessed the efficacy of 106 BMPs that were installed at 45 of these sites to determine how long BMPs remain intact over time. Funding for the study was provided by the Vermont Water Resources and Lake Studies Center and the Vermont Agency of Natural Resources Ecosystem Restoration Program. Each BMP was assigned to one of four categories, based on construction technique, materials, purpose, and behavior over time: stonework, stream and ditch culverts, revetments, and vegetated soil stabilization. Numerous factors were included in determining the condition of BMPs at each of the locations. These factors included age of the BMP, road gradient, the presence of a vegetated buffer, exposure to extreme flood events, and several road design and placement factors. After assessment of the BMPs, each site was categorized as all intact, with no loss of capacity to reduce erosion, compromised, or failed if the installation was no longer functioning to improve water quality. The strongest predictor of site BMP condition was road grade; steeper roads are more likely to fail. While a trend of loss of capability of BMP was associated with age, time since BMP installation was not a significant predictor of BMP condition, suggesting that other factors, including topographic setting and flood exposure are more important predictors of BMP efficacy, and that the design life of BMPs assessed (all less than 10 years at the time of assessment) has not yet been exceeded. Exposure to extreme floods and the presence of vegetated borders were also important predictors of BMP condition. Vegetated borders using grasses and herbaceous plants may be a viable solution, especially when used in conjunction with other BMPs, such as within revetments and roadside ditches. The study results indicate that with proper installment and maintenance, BMPs can remain intact for a decade or more. The Better Backroads program has resulted in improvement of unpaved roads throughout Vermont and reduced sediment and nutrient runoff into surface waters. Another element of Wemple’s study documents reductions in sediment and phosphorus production from gravel roads following installation of BMPs. Results of this work will be available in January 2015.