Performance and Feasibility Study of Vegetated Roadsides as a Low-Impact-Development Practice for Linear Transportation Systems

Water quality improvement, constituent mass transport mitigation, and hydraulic performance of vegetated roadsides were evaluated over 16 storm events for two vegetated roadside strips along Lorton Road, Fairfax County, Virginia. Automated, flow-weighted sampling practices were employed to develop composite samples and event mean concentrations representative of an entire storm event. Lorton Road and two vegetated roadside strips were monitored for flow rate and volume to determine hydraulic performance, as well as thermal monitoring of the runoff to determine thermal load mitigation. Collected samples were analyzed for 13 water quality constituents: total suspended solids, total nitrogen, nitrates, phosphate, oil and grease, chemical oxygen demand, total coliform bacteria, E. coli, cadmium, chromium, copper, lead, and zinc. Varying vegetation management practices were employed at each vegetated strip to determine the impact of vegetation management on vegetated roadside performance. The managed and unmanaged vegetated strips achieved a mean peak flow reduction of 76.3% and 89.5%, respectively, while achieving a mean total flow reduction of 80.7% and 87.3%, respectively. The relatively high degree of stormwater infiltration allowed for moderate to high mass loading mitigation for each of the 13 water quality constituents monitored. A Sign test analysis of the constituent mass load data revealed that the effluent of both vegetated strips were statistically lower than the Lorton Road runoff for all 13 constituents and both hydraulic parameters. Thermal load was substantially reduced in both the managed and unmanaged vegetated strip effluent. The unmanaged vegetated strip effluent had statistically lower peak flows and mass loads of total nitrogen, phosphate, copper, and zinc compared to the managed vegetated strip.