Date of Award
Master of Science
Jon M. Hathaway
Qiang He, John S. Schwartz
Across the country, the impacts of stormwater runoff are being managed through the National Pollutant Discharge Elimination System intended to ensure the licensee makes advances toward more environmentally-sensitive management strategies. Departments of Transportation fall within this regulatory framework, being tasked with reducing the volume of runoff as well as pollutant concentrations leaving their catchments. Stormwater runoff along highways contains pollutants which may be detrimental to local surface waters. However, the highway environment also has substantial amounts of green space. There are questions as to how much runoff reduction and pollution abatement are provided by these spaces, as their function will have a dramatic impact on stormwater management strategies. A highway median swale, located on Asheville Highway, Knoxville, Tennessee, was monitored over an 11-month period. The total catchment was 1.58 acres, with 0.64 acres of roadway draining to 0.94 acres of vegetated median. Runoff volume, rainfall, and water quality data were monitored. The results of this study indicated that 87.2% of runoff volume was reduced by the swale. Conversely, water quality results were variable. While 91.0% of total suspended solids were reduced, the results for nutrients and chloride were variable. Chloride and phosphate were exported while ammonium and nitrite-nitrate were reduced. The swale was also found to export heavy metals: copper, lead, and zinc. The reason for this variable performance may be related to the low pollutant concentrations entering the swale, or the fact that the inlet flume only captured a portion of the runoff entering the system. This may have resulted in a poor representation of the inflows to the system. The Source Loading and Management Model for Windows (WinSLAMM) was used to model the swale’s runoff reduction performance. To calibrate the model, adjustments were made to measured onsite infiltration rates. Adjusting the infiltration rates had considerable effects on the model’s output, and the calibrated model was only 28.4% different from the measured runoff volume. WinSLAMM proved to be a beneficial resource to assess green space performance; however, future studies are needed to determine which model inputs affect performance the most, which can be estimated, and which require on-site measurements.
Young, Bailee, "Examining the Runoff Reduction Potential of Highway Swales. " Master's Thesis, University of Tennessee, 2017.