Monitoring and Assessment of Sediment Basins at Highway Construction Sites

Sediment basins with outlet orifice skimmers are one of forty erosion prevention and sediment control (EPSC) devices that the Tennessee Department of Transportation (TDOT) utilizes to meet regulatory runoff quality permitting requirements at their highway construction sites. Regulations set in place by the US Environmental Protection Agency (US EPA) and Tennessee Department of Environment and Conservation (TDEC) require performance standards that often affect TDOT’s existing design criteria for stormwater control measures (SCM). TDOT has a need to update their manual’s engineering design criteria for sediment basins based on new regulations and extended data sets, including field verification.The goal of this thesis is to begin performance analysis of current TDOT design criteria for sediment basins, basing the basin sizes on Neff and Schwartz’s (2013) modeling efforts and other basin attributes on TDOT’s Drainage Manual. This study monitored the influent and effluent of two separate highway sites with varying catchment slopes, soil types, and drainage areas. The monitoring devices used at each site were chosen for the locational constraints; the following were collected for six and five collection events: inlet and outlet water samples, flume sediment deposits, weather data, and volumetric flow data. The field data was analyzed to assess basin performance and characterize particle size variability.Results showed that the Morgan County and Knox County basins performed an average of 76.8% and 97.4% mass sediment reduction between the influent and effluent, respectively. There was a large difference in contributing sediment masses, Morgan County had an average inlet mass of 1.93 x 10³ kilograms of soil, where Knox County had an average of 1.60 x 10^-3 kilograms. RUSLE2 modeled sediment yield for Morgan County resulted in 19.0 t/ac compared to a field value of 22.0 t/ac; Knox County resulted in 3.8 t/ac compared to field value of 0.13 t/ac. Findings emphasize that sediment basins are not going to be the most cost efficient and appropriate BMP at every highway construction site, but when they are, it is critical that they are designed appropriately and implemented with care, taking into account alternative design changes when needed.