CHARACTERIZING SEDIMENT TRANSPORT DURING STORM FLOW THROUGH AN INNER BLUEGRASS KARST AQUIFER

The characterization of sediment transport through a karst aquifer can reveal possible vectors for contaminant transport as well as sediment provenance (i.e. urban vs. agricultural). We are characterizing sediment transport in the Blue Hole karst groundwater basin in Woodford County, Kentucky. Blue Hole spring emerges ~ 1 km west of downtown Versailles. Previous dye traces have shown that sources for recharge include Big Spring (a swallet in downtown Versailles) and a sinkhole located on a farm ~ 1 km southeast of downtown. To characterize discharge at Blue Hole spring, stream stage and temperature are monitored every 15 minutes with a thermistor and pressure transducer in a stilling well connected to a datalogger. Discharge is measured weekly by wading with a flow meter and top-setting rod. Specific conductance and pH are also measured weekly. During low flow, sediment from Big Spring, the farm sinkhole, and Blue Hole spring was collected for analyses of grain size, mineralogy, and particulate organic carbon for comparison with the suspended sediment. During a recent high-flow event, a quantitative dye trace using Rhodamine WT was conducted from Big Spring to Blue Hole spring to observe dye travel time during storm flow. Flow rates vary from ~ 1 cfs at base flow to ~ 30 cfs at storm flow. Specific conductance ranges from ~ 0.640 – 0.745 mS/cm at base flow to ~ 0.400 – 0.500 mS/cm during storm flow, which is consistent with displacement of pre-event water by rainfall. Pending work includes grain size and particulate organic carbon (POC) analyses on bed sediments, characterization of bed sediment mineralogy by X-ray diffraction, calculating the percentage and mass of dye recovered from the quantitative trace, and correlating stream stage to discharge using a rating curve. During a storm, total suspended sediment concentration, grain size, mineralogy, POC, specific conductance, pH, spring temperature, and discharge will be measured at Blue Hole spring. A future qualitative dye trace will determine if the farm sinkhole discharges directly to Blue Hole or Big Spring. Pending results of the qualitative trace from the farm sinkhole, we will conduct simultaneous traces from Big Spring and the farm sinkhole during storm flow to characterize suspended sediment as urban or agricultural in origin.