THERMAL PROFILING OF FOCUSED GROUNDWATER DISCHARGE ALONG A CHANNELIZED STREAM IN WESTERN KENTUCKY

In general, groundwater temperature remains constant year-round while stream temperature fluctuates seasonally. We have utilized temperature differences in summer and in winter to delineate sites of groundwater discharge within the bed of Little Bayou Creek, a first-order perennial stream in western Kentucky. Multiple bed and bank springs have been observed along a channelized reach ~ 300 m long. On January 3-8, 2011, we used a stainless-steel temperature probe with a digital thermometer on a grid at intervals of 10 ft (3 m) along the stream and 3 ft (0.9 m) across the stream. Using kriging interpolation in Surfer 9, quasi-3-D surface maps of temperature at the top of the stream bed and at total probe penetration depth were generated for each of three sub-reaches. Probe depth is positively correlated with temperature at 95% confidence level with r² coefficients of 0.64, 0.43, and 0.73 for each of the subreaches. Locations of springs were inferred and, in most cases, observed where temperatures were markedly (5 to 8 ^oC) above background. The standard deviation in temperature anomalies along the streambed and at the springs was 1.9 ^oC. In comparing streambed temperature anomalies from January 2011 with those observed during probing conducted August 8-12, 2002, we observed spatial shifts of a few meters in some locations. We are planning to repeat temperature probing during August 2011 and deploy fiber-optic distributed temperature sensing (DTS) equipment during August-September 2011. In particular, the DTS should enable us to examine groundwater discharge locations in finer detail (meter-scale resolution) for comparison with results of probing.