INTEGRATING HYDRAULIC AND THERMAL TECHNIQUES TO EXAMINE FOCUSED GROUNDWATER DISCHARGE AT MULTIPLE SCALES

Focused groundwater discharge in unlithified sediments can result in soil piping, which promotes erosion of stream banks and beds. We have used a combination of techniques to examine spatial persistence and temporal variability in focused discharge along a first-order perennial stream, Little Bayou Creek, in the Gulf Coastal Plain of western Kentucky. Along a reach of ~ 300 m, we gauged baseflow at 3-5 month intervals by wading with a current meter and top-setting rods (September 1999 - May 2001 and October 2010 - February 2012) and by dye dilution (January 2011 - February 2012). Using a digital thermometer with a 1.2-m-long stainless-steel probe, we measured bed temperatures on a grid (at ~ 3-m by 1-m spacing) in August 2002, January 2011, and August 2011. We also used distributed fiber-optic temperature sensing (DTS) along the reach for 10 days in September-October 2011.

Baseflow measured by both wading and dye dilution typically increased from the upstream end to the downstream end of the reach, but not monotonically. Baseflow values tended to be greater during late spring and early summer than early winter. Temperature probing tended to corroborate visual observations of groundwater discharge. Locations of some springs have persisted within ~ 1-2 m during more than a decade, whereas other springs have disappeared or emerged over periods of months. Some, but not all, thermal anomalies delineated by temperature probing in August 2011 coincide with those evident 2 months later from DTS. Temperature probing suggests that the area of focused discharge is 3-6% of the study reach.