37-5 Use of Different Thermal Techniques for Delineating Groundwater Discharge to a Coastal Plain Stream over Multiple Decades

Session: Innovations in Research of Groundwater-Surface Water Interactions over Multiple Spatio-Temporal Scales

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Abstract:

At depths > ~ 10–25 m below land surface, groundwater temperature tends to be relatively constant, making it a useful tracer of discharge to streams, whose temperatures fluctuate diurnally and seasonally. Since 1996, we have measured temperature to corroborate and infer discharge to Little Bayou Creek, a first-order stream in the Gulf Coastal Plain of western Kentucky. Groundwater discharges from the semi-confined Regional Gravel Aquifer (RGA) via springs and seeps along the lower ~ 2.5 km of the creek, which has been channelized. Groundwater temperature in the study area is ~ 14–15 °C; stream temperatures range from < 1 °C in winter to > 25 °C in summer.

We used different techniques to assess how discharge varies over various spatial (meter to kilometer) and temporal (storm event, seasonal, annual, and decadal) scales. In August 2002, January 2011, and August 2011, we measured streambed temperatures along the uppermost ~ 300 m of the channelized reach, using a 1.2-m stainless-steel probe and digital thermometer on a grid at 0.30-m transverse and 3.0-m longitudinal spacings. On July 3–10, 2024, we used fiber-optic distributed temperature sensing (FO-DTS) along the upper ~ 950 m of the channelized reach. We flew drone-based thermal cameras (DBTC) along the entire channelized reach at heights of ~ 60 m (above the tree canopy, during leaf-off conditions) on February 29 – March 1, 2024, and ~ 1.5 – 9 m (below the canopy, during leaf-on conditions) on August 6–7, 2024.

Along the uppermost ~ 300 m of the channelized reach, discharge is focused through heterogeneities in clayey sediments overlying the RGA. Discharge is more diffuse downstream where the channel is incised into the RGA. Locations of some springs and seeps have persisted, while others have evolved by erosion and sedimentation (e.g., piping and bank collapse). Flow of springs and seeps fluctuated seasonally, but their temperatures were relatively constant, apart from temporary perturbations associated with gradient reversals (i.e., bank storage). DBTC imaging identified new and previously known discharge locations. Below-canopy temperature ranges were similar to ground-based measurements; above-canopy surveys identified temperature contrasts rather than absolute temperature values. In deeper pools, FO-DTS identified some anomalies that were not visible or detectable by DBTC. Compared to DBTC, temperature probing and FO-DTS are more time- and labor-intensive.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7547

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