COMPREHENSIVE GEOLOCATION OF PREFERENTIAL GROUNDWATER DISCHARGES USING HEAT TRACING TECHNIQUES (Invited Presentation)

Discharge of groundwater to surface water bodies is often highly preferential in space, so that a relatively small fraction of the sediment/water interface controls the transfer of heat, gas, and dissolved chemistry from aquifer to channel. Therefore, preferential discharges are not well captured by random and transect-based sampling regimes, particularly at large scales. Recent advances in spatially distributed temperature sensing techniques using remote thermal infrared and direct-contact fiber-optic methods allow comprehensive detection of preferential discharge zones. We show how radiometric infrared data collected with small drones along mountain streams can be used to pinpoint discharges in rugged terrain that are easy to miss with ground-based surveys. Handheld infrared data are more practically collected from watercraft along lowland rivers, guiding geochemical and age dating sampling over 10’s of km in “real time”, such that discharging groundwater can be tied to watershed-scale numerical models. However, remote sensing with thermal infrared cannot penetrate the water column, so submerged discharges may be missed. In cases where niche groundwater-based aquatic habitat characterization necessitates subsurface detail, fiber-optic cables can be deployed along the sediment-water interface to collect fine scale (e.g. 0.25 m) temperature patterns over space and time. We debut a new graphical user interface software that can be used to quickly process fiber-optic data by calculating various statics that may indicate discharge processes, and by automatically plotting data in map view, efficiently enabling geolocation. The combined advances in sensor technology and post-processing software are bringing reconnaissance-based heat tracing solidly into the applied surface water/groundwater exchange characterization toolkit.