Thermal Imagery of Groundwater Seeps: Possibilities and Limitations

Abstract

Quantifying groundwater flow at seepage faces is crucial because seepage faces influence the hydroecology and water budgets of watersheds, lakes, rivers and oceans, and because measuring groundwater fluxes directly in aquifers is extremely difficult. Seepage faces provide a direct and measurable groundwater flux but there is no existing method to quantitatively image groundwater processes at this boundary. Our objective is to determine the possibilities and limitations of thermal imagery in quantifying groundwater discharge from discrete seeps. We developed a conceptual model of temperature below discrete seeps, observed 20 seeps spectacularly exposed in three dimensions at an unused limestone quarry and conducted field experiments to examine the role of diurnal changes and rock face heterogeneity on thermal imagery. The conceptual model suggests that convective air-water heat exchange driven by temperature differences is the dominant heat transfer mechanism. Thermal imagery is effective at locating and characterizing the flux of groundwater seeps. Areas of active groundwater flow and ice growth can be identified from thermal images in the winter, and seepage rates can be differentiated in the summer. However, the application of thermal imagery is limited by diverse factors including technical issues of image acquisition, diurnal changes in radiation and temperature, and rock face heterogeneity. Groundwater discharge rates could not be directly quantified from thermal imagery using our observations but our conceptual model and experiments suggest that thermal imagery could quantify groundwater discharge when there are large temperature differences, simple cliff faces, non-freezing conditions, and no solar radiation.

Quantifying thermal refugia connectivity by combining temperature modeling, distributed temperature sensing, and thermal infrared imaging

“…Thus, monitoring suggests that large diversions and return flows can create warm water conditions when active, but they may also recharge shallow aquifers, increase shallow groundwater contributions, and create pockets of cold water. Shallow subsurface contributions to Wabuska Drain may not occur when groundwater levels decline outside of irrigation season (Naranjo and Smith, 2016). The 300 m reaches with the greatest temperature ranges corresponded to locations of canal diversions, return flows, and groundwater seeps (Fig.…”

Improved Prediction of Management‐Relevant Groundwater Discharge Characteristics Throughout River Networks

“…TIR has been used to map groundwater discharge zones at both broad (Fullerton et al, 2015; Liu et al, 2016) and fine spatial scales (Hare et al, 2015; Harvey et al, 2019). Although TIR often locates discrete discharge zones at much finer resolution (meters to tens of meters) than the typical groundwater flow model cell (hundreds of meters), clusters of discharge zones are often observed with TIR and reflect larger scale underlying physical controls (Mundy et al, 2017). As a first step, discharge zone maps can be qualitatively and quantitatively compared to modeled patterns to assess model predictions.…”

Complexity of hydrogeologic regime around an ancient low‐angle thrust fault revealed by multidisciplinary field study

“…Thus, examining seeps can provide valuable information about the fracture networks and permeability of the rock mass, in addition to providing a minimum elevation of the water table. Detailed observations of frozen seeps in an abandoned quarry in a similar climate indicate that the seeps can freeze over in extreme cold events (<−20°C), but generally the groundwater inexorably flows onto the cliff face, slowly increasing the volume of the frozen seep when air temperatures are below 0°C (Mundy et al ., submitted). Therefore, the cumulative volume of the frozen seep after a period of freezing temperatures is a time‐integrated average of the groundwater flow from that seep.…”