Mapping Groundwater Discharge Along Lake Margins Using Satellite And UAV Thermal Imagery

Effective watershed management decisions depend on understanding groundwater-surface water interactions. Traditional hydrogeological investigations are invasive, time-consuming, and expensive; therefore, regions that lack accessibility or agency funding need other ways of evaluating groundwater-lake interactions. Heat has long been known to be an effective groundwater tracer. Groundwater is insulated from most solar radiation, and its temperature does not fluctuate greatly from the annual average air temperature year-round in higher latitudes. In contrast, lakes are directly exposed to solar radiation, and water temperature fluctuates greatly both seasonally and diurnally. The winter and summer seasons produce the greatest contrast between groundwater and surface water temperatures. An empirical groundwater flow model of the water table near Detroit Lakes, Minnesota, was created using digital elevation model data and GIS analysis tools. This model estimates the distribution of potential groundwater discharge zones for further investigation with thermal imagery. Thermal remote sensing data acquired by satellite (ASTER) are freely available, non-invasive, and may serve as an effective means to identify potential areal groundwater recharge and discharge. Higher resolution thermal data were collected by using a DJI Matrice 600 UAV fitted with a FLIR Zenmuse XT thermal imaging sensor, which provides a potentially fast, minimally invasive, and cost-effective method for identifying possible groundwater discharge points within waterbodies at regional scales. Results suggest that large, well-defined springs and seeps can be identified with UAS imagery, but that slower groundwater seepage in shoreline areas is obscured by land cover, weather conditions, emergent vegetation, sediment characteristics, and other factors. The large scale of imagery coupled with local thermal heterogeneity leads to limited information on groundwater discharge from satellite imagery