Detecting groundwater discharge to a small river channel using ground-based thermal infrared imagery and radon-222

Understanding river–groundwater interaction is important for assessing the hydrologic, ecologic and biogeochemical processes in the hyporheic zones. Various field methodologies exist to evaluate their interaction, such as direct seepage-metre measurements (Rosenberry, 2008) or streambed temperature profiling (Anibas et al., 2018). Moreover, a number of different environmental tracers (Cook, 2013) are used in this context, for example radon (222Rn), which is generated in the subsurface from uranium-series isotopes and its concentration decreases due to fast decay (half-life of 3.8 days) and gas exchange with the atmosphere.