Ground‐based thermal imaging of groundwater flow processes at the seepage face

There is no existing method to quantitatively image groundwater processes along a seepage face. Thus, it is often difficult to quantify the magnitude and spatial variability of groundwater flux. The objective of this work is to assess the use of ground‐based thermal remote sensing for fine‐scale mapping of groundwater discharge and for locating the water table position along a stream bank seepage face. Seepage faces are poorly understood and often neglected in regional hydrologic studies though they likely exert significant influence on hydrologic and ecologic processes in riparian zones. Although the importance of riparian areas is broadly recognized, our ability to quantify hydrologic, ecologic and biogeochemical processes and ecosystem services is hampered by our inability to characterize spatially variable processes such as groundwater discharge. This work employs a new, transferable, non‐invasive method that uses heat as a natural tracer to image spatially‐variable groundwater flow processes and distinguish between focused and diffuse groundwater discharge to the surface. We report, for the first time, that thermal remote sensing of groundwater at the seepage face provides indirect imaging of both the saturated zone‐unsaturated zone transition and groundwater flux at the centimeter scale, offering insight into flow heterogeneity.