Thermal imaging survey for characterizing bedrock groundwater discharge: comparison between sedimentary and volcanic catchments

Abstract

Groundwater discharge from bedrock varies depending on catchment conditions, particularly geology. In this study, we demonstrated the usefulness of a thermal infrared (TIR) camera for understanding the differences between two Mesozoic–Paleogene sedimentary catchments and two Quaternary volcanic catchments in Hokkaido, Japan. The TIR video survey effectively identified bedrock springs because of their low summer temperatures. Discharge rate of the cold bedrock springs was <0.005 L/s in the sedimentary catchments, whereas it exceeded 1 L/s in the volcanic catchments. However, the densities of bedrock springs were similar; they existed one point every 0.08–0.4 and 0.09–0.1 km in the sedimentary and volcanic catchments, respectively. Furthermore, differences in the concentrations of weathering-derived solutes from stream water were more than twice (up to 15 times) for some bedrock springs in the sedimentary catchments, whereas they were negligible for all springs in the volcanic catchments. These findings suggest that contributions from bedrock springs cannot be ignored even in sedimentary catchments with low bedrock permeability, especially when studying water chemistry. Spring water surveys using a TIR camera represents a fast and labor-saving method for characterizing bedrock groundwater discharge in catchments.