10:45 AM - 11:05 AM
[ACG48-06] Mapping and sampling spring water using thermal video: a simple characterization of mountain-scale groundwater discharge
★Invited Papers
Keywords:Thermal image, Spring water, Water temperature, Water chemistry, Groundwater discharge
In mountainous areas, many insights into runoff mechanisms of water and solutes have been obtained from observations at the hillslope or small catchment scale. On the other hand, water that percolates into deep parts of the mountains, such as within the bedrock, affects the downstream discharge and chemistry without contributing runoff from small catchments. Thus, groundwater dynamics cannot be revealed only by observations within small headwater catchments. The surveying of spring water along streams is a fast and labor-saving method that does not require observation wells, and may be effective for simple understanding of groundwater dynamics on a mountain scale. Springs along mountain streams are often difficult to detect with the naked eye because of their gradual seepage. However, springs from deep depths can be easily identified by using a thermal infrared (TIR) camera in summer or winter because of their stable water temperature throughout the year, although aerial remote sensing is difficult in mountain streams where the channel is covered by riparian forest. Therefore, we have developed a real-time monitoring and postprocessing method of ground-based TIR video for determining groundwater discharge sampling points and mapping the surface water temperature. In this presentation, we present the results of a one-day summer survey using this method in five watersheds in Hokkaido, Japan, to estimate the characteristics of groundwater discharge.
Our method could map not only the locations of cold springs in summer but also the spatial heterogeneity of the stream temperature associated with groundwater inputs at a watershed underlain by Holocene volcanic ash. Comparison of two Mesozoic–Paleogene sedimentary watersheds and two Quaternary volcanic watersheds showed that discharge rate of the cold bedrock springs was <0.005 L/s at the sedimentary sites, whereas it exceeded 1 L/s at the volcanic sites. However, the densities of bedrock springs were similar irrespective of the geology. 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 watersheds, whereas they were negligible for all springs in the volcanic watersheds. These findings suggest that contributions from bedrock springs cannot be ignored even in sedimentary watersheds with low bedrock permeability, especially when studying water chemistry. Mapping and sampling of spring water using a TIR video was effective as a simple method for characterizing groundwater discharge on a mountain scale.
Our method could map not only the locations of cold springs in summer but also the spatial heterogeneity of the stream temperature associated with groundwater inputs at a watershed underlain by Holocene volcanic ash. Comparison of two Mesozoic–Paleogene sedimentary watersheds and two Quaternary volcanic watersheds showed that discharge rate of the cold bedrock springs was <0.005 L/s at the sedimentary sites, whereas it exceeded 1 L/s at the volcanic sites. However, the densities of bedrock springs were similar irrespective of the geology. 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 watersheds, whereas they were negligible for all springs in the volcanic watersheds. These findings suggest that contributions from bedrock springs cannot be ignored even in sedimentary watersheds with low bedrock permeability, especially when studying water chemistry. Mapping and sampling of spring water using a TIR video was effective as a simple method for characterizing groundwater discharge on a mountain scale.