Seasonal Change of Underground Temperature and Its Geothermal Utilization in Gifu City, Japan

Abstract

Seasonal change of underground temperature has been measured in the alluvial fan of the Nagara River, central Japan. Underground temperature of the most boreholes are fluctuated not only near-surface but also in the aquifers. The maximum differences of seasonal temperature of each borehole basically become larger toward the apex of the fan. The maximum temperature of each borehole is generally not in summer season, and this is not coincident with the temperature change of river water. These suggest that the groundwater in the alluvial fan recharge from the river water, and that the seasonal change of the underground temperature results from the lateral flow of the recharged groundwater. In the area where underground temperature become lower in the summer and higher in the winter, this seasonal change of underground temperature would greatly improve the efficiency of the geothermal heat pumps.