Abstract
Groundwater temperature is one of the most effective environmental tracers. Groundwater temperatures are lower than average in recharge areas, and higher than average in discharge areas. Using this principle, groundwater flow around the Bibi River in Hokkaido was clarified as follows: (a) The upper Toasa River basin except for the Umaoi Hills belongs to the Bibi River groundwater basin. (b) The groundwater divide between the Bibi River and the Toasa River runs across the middle of the Toasa River Basin. (c) The western boundary of the Bibi groundwater basin locates at the 90m volcanic ash plateau, and there is very little leakage from Lake Shikotsu into the Bibi River groundwater basin. (d) The divide in the groundwater found from groundwater temperature is consistent with that estimated from the thermal advection-dispersion analyses by means of the finite element method, the groundwater table and the water balance.
Recently, groundwater temperature has found use as an index of global warming. Such an increase was found in the study area, owing to urbanization. Additionally, further development projects will require assessments on the groundwater flow system, and this study suggests that the change in groundwater temperature is an effective tool for these assessments.
