Geosphere stability project, 5; Estimation of groundwater recharge rate in consideration of long-term changes in surface hydrological environment

Takeuchi, Ryuji  ; Onoe, Hironori ; Yasue, Kenichi

In geological disposal for high-level radioactive waste, time scale for assessment is equal to or more than several hundreds of thousand years. During this time, the surface hydrological environment might change. Especially, changes of precipitation, evapotranspiration and runoff volume might cause a change of groundwater recharge rate (GRR), which is upper boundary condition of groundwater flow for deep underground. This study shows the method to estimate GRR considering the influence of changes for climate condition and landform condition as an example in Tono area. The GRRs of 0.45 Ma are estimated 118% to 237% of the current GRR, and the GRRs of 0.14 Ma are estimated 81% to 196% of the current GRR. In the result of current topography in the glacial period, the recharge rate is estimated 58% to 72% of the current GRR. However it's not possible to estimate the runoff volume based on the topography of 1.0 Ma, which is estimated poor undulations and flat terrains.