A Study on groundwater infiltration in the Horonobe area, northern Hokkaido, Japan

Yokota, Hideharu; Yamamoto, Yoichi; Maekawa, Keisuke  ; Hara, Minoru*

It is important for assessing the safety of geological disposal of high-level radioactive waste to understand groundwater flow as the driving force of mass transport. In the groundwater-flow simulation, hydraulic boundary conditions are required, including groundwater recharge rates. However, infiltration of water from the surface is difficult to clarify in detail because water near the surface is sensitive to external influence such as climatic variations. In the Horonobe area of northern Hokkaido, the Japan Atomic Energy Agency has been carrying out various hydrological observations to estimate the recharge rate. In the Horonobe area, subsurface temperature and soil moisture content have been observed at HGW-1 site and Hokushin Meteorological Station. These results have revealed the groundwater infiltration and recharge occurring throughout year, the shallow groundwater-infiltration velocity depending on the depth, and the position of Zero Flux Plane. In the future, it is necessary to quantitatively assess the shallow groundwater infiltration and recharge rate, the intermediate runoff, and the evapotranspiration based on the observed data of the weighing lysimeter, the tensiometer, and so on.