Groundwater flow analyses in Japan; Part 1 : Groundwater flow analyses in central Japan

Yanagizawa, Koichi; Imai, Hisashi; not registered; Wakamatsu, Hisanori; Umeda, Koji

Groundwater flow was analysed in the two areas of different scale situated in central Japan, in order to estimate hydrological condition existing at the deep underground in Japan. For the analysis in the Central Japan area (300 500km 10km deep), a hydrogeological model (a model expressing distribution of hydraulic conductivity) was built up with data from literature published so far. The model in the Tono area (8 7km 3km deep) which is a part of the Central Japan area, a hydrogeological model was built up with field data from the area studied. Based on these models, steady state three-dimensional groundwater flow under a saturated-unsaturated condition was calculated by means of FEM. The results are as follows: (1)In the Central Japan area, distribution of piezometric head harmonizes with topography in the area. (2)In the Tono area, distribution of piezometric head in the sub-surface part is governed by local topography, while that in the deeper part is governed by underlying regional topography. (3)In both areas, vertical variation of piezometric head is rather small without the shallow part, which indicates hydrostatic distribution. (4)Hydraulic gradient is less than 0.04 in the most part below GL-500m in both areas. (5)The results of the analysis in the Central Japan area show that types of distribution of hydraulic conductivity below EL-3,000m, of relationship between saturation ratio and pressure head, and of lateral boundary condition, do not remarkably affect the flow situation.