Groundwater flow analyses in Japan; Part2: A Case study in northeast Japan

not registered  ; Umeda, Koji; Koide, Kaoru; Imai, Hisashi*; Yanagizawa, Koichi

An extensive study program has been carried out by PNC to estimate hydrogeological characteristics of deep underground in Japan. As a part of this program, groundwater flow analyses in Northeast Japan were conducted. For the analyses of Northeast Japan area (300 500km 10 km deep), a hydrogeological model expressing topography, distribution of hydraulic conductivity was developed with information available from open literature. By the use of this model, steady state three-dimensional groundwater flow under a saturated-unsaturated condition was calculated by means of finite element method. The results are as follows : (1)Distribution of piezometric head corresponds with topography in the study area. (2)Piezometric head distribution is hydrostatic below E,L. -1000 m in thc study area. (3)Hydraulic gradient in the study area is less than 0.04 below E.L. -500 m. (4)Analytical seepage points appear in principal catchment areas. (5)Difference of boundary conditions such as permeable or impermeable at the shore side of this model does not affect the results of the analyses. (6)In case of setting higher hydraulic conductivity to Holocene and Pleistocene scdimentary rocks than that to Pliocene sedimentary rocks, the results of the analysis are as same as the inverse case while discharge rate decreases.