Abstract
Groundwater in the granite region is probably kept partly in the weathering crust ("Masa" zone) and partly in and near faults or sheared zones after going along joints and fissures innumerably developed in the granitic rock body. In the case of no artificial effect, groundwater flow will be controlled by the potential energy. Therefore, the head potential at a certain point under groundsurface is given by the linear function of gravity accelaration. The geologic cross section of the north eastern district of Mt. Otakine, Central Abukuma mountains where mostly composed of granitic rocks was simplified to get the head potential at everypoint within the section by ADI method, and equipotential lines and flow lines were drawn. It is assumed that both sides and bottom of the model are impermeable, and groundwater table with the constant level coinsides with the topographic plane. Calculation was practiced on five models i.e. the homogeneous one layer model (for both the actual topographic plane and the summit level), fault model in which permeability within the fault zones is lower than that of the adjacent area, rock body model in which permeability differ with each body and the weathering grade model in which permeability differs in according to the weathering grade, and discussed how the groundwater flow system is affected by topographic plane, fault, rock body distribution and weathering grade distribution in comparison with flow net patterns drawn on each model. Further, the significance of the summit level model was referred. Namely, it is the model which changed one of the exterior boundary conditions of the actual topographic plane model. It is necessary to try simulations which changed the exterior and interior boundary conditions for the problems which necessitate to take account of the change of topographic and geologic conditions.
