The flow mechanism of groundwater in granite areas, especially that of deep cyclic water, was elucidated in our earlier paper by conducting geological and topographical analyses of the relationship between fracuture systems and their permeability. Futhermore, fracture systems were classified into six series (A to F) based upon small fault and fracture analyses. The A1, A2, D and F1 series are associated with the type of faults characterized by low permeability and the C1, C2 and F2 with those typified by high permeability. The quality of groundwater is also indicative of the regional flow system because of a relatively high sodium and bicarbonate concentrations and high pH value of the water.
To verify these earlier results, water catchment boring by the collectorwell method, analysis of fractures in recovered core samples, and analysis of the quality of water were conducted. The C2 type faults, striking ENE and dipping southward, are interpreted to act as impermeable barriers. The quality of waters in this type of faults suggests that there is a regional flow system of waters, because these waters are characterized by a relatively high temperature, high sodium and bicarbonate concentrations and high pH value. The total discharge of groundwaters into a bore hole from the C2 type faults amounted to 1800 m3/day. Such a large amount of discahrge is explainable if groundwater in the fault system is under a confined condition.
The geological profile of faults and rock body was analyzed in detail by employing the electrical prospecting method with dipole-dipole array. The method of research as described here has a wide applicability to groundwater analyses in other areas whose foundation is a granite rock body. The stable supply of water is obtainable in such a hard-rock area where hydrogeological conditions similar to those observed in this study are widely developed.
In the southern Abukuma plaleau, there are many springs whose presence suggests the existence of a regional groundwater flow system. These springs are situated at a site lying lower in altitude than the surrounding area. Such a finding gives a possibility that a sufficient supply of water can be exploited from this regional flow system in future. The present study clearly demonstrates that a combined analytical method of aerial photograph interpretation, field observation, electric prospecting and water quality analysis provides a reliable information deciphering the flow of groundwater in a block mass.
