阿蘇火山体における循環地下水の特性について

抄録

Volcanic drainage basins are generally the regions with the distinguished hydrological characteristics. This paper, proposes a hydrological model which sets recharging zone and discharging zone in the groundwater basin, taking the Aso caldera basin as research field.
First, the characteristics of recharging zone which is the main field of infiltration and recharging is described, and it is pointed out that the continuous processes from infiltration in recharging zone to discharge of groundwater in discharging zone are main processes in hydrologic cycle of volcanic drainage basin.
Then, the fact that in hydrologic cycle the chemical composition of groundwater is indicative of its origin and history gives some idea of a fact. For example, the calcium ion, which is in nature minor dissolved constituent in the groundwater of volcanic zone, increases as the materials for agriculture are supplied to the drainage area artificially. The variation of the concentration represents the rate of recharge, and the result is useful to know the actual condition of recharging in field. Since the concentration of anion species SO₄^2-shows also increasing trend with groundwater movement, the fact helps to classify the boundary of groundwater zone.
Next, the variation of groundwater storage is simulated by Sugawara's tank model for simulating daily discharge through the channel. And it is proved that the calculated results of groundwater level is comparable to the variation of real groundwater level. On hydrological balance of the basin, volumetric rate of flow through groundwater zone is estimated, as a results the actual condition of groundwater flow in hydrologic cycle of volcanic drainage basin is clarified.