Fluctuations of the Level of Groundwater Table as Related to the Water Balance in Unsaturated Moist Zone of the Soil

Abstract

The relations between the water balance in unsaturated moist zone and the change in the level of groundwater table were investigated on the basis of the observation data obtained on the level grassland. The results are as follows :
(1) When fine weather lasted, the deficit of total soil moisture in unsaturated zone below that which was expected under the hydrologically equipotential condition was shown to increase linearly with increasing water table depth. During the growing season, the upward moisture transfer from saturated zone increases with increasing soil moisture deficit, and it finally approaches a constant value satisfying the demand of consumptive use of vegetation.
(2) It was observed that the soil moisture deficit is filled up by infiltrating water from each rainfall and the excess water is recharged to the groundwater. This process is rapidly completed within fairly shorter duration than the discharging process by evapotranspiration, being promoted by the increasing permeability of unsaturated zone.
(3) The larger value of storage coefficient was obtained for the discharging process than for the recharging one. To explain this fact, the hydrological meaning of storage coefficient of unconfined aquifer was discussed in relation to the conditions of the soil moisture distribution above the groundwater table.