Analysis of pattern of recharge to the deep groundwater table

The deep phreatic groundwater level in the Beppu alluvial fan area presents a typical annual variation under the influence of the seasonal variation in rainfall, though the effect of each rainfall on it is not clear. The level also fluctuates due to the barometric pressure change, being different from shallow phreatic groundwater levels. These phenomena are analyzed in the present study by the theories of pressure propagation and infiltration through the thick unsaturated layer. The infiltration process of the rainfall is approximately described by the linear diffusion equation, which gives a reasonable relation between the rainfall at the ground surface and the recharge at the water table. In the course of the analysis, a method for the evaluation of some hydrological properties of the water-bearing layer is presented.