Fluctuations of Ground Water Levels in Relations to Precipitation, Soil Moisture and Stream Level

Abstract

In this paper the authors deal with the fluctuations of un-confined ground water levels in relations to precipitation, soil moisture and stream fluctuation in the dry field on R. Tone alluvialfan, Saitama Prefecture.Rapid rise of ground water levels is caused by supply of gravitational water which is excess water over the field capacity of soil (a part of precipitation this case), then successive gradual subsidence of them with effluent to streams is observed. By defining the field capacity of soil and evapotranspiration from land surface in each day, the quantity of gravitational water can be estimated. In the studied area, the regularity between the rise of ground water levels and the quantity of gravitational water can be recognized, therefore from the ratio of them the effective porosity of the water bearing layer (gravel) is obtained as 15 per cent.The fluctuation of stream levels in a period of a few days influences the ground water table in wells only adjacent to flooding streams. Though in a alluvial fan with conct to streams, the fluctuation of ground water level is governed greatly by precipitation- and a little by stream fluctuation in a whole area.