Analysis of Base Flow and Estimation of Droughty Discharge from Several Catchments in Relation to Land Use.

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In this research, the characteristics of base flow discharge (groundwater flow discharge) has been investigated in several experimental catchments, which are different in land use, to clarify the mechanism of groundwater runoff and estimate the droughty discharge, One of them is a grassland catchments in Shikoku Karst, and others are a developed farm land, an orchard and a forest catchment. The results are summarized as follows.(1) In a grassland catchment, the droughty, low and ordinary discharge are greater than those of other catchments because of much rainfall and geology. In other catchments which are in southern parts of Ehime prefecture, the droughty discharge are less than 0.5mm/day and much less when compared to the mean values of that in Japan.(2) The characteristics of direct runoff in each catchment has has been investigated to discuss the recharge to groundwater during storms. As results, the recharge rates (seepage rates from upper to groundwater) are estimated to be about 0.6mm/hr for the grassland cathcment and 0.2mm/hr for others. Substituting these values into equations which express the dynamics of base flow runoff, we could obtain close agreements between the calculated and observed groundwater discharge.(3) A long-term runoff analysis model has been developed to predict the droughty and low discharge from the farm land and forest catchment. Comparing the predicted discharges, it is concluded that evapotranspiration loss as well as runoff characteristics is very important when we discuss difference in droughty or low discharge in relation to land use of catchments.