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

本研究以四国喀斯特草原集水区、发达农田、果园和森林集水区为研究对象，对不同土地利用方式的集水区基底流（地下水流量）特征进行了研究，阐明了地下水径流机制，并对干旱流量进行了估算。结果总结如下：(1)草原集水区由于降水多、地质条件好，旱涝、低流量和普通流量大于其他集水区。爱远县南部其他集水区的干旱流量均小于0.5mm/d，远低于日本的平均值。(2)研究了各流域直接径流的特征，探讨了暴雨对地下水的补给。结果表明，草地流域的补给速率（从上层到地下水的渗流速率）约为0.6mm/hr，其他流域约为0.2mm/hr。将这些值代入表示基流径流动力学的方程中，我们可以得到地下水流量的计算值与观测值之间的密切吻合。(3)建立了长期径流分析模型，用于农田和森林流域干旱低流量的预测。通过对预测流量的比较，得出蒸散损失和径流特征在讨论与流域土地利用有关的干旱或低流量差异时非常重要的结论。

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.