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地区的草地集水区为研究对象，以农田、果园、森林集水区为研究对象，通过对不同土地利用方式的集水区基流（地下水流）特征的研究，探讨了地下水径流的形成机理，并估算了干旱径流量。结果总结如下。(1)草原集水区由于降雨量大、地质条件特殊，其枯水、枯水和常流量均大于其它集水区。在爱媛县南部的其他集水区，干旱流量小于0.5mm/天，与日本的平均值相比，少得多。(2)研究了各流域的直接径流特征，探讨了暴雨对地下水的补给。结果表明，草地径流的补给速率（从上层向地下水的渗漏速率）约为0.6mm/hr，其它地区约为0.2mm/hr。将这些值代入表达基流径流动态的方程中，我们可以得到计算的地下水流量与观测的地下水流量之间的密切协议。(3)建立了一个长期径流分析模型，用于预测农田和森林集水区的干旱和枯水径流。比较预测的流量，得出的结论是，蒸散损失以及径流特性是非常重要的，当我们讨论干旱或低流量的差异与土地利用的集水区。

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.