Averaging Process of Runoff Characteristics within Small Watersheds

流域内的径流现象是地质和水力性质差异很大的不同区域内的水流特征的平均过程的结果。本研究项目旨在研究小流域径流特征的平均过程，并与地表、中间带和地下含水层的流动过程的物理阶段相联系。为此，在两个试验流域观测了降水、土壤湿度、河流流量和地下水位波动等水文量。根据实测数据，讨论了平均过程。通过本项目所获得的结果总结如下：<i>)由于地质条件的不同，地下水位的局部波动具有很大的多样性。通过统计分析，讨论了地下水动态的时间和空间尺度。用<(delta)^(18)> o -氧示踪剂澄清了小流域内雨水的流动路径。因此，即使是直接径流成分也可能主要由流经次表层的径流成分提供。这些结果已应用于讨论更大流域和城市地区的降雨径流过程。然后，对实际流域径流过程的平均过程或集总尺度有了一些新的认识。

The runoff phenomena in a watershed appear as the results of the averaging process of the flow charactersitics within various regions with wide diversities in geological and hydraulic properties. This research project intends to investigate the averaging process of runoff characteristics within a small watershed in connection with the physical phases of flow process in the ground surface, intermediate zone and also ground water aquifer.For this purpose the hydrological amounts such as rainfall, soil moisture, river discharge and ground water level fluctuations etc have been observed in the two Test Basins. Based on the observed data, the averaging processes have been discussed. The results obtained through this project are summarized as follows.<i> ) The local fluctuations of ground water level have great diversity due to the geological conditions. The time and spatial scales of ground water behaviours have been also discussed through the statistical analyses.<ii> ) The flow pathes of rainfall-water within a small watershed have been clarified by means of the <(delta)^(18)> O-Oxyzen-tracer. It is then suggested that even the direct runoff component may be supplied mainly by the flow component through the sub-surface region.<iii> ) These results have been applied to discuss the rainfall-runoff process in rahter greater watersheds and also the urban region. Then several knowledges have been newly derived with respect to the averaging process or lumping scales of runoff processes within actual watersheds.