| Summary: | 碩士 === 國立臺灣大學 === 森林學研究所 === 91 === A forest watershed has water resources conservation utility and runoff regulation which result from the effect of interception, evapotranspiration, infiltration and storage. It plays an important role in hydrologic circulation. This study tries to define pre-anhyetism duration and minimum rainfall that influences the base flow of the catchment. The rainfall and runoff data of NO.4 and NO.5 experimental watershed in Lien-Hua-Chi had been collected hourly since 1990~1994.In this study, we use Barnes formula to analyze the recession curve of hydrographs influenced by effective precipitation. The purpose of this study is trying to find out the correlation between recession constant and rainfall duration. We also investigated the effect of physiographic factors such as vegetation cover , geographic factors and watershed area. This study would help to understand the hydrograph of forest watershed reacts on rainfall event and would stress the importance of forest watershed on hydrologic cycle.
The results are summarizes as follows :
1. Rainfall properties has great effect on surface runoff . The status of partial un-saturated soil would influence interflow, and rainfall also influences interflow when total rainfall is heavy. Base flow is mainly related to geographic factors, and the coefficient of base flow can represent geographic conditions of watersheds.
2. If watershed area is too small, the effect of rainfall and runoff will be more sensible. Hence we need to consider time of concentration while analyzing hydrologic duration scale.
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