Recently, a lot of researchers have been interested in `scale issues' in the research area of hydrology. 'Scale issues' include various questions to be solved, including lots of issues regarding runoff process. For example, the relationships between some hydrological processes which control runoff process and catchment scale have been studied. Recently, some researchers have tried to clarify the runoff system using mean annual flood (MAF) per unit area and coefficient of variation (CV) of annual flood.In this study, analysis of runoff process by CV and MAF was carried out. First, CV/MAF versus catchment area were plotted for 285 catchments in Japan. Secondly, Eagleson's method was used in order to calculate MAF and CV. The aim of this study is to develop model for numerical analysis of runoff, which will be combined to analysis by the data of 285 catchments. The model used in this study could estimate MAF qualitatively, but further consideration is necessary in regard to CV.

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