Application of runoff coefficient and rainfall-intensity-ratio to analyze the relationship between storm patterns and flood responses

Abstract. The analysis of the effects of storms on floods is essential for designing hydraulic structures and flood plains. Observations of the flow time series for the various catchment sizes are needed to understand the effects on floods, but it is not easy to obtain these datasets because most stream channels are ungauged. Hence, a reasonable method for generating the flow time series for the ungauged catchments is needed to secure the datasets. A quantitative analysis for investigating the relationship between the natural storm patterns, the peak flows, the volumes of floods, and their durations for the various catchment sizes is also needed. This study suggests a method to investigate quantitatively the relationship between storms and floods using datasets generated for the ungauged catchments. The relationship between the runoff coefficients and the rainfall-intensity-ratios with respect to catchment sizes for the dependent catchments showed that the events can be separated into four physically reasonable types using the pattern of storms and flood responses. This indicates that the relationship between the pattern of storms and flood responses for any event in terms of dependent catchments can be analyzed using plots of runoff coefficients and rainfall-intensity-ratios versus the catchment size. There are correlations between the runoff coefficients and the rainfall-intensity-ratios for the independent catchments, but these correlations have no relationship with the four types of events from the dependent catchments.