Adjustment Formula Development of Design Rainfall-Runoff Analysis Method by Natural Flow-Regional Frequency Analysis

Abstract

In this study, flood quantiles were evaluated at ungauged watershed by adjusting the flood quantiles from the design rainfall - runoff analysis (DRRA) method. As a result of comparing the flood frequency analysis (FFA) and design rainfall - runoff analysis, it was found that the flood quantiles estimated by the design rainfall - runoff analysis method were over estimated by 52%. In addition, a practical method was suggested to make an flood index using natural flows to apply the regional frequency analysis (RFA) to ungauged watersdes. Condisering the relationships among DRRA, FFA, and RFA, we derived an adjusting formula that can be applied to estimate flood quantiles at ungauged watersheds. We also employed Leave-One-Out Cross-Validation and skill score to verify the method proposed in this study. As a result, the proposed model increased the accuracy by 23.2% compared to the existing design rainfall - runoff analysis method.