Empirical Formulas of Flood Peak Discharge Based on Variable Fuzzy Clustering in Small Mountainous Watersheds

Flash floods in mountainous watersheds are often caused by the rainstorm. They are different from regular floods by having a smaller timescale and a faster flowing front of water and debris. The storm flood in mountainous watersheds presents strong nonlinearity, and the related hydrological calculation remains one of the critical challenges for accurate flash flood forecasting, which is further constrained by the availability of local datasets. In this paper, we present the empirical formulas derived from the distributed unit hydrographs which are subtracted from the rainfall intensity and the spatial variation of terrain, land use and soil type within each watershed. By selecting 26 774 small mountainous watersheds in Gansu province as study sites, we utilize variable fuzzy clustering method to capture the variation of unit hydrographs, and the empirical formulas between the watershed characteristics and the peak discharge of unit hydrographs are obtained in each cluster. The results show that variable fuzzy clustering method performs well in the classification of the distributed unit hydrographs, the derived empirical formulas can produce reliable results on the calculation of flood peak discharge in small mountainous watersheds. Meanwhile, flood peak discharge is mainly affected by drainage area, main channel network length and corresponding longitudinal gradient, and the derived empirical formulas show wide application potential in the hydrological calculation of rainstorm in small mountainous watersheds, especially in ungauged basins. © 2019, Editorial Department of Advanced Engineering Sciences. All right reserved.