Flood frequency analysis for an ungauged Himalayan river basin using different methods: a case study of Modi Khola, Parbat, Nepal

Predicting flood discharges in the rivers of an ungauged basin is tedious because essential hydrological data is lacking. In mountainous countries like Nepal, the design of hydraulic structures in these steeply sloped rivers is of prime importance for flood control, as well as for electricity generation where hydraulic head is gained over short, steep reaches. This study illustrates a variety of approaches that can be used to perform flood frequency analysis of typical ungauged mountainous rivers, where discharge data are available from hydrologically similar catchments. The various methods are evaluated by comparing the goodness of fit of an array of hydrologic distribution functions. From each probability density function or regional empirical method, we predict the multi-year return periods for floods, information that is generally required to design the hydraulic structures. The analysis was done based on the annual maxima, peaks above threshold, and widely used regional empirical methods. This analysis was accomplished using the discharge data of Nayapul station near Jhapre Bagar collected from the Department of Hydrology and Meteorology, Government of Nepal, Kathmandu. The analysis and results of this study paved the way for the hydraulic design of water systems in the ungauged study region and demonstrated how the information acquired can be used for water resource management in catchments with similar hydrologic features.