Flood Hazard Mapping and Vulnerability Analysis Along Seti River in Pokhara Metropolitan City

Flood is frequent during every monsoon in Nepal which poses threat to life and property in lowland areas. Among 6000 rivers and rivulets, most are prone to floods in Nepal. Seti River flows from Machhapuchhre Rural Municipality in the north, along the center of Pokhara Metropolitan City, and toward Tanahu which meets with Madi River there. Seti flood of 2012 was one of the devastating floods which took the life of many people and destroyed infrastructures along its way. So, Pokhara Metropolitan City lies at a high risk of flood impacts. Hydrodynamic simulation using HEC-RAS and GIS is one of the important methods of estimating the probable loss due to flood of various scenarios quantitatively. In this study, flood hazard maps of Seti River across Pokhara Metropolitan City has been prepared for different flood scenarios. The flood frequency analysis was performed using Gumbel, Log-Pearson, Log Normal, and Fullers Method. The goodness of fit was performed using chi square test, and results of Gumbel method was used as it was found more appropriate than other methods for this basin. One-dimensional steady hydrodynamic modeling was done to create water surface profile which was used to prepare hazard maps and vulnerability maps for various return periods. The model was evaluated using statistical parameters, coefficient of determination R²), and Nash–Sutcliffe efficiency (NSE) whose values were found to be 0.951 and 0.819, respectively. The maps prepared can be used for planning the built-up areas along the river sides and may help in decision making for flood mitigation measures.