Hydrological and Hydraulic Modeling for Flood Analysis: A Case Study for Modi Catchment

534 Abstract— With the development of floodplains and climate change, the risks associated with flooding have increased, leading to increased flooding in floodplains. According to data from the Department of Hydrology and Meteorology, Nepal ranks 20th among countries in the world in the number of people affected by floods each year. Assessing the extent and depth of flooding has always been one of the main goals of water resources managers. This research aims to develop the Hydrological Engineering Center Hydrological Modeling System (HEC-HMS) and Hydrological Engineering Center River Analysis System (HECRAS) models for the Modi River Basin in Nepal. HEC-HMS is one of the hydrological models used to simulate the process of runoff and rainfall in different geographical areas. In this study, the precipitation data of seven meteorological stations and flow data of the hydrological station within the Modi River basin were used. The calibration was performed using data from 2006 to 2010 and was consequently validated using data from 2011 to 2013 at a daily time step. The efficiency of model was evaluated based on calculated statistical parameters (NSE, R) and comparing the simulated and observed discharge flows. The performance of this model during calibration was very good, with the coefficient of determination R = 0.81, Nash-Sutcliffe Efficiency NSE = 0.78. Similarly, the performance of the model during the validation period was also very good, R = 0.80, NSE = 0.78. Based on these performance results, the HEC-HMS model made a satisfactory prediction of water flow in the Modi Basin. In addition, the flood map produced by HEC-RAS was used to study the flood range and its characteristics. The Modi River basin is dominated by forest lands and hence the flood plain mapping showed the inundation of forest and trees at the lower reach of basin. It indicated that the future settlement at the vicinity of river has been found to be at high risk of flood. The study also showed that the structure of hydropower station also lies in flood hazardous zone. The model can be used as a reference for water resources management and flood control in the Modi River Basin, and can also be applied to other river basins.