Formulation of Flood Inundation Map in Jamalpur District by Mathematical Modeling using HEC Packages

Abstract

Bangladesh lies in the convergence zone of three large rivers of the world-Ganges, Brahmaputra, Meghna, which is called the GBM basin. The Ganges, Brahmaputra and Meghna (GBM) river basins occupy about 1.75 x 106 km2 of the Himalayan region. More than half a billion people in Nepal, India, Bhutan and Bangladesh are directly or indirectly dependent on the water resources of the GBM rivers. Being in this zone, Bangladesh faces heavy rainfall in the monsoon season of June to October, thus a huge amount of water drains out each year through the country. This drain out, along with various other reasons, causes frequent flooding all over Bangladesh. Thus, it is necessary to develop tools for the hydrological study of these three river basins or prediction tools to understand the consequence of different rainfall patterns. The reason of flood in the northern and mid-northern part of Bangladesh is overflowing of Brahmaputra (Jamuna) river. In this thesis work, different hydrologic and hydrodynamic models have been used to go through a number of steps and ultimately, a flood inundation map of Jamalpur district, which lies in the bank of Jamuna river, has been generated. The hydrologic model, HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System) has been used to delineate the whole Brahmaputra watershed which lies mostly in the Indian north-eastern region, on the foothills of the Himalayas. Gridded rainfall gages from NASA (National Aeronautics and Space Administration) were used for precipitation input. The model was calibrated and validated for 2 different years at Bahadurabad point at Jamalpur. The purpose of calibration and validation was to set up a certain set of model parameters for different rainfall patterns. HECRAS (Hydrologic Engineering Center-River Analysis System) mathematical model was used to point out the water level for the resultant discharge. With the help of Arc-GIS (Geographical Information System) and HEC-GeoRAS (Hydrologic Engineering Center-Geographic River Analysis System), the flood inundation map of Jamalpur was generated for some of the highest water levels. Expectedly, the highest amount of inundation was observed in the months of July, August and September, the months of high monsoon rainfall. Some of the shortcomings of the thesis work were not counting on the land use pattern of the Brahmaputra basin for discharge, using arithmetic mean for sub basin rainfall gage weights, using observed water level in the downstream boundary condition for HEC-RAS etc. The flood inundation mapping can be used for future flood hazard management for predicted rainfall and help mitigate the damage and further losses. The hydrologic modeling can be used for further calibration for future precipitation prediction, also can be used for categorizing hydrologic characteristics for Brahmaputra basin.