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 midnorthern
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.