Abstract
Introduction
In this study, we investigated 2004 flood in the Meghna river basin around Bhairab Bazar in Bangladesh. In 2004, flood situation became worst in 21st century, it is because the flood peaks of three major rivers (GBM), the Ganges (Harding Bridge), Brahmaputra (Bahadurabad) and Meghna (Bhairab Bazar) stations were coincidently synchronized on 24th July in 2004.
Synchronization of the flood peaks is not a historically unusual event; unusual was the early occurrence of the synchronization of flood peaks, which never happened before in the history of Bangladesh floods. As a result, vast area of the country was inundated.
Data and Method
In this study, we used yearly maximum water extent images of RADARSAT from 2000 to 2004 and the images of June, July and September 2004. These data were derived from CEGIS, Dhaka, Bangladesh.
Hydrological data of 95 stations of GBM (2000 to 2006) were received from BWDB, FFWC and CEGIS. Precipitation data (1998 to 2006) of 51 gauging station and Cherrapunji were received from BWDB, FFWC and NOAA. GIS depicted flooding area very precisely and we used social and infrastructure flood damage data of 2004, which were received from CEGIS and Ministry of Agriculture, Dhaka, Bangladesh.
Results and Discussion
The northeastern part appears large inundation area and long duration of flood; it was determined by RADARSAT time series maps of 2004 (Fig.1). By overlaying RADARSAT inundation maps of 2004 flood and 2000 to 2004 yearly inundation maps, we compared these extents of flooding with ground data.
RADARSAT, precipitation data and hydrological data were coincident in 2004. It was revealed that consistent inundation area estimates are possible by using remote sensing and GIS data i.e., the northeastern part was inundated about 29,900.72 km2 which was determined by RADARSAT data.
Annual rainfall around Bhairab Bazar and Cheerapunji was found about 8,000 mm. Annual rainfall anomaly maps from 2000 to 2005 indicate exceptionally high and prolonged rainfall around Bhairab Bazar in 2002 and 2004 (Fig 2), which contributes severe flood around Bhairab Bazar in 2004.
Surface characteristics of the Meghna river basin were found severe and significant contributor to the flooding in the Meghna basin, as it is always the case including the flooding in 2004. Causing huge deaths and damages to houses and infrastructures were indicated by flood damage maps and hazard maps of 2004 (Figures not shown).
Conclusion
The promising results of this study indicate that the major parts of the study area are severely vulnerable to floods, causing a lot of damages to houses and infrastructures. The investigation of flood and hydrological characteristics of GBM Rivers from 2000 to 2006 revealed that it is very crucial for Bangladesh to monitor and assess the flood disaster and flooded area every year using remote sensing and GIS technique which may reduce the cost of general survey and hazard mapping services.
