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ABSTRACT
Bangladesh suffered damage on account of the most catastrophic floods of 1987, 1988 and 1998, resulting in untold suffering of the people. This paper demonstrates the technique to develop a flood hazard map and a land development priority map for countermeasure against flood damage. To create the final products, flood hazard map and land development priority map, National Oceanographic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) data for the flood events of 1988, 1995 and 1998 were incorporated with Geographical Information System data of physiographic divisions, geologic divisions, land cover classification, elevation height, drainage network, administrative districts and population density. Flood-affected frequency and flood depth categories were estimated using NOAA AVHRR images. Special attention was paid to population density for the construction of the land development priority map, because highly dense populated areas represent the highly important urban and industrial areas of Bangladesh. The land development priority map offers a new opportunity for flood risk management, planning, design and operation of flood control measure in Bangladesh, and should be useful in assigning priorities for the development of at-risk-areas.

INTRODUCTION
There have been many destructive floods in Bangladesh, including very severe floods of 1987, 1988 and 1998. The 1988 flood set a new record for flooded area, while 1998 flood was unprecedented with its long duration. Different Governmental organizations such as Bangladesh University of Engineering and Technology, Space Research and Remote Sensing Organization, and the Bangladesh Water Development Board normally investigate the flood conditions in Bangladesh. After the big flood of 1987, a Japanese inquiry commission investigated the disaster from the aspect of meteorology, geomorphology, hydrology, river engineering and sociology in order to be able to plan structural and non-structural countermeasures (Muramoto 1988; Oya 1993). In 1988, Bangladesh experienced one of the worst floods in living memory, which resulted in a total cost to the national economy of approximately $2 billion, and it was estimated that 45 million people were directly affected (Brammer 1990). The official death toll was put at 2379; the number of houses affected was 12.8 million, including 3.8 million totally destroyed; and crop damage was 7.54 million ha (Sado & Islam 1997). In addition, the damage to the infrastructure was enormous. Therefore, flood management is necessary not only for saving lives, but also for safety of crops and infrastructure. Then a study team comprising a core group of international consultants provided by the United Nations Development Program (UNDP), the Asian Development Bank, the European Economic Community, and the World Bank (Bangladesh government and UNDP 1989; World Bank 1989) and local experts investigated the flood damages and its remedy. In the course of its work, the team consulted various donor country missions to Bangladesh. Different donor countries have made extensive investments in the development of flood control works.

Although various flood control and management measures have been adopted and some flood control works have been done by extensive investment of the donor countries, the 1998 and 2003 severe floods proved that floods and damages are not decreasing. The flood damage potential is increasing due to the possible causes of climate change, urban concentration in the three river basins, encroaching of settlements into flood prone areas, and overreliance on the safety provided by flood control works such as levees, reservoirs, and so on (Kundzewich & Takeuchi, 1999). Bangladesh lies in the downstream area of the three river basins of the Ganges, Brahmaputra and Meghna as shown in Fig. 1. The three mighty rivers enter Bangladesh from India through northwest, north, and northeast of the country, respectively. High magnitude floods strike on a regular basis in these river basins in Bangladesh, India and the peninsular area (Bhattacharyya 1997; Kale & Pramod 1997; Kundzewich & Takeuchi 1999; Muramoto 1988; Rahman 1996; Islam & Sado 2000c) because of the passage of tropical depressions and cyclone storms during the monsoon season. Bangladesh has limited control over the Ganges, Brahmaputra and Meghna Rivers. For adequate and timely flood forecasting, Bangladesh depends on information from surrounding countries. The frequently occurring floods are very costly in terms of human life and economic loss. Therefore, the ability to estimate damages associated with the flood events is very important and is necessary for the evaluation of future alternate flood control policies. In a roundtable discussion following the 1998 flood event, experts from different fields recommended the need for flood hazard maps for proper planning and management for future flood disasters (Center for Alternatives 1998; Nishat 1998). In our previous studies (Islam and Sado 2000a,b,c), we have developed flood hazard maps using only the 1988 event. Therefore, in this study we focus on the 1988 and 1998 severe floods and 1995 medium flood.


Fig. 1. Whole are of Bangladesh selected for study
The capacity of the European Remote Sensing Satellite (ERS) and Landsat series of satellites to assess flooding has been well documented (Hallberg et al. 1973; Rango & Salomonson 1973) as well as some works already done using NOAA AVHRR data (Wiesnet et al. 1974; Hue et al. 1985a,b,c; Ali & Quadir 1987; Islam & Sado 2000a,b,c). NOAA AVHRR data are found to be very useful for monitoring large surface phenomena, such as floods, in the fields throughout the world on local, regional, and international scales. The results of analysis of NOAA AVHRR data, from the series of NOAA satellite 10 and 12, are used for the flood hazard assessment in Bangladesh in this paper. There are no available land development priority maps in Bangladesh incorporating flood hazard assessment and population density.

The objective of this study is to utilize Remote Sensing (RS) technique with the available geographic information system (GIS) data to construct a set of GIS data, a flood hazard map, and land development priority map to help the responsible authorities develop, design, and operate flood control infrastructure and prepared aid and relief operations for high-risk areas during future floods. The GIS plays a major role in flood control technique, and the integration of this data in a spatial database is crucial --especially for a development country. The role of GIS as a tool to enable the visualization and analysis of inundation with RS for flood hazard assessment, and the development of a map for land development on priority basis, is obviously important. Consequently, the paper presents a unique use of GIS and RS to delineate flood prone areas, and shows how to determine the relative sensitivity of the individual pixel of flood prone areas within Bangladesh. This enhances the capability in Bangladesh to utilize GIS for water resources planning and management, and may help implement or act as the basis for a hydrological decision support system to ascertain critical locations. This technique can be used from a local or regional scale to a global scale.

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