Description of study area
The study area is Dhaka Metropolitan of Bangladesh.Geographically, it is located between 23°58’ and 23°90′ North latitudes and 90°33’and 90°50′East longitudes (Fig. 1). Topographically, the area is a flat land and is located mainly on an alluvial terrace, popularly known as the Modhupur terrace of the Pleistocene period (Miah and Bazlee 1968). The surface elevation of the area ranges between 1 and 14 m (Fig. 1) and most of the built-up areas located at the elevations of 6–8 m (FAP 8A 1991). The area of investigation covers 416 km2 and is surrounded by four major river systems, namely the Buriganga, Turag, Tongi and Balu, which are flowing to the south, west, north and east sides, respectively. These rivers are mainly fed by local rainfalls and also receive spills from three mighty rivers crisscrossing the country, namely the Ganges, Brahmmaputra and Meghna through their tributaries and distributaries in the monsoon. Regionally, the area is located in the central Bangladesh, and lies in the sub-tropical monsoon zone under the humid climatic condition. The city experiences about 2,000 mm annual rainfall, of which more than 80% occurs during
the monsoon season (June–September). Currently, the annual population growth rate of the city is 5% compared with an annual average of 2.1% for Bangladesh (BBS2001). The process of urbanization in Dhaka is providing both challenges and opportunities. For instance, Dhaka contributes 19% Gross Domestic Product (BBS 2001) to the national economy and is playing a pivotal role in terms of social development and cultural enhancement.