Dhaka, the capital city of Bangladesh is one of the populous Mega City in the world. As the growth of urban population tacking place at an exceptionally rapid rate, the city is unable to cope with changing situations due to their internal resource constraints and management limitations. In recent years Dhaka City is facing extensive water logging during the monsoon (May to October) as a common and regular problem of the city like water pollution, traffic congestion, air and noise pollution, solid waste disposal, black smoke etc. This paper focuses on the rainfall induced flooding that is caused by high intensity storm rainfall runoff in the city area that is inundated for several days mainly due to lack of proper drainage system and inefficient management. It ascertain the inherent causes of such water logging and its effects on the city life from the perception of authorities of different development organizations, experts and people living in different parts of Dhaka City.
Heavy downpour occurs in Dhaka City during monsoon, as it is located on the extensive floodplains of Ganges and Brahmaputra. But the unplanned spatial development activities and growth of habitation due to rapid population growth are causing encroachment on retention areas and natural drainage paths with little or no care of natural drainage system that creating obstacles to properly drained out the urban runoff. Therefore water logging is tacking place as different parts of the city remains inundated for several days. Inadequate drainage sections, conventional drainage system with low capacity and gravity, natural siltation, absence of inlets and outlets, indefinite drainage outlets, lack of proper maintenance of existing drainage system, and over and above disposal of solid waste into the drains and drainage paths are accounted for the prime causes of blockage in drainage system and water logging. In addition, seasonal tidal effect and the topography of the city area also causing water logging.
This water logging becomes a burden for the inhabitants of Dhaka City and creating adverse social, physical, economic and environmental impacts. Disruption of traffic movement and normal life; damage of structures and infrastructure; destruction of vegetation and aquatic habitats; loss of income potentials are the encountered effects of water logging on city life. The storm water becomes polluted as it mixes with solid waste, clinical waste, silt, contaminants, domestic wastes and other human activities that increase the water born diseases. The stagnant storm water leads to the creation of breeding sites for diseases vectors that becomes a hazard to health as well as being unsightly and foul smelling.
Management of drainage system of Dhaka City is presently a challenge for the urban authorities because of rapid growth of population and unplanned development activities. Therefore, a close coordination among urban authorities and agencies and collaboration between public and private sectors is needed for effective management and sustainable operation of urban drainage system.