Causes and solutions to waterlogging in Dhaka city
The problem of waterlogging is not only for the people of Dhaka, but also for other big metropolitan cities including Chittagong due to unplanned urbanization. However, the problem of waterlogging became apparent in Dhaka and Chittagong cities due to rain. The residents of Dhaka are once again facing the threat of severe waterlogging, as incessant rain has inundated many parts and major roads of the capital. Basically, the water in Dhaka should reach rivers through canals and drainage lines of Dhaka Wasa. But the drainage lines are clogged and canals have been illegally occupied.
Dhaka, the capital city of Bangladesh is one of the most populous Mega Cities 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 waterlogging during the monsoon (May to October). The common and regular problems of the city are water pollution, traffic congestion, air and noise pollution, solid waste disposal, black smoke etc. 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.
The Bangladesh Institute of Planners (BIP) found in a study that at least 3,483 acres of water-bodies and lowlands across the metropolitan area in Dhaka have been filled up in the last nine years and 36% of the water-bodies in Dhaka had been filled up, violating the Detailed Area Plan (DAP) for the capital adopted in 2010. It also said that the parts of the city under the jurisdiction of Rajdhani Unnayan Kartripakkah (Rajuk) had 100,937 acres of water-bodies and lowlands in nine years ago, but 22% of those--22,156 acres--have been filled up since then, greatly contributing to the perennial water-logging issue.
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 waterlogging 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 waterlogging.
In Dhaka, the drainage system, water pump, canals, and rivers are maintained by a total seven government agencies: The Bangladesh Water Development Board (WDB), Bangladesh Inland Water Transport Authority (BIWTA), Rajdhani Unnayan Katripakha (Rajuk), Dhaka District Administration, Dhaka Water Supply and Sewerage Authority (Dhaka Wasa), Dhaka South City Corporation (DSCC) and Dhaka North City Corporation (DNCC). Each of the organizations works separately to improve the drainage system in different parts of the capital.
Dhaka Wasa works on the storm drain system, which handles surface water. Most drains in Dhaka are clogged by solid waste and plastic garbage, due to irregular cleanup and lack of awareness of city dwellers. This waterlogging 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 effects of waterlogging on city life. The rain 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 rain 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.
Dhaka used to have 65 natural canals running throughout the city, but the number currently stands at only 26, as most of them are clogged by garbage and illegal occupiers. The city has been planned in such a manner that does not consider the connectivity of the water management. There is no shortcut remedy. It has already been blocked the natural connectivity to accommodate the high population density in this mega-city and it has made it a concrete jungle. Now, it has to improve the efficiencies of all existing waterbodies first, and then immediately recover all the canals from grabbers and re-install their connectivity, to help the water drain from city properly.
Both Dhaka city corporations said illegally occupied city canals must be reclaimed to save Dhaka, as the blocking of the canals is largely responsible for the waterlogging. Dhaka was supposed to have 12% Aadhar (reservoir), which is now only 3%. All the ponds and waterbodies have been filled up. Also, unplanned urbanization has put in trouble, as 330 sq-km out of the total 400 sq-km area of Dhaka has already full of houses, hampering water flow routes and the authorities in the process of mapping problem areas are not serious to find a solution.
The problem is that due to lack of proper maintenance of box culverts, water flows very slowly- at maybe at 5-10% the speed of the usual flow. It has been observed the most city canals have been illegally occupied by Dhaka WASA, and the few remaining ones are not even cleaned regularly. It has to be emphasized the need to increase the capacity of public service organizations and raise public awareness in order to address water logging.
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 cooperation between public and private sectors is needed for effective management and sustainable operation of urban drainage system.
Md Zillur Rahaman, Banker and Freelance Contributor