Sep 16, 2011

Dhaka City Drainage: Cause & Scenario


In the last 3 decades, Dhaka has grown radically at a great pace. It had been a provincial capital in the pre-independence era transforming into the capital of independent Bangladesh in 1971. Presently Dhaka has become the nerve center of the entire country. All activities related to economy, culture, politics, administration, education, health and society as a whole are centered based on Dhaka. The city has witnessed major growth in population over the last 3 decades; this is mainly due to migration from the countryside and townships. Since 1971, the population of the city has grown from about 1 million to more than 12 million in 2004. In another 20 years, Dhaka will be among the 10 most densely populated mega cities of the world with about 20 million people. The city area has also expanded. The total area of Dhaka, its satellite town Narayanganj and suburban areas (including Keraniganj, Tongi and Savar) is around 792 sq. km. Between 1990 and 2000, the built-up area has increased by around 46% (JICA Baseline Study, 2000). The city expansion occurred both horizontally and vertically. 

Presently Dhaka’s growth picked up at a tremendous pace and private initiatives are playing the dominant roles. The intervening ditches, swamps and marshes are filling up by land developers in an unplanned manner. Dhaka is growing in a haphazard manner and the topography of the area dictating the terms and direction of the growth. Over the years most of the low-lying areas of western Dhaka have been filled in to meet the city’s residential and commercial demands. The private developers are filling in the eastern side of the city. The population boom of the city has made the city to be one of the most densely populated cities of the world having acute problems in drainage of storm water. The development of urban facilities, like water supply and drainage, lags far behind the rapid urbanization. Increased urban developments are not providing sufficient drainage resulting in water logging leaving parts of Dhaka inundated for several days. This causes naturally large infrastructure problems for the city. The unplanned development is also intervening the existing drainage system and causing drainage congestions. Due to all these reasons in recent years the Dhaka Metropolitan area has been exposed to water logging. The city experience serious water logging problems in the year 1967; at the time after a heavy rainfall in month of September most of the main roads and then urban area was inundated. Relatively low intensity of rain causes serious problems for certain areas of the city. The effect of the water logging causes great traffic problems and also increasing the risk of environmental hazards due to the presence of sanitary wastewater. 

In recent times it has been observed that the water logging in the city areas becomes acute even in a normal rainfall event. Many areas in the city, main roads, lanes and by-lanes go underwater causing major disruption to city life and traffic movement. The effect of the water logging causes serious damage to the roads, reduce the design life, and increase the maintenance cost and sufferings of the city dwellers. 

Early nineties, a Master Plan was formulated under Flood Action Plan (FAP 8A). By the elapsed time between the preparation of the Plan and its implantation, the drainage scenario has changed quite significantly due to various changes in the topography, landuse and interventions. Situation of storm water drainage is a currently also in a bad shape. There was a time when Dhaka city was interconnected with numerous natural channels and wetlands which acted as conveyance passages and temporary detention system for storm water generated in the city. These are being continuously filled up by new settlements. During the period from 1990-2000, about 268 sq. km areas of wetlands in and around Dhaka city has been filled up. Unplanned expansion of city is destroying the entire natural drainage system causing flooding due to poor drainage in many parts of the city. Authority has service area of 140 sq.km, which includes 8 km box culvert and 65 km open channel. There are 225 km of pipe drain and 3 pump stations having capacity of 41.6 cumec against estimated storm water generation of 140 cumec. 


Coverage                           Area                   Area in Sq. Km

--------------------------------------------------------------------

                                      DCC area                     360 
Water Supply              Outside DCC area       90 

                                      Narayanganj                20 

                                      Total                            470 
Sewerage                     DCC area                    110 (30 % of DCC area)
Drainage                      DCC area                    140 (38 % of DCC area)