Fragile physical environment
of Dhaka megacity
by Nurul Islam Nazem
Bangladesh is one of the most densely populated countries in Asia. It is also a country which is experiencing rapid urbanization. The growth of Dhaka, the capital city, is even faster. In recent years, the city has experienced a significant growth of industrial, commercial and service sector activities, apart from its population growth and physical expansion. Physical expansion has taken place in all directions especially towards the north. Much of this growth has taken place without planning, which has caused massive environmental deterioration. This paper provides evidence as to how the rapid growth of population and unplanned human activities in Dhaka Megacity region deteriorated its natural environment, especially how the rivers and other wetlands in and around Dhaka city were destroyed.
Around Dhaka city there are four rivers which have historically provided lifelines to its land and people. These rivers drain Dhaka city, and facilitate easy transport and business opportunity since time immemorial. In recent years however, the rivers and associated wetlands are under severe threat due to encroachment, pollution, siltation and malfunctioning. Wetlands and open spaces have been filled up, mostly by grabbers, and converted into poorly developed slums and also for other residential, commercial and industrial purposes. Hundreds of brick fields, CNG stations, industries and other infrastructure have been built, in many cases on illegally occupied wetlands and rivers. The wastes from industries, both liquid and solid, a large amount of human excreta from houses, directly goes into rivers and water bodies. In fact, rivers have become a dumping ground for all kinds of wastes. Unabated encroachment that prevents the free flow of water, along with all sort pollution, makes the water unusable and odorous. The rivers become biologically dead because of the intensity of such pollution.
The control and management of these rivers and water bodies are poor because of noncompliance of rules and regulations. Rich and the powerful people are involved in the process of making the rivers and water bodies non-functional. The authorities in the past were not adequately proactive and over the years the rivers, canals and water bodies in and around Dhaka city have deteriorated to such an extent that, in the near future, surface water in the city would be a rare commodity and the consequent environmental conditions would be detrimental to the life and livelihood of the people in the city. Recently, however some sporadic initiatives were taken to restore the fragile condition of rivers and water bodies of Dhaka to their original shape. Such move seems to be inadequate and fraught with many problems.
State of physical environment
Dhaka is situated on the southern tip of the Pleistocene alluvial terrace, known as Madhupur tract. The undulating physiology of the city and its surroundings in the north are characterized by flat (plateau like) hillocks and dendritic pattern of drainage systems. However, most of Dhaka city, particularly its surroundings, are dominated by Holocene deposits and have developed as low-lying flood plains. The elevation of the city ranges from 2 to 13 meters above sea level. Central Dhaka occupies a relatively small proportion of flood free land. Outside Dhaka Metropolitan Area (DMA), flood free land is available at Tongi, about 20 km. north, and Savar, about 30 km. north-west, from the city centre. Most of the remaining areas, particularly to the south, west and east are flood prone.
The physical environmental profile of the city has become fragile during recent years, mostly due to human interventions and unplanned urbanisation. Some notable environmental concerns are poor drainage conditions, severe water logging, surface water pollution and loss of wetland and green coverage. The land and the environment of the city has now become overburdened due to massive unplanned development activities and human intervention, which would ultimately lead Dhaka to become a non-liveable city, unless measures are taken to restore its environment and implement sustainable development strategies.
A study shows that liquid waste from industries and sewage disposal into the rivers not only pollute the surface water but also threatens the ground water. The rivers Buriganga, Balu, Turag and Sitalakshya together receive a huge amount of untreated sewage and industrial wastes, including solid wastes from streets through drains, canals and direct disposal. The water in the surrounding rivers, lakes and canals has already exceeded the standard limits of water quality parameters, such as DO, BOD, COD and pH.
Canals and water bodies within DMA area are filled up by the grabbers. The situation has become very bad in recent years. As a result, the city has lost its water draining capacity drastically; thus contributing to severe water logging and flooding. During normal flooding, all low lying areas of the city which were mostly occupied by the poor, goes under water. During severe flooding, like the ones that occurred in 1987, 1988, 1991 and 2004, 75 percent of the city area was under floodwater causing colossal damage to life and property.
Depletion of ground water is another serious problem in Dhaka city. Between 1996 and 2003 the water level went down from 26.6 meter to 46.24 meter. The primary reason is that the rate of extraction of water is much higher than its recharge rate. The annual rate of depletion varies between 0.3 meter and 1 meter. The recharge rate is low. Thus, the physical environment in Dhaka Metropolitan Area is already in a fragile condition. The condition will worsen further if unplanned and illegal earth filling of wetlands continues in the future.
The studies show that non-urban land around Dhaka is diminishing fast. So are water bodies. Secondly, much of the residential areas of Dhaka were characterized as low density. These were mostly informal type of rural housing. However, the central part of Dhaka is highly dense. Agricultural land above flood level may be converted to urban use, but the low lying agricultural land and water bodies must be preserved for the sustainability of natural ecology.
Rivers and water bodies in DMA
There were more than 40 canals within the DMA which have historically played a remarkable role in draining Dhaka. In recent years most of these canals were grabbed and filled up. Thus, the whole system of draining Dhaka is not working properly. The canals flowing through different areas finally join the rivers. For example, Segunbagicha-Jirani-Dolai khal joins with the Balu and Buriganga. Ibrahimpur-kallyanpur Khal joins with the Turag. Dhanmondi, Gulshan, Banani, Begunbari khal joins the Balu River. The major lakes are Dhanmondi, Gulshan, Ramna and Crescent. The length and catchment area of the major canals were found to be 17.4 km and 70 sq. Km respectively.
The lakes and ponds were found scattered in different areas of the city. Most of these ponds support the informal settlements (slums and squatters settlements) of the city, especially for washing and bathing of the dwellers. Some of these water bodies are being polluted through disposal of sewage and waste by the lakeside settlements.
Recent satellite images (2009) show the rivers, canals and water bodies of Dhaka Metropolitan Area (DMA). The existing surface water area of Dhaka city, under the above mentioned categories, is about 61.31 sq km, which is about 20 percent of the DMA area (306 sq km). Out of this, Buriganga, Turag, Balu and Tongi Khal (including internal canals) constitute 12.26 sq km or 4 percent of the area. On the other hand, perennial water bodies in DMA excluding the canals and rivers were found to take about 26 sq km (9.44 percent). There are also other temporary water bodies (shallow water in low lying land) found mainly in eastern Dhaka. The area of such water bodies is 23.07 sq km or 7.54 percent. Thus, the present assessment shows that the available water body within the city is around 12.5 percent which increases to around 20 percent during the wet season. This includes four rivers, identified canals, lakes and many small ponds.
Historically, the use of land for the development of the city started from Old Town, along the bank of the river Buriganga. Later it expanded towards the north and the flow of expansion more or less continued along the buildable highlands. In the course of time, due to pressure of population, low lying marginal lands were also being occupied. The City Corporation area which is less than a quarter of the megacity area is the central city. The elevation of the DCC area varies from 2 to 13 meters above the mean sea level (msl), while most of the developed areas are at an elevation of 6 to 8 meters above mls. The land area above 8 meters covers only about 20 sq km of DCC land, while that between 6-8 meters cover 75 sq km. Most of the area, about 170 sq km of land area, is below 6 meters of msl. This indicates that a large area of the city is vulnerable to flooding.
Water management policy approaches
The policy approach to Dhaka megacity water management should follow certain guidelines. First, planning the water management of the city and the implementation of policy should be ahead of demand. Secondly, preparing judicious land use plan integrating water bodies is necessary. Third, proper management of catchment areas of rivers around Dhaka city should be given the utmost priority. Fourth, strict legislation against illegal grabbing, encroachment of water body, polluting rivers and water bodies of the city should be prepared; and finally, continuous monitoring of the management programme should be carried out. However, the whole process of development should be carried out through a number of steps:
Step 1: A comprehensive zoning on the basis of land use is necessary for Dhaka. However, for metropolitan area such comprehensive zoning may not be possible as most of the areas are already built-up except the eastern fringe. It is still possible to make zoning. During zoning exercise, urban ecology must be considered. Urban ecology is an interactive relationship of various activities and functions on the developing space without harming natural setting of the area. Where zoning is not possible, natural setting must be conserved. The natural setting includes physiology, land slopes, all water bodies including rivers and canals, natural vegetation and so on.
Step 2: Each zone or ecological unit (such as residential, industrial or commercial areas etc) must be related to other units, functionally as well as ecologically. The various land-use zones in a city are interdependent and strongly related to other zones by communication networks, movement of people and goods and services. Thus, a river or water body in one unit must flow with equal strength to the other units without interruption, alteration and pollution. At the same time good communication networks to facilitate movement of people and goods has to be ensured in such a manner that each ecological unit turns functionally efficient, sustainable and liveable.
Step 3: Transport and land use are interrelated phenomena. Land use generates traffic and likewise the transport network generates land use. This principle is equally applicable for river network. Rivers must be considered as means of easy access to city functions. To facilitate this, river flows must be kept alive and the fronts of all rivers must be developed in such a manner that no one can encroach or misuse the rivers and make rivers backyard.
Step 4: River front development is a dynamic concept. It provides the city a life line, giving easy access to the cities major commercial and industrial hubs, and also provides scenic landscapes. The idea of river front development is generated from controlling the land-use along the rivers. The suggested land-use for river fronts are tree lines, drive ways or walk ways, limited commercial and non-industrial establishments, recreational establishments, Ghats and port facilities at certain points, hubs of transport facilities with multimodal arrangements. The most important concept of river front development is keeping the faces of all establishments towards the rivers. Thus, the developments along the river banks (on natural levees) must face rivers.
Step 5: Disposal of wastes, either solid or liquid of any kind, to the rivers must be prohibited. Particularly, industries like tanneries and textiles constantly dump untreated and under treated toxic refuse, untreated sewage and solid municipal wastes into the rivers. Thus rivers are getting squeezed from all sides. Grabbers occupy rivers and reclaim land for development. Such acts should be banned by law and be considered as punishable acts.
Step 6: After identification of the river bank, a zone of at least 20-30 meter from identified bank should be acquired by the government (if such land is not available from government Khas land). Use of this land may be specified as tree covers, gardens, riverfront parks etc, along the river followed by driveway or walkway (depending on the local situation). Other than this, at some places, yard/ghat/terminals can be constructed to facilitate water transport and the movement of people and goods. But, under no circumstances can land-use which may pollute the water (such as waste dump/bin, katcha bazaar etc) be allowed along the bank.
Step 7: Like rivers, other water bodies are also equally important for Dhaka. Water bodies can help recharge ground water table, which is depleting fast. Secondly, these water bodies can capture storm water and prevent floods and water logging. Third, the water bodies can help keep the temperature low during the day time. And finally, the water bodies can be used for recreation purposes, which is very essential for Dhaka. Thus, all water bodies within the limits of greater Dhaka needs to be defined and mapped by appropriate authority through gazette notifications. These water bodies may be permanent or seasonal.
Step 8: The water bodies can be owned by the government or by private owners (the landowner). The use of such water body should be restricted and controlled by an appropriate authority. The authority (government) can also lease out such water bodies to interested parties provided the rules of water use are strictly maintained. Water bodies can be used as pond, lake, fishing ground, water park etc. Seasonal water bodies can also be used for agriculture. However, demarcated water bodies cannot be changed into other uses except for those identified.
The writer is Professor in the Department of Geography and Environment, University of Dhaka, and Honorary Secretary, Centre for Urban Studies (CUS).