The Ganges-Brahmaputra Delta, also known as Ganges Delta, Sunderbans Delta or Bengal Delta is situated in south Asia. The delta plain is formed by the meeting of the rivers Ganges, the Brahmaputra and Meghna which stretches across 5 coriparian (or water sharing) countries: Bangladesh, India, Nepal, Bhutan and China. Together, these three rivers drain a catchment area of about 1.72 million sq km, at the southern side of the Himalaya. Out of this large catchment area, only 7% lies in Bangladesh.
|Rivers||Total catchment area (sq km)||Catchment area (sq km)|
Bangladesh itself is a great delta formed by the alluvial deposits of these three mighty Himalayan Rivers. The mighty Ganges and Brahmaputra rivers are called the "Padma" (pronounced 'Podda' in Bengali) and the "Jamuna" respectively in Bangladesh. Both of these massive rivers join several other smaller tributaries to eventually become the Lower Meghna, forming the great Gangetic Delta. This has a surface area of some 100,000 sq km, making it the world's largest Delta. It stretches from Meghna River (in Bangladesh) on the east to the Hughli River (in India) on the west. Approximately two-thirds of the delta is in Bangladesh, the rest lies in the state of West Bengal, India. Kolkata and Chittagong are the principal seaports on the delta.
Where the land ends, the Bay of Bengal begins. The delta is approximately 220 miles (350 km) wide along the coast. As the rivers empty it discharges large quantities of sediment into the Bay of Bengal therefore most of the sea adjacent to Bangladesh is quite shallow.
The Bengal delta occupies an unique position among the larger deltas of the world for its varied and complex river and drainage system. The whole delta is cross-crossed by innumerable large and small channels of which some are decaying, some are active, while some others are being drained only by the tidal flow. In the northeastern part of the delta there are some abandoned or partially abandoned courses of decaying rivers while the eastern and southeastern delta is characterised by the flow of active rivers with heavy discharges.
At its widest point near Bhola Island, the river stretches to a yawning 12km-wide breadth on its final leg towards the sea. Seen from a boat, the distinctions between land, river, ocean and sky become decidely uncertain.
The world's largest mangrove forest, the Sundarbans, is located where the land meets the water. The Sundarbans forest spans Bangladesh and India, with each country’s forest listed as a UNESCO World Heritage site. The Sundarbans - which is Bangla for 'beautiful forest' – is also a vast wildlife preserve and provides critical habitat for numerous species, including the Bengal tiger and the estuarine crocodile. In fact, it is the largest remaining habitat of the Bengal tiger.
An extensive and intricate web of rivers is Bangladesh's most significant geographical feature. There are about 405 rivers – known as “nodi” in Bengali - in Bangladesh of which 57 are transboundary rivers (i.e. crosses national borders). Out of these 57 rivers, 54 are common with India and 3 with Myanmar (also known as Burma).
The Ganges River, India’s most sacred river (known as ‘Ganga’ in Indian languages), divides into many distributaries including the Hughli (also spelt Hooghly) River near Kolkata. It enters western region of Bangladesh, near Rajshahi, and forms another major distributary: Padma Nodi.
Elsewhere, the Brahmaputra River enters northern region of Bangladesh and forms the Jamuna Nodi. Both the Padma (pronounced "Podda" in Bengali) and Jamuna merge near the town of Paturia at the heart of the country and continue downstream as just the Padma Nodi until it reaches the coast, some 250 km away. About halfway down the Padma, near the town of Chandpur, the Meghna Nodi joins from the eastern side.
|4. Ganges-Padma||378 (Ganges 258, Padma 120)|
|7. Brahmaputra-Jamuna||276 (Jamuna 207)|
|8. Old Brahmaputra (Mymensingh)||276|
The rivers bring down the rich alluvial soil that forms the Ganges Delta, and they provide the main means of transportation throughout the country. Rivers are also a source of hydroelectric power, a notable example being the Karnaphuli River in Chittagong in the southeast.
Preparing a complete list of the rivers of Bangladesh is more or less tough as often a single river possesses different names at different places. Even a five or six-kilometre segment has a different name upstream or downstream. Also a single name is used for different rivers in different locations.
Because the rivers are subject to constant and often rapid change, Bangladesh's topography never remains the same for long.
A classic example of this occurred in 1787 when the Tista River experienced massive flooding. Waters were diverted eastward, where they met and reinforced the Brahmaputra River. The swollen Brahmaputra then cut into a minor stream and by the early 1800s the minor stream had become the river's main watercourse, now called the Jamuna. The Brahmaputra, now a considerably smaller river below the juncture with the Jamuna, still flows along the old course.
Water is Bangladesh’s blessing and curse. The entire low-lying region is plagued for nearly half the year by severe storm surges and powerful low-pressure cyclones which result with the monsoons arriving from the Bay of Bengal. The monsoon rains cause the country’s three major rivers, the Padma, Meghna and Jamuna, and their tributaries to swell resulting in devastating floods, heavy damage to crops and shelters, and loss of human life. During the rest of the year, the dry season brings almost no rainfall, and droughts threaten the livelihoods of people and the health of the natural environment.
Almost all of the country's rainfall comes during June to September, as northerly winds blow moisture up from the Bay of Bengal into the mountain wall that is the Himalayas. As the moisture accumulates, the skies eventually belch out their water over Bangladesh and the surrounding regions. Like many other areas that experience monsoonal rain, it seldom rains all day every day. But there can be spells where it drizzles for an entire week, and nearly everything becomes sodden, even if it's inside and well out of the rain.
If you ever wanted to experience the living reality of the idiom 'when it rains, it pours' Bangladesh is the place to be. During the yearly south Asian monsoon, almost all the water collected by the Himalayas in Nepal, north/northeast India and Bhutan transits through Bangladesh on its journey to the Bay of Bengal, deposition life-giving minerals to the soil all along the Ganges Delta, the largest river delta in the world. It is here that the mountains literally crumble to the sea. This has resulted in Bangladesh's flatland alluvial topography, which is the defining characteristic of the country except in the hilly regions of the southeast and northeast.
...As the rivers have gradually shaped and reshaped this land, they have also shaped the destinies of its people. It would be a mistake to picture the historic locations of Bangladesh's rivers according to current maps. For instance, the Brahmaputra used to flow east of Dhaka's present location before a major flood caused it to change course over a 30-year span during the mid-18th century. Simultaneously, the Ganges has also undergone similar changes as it used to flow through West Bengal via the Hooghly River (today much smaller than it used to be).
As the rivers have gradually shaped and reshaped this land, they have shaped the destinies of its people. It would be a mistake to picture the historic locations of Bangladesh’s rivers according to current maps. For instance, the Brahmaputra used to flow east of Dhaka’s present location before a major flood caused it to change course over a 30-year span during the mid-18th century. Simultaneously, the Ganges has also undergone similar changes, as it used to flow through West Bengal via the Hooghly River (today much smaller that it used to be).
Nowhere is this destiny more uncertain than in the country’s two disaster-prone areas. Firstly, the coast bordering the Bay of Bengal is vulnerable to tidal surges from cyclones. Secondly, the country’s char areas, or river islands, are also extremely prone to seasonal flooding. These islands lie mostly in the northern reaches of the Jamuna River of Rajshahi Division. Many inhabited islands are destroyed and reformed each year by flooding. Despite the fact most of the islands are little more than infertile sandbars, poverty forces millions of people to live on them under the risk that their houses could be swept away each year.
In the Lower Meghna region, another area of exposure lies directly adjacent to the Bay of Bengal. Here, two processes of land loss and land accretion happen simultaneously. While the Meghna tears away strips of land beneath the villages each year, its decreasing speed causes it to deposit massive amounts of Himalayan silt into the bay, forming new land that becomes populated almost immediately despite the fact that the precious land doesn’t become fully fertile for years. Some geologists even claim that Bangladesh is ‘gaining landmass’, putting the supposed doomsday scenario of climate change into question.
M. H. Ali, author of "Fundamentals of Irrigation and On-Farm Water Management, Volume 1" (2010)