DRAINAGE

The most significant feature of Bangladesh landscape is provided by the river , which have molded not only its physiography but also the way of life of the people. Rivers in Bangladesh, however ,are subject to constant and sometimes rapid changes of course, which can affect the hydrology of a large region; consequently, no description of Bangladesh’s topography retains its absolute accuracy for long. One spectacular example of such a change occurred in 1787, when the Tista River underwent exceptionally high flooding; its water were suddenly diverted eastward, when they reinforced the Brahmaputra. The swollen Brahmaputra in turn began to cut into a minor stream, which by the early 1800s become the river’s main lower course, now known as the Jamuna. A much smaller river now flows though the Brahmaputra’s former course. 
Each year between June and October the river overflow their banks and inundate the countryside, rising most heavily in September or October and receding quickly in November. The inundations are both a blessing and a curse. Without them, the fertile silt deposits would not be replenished, but severer floods regularly damage crop and main hamlets and sometimes take a heavy toll on human and animal populations.
The rivers may be divided into five systems: (1) The Ganges or Padma, and it’s deltaic streams, (2) The Meghna and the Surma river system, (3) The Jamuna and it’s adjoining channels, (4) The North Bengal rivers, and (5) The rivers of Chittagong Hill Tracts and the adjoining plains.
The Ganges is the pivot of the deltaic river system of Bengal. The river and it’s tributaries enclose a large area of southwestern Bangladesh, and the Ganges Delta covers about 20,000 square miles. The Ganges river system is divided into two segments, the Ganges and the Padma; although within Bangladesh the entire length of the river is called the Padma. The Ganges enters the Bangladesh from the west and forms, for about 90 miles, the boundary between Bangladesh and West Bengal. It forms numerous distributaries and spill channels and reaches it’s confluence with the Jamuna west of Dhaka, after which their combined waters are known as the Padma. The Padma flows southwest to join the Meghna near Chandpur and enters the Bay of Bengal through the Meghna estuary and lesser channels. Except where it is confined by high banks, The Ganges main channel changes course every two or three years. It’s water appears muddy owing to the volume of silt carried by the river. Silt deposits build temporary islands that reduce navigability but are so highly fertile that they have been decades a source of feuds among peasants who rush to occupy them. 
The Meghna is formed by the union of the Sylhet-Surma and Kusiyara rivers. These two rivers are branches of the Barak River, which rises in the Nagar-Manipur watershed in India. The main branch of the Barak, the Surma, is joined near Azmiriganj in northeastern Bangladesh by the Kalni and fadown by the Kusiyara branch. The Dhaleswari, a distributary of the Jamuna River, joins the Meghna a few miles above the junction of the Padma and the Meghna. As it meanders south, the Meghna grows larger after receiving the waters of a number of rivers, including the Burhi Ganga and the Sitallakhya.
The Jamuna and its adjoining channels cover a large area from north-central Bangladesh to Meghna River in the southeast. The Jamuna receives waters from a number of rivers, especially on it’s right bank, and, with it’s notoriously shifting channels, not only prevents permanent settlement along it’s banks but also inhibits communication between the northern area of Bangladesh and the eastern part, where Dhaka is situated.
The Tista is the most important water carrier of northeastern Bangladesh. Rising in the Himalayas near Sikkim, India, it flows southward, turning southeast near Darjiling to erter Bangladesh and eventually meeting the Jamuna. Navigation of it’s lower reaches is made difficult by the shoals and quicksand that from near the junction with thr Brahmaputra.
Four main rivers constitute the river system of the Chittagong Hills and the adjoining plains-the Feni, the Karnaphuli, the Sangu, and the Matamuhari. Flowing generally west and southwest across the coastal plain, they debauches into the Bay of Bengal. Of these rivers the longest is the Karnaphuli, which is dammed at Kaptai, about 30 miles upstream from it’s mouth near the city of Chittagong.
None of the major rivers of Bangladesh originates within the country’s territory. The headwaters of the Surma are in India; the Ganges rises in the Nepal and the Brahmaputra in China, but they too, reach Bangladesh across Indian Territory. Thus Bangladesh lacks full control over the flow of any of the streams that irrigate it. The construction of a barrage upstream at Farakha in West Bengal led to the diversion of a considerable volume of water from the Ganges, and the flow to western Bangladesh is insufficient in the dry season from November to April. The equitable distribution of the river’s water has been since the 1970s a source of friction between India and Bangladesh.