Bangladesh is a South Asian republic in the northeastern Indian subcontinent, in the delta of the Padma (Ganges [Ganga]) and Jamuna (Brahmaputra) rivers.


Bangladesh ("Land of the Bengals"), a riverine country, is one of the world's most densely inhabited countries, with a mainly Muslim population. The area originally comprised the province of Bengal in British India, together with what is now the Indian state of West Bengal, as the eastern section of the historical region of Bengal. When India was partitioned in 1947, it became the Pakistani province of East Bengal (later renamed East Pakistan), one of Pakistan's five provinces divided by 1,800 kilometers of Indian territory. Bangladesh became an independent country in 1971.


Relief


Bangladesh occupies the eastern two-thirds of the deltaic plain of the Padma (Ganges [Ganga]) and Jamuna (Brahmaputra) rivers, stretching northward from the Bay of Bengal. The plain is a flat surface of recent alluvium with a gentle slope and an elevation of less than 30 feet (9 metres) above sea level, except for small higher areas of jungle-covered old alluvium (rising to about 100 feet [30 metres]) in the northwest and north-central—in the Barind and Madhupur Tracts, respectively. The Sylhet and Chittagong Hills regions in the northeast and southeast, The alluvial plains give way to ridges that run mostly north-south and are part of the mountains that separate Bangladesh from Myanmar and India. Bangladesh is bordered on the south by the Sundarbans, a vast area of swampy deltaic forest.


Northwestern Bangladesh is home to the Padma and Jamuna rivers. The Bhar Basin stretches southeast from the Barind for roughly 100 miles (160 kilometers) to the Padma and Jamuna's confluence. During the summer monsoon season, this region is inundated to a depth of more than 10 feet in some spots (3 metres). The huge marshy region known as the Chalan wetlands, sometimes known as Chalan Lake, lies at the heart of the basin's western drainage.The Jamuna floodplains, which are north of the Bhar Basin and east of the Barind, run from Assam's border in the north to the Padma and Jamuna's confluence in the south. The Jamuna, which often breaches its banks in disastrous floods, dominates the area. The lower Padma floodplain is located south of the Bhar Basin.


The Madhupur Tract is located in north-central Bangladesh, east of the Jamuna floodplains. It consists of a high plateau with agricultural valleys contoured by hillocks ranging in height from 30 to 60 feet (9 to 18 meters). Sal trees grow in the Madhupur Tract, and its hardwood is equivalent to teak in terms of value and function. The Northeastern Lowland is located east of the Madhupur Tract in northeastern Bangladesh. It contains a significant number of lakes and includes the southern and southwestern sections of the Sylhet area (including the Surma River valley plain) and the northern part of the Mymensingh area.The Sylhet Hills are a collection of hillocks and hills in the extreme northeast of the area, ranging in elevation from around 100 feet (30 meters) to more than 1,100 feet (330 metres).


The flood basin of the Meghna River, which includes the low and fertile Meghna-Sitalakhya Doab, was built up by the Brahmaputra River in its ancient course (the Old Brahmaputra River) in east-central Bangladesh (the land area between those rivers). The Titas distributary enriches the region, and land areas are produced and modified by the deposition of silt and sand in the Meghna River's riverbeds, particularly between Bhairab Bazar and Daudkandi. This is where Dhaka is located.


The vast lakes in the middle portion of the Bengal Delta, to the south of the upper Padma, make up the Central Delta Basins in southern Bangladesh. The basin covers roughly 1,200 square miles in total (3,100 square km). The Immature Delta is a geographical mass in southern Bangladesh that borders the Bay of Bengal. The belt, a 3,000-square-mile (7,800-square-kilometer) lowland, includes the reclaimed and farmed areas to the north, as well as the enormous mangrove forest known as the Sundarbans. A network of streams that run around approximately rectangular islands crisscross the area closest to the Bay of Bengal.The Dhaleswari-Padma Doab and the estuary islands of different sizes found from the Pusur River in the southwest to the island of Sandwip near Chittagong in the southeast make up the Active Delta, which is located north of the Central Delta Basins and east of the Childish Delta.


The Chittagong region, located south of the Feni River in southeastern Bangladesh, includes many hills, hillocks, valleys, and woods and is considerably distinct in appearance from the rest of the nation. The coastal plain, which stretches southward from the Feni River to Cox's Bazar and ranges in width from 1 to 10 miles, is partially sandy and partly made up of salty clay (1.6 to 16 km). Off the coast of Myanmar, the region contains a handful of offshore islands and one coral reef, St. Martin's.Low hills of soft rocks, mostly clay and shale, make up the mountainous area known as the Chittagong Hill Tracts in the extreme southeast. The elevation of the north-south ranges is often less than 2,000 feet (600 meters).


The rivers, which have shaped not only Bangladesh's physiography but also its people's way of life, are the most prominent element of the country's terrain. Rivers in Bangladesh, on the other hand, are susceptible to frequent and often fast changes in course, which can have an impact on the hydrology of a vast area; as a result, no description of Bangladesh's topography can be said to be completely accurate for long. In 1787, the Tista River experienced unusually significant floods, and its waters were abruptly redirected eastward, where they strengthened the Brahmaputra.The swelling Brahmaputra cut into a smaller stream, which became the river's primary lower flow, now known as the Jamuna, by the early 1800s. The Brahmaputra's old channel is now occupied by a considerably smaller river (the Old Brahmaputra).


The rivers overrun their banks and inundate the land every year between June and October, peaking flood September or October and rapidly retreating in November. Both a blessing and a curse, the floods are a blessing and a curse. The fertile silt deposits would not be renewed without them, yet strong floods routinely destroy crops, destroy hamlets, and take a toll on human and animal populations.


The Padma (or Ganges) and its deltaic flows, the Meghna and Surma river regions, the Jamuna and its surrounding channels, the North Bengal rivers, and the waterways of the Chittagong Hill Tracts and the adjoining plains are the five river systems. The larger Ganges is the center of the Bengal historical region's deltaic river system. The larger Ganges Delta is 23,000 square miles (60,000 square kilometers) in size, with the majority of it located in southwestern Bangladesh. In Bangladesh, the Ganges is known as the Padma, and it is separated into two sections: upper and lower Padma.The river enters Bangladesh from the west and forms the border between Bangladesh and West Bengal for roughly 90 miles (145 kilometers). The upper Padma creates several distributaries and spill channels as it runs deeper into Bangladesh, eventually meeting up with the Jamuna west of Dhaka, where their combined waters form the lower Padma, which is the Padma proper from a hydrological standpoint.The lower Padma joins the Meghna at Chandpur and flows southeast into the Bay of Bengal through the Meghna estuary and smaller channels. The top Padma's main channel changes course every 2 - 3 years, except where it is hemmed in by steep banks. Because of the amount of silt transported by the river, the waters seem murky. Silt deposits form ephemeral islands that obstruct navigation but are so fertile that they have been a cause of feuds among peasants for decades as they rush to claim them.


The Meghna is produced when the Sylhet-Surma and Kusiyara rivers come together. These are two forks of the Barak River, which originates in India's Nagar-Manipur basin. The Surma, the Barak's major branch, is joined by the Kalni near Azmiriganj in northeastern Bangladesh, and the Kusiyara branch farther down. A few kilometers before the convergence of the lower Padma and the Meghna, the Dhaleswari, a Jamuna River distributary, enters the Meghna. The Meghna rises in size as it travels south, taking water from numerous rivers, including the Buriganga and the Sitalakhya.


The Jamuna and its tributaries go from north-central Bangladesh to the Meghna River in the southeast, covering a huge region. A number of rivers enter the Jamuna, particularly from the west, and their frequently changing courses not only preclude permanent settlement along the river's banks, but also obstruct connection between Bangladesh's northern and eastern regions, where Dhaka is located.


The Tista is Bangladesh's most significant waterway in the northwest. It begins in the Himalayas in Sikkim, India, and runs south until turning southeast at Darjiling (Darjeeling) and entering Bangladesh, where it meets the Jamuna. The Tista's lower sections are difficult to navigate due to the shoals and quicksand that surround the two rivers' confluence.


The Feni, the Karnaphuli, the Sangu, and the Matamuhari are the four main rivers that run through the Chittagong Hills and lowlands. They drain into the Bay of Bengal after flowing roughly west and southwest through the coastal plain. The Karnaphuli is the longest of these rivers, and it is dammed at Kaptai, some 30 miles (50 kilometers) upstream from its mouth in Chittagong.


None of Bangladesh's main rivers originate within the country's borders. The Surma's sources are in India; the higher Padma rises in Nepal, and the Jamuna in China, but both rivers flow through Indian territory to reach Bangladesh. As a result, Bangladesh has no complete control over the flow of any of the rivers that water the country.The building of a barrage upstream in West Bengal has resulted in a significant amount of water being diverted from the Ganges in India, and the flow to western Bangladesh is insufficient during the dry season, which runs from November to April. Since the 1970s, the fair sharing of the river's resources has been a subject of contention between India and Bangladesh.