Bangladesh constitutes the eastern two-thirds of the Ganges-Brahmaputra deltaic plain, which stretches northward from the Bay of Bengal. It has the largest area of river delta in the world, with three main rivers, the Ganges, the Bhrahmaputra and the Meghna. Bangladesh occupies the alluvial plain and delta of the lower Bhrahmaputra River, together with a triangle between the Bhrahmaputra and the Ganges, and the triangular plain to the south of the Shillong plateau and the Arakan range on the east. A narrow coastal plain extends southwards at the foot of the Arakan Hills, some of the lower foothills lie within the frontier behind Chittagong. The southern part of the delta is crossed by a complex system of distributaries and interlinking waterways. The southern fringe consists of a series of low muddy islands separated by narrow tidal creeks, with mangrove swamps along the seaward margin. The soil is mostly fine alluvium but there are patches of coarser material, as in the Madhupur jungle. The myriad tributaries and distributaries of the three main rivers divide the entire country.
In Bangladesh three geographical zones can be distinguished:
Except for small higher areas of jungle-covered old alluvium (rising to about 100 feet [30 metres]) in the northwest and north-centre--called, respectively, the Barind and Madhupur tracts--the plain is a flat surface of recent alluvium, having a gentle slope and generally with an elevation of less than 30 feet above sea level. In the northeast and southeast the alluvial plains--called, respectively, the Sylhet and Chittagong hills--give place to ridges, running mainly north-south, that form part of the mountain divide with Myanmar and India. Bangladesh is fringed on the south by the Sundarbans, a huge expanse of marshy deltaic forest.
The Barind Tract is a triangular wedge of land in northwestern Bangladesh located between the Ganges floodplains (also known in Bangladesh as the Padma) and the Jamuna (the main channel of the lower Brahmaputra). The soil of this region is hard, reddish clay, and the region is comparatively elevated. A depression called the Bhar Basin extends southeast of the Barind Tract for about 100 miles between the floodplains of the Ganges and Jamuna rivers to their confluence. This area is inundated during the summer monsoon season, in some places to a depth of 12 feet. The drainage of the western part of the basin is centred in the vast marshy area called the Chalan Beel (Chalan wetlands). The floodplains of the Jamuna, which lie north of the Bhar Basin and east of the Barind Tract, stretch from the border with Assam in the north to the confluence of the Ganges and Jamuna in the south. The area is dominated by the Jamuna, which frequently overflows its banks in devastating floods. South of the Bhar Basin is the floodplain of the Ganges.
In north-central Bangladesh, east of the Jamuna floodplains, is the Madhupur Tract. It consists of an elevated plateau, with hillocks varying in height from 30 to 60 feet, and cultivated valleys. The Madhupur Tract contains sal trees, whose hardwood is comparable in value and utility to teak. East of the Madhupur Tract, in northeastern Bangladesh, is a region called the Northeastern Lowland. It encompasses the southern and southwestern parts of the Sylhet area (including the valley plain of the Surma River) and the northern part of the Mymensingh area and has a large number of lakes. The Sylhet Hills in the far northeast of the region consist of a number of hillocks and hills ranging from 100 feet to more than 1,100 feet in height.
In east-central Bangladesh the Brahmaputra River in its old course built up the Meghna Flood Basin, which includes the low and fertile Meghna-Lakhya Doab (the land area between those rivers). This area is enriched by the Titas distributary, and land areas are formed and changed by the deposition of silt and sand in the riverbeds of the Meghna River, especially between Bhairab Bazar and Daudkandi. Dhaka, the capital city is located in this region.
In southern Bangladesh the Central Delta Basins include the extensive lakes in the central part of the Bengal Delta, to the south of the Ganges. The basin's total area is about 1,200 square miles. The belt of land in southwestern Bangladesh bordering the Bay of Bengal constitutes the Immature Delta. The belt--a lowland of some 3,000 square miles--contains, in addition to the vast mangrove forest known as the Sundarbans, the reclaimed and cultivated lands to the north of it. The area nearest the Bay of Bengal is crisscrossed by a network of streams that flow around roughly oblong islands. The Active Delta, located north of the Central Delta Basins and east of the Immature Delta, includes the Dhaleswari-Padma Doab and the estuarine islands of varying sizes that are found from the Pusur River in the southwest to the island of Sandwip near Chittagong in the southeast.
Lying to the south of the Feni River in southeastern Bangladesh, the Chittagong region has many hills, hillocks, valleys, and forests and is quite different in aspect from other parts of the country. The coastal plain is partly sandy and partly composed of saline clay; it extends southward from the Feni River to the town of Cox's Bazar and varies in width from 1 to 10 miles. The region has a number of offshore islands and one coral reef, St. Martin's, off the coast of Myanmar. The hilly area known as the Chittagong Hill Tracts in the far southeast consists of low hills of soft rocks, mainly clay and shale. The north-south ranges are generally below 2,000 feet in height.
Physiographic Map of Bangladesh (122Kb)
Link to Shaded Relief Map of Bangladesh (423Kb)
