Relief

Stretching northward from the Bay of Bengal, Bangladesh constitutes roughly the eastern two-thirds of the deltaic plain of the Padma (Ganges [Ganga]) and Jamuna (Brahmaputra) rivers. Except for small higher areas of jungle-covered old alluvium (rising to about 100 feet [30 metres]) in the northwest and north-centre—in the Barind and the Madhupur Tract, respectively—the plain is a flat surface of recent alluvium, having a gentle slope and an elevation of generally less than 30 feet (9 metres) above sea level. In the northeast and southeast—in the Sylhet and Chittagong Hills areas, respectively—the alluvial plains give place to ridges, running mainly north-south, that form part of the mountains that separate Bangladesh from Myanmar and India. In its southern region, Bangladesh is fringed by the Sundarbans, a huge expanse of marshy deltaic forest.

The Barind is a somewhat elevated triangular wedge of land that lies between the floodplains of the upper Padma and Jamuna rivers in northwestern Bangladesh. A depression called the Bhar Basin extends southeast from the Barind for about 100 miles (160 km) to the confluence of the Padma and Jamuna. This area is inundated during the summer monsoon season, in some places to a depth exceeding 10 feet (3 metres). The drainage of the western part of the basin is centred in the vast marshy area called the Chalan wetlands, also known as Chalan Lake. The floodplains of the Jamuna, which lie north of the Bhar Basin and east of the Barind, stretch from the border with Assam in the north to the confluence of the Padma 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 lower Padma.

In north-central Bangladesh, east of the Jamuna floodplains, is the Madhupur Tract. It consists of an elevated plateau on which hillocks ranging in height from 30 to 60 feet (9 to 18 metres) give contour to 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 in elevation from about 100 feet (30 metres) to more than 1,100 feet (330 metres).

In east-central Bangladesh the Brahmaputra River in its old course (the Old Brahmaputra River) built up the flood basin of the Meghna River, the region that includes the low and fertile Meghna-Sitalakhya 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 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 upper Padma. The basin’s total area is about 1,200 square miles (3,100 square km). The belt of land in southwestern Bangladesh bordering the Bay of Bengal constitutes the Immature Delta. A lowland of some 3,000 square miles (7,800 square km), the belt 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 is the Chittagong region, which 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 (1.6 to 16 km). 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 (600 metres) in elevation.