Most of the areas of Bangladesh lies within the broad delta formed by the Ganges and Brahmaputra rivers.
Lands are exceedingly flat, low-lying, and subject to annual flooding.
Much fertile, alluvial soil is deposited by the floodwaters. The only significant area of hilly terrain, constituting less than one-tenth of the nation's territory, is the Chittagong Hill Tracts in the narrow southeastern panhandle of the country. Small, scattered hills lie along or near the eastern and northern borders with India. The soil here is much less fertile than the annually replenished alluvium of the surrounding floodplain. They include hundreds of brooks and a good number of big ones.