Natural Levees and Landform Evolutions in the Bengal Lowland

This paper analizes the characteristics of natural levees and evolution of landforms in the Bengal Lowland. The natural levees in the lowland are classified into four types, such as broad and obscure, broad and distinct, narrow and continuous, and discotinuous types. Narrow and continuous natural levees are further sub-classified into those of meandering, dendritic and irregular patterns. Discontinuous natural levees are also sub-classified into an arc-shaped, mottled pattern and natural levees on the channel bars. Regional distribution of these types of natural levees was considered in relation to the condition of floodings and to the river shiftings reconstructed from various documents and maps. Broad and obscure natural levees were formed according to the shiftings of the Ganges River in the ancient times. Broad and distinct natural levees were formed along the distributaries of the Ganges River by the middle of the eighteenth century. Arcshaped and mottled distributed natural levees were formed by the main flow of the Brahmaputra River and its distributaries by 1830 AD., during the period when the Brahmaputra River had been flowing along the east of the Madhupur Jungle. After the shiftings of the two rivers, natural levees distributed in a dendritic pattern and a meandering pattern have been formed in the deep flooding area and moderate and shallow flooding areas respectively. Natural levees on the channel bars have been formed along the two rivers and small natural levees of irregularly distributed pattern extended in the region under the influence of the tide.