ABSTRACT
The Ganges, Brahmaputra and Meghna/Barak (GBM) river systems occupy about 175 million hectares (mha) of South Asia (Fig. 3.1) and supports more than 500 million people (Verghese and Iyer, 1993). They are unique in the world with respect to water and sediment supplies, channel processes, and instability. While the Brahmaputra ranks fourth among the largest rivers of the world with regard to mean annual discharge, the Ganges ranks thirteenth (Mirza, 1997). The estimated annual sediment yield of the Brahmaputra is 1,028 tons/km2, the highest among the world’s largest rivers. On the other hand, the sediment yield of the Ganges is only 502 tons/km2 although its basin area is two times that of the Brahmaputra (Barua, 1994). The swinging and avulsion of the courses of the Ganges and Brahmaputra Rivers in recent history have significant influence on the morphology of their alluvial floodplains (Rahman, 1993; Brammer, 1996). They are characterized by high flows during the monsoon and low flows during the dry season. For example, the ratio of monsoon flow to dry season flow of the Ganges River at Hardinge Bridge in Bangladesh is 6:1 (Mirza and Dixit, 1997). The high flows often cause floods in many parts of these vast river basins.
