Sông Hằng, Brahmaputra và Meghna / Barak (GBM) hệ thống sông chiếm khoảng 175 triệu ha (MHA) của Nam Á (Hình ) và hỗ trợ hơn 500 triệu người (Verghese và Iyer, 1993). Họ là duy nhất trên thế giới đối với nước và trầm tích vật tư, quá trình kênh, và sự bất ổn. Trong khi Brahmaputra đứng thứ tư trong số các con sông lớn nhất của thế giới đối với có nghĩa là xả hàng năm, sông Hằng đứng thứ mười ba (Mirza, 1997). Ước tính sản lượng trầm tích hàng năm của Brahmaputra là tons/km2,. | 3 Are Floods Getting Worse in the Ganges Brahmaputra and Meghna Basins M. MONIRUL QADER MIRZA R. A. WARRICK N. J. ERICKSEN G. J. KENNY INTRODUCTION The Ganges Brahmaputra and Meghna Barak GBM river systems occupy about 175 million hectares mha of South Asia Fig. 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. Sitting at the confluence of the three major rivers Bangladesh area 148 000 sq. km is considered to be the most flood-affected country in the world followed by India. Every year slightly over one-fifth of its land area becomes flooded and in extreme cases more than two-thirds of the country is affected. In upstream India area 3 280 000 sq. km floods annually inundate an area larger than half of Bangladesh. Available information shows that in recent years flood damage in Nepal India and Bangladesh is increasing. Substantial increases in flood damage in Nepal during the 1980s were reported by the Asia Development Bank ADB .
