ABSTRACT
The mountain regions are more vulnerable to natural disaster due to its varying nature of relief where the developmental activities over the years has further accentuated the problem by upsetting the natural equilibrium of various physical processes operating in the mountain ecosystem. In India, most of the floods result from 75% of the annual average rainfall occurs during south–west monsoon season. During this season, the rainfall is highly non-uniform in time and space. The regions experiencing intense rainfall are affected due to flooding, whereas the regions having deficient rainfall face the problems of drought. There are incidents when one part of the country is experiencing flood while another is in the grip of severe drought. The flood problem varies from one river system to another. The rivers originating in the Himalayas carry a large amount of sediment, causing erosion of the banks in the upper reaches and over-topping in the lower segments. The Ganga–Brahmaputra–Meghana basin is one of the largest in the world. Flood is a common phenomenon in the Brahmaputra valley. All the districts of the Brahmaputra valley in Assam are inundated almost every year. An area of 30 out of 78 lakh ha, that is, about 45% of Assam’s total area, is flood prone. In Ganga basin, in general, the flood problem increases from west to east and from south to north. There is a problem of drainage congestion in the extreme western and north-western parts. The rivers such as Gandak, Burhi Gandak, Bagmati and Kamla and other small rivers of the Adhwara Group, Kosi in lower reaches and Mahananda at the eastern end spill over their banks causing considerable damage. High floods also occur in the river Ganga in some of the years causing considerable inundation of the marginal areas in Bihar. The main rivers of North West region are the tributaries of river Indus, namely Sutlej, Beas, Ravi, Chenab, and Jhelum, all flowing from the Himalayas. These rivers carry quite substantial discharges during monsoon season and also large volumes of sediment. Compared to the Ganga and Brahmputra river regions, the flood problem is relatively less in this North West region (CWC, 1980; Allen et al., 2016).
