ABSTRACT
The South Asia region contains many large river systems: Ganges, Brahmaputra, Meghna, Indus, Godavari, Mahanadi, and Narmada (Fig. 1.1), which support millions of people. The river systems of South Asia can be classified into four major groups (a) Himalayan rivers; (b) Deccan rivers; (c) Coastal rivers; and (d) Rivers of the inland drainage basin. Table 1.1 lists these major rivers of South Asia, their origins and sources of water. The Himalayan rivers are formed by melting snow and glaciers and have continuous flow throughout the year. Snow and rainfed river basins occupy 2.32 million km2 or 55% of basin areas while the remaining 1.90 million km2 or 45% of basin areas belong to rainfed rivers. Snow and glaciers are partial sources of water for the large rivers: the Ganges, Brahmaputra and Indus, which originate in the Himalayas (Fig. 1.1). The rivers of the Deccan plateau are rainfed and fluctuate in volume, many of them being non-perennial; the coastal rivers, which,especially on the West Coast, are short in length with small catchment areas, most of them being non-perennial; and the rivers of the inland drainage basin in Western Rajasthan, which are ephemeral, drain towards the silt lakes such as Sambhar, or are lost in the desert sands.
