RIVER SYSTEMS OF INDIA

The drainage of the sub-continent is related to the evolution of the physiographic divisions of the region. Situated within the high precipitation area under mon­soonal domain, India is drained by numerous rivers falling either into the Bay of Bengal or the Arabian Sea. The Ganga, Brahmaputra, Mahanadi, Godavari, Krishna and Cauvery are the major river systems draining into the Bay of Bengal whereas the major river systems draining into the Arabian Sea are the Indus, Sabarmati, Narmada, Tapti and rivers of the west coast farther south. Indian rivers may be classified into four types depending upon the natuw of the river, geographical location, source and drainage area covered: Himalayan, peninsular, coastal and rivers of inland drainage basin.
The rivers constitute an important natural resource as they make a great contribution to irrigation, domestic and industrial water supply, hydropower generation and inland water transport. According to size, rivers of India can be classified as follows.
(a) Major rivers having catchment area of over 20,000 sq km each. There are 14 such basins, having high rainfall (i.e., 63 million cubic metres per 100 sq km).
(b) Medium rivers, having a catchment area of 2,000­20,000 sq km each. 44 rivers fall in this category. These have medium rainfall (i.e., 45 million cu m per 100 sq km).
(c) Minor rivers having a catchment area of less them 2,000 sq km each. There are a large number of such rivers. These have low rainfall (i.e., 25 million cu m per 100 sq km).

HIMALAYAN RIVERS The Himalayan rivers play an important role as they flow cutting longitudinal and trans­verse sections in valleys, regimes, terraces, cones and fans in the piedmont base and shifting beds in the plains. The Himalayan rivers fall into four broad groups:
(a) The Pre-Himalayan rivers like the Arun, Indus, Sutlej and Brahmaputra.
(b) The Great Himalayan rivers like the Ganga, Kali, Ghagra, Gandak and Teesta.
(c) The Lesser Himalayan rivers like the Beas, Ravi, Chenab and Jhelum.
(d) The Siwalik rivers like the Hindon and the Solani.
The Himalayan rivers rise from the Great Himalaya,
Karakoram, Ladakh, Zanskar, Kailash and the Trans-Hima­layan ranges and ultimately join together to form three great river systems. These are the Indus system, the Ganga system and the Brahmaputra system.