The Indian drainage may be broadly divided into two major systems on the basis of their orientation to the sea. These include: (l) the Bay of Bengal Drainage, and (2) the Arabian Sea Drainage.
These are separated from each other through the Delhi ridge (the Satluj-Yamuna divide), the Aravallis, the Sahyadris and Amarkantak. About 77 per cent of the drainage area of the country comprising the Ganga, Brahmaputra, Mahanadi, Godavari, Krishna, Penner, Kaveri, Vaigai basins is oriented towards the Bay of Bengal.
This includes majorparts of the Himalayas, the Great Plains, the Peninsular Uplands and the Eastern Coastal Plains. The Arabian Sea drainage area spreading over to 23 percent of the country’s surface flow area is confined to the north-western Himalayas, Punjab Plains, Rajasthan Plains, Gujarat Plains, Central Plateaus and the Western Coastal Plains. It commands river basins like Indus, Narmada, Tapi, Lune, Mahi and a number of swift flowing western coast rivers descending from the. Sahyadris.
Similarly on the basis of its mode of origin the Indian drainage may also be distinguished as the Himalayan drainage and the peninsular drainage. Here again there is no clear cut line of demarcation between these two drainage systems, as many of the Peninsular streams like the Chambal, the Betwa, the Son etc., much older in age and origin, form part of Krishna, Godavari, Pennar, Kaveri, Vaigai, west flowing Narmada, Tapi and West coast rivers. These have their outlet either to the Bay of Bengal or to the Arabian Sea.
Owing to complex physiographic and lithological characteristics and long geological history the river systems of India have formed varied drainage patterns.
These include antecedent pattern (by the Indus, Brahmaputra, the Satluj etc.), superimposed pattern (by Damodar, Subarnarekha, Chambal and Banas etc), dendritic pattern (by the rivers of the Ganga plain and South India), rectangular pattern (by Kosi and its tributaries and in the sandstone areas of the Vindhyas), radial pattern (in Amarkantak region by the Son, Mahanadi and Narmada), trellis pattern (in old folded areas of Singhbhum), parallel pattern (in Bijawar area and West Coastal Plain), inland drainage (in Rajasthan
(a) West flowing (10): Shetrunji, Bhadra, Dhadar, Burhabalang, Baitarni, Puma, Ambika, Vaitarna, Ulhas, Savitri, Mandavi, Gangavati, Kalinadi, Sharavati, Netiavati, Ghaliar, Bharatpuzhe, Periyar, and Pamba.
(b) East flowing (21): Rushikulya, Vamasdhara, Nagavali, Sarda, Yeleru, Gundlakamma, Musi, Paleru, Muneru, Kunleru, Kaitalaiyar, Palar, Gingee, Pannaiyar, Vellar, Vaigai, Cundar, Varshalli, Vaippar, and Tamrapani.
(c) Flowing into other countries (4): Karnaphali, Kaldan, Imphal, and Tixu Nanitaluk. Their mountain reaches but depicts maturity during their sojourn through the Great Plains forming depositional features like flat valleys, of-bow lakes, natural levees, flood plains and deltas.
The Himalayan courses of these rivers are highly tortuous but in plains they display a strong meandering tendency and shift their courses frequently. This poses problem in the utilisation of these rivers as dependable source of navigation and irrigation. The river regimes, although perennial, exhibit wide seasonal fluctuations; causing devastating floods during rainy season but shrinking to the bottom of the valley with a number of shoals during dry season.
These rivers continue to perform intensive erosional activity as is evident in the huge loads of sands and silt transported by them annually. The transverse sections of the Himalayan valleys with alternately Vs and Us signify the continuation of the process of the upliftment of the Himalayas.
Another well-known characteristic of the Himalayan Rivers is that where they cut across the mountains after flowing in longitudinal valleys they are joined at the bends by tributaries flowing down from the north (Mehdiratta, 1962, pp. 24-25). Many of the great Himalayan Rivers are older than the mountains they traverse.
The water of the Himalayan Rivers is utilised by numerous purposes, drinking, irrigation, river-transport, power generation, industrial use and tourism development.
Desert area by revers like Rupnarain, Medha, Jojari etc), and subsequent pattern (in the Peninsular foreland by the Chambal, Ken, Sindh, Betwa and Son).
On the basis of the size of the catchment area the drainage basins of the country may be grouped under three categories (Rao, 1977): (a) Major, having a catchment area of over 20,000 sq. km. This includes 14 drainage basins belonging to the Ganga, Indus, Godavari, Krishna, Brahmaputra, Mahanadi, Narmada, Kaveri, Tapi, Penner, Brahmani, Mahi, Subarnarekha, and Sabarmati which are characterised by high rainfall (i.e., 63 million cu. m/100km2 area), (b) Medium, having a catchment area of2,000- 20,000 sq. km This incorporates 44 river basins which generally receive medium rainfall (i.e., 45 million cu.m./lOO km2area), (c) Minor, with a catchment area of less than 2,000 sq. km. each. This includes a fairly good number of small rivers flowing in the area of low rainfall (i.e., 25 million cu. m. 100 km2 area).
Of the total annual run-off of the country (i.e., 18,58, 100 million cu. m) 84 per cent is carried over by the major river basins, while medium and minor (including inland drainage) river basins each contribute 8 per cent of annual yield of water (Das Gupta, 1989). The total catchment area of all river basins is 3,287,782 sq. km in which the medium and minor river basins occupy 7,11,833 sq. km of the area (21.6%).