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The Indian drainage system consists of a large number of small and big rivers.
It is an outcome of:
1. On the basis of discharge of water – the Arabian Sea drainage and the Bay of Bengal drainage:
On the basis of discharge of water (orientations to the sea), the drainage system of India may be grouped into:
They are separated from each other by the Delhi ridge, the Aravalis and the Sahyadris (water divide is shown by a line in the following map).
Nearly 77 percent of the drainage area consisting of the Ganga, the Brahmaputra, the Mahanadi, the Krishna, etc. is oriented towards the Bay of Bengal while 23 percent comprising the Indus, the Narmada, the Tapi, the Mahi and the Periyar systems discharge their waters in the Arabian Sea.
1. Rivers of the inland drainage basin (endorheic basin): When a river does not reach the sea but disappears into the sand, such a region is called an area of inland drainage. Inland drainage streams are ephemeral streams (short-lived). E.g.:
2. On the basis of the size of the watershed:
3. On the basis of the mode of origin, nature and characteristics:
There is no clear-cut line of demarcation between these two drainage systems, as many of the peninsular rivers like the Chambal, Betwa, Sind, Ken and Son are much older in age and origin than the Himalayan rivers.
Let’s follow this line of classification and look at the drainage system of India in detail. We begin with the Himalayan drainage.
Evolution of the Himalayan Drainage System:
There is a difference of opinion about the evolution of the Himalayan Rivers. However, geologists believe that:
Evidences: The remarkable continuity of the Shiwalik and its lacustrine origin and alluvial deposits consisting of sands, silt, clay, boulders and conglomerates support this viewpoint.
The dismemberment was probably due to the Pleistocene upheaval in the western Himalayas, including the uplift of the Potwar Plateau (Delhi Ridge), which acted as the water divide between the Indus and Ganga drainage systems.
Likewise, the downthrusting of the Malda gap area between the Rajmahal hills and the Meghalaya plateau during the mid-pleistocene period, diverted the Ganga and the Brahmaputra systems to flow towards the Bay of Bengal.
Let’s take up the three major river systems of the Himalayan drainage individually:
1. The Indus River System
Let’s look at some important tributaries of Indus:
The Indus water treaty: The waters of the Indus river system are shared by India and Pakistan according to the Indus Water Treaty signed between the two countries on 19th September 1960. According to this treaty, India can utilise only 20 percent of its total discharge of water. The Indus water treaty was recently in news. Remember why? Read here!