Answer:
Indian drainage system consists of a large number of small and big rivers. It is the outcome of the evolutionary process of the three major physiographic units and the nature and characteristics of precipitation.
The Peninsular drainage system is older than the Himalayan one as evident from the broad, largelygraded shallow valleys, and the maturity of the rivers. Three major geological events have shaped the present drainage systems of Peninsular India:
• Subsidence of the western flank of the Peninsula leading to its submergence below the sea during the early tertiary period. Generally, it has disturbed the symmetrical plan of the river on either side of the original watershed.
• Upheaval of the Himalayas when the northern flank of the peninsular block was subjected to subsidence and the consequent trough faulting.
• Slight tilting of the peninsular block from northwest to the southeastern direction gave orientation to the entire drainage system towards the Bay of Bengal during the same period.
Peninsular river system follows various drainage patterns due to different geographical factors present in the region:
• Heavily fractured and faulted terrain bears Rift Valley of rivers Narmada and Tapi causing rectangular and trellised drainage patterns.
• Extensive Basaltic Deccan plateau surfaces with low gradient exhibits dendritic pattern where the river channel follows the slope of the terrain. This is observed in case of rivers like Chambal and Son.
• Low uplands such as Amarkantak Plateau, Ranchi Plateau etc. produce radial drainage pattern. For e.g. – from Amarkantak hill, rivers like Narmada, Son and Mahanadi flow in different directions.
• Western coastal plains cause parallel drainage patterns where streams originate from Western Ghats (which acts as major water divide) and drain in straight courses towards west. Examples include sharavathi, netravathi and Mandovi Rivers.
• East flowing peninsular rivers like Godavari, Krishna and Cauvery develop dendritic drainage pattern. Thus, different geographical features such as plains, low uplands and plateaus have led to a mixed type of drainage pattern in peninsular India.
