There are differences in the opinion of geographers on the origin of peninsular drainage system. However, there are two accepted views.
According to one hypothesis the existing Peninsula is the remaining half of a land mass, which had the Western Ghats very near its centre as its primeval water-shed for two drainage systems, one easterly and the other westerly.
Sometimes during the early Tertiary period half of the Peninsula lying west of the Western Ghats is presumed to have cracked and sunk beneath the Arabian Sea.
This was due to the formation of a great normal fault along the Western Ghats. This argument is supported by the straight coastline, steep slope, and absence of delta deposits along the Sahyadri coast.
There is a second probably theory which is supported by the exceptional flow of Narmada and Tapi in Rift Valleys.
These faults are said to have originated with the bending or ‘sagging’ of the northern part of the Peninsula at the time of the upheaval of the Himalayas.
During the same time the peninsular block, south of the cracks, tilted slightly eastwards, giving a new orientation to the entire drainage towards the Bay of Bengal.
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