Here is your short paragraph on the evolution of the Peninsular Drainage!
Geologists believe that the Sahyadri-Aravali axis was the main water divide in the geological past.
One hypothesis assumes that the existing peninsula is the remaining half of bigger landmass. The Western Ghats were located in the middle of this landmass dividing the entire drainage into two symmetrical parts—one flowing in the east and the other flowing in the west.
But the western part of the Peninsula cracked and submerged in the Arabian Sea and disturbed the symmetrical plan of the rivers on either side of the watershed during the early Tertiary period. During the collision of the Indian plate, a second major distortion was introduced in that the Peninsular block was subjected to subsidence and consequent trough faulting through which now flow main west flowing rivers of the Peninsula, namely the Narmada and the Tapi. This is amply proved by the straight coastline, steep western slope of the Western Ghats, and the absence of delta formations on the western coast.
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Another view is put forward keeping in view the exceptional behaviour of the Narmada and the Tapi. It is believed that these two rivers do not flow in the valleys formed by the rivers themselves. Rather they have occupied two fault planes or alluvium filled rifts in rocks running parallel to the Vindhyas. These faults are supposed to be caused by bend or ‘sagging’ of the northern part of the Peninsula at the time of upheaval of the Himalayas.
According to D.N. Wadia (1975) the Peninsular block, south of the cracks, tilted slightly eastwards thus giving new orientation to the entire drainage towards the Bay of Bengal. While this line of thought explains the present drainage system of the Peninsular India with greater satisfactions, it still leaves some questions to which there is no satisfactory answer. R.C. Mehdiratta (1962) argues that tilting should have increased the gradient of the river valleys and caused some rejuvenation of the rivers.