The current drainage system can be divided into Himalayan and the Peninsular rivers. The Himalayan rivers are perennial as they are fed by snow melting and precipitation. On the other hand, the peninsular rivers are dependent on precipitation, hence known as ephemeral.

Characteristic Features and Evolution of the current drainage system

Evolution of the current drainage system in Indian-subcontinent is the result of interplay of factors, like change of relief, precipitation etc. On this basis, drainage system in Indian-subcontinent is divided into - Himalayan and Peninsular drainage system.

Himalayan Rivers – During the Miocene period the Himalayas from Assam to Punjab and Sind was drained by the river Shiwalik or Indo-Brahma. Later it is dismembered due to the following factors:

1. In the Pleistocene period, western Himalayas witnessed upheaval, including the uplift of the Potawar Plateau (Delhi Ridge), which caused dismemberment of Indus and Ganga river system by acting as a water divide.
2. During the same period, the crustal down thrusting occurred in the area between the Rajmahal hills and the Meghalaya Plateau. It resulted into dismemberment of the Ganga and Brahmaputra river system. It led to diversion of the Ganga and the Brahmaputra towards the Bay of Bengal.

Peninsular Rivers – They are older than Himalayan Rivers, which is evident from the broad valleys and the maturity of rivers. Western Ghats act as the main water divide. It is the outcome of following 3 major events:

1. In the early Tertiary period, the western flank of the peninsula subsided leading to its submergence below the sea. Consequently, the direction of the river on either side of the original watershed got disturbed.
2. Later during the Pleistocene period, at the time of upheaval of Himalayas the northern flank of the peninsula subsided beneath the Eurasian plate thereby resulting into trough faulting. The Narmada and Tapi flow through these trough faults.
3. Subsidence of northern flank has also resulted into slight tilting of the peninsular block from the northeast to the south-eastern. It changed orientation of major peninsular rivers towards the Bay of Bengal.

Thus, the interplay between the three major physiographic units and the nature and characteristics of precipitation finally shaped the current drainage system in the Indian sub-continent.