Evolution of Himalayan & Peninsular Drainage

EVOLUTION OF HIMALAYAN DRAINAGE

History of Himalayan Rivers is a topic of debate. But according to geologists, a powerful river called Shivalik or Indo-Brahma traversed the entire longitudinal extent of Himalaya from Assam to Punjab and onwards to Sind, and finally discharged into Gulf of Sind near lower Punjab during Miocene period some 5-24 million years ago.
It is opined that in due course of time Indo–Brahma river was dismembered into three main drainage systems:
Indus and its five tributaries in Western part
Ganga and its Himalayan tributaries in Central part
Brahmaputra in Assam and its Himalayan tributaries in the eastern part.
Dismemberment was probably due to
Pleistocene upheaval in Western Himalayas, including uplift of Potwar Plateau (Delhi Ridge), which acted as the water divide between the Indus and Ganga drainage systems.
Down thrusting of Malda gap between Rajmahal hills and Meghalaya plateau during mid-Pleistocene period, diverted Ganga and Brahmaputra systems to flow towards Bay of Bengal.

The current drainage networks in Peninsular India are a result of three significant geological phenomena that occurred in the distant past:

Subsidence of western flank of Peninsula leading to its submergence below the sea during the early tertiary period. In general, it has disrupted the river’s symmetry on either side of the original watershed.
Upheaval of Himalayas when the northern flank of the Peninsular block was subjected to subsidence and the consequent trough faulting. The Narmada and The Tapi flow in trough faults and fill the original cracks with their detritus materials. Hence, there is a lack of alluvial and deltaic deposits in these rivers.
During the same time period, a slight tilt of the Peninsular block in a southeastern direction oriented the entire drainage system towards the Bay of Bengal.

Himalayan drainage	Peninsular drainage
Perennial nature: glaciers and rainwater are the main sources.	Seasonal nature: rainwater is the main source.
River regimes have two maxima; one during summers due to glacial melt and second during SW monsoon.	River regime has one maxima; during SW monsoon period. River Kaveri increases its flow two times a year and flows throughout the year; Upper reaches get water during SW monsoon and lower reaches get water during NE retreating monsoon.
Length of rivers are relatively longer.	Rivers are relatively shorter
Size of river basins are relatively larger.	Their basins are relatively smaller
River valleys are deeper because of high erosion.	River valleys are shallower because of lesser erosion.
They have highly meandering paths as they pass through soft sedimentary rocks.	They have straighter courses as they move through hard peninsular rocks
They form larger deltas.
Drainage Basins Comparison: River basin is considered as the basic hydrological unit for planning and development of water resources. There are 12 major river basins with catchment area of 20000 km² and above. The total catchment area of these rivers is 25.3 lakh km². The major river basin is the Ganga-Brahmaputra-Meghna , which is the largest with catchment area of about 11.0 lakh km² (more than 43% of the catchment area of all the major rivers in the country).Ganga > Indus > Godavari > Krishna > Brahmaputra > Mahanadi > Narmada > Kaveri > Tapi