Introduction-
- Drainage refers to the movement of water through well-defined channels, forming a network called a drainage system.
- Drainage basin : The specific area from which a river collects water is called its catchment area, while the larger region drained by a river and its tributaries is known as a drainage basin.
- The watershed : It defines the boundary between two drainage basins, with catchments of large rivers often referred to as river basins, and those of smaller water bodies called watersheds.
Difference between a river basin and a watershed-
- Watersheds are small in area while the basins cover larger areas
Division of Indian drainage system-
Indian drainage system may be divided on various bases.
A. On the basis of discharge of water (orientations to the sea), it may be grouped into
(i) The Arabian Sea drainage.
(ii) The Bay of Bengal drainage.
- They are separated from each other through the Delhi ridge, the Aravalis and the Sahyadris
- Nearly 77 per cent of the drainage area consisting of the Ganga, the Brahmaputra, the Mahanadi, the Krishna, etc. is oriented towards the Bay of Bengal
- Around 23% of India's river systems, including the Indus, Narmada, Tapi, Mahi, and Periyar, flow into the Arabian Sea.
B. On the basis of the size of the watershed, the drainage basins of India are grouped into three categories:
(i) Major river basins
- The major river basins refer to catchment areas that exceed 20,000 square kilometers. These basins encompass 14 drainage systems, including the Ganga, Brahmaputra, Krishna, Tapi, Narmada, Mahi, Pennar, Sabarmati, Barak, among others.
(ii) Medium river basins
- Medium river basins refer to the river basins with a catchment area ranging from 2,000 to 20,000 sq. km. There are 44 river basins falling under this category, including but not limited to Kalindi, Periyar, Meghna, and others.
(iii) Minor river basins
- It is the Basin with catchment area of less than 2,000 sq. km include fairly good number of rivers flowing in the area of low rainfall.
Evolution of Drainage system of Indian rivers
- The diastrophic movements, which helped in the formation of the Himalayas, have been responsible for drainage charges of rivers.
- These movements are responsible for the emergence of Himalayas out of the Tethys Sea. This sea was filled up by sediments brought by the rivers, flowing from two land masses- Gondwana land and Angaraland.
- During the first Himalayan upheaval in Oligocene period, part of Tethysian geosyncline was uplifted. This incidence is marked as an initiation of the Himalayan drainage.
- It is the assumption that the upheavals of Himalayas have been responsible for the changes in the river system of Punjab and Sindh. After the formation of the Shiwaliks, an earth movement took place in Punjab, which disrupted the drainage system of this Great River.
- The uplift of the Shiwalik Range gave the origin and development of three river system, which are known as the Indus system, Punjab Rivers system and Ganga system.
- After the developments of these systems, a number of changes took place. The dismemberment of the Indo-Brahma River, the Indus and its tributaries, the Ganga and its tributaries and the Brahmaputra and its tributaries came into being
- Geologists have forwarded this view also that in historical epoch, Sutlej and Yamuna were having their course of flow through Rajasthan. Saraswati River, which is now disappeared, was having its course near Nahan.
- River Yamuna, in the north of Delhi was having its course in the west of Karnal.
- In the early Christian era, Sutlej was an independent river. It emptied itself into the sea, but now it joins Indus River
Formation of 3 main Drainage system in Himalaya
According to geologists, during the Miocene period, which was approximately 5-24 million years ago, a massive river known as Shiwalik or Indo-Brahma flowed across the entire longitudinal expanse of the Himalayas, from Assam to Punjab, and ultimately drained into the Gulf of Sind near lower Punjab.
It is opined that in due course of time Indo– Brahma river was dismembered into three main drainage systems:
(i) The Indus and its five tributaries in the western part;
(ii) The Ganga and its Himalayan tributaries in the central part; and
(iii) The Brahmaputra in Assam and its Himalayan tributaries in the eastern part