Key Points

The flow of water through well-defined channels is called drainage, and the network of these channels is a drainage system. An area drained by a single river and its tributaries is known as a drainage basin.

A watershed is the boundary line separating one drainage basin from another. Watersheds are small in area, while river basins, which are catchments of large rivers, cover much larger areas.

Key patterns are Dendritic (tree-branch like), Radial (streams flow in all directions from a hill), Trellis (tributaries join main river at right angles), and Centripetal (rivers discharge into a central lake or depression).

Indian drainage is classified based on discharge into the Arabian Sea drainage and the Bay of Bengal drainage. By origin, it is classified into the Himalayan drainage and the Peninsular drainage.

Himalayan rivers are perennial as they are fed by both snowmelt and precipitation. They form deep gorges and V-shaped valleys in mountains and display strong meandering tendencies on the plains.

Geologists believe a single mighty river, the Shiwalik or Indo-Brahma, flowed from Assam to Punjab. It later dismembered into the present-day Indus, Ganga, and Brahmaputra systems due to geological upheavals.

Originating from the Bokhar Chu glacier in Tibet, the Indus is one of the world's largest river basins. Its five main tributaries in Punjab (Satluj, Beas, Ravi, Chenab, Jhelum) are collectively known as the Panjnad.

The Ganga originates as the Bhagirathi from the Gangotri glacier and is joined by the Alaknanda at Devprayag. It is India's largest river system, with major tributaries like the Yamuna, Ghaghara, Son, and Kosi.

Originating from the Chemayungdung glacier in Tibet where it is called Tsangpo, it enters India as the Siang. It is known for floods, channel shifting, and bank erosion in the Assam valley.

The Peninsular drainage system is older than the Himalayan one, characterized by broad, shallow valleys, a fixed course, and non-perennial flow. The Western Ghats act as the main water divide.

Most major Peninsular rivers flow eastwards and drain into the Bay of Bengal, forming deltas. These include the Mahanadi, the Godavari (also called Dakshin Ganga), the Krishna, and the Kaveri.

The Narmada and the Tapi are the two major rivers that flow westwards through rift valleys to drain into the Arabian Sea. They form estuaries rather than deltas.

The Kosi river is notoriously known as the 'sorrow of Bihar' for frequently changing its course and causing devastating floods. The Damodar was once known as the 'sorrow of Bengal'.

Key problems in using river water include uneven seasonal flow causing floods and droughts, river water pollution from industrial and domestic waste, and interstate disputes over water sharing.

The Namami Gange Programme is an Integrated Conservation Mission started in June 2014 by the Union Government. Its main objectives are the effective abatement of pollution, and the conservation and rejuvenation of the River Ganga.