Key Points

The term drainage describes the river system of an area. The area drained by a single river system is called a drainage basin.

An elevated area, such as a mountain or an upland, that separates two drainage basins is known as a water divide.

Indian rivers are divided into two major groups: the Himalayan rivers and the Peninsular rivers, based on their origin.

Himalayan rivers are mostly perennial as they get water from both rain and melted snow. They have long courses and form features like gorges, meanders, and deltas.

A large number of Peninsular rivers are seasonal, as their flow depends on rainfall. They have shorter and shallower courses compared to Himalayan rivers.

The Indus river rises in Tibet near Lake Mansarowar and flows west into the Arabian Sea. Its main tributaries include the Zaskar, Nubra, Satluj, Beas, and Ravi.

The headwaters of the Ganga, the Bhagirathi and the Alaknanda, join at Devaprayag. The Ganga has major tributaries like the Yamuna, Ghaghara, Gandak, and Kosi.

The Brahmaputra originates in Tibet, where it is known as Tsang Po. It enters India through Arunachal Pradesh and is known for forming a braided channel and causing floods in Assam.

The Narmada and the Tapi are the only long Peninsular rivers that flow west through rift valleys and form estuaries before draining into the Arabian Sea.

The Narmada river originates in the Amarkantak hills in Madhya Pradesh. It flows through a deep gorge in the 'Marble rocks' near Jabalpur.

The Godavari is the largest Peninsular river, with a length of about 1500 km. It is also known as the Dakshin Ganga.

Most major Peninsular rivers like the Mahanadi, Godavari, Krishna, and Kaveri flow eastwards and drain into the Bay of Bengal, forming deltas at their mouths.

India has many lakes, which can be freshwater like Wular Lake in Jammu and Kashmir, or saltwater like Sambhar Lake in Rajasthan.

Lakes are formed by various processes, including glacial action, river action (ox-bow lakes), coastal processes (lagoons like Chilika), and human activities like damming rivers.

Rivers and lakes are vital for the economy as they provide water for irrigation, domestic use, navigation, and hydro-power generation. They also support tourism.

The quality of river water is severely affected by the dumping of untreated sewage and industrial effluents. This rising pollution has led to river cleaning action plans.

According to the Indus Water Treaty, India can use only 20 percent of the total water carried by the Indus river system.

Formed by the Ganga and Brahmaputra rivers, the Sundarban Delta is the world's largest and fastest-growing delta. It is home to the Royal Bengal tiger.