Drainage System of India

Every river is a small part of a bigger picture. The area from which a river and its tributaries collect rainwater and melted snow is its drainage basin (also called the catchment area). A high ridge that separates one basin from the next is a water divide (watershed). The river, its tributaries and its distributaries together make a river system. India's rivers fall into two great families, and almost every exam question in this chapter is really asking which family a river belongs to.

Ask one question about any river: where does its water come from? If it comes from melting glaciers and rain, the river flows all year (perennial) and carries a huge load of silt: this is a Himalayan river (Indus, Ganga, Brahmaputra). If it comes only from the monsoon rain, the river swells in the rainy season and shrinks in summer (seasonal): this is a Peninsular river (Godavari, Krishna, Kaveri). Everything else, from delta shape to dam sites, follows from this one difference.

Most of the Peninsular rivers flow east into the Bay of Bengal because the plateau tilts gently towards the east. The Western Ghats run close to the west coast and act as the main water divide: the short, fast streams on their western face fall steeply into the Arabian Sea, while the long rivers on the eastern side take a slow, winding road to the Bay of Bengal. Two rivers, the Narmada and the Tapi, break this rule and flow west because they run in long, narrow rift valleys (blocks of land that sank between two faults). Overall, about three-fourths of India's drainage reaches the Bay of Bengal and about one-fourth reaches the Arabian Sea; a small area, such as the rivers of the Thar desert, has inland drainage that never reaches the sea.

The Indus (Sindhu) is the great western river of the Himalayan family and the river that gave India its name. It rises in Tibet, near Lake Mansarovar and Mount Kailash, from the Bokhar Chu glacier, where Tibetans call it Sengge Khambab / Singi Khamban ('Lion's Mouth'). It flows north-west through Tibet and then enters India in Ladakh, running between the Ladakh range and the Zaskar range. After a deep gorge near Gilgit it bends sharply round Nanga Parbat, enters Pakistan, receives the Panjnad (the joint waters of the five Punjab rivers) at Mithankot and finally falls into the Arabian Sea near Karachi. Inside India it flows only through Ladakh, so the Indus basin in India is mostly the basin of its five Punjab tributaries.

Think of the Indus system as a fan of five fingers spread out over Punjab. Five rivers (Jhelum, Chenab, Ravi, Beas, Sutlej) rush down from the Himalaya, flow south-west, and join one after another until a single stream, the Panjnad ('five waters'), meets the Indus in Pakistan. 'Punjab' itself means 'land of five waters'. The land between each pair of these rivers is a doab, and every doab has its own name.

Which Indus tributaries does India control? The Indus Waters Treaty (1960), signed at Karachi by Jawaharlal Nehru and Ayub Khan with the World Bank as a friendly party, divided the six rivers. The three eastern rivers (Ravi, Beas, Sutlej) were allotted to India for unrestricted use. The three western rivers (Indus, Jhelum, Chenab) went mainly to Pakistan, while India may use them only in limited ways such as run-of-the-river hydroelectric plants (Salal, Baglihar, Kishanganga) and some irrigation. The treaty set up a Permanent Indus Commission. In April 2025, India placed the treaty in abeyance.

The Ganga is India's national river (declared in 2008) and the lifeline of the Northern Plains. Its headstream, the Bhagirathi, rises from the Gaumukh snout of the Gangotri glacier in Uttarakhand. Its other great headstream, the Alaknanda, comes from the Satopanth and Bhagirath Kharak glaciers. The two meet at Devprayag, and from there the combined stream is called the Ganga. At Haridwar the river leaves the mountains and enters the plains. It then flows through Uttarakhand, Uttar Pradesh, Bihar, Jharkhand (a short stretch) and West Bengal, about 2,525 km in all. Near Farakka in West Bengal it splits: the Bhagirathi-Hooghly continues in India, while the main stream goes to Bangladesh as the Padma, meets the Brahmaputra (Jamuna) and then the Meghna, and falls into the Bay of Bengal through the Sundarbans delta.

The Ganga's tributaries follow a simple geometry. Coming from the Himalaya in the north, the big tributaries join from the left (north) bank: Ramganga, Gomti, Ghaghara, Gandak, Kosi, Mahananda. From the south, from the Peninsula, only a few reach the Ganga, on the right bank: Yamuna (which carries Chambal, Sindh, Betwa and Ken into the Ganga system) and Son. Himalayan tributaries are powerful and flood-prone because glaciers and heavy rain feed them.

A few more Ganga facts that exams like. The Ganga Action Plan was launched in 1985-86 to clean the river, and the Namami Gange mission began in 2014-15. The Ganga river dolphin (Susu) is India's National Aquatic Animal (2009), and the Vikramshila Gangetic Dolphin Sanctuary in Bhagalpur (Bihar) protects it. The Farakka Barrage (West Bengal, commissioned in the 1970s) diverts water into the Bhagirathi-Hooghly to flush silt from Kolkata port; the Ganga Water Treaty (1996) shares the Farakka waters with Bangladesh for 30 years. National Waterway-1 (Prayagraj to Haldia, about 1,620 km) is on the Ganga.

The Brahmaputra rises in Tibet, from the Chemayungdung (Angsi) glacier in the Kailash range, not far from the sources of the Indus and the Sutlej. In Tibet it is called the Yarlung Tsangpo ('Tsangpo' simply means 'river' in Tibetan). It flows east for more than a thousand kilometres, parallel to the Himalaya and north of it, carrying less water because Tibet is dry. Then, near the peak Namcha Barwa, it makes a sudden U-turn (the 'Great Bend') through a huge gorge and enters India in Arunachal Pradesh as the Siang (Dihang). After it meets the Dibang and the Lohit near Sadiya, it is known as the Brahmaputra and flows west through the Assam valley. In Bangladesh it is called the Jamuna; it joins the Ganga (Padma) and then the Meghna before falling into the Bay of Bengal.

In Assam the Brahmaputra becomes a wide braided river. It carries a heavy load of silt from the young Himalaya, but the plain is almost flat, so the river drops the silt in its own bed, builds sand-bars and splits into many channels. When the monsoon rains arrive, the channels cannot carry the water, and the river floods and changes its course. That is why Assam has frequent floods and erosion, and why river islands like Majuli exist.

Two other rivers of the east complete this topic. The Barak rises in the hills of Manipur, flows through Cachar in south Assam, and goes into Bangladesh as the Surma-Meghna; it is the second largest river of the north-east after the Brahmaputra. The Teesta (Sikkim and West Bengal) is an important Himalayan tributary of the Brahmaputra; in October 2023 a glacial lake outburst in north Sikkim caused a devastating flash flood on it. India and Bangladesh have still not signed a Teesta water-sharing agreement.

The Peninsular rivers are older than the Himalayan rivers. Their valleys are broad and shallow, their courses are fairly fixed, and they have already cut down close to their base level, so they do not meander much. They split into two sets by direction. The big east-flowing rivers (Mahanadi, Godavari, Krishna, Kaveri, with Pennar, Brahmani, Baitarani, Subarnarekha) rise in or near the Western Ghats, cross the whole plateau and fall into the Bay of Bengal, where they build deltas. The west-flowing rivers are fewer: the two big ones, Narmada and Tapi, and many short streams of the west coast that fall quickly from the Ghats into the Arabian Sea, forming estuaries.

Why do the Narmada and the Tapi flow west when almost everything else on the plateau flows east? Because they do not follow the tilt of the land: they follow two long rift valleys (troughs formed when a strip of land sank between two parallel cracks). The Narmada runs between the Vindhya (north) and the Satpura (south); the Tapi runs just south of the Satpura. A rift-valley river has a straight course and no space to spread its silt, so it makes an estuary, not a delta.

A multipurpose river valley project uses one dam for many jobs at once: irrigation, hydroelectric power, flood control, drinking water, navigation, fish farming and sometimes tourism. After Independence, Jawaharlal Nehru called such dams the 'temples of modern India'. The first great project was the Damodar Valley Corporation (DVC, 1948), modelled on the Tennessee Valley Authority of the USA, to tame the flood-prone Damodar ('Sorrow of Bengal'). Because India's rivers are seasonal and monsoon-fed, storing water in reservoirs is the only way to turn a rainy-season flood into a year-round supply.

Three words, three jobs. A dam holds water in a reservoir. A spillway lets extra water pass safely when the reservoir is full, controlling the release. A barrage (like Farakka, Harike, Kota) is a lower structure with gates that raises the water level just enough to feed canals or divert flow; it does not store much water. A weir is a still smaller overflow structure. Dams may be of earth, rock, masonry or concrete; they can be classified by structure (gravity, arch, buttress, earthfill), purpose and height.

Rivers do not respect state borders, so sharing their water leads to disputes. Article 262 of the Constitution lets Parliament make a law to settle inter-state river-water disputes, and Parliament passed the Inter-State River Water Disputes Act, 1956 to set up tribunals for this. Some famous disputes are in the table below. India also shares rivers with its neighbours: the Indus Waters Treaty (1960) with Pakistan, the Ganga Water Treaty (1996) with Bangladesh (a 30-year treaty on sharing Farakka waters in the dry season), and the Kosi (1954), Gandak (1959) agreements and the Mahakali Treaty (1996) with Nepal. The Teesta water-sharing agreement with Bangladesh is still pending.

A lake is a body of standing water in a hollow of the land, and every lake has a story of how the hollow was made. Seeing the cause helps you remember the place. India's lakes are scattered from Ladakh to Kerala, and exam questions usually ask for four things about a lake: the state, the type (freshwater / saltwater / lagoon), the cause of its origin, and what is special about it.

India has about 14,500 km of navigable inland waterways (rivers, canals, backwaters), looked after by the Inland Waterways Authority of India (IWAI), set up in 1986 with headquarters at Noida. Under the National Waterways Act, 2016, 111 waterways have been declared national waterways. The first five are the best-known and are asked most often.