Drainage System of India: Rivers, Basins and Patterns

1. Drainage, basins and watersheds: the vocabulary and the classifications

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• Drainage is water flowing through well-defined channels. A drainage system is the network of those channels. Its pattern depends on geological age, rock type and structure, topography, slope, the amount of water and how regularly it flows. Choked or poorly defined channels cause floods.
• Catchment area is the area from which a river collects its water. The catchment of a large river is a river basin. The catchment of small rivulets and rills is usually called a watershed.
• A drainage basin is the whole area drained by a river and its tributaries. The watershed is also the boundary line between two basins. A basin works as one unit, because what happens upstream affects everything below. That makes basins the best micro, meso and macro planning regions.
• Arabian Sea and Bay of Bengal drainage:
• About 77% of the drainage area drains to the Bay of Bengal (Ganga, Brahmaputra, Mahanadi, Godavari, Krishna, Kaveri).
• About 23% drains to the Arabian Sea (Indus, Narmada, Tapi, Mahi, Periyar).

• The divide runs along the Delhi ridge, Aravallis and Sahyadri.

• Classification of river basins by size:

Class	Catchment	Number	Examples
Major	> 20,000 sq km	14	Ganga, Brahmaputra, Krishna, Tapi, Narmada, Mahi, Pennar, Sabarmati, Barak
Medium	2,000–20,000 sq km	44	Kalindi, Periyar, Meghna
Minor	< 2,000 sq km	many	mostly in low-rainfall areas

• NCERT uses older CWC data. The CWC–NRSC River Basin Atlas (2012) uses 20 basins (verify current).
• By origin, rivers are Himalayan or Peninsular. This is the "most accepted" scheme and Class 11 follows it. Its flaw is that the Chambal, Betwa and Son belong to the Ganga system but are much older Peninsular rivers.

2. Drainage patterns

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A drainage pattern is the shape a river and its tributaries make on a map. Slope, rock structure and history control it.

• Dendritic drainage pattern: tree-like. Tributaries join at acute angles (narrower than a right angle). It forms on uniform rock and gentle slopes, as in the rivers of the northern plain.
• Radial drainage pattern: rivers flow outward in all directions from a high centre.
• The Amarkantak plateau (Maikal range, Madhya Pradesh–Chhattisgarh border, about 1,057 m at the Narmada source) is the classic Peninsular example.

• The Narmada flows west, the Son north, and Mahanadi headwaters such as the Arpa east and south. The plateau is part of a biosphere reserve.

• Trellis drainage pattern: main tributaries run parallel and secondary streams join them at right angles. It forms on alternating bands of hard and soft rock in folded country. Beyond NCERT, examples are the folded Himalayas and Singhbhum.

• Centripetal drainage pattern: streams flow inward from all sides into a lake or depression, as at Loktak (Manipur) and the Sambhar basin.
• Beyond NCERT:
• Rectangular: right-angled bends that follow joints and faults (parts of the Vindhyas, the Chambal area).
• Annular: rings of streams around an eroded dome.
• Parallel: short streams running side by side down the Western Ghats.

• Deranged: a disordered pattern on glaciated ground.

• Exam pairs: dendritic vs trellis (rock uniformity), radial vs centripetal (outward vs inward).

3. The Himalayan drainage: character and evolution

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• Himalayan drainage system: the Indus, Ganga and Brahmaputra basins.
• They are fed by both snowmelt and rain, so they are perennial.
• In the mountains they cut giant gorges, V-shaped valleys, rapids and waterfalls.

• On the plains they build floodplains, oxbow lakes, braided channels and deltas. They meander and shift course.

• Kosi, the "sorrow of Bihar":

• Huge silt from its upper reaches blocks its channel.

• The river then shifts course. Beyond NCERT, it moved about 120 km west in two centuries, and its embankment breached at Kusaha in August 2008.

• Water tower of Asia: the Himalaya–Tibet ice mass is the largest outside the poles. Beyond NCERT (ICIMOD 2019), it feeds rivers used by about 2 billion people, and glacier melt threatens this supply.

• Antecedent river: a river older than the mountains it crosses. It kept cutting down as the land rose, so it flows through deep cross-gorges.
• Examples: the Indus, Satluj, Kosi (Arun), Subansiri and Brahmaputra (gorge at Namcha Barwa).

• Class 11 names the Satluj, Kosi and Subansiri.

• Indo-Brahma river (also called the Shiwalik river):

• Before: in the Miocene (about 5–24 million years ago), one great river ran from Assam to Punjab and Sind and into the Gulf of Sind.
• Evidence: the continuous Shiwalik deposits of lake and river sands, silt, clay, boulders and conglomerates.

• Break-up: it split into three systems: the Indus with its five tributaries (west), the Ganga (centre) and the Brahmaputra in Assam (east).

• Causes of the break-up:

• Pleistocene uplift in the western Himalayas, including the Potwar plateau, created the Indus–Ganga divide. NCERT writes "Potwar Plateau (Delhi Ridge)", but the Potwar plateau itself lies in Pakistan's Punjab.

• Mid-Pleistocene down-throw of the Malda gap, between the Rajmahal hills and the Meghalaya plateau, turned the Ganga and Brahmaputra towards the Bay of Bengal.

• Indus–Ganga water divide: a low divide through Haryana and Delhi, linked to the Delhi ridge.

• Mansarovar and Rakas Tal: twin high lakes near Mount Kailash in Tibet. The Satluj flows out of Rakas Tal. The Indus, Brahmaputra and Karnali (Ghaghara) rise nearby.

4. The Indus system

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• Indus river (Class 11 figures):
• Basin of 11,65,000 sq km (3,21,289 sq km in India). Length 2,880 km (1,114 km in India).

• It rises near the Bokhar Chu glacier (31°15'N, 81°40'E) at 4,164 m in the Kailash range, Tibet. There it is called Singi Khamban ("Lion's mouth").

• Course of the Indus:

• It flows northwest between the Ladakh and Zaskar ranges.
• It cuts a gorge near Gilgit and enters Pakistan near Chilas (Dardistan).
• It leaves the hills at Attock, where the Kabul joins on the right bank.
• Other right-bank tributaries rise in the Sulaiman range: the Khurram, Tochi, Gomal, Viboa and Sangar.
• The Panjnad joins just above Mithankot, and the river ends in the Arabian Sea east of Karachi.

• In India it flows only through Ladakh and Jammu and Kashmir.

• Shyok river: rises from the Rimo glacier near the Karakoram, receives the Nubra and joins the Indus in Baltistan. The Galwan is its tributary.

• Panjnad: the five rivers of Punjab, the Jhelum, Chenab, Ravi, Beas and Satluj. Trap: the Indus itself is not one of them.
• The five rivers:
• Jhelum river: rises from a spring at Verinag at the foot of the Pir Panjal. It flows through Srinagar and Wular lake, then through a gorge into Pakistan, and joins the Chenab near Jhang.
• Chenab river: the largest Indus tributary. The Chandra and Bhaga meet at Tandi near Keylong (Himachal Pradesh), so it is also called Chandrabhaga. It flows 1,180 km before entering Pakistan. Beyond NCERT, it is spanned by the Chenab rail bridge (opened 2025), the world's highest railway arch bridge.
• Ravi river: rises west of the Rohtang pass in the Kullu hills. It flows through the Chamba valley between the Pir Panjal and Dhauladhar and joins the Chenab near Sarai Sidhu.
• Beas river: rises at Beas Kund (about 4,000 m) near Rohtang. It flows through the Kullu valley, with gorges at Kati and Largi, and meets the Satluj at Harike. It lies wholly in India.

• Satluj river: rises at Rakas Tal (4,555 m), where it is called Langchen Khambab. It runs about 400 km parallel to the Indus and enters India at Shipki La. It is antecedent, leaves its gorge at Rupar and feeds Bhakra Nangal.

• Indus Waters Treaty 1960 (beyond NCERT):

• India gets the eastern rivers (Ravi, Beas, Satluj).
• Pakistan gets the western rivers (Indus, Jhelum, Chenab), with limited non-consumptive use by India, such as run-of-river power. Indian projects on the western rivers include Kishanganga, Ratle and Pakal Dul.
• India put the treaty in abeyance in April 2025 (verify current).

5. The Ganga system: headwaters, main stem and delta

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• Ganga river: India's most important river, both for its basin and for its culture.
• Gangotri glacier: in Uttarkashi district, Uttarakhand. Its snout at Gaumukh (3,900 m) is the source of the Bhagirathi river.
• The Bhagirathi cuts the Central and Lesser Himalayas in narrow gorges. The Tehri dam is on it.

• The glacier is retreating.

• Alaknanda river: rises in the Satopanth glacier above Badrinath. At Devprayag the Bhagirathi and Alaknanda meet, and the river is called the Ganga from there on.

• Panch Prayag, the five confluences on the Alaknanda in downstream order: 1. Vishnuprayag (Dhauliganga, at Joshimath) 2. Nandprayag (Nandakini) 3. Karnaprayag (Pindar) 4. Rudraprayag (Mandakini) 5. Devprayag (Bhagirathi)

• A confluence is where rivers meet. Other examples: the Triveni Sangam at Prayagraj (Ganga, Yamuna and the mythical Sarasvati) and Harike (Beas–Satluj).

• Main stem:
• The Ganga enters the plains at Haridwar and flows south, then southeast, then east.
• Length 2,525 km: Uttarakhand 110 km, Uttar Pradesh 1,450 km, Bihar 445 km, West Bengal 520 km.

• Tributaries: the Son is the main right-bank tributary. Left-bank tributaries are the Ramganga, Gomati, Ghaghara, Gandak, Kosi and Mahananda.

• Ganga basin: about 8.6 lakh sq km in India. Beyond NCERT, that is about 26% of India's area across 11 states, supporting over 500 million people.

• Delta: near Farakka the river splits into the Bhagirathi–Hugli and the Padma river.
• The Hugli reaches the sea at Sagar Island, where the Gangasagar Mela is held at Makar Sankranti.

• In Bangladesh the Padma receives the Jamuna (Brahmaputra) and then reaches the sea as the Meghna.

• Cleaning the Ganga:

• Namami Gange was approved in June 2014 as the flagship Integrated Conservation Mission.
• Its pillars are sewerage, river-front development, surface cleaning, biodiversity, afforestation, public awareness, industrial effluent monitoring and Ganga Gram.
• Beyond NCERT: the Ganga Action Plan (1985), the Ganga declared National River (2008), and the Gangetic dolphin declared National Aquatic Animal (2009).

6. Tributaries of the Ganga: Yamuna, the Peninsular feeders and the Himalayan left-bank rivers

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• Yamuna river: the westernmost and longest Ganga tributary.
• It rises in the Yamunotri glacier on the western slopes of the Banderpunch range (6,316 m) and joins the Ganga at Prayagraj.
• Right-bank tributaries come from the Peninsular plateau: the Chambal, Sind, Betwa and Ken.
• Left-bank tributaries: the Hindan, Rind, Sengar and Varuna.
• Its water feeds the Western and Eastern Yamuna canals and the Agra canal.

• States drained: Uttarakhand, Himachal Pradesh, Haryana, Delhi and Uttar Pradesh.

• Chambal river: rises near Mhow on the Malwa plateau.

• It flows north through a gorge above Kota. The Gandhi Sagar dam is on it.
• It then passes Bundi, Sawai Madhopur and Dholpur to the Yamuna.

• It is known for its badland ravines (land cut into deep gullies by erosion). The National Chambal Sanctuary (1979) protects gharials.

• Betwa and Ken rivers: rise in the Vindhyan region and drain Bundelkhand. They are joined by the Ken–Betwa link (Section 12).

• Son river: the large south-bank tributary from Amarkantak. It forms waterfalls at the edge of the plateau and joins the Ganga near Arrah, west of Patna.
• Damodar river: flows in a rift valley (a valley formed where land sank between faults) on the eastern edge of Chotanagpur to the Hugli. The Barakar is its main tributary. Once the "sorrow of Bengal", it was tamed by the Damodar Valley Corporation (1948, modelled on the Tennessee Valley Authority).
• Himalayan left-bank rivers, west to east:
• Ramganga: rises near Gairsain, enters the plains near Najibabad and joins the Ganga near Kannauj.
• Ghaghara river: rises in the Mapchachungo glaciers. It receives the Tila, Seti and Beri, cuts a gorge at Shishapani, receives the Sarda in the plains and joins the Ganga at Chhapra.
• Sarda river: rises in the Milam glacier as the Goriganga. It is called the Kali (or Chauk) along the India–Nepal border and joins the Ghaghara.
• Gandak river: formed by the Kaligandak and Trishulganga in Nepal, between Dhaulagiri and Everest. It enters India in Champaran and joins the Ganga at Sonpur near Patna.
• Kosi river: antecedent. Its main stream, the Arun, rises north of Everest. With the Son Kosi (west) and Tamur Kosi (east), it forms the Sapt Kosi.
• Mahananda river: rises in the Darjiling hills. It is the last left-bank tributary, joining in West Bengal.

7. The Brahmaputra system

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• Brahmaputra river: one of the world's largest rivers. It rises in the Chemayungdung glacier of the Kailash range, near Mansarovar.
• Yarlung Tsangpo: the river's name in Tibet. "Tsangpo" means "the purifier".
• It flows east for about 1,200 km through dry, flat southern Tibet.
• The Rango Tsangpo is its main right-bank tributary there.

• It cuts a deep gorge round Namcha Barwa (7,755 m).

• Siang river (also called the Dihang): the name of the river where it leaves the foothills. It enters India west of Sadiya (Arunachal Pradesh). After the Dibang (Sikang) and Lohit join on the left bank, it is called the Brahmaputra.

• Assam valley stretch (about 750 km):
• Left-bank tributaries: the Burhi Dihing and Dhansari (South).

• Right-bank tributaries: the Subansiri, Kameng, Manas and Sankosh.

• Subansiri river: an antecedent river that rises in Tibet. The 2,000 MW Subansiri Lower project is on it (commissioning; verify current).

• Into Bangladesh:
• The river enters Bangladesh near Dhubri.
• The Tista river (from Sikkim, through north Bengal) joins on the right bank. Sharing its water is a pending India–Bangladesh issue.

• From there the river is called the Jamuna. It merges with the Padma and reaches the Bay of Bengal.

• Why it floods:

• It has large tributaries and a very wet catchment.

• So it carries heavy silt, which causes floods, channel shifting and bank erosion.

• Beyond NCERT:

• China began a very large hydropower project (about 60 GW) on the lower Yarlung Tsangpo near Medog in July 2025 (verify current).
• India's proposed answer is the Siang Upper Multipurpose Project (about 11,000 MW), which faces local opposition.

8. The Peninsular drainage: character, evolution and contrast with the Himalayan rivers

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• Peninsular drainage system: older than the Himalayan system.
• Its valleys are broad, shallow and largely graded (smoothed to a gentle, even slope).
• Its rivers have fixed courses, few meanders and non-perennial flow. The Narmada and Tapi, which flow in rift valleys, are the exceptions.

• The Western Ghats are the main divide.

• East-flowing rivers of the Peninsula (Mahanadi, Godavari, Krishna, Kaveri) follow the plateau's tilt to the Bay of Bengal and build deltas. The Chambal, Sind, Betwa, Ken and Son belong to the Ganga system.

• Evolution of the Peninsular drainage, in three events: 1. The western flank subsided below the sea in the early Tertiary. This broke the balanced arrangement of rivers on both sides of the old divide. 2. During the Himalayan uplift, the northern flank sank and trough faults formed. The Narmada and Tapi flow in these faults and fill them with debris, so they build no deltas. 3. A slight tilt of the block from northwest to southeast turned most rivers towards the Bay of Bengal.

• Perennial and non-perennial rivers: perennial rivers (snow-fed Himalayan) flow all year. Non-perennial or ephemeral rivers (most Peninsular and desert streams) flow mainly in the rains.

Feature	Himalayan	Peninsular
Source of water	snow + rain, perennial	rain only, seasonal
Basin	very large	smaller
Valleys	deep gorges, antecedent, youthful	broad, graded, mature
Course on plains	meandering, shifting	fixed, few meanders
Mouth	big deltas	deltas in the east, estuaries in the west
Silt load	high	low

• River regimes (from the earlier NCERT edition). A regime is the seasonal pattern of a river's flow.
• Ganga: highest in August–September, lowest in January–June. It has two sources of high water, snowmelt in early summer and the monsoon.
• Narmada: very low from January to July, peaking in August.
• Godavari: lowest in May, highest in July–August.

9. The east-flowing Peninsular rivers: Mahanadi, Godavari, Krishna and Kaveri

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• Mahanadi river:
• Rises near Sihawa (NCERT: Raipur district; now Dhamtari district), Chhattisgarh, and flows through Odisha to the Bay of Bengal.
• Length 851 km. Basin 1.42 lakh sq km: 53% in Madhya Pradesh and Chhattisgarh, 47% in Odisha.

• Some navigation in the lower course. Beyond NCERT: the Hirakud dam (1957), the delta near Cuttack, and the Mahanadi tribunal (2018; verify current).

• Godavari river: the largest Peninsular system, called the "Dakshin Ganga".

• Rises near Trimbakeshwar, Nashik district (Maharashtra). Length 1,465 km. Basin 3.13 lakh sq km: 49% Maharashtra, 20% Madhya Pradesh and Chhattisgarh, the rest Andhra Pradesh (now also Telangana).
• Tributaries: the Penganga, Indravati, Pranhita, Manjra.

• It forms a gorge at Polavaram and floods heavily below it. It is navigable only in the delta and splits into a large delta after Rajahmundry.

• Krishna river: the second largest east-flowing river.

• Rises near Mahabaleshwar in the Sahyadri. Length 1,401 km.
• Tributaries: the Koyna, Tungabhadra, Bhima.
• Basin: 27% Maharashtra, 44% Karnataka, 29% Andhra Pradesh and Telangana.

• Beyond NCERT: the Nagarjunasagar and Srisailam dams.

• Kaveri river:

• Rises at Talakaveri, in the Brahmagiri hills (1,341 m) of Kodagu, Karnataka. Length 800 km. Basin 81,155 sq km: 3% Kerala, 41% Karnataka, 56% Tamil Nadu.

• Tributaries: the Kabini, Bhavani, Amravati.

• Why the Kaveri flows all year:

• Its upper catchment gets the southwest (summer) monsoon.
• Its lower catchment gets the northeast (winter) monsoon.

• So its flow changes less than that of any other Peninsular river.

• Kaveri dispute (beyond NCERT): Cauvery Water Disputes Tribunal award (2007), Supreme Court judgment of 16 February 2018, and the Cauvery Water Management Authority (2018).

• Smaller east-flowing rivers: the Subarnarekha, Baitarani, Brahmani, Vamsadhara, Pennar, Palar and Vaigai.

10. The west-flowing rivers, rift valleys and the Luni's inland drainage

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• Narmada river: the largest west-flowing river.
• It rises on the western flank of Amarkantak (about 1,057 m).
• It flows in a rift valley between the Vindhyas (north) and the Satpura (south).
• After about 1,312 km it meets the Arabian Sea south of Bharuch in a 27 km estuary. Catchment about 98,796 sq km.

• The Sardar Sarovar project is on it.

• Marble Rocks and Dhuandhar Falls: at Bhedaghat near Jabalpur, the Narmada cuts a gorge through white marble. It drops about 30 m at Dhuandhar ("smoke-mist") falls.

• Beyond NCERT: the Narmada tribunal award (1979, among Gujarat, Madhya Pradesh, Maharashtra and Rajasthan) and the Narmada Bachao Andolan (a campaign against displacement by the dams).
• Tapi river:
• Rises at Multai (Betul district, Madhya Pradesh). Length 724 km. Basin 65,145 sq km: 79% Maharashtra, 15% Madhya Pradesh, 6% Gujarat.

• It flows in a rift valley between the Satpura and the Ajanta–Satmala hills and reaches the sea near Surat.

• Narmada and Tapi as west-flowing rivers:

• Cause: they flow west along trough faults.
• Process: their channels are filled with debris, the rock is hard, they carry little silt, and tides scour their mouths.

• Result: they form estuaries (wide, open river mouths where tides mix fresh and sea water), not deltas.

• West-flowing rivers of the Peninsula:

• In Gujarat: the Sabarmati and Mahi (which crosses the Tropic of Cancer twice).
• Short, swift Western Ghats streams: the Vaitarna, Kalinadi, Sharavati, Mandovi, Zuari, Netravati, Bharathapuzha and Periyar.

• They form estuaries and lagoons and have good hydropower potential.

• Jog Falls: about 253 m on the Sharavati (Shivamogga district, Karnataka). It is among India's highest plunge falls, with the Linganamakki dam upstream.

• Luni river: the largest river system of Rajasthan west of the Aravallis.
• It rises near Pushkar as two branches, the Saraswati and Sabarmati, which join at Govindgarh.
• It flows west to Telwara, then southwest into the Rann of Kachchh.

• It is wholly ephemeral and salty downstream.

• Inland drainage: streams that never reach the sea but end in a lake, playa (a shallow salt flat) or the sand, as is common in the Thar. Sambhar is an example.

11. Lakes of India

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• Lakes by origin (beyond NCERT):

Origin	Examples
Tectonic	Wular (partly), Pangong Tso
Glacial and high-altitude	Tso Moriri, Tsomgo
Lagoon (coastal)	Chilika, Pulicat, Vembanad
Oxbow (river-made)	Kanwar Tal (Bihar)
Crater	Lonar (Maharashtra, meteorite impact; Ramsar 2020)
Inland saline	Sambhar, Didwana
Man-made	Gobind Sagar, Nagarjuna Sagar

• Freshwater and Himalayan lakes:
• Wular Lake: in the Kashmir valley, one of Asia's largest freshwater lakes. The Jhelum flows through it and it soaks up floodwater. Ramsar site since 1990. It is shrinking from silt and encroachment.
• Loktak Lake: in Manipur, the North-East's largest freshwater lake. It is known for phumdis (floating mats of vegetation). Keibul Lamjao, the only floating national park, is on it and is home to the sangai deer. Ramsar 1990; on the Montreux Record (the Ramsar list of threatened sites).

• Pangong Tso: about 134 km long at about 4,350 m in eastern Ladakh, with roughly two-thirds in Tibet. It is brackish and has no outlet. It was an India–China friction point in 2020–21.

• Coastal lagoons and wetlands:

• Chilika Lake: in Odisha, at the Mahanadi delta. It is Asia's largest brackish-water lagoon and one of India's first two Ramsar sites (1981). It has Irrawaddy dolphins and Nalabana bird sanctuary. It was taken off the Montreux Record in 2002.
• Pulicat Lake: on the Andhra Pradesh–Tamil Nadu border, India's second-largest brackish lagoon. The barrier island of Sriharikota (ISRO's launch centre) separates it from the sea.
• Kolleru Lake: a freshwater lake in Andhra Pradesh between the Godavari and Krishna deltas. It has been damaged by aquaculture (fish and prawn) ponds. Ramsar 2002.

• Vembanad Lake: in Kerala, from Alappuzha to Kochi. It is India's longest lake. Vembanad–Kol became a Ramsar site in 2002, and the Nehru Trophy boat race is held there.

• Saline:

• Sambhar Lake: in Rajasthan near Jaipur, India's largest inland saline lake. It is a major salt source and a Ramsar site (1990). Mass bird deaths in 2019 were caused by avian botulism.

• India's current Ramsar count changes often (verify current).

12. Using river water: usability, disputes and interlinking

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• Usability of river water: India's rivers carry huge volumes, but unevenly in time and space.
• Monsoon floodwater runs to the sea.
• One region floods while another faces drought.

• Class 11 asks whether this is a problem of availability or of management.

• Problems that limit use: too little water, pollution, silt, uneven seasonal flow, inter-state disputes, and channels shrinking as settlements spread towards the thalweg.

• Thalweg: the line joining the deepest points of a river channel. It is also used to fix river boundaries.

• Sources of pollution: sewage, industrial effluents, cremation, idol immersion, and bathing and washing.

• Inter-basin transfers named by Class 11:
• Periyar diversion: Kerala to Tamil Nadu's Vaigai.
• Indira Gandhi Canal: from Harike into the Thar.
• Kurnool–Cuddapah canal: an early Krishna–Pennar transfer.
• Beas–Satluj link: carries Beas water to the Satluj for Bhakra.

• Ganga–Kaveri link canal: K.L. Rao's 1972 proposal for a canal of about 2,640 km. It was dropped because water would have to be lifted about 450 m onto the plateau.

• Interlinking of rivers (beyond NCERT):

• The National Perspective Plan (1980) has 30 links: 16 Peninsular and 14 Himalayan. NWDA (set up 1982) studies them.

• Ken–Betwa is the first link under way. Cabinet approved it on 8 December 2021 (about ₹44,605 crore), and the foundation stone was laid on 25 December 2024. Its Daudhan dam will submerge part of Panna Tiger Reserve.

• Parbati–Kalisindh–Chambal–ERCP link: merged with Rajasthan's Eastern Rajasthan Canal Project and agreed by Rajasthan and Madhya Pradesh in 2024. It is meant to supply water to eastern Rajasthan.

• Godavari–Cauvery link: would carry Godavari "surplus" through the Krishna and Pennar basins to the Cauvery (verify current).
• Debates over interlinking: whether real surpluses exist, enough flow left for river ecology, deltas losing silt, people displaced, cost, earthquake risk, and state consent.
• Inter-State River Water Disputes Act 1956:
• Made under Art. 262. It lets the Centre set up tribunals, and their awards are final.
• The Supreme Court still hears appeals against awards under Art. 136 (Cauvery case, 2018).
• Tribunals so far: Krishna, Godavari, Narmada, Ravi–Beas (1986), Cauvery, Vansadhara, Mahadayi and Mahanadi.

• A 2019 bill for a single permanent tribunal is pending (verify current).

• Krishna water dispute:

• The Bachawat tribunal gave its award in 1976.
• The Brijesh Kumar tribunal (set up 2004; reports 2010 and 2013) took the dispute up again.

• Telangana's creation in 2014 reopened sharing between Telangana and Andhra Pradesh (verify current).

• Satluj–Yamuna Link canal: a 214 km canal to carry Haryana's share of Ravi–Beas water. Haryana completed its part, but Punjab stopped work. Punjab's 2004 law ending the water agreements was struck down in 2016. The matter is still before the Supreme Court (verify current).

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Exam angles

Prelims — high-yield facts and traps

• Patterns: dendritic (northern plain), radial (Amarkantak), trellis (folded hard and soft rock), centripetal (Loktak, Sambhar).
• Drainage shares: Bay of Bengal 77%, Arabian Sea 23%. The divide runs along the Delhi ridge, Aravallis and Sahyadri. Major basins are over 20,000 sq km (14 of them).
• Sources:
• Indus: Bokhar Chu
• Satluj: Rakas Tal
• Brahmaputra: Chemayungdung
• Bhagirathi: Gaumukh
• Alaknanda: Satopanth
• Yamuna: Yamunotri (Banderpunch)
• Jhelum: Verinag
• Beas: Beas Kund
• Chambal: Mhow
• Narmada and Son: Amarkantak
• Tapi: Multai
• Mahanadi: Sihawa
• Godavari: Nashik
• Krishna: Mahabaleshwar
• Kaveri: Talakaveri

• Luni: near Pushkar

• Confluences:

• Devprayag (Bhagirathi + Alaknanda)
• Harike (Beas + Satluj)
• Tandi (Chandra + Bhaga)
• Attock (Kabul + Indus)
• Mithankot (Panjnad + Indus)
• Sonpur (Gandak + Ganga)

• Chhapra (Ghaghara + Ganga)

• Panch Prayag order: Vishnu → Nand → Karna → Rudra → Dev.

• Antecedent rivers: Indus, Satluj, Kosi, Subansiri, Brahmaputra. Rift-valley rivers: Narmada, Tapi, Damodar.
• Traps:
• "The Indus is one of the Panjnad rivers": FALSE.
• "The Krishna is the largest Peninsular river": FALSE (it is the Godavari).

• "The Narmada builds a delta": FALSE (it forms an estuary).

• "Sorrow of" pairs: Kosi = Bihar, Damodar = Bengal.

• Superlatives: Chenab is the largest Indus tributary. Yamuna is the longest Ganga tributary. Godavari is the "Dakshin Ganga".
• Banks:
• Right bank: Son (of the Ganga); Chambal, Betwa, Ken (of the Yamuna); Subansiri, Manas, Kameng (of the Brahmaputra).

• Left bank: Dibang, Lohit, Burhi Dihing (of the Brahmaputra).

• Lakes:

• Chilika: largest brackish lagoon, Ramsar 1981
• Pulicat: Sriharikota
• Loktak: phumdis, Keibul Lamjao
• Sambhar: largest inland saline lake
• Vembanad: longest lake

• Lonar: crater lake

• Interlinking and disputes: NPP 1980 has 30 links (16 Peninsular, 14 Himalayan). Ken–Betwa is the first. Disputes come under Art. 262 and the 1956 Act.

Mains — GS-I themes

1. Contrast Himalayan and Peninsular rivers in origin, regime, landforms and usefulness.
2. Why do the Narmada and Tapi form estuaries while the east-flowing rivers build deltas?
3. The Indo-Brahma hypothesis and the role of Himalayan uplift and the Malda gap in shaping north Indian drainage.
4. River interlinking: the water logic against the ecological, social and federal costs (GS-I/III).
5. Inter-state river disputes: why tribunals take decades and how the system could be reformed (GS-II).
6. River basins as planning units: integrated basin management and lessons from Namami Gange (GS-III).

Current-affairs hooks

• Ken–Betwa construction and its effect on Panna Tiger Reserve. Progress of PKC–ERCP (verify current).
• China's Medog project on the Yarlung Tsangpo and India's Siang Upper project (verify current).
• Indus Waters Treaty in abeyance, and projects on the Chenab and Jhelum (verify current).
• Rulings of the Cauvery authority, the Krishna tribunal, and the Mahadayi and Mahanadi tribunals (verify current).
• New Ramsar sites, restoration of Wular and Loktak, and Namami Gange water-quality reports.
• Floods: Kosi embankments, Brahmaputra bank erosion, and the Punjab floods of 2025.