Drainage System

Why this chapter matters for UPSC: This is Chapter 3 (Unit II, "Physiography") of India: Physical Environment in the current rationalised NCERT (Reprint 2026-27). It covers how drainage is classified, how the Himalayan and Peninsular systems evolved, the major river systems one by one, and the problems in using river water. Prelims asks about sources, tributaries, sequences and confluences; Prelims 2026 had an identify-the-river question on the Sutlej (Q35). Mains asks about interlinking (GS1 2020, GS3 2017), the Indus Waters Treaty (GS1 2016) and Ganga cleaning (GS3 2015).

Contemporary hook: India placed the Indus Waters Treaty (1960) in abeyance on 23 April 2025, after the Pahalgam terror attack (MEA). China began construction of a hydropower project on the lower Yarlung Tsangpo, the upper Brahmaputra, on 19 July 2025 (China Daily). The 30-year India–Bangladesh Ganga Waters Treaty, signed on 12 December 1996, reaches the end of its term in December 2026.

🧠 First Principles — Read This First

Rain that falls on land has to go somewhere. Where it runs off through well-defined channels, NCERT calls the flow drainage and the network of channels a drainage system. The area a river and its tributaries drain is its drainage basin. The high ground separating one basin from the next is the water divide.

A useful picture is a roof. Rain falling on one side of the ridge runs into one gutter, rain on the other side into the other gutter. In India the main "ridge" separating rivers that reach the Arabian Sea from those reaching the Bay of Bengal runs along the Delhi ridge, the Aravalis and the Sahyadris (Western Ghats). Because the Western Ghats stand close to the west coast and the plateau tilts towards the south-east, most large Peninsular rivers flow the long way east, to the Bay of Bengal.

The second idea is age and water source. Himalayan rivers are fed by both melting snow and rain, so they flow all year (perennial). They are still cutting down through rising mountains, so they make gorges and carry heavy loads of sediment. Peninsular rivers depend on rain alone, so their flow drops sharply in the dry season. They are older and run in broad, shallow, graded valleys on a fixed course.

The third idea is where a river ends. A river that brings a lot of sediment to a shallow sea builds a delta. A river that runs in a narrow trough to a deeper, tidal coast ends in an estuary. The Narmada and Tapi are the classic estuary rivers.

UPSC uses all three: divide and direction for map questions, the two families for comparison answers, and delta versus estuary for reasoning questions.

PART 1 — Quick Reference

Table 1: Ways of Classifying Indian Drainage (NCERT)

Table 2: Himalayan vs Peninsular Rivers (NCERT)

Table 3: Major Rivers — NCERT Figures

NCERT's Godavari paragraph names Andhra Pradesh only; Telangana, formed in 2014 out of Andhra Pradesh, now holds part of the basin. NCERT's Krishna paragraph already names "Andhra Pradesh and Telangana".

Table 4: Ganga Tributaries (NCERT)

Yamuna's own tributaries: Chambal, Sind, Betwa and Ken on the right (from the Peninsular plateau); Hindan, Rind, Sengar and Varuna on the left.

Table 5: Drainage Patterns (NCERT)

PART 2 — Concepts & Narrative

Basins, Watersheds and Divides

NCERT defines a catchment area as the area a river drains, and a drainage basin as the area drained by a river and its tributaries. The boundary between two basins is the watershed. In practice large catchments are called river basins and those of small rivulets and rills are called watersheds; watersheds are small, basins large. Basins and watersheds are marked by unity. What happens in one part affects the other parts and the whole, which is why NCERT calls them the most appropriate micro, meso and macro planning regions.

Evolution of the Himalayan Drainage

NCERT notes that opinions differ, but geologists believe a mighty river called the Shiwalik or Indo-Brahma once ran the whole length of the Himalaya, from Assam to Punjab and on to Sind. It drained into the Gulf of Sind near lower Punjab during the Miocene, some 5–24 million years ago. The continuity of the Shiwaliks, their lacustrine origin, and their alluvial deposits of sand, silt, clay, boulders and conglomerates support this view.

The Indo-Brahma was later dismembered into three systems: the Indus and its five tributaries in the west, the Ganga and its Himalayan tributaries in the centre, and the Brahmaputra in Assam with its Himalayan tributaries in the east. NCERT gives two causes. First, a Pleistocene upheaval in the western Himalaya, including the uplift of the Potwar Plateau (Delhi Ridge), which became the divide between the Indus and Ganga systems. Second, the down-thrusting of the Malda gap between the Rajmahal hills and the Meghalaya plateau in the mid-Pleistocene, which diverted the Ganga and Brahmaputra to the Bay of Bengal.

Behaviour on the plains. Entering the plains, Himalayan rivers build flat valleys, ox-bow lakes, flood plains, braided channels and, near the mouth, deltas. They meander strongly and shift course often. NCERT's example is the Kosi, the "sorrow of Bihar". It brings a huge quantity of sediment from its upper reaches and deposits it in the plains, the channel gets blocked, and the river changes course.

The Indus System

The Indus (Sindhu) is the westernmost Himalayan river in India. Its basin covers 11,65,000 sq km, of which 3,21,289 sq km is in India, and it is 2,880 km long, 1,114 km in India. It rises from a glacier near Bokhar Chu (31°15'N, 81°40'E) in Tibet, at 4,164 m in the Kailash range, where it is called Singi Khamban, the Lion's mouth. It flows north-west between the Ladakh and Zaskar ranges, passes through Ladakh and Baltistan, and cuts across the Ladakh range in a gorge near Gilgit in Ladakh. NCERT says it enters Pakistan near Chilas in the Dardistan region, and that the Indus flows in India through the UTs of Ladakh and Jammu & Kashmir.

Himalayan tributaries of the Indus: Shyok, Gilgit, Zaskar, Hunza, Nubra, Shigar, Gasting and Dras. The river leaves the hills near Attock, where the Kabul joins on its right bank. Other right-bank tributaries, the Khurram, Tochi, Gomal, Viboa and Sangar, rise in the Sulaiman ranges. The river flows south and receives the Panjnad, the combined five rivers of Punjab (Satluj, Beas, Ravi, Chenab, Jhelum), a little above Mithankot. It enters the Arabian Sea east of Karachi.

The five rivers (NCERT):

• Jhelum: rises from a spring at Verinag at the foot of the Pir Panjal in the south-east of the Kashmir valley. It flows through Srinagar and the Wular lake, enters Pakistan through a deep narrow gorge, and joins the Chenab near Jhang.
• Chenab: the largest tributary of the Indus. It is formed by the Chandra and the Bhaga, which meet at Tandi near Keylong in Himachal Pradesh, so it is also called Chandrabhaga. It flows 1,180 km before entering Pakistan.
• Ravi: rises west of the Rohtang pass in the Kullu hills and flows through the Chamba valley, draining the area between the south-eastern Pir Panjal and the Dhauladhar. It joins the Chenab near Sarai Sidhu.
• Beas: rises at Beas Kund near the Rohtang Pass (4,000 m), flows through the Kullu valley, forms gorges at Kati and Largi in the Dhaoladhar range, and meets the Satluj near Harike.
• Satluj: rises in Raksas tal near Mansarovar (4,555 m), where it is called Langchen Khambab. It flows almost parallel to the Indus for about 400 km before entering India through the Shipki La, and comes out of a gorge at Rupar. It is an antecedent river and feeds the canal system of the Bhakra Nangal project.

The Ganga System

NCERT calls the Ganga the most important river of India by basin and by cultural significance. It rises in the Gangotri glacier near Gaumukh (3,900 m) in Uttarkashi district, where it is called the Bhagirathi, and cuts through the Central and Lesser Himalaya in narrow gorges.

The Ganga basin, about 8.6 lakh sq km in India, is the largest in India (NCERT's exercise answer to "largest river basin in India"). It carries perennial rivers from the Himalaya and non-perennial rivers from the Peninsula. The Son is its major right-bank tributary. The important left-bank tributaries are the Ramganga, Gomati, Ghaghara, Gandak, Kosi and Mahananda (Table 4). The Yamuna joins on the right bank at Prayag. Much of its water feeds the Western and Eastern Yamuna canals and the Agra canal for irrigation.

The Chambal rises near Mhow on the Malwa plateau of Madhya Pradesh. It flows north through a gorge upward of Kota in Rajasthan, where the Gandhisagar dam has been built, then past Bundi, Sawai Madhopur and Dholpur to join the Yamuna. It is known for its badland topography, the Chambal ravines. The Sarda (Saryu) rises in the Milam glacier in the Nepal Himalaya as the Goriganga. Along the India–Nepal border it is called the Kali or Chauk, and it joins the Ghaghara.

The Brahmaputra System

The Brahmaputra rises in the Chemayungdung glacier of the Kailash range near Mansarovar. It flows east for nearly 1,200 km through dry, flat southern Tibet as the Tsangpo ("the purifier"). The Rango Tsangpo is its major right-bank tributary there. It then carves a deep gorge in the Central Himalaya near Namcha Barwa (7,755 m) and emerges from the foothills as the Siang or Dihang and enters India in Arunachal Pradesh. Flowing south-west, it receives its main left-bank tributaries, the Dibang (Sikang) and the Lohit; from there on it is the Brahmaputra.

In its 750 km course through the Assam valley it receives many tributaries. The main left-bank ones are the Burhi Dihing and Dhansari (South); the main right-bank ones are the Subansiri (which rises in Tibet and is antecedent), Kameng, Manas and Sankosh. It enters Bangladesh near Dhubri, where it turns south (NCERT Ch 2: an almost 90° turn). In Bangladesh the Tista joins it on the right bank, and from there it is called the Jamuna. It finally merges with the Padma, which flows into the Bay of Bengal. The Brahmaputra is known for floods, channel shifting and bank erosion, because most of its tributaries are large and bring heavy sediment from a catchment with heavy rainfall. NCERT Class 9 records Majuli, in the Brahmaputra, as the largest inhabited riverine island in the world.

The Peninsular Drainage System

The Peninsular system is older than the Himalayan one, as shown by its broad, largely graded, shallow valleys and the maturity of its rivers. Most major Peninsular rivers, except the Narmada and the Tapi, flow west to east. The Chambal, Sind, Betwa, Ken and Son, rising in the northern Peninsula, belong to the Ganga system. The other major Peninsular systems are the Mahanadi, Godavari, Krishna and Kaveri.

Mahanadi. It rises near Sihawa in Raipur district, Chhattisgarh, and runs through Odisha to the Bay of Bengal. It is 851 km long with a catchment of 1.42 lakh sq km. Some navigation is carried on in the lower course.

Godavari. The largest Peninsular system, also called the Dakshin Ganga. It rises in Nasik district and is 1,465 km long with a catchment of 3.13 lakh sq km. Its principal tributaries are the Penganga, Indravati, Pranhita and Manjra. It floods heavily in its lower reaches south of Polavaram, where it forms a picturesque gorge. It is navigable only in the deltaic stretch, and after Rajamundri it splits into several branches forming a large delta.

Krishna. The second largest east-flowing Peninsular river. It rises near Mahabaleshwar in the Sahyadri and is 1,401 km long. Its major tributaries are the Koyna, Tungabhadra and Bhima.

Kaveri. It rises in the Brahmagiri hills (1,341 m) of Kodagu district, Karnataka, and is 800 km long, draining 81,155 sq km. Its upper catchment receives rain in the south-west monsoon (summer) and its lower part in the north-east monsoon (winter). So it carries water throughout the year with less fluctuation than other Peninsular rivers. Its main tributaries are the Kabini, Bhavani and Amravati. On the inter-state sharing of its water, the Supreme Court's judgment of 16 February 2018 (State of Karnataka v State of Tamil Nadu) allotted Karnataka an additional 14.75 TMC and required it to release 177.25 TMC at the inter-state border at Billigundulu. The Centre then notified a scheme setting up the Cauvery Water Management Authority (2018).

Narmada. It rises on the western flank of the Amarkantak plateau at about 1,057 m. It flows in a rift valley between the Satpura (south) and the Vindhyan range (north), and forms a gorge in marble rocks and the Dhuandhar waterfall near Jabalpur. After about 1,312 km it meets the Arabian Sea south of Bharuch in a broad 27 km estuary. Its catchment is about 98,796 sq km. The Sardar Sarovar Project has been built on it. NCERT asks readers to look up the conservation mission "Namami Devi Narmade".

Tapi. The other important west-flowing river. It rises at Multai in Betul district, MP, is 724 km long, and drains 65,145 sq km.

Luni. The largest river system of Rajasthan west of the Aravali. It rises near Pushkar in two branches, the Saraswati and the Sabarmati, which join at Govindgarh. It flows west till Telwara, then south-west to the Rann of Kachchh. The whole system is ephemeral.

Using River Water

NCERT's point is that Indian rivers carry huge volumes of water, but unevenly in time and space. Perennial rivers flow all year; non-perennial rivers have little water in the dry season. In the rains much water is lost in floods, and one part of the country can be flooded while another is in drought. NCERT asks whether this is a problem of availability or of management. It then poses inter-basin transfer and lists examples for teachers to explain: the Periyar Diversion Scheme, the Indira Gandhi Canal Project, the Kurnool–Cuddapah Canal, the Beas–Satluj Link Canal and the Ganga–Kaveri Link Canal.

It also lists the problems in using river water for the reader to rank: insufficient quantity, pollution, silt load, uneven seasonal flow, inter-state disputes, and shrinking channels as settlements extend towards the thalweg. On pollution, it names city sewage, industrial effluents, cremation on river banks, festival immersions, and mass bathing and washing.

PART 3 — UPSC Integration

PYQ Pattern

• Prelims 2026 Q35 (prelims-2026-gs1-035): identify the river from four clues (antecedent; three countries; Tibetan source and irrigation; no distributaries). Answer: the Sutlej.
• Prelims 2024 (bank geo-064): west-to-east order of Himalayan rivers joining the Ganga below Prayagraj. Prelims 2016 (geo-003): tributaries of the Brahmaputra (Dibang, Kameng, Lohit).
• Mains GS1 2013 (gs1-pyq-2013-22b): no deltas on Western Ghats rivers.
• Mains GS1 2016 (gs1-pyq-2016-18): the Indus Waters Treaty and its implications.
• Mains GS1 2020 (gs1-pyq-2020-07): impact of melting Himalayan glaciers on India's water resources (the perennial, snow-fed character of Himalayan rivers).
• Mains GS1 2020 (gs1-pyq-2020-14) and GS3 2017 (gs3-pyq-2017-28): interlinking of rivers.
• Mains GS3 2015 (gs3-pyq-2015-75): Namami Gange and NMCG.

Mains Frameworks

1. Two families → two water problems. Perennial Himalayan rivers bring dependable flow but also floods, silt and channel shifting (Kosi, Brahmaputra). Seasonal Peninsular rivers need storage to carry water through the dry months. NCERT's own framing: uneven distribution in time and space.
2. Structure → river mouth. East-flowing rivers form deltas; the Narmada and Tapi flow through trough faults and form estuaries.
3. Shared rivers → diplomacy. India is a lower riparian to China on the Brahmaputra and an upper riparian to Pakistan on the Indus and to Bangladesh on the Ganga. Use the dated facts: IWT in abeyance (23 Apr 2025), Medog groundbreaking (19 Jul 2025), Ganga treaty term ending December 2026.

Exam Strategy

Prelims traps from this chapter

• Largest basin in India: Ganga. Largest Peninsular system: Godavari.
• The Yamuna joins the Ganga on the right bank. It is the westernmost and longest tributary, but it is not a left-bank tributary. The Sarda/Kali joins the Ghaghara, not the Ganga directly.
• Indus: 2,880 km total, 1,114 km in India; rises near Bokhar Chu, not in Mansarovar lake. The Satluj rises in Raksas tal.
• Chenab is the largest Indus tributary. The Jhelum flows through Wular lake.
• Devprayag: Bhagirathi + Alaknanda. Vishnu Prayag (Joshimath): Dhauli + Vishnu Ganga. Rudra Prayag: Mandakini. Karna Prayag: Pindar.
• Polavaram is on the Godavari. NCERT locates the Godavari's lower-reach floods and gorge south of Polavaram.
• Damodar was the "sorrow of Bengal"; Kosi is the "sorrow of Bihar".
• Amarkantak is NCERT's example of radial drainage: the Narmada rises on its western flank and the Son on the plateau. The Mahanadi rises near Sihawa (Raipur district, Chhattisgarh), not at Amarkantak.
• Brahmaputra names: Tsangpo (Tibet), Siang/Dihang (Arunachal), Brahmaputra (after the Dibang and Lohit join), Jamuna (Bangladesh, after the Tista joins).
• Narmada estuary: 27 km. Kaveri is the least seasonal Peninsular river because it gets rain from both monsoons.

Mains question patterns

• "Compare Himalayan and Peninsular rivers" (NCERT exercise 4(i)): source, flow regime, valley form, course stability, mouth.
• "Interlinking: viable or not?": NCERT's own objections (lifting water to the plateau, uncertain surplus) plus Ken–Betwa's dated status.

Practice Questions

1. Prelims 2026 Q35 (prelims-2026-gs1-035): "Identify the river of the Indian sub-continent on the basis of the following information: 1. It has an antecedent drainage system 2. It flows through three countries 3. It originates in the Tibetan Plateau and is an important river for irrigation 4. It does not form distributaries." (a) Brahmaputra (b) Indus (c) Sutlej (d) Teesta. (Answer: c)
2. Prelims 2024 (bank ID geo-064): "With reference to Himalayan rivers joining the Ganga downstream of Prayagraj from West to East, which one of the following sequences is correct?" (a) Ghaghara — Gomati — Gandak — Kosi (b) Gomati — Ghaghara — Gandak — Kosi (c) Ghaghara — Gomati — Kosi — Gandak (d) Gomati — Ghaghara — Kosi — Gandak. (Answer: b)
3. Prelims 2016 (bank ID geo-003): "Which of the following is/are tributary/tributaries of Brahmaputra? 1. Dibang 2. Kameng 3. Lohit. Select the correct answer using the code given below." (a) 1 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3. (Answer: d)
4. Mains GS1 2016 (gs1-pyq-2016-18): "Present an account of the Indus Water Treaty and examine its ecological, economic and political implications in the context of changing bilateral relations."
5. Mains GS1 2020 (gs1-pyq-2020-14): "The interlinking of rivers can provide viable solutions to the multidimensional interrelated problems of droughts, floods, and interrupted navigation. Critically examine."

📦 Revision Capsule

Sources

Sources

• NCERT, India: Physical Environment, Textbook for Class XI, Chapter 3 "Drainage System", rationalised edition, Reprint 2026-27 — kegy103.pdf. Chapter 2 for the Haryana–Delhi divide and the Dhubri turn — kegy102.pdf.
• NCERT, Contemporary India – I, Class IX, Chapter 2 (2019-20 reprint): Majuli. Printed citation.
• PIB (Ministry of Home Affairs), maps of the UTs of J&K and Ladakh, 2 Nov 2019, as reproduced by the High Commission of India, Lilongwe — hcililongwe.gov.in.
• World Bank, "Fact Sheet: The Indus Waters Treaty 1960 and the Role of the World Bank" (11 Jun 2018, last updated 21 Jun 2023) — worldbank.org.
• MEA, Transcript of special briefing by the Foreign Secretary on CCS decisions, 23 Apr 2025, as reproduced by the Embassy of India, Hanoi — indembassyhanoi.gov.in.
• Treaty between India and Bangladesh on Sharing of the Ganga/Ganges Waters at Farakka, 12 Dec 1996 (Article XII: thirty-year term), text hosted by the ADB Law and Policy Reform portal — lpr.adb.org.
• China Daily, "Mega-hydro project launched in Xizang", 21 Jul 2025 — regional.chinadaily.com.cn.
• Deccan Herald (PTI), "Carefully monitoring Brahmaputra-related developments, including China's mega dam plan: Govt", 13 Feb 2025 (Rajya Sabha written reply) — deccanherald.com.
• PIB, "Ken-Betwa Link Project: Frequently Asked Questions", 21 Aug 2026 — static.pib.gov.in.
• Supreme Court of India, State of Karnataka v State of Tamil Nadu, judgment of 16 Feb 2018 (Cauvery), summary and text at India Environment Portal — indiaenvironmentportal.org.in.
• Question texts: BharatNotes Prelims 2026 bank (prelims-2026-gs1-035), Prelims geography bank (geo-003, geo-064), Mains GS1 and GS3 banks.