Drainage Systems of India

Classification of Indian Drainage

Based on Discharge Orientation (Direction of Flow)

Dividing line: Delhi Ridge → Aravallis → Western Ghats separates the two systems.

Why Bay of Bengal receives far more freshwater?

• Receives rainfall from both SW and NE Monsoons.
• All major Himalayan rivers (Ganga–Brahmaputra) drain eastward.
• All major Peninsular rivers (except Narmada, Tapi) flow east.
• More cyclonic rainfall in Bay of Bengal drainage area.

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Based on Watershed Size (CWC Classification)

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Based on Drainage Type

• Exorheic (external drainage): Flows to the sea — Ganga, Godavari, Narmada.
• Endorheic (internal/inland drainage): Does not reach the sea — Luni, Ghaggar, Rupen (drains into salt lakes/desert).

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Based on Origin

Himalayan vs Peninsular Rivers — Comparison

Exceptions in Peninsular rivers:

• Narmada and Tapi: Flow west through rift valleys → form estuaries (not deltas); have meanders and perennial flow unlike other peninsular rivers.
• Why no delta for west-flowing peninsular rivers: Steep gradient + short distance + rocky terrain → no silt deposition at mouth.

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The Indus River System

Overview

• Basin covers Tibet, India, Afghanistan, and Pakistan.
• In India: covers J&K, HP, Punjab, Rajasthan, Haryana, Chandigarh — ~9.8% of India's total geographical area.
• Bounded by: Himalayas (east), Karakoram/Haramosh (north), Sulaiman/Kirthar ranges (west), Arabian Sea (south).
• Total length: 3,180 km (one of the longest rivers in Asia).

Indus River (Main)

• Origin: Near Bokhar Chu glacier in the Kailas Mountain Range, Tibet (~4,600 m); known as Singi Khamban ("Lion's Mouth") at source.
• Flows through Ladakh (1,114 km in India), enters Pakistan near Chilas (Dardistan region).
• Discharges into the Arabian Sea near Karachi.
• Left bank tributaries (joining from the east): Jhelum, Chenab, Ravi, Beas, Sutlej, Zanskar, Shyok.
• Right bank tributaries (joining from the west): Gilgit, Kabul, Kurram, Gomal, Tochi.
• Important city: Leh is on the right bank of the Indus.

Key Tributaries of the Indus

Jhelum (Vyeth / Hydaspes)

• Origin: Spring at Verinag, J&K, at the foot of the Pir Panjal Range.
• Kashmiri name: Vyeth; Sanskrit: Vetesta; Greek: Hydaspes.
• Flows through Srinagar → Wular Lake (largest freshwater lake in India) → cuts gorge through Pir Panjal → Pakistan.
• Joins the Chenab near Jhang, Pakistan.
• Key HEP: Uri HEP (480 MW), Baramulla, J&K; Kishenganga HEP (330 MW) (on Kishenganga tributary, J&K).
• Important cities: Srinagar, Baramulla, Uri.

Chenab (Chandrabhaga / Askini)

• Largest tributary of the Indus.
• Formed by confluence of Chandra and Bhaga rivers at Tandi, Lahaul and Spiti, HP (near Baralacha La Pass).
• Flows through HP and J&K; joins Indus near Shorkot, Pakistan.
• Old name: Askini.
• Key HEP: Baglihar Dam (450 MW) — Ramban, J&K; Dulhasti HEP (390 MW) — Kishtwar, J&K; Salal Dam (690 MW) — Reasi, J&K.

Ravi

• Origin: Near Rohtang Pass, Kullu hills, HP; flows through Chamba Valley.
• Drains area between Pir Panjal and Dhauladhar ranges.
• Joins Chenab near Sarai Sidhu, Pakistan.
• Key HEP: Chamera Dam I, II, III (Chamba, HP); Ranjit Sagar Dam (Kathua, Punjab).
• Cities: Amritsar, Pathankot.

Beas

• Origin: Beas Kund (glacial lake), near Rohtang Pass, HP.
• Flows through Kullu Valley; forms gorges in Dhauladhar.
• Enters Punjab plains; joins Sutlej near Harike.
• Key HEP: Pandoh Dam (Mandi, HP); Pong Dam / Maharana Pratap Sagar (Kangra, HP).
• Cities: Manali, Kullu, Mandi.

Sutlej (Langchen Khambab)

• Longest tributary of the Indus.
• Origin: Raksas Tal (glacial lake), near Lake Manasarovar, Tibet.
• Flows parallel to Indus before entering India through Shipki La.
• Antecedent river — existed before Himalayan formation.
• Feeds the Bhakra-Nangal canal system (largest multipurpose project in India).
• Key HEP: Bhakra Dam (225.5 m; 2nd highest gravity dam in Asia) — Bilaspur, HP; Nathpa Jhakri HEP (1,500 MW); Kol Dam.
• Cities: Ferozpur, Ludhiana.

Punjab = Punj (five) + Aab (water) = Land of Five Rivers = Jhelum, Chenab, Ravi, Beas, Sutlej. Today only Ravi, Beas, Sutlej flow in Indian Punjab; Jhelum and Chenab are in Pakistan's Punjab.

Panjnad River: All five rivers ultimately merge to form the Panjnad, which joins the Indus above Mithankot.

UPSC Prelims 2021: Among Chenab, Jhelum, Ravi, Sutlej — which one joins the Indus directly? Answer: (d) Sutlej ✓ (the other three first join Chenab or each other before reaching Indus)

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Indus Waters Treaty (IWT) — Updated to April 2026

Background:

• Signed: September 19, 1960 between India and Pakistan; brokered by the World Bank.
• No expiry date; meant to be permanent.

Water allocation:

Recent Developments — Critical for UPSC 2026:

• India had been seeking renegotiation of the IWT (January 2023 notice to Pakistan), citing changed circumstances (climate change, population growth).
• April 23, 2025: Following the Pahalgam terror attack (26 people killed, including foreign tourists), India formally put the IWT "in abeyance" — effectively suspending it.
• Pakistan rejected the move as a breach of international law; stated no provision exists for suspension.
• IWT has no clause for withdrawal or suspension — India's move is unprecedented.
• As of April 2026: Treaty remains "in abeyance"; no bilateral mechanism functioning.

UPSC Mains Angle: "Discuss the significance of the Indus Waters Treaty and critically evaluate India's decision to put it in abeyance in 2025."

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The Ganga River System

Ganga River

• Sacred river of India; drains ~26% of India's total geographical area.
• Basin: ~8.6 lakh km²; the most populous river basin in the world (~500 million people).
• Forms the largest delta in the world — the Sundarbans Delta (shared by India and Bangladesh).

Origin and course:

• Bhagirathi River originates from Gangotri Glacier, Uttarkashi, Uttarakhand (~3,892 m).
• Joined by Alaknanda (from Satopanth Glacier, Chamoli) at Devprayag → becomes the Ganga.
• Major confluences in Uttarakhand (Panch Prayag):

• Enters plains at Haridwar (crossing Shiwalik range).
• Flows through UP, Bihar, West Bengal; enters Bangladesh as Padma.
• Joins Brahmaputra (Jamuna) → forms Meghna → Bay of Bengal.
• Total length in India: ~2,525 km | Total basin length: ~2,900 km.

Major Left Bank Tributaries of Ganga

Kosi River: Drains ~95,000 km²; carries enormous sediment from Nepal Himalayas; historically changed course 120 km westward over the past 200 years; caused frequent devastating floods in Bihar.

Major Right Bank Tributaries of Ganga

Yamuna (Kalindi):

• Origin: Yamunotri Glacier (4,421 m), Uttarkashi, Uttarakhand.
• Joins Ganga at Prayagraj (Triveni Sangam).
• Right bank tributaries: Chambal, Betwa, Ken, Sind.
• Left bank: Hindon, Tons, Gomti (not directly).
• Flows through Delhi, Agra, Mathura — highly polluted stretch.

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The Brahmaputra River System

Overview

• One of the longest rivers in Asia (~2,900 km total; ~916 km in India).
• Drains Tibet, India, and Bangladesh.
• In India: flows through Arunachal Pradesh and Assam.
• Known by different names in different countries:

Origin: Chemayungdung Glacier, Kailash Mountain Range, Tibet (~5,150 m); known as Tsangpo ("Purifier").

Course:

• Flows east through Tibet for ~1,700 km (parallel to Himalayas).
• At Namcha Barwa (eastern syntaxial bend), makes a dramatic U-turn → cuts the Tsangpo Gorge (world's deepest gorge, ~5,500 m deep, ~60 km long).
• Enters India through Arunachal Pradesh (called Dihang/Siang).
• Enters Assam and broadens dramatically — average width up to 10 km in Assam plains (braided river).
• One of the highest-discharge rivers in the world.
• Joins Ganga (Padma) in Bangladesh → forms Meghna → Bay of Bengal.

Key Tributaries of Brahmaputra in India

Left bank (from north, from Arunachal side):

• Lohit, Dibang, Subansiri, Jiabhorali (Kameng), Manas, Sankosh, Teesta.

Right bank (from Meghalaya/Assam):

• Kopili, Digaru, Kulsi.

Teesta River:

• Originates in Sikkim Himalayas.
• Flows through Sikkim → West Bengal → joins Brahmaputra in Bangladesh.
• Site of the October 2023 GLOF (South Lhonak Lake).
• Teesta III Dam (510 MW) was destroyed in the 2023 GLOF.

Brahmaputra — Special Features

• Antecedent river — predates the Himalayas; maintains its course despite uplift.
• Has the highest hydropower potential in India (~60,000 MW in NE India).
• Carries enormous sediment → Assam plains frequently flood (annual floods in Assam are largely natural but worsened by deforestation).
• Majuli Island in Brahmaputra: world's largest river island (eroding; designated as India's first island district in 2016 — Assam).
• Kaziranga National Park is located on the floodplain of the Brahmaputra.

China's Mega-Dam on Yarlung Tsangpo — Critical Current Affairs 2025

Updated July 2025: China has begun construction of the world's largest hydropower project on the Yarlung Tsangpo (upper Brahmaputra) in Tibet.

India's concerns:

1. Water manipulation: China could control dry-season flow and flood-season releases — affecting Assam's agriculture and flood cycles.
2. Sediment trapping: Dam will trap nutrient-rich sediment that currently fertilises Assam's floodplains.
3. Geopolitical leverage: Control over Brahmaputra water as strategic pressure on India.
4. No water-sharing treaty: Unlike the Indus Waters Treaty with Pakistan, India and China have no river-water sharing agreement.

India's counter-plan: The Siang Upper Multipurpose Project (SUMP) on the Siang River in Arunachal Pradesh — 11,000 MW installed capacity — to serve as a "balancing reservoir" to mitigate Chinese dam effects.

UPSC Mains Angle: "China's construction of a mega-dam on the Yarlung Tsangpo poses significant challenges for India. Discuss the hydrological, ecological, and geopolitical implications and evaluate India's response."

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Peninsular River Systems

Overview

• Older than Himalayan rivers; in mature stage of erosion.
• Mostly flow east to Bay of Bengal; only Narmada and Tapi flow west to Arabian Sea.
• Seasonal; dependent on monsoon; harder rock basins = lower sediment load.
• Form large, fertile deltas at their mouths (east coast).

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Mahanadi River System

• Origin: Near Raipur, Chhattisgarh (on the Eastern Ghats slopes).
• Length: ~890 km | Basin: ~1.41 lakh km² (Chhattisgarh, Jharkhand, Odisha, Maharashtra, MP).
• Drains into the Bay of Bengal near Paradip (Odisha).
• Hirakud Dam (Sambalpur, Odisha): One of the longest earthen dams in the world (4.8 km); also has concrete sections; total length ~26 km.
• Forms a large delta shared with rivers Brahmani and Baitarani.
• Famous for: Significant flood hazard in lower Odisha; Chilika Lake nearby.

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Godavari River System

• "Vridha Ganga" (Old Ganga) — largest peninsular river.
• Origin: Trimbakeshwar, Nasik, Maharashtra (Western Ghats, ~920 m).
• Length: ~1,465 km | Basin: ~3.13 lakh km² — second largest river basin in India after Ganga.
• Drains: Maharashtra, Telangana, Andhra Pradesh, Chhattisgarh, Odisha.
• Enters Bay of Bengal near Rajahmundry (AP) through a large delta.
• Also called Dakshina Ganga ("Ganga of the South").

Major tributaries:

• Left bank (right side when flowing east): Penganga, Wainganga, Wardha (→ Pranhita), Indravati, Sabari, Sileru.
• Right bank: Purna, Maner, Manjra.

Pranhita River: Formed by confluence of Wardha and Wainganga → largest tributary of Godavari.

Key HEP: Pochampad (Sriram Sagar) Dam (Telangana); Nagarjunasagar Dam (on Krishna, not Godavari — common confusion).

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Krishna River System

• Origin: Near Mahabaleshwar, Satara, Maharashtra (Western Ghats, ~1,337 m).
• Length: ~1,400 km | Basin: ~2.58 lakh km².
• Drains: Maharashtra, Karnataka, Andhra Pradesh.
• Enters Bay of Bengal near Machilipatnam (Vijayawada) through a large delta.

Major tributaries:

• Left: Bhima (longest; from Pune area), Musi (flows through Hyderabad; heavily polluted), Dindi, Peddavagu.
• Right: Tungabhadra (most important right bank tributary; formed by Tunga + Bhadra), Ghataprabha, Malaprabha, Vedavathi.

Tungabhadra: Source of the Hampi ruins irrigation; Tungabhadra Dam (Hospet, Karnataka) — irrigates large areas of Karnataka and AP.

Key HEP: Nagarjunasagar Dam (telangana-AP border; India's largest masonry dam); Srisailam Dam (AP-Telangana).

Krishna Water Dispute: Karnataka, AP, and Telangana. Bachawat Tribunal (1973) and Brijesh Kumar Tribunal (2010) have made awards.

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Cauvery River System (Kaveri)

• Origin: Talakaveri, Kodagu (Coorg), Karnataka (Western Ghats, ~1,341 m).
• Length: ~800 km | Basin: ~81,155 km².
• Drains: Karnataka, Tamil Nadu, Kerala (tiny part), Puducherry.
• Enters Bay of Bengal near Cauvery Delta (Kaveri Delta) — one of the most fertile deltas; called the "Granary of South India".
• Famous waterfall: Hogenakal Falls (Karnataka-TN border); Shivanasamudra Falls (Karnataka — first major HEP in India, 1902).

Major tributaries:

• Left: Harangi, Hemavathi, Shimsha, Arkavathi (joins near Mysuru).
• Right: Lakshmantirtha, Kabini, Suvarnavathi, Bhavani, Noyil, Amaravathi.

Key HEP: Krishnarajasagar (KRS) Dam — Mysuru, Karnataka; Mettur Dam — Salem, TN.

Cauvery Water Dispute:

• India's oldest inter-state water dispute (colonial roots).
• Parties: Karnataka, Tamil Nadu, Kerala, Puducherry.
• Supreme Court final order (February 16, 2018): Allocated 404.25 TMC to Tamil Nadu, 284.75 TMC to Karnataka, 30 TMC to Kerala, 7 TMC to Puducherry.
• 2023 Crisis: TN demanded 24,000 cusecs amid drought; Karnataka refused (44% deficit in Cauvery catchment). CWMA directed 5,000 cusecs release; Supreme Court upheld CWMA authority.
• As of 2024-25: The dispute continues intermittently due to rainfall variability.

UPSC Mains Angle: "Examine the factors responsible for the Cauvery water dispute. Suggest institutional mechanisms for sustainable river water sharing."

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Narmada River System

• Origin: Amarkantak Plateau, Anuppur, MP (~1,057 m) — same plateau as Son River.
• Length: ~1,312 km | Basin: ~98,796 km².
• Drains: MP (~86% of basin), Maharashtra, Gujarat.
• Flows west through a rift valley (graben between Vindhyas and Satpura ranges).
• Drains into the Arabian Sea near Bharuch (Broach), Gujarat, through a long estuary (not delta).
• Also called Rewa in its upper course.

Key HEP: Sardar Sarovar Dam (Bharuch, Gujarat) — highest dam in India (163 m); the Narmada Valley Development Project was highly controversial (NBA — Narmada Bachao Andolan, led by Medha Patkar).

Other dams: Bargi Dam (Jabalpur); Omkareshwar Dam; Maheshwar Dam.

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Tapi (Tapti) River System

• Origin: Betul, Satpura Range, MP (~752 m).
• Length: ~724 km | Basin: ~65,145 km².
• Drains: MP, Maharashtra, Gujarat.
• Flows west through a rift valley (parallel to Narmada ~80 km south).
• Drains into the Arabian Sea near Surat, Gujarat, through an estuary.
• Also called Tapti.

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Other Important Peninsular Rivers

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River Interlinking in India

National Perspective Plan (NPP)

• Concept proposed in 1980 by the then Water Resources Ministry.
• Implemented by the National Water Development Agency (NWDA).
• Proposes 30 river links total:
  • 14 Himalayan component links
  • 16 Peninsular component links
• Goal: Transfer surplus water from flood-prone basins to drought-prone basins.

Ken-Betwa Link Project (KBLP) — First Project

• Foundation stone laid by PM Modi: December 25, 2024 at Khajuraho, MP — marks first actual implementation of the NPP.
• Approved: Cabinet approval December 2021; GoI central support: ₹39,317 crore of total ₹44,605 crore.
• Target completion: March 2030.
• Purpose: Transfer surplus water from Ken River (MP) → Betwa River (UP/MP) → irrigate water-scarce Bundelkhand region.
• Cost: ₹44,605 crore (at 2020-21 price levels).
• Benefits: Irrigation to 10.62 lakh ha; drinking water to 62 lakh people; HEP of 103 MW + 27 MW solar.
• Key structure: Daudhan Dam (77 m tall, 2 km wide) on Ken River + 230 km canal.
• Controversy: ~6,000 ha of Panna Tiger Reserve core area will be submerged.
• Rivers involved: Ken flows to Yamuna (tributary of Ganga); Betwa also flows to Yamuna. Both are Ganga tributaries.
• NPP Status (July 2025): PFRs complete for all 30; FRs for 26; DPRs for 11 link projects.

UPSC Mains Angle: "Critically evaluate the Ken-Betwa Link Project. How does it balance development imperatives with ecological concerns?"

Other Proposed Links (Selected)

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Major Dams and Hydropower Projects

Recently Commissioned / Inaugurated (2020–2026)

Northeast Hydropower Bundle (2023)

• 5+ GW of projects in NE India handed to SJVN in July 2023:
  • Etalin HEP (Dibang): 3,097 MW (Arunachal) — India's proposed largest HEP
  • Attunli HEP: 680 MW
  • Emini HEP: 500 MW
  • Amulin HEP: 420 MW
  • Mihumdon HEP: 400 MW

Important Existing Projects

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Inter-State Water Disputes

SYL Canal (Sutlej-Yamuna Link):

• Required for Haryana's share of Ravi-Beas waters.
• Punjab has refused to complete the canal.
• Supreme Court orders Punjab to complete construction; Punjab legislation declaring void challenged.
• As of 2026: Unresolved; politically sensitive.

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UPSC Corner

Key One-Liners

• 77% of India's drainage → Bay of Bengal | 23% → Arabian Sea
• Ganga basin = ~26% of India's geographical area = most populous basin in the world
• Brahmaputra in Tibet = Tsangpo | in Arunachal = Dihang/Siang | in Bangladesh = Jamuna
• Majuli = world's largest river island (Brahmaputra, Assam)
• Sundarbans Delta = world's largest delta (India + Bangladesh)
• Godavari = longest/largest peninsular river = "Dakshina Ganga" = "Vridha Ganga"
• Cauvery delta = "Granary of South India"
• Hirakud Dam = longest earthen dam in world (4.8 km, Mahanadi, Odisha)
• Tehri Dam = India's tallest dam (260 m, Bhagirathi, Uttarakhand)
• Ken-Betwa = foundation stone December 25, 2024 = India's first river interlinking project under NPP
• IWT in abeyance since April 23, 2025 (post-Pahalgam attack)
• Kosi = "Sorrow of Bihar" | Damodar = "Sorrow of Bengal"

Mains GS1 Questions

1. "Discuss the factors responsible for the seasonal nature of most peninsular rivers compared to the perennial nature of Himalayan rivers."
2. "Critically evaluate the National River Interlinking Project with special reference to Ken-Betwa Link."
3. "Examine the Cauvery water dispute. What does it reveal about the challenges of inter-state water management in India?"
4. "The Indus Waters Treaty has been a model of conflict resolution. Discuss its significance and evaluate India's decision to put it in abeyance."
5. "What are antecedent rivers? Explain the role of the Brahmaputra as an antecedent river."

MCQ Trap Awareness

• Trap: "Godavari is longer than Krishna" → True (1,465 km vs 1,400 km) but Krishna basin is smaller.
• Trap: "Narmada and Tapi form deltas" → False — they form estuaries.
• Trap: "Bhakra Dam is on Sutlej" but "Nathpa Jhakri is on Beas" → Wrong — Nathpa Jhakri is also on Sutlej.
• Trap: "Cauvery originates in Tamil Nadu" → False — originates in Karnataka (Talakaveri, Kodagu).
• Trap: "Luni river drains into Arabian Sea" → Incorrect — Luni is endorheic, draining into the Rann of Kutch (evaporates).
• Trap: "Ken-Betwa links rivers in different basins" → Incorrect — both Ken and Betwa are Yamuna tributaries (Ganga basin); it links rivers within the same Ganga basin.