← Indian Geography

Ganga River System

6 min read indian-geography ganga-river ganga-basin sacred-river

Introduction

The Ganga (Ganges) River system is the largest river basin in India, draining approximately 8,61,452 square kilometers — roughly 26% of India’s total geographical area — across eleven states. The river itself flows for 2,525 km from its source at Gaumukh (the terminus of the Gangotri Glacier) at approximately 3,892 meters elevation in Uttarakhand to its mouth at the Bay of Bengal, traversing five states (Uttarakhand, Uttar Pradesh, Bihar, Jharkhand, West Bengal) before entering Bangladesh and ultimately discharging into the Bay of Bengal. The Ganga basin supports approximately 43% of India’s population (about 550 million people), making it the most densely populated river basin in the world. The river holds profound religious and cultural significance in Hinduism — it is personified as the goddess Ganga and considered capable of purifying sins.

The Headwaters — Bhagirathi and Alaknanda

The Ganga in its upper reaches has two primary source streams:

The Bhagirathi: Considered the true source stream of the Ganga, the Bhagirathi rises from Gaumukh (“Cow’s Mouth”), the snout of the Gangotri Glacier in Uttarkashi district of Uttarakhand. The Gangotri Glacier, approximately 30 km long and receding at an alarming rate of 20-25 meters per year due to climate warming, is the largest glacier in the Garhwal Himalaya. The Bhagirathi flows through a narrow, deep gorge with several dangerous rapids, passing Gangotri town (one of the Char Dham pilgrimage sites). The Tehri Dam on the Bhagirathi — a 260.5 meter high earth and rock-fill dam, one of the world’s tallest — was controversially constructed and commissioned between 2006-2012, generating 2,400 MW of hydroelectricity.

The Alaknanda: Rising from the Alakapuri Glacier near Badrinath, the Alaknanda flows southwestward, receiving the Dhauliganga near Vishnuprayag, the Nandakini at Nandaprayag, the Pindar at Karnaprayag, and the Mandakini at Rudraprayag. The five sacred confluences (Panch Prayag) are major pilgrimage sites. The Alaknanda-Bhagirathi confluence at Devprayag (elevation 830 m) officially marks the formation of the Ganga River proper.

The Himalayan Tributaries

The Ganga receives numerous large, perennial Himalayan tributaries, primarily from the north:

The Yamuna: The longest and most important right-bank tributary (approximately 1,376 km), the Yamuna originates from the Yamunotri Glacier at an elevation of approximately 6,387 meters in the Bandarpunch massif of Uttarakhand. The river flows through the Siwalik dun valleys, emerges onto the plains at Tajewala (where the Eastern and Western Yamuna Canals divert its water), and passes through Delhi — the national capital, where the river receives massive volumes of untreated sewage and industrial effluent resulting in severe pollution. At Prayagraj (Allahabad), the Yamuna meets the Ganga at the Triveni Sangam — the most sacred confluence in Hinduism — where the mythical Saraswati is also said to join. Key tributaries of the Yamuna include the Chambal (which drains the Malwa Plateau and is famous for its unique Gangetic river dolphin population), Sind, Betwa, and Ken.

The Ramganga: Originating from the Doodhatoli Range in Uttarakhand, this left-bank tributary joins the Ganga near Kannauj. Its waters are harnessed by the Ramganga Dam (Kala Garh Project).

The Gomti: A sluggish, low-gradient river originating from Fulhar Jheel (a natural lake) near Pilibhit, Uttar Pradesh, the Gomti joins the Ganga near Saidpur, downstream of Varanasi. Lucknow, the capital of Uttar Pradesh, is situated on the Gomti’s banks.

The Ghaghara (Karnali): The largest left-bank tributary by discharge, the Ghaghara originates from the Mapchachungo Glacier in the Nepal Himalaya near the Tibetan border. Known as the Karnali in Nepal, it enters India near Bahraich, Uttar Pradesh. The river carries enormous sediment loads and exhibits a braided channel pattern with frequent course changes. It joins the Ganga near Chhapra, Bihar. The river’s catchment in the Nepal Himalaya receives some of the highest rainfall in the Himalayan region, contributing to its high discharge.

The Gandak: Rising near the junction of the Dhaulagiri and Annapurna ranges in Nepal, the Gandak enters the Ganga at Sonpur (near Patna, Bihar). The river is known for its shifting channel and heavy sediment load. The Valmiki Tiger Reserve is situated in the Gandak basin on the Indo-Nepal border.

The Kosi: Infamous as the “Sorrow of Bihar,” the Kosi originates from the confluence of the Sun Kosi, Arun, and Tamur rivers in Nepal’s Mahabharat Range and Tibet. The river enters India near Bhimnagar, Bihar. The Kosi has shifted westward by approximately 112 km since 1736 through a series of catastrophic avulsions, the most recent major shift occurring in 2008 when the river breached its eastern embankment at Kusaha, displacing over 3 million people. The Kosi megafan — a massive alluvial cone covering approximately 15,000 square kilometers — is one of the world’s largest. The river joins the Ganga at Kursela in Bihar.

The Damodar: A right-bank tributary rising from the Chota Nagpur Plateau, the Damodar was historically notorious for flooding (“Sorrow of Bengal”) before the Damodar Valley Corporation (DVC), modeled on the Tennessee Valley Authority, implemented a comprehensive program of dams, barrages, and canals since 1948. The river now contributes to the industrial water supply for the coal and steel belt of eastern India.

The Ganga Plains Hydrology

The Ganga’s discharge exhibits extreme seasonality driven by the monsoon. At Farakka (near the Bangladesh border), the average annual discharge is approximately 16,650 cubic meters per second, but dry-season flows (March-May) can drop to 1,500 cubic meters per second while peak monsoon flows (August-September) can exceed 60,000 cubic meters per second. The Himalayan tributaries contribute approximately 70% of the Ganga’s total annual flow, with the remaining 30% from peninsular tributaries (Chambal, Betwa, Ken, Son, and Damodar).

The Farakka Barrage (commissioned 1975), located approximately 18 km from the Bangladesh border, diverts water through a 38-km feeder canal into the Bhagirathi-Hooghly channel to maintain the navigability of the Kolkata Port by flushing accumulated silt. The barrage has been a source of prolonged dispute between India and Bangladesh (settled through the 1996 Ganges Treaty establishing water-sharing principles).

The Ganga Delta

The Ganga, branching into distributaries in West Bengal (the Hooghly/River Bhagirathi-Hooghly system flowing south passes Kolkata) and entering Bangladesh (where it is known as the Padma), forms the world’s largest delta — the Ganga-Brahmaputra-Meghna Delta, covering 105,000 square kilometers. The delta is characterized by:

  • The Sundarbans — the world’s largest mangrove forest (approximately 10,000 square kilometers, of which roughly 4,000 square kilometers are in India and the remainder in Bangladesh), a UNESCO World Heritage Site and habitat of the Royal Bengal Tiger
  • Highly dynamic channels exhibiting rapid erosion, accretion, and migration
  • Tidal influence extending over 100 km inland
  • The phenomenon of island formation/disappearance through fluvial and marine deposition/erosion — New Moore Island (South Talpatti) emerged in the 1970s and subsequently vanished by 2010.

The Ganga carries approximately 729 million tonnes of suspended sediment annually to the Bay of Bengal (the combined Ganga-Brahmaputra-Meghna system delivers over 1 billion tonnes), constructing what is known as the Bengal Fan — the world’s largest submarine fan, extending approximately 3,000 km southward into the Bay of Bengal and Indian Ocean, with sediment thickness exceeding 16 km in places.