Indo-Ganga-Brahmaputra plain

Also called: Indo-Gangetic plain, Northern Plains, Ganga plain, Gangetic plain · Topic: Structure and Physiography of India: Himalayas, Plains, Peninsula, Coasts and Islands · NCERT: Class 6, Ch 3 "Landforms and Life"; Class 7, Ch 1 "Geographical Diversity of India"; Class 11, Ch 2 "Structure and Physiography"

Meaning

The Indo-Ganga-Brahmaputra plain (also called the Northern Plain or Indo-Gangetic plain) is a wide, flat lowland between the Himalayas in the north and the Peninsular Plateau in the south. It is built of alluvium (loose clay, silt, sand and gravel that rivers carry and drop) laid down by the Indus, the Ganga and the Brahmaputra river systems.

It is India's food bowl and its most crowded region. Deep, fertile soil, flat land and rivers that flow all year support intensive farming, dense population and a dense transport network.

Explanation

How it formed (cause → process → result)

• Cause: the Himalayan orogeny. An orogeny is a mountain-building event.
• In the Tertiary period, the Indian plate pushed into the Eurasian plate.

• The Himalayas rose.

• Process: a hollow formed and then filled.

• A long, deep hollow called a foredeep formed between the new mountains and the Peninsular Block.

• In the Quaternary period (the last ~2.6 million years), rivers from the Himalayas and the Peninsula filled this hollow with sediment.

• Result: a huge alluvial plain.

• It is about 3,200 km long from west to east.
• It is 150-300 km wide. It is wider in the west and narrower in the east.
• The alluvium is up to 1,000-2,000 m thick.
• It is almost featureless and lies only 50-150 m above sea level.

Regional divisions (west to east)

Part	Main rivers	Key point
Punjab-Haryana plain	Satluj, Beas, Ravi (Indus tributaries)	Mostly made of doabs; drains to the Arabian Sea
Ganga plain	Ganga, Yamuna, Ghaghara, Gandak, Kosi, Son	Largest part; runs from Delhi to West Bengal
Brahmaputra plain	Brahmaputra and its tributaries	Narrow valley in Assam; braided channels, river islands, floods

• Doab: the land between two rivers that meet (do = two, ab = water).
• Water divide: a water divide is high ground that separates two river basins. In the plain it is low and hard to see.
• Haryana and Delhi separate the Indus system, which drains west to the Arabian Sea, from the Ganga system, which drains east to the Bay of Bengal.

Relief zones from north to south

Order: Shiwalik foothills → Bhabar → Tarai → Bhangar/Khadar → delta.

• Bhabar. This is a belt of boulders, pebbles and gravel at the foot of the Shiwaliks. It is 8-10 km wide.
• At the break of slope (where steep hills suddenly meet flat ground), rivers slow down and drop their heaviest load first.
• The material is very porous, so small streams sink into it and disappear.

• The surface is dry and poor for farming.

• Tarai. This is a wet, marshy belt south of the bhabar. It is 10-20 km wide.

• Water that sank into the bhabar flows underground and comes back up where finer sediment begins.
• The streams that come back up have no proper channels, so they form marshes and swamps, thick forest and tall grassland.

• Much of the tarai was cleared for farms after 1950, for example in Udham Singh Nagar (Uttarakhand).

• Bhangar. This is older alluvium on raised terraces above flood level. A terrace is a flat step of land beside a river, left high when the river cut deeper.

• It contains kankar (lime nodules, or lumps of calcium carbonate).

• Floods do not reach it, so its soil is not renewed. It is less fertile than khadar.

• Khadar. This is newer alluvium on floodplains (low land beside a river that floods).

• Floods spread fresh silt over it almost every year.

• It is very fertile and is the best farmland in the plain.

• Delta. At the river mouth the water slows and drops its fine silt. The river then splits into distributaries (branches flowing away from the main river), and new land builds out into the sea.

River landforms (mature stage)

• In the mature stage the slope is gentle. The river spreads sideways and drops sediment instead of cutting downward.
• Meanders are loop-like bends. The river wears away the outer bank and drops sediment on the inner bank.
• Oxbow lakes form when the river cuts through the narrow neck of a meander and leaves the old loop behind.
• Braided channels are many thin channels that split and join around sand bars. They form when a river carries a heavy load down a gentle slope. They are typical of the Brahmaputra.

Where it occurs

• Indus part: the Punjab-Haryana plain, with the Bist-Jalandhar doab (between the Beas and the Satluj) and the Bari doab (between the Beas and the Ravi).
• Ganga part: from Delhi to West Bengal. It includes the Ganga-Yamuna doab and the Kosi in Bihar.
• Brahmaputra part: the Assam valley.
• The Brahmaputra rises in Tibet as the Tsangpo and enters Arunachal Pradesh as the Siang/Dihang.
• In Assam it flows north-east to south-west.

• At Dhubri it turns almost 90° south and enters Bangladesh, where it is called the Jamuna.

• Majuli is a river island in the Brahmaputra in Assam. It became India's first island district in 2016. Its area fell from 734 sq km in 1914 to 502 sq km in 2004 [3].

• Piedmont belts (piedmont means "at the foot of the mountain"):
• The bhabar-tarai belt runs along the Shiwaliks.
• The Duars are in north Bengal and Assam and are known for tea gardens.

• The Chos are seasonal torrents in the Punjab Shiwaliks (Hoshiarpur area).

• Protected areas on the plain:

• Corbett (Uttarakhand) lies in the bhabar.
• Dudhwa (UP) is a tarai reserve with northern swamp deer.
• Valmiki (Bihar) joins Chitwan in Nepal.

• All three lie in the Terai Arc Landscape [5][6][7].

• Delta: the Ganga-Brahmaputra delta (Sundarbans) is in West Bengal and Bangladesh.

• The Ganga splits at Farakka into the Hooghly and the Padma.
• About 60% of the Sundarbans lies in Bangladesh [4].

Don't confuse with

• Bhabar vs Tarai: in the bhabar, streams disappear into coarse gravel. In the tarai, the same water comes back up and forms marshes.
• Bhangar vs Khadar: bhangar is older alluvium on terraces, with kankar and lower fertility. Khadar is newer alluvium on floodplains, renewed by floods every year and very fertile.
• Indo-Ganga water divide vs the Aravallis: the divide between the Indus and Ganga systems is the low ground of Haryana and Delhi, not the Aravalli hills.
• Northern Plain vs Peninsular Plateau: the plain is young Quaternary alluvium filling a foredeep. The Peninsular Plateau is an old, hard Archaean block.

Prelims Hooks

• Order from north to south: Shiwalik → Bhabar (8-10 km) → Tarai (10-20 km) → Bhangar → Khadar.
• Size: about 3,200 km long and 150-300 km wide. It is wider in the west, lies at 50-150 m above sea level, and its alluvium is up to 1,000-2,000 m thick.
• Kankar belongs to bhangar, not khadar.
• Brahmaputra: it turns south at Dhubri (Assam) and becomes the Jamuna in Bangladesh.
• Matches:
• Duars → north Bengal and Assam (tea).
• Chos → Punjab Shiwaliks.
• Corbett → bhabar.
• Dudhwa → tarai, northern swamp deer.

• Valmiki → Bihar's only tiger reserve [5][6][7].

• Trap: the Sundarbans is the world's largest delta and largest mangrove forest, but about 60% of it is in Bangladesh [4]. The Indian part became a World Heritage Site in 1987 [8].

Mains Points

• Demographic and farming heartland (GS-I):
• Deep alluvium, flat land and Himalayan rivers that flow all year support intensive farming of wheat, rice, sugarcane and jute.
• They also support dense settlement, a dense road and rail network, and inland waterways. NW-1 runs on the Ganga-Bhagirathi-Hooghly and NW-2 on the Brahmaputra.

• The deep alluvium also stores rich groundwater.

• Same features, recurring hazards (GS-I/GS-III):

• The gentle slope and heavy sediment load cause floods, waterlogging in khadar areas and avulsion (a river suddenly moving to a new course). The Kosi, the "Sorrow of Bihar", is an example.
• Majuli lost 206.7 sq km between 1949 and 2004. Its loose silt soil, the shifting braided channels and the 1950 Assam earthquake all made the erosion worse [3].

• The Brahmaputra Board's embankments and RCC porcupine screens (concrete frames that slow the water and trap silt) need to be combined with basin-level river management [3].

• Ecology under pressure (GS-III):

• After 1950, much of the tarai was cleared for farms, which broke up the habitat. The Terai Arc Landscape now links Corbett, Dudhwa and Valmiki with Nepal's parks across the border [5][7].
• At the delta end, sea-level rise could destroy 75% of the Sundarbans forest by 2100 [4].
• Mangroves protect the coast from storm surges, so West Bengal's mangrove cover matters for disaster risk reduction. It stands at 2,119.16 sq km, which is 42.45% of India's total (ISFR 2023) [2].

Related concepts

• Bhabar
• Tarai
• Bhangar
• Khadar
• Piedmont alluvial plains
• Riverine island
• Majuli
• Ganga-Brahmaputra delta

Read more

• The Northern Plain: bhabar, tarai, bhangar, khadar and the deltas