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

Detail

1. What the Northern Plain is and how it formed

• The Indo-Ganga-Brahmaputra plain is a wide, flat lowland between the Himalayas in the north and the Peninsular Plateau in the south (Figure 2.4, Class 11).
• Alluvium means loose clay, silt, sand and gravel that rivers carry and drop.

• The plain is built of alluvium brought down by three river systems: the Indus, the Ganga and the Brahmaputra.

• How it formed:

• In the Tertiary period the Himalayan orogeny took place. An orogeny is a mountain-building event. Here, the Indian plate pushed into the Eurasian plate and the Himalayas rose.
• A long, deep hollow (a foredeep) formed between the new mountains and the Peninsular Block.

• In the Quaternary period (the last ~2.6 million years), Himalayan and Peninsular rivers filled this hollow with sediment. The result is the plain we see today.

• Size and shape:

• About 3,200 km long from west to east.
• 150-300 km wide. It is wider in the west and narrower in the east.
• Alluvium is up to 1,000-2,000 m thick.

• It is a nearly featureless plain, only 50-150 m above sea level.

• Water divide (watershed): 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.

• The Dhubri turn:
• The Brahmaputra rises in Tibet as the Tsangpo.
• It enters India in Arunachal Pradesh as the Siang/Dihang.
• In the Assam valley it flows north-east to south-west.
• At Dhubri (western Assam) it turns almost 90° south and enters Bangladesh, where it is called the Jamuna.

2. Regional divisions (west to east)

Part	Main rivers	Key point
Punjab-Haryana plain	Indus tributaries: Satluj, Beas, Ravi	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

3. Zones from north to south

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

(a) Bhabar

• Bhabar is a narrow belt of coarse, porous sediment at the foot of the Shiwalik hills. It is 8-10 km wide and runs parallel to the hills.
• How it forms:
• A break of slope is the point where steep hills suddenly meet flat ground.
• At this point, rivers coming out of the mountains slow down and lose energy.
• They drop their heaviest load first: boulders, pebbles and gravel.

• This coarse material is very porous, so small streams sink into it and vanish from the surface.

• The bhabar is dry on the surface and poor for farming.

• Corbett Tiger Reserve (Uttarakhand) lies in the bhabar tract and is the most intact habitat unit in the region [6].

(b) Tarai

• Tarai is a wet, marshy belt just south of the bhabar. It is 10-20 km wide.
• How it forms:
• Water that sank into the bhabar flows underground.
• Where finer, less porous sediment begins, this water comes back up to the surface.
• The streams that reappear have no proper channels. They spread out and form marshes and swamps.

• The result is thick forest, tall grassland and rich wildlife.

• Land-use change: much of the tarai was cleared for farms after 1950. Refugees and other settlers were resettled there, for example in Udham Singh Nagar (Uttarakhand) and in the Uttar Pradesh tarai.

• Protected areas that remain:
• Dudhwa Tiger Reserve (UP) is a typical tarai ecosystem. It is made up of Dudhwa National Park, Kishanpur Wildlife Sanctuary and Katerniaghat Wildlife Sanctuary. It is the only place in India with a likely viable population of the nominate (original) sub-species of the northern swamp deer [7].
• Valmiki Tiger Reserve is Bihar's only tiger reserve. It joins Chitwan National Park in Nepal and connects with Sohagi Barwa Wildlife Sanctuary in UP [8].
• All three reserves (Corbett, Dudhwa, Valmiki) fall in the Terai Arc Landscape, a forest-grassland belt that crosses the India-Nepal border. It supports tigers, elephants and rhinos [6].
• In the wet tarai, tall grasslands shelter many ungulates (hoofed animals such as deer) and the predators that hunt them [7].

(c) Bhangar

• Bhangar is older alluvium that sits on raised terraces above the flood level. A terrace is a flat step of land beside a river, left high when the river cut deeper.
• Floods do not reach it, so its soil is not renewed.
• It contains kankar, which are lime nodules (lumps of calcium carbonate) in the soil.
• Its soil is coarser and less fertile than khadar.

(d) Khadar

• Khadar is newer alluvium on the floodplains, the low land next to a river that floods.
• Floods spread fresh silt over it almost every year.
• Its soil is fine and very fertile, which makes it the best farmland in the plain.

Feature	Bhangar	Khadar
Age of alluvium	Older	Newer
Position	Terraces above flood level	Floodplains
Renewed by floods?	No	Yes, almost every year
Kankar	Present	Absent
Fertility	Lower	High

4. Piedmont alluvial plains

• Piedmont means "at the foot of the mountain". A piedmont alluvial plain forms where rivers leave the hills, slow down and drop coarse sediment at the mountain foot.
• Examples:
• Bhabar-tarai belt along the Shiwalik foothills.
• Duars: foothills of north Bengal and Assam, famous for tea gardens.

• Chos: seasonal torrents in the Punjab Shiwaliks (Hoshiarpur area). They cut deep gullies and badly erode the land.

• Doab: the land between two rivers that meet (do = two, ab = water). Examples are the Ganga-Yamuna doab and the Punjab doabs: Bist-Jalandhar (Beas-Satluj) and Bari (Beas-Ravi).

5. River landforms of the plain

• The plain shows mature-stage river landforms. In this stage the slope is gentle and the river spends its energy flowing sideways and depositing sediment instead of cutting downward.

Landform	What it is	How it forms
Meander	A loop-like bend in a river	Water erodes the outer bank and drops sediment on the inner bank
Oxbow lake	A curved lake cut off from the river	The river breaks through the narrow neck of a meander and leaves the old loop behind
Sand bar	A ridge of sand in the channel	The current slows and drops sand
Braided channel	Many thin channels splitting and joining around bars	A river carrying a heavy load on a gentle slope drops sediment, splits, and keeps shifting

• Brahmaputra plain: it is known for riverine islands, sand bars, yearly floods and shifting braided channels.
• A riverine island is land surrounded by river channels inside a wide, braided river.

6. Majuli: river island under threat

• Location: in the Brahmaputra in Assam, with the Subansiri river on its north side.
• It is often called the world's largest river island. The Government of India calls it the "world's largest inhabited river island" [4].
• Culture: it is a centre of Vaishnavite satras, monasteries started under the Neo-Vaishnavite movement of Srimanta Sankardeva.
• District: it became Assam's (and India's) first island district in 2016.
• Area:
• Majuli district covers 1,245 sq km.
• The main island covers about 522 sq km [3].
• The island measured 734 sq km in 1914 and fell to a low of 502 sq km in 2004.
• It lost 206.7 sq km between 1949 and 2004 [3].

• (A commonly quoted older figure is about 1,250 sq km shrinking to roughly 350-500 sq km.)

• Why it is eroding:

• The island is part of the Brahmaputra's alluvial floodplain. Its soil is mostly silt with no cohesion (it does not stick together), so water washes it away easily [3].
• Erosion became severe after the 1950 Assam earthquake [3]. The earthquake raised the riverbed and sent much more sediment downstream.

• The braided channels keep shifting and attacking the banks.

• Response: the Brahmaputra Board began protection works in January 2004. These include embankments, RCC porcupine screens (concrete frames that slow water and trap silt), and spurs and dampeners that push the current away from the bank [3].

7. The deltas: Ganga-Brahmaputra delta (Sundarbans)

• A delta is a fan-shaped area of land formed at a river mouth.
• How it forms:
• The river reaches the sea and slows down.
• It drops its fine silt.
• Its channel splits into distributaries, which are branches flowing away from the main river.

• New land slowly builds out into the sea.

• Course to the sea: the Ganga splits at Farakka. The Hooghly (Bhagirathi-Hooghly) flows through West Bengal. The main flow, the Padma, enters Bangladesh, joins the Jamuna (Brahmaputra) and then the Meghna, and reaches the Bay of Bengal.

• The Sundarbans is the world's largest delta and world's largest mangrove forest. It is named after the sundari tree.
• Mangroves are salt-tolerant trees of tidal coasts. Many have breathing roots that stick up out of the mud.
• Total area is about 10,000 sq km. About 60% lies in Bangladesh and the rest in India [5].
• India's share — flag: UNESCO's split gives India about 40%. NCERT books disagree. One Class 7 chapter says "about half"; another NCERT book says "about one-third". Either way, India holds the smaller share.

• Mangrove cover: West Bengal had 2,119.16 sq km of mangrove cover in ISFR 2023. That is a gain of 22.16 sq km over ISFR 2013 (2,097 sq km) [2]. West Bengal has India's largest mangrove cover, at 42.45% of the national total (ISFR 2023) [2].

• Wildlife: the Royal Bengal tiger lives here. The Sundarbans holds the single largest tiger population in the world, adapted to an almost amphibious life (living on land and swimming between islands) [5].

• Protected status:
• India's Sundarbans National Park became a UNESCO World Heritage Site in 1987 [9].
• Bangladesh's Sundarbans is a separate World Heritage Site [5].

• Bangladesh's part is also a Ramsar site, designated in May 1992 and enlarged from 596,000 to 601,700 ha [10]. (A Ramsar site is a wetland of international importance under the Ramsar Convention.)

• Threats:

• Sea-level rise: a UNESCO report warns it could destroy 75% of the forest by 2100 [5].
• Cyclones: the Bay of Bengal sends frequent cyclones and storm surges into the delta.
• Salinity: less fresh water flows down the rivers, so the water gets saltier.

8. Why the Northern Plain matters

• Agriculture: deep, fertile alluvium grows wheat, rice, sugarcane and jute, so it is India's food bowl.
• Population:
• Fertile soil, flat land and steady water supply support a very dense population.

• Satellite images of India at night show the plain as a bright band of lights.

• Transport:

• Flat land made it easy to build a dense road and rail network.

• Rivers carry boats and cargo. National Waterway-1 runs on the Ganga-Bhagirathi-Hooghly system, and NW-2 on the Brahmaputra.

• Water: the deep alluvium holds rich groundwater reserves.

Prelims Hooks

• North to south order: Shiwalik → Bhabar → Tarai → Bhangar → Khadar. Bhabar is the zone where streams disappear. Tarai is the zone where they re-emerge.
• Widths: Bhabar 8-10 km, Tarai 10-20 km. Plain is 3,200 km long and 150-300 km wide, at 50-150 m above sea level.
• Kankar (lime nodules) belongs to bhangar, not khadar. Khadar is the newer, more fertile alluvium on floodplains.
• Water divide between the Indus and Ganga systems: Haryana and Delhi, not the Aravallis.
• The Brahmaputra turns south at Dhubri (Assam) to enter Bangladesh, where it is called the Jamuna.
• Matches: Duars → north Bengal and Assam (tea); Chos → Punjab Shiwaliks; Doab → land between two rivers.
• Tiger reserve matches: Corbett → bhabar (Uttarakhand); Dudhwa → tarai, northern swamp deer (UP); Valmiki → Bihar's only tiger reserve, next to Chitwan in Nepal [6][7][8].
• Majuli: in the Brahmaputra, Assam; became a district in 2016; island area 734 sq km (1914) → 502 sq km (2004) [3].
• Sundarbans: about 60% in Bangladesh [5]. West Bengal has India's largest mangrove cover, 42.45% (ISFR 2023) [2]. The Indian part became a World Heritage Site in 1987 [9].
• Trap: the Sundarbans is the world's largest delta and largest mangrove forest, but most of it lies in Bangladesh, not India.

Mains Points

• Plain and population (GS-I): deep alluvium, flat land and perennial Himalayan rivers lead to intensive farming, dense settlement and dense transport links. This makes the Indo-Gangetic belt India's demographic and agricultural heartland. The same features cause recurring floods, river avulsion (a river suddenly shifting to a new course; for example, the Kosi is called the "Sorrow of Bihar") and waterlogging in khadar areas.
• Tarai transformation (GS-III, environment): after 1950, swamp forest was cleared for resettlement and farming. The tarai became a farming belt, but habitat broke up. Today the Terai Arc Landscape links Corbett, Dudhwa and Valmiki with Nepal's parks, which shows that wildlife corridors across borders are needed [6][8].
• River-island erosion (GS-III, disasters):
• Majuli lost 206.7 sq km between 1949 and 2004 [3].
• This shows how braided, sediment-heavy rivers, earthquakes (1950) and loose silt soils combine to cause erosion.

• Responses such as embankments and porcupine screens by the Brahmaputra Board need to be combined with basin-level river management [3].

• Sundarbans and climate (GS-III):

• Sea-level rise could destroy 75% of the forest by 2100 [5].
• Frequent Bay of Bengal cyclones and rising salinity threaten livelihoods and tigers.
• Mangroves act as a natural barrier against storm surges. This is why the small gain in West Bengal's mangrove cover (ISFR 2023) matters for disaster risk reduction [2].