Indo Gangetic Plains

• The 300m contour line divides the Himalayas and the Gangetic Basin.
• The southern boundary is demarcated by the edge of the peninsula which coincides with 75m contours in most of its length and 35m in the northeastern section, towards the delta.
• The plains are extremely flat with a slope of nearly 1:1000 to 1:2000
• The plains are flat and are rolling with monotonous character.

Formation of Indo–Gangetic–Brahmaputra Plain

• Indo-Gangetic plain’s formation is closely related to the formation of the Himalayas.
• Rivers that were previously flowing into the Tethys sea deposited a huge amount of sediments in the Tethys Geosyncline.
• These sediments were uplifted, folded, and compressed to form the Himalayas due to the northern movement of the Indian Plate.
• The northern movement of the Indian Plate also created a trough to the south of the Himalayas.

Depositional Activity

• During the initial stages of upliftment of sediments, existing rivers changed their course several times and were rejuvenated each time.
• Rejuvenation occurred due to intense headward and vertical downcutting of the soft strata overlying the harder rock stratum.
• Headward and vertical erosion in the initial stages and lateral erosion in later stages contributed a huge amount of conglomerates (rock debris, silt, clay, etc.) which were carried downslope.
• These conglomerates were deposited in the depression (Indo-Gangetic Trough or Indo-Gangetic syncline) between peninsular India and the convergent boundary (the region of present-day Himalayas).

New rivers and more alluvium

• The formation of Himalayas and glaciers led to the emergence of new rivers
• These rivers and glacial erosion contributed to the deposition of alluvium in the depression between peninsular India and Himalayas
• The accumulation of sediment caused the Tethys sea to recede
• The depression was ultimately filled with sediment, leaving behind a featureless aggradational plain
• This plain is called the Indo-Gangetic plain and was formed by fluvial deposition
• Upper peninsular rivers also contributed, but to a lesser extent
• In recent times, the three major river systems of Indus, Ganga, and Brahmaputra have become predominant in the deposition of sediment
• Due to this, the plain is also known as the Indo-Gangetic-Brahmaputra Plain
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Longitudinal Profile – Indo Gangetic Plains

Bhabhar Region

• The bhabar belt is adjacent to the Shiwalik foothills and consists of coarser materials.
• It is a narrow and porous stretch of the Indo-Gangetic plain, about 8-16 km wide and running east-west along the foothills.
• The bhabar belt shows remarkable continuity from the Indus to the Tista and is formed by the merging of alluvial fans deposited by rivers descending from the Himalayas.
• The porosity of the bhabar is due to the deposition of a huge number of pebbles and rock debris, which causes streams to disappear and results in dry river courses except in the rainy season.
• The Bhabar belt is comparatively narrow in the east and extensive in the western and north-western hilly region, stretching from Punjab to Assam Himalayas.
• The area is not suitable for agriculture, and only big trees with large roots thrive in this belt due to its complex profile and general slope of 1:6000.

Terai Plains

• Terai is a narrow, damp and densely forested tract to the south of Bhabar, running parallel to it.
• It is about 15-30 km wide and widest along Bihar and eastern Uttar Pradesh.
• The underground streams of the Bhabar belt re-emerge in this belt.
• Terai is more marked in the eastern part because of higher rainfall.
• Most of the Terai land has been deforested for agriculture, especially in Punjab, Uttar Pradesh, and Uttarakhand.
• The soils in Terai are Nitrogen-rich and have a humus content.
• Crops like sugarcane, rice, and wheat are grown in Terai, giving good yields.

Bangar Region

• Bhangar is the older alluvium along the river beds forming terraces higher than the flood plain.
• The terraces often have calcareous concretions known as ‘KANKAR’.
• Regional variations of Bhangar include ‘The Barind plains’ in the deltaic region of Bengal and the ‘bhur formations’ in the middle Ganga and Yamuna doab.
• Bhur denotes an elevated piece of land along the banks of the Ganga river, especially in the upper Ganga-Yamuna Doab, formed due to the accumulation of wind-blown sands during hot dry months.
• Bhangar contains fossils of animals like rhinoceros, hippopotamus, elephants, etc.
• Kankar deposits in Bhangar are fragments of Limestone and natural supplements of bases to the soil.
• Bhangar has been seriously degraded in several parts of UP, where it is called Usar due to salinization.
• Barind Tract (Barind Plains)
  • The Barind Tract is a large physiographic unit located in northwestern Bangladesh and north-central West Bengal state, India.
  • It is the largest unit of its kind in the Bengal Basin and dates back to the Pleistocene era.
  • The region lies northwest of the confluence of the upper Padma and Jamuna rivers and is bordered by the floodplains of the Mahananda and Karatoya rivers.
  • The Barind is a high, undulating region with reddish and yellowish clay soils.
  • It has been recognized as a unit of old alluvium for a long time.

Khadar Region

• The Khadar is composed of newer alluvium and forms the flood plains along the river banks.
• A new layer of alluvium is deposited by river flood almost every year.
• This makes them the most fertile soils of Ganges.

Reh or Kollar

• Reh or Kollar comprises saline efflorescences of drier areas in Haryana.
• Reh areas have spread in recent times with an increase in irrigation (capillary action brings salts to the surface).

Transverse Profile – Indo Gangetic Plains

Rajasthan Plain

• The Ghaghar basin is located in the North, while the Aravallis are in the East.
• The region is part of the Thar desert but has alluvial deposits of Indus and its tributaries.
• Due to the upliftment of the Himalayas, the river channels have shifted to the west.
• The plain is undulating and has an average elevation of 325 meters above sea level.
• The 25cm isohyte divides the plain into Marusthali in the west and Rajasthan Bagar in the east.
• Marusthali is a desert with shifting sand dunes called Dhrian, and it receives only 25cm of rainfall per year.
• The only tree in this region is Khejri, which is associated with the Bishnoi tribe.
• Rajasthan Bagar is a semi-arid fertile tract with green patches called Rohi.
• To the north of Luni, a sandy desert is known as Thali.
• Saline Lakes:
  • North of the Luni, there is inland drainage having several saline lakes. They are a source of common salt and many other salts.
  • Sambhar, Didwana, Degana, Kuchaman, etc. are some of the important lakes. The largest is the Sambhar lake near Jaipur.

Punjab Plain

• Plain formed by five important rivers of the Indus system
• Primarily made up of ‘doabs’ (land between two rivers)
• There are 5 doabs (Chaj, Rechna, Bist, Bari, and Sindsagar)
• Punjab means “Land of Five Waters”
• Extremely fertile plains but poor drainage and flood-prone
• Total area of the plain is about 1.75 lakh sq km
• Average elevation of the plain is about 250m above mean sea level
• Bounded by a 291m contour line parallel to Delhi-Ambala ridge
• Eastern boundary marked by subsurface Delhi-Aravali ridge
• Northern part of the plain has been intensively eroded by numerous streams called Chos
• South of the Satluj river is Malwa plain of Punjab
• Area between Ghaggar and Yamuna rivers is termed as ‘Haryana Tract’
• Ghaggar river is considered to be the present-day successor of the legendary Saraswati River.

Gangetic Plain

• This is the largest unit in India, stretching from Delhi to Kolkata, covering an area of about 3.75 lakh sq km.
• The plain was formed by the deposition of alluvium brought by the Ganga river and its tributaries from the Himalayas, as well as the peninsular rivers that join the Ganga river system.
• The slope of the plain is generally towards the east and southeast.
• The area is marked by local prominences such as levees, bluffs, oxbow lakes, marshes, and ravines due to sluggish river flow in the lower sections of Ganges.
• Frequent floods occur in the area as the courses of almost all the rivers keep on shifting. The Kosi river is particularly known for causing floods and is often called the ‘Sorrow of Bihar’.
• Divisions of Ganga plains:
  • Upper Gangetic Plain:
    • Boundaries: 291m contour in the west, 300m contour in the north, 75m contour in the south, and 100m contour in the east.
    • Includes:
      • Rohilkhand Plains: fertile, Sharda and Ramganga doabs, located in Bareilly, Muzaffarnagar, and home to the Rohila tribe (Afghan).
      • Ganga-Yamuna Doab: largest doab of India, famous for sugarcane cultivation, has fine dust deposits from aeolian process.
      • Yamuna-Chambal Basin: badland region due to gully erosions and ravines, largest degraded area of India.
  • Middle Gangetic Plain:
    • Transitional plain with very fertile loam deposits and high groundwater level.
    • Includes 3 sections:
      • Awadh Plain: flood-prone, located between Ghaghra and Gomti rivers in eastern UP.
      • Mithila Plain: flood-prone, located between Gandak and Kosi rivers.
      • Magadh Plain: located east of R.Son and not flood-prone.
  • Lower Gangetic Plain:
    • Paradelta in north, erosion-bound inverted triangle in north part of West Bengal.
    • Rarh Plains: located west of Chota Nagpur plateau, has laterite deposits, 35m contour line separates it from Chota Nagpur plateau.
    • Delta Plains: most extensive part of Sunderbans (1/3 in India), famous for inland fishing and jute cultivation, and known for mangrove forests and tidal forests located towards the coastline.

Ganga-Brahmaputra Delta

• This is the largest delta in the world.
• The Ganga river divides itself into several channels in the delta area. The slope of the land here is a mere 2 cm per km. Two-thirds of the area is below 30 m above mean sea level. [Highly vulnerable to sea-level changes]
• The seaward face of the delta is studded with a large number of estuaries, mud flats, mangrove swamps, sandbanks, islands, and forelands.
• A large part of the coastal delta is covered tidal forests. These are called the Sunderbans because of the predominance of the Sundri tree here.

Brahmaputra Plain

• The Brahmaputra Plain is also called the Brahmaputra Valley, Assam Valley or Assam Plain.
• It is mainly located in the state of Assam.
• Its western boundary is the Indo-Bangladesh border and the lower Ganga Plain.
• Its eastern boundary is the Purvanchal hills.
• It was formed by the deposition of the Brahmaputra river and its tributaries.
• The tributaries create alluvial fans, leading to river meandering and the formation of bill and ox-bow lakes.
• There are marshy areas in the plain.
• The alluvial fans formed by coarse debris create terai or semi-terai conditions.

Significance of the Plain

• One-fourth of India’s land holds half of its population.
• Flat surface, fertile alluvial soils, favorable climate, and slow-moving perennial rivers facilitate intense agriculture.
• Punjab, Haryana, and the western part of Uttar Pradesh are the granaries of India due to extensive irrigation.
• The entire plain, except the Thar Desert, has a close network of roads and railways, leading to large-scale industrialization and urbanization.
• The banks of sacred rivers like Ganga and Yamuna have many religious places dear to Hindus, where Buddhism, Jainism, Bhakti, and Sufi movements flourished, making it a significant cultural tourism destination.