Regional Division of Plains - Geography for UPSC CSE PDF Download

Regional Divisions of the Indo-Gangetic-Brahmaputra Plains

1. Sindh Plain
2. Rajasthan Plain
3. Punjab Plain
4. Ganga Plain
5. Brahmaputra Plain
6. Ganga-Brahmaputra Delta

Sindh Plain (Pakistan)

• The plain is largely composed of older alluvial deposits known as bhangar.
• Dhors are long, narrow depressions on the plain that mark the remnants of former river courses.
• Dhand denotes alkaline or saline lakes that occur within some dhors.

Rajasthan Plain

• The Rajasthan Plain is dominated by the Thar (Great Indian) Desert, locally called Marusthali, and includes the greater Marwar plain.
• The plain is an undulating plain with a typical, wave-like surface; its average elevation is about 325 m above mean sea level.
• At the surface the region appears to be an aggradational plain, but a number of outcrops of gneisses, schists and granites show that geologically it is part of the Peninsular Plateau.
• The eastern Marusthali is rocky while the western sector is covered by shifting sand dunes called Dhrian.
• The area east of the Aravalli up to the desert margin forms a semi-arid belt known as the Rajasthan Bagar.
• The plain is drained by several short seasonal streams originating in the Aravalli; these support limited agriculture in pockets of fertile tracts.
• Luni is an important seasonal stream that drains into the Rann of Kachchh. The tract north of the Luni is called the thali or sandy plain.

Saline Lakes

• The inland drainage north of the Luni has produced several saline lakes that are sources of common salt and other mineral salts.
• Important lakes include Sambhar (the largest, near Jaipur), Didwana, Degana, and Kuchaman.

Punjab Plain

• The Punjab Plain was formed by deposition from the five major rivers of the Indus system and is largely an extensive alluvial tract.
• The plain is made up of a series of doabs - tracts of land lying between two rivers.
• Continuous depositional processes by successive rivers have joined many doabs to give the plain a relatively homogenous appearance.
• Punjab literally means "the land of five waters"; the five rivers are the Jhelum, Chenab, Ravi, Sutlej and Beas.
• The total area of the Punjab Plain is about 1.75 lakh sq km.
• The average elevation of the plain is about 250 m above mean sea level.
• The eastern boundary between the Punjab and the Haryana plains is associated with the subsurface Delhi-Aravali ridge.
• The northern fringe near the Siwalik hills has been deeply incised by numerous streams called chos, producing extensive gullying and eroded landforms typical of arid and semi-arid landscapes.
• To the south of the Sutlej lies the Malwa plain of Punjab.
• The tract between the Ghaggar and the Yamuna in Haryana - often called the Haryana Tract - acts as a water divide between the Yamuna and the Sutlej.
• The Ghaggar is considered the present-day successor of the legendary Saraswati river in many reconstructions and local traditions.

Ganga Plain

• The Ganga Plain is the largest single unit of the Indo-Gangetic Plain within India, extending roughly from the Delhi region in the west to Kolkata in the east; its area is about 3.75 lakh sq km.
• It has been built up by vast quantities of alluvium transported from the Himalayas by the Ganga and its tributaries.
• Peninsular tributaries such as the Chambal, Betwa, Ken and Son have also contributed to its formation by supplying additional alluvial material.
• The general slope of the Ganga Plain is towards the east and south-east, which influences drainage and river behaviour.
• In the lower reaches the rivers move slowly; this leads to the formation of characteristic fluvial landforms such as levees, bluffs, ox-bow lakes, marshes and ravines.
• The rivers of the plain are highly mobile and frequently change course; this, together with intense monsoon discharge, makes much of the plain prone to flooding. The Kosi in Bihar is a well-known example and has long been called the "Sorrow of Bihar" due to recurrent floods and course shifts.

Regional divisions of the Ganga Plain

• Rohilkhand Plain
• Avadh Plain
• Mithila Plain
• Magadh Plain

Ganga-Brahmaputra Delta

• The Ganga-Brahmaputra Delta is the largest delta in the world.
• In the delta the Ganga and Brahmaputra rivers split into numerous distributary channels; the local slope is extremely gentle - about 2 cm per km - and approximately two-thirds of the delta lie below 30 m above mean sea level, making it highly vulnerable to sea-level changes and storm surges.
• The seaward margin of the delta is complex and is characterised by many estuaries, mudflats, sandbanks, islands, forelands and tidal inlets.
• Extensive mangrove forests (tidal forests) cover large parts of the coastal delta; this area is known as the Sunderbans, named for the predominance of the Sundri tree.

Brahmaputra Plain (Assam Valley)

• Also called the Assam Valley, the Brahmaputra Plain occupies most of the valley of the Brahmaputra River in Assam.
• Its western limit is close to the Indo-Bangladesh border and the edge of the lower Ganga Plain; the Purvanchal hills form the eastern boundary.
• The plain is primarily an aggradational plain, built up by heavy deposition of sediments carried by the Brahmaputra and its tributaries.
• Tributaries descending from the hills deposit coarse sediments that form alluvial fans; such deposition causes the tributary channels to split and braid, promoting meandering, formation of ox-bow lakes and river-cut billows.
• Large marshy tracts and floodplains are common; in some areas the coarser alluvial debris and fan deposition produce terai or semi-terai conditions at the foot of the hills.

Significance of the Indo-Gangetic-Brahmaputra Plains

• Approximately one-quarter of the country's land area contains about half of the national population, making these plains among the most densely populated regions.
• Fertile alluvial soils, flat terrain, slow-moving perennial rivers and a climate favourable for agriculture sustain highly intensive cropping systems.
• Extensive irrigation development has turned regions such as Punjab, Haryana and western Uttar Pradesh into major grain-producing areas; prairies and similar extensive fertile plains are often termed the world's granaries.
• Well-developed networks of roads and railways across most of the plain (except the Thar Desert) facilitate industrial growth and urbanisation, linking agricultural production with manufacturing and markets.
• The plains have great cultural and religious significance: major cities, pilgrimage centres and historic sites lie along riverbanks (for example, settlements on the Ganga and Yamuna). The region was also the cradle for major religious movements including Buddhism, Jainism, and later Bhakti and Sufi traditions.

Key Terms and Short Definitions

• Bhangar - older alluvium forming slightly higher, well-drained terraces often containing calcareous nodules (kankar).
• Khadar - newer, low-lying alluvium deposited during floods; generally more fertile and level than bhangar.
• Doab - tract of land lying between two converging rivers (e.g., the land between the Ganga and Yamuna).
• Aggradational plain - a plain primarily built up by deposition of sediment (opposite of degradational or erosional plain).
• Alluvial fan - fan-shaped deposit of coarse sediments formed where a fast-flowing mountain stream loses velocity on entering a plain.
• Levee - natural embankment formed by deposition of coarser sediments near a river channel during floods.
• Oxbow lake - a crescent-shaped lake formed when a meander is cut off from the main channel.
• Terai - marshy, humid belt at the foot of the Himalaya formed by the deposition of alluvium and groundwater emergence.

Formation Processes and Major Landforms (Brief)

• Himalayan rivers erode bedrock in the mountains and transport vast quantities of sediment downstream; deposition over geologic time has created extensive alluvial plains.
• In the lower courses, reduced gradient causes rivers to meander, form oxbow lakes, construct levees and develop marshes and backswamps.
• In areas where tributaries descend from hills, sudden loss of slope causes deposition of coarse material in the form of alluvial fans and braided channels.
• In deltaic zones, repeated splitting of channels and tidal action build landforms such as mudflats, sandbars, tidal marshes and mangrove forests.

Summary

The Indo-Gangetic-Brahmaputra plains comprise a continuous belt of fertile alluvial land formed by Himalayan and peninsular rivers. They include distinct regional units - Sindh, Rajasthan, Punjab, Ganga, Brahmaputra plains and the vast Ganga-Brahmaputra delta - each with characteristic landforms and resources. These plains support high population densities, intensive agriculture, major transport networks, and rich cultural landscapes, while being vulnerable to floods, river channel shifts and, in the coastal delta, to sea-level changes.