The plain stretches from east to west to a distance of 2,400 km with a varying width ranging from 240 kms to 320 kms and forms a great curve from the Satluj to the Bay of Bengal, covering an area of about 750,000 sq. kms. Of this about one-third lies in the arid region of western Rajasthan.
The surface of the plain is at tide level near the mouth of the Ganga but in Punjab it is over 200 m above sea level. It is uniformly a level plain without any interruption except a few outliers of the Aravalli hills, such as, in the vicinity of Delhi. These form isolated low hills or ridges and emerge out of the surrounding alluvium as islands in the oceans.
The uniformity of the level of this plain is due to the deposition of silt into the water and the absence of any earth movement which did not disturb the flatness even at a later stage. The deposits include great thickness of sand, clay, loam and silt. The clay element dominates towards the mouth of the rivers, whereas the sands are predominant in the upper reaches.
These plains are remarkably homogeneous with little relief changes for hundreds of kilometres. In these featureless alluvial expanses are found differences of slopes and aspect, such as the Bhangar and the Khadar. The Bhangar represents the upland formed by the deposition of the older alluvium in the river beds. The Khadar are lowlands formed by the deposition of detritus of new alluvium in the river beds.
These are often liable to inundation during floods. These two are separated from each other by the river terraces. The uplands in the neighbourhood of the rivers are broken into extensive ravine lands extending over thousands of kilometres area on both sides of the rivers in the southern Uttar Pradesh, eastern Rajasthan and Madhya Pradesh.
(a) Bhabar and Tarai:
The great plains are bordered in the north by two narrow belts from end to end. All along the Himalaya and other hilly regions where they join the plains, there are forelands known locally as bhabar or ghar in which are deposited coarse sand and pebbles brought down from the hills by the swift-flowing mountain streams.
Except during the rainy season, these are marked by Dry River courses in which the water of the smaller streams sink underground. Only the larger rivers flow on the surface in the bhabar area. These bhabar lands are narrower in the east and extensive in the western and north western hilly region.
The water that sinks underground in the bhabar reappears on the surface where the plains begin. This water converts large areas along the rivers into swamps known as Tarai, which is largely ill-drained and densely forested. The Tarai is more marked in the eastern regions, due to greater rainfall, than in the west.
(b) The Indus Basin:
The Indus basin is located in the states of Jammu and Kashmir, Himachal Pradesh and Punjab. The Indus is over 2,900 kms in length. Its main tributaries are the Satluj, Beas, Ravi, Chenab and Jhelum. The Indus plain has a very gentle slope.
The plain stretches over 1,200 kms between the Arabian Sea in the south-west and foot-hills of the Western Himalaya in the north-east. Over this total distance, the overall fall of the plain is hardly 300 metres or so. The rivers have made the plain very fertile and it now possesses one of the densest networks of canals for irrigation.
(c) The Ganga Basin:
The Ganga rises in Uttarakhand Himalaya at Gangotri and after reaching Haridwar it enters the northern Plains. On its west lies the Yamuna which joins it at Allahabad. The Yamuna in turn is joined by the Chambal, Sind, Betwa and Ken. They all flow through the Malwa Plateau before entering into the plains.
The Sone is the only big river to join the Ganga directly from the southern plateau. Further east, the Damodar draining the Chottanagpur plateau joins the Ganga. The big Himalayan rivers joining the Ganga downstream of Allahabad from west to east are Gomti; Ghaghara, Gandak and Kosi.
The Ganga river system drains most of Haryana, south-east Rajasthan, northern Madhya Pradesh, Uttar Pradesh and Bihar. Ambala is located on the water divide between the Indus and the Ganga river systems. The plains from Ambala in the north-west to Sundarbans in the east stretch over nearly 1,800 kms.
During its entire stretch from Haryana to Bangladesh, there is hardly a fall of 300 metres in its slope. The zig-zag or meandering course of the rivers tell us how level are the plains. The length of the Ganga is nearly 1,900 kms.
(d) The Brahmaputra Valley:
The Brahmaputra originates in Tibet near the source of the Indus and the Sutlej. It carries a tremendous volume of water. The river is as long as the Indus but most of its course lies in Tibet. It flows parallel to the Himalayan Mountains in Tibet, where it is known as Tsangpo.
When it takes a hairpin turn around Namcha Barwa (7,757 m), the under cutting done by the powerful river is of the order of 5,500 meter. Here and in Arunachal Pradesh it is known as Dihang. After the confluence of Lohit, Dihang and Dibang, it is called the Brahmaputra.
Besides a great volume of water, it also carries huge amounts of silt with it. In northern Bangladesh it is known as Jamuna and in the central part it is called Padma. Further south, the Ganga and the Brahmaputra meet and the joint stream is called Meghna.
(e) The Ganga-Brahmaputra Delta:
It is the largest and the fastest growing delta of the world. Besides being well-watered, it is also the most fertile. The Brahmputra after joining the Ganga splits into numerous distributaries. Due to the gentle slope or gradient, the river becomes sluggish, and islands of silt and mud develop in its channel.
To circumvent these obstructions, the river tends to split into a number of channels. The process is repeated several times to develop a classical delta. The lower part of the delta becomes marshy where fresh water and sea water get mingled owing to high and low tides.
Significance of the Great Plains:
The northern plains is a riverine region, being bountifully endowed with the fertile soil, favourable climate, flat surface rendering possible the construction of roads and railways, and slow moving rivers.
All these factors have made this plain very important. An extensive system of irrigation, developed on the tributaries of the Satluj, the Ganga, the Jamuna and others, has turned the once dreary and desolate tracts of Punjab, Haryana, northern Rajasthan and Uttar Pradesh, into populous spots of smiling plenty.
(a) Heavy Concentration of Population:
The great plain of India with its deep, fertile, stoneless, alluvial soil and its many rivers, is the most favourable and most desirable part of the sub-continent. The five rich states of the plain (Punjab, Haryana, Uttar Pradesh, Bihar and West Bengal), which contain about one-third of the total land area, but in which about 40% of the country’s population lives, support one of the densest populations in the world.
(b) Cultural and Political Importance:
A significant fact is that in view of the immense concentration of population and resource the Ganga valley has always dominated North India. It is the dominant area from which not only the political power but also economic and cultural movements spread to Aryavarta (i.e., the area lying north of the Vindhyas). Delhi, Patna and Kolkata have served as the political capitals of the country.
(c) Social and Religious Significance:
It has been famous for its inexhaustible people who wanted to enjoy its bounty either through sword or through the scale; for its literature and art; for its historical monuments and archaeological sites. The Ganga has been the sacred river par excellence and the area from Gaya to Mathura, from Sangam to Haridwar, is recognised by everyone as the ‘holy land of Hinduism’.
Along the bank of its sacred rivers arose cities like Mathura, Prayag, Haridwar, Mukteshwar, Ayodhya and Kashi which became centres of power and retreats, gave shelter to seekers of knowledge and truth. Here flourished the religions of Buddha and Mahavira and the movements of Bhakti and Sufism.
(d) Economic Significance:
The plains have a fertile soil and because of the slow moving perennial water courses and favourable climate and they are, the great agricultural tracts of the country, raising bumper crops of rice, wheat, oilseeds, sugarcane, tobacco and jute. These plains have given birth to and nursed and nourished the unique Hindu civilizations in its river valleys—the Harappa, Mohenjodaro, Pilibanga, Lothal civilizations. They are even now the foci of industrial and commercial activities.
The life in the plains is quite easy as contrasted to the hard struggle for existence in the mountain areas, and this has brought about a desire for ease and pleasure and peace, but the development of the intellect has bred cunning or shrewdness and ambitions. The people of the plains, therefore, have tended to become political-minded and intriguing. They have developed a great diversity of occupations, commercial and industrial. They are amenable to discipline but they are not martial.