The Great Plains
In front of the Himalaya stretch the Great Plains of India, fanning out at the both ends, so as to include the Ganga delta on the east and Rajasthan’s arid and semi-arid plains on the west. The central and eastern parts have been built up by the Ganga and its tributaries, The Punjab plains occupy the western part of the Great Plains where the tributaries of the Indus flow in a south-westerly direction in contrast to the south-east flowing Ganga and its tributaries. Arid conditions have set in over the southern part of Punjab and continue more forcefully in West Rajsthan which, though originally a part of the Indo-Ganga plains, is passing today through a different landscape cycle; this section of the Great Plains forms a distinctive region called the Western Arid Plain.
The northern plains are formed by the alluvial deposits brought by the rivers – the Indus, the Ganga and the Brahmaputra.These plains extend approximately 3,200 km from the east to the west. The average width of these plains varies between 150-300 km. The maximum depth of alluvium deposits varies between 1,000-2,000 m. From the north to the south, these can be divided into three major zones: the Bhabar, the Tarai and the alluvial plains. The alluvial plains can be further divided into the Khadar and the Bhangar.
Bhabar is a narrow belt ranging between 8-10 km parallel to the Shiwalik foothills at the break-up of the slope. As a result of this, the streams and rivers coming from the mountains deposit heavy materials of rocks and boulders, and at times, disappear in this zone.
South of the Bhabar is the Tarai belt, with an approximate width of 10-20 km where most of the streams and rivers re-emerge without having any properly demarcated channel, thereby, creating marshy and swampy conditions known as the Tarai. This has a luxurious growth of natural vegetation and houses a varied wild life.
The south of Tarai is a belt consisting of old and new alluvial deposits known as the Bhangar and Khadar respectively. These plains have characteristic features of mature stage of fluvial erosional and depositional landforms such as sand bars, meanders, oxbow lakes and braided channels. The Brahmaputra plains are known for their riverine islands and sand bars. Most of these areas are subjected to periodic floods and shifting river courses forming braided streams. The mouths of these mighty rivers also form some of the largest deltas of the world, for example, the famous Sunderbans delta. Otherwise, this is a featureless plain with a general elevation of 50-150 m above the mean sea level.
The states of Haryana and Delhi form a water divide between the Indus and the Ganga river systems. As opposed to this, the Brahmaputra river flows from the northeast to the southwest direction before it takes an almost 90° southward turn at Dhubri before it enters into Bangladesh. These river valley plains have a fertile alluvial soil cover which supports a variety of crops like wheat, rice, sugarcane and jute, and hence, supports a large population. The Great Plains are an alluvium-filled trough. In other words, they are a classical example of an aggradational plain, the depth of which varies from place to place, perhaps nowhere exceeding 400 m. The thickness of the alluvium is probably at its maximum in the Ganga Plains and at its minimum in the Western arid plains.
The total area of the Great Plains is 652,000 sq. km., of which one-third lies in the arid western part of Rajasthan. Another one-third lies in Uttar Pradesh; and three other States, Punjab, Bihar and West Bengal, have more or less equal shares.
Western Arid Plains
These plains extends for 640 km. from north-east to south-west with an average width of 300 km. from west to east covering 1,75,000 sq.km. It has a well defined boundary on the east marked by Aravalli range. This track has two regional slopes, westwards to the Indus valley and southwards to the Rann of Kutch; and the latter was the main outlet of the Rajasthan rivers before the advent of arid conditions in this part of India about 1,000 years ago.
This part of the country is often described as desert, but detained investigations of surface features, ground-water conditions and forest flora reveal that it is not really a desert. The fact that it is not really a desert. The fact that a good harvest of wheat, jowar and bajra can be raised wherever water is obtained either from wells or from canals supports this statement. It is also not uncommon to find in the monsoon months, large patches of luxuriant grass affording pasturage to heads of cattle and flocks of sheep. A region of moving sands and deficient rainfall, its ancient name, Murusthali, is more appropriate than the present name, the Thar desert.
The Luni (or Salt River) is the only living river of the arid plains, and in years of deficient rainfall, this carries a mere trickle of water. It issues from the Ana Sagar, about 5 km. south-west of Ajmer, and flows westwards for 450 km. before entering the Rann of Kutch.
There are a number of salt lakes in this arid region, of which the Sambar is the largest. It lies astride the Aravalli range, 60 km. west of Jaipur town, covering 300 sq. km. during the rains, while in the dry months its surface is encursted with dazzlingly white saline soils.
Extending from the west of the Yamuna river on the south-east to the Ravi on the north-west, this physiographic province conforms to the present State of Punjab. It slopes southwards, being perhaps titled in that direction by the northward extension of the Aravalli, now buried under alluvium, and owes its origin and importance primarily to the aggradational work of the Sutlej, Beas and Ravi of the Indus river system.
The Punjab plains are remarkably flat and, with the exception of the Hoshiarpur plains, the general elevation varies between 200 and 240m. Narrow strips of low-layin g flood plains, known as bets, are easily distinguishable. Formed by the shifting of river courses, they range in width from 1 to 12 km. Steep bluffs, 5 to 10 m. high, separate the higher plains, the bangars, from the adjoining bets. The Doab plains occupy the north-eastern part of this region. Between the Ravi and the Beans lies the northern part of the Bari Doab with Amritsar as its central point.
The east-central part of these plains receive higher rainfall and have a fertile light loamy soil. Farther south lies the Haryana plain, once a rich and fertile tract through which the Sarasvati used to flow in earlier periods. The two other sections, the Bhiwani Bagar and the Rewari upland are typical semi-arid, steppe-like plains with deep water-tables and shifting sands.
The Ganga Plains
The Ganga plains occupy about 357,000 sq. km. and lie in Uttar Pradesh, Bihar and West Bengal. The Yamuna flows near the western boundary of this tract for 800 km and eventually joins the Ganga at Allahabad. The region between these two rivers is the Ganga-Yamuna Doab. North of the Ganga, the alluvial plains are further sub-divided into Rohikhand in the west and Avadh in the east.Further east, the alluvial plains of Bihar make two sections in the north and the south, each with a distinctive character. The eastern portion of the Great Plains comprises two other regions, the Bengal basin and the North Bengal plains. The former includes the present Ganga delta and the latter an old delta of that river.
The Ganga Yamuna Doab
A number of minor streams, between the two Ganga and Yamuna, flow through this section and help in improving the drainage conditions. Of these, the Hindan is the largest . The upper Doab is heavily irrigated by the Eastern Yamuna and upper Ganga Canals. Rain fall is also much heavier here than in other doabs, ranging from 600mm. in the south to 1,000mm. in the north.
The 200-m. contour line may be taken as the boundary between the upper and Middle Doabs, and the 100-m. contour line between the Middle and Lower Doabs.
The Lower Doab proper is still more flat, though the crests of its two swells rise a little higher than those of the corresponding swells in the transitional area. The absence of dendritic drainage pattern is due to the extreme flatness of the surface. This also accounts for the parallelism of all the major and minor streams. Unlike the Yamuna, the Ganga us a braided river with a number of channels and sand-bars. Its aggradational character is well displayed at its confluence with the Yamuna at Allahabad; the cler stream of the Yamuna mingles with the muddy waters of the Ganga.
East of the Ganga-Yamuna Doab is another vast stretch of alluvial plains, from the foot of the Himalayas to the Ganga. Its easter limit is not well-defined as it merges imperceptibly into the Avadh plains. This section lies entirely in Utter Pradesh, covering about 35,0000sq. km. The regional slope is to the south-east and the Ramganga, Gomati and Sarda flow in that direction. The level of the land increases from 132 m. on the east to 274 m. on the west. The bhabar and tarai plains are well developed in the north.
The major portion of the lowland north of the Ganga, gently sloping eastwards, comes within the physiographic region. A secondary slope towards the south has also developed, especially in the northern part of the region, due perhaps to a slight local tilt. Belted strips of khadar and bangar are very conspicuous in the three plains into which this area is sub-divided: Purabiya, Sarjupar, and Gomati plains. The Ghaghra is the master-stream traversing the whole length of the Avadh plains in a wide sandy bed. Its numerous bars and channels suggest that it is an aggrading river and has been continually shifting its course within a belt of about 55 km. in places. Another consequent river, the Rapti, joins the Ghaghra near Dohrighat, and unlike the Ghaghra, it transports more silt and makes its flood plains very productive. The Gomati is a sluggish stream, with an intricate series of meanders strem, with an intricate series of meanders, and its banks, wherever high, confine the river within its bed even when the river is in flood.
The Avadh plains end in Uttar Pradesh and the next stretch of the Great Plains lies in Bihar, covering about 88,000 sq.km. The plains here are narrowed eastwards by the prolongation of the Rajmahal hills and the two parts lying north-south of the Ganga differ in relief and river conditions.
This physiographic region is a land of rivers. The Ganga flows majestically along its southern border, receiving on its left bank three of the Major Himalayan rivers, the Ghaghra (Sarju), Gandak and Kosi, and a large number of mountain – streams from the north. The combined work of these has resulted in a 2,000-m deep through at the foot of the Nepal Himalaya being filled up with alluvial deposits. One of the most extensive alluvial plains of the world 54,400 sq. km. in North Bihar, was thus formed. The general slope of the plain is towards the south-east in the western part and south in the eastern part, averaging 20 cm. to the kilometer. A long line of marshes extends from a little east of Chapra to near Khagaria, parallel to the Ganga, locally known as caurs. Some of them are deep enough to contain water throughout the year (e.g., the Kabar Tal). South of the caurs, the surface rises towards the Ganga, traces of natural levees marking its former bank.
West of the Rajmahal hills, the South Bihar plains increase in width to a maximum of 120 km. The dominant regional slope of this physiographic region, about 9 cm. per kilometer, is towards the north or north-east. The monotony of the North Bihar landscape is relieved here, though at least two of the essential features of the north are repeated. The south bank of the Ganga is equally high and on its outward side, occur vast depressions, designated as jala near Patna and tal farther east near Mokamesh; on its south, the courses of the smaller north flowing streams are deflected eastwards.
North Bengal Plains
The plains in North Bengal cover 23,000sq. Km., extending from the foot of the Estern Himalays to the northern limit of the Bengal basin. Its estern part is drained by thr river joining the Bharamaputra, and the western part by the tributaries of the Ganga. This region has evelved from an extensive sheet of waste materials brought down from the estern Himalays by a number of powerful steams like the Tista, Jaldhaka and Torsa. Its northern fringe, known as the western Duars, is most typical. Well drained, it constitues the idea home of tea plantations wherever soil have been improved and other facilities provided.
The Bengal basin embraces most of the alluvial plains of West Bengal and Bangladesh. It is so flat and so low that a mere six-metre rise of the sea-level would submerge Kolkata and its environs. The Ganga delta occupies the major portion of the Bengal Basin. Like any great delta of the world, it has a web of distributaries near its seaward face, and shallow tidal depressions near Kolkata contain salt water. The delta has its seaward face influenced more by the tidal estuaries and less by the waves, with the result that the indented coastline is a maze of sand-banks, mud-flats, mangrove swamps, islands and forelands. The heavily forested Sundarbans in the south and the east Bharirathi plain in the north, with its dead and dying rivers, offer contrasting features.