Despite the fact that the Great Plain of North India is viewed as a single geographical unit with a low elevation and mild slope, different areas of this enormous territory exhibit varied fluvial patterns, flow directions, and geomorphology, allowing it to be separated into four primary regions:

(A) The Rajasthan Plain.

(B) The Punjab-Haryana Plain.

(C) The Ganga Plain.

(D) The Brahmaputra Plain.

1. The Rajasthan Plain:

The Thar of the Great India Desert, which includes western Rajasthan and parts of Pakistan, forms the western extremity of India's Great Plain. The desert is approximately 650 kilometres long and 250-300 kilometres wide. It has a total size of around 2.0 lakh square kilometres, of which 1.75 lakh square kilometres are in India. The Indian desert is divided into two thirds in Rajasthan, west of the Aravali Range, and one-third in the neighbouring states of Haryana, Punjab, and Gujarat. The Central Arid Zone Research Institute in Jodhpur recently conducted several geomorphic research employing remote sensing techniques in conjunction with ground truth. This wide desert is characterised by an undulating plain with an average height of 325 metres above sea level. Near the Indo-Pak border, as well as the Indus Valley and the Rann of Kachchh, it drops to about 150 metres above sea level. The desert proper is known as Marusthali, and it covers the majority of the Marwar Plain. The Marusthali has an average elevation of 200-250 metres above sea level. It has a large expanse of sand with a few outcrops of gneisses, schists, and granites, indicating that it is geologically a part of the Peninsular Plateau and that it appears to be an aggradational plain solely on the surface. The eastern half of the Marusthali is mostly stony, while the western part is covered with changing sand dunes known locally as dharian.

The Rajasthan Bagar is a semi-arid plain that runs from the eastern edge of the Thar Desert to the Aravali Range. From the margin of the Aravalli in the east to the 25 cm isohyets (line uniting places of equal rainfall) in the west, it runs north-east to south-west. It is drained by a number of short seasonal streams that originate in the Aravali and supports agriculture in some rich rohi spots. Even the main river, the Luni, is a seasonal stream that flows to the Rann of Kachchh in the south-west. The thali, or sandy plain, is located north of the Luni.

The geomorphological properties of this Great Desert, especially its sand dunes, have been studied using LANDSAT imagery. In this desert, six types of sand dunes have been recognised based on morphological, geographical, and spectral characteristics: obstacle, parabolic, longitudinal, transverse, barchans, and shrub-coppice. The average height of the dunes varies from 8 metres in Jaipur and Sikar to 30 metres in Barmer. The length of the dunes varies widely, with some measuring up to 10 kilometres.

On the eastern edge of the Thar Desert, north of the Luni basin, there is a significant tract of inland drainage with multiple saline lakes. They are an excellent source of common salt as well as a variety of other salts. The lakes of Sambhar, Didwana, Degana, Kuchaman, Sargol, and Khatu are among the most important. The Sambhar Lake, located 65 kilometres west of Jaipur, is the largest and most impressive. This lake, which is about 30 km long with an average width of 3-8 km and is located at an altitude of around 360 m in the Aravali region, is about 30 km long with an average width of 3-8 km. During the wet season, it covers roughly 225 square kilometres, but during the dry season, it diminishes dramatically.

2. The Punjab-Haryana Plain:

To the east and north, the Great Indian Desert gradually gives way to the rich plains of Punjab and Haryana. The plain stretches for 640 kilometres from north to south and is around 300 kilometres broad in the east-west direction. This plain covers around 1.75 million square kilometres in total. The Yamuna River forms its eastern border in Haryana. The plain's average elevation is around 250 metres above sea level. It rises almost 300 metres above sea level in the north and dips to roughly 200 metres in the south. The underlying Delhi-Aravali ridge controls a flat to slightly convex planation in part of the plain.

The Punjab plain—the region of five rivers—is a section of the plain produced by alluvial deposits from five rivers: the Sutlej, the Beas, the Ravi, the Chenab, and the Jhelum. It consists mostly of 'doabs,' or land between two rivers. These doabs are listed in order from east to west:

1. Bist-Jalandhar Doab: lying between the Beas and the Sutlej;
2. Bari Doab: between the Beas and the Ravi;
3. Rachna Doab: between the Ravi and the Chenab;
4. Chaj Doab: between the Chenab and the Jhelum; and
5. Sind Sagar Doab: between the Jhelum-Chenab and the Indus.

The river depositional process, which has been going on for a long time, has brought these doabs together and given the entire area a homogeneous gemorphological entity. River streams, on the other hand, have formed huge flood plains of khaddar flanked by cliffs, locally known as dhayas, out of the bulk of alluvium. These cliffs have been significantly gullied, reaching heights of 3 metres or more. Though prone to flooding, the Khaddar belt, sometimes known as bet lands, is agriculturally valuable.

Numerous streams known as Chos have eroded the northern half of area, which borders the Shiwalik highlands. This has resulted in massive gullying. Chos erosion is notably noticeable in Punjab's Hoshiarpur district. Nearly a hundred Chos debouch on the plains in a short period of about 130 km. The Malwa Plain in Punjab is located to the south of the Sutlej River.

Haryana Tract refers to the land between the Ghaggar and Yamuna rivers in the state of Haryana. Between the Yamuna and the Satluj Rivers, it serves as a water divide. The Ghaggar, which is thought to be the modern-day successor of the mythological Saraswati River, is the sole river that runs between the Yamuna and the Satluj.

3. The Ganga Plain:

This is the largest unit of the Great Plain of North India, ranging from Delhi to Kolkata in the states of Uttar Pradesh, Bihar, and West Bengal, and encompassing around 375 lakh square kilometres. The Ganga is the master river, and this plain is called after it. The Ganga, along with its many tributaries that originate in the Himalayan ranges, such as the Yamuna, Gomati, Ghaghara, Gandak, Kosi, and others, has carried massive amounts of alluvium from the mountains and deposited it here to construct this vast plain. Peninsular rivers that join the Ganga river system, including as the Chambal, Betwa, Ken, Son, and others, have also contributed to the creation of this plain. The entire plain has a broad east-southeast slope to it. This plain can be further broken into the three sections below, depending on its geographical variations:

(a) The Upper Ganga Plain.

(b) The Middle Ganga Plain.

(c) The Lower Ganga Plain.

a) The Upper Ganga Plain:

The 300 m contour in the Shiwaliks in the north, the peninsular boundary in the south, and the course of the Yamuna River in the west define the upper part of the Ganga Plain. Its eastern boundary is a bit hazy, and it's a point of contention among geographers. L.D Stamp's restriction, which was later adopted by O.H.K Spate and roughly corresponds to 100 cm isohyets, appears to be far from feasible. Geographers have acknowledged the 100 m contour (a line connecting places of equal height) as the most effective line of demarcation physiographically. This plain is around 550 kilometres long in east-west direction and nearly 380 kilometres wide in north-south direction, with a total size of 1.49 million square kilometres. Its altitude ranges from 100 to 300 metres above sea level. The Ganga and its tributaries, such as the Yamuna, Ram Ganga, Sarda, Gomati, and Ghaghara rivers, drain the plain. Almost all rivers run in a NW-SE direction, parallel to the land's contours. The land's average gradient is roughly 25 centimetres per kilometre. In the northern part, the grade is quite high. As the gradient lowers, the rivers flow more slowly in the plain.

The tarai-bhabar submontane belt, as well as river bluffs, river meanders and oxbow lakes, levees, abandoned river courses, sandy stretches (Bhurs), and the river channels themselves, break up the monotony of this flat and featureless plain. The Ganga-Yamuna Doab, in the western half of the plain, is higher than the rest. The low lying Rohilkhand plains lie east of this doab, merging with the Awadh lowlands further east. The Ghaghara is the Awadh Plains' principal watercourse. Because the river meanders across this area, the Khadar of this river is quite large. Furthermore, it frequently alters its course. This Khadar stretches for 55 kilometres in certain locations. As a result, there is always the threat of severe floods.

b) The Middle Ganga Plain:

The Middle Ganga plain lies to the east of the Upper Ganga plain, occupying parts of Uttar Pradesh and Bihar. It stretches for around 600 kilometres east-west and nearly 330 kilometres north-south, covering a total area of about 1.44 million square kilometres. The Himalayan foothills and the peninsular edge, respectively, define its northern and southern limits. Its western and eastern borders are ill-defined, and the region is wide open on all sides, giving it the personality of the huge isotropic Ganga Plain's east-west continuum.

There is no physical boundary worth mentioning, and the plain silently opens up in the west from the upper Ganga Plain and dies out in the east from the lower Ganga Plain. As such, it is the quintessential transitional zone, nestled among the vastness of the Ganga valley. However, there have been various attempts to define the western and western bounds of this transitional zone. The 100 m contour in the west, 75 m contour in the north-east, and 30 m contour in the south-east are the most often acknowledged limits. Clearly, this is a very low plain, with no area above 150 metres in elevation.

The Ghaghara, Gandak, and Kosi Rivers, all tributaries of the Ganga that originate in the Himalayas, drain this plain. These rivers are responsible for filling a 2,000-meter-deep valley at the foot of the Nepal Himalayas with alluvial sediments. They run slowly on this flat land, resulting in local prominences such as levees, bluffs, oxbow lakes, marshes, tals, ravines, and other features. Due to the predominance of the khadar, the kankar formation is comparatively smaller. Almost all of the rivers are constantly changing their courses, leaving this area vulnerable to flooding.

In this regard, the Kosi River is well-known. It used to run near Purnea in 1736, but currently it flows about 110 kilometres west of the town. Its water level has increased 10 metres in as little as 24 hours on occasion. It's been dubbed the 'Sorrow of Bihar' for a long time. Both India and Nepal are making valiant efforts to tame this river. The Ganga-Ghaghara doab, Ghaghara-Gandak doab, and Gandak-Kosi doab are the main units of this plain (Mithila Plain).

Some rivers join the Ganga from the south as well, the most important of which is the Son. The gradient is a little greater here, at 45 centimetres per kilometre, compared to 9-10 centimetres per kilometre in east Uttar Pradesh and only 6 centimetres per kilometre on the Mithila Plain. The Magadh Plain is located east of the Son River.

c) The Lower Ganga Plain:

The Kishanganj tehsil of Bihar's Purnea district, all of West Bengal (excluding the Purulia district and the mountainous areas of Darjeeling district), and most of Bangladesh are part of this plain. It stretches for 580 kilometres from the Darjeeling Himalayan foothills in the north to the Bay of Bengal in the south, and for nearly 200 kilometres from the Chotanagpur Highlands in the west to the Bangladesh border in the east. This plain covers an area of around 81 thousand square kilometres. Its width varies widely, and between the Rajmahal Hills and the Bangladesh border, it narrows to just 16 kilometres. The western limit of the 50 m contour is a tight fit.

The Tista, Jaldhaka, and Torsa rivers deposited sediment in the northern section of this plain. The Duars (Darjeeling Tarai) and the Barind plain, a stretch of historic alluvium between the Kosi- Mahananda corridor in the west and the river Sankosh in the east, also define this region. About two-thirds of the plain is made up of the delta formation. This is the world's largest delta. In the delta area, the Ganga River splits into multiple rivers. The ground here has a slope of only 2 centimetres per kilometre. Two-thirds of the land is less than 30 metres above sea level.

If the sea level raised just 7 metres, the entire land up to Kolkata would be entirely flooded. A great number of estuaries, mud flats, mangrove swamps, sandbanks, islands, and forelands dot the delta's seaward face. Tidal forests cover a large portion of the coastal delta, making it virtually inaccessible. Because of the abundance of various trees, these are known as the Sunderbans.

4. The Brahmaputra Plain:

Because most of the Brahmaputra valley is located in Assam, it is also known as the Assam Valley or Assam Plain. It is a well-defined geographical unit girdled in the north by the Eastern Himalaya of Arunachal Pradesh, the Patkai and Naga Hills in the east, and the Garo-Khasi-Jaintia and Mikir Hills in the south by the Garo-Khasi-Jaintia and Mikir Hills. The Indo-Bangladesh border, as well as the lower Ganga plain's boundary, comprise its western limit.

This plain is around 720 km long and 60-100 km wide, stretching from the easternmost tip of Assam near the syntaxial curve of the Eastern Himalayas to the west of Dhubri near the Bangladesh border. The plain is around 56 thousand square kilometres in size. It is an aggradational plain formed by the Brahmaputra and its tributaries' depositional action. Towards Sadiya, the Brahmaputra River reaches this plain and travels southwards to Bangladesh before turning south near Dhubri. The plain's overall elevation varies from 130 metres in the east to 30 metres in the west. In the direction of N.E. to S.W., the average gradient of the terrain is 12 cm per km.

The area is well defined by a 150-meter contour beyond which the neighbouring hill landscape takes over. The northern boundary has a severe descent from Arunachal Pradesh's foothills, whereas the southern margin has a moderate fall from the hill ranges. The Brahmaputra River's numerous tributaries from the north debouch suddenly on the main valley, forming a number of alluvial fans. As a result, the tributaries split into numerous channels, resulting in river meandering and the formation of bills and ox-bow lakes. This area contains significant marshy areas. The coarse alluvial debris generated alluvial fans, which resulted in the formation of tarai or semi-tarai conditions. There are a lot of bills and ox-bow lakes in the south, and some of the tributaries have meandering channels.