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Physiography of Assam & Assam Physiographic Divisions | North East India Info

Assam a state in the northeast region of India is a unique geographical entity presenting a rich physical and cultural diversity. The natural landscape of the state is however, changing fast with the growth of industrialization and urbanization and especially the ever-increasing inflow of people from within and outside the country.

Assam located in the tropical latitude 24.30 N and 280 N and eastern longitudes 89.50 E and 96.10 E. surrounded on three sides by hills and mountains. Assam is bounded to the north by the kingdom of Bhutan and the state of Arunachal Pradesh, to the east by the states of Nagaland and Manipur, to the south by the states of Mizoram and Tripura, and to the west by Bangladesh and the states of Meghalaya and West Bengal.

The state of Assam is comprised of three physiographical divisions, namely, the Brahmaputra Valley, the Barak Valley and the Karbi-Anglong and the North-Cachar hills. The Brahmaputra Valley, which forms the northern part, is the largest in size comprising 71.7 % of the total geographical area of the state. On the other hand the Barak Valley region which forms the southern part is comparatively smaller in size. The two Valleys derived their names from the respective main rivers, the Brahmaputra and the Barak flowing through East to West in the Valleys. The hill regions formed by the Karbi-Anglong and the North-Cachar hills stands separated into the two valleys from the middle.

physiography map showing physical division and features of Assam

Physiographical Divisions of Assam

The Brahmaputra Valley

Brahmaputra Valley is situated in Assam, the frontier province of India on the extreme north-east. Assam is located between 24°8’ to 27°56 north latitudes and 89°41 ’ to 96°02 East longitudes. The area of the Brahmaputra Valley is 54,315 square Kilometers. The Valley of Brahmaputra is surrounded by the Arunachal Himalaya in the North, Patkai and Arunachal hills in the East and Naga Hills, Karbi and Meghalaya Plateau in the South. Its western side is open and joined to the Ganga plain.

The Brahmaputra Valley is an alluvial plain it about 720 Km wide from north-east to the west and average 90 Km wide from north to south. The Brahmaputra is one of the largest and youngest rivers in the world. It flows majestically through the heart of Brahmaputra Valley. The total length of the Brahmaputra Rivers about 2,897 Kilometres and its drainage area measure about 9, 35, 504 Square kilometers. Its flows for about 724 Kilometres down the Assam Valley. It is navigable all year. In monsoon, it grows like a sea.

The Brahmaputra divides its Valley into three geographical areas called the Uttarkol or North Bank, Dakhinkol or the South bank and the Majuli or the largest riverine island in the middle. After crossing the State of Assam the river turns south, flowing through Bangladesh and joining with the Padma River, it flows as Meghna and falls into the Bay of Bengal. It is on the bank of this river the civilization of Assam grows. So the history of Assam is indeed is the history of the civilization of the Brahmaputra Valley. The Valley of Brahmaputra is spreading flat and wide, from east to west in the lower portion to project northward in its upper portion where it tapers off.

The mighty Brahmaputra with its innumerable tributaries (Buridihing in Dibrugarh district; Disang, Dikhaw, Bhogdoi, Jhanji and Dhansiri in Sibsagar district; Subansiri in Lakhimpur district, Kapil i in Nagaon district and Bharal i and Barnadi in Darrang district; Pagladia , Beki, Manas, D igaru, Kulsi in Kamrup district; Sankosh , Krishnai , Soralbhanga , Champamati in Goalpara district) from either side make up the total drainage system of the valley.

Depending upon the topography, Physiography, various climatic conditions and the cropping pattern, the Brahmaputra valley itself can be divided into k Zones, viz., upper Brahmaputra valley, central Brahmaputra valley, north bank plains and the lower Brahmaputra valley.

Upper Brahmaputra Valley

It consists of Dibrugarh and Sibsagar districts, including the Majuli Island. The area slopes down gradually from the hills of the Arunachal Pradesh, Nagaland and Karbi Anglong districts. The upper slopes are very suitable for tea plantation.

Central Brahmaputra Valley

In the central Brahmaputra valley region, lays Nagaon district. It is situated on the south bank of the Brahmaputra and on the west of the upper Brahmaputra valley, which alone is considered as a distinct region. The district is encircled by hills of Shillong plateau on the east, west and south; and on the north lies the mighty Brahmaputra.

Numerous isolated hillocks found lying scattered and even along the Brahmaputra bank, which are in fact outliers of the Shillong plateau. Thus the northern boundary' of the district is for the most part higher than the central p la in s of the region which has an appearance of being encircled by hills on all sides.

Due to the physiographic condition, Nagaon district frequently inundated by flood during the rainy season. Tall grasses are found to grow abundantly along the bank of the Brahmaputra and especially on the north-eastern part. The world-famous Kaziranga wildlife sanctuary constitutes such a part of the Nagaon district while other par constituted by a part of the Sibsagar district.

North Bank Plain region: 

On the northern bank of the river Brahmaputra, there lies a distinct region comprising of Lakhimpur and Darrang districts. Physiographically, the entire region can be divided into 3 small parallel belts.

The foot hills proper, with alluvial soil structure, is under deep forest. There are small tea estates extending from the Subansiri river to the Barnadi. The central belt is a narrow one having alluvial soil and is suitable mainly for rice cultivation. The low-lying belt which includes the area on the edge of the Brahmaputra, the area between the river Subansiri district is inundated by floods almost every year.

The Lower Brahmaputra Valley region: 

The lower Brahmaputra valley region consists of Kamrup and Goalpara districts which form the lower Assam plains. There lie the folded ranges of the Himalayas on the north side and Shillong plateau on the south. The entire area on the southern side of the Brahmaputra is belted with spurs of the plateau.

As a matter of fact some of the outlines of the plateau are found even on the north bank of Brahmaputra. The northern foothills are covered by critically dense forests and tall grasses. Valuable timber trees like 'Sal' and ’Teak' grow abundantly on the foothills of the southern part. The central portion of the lower Brahmaputra valley region is famous for the cultivation of rice.

The Barak Valley

The Barak Valley region has an undulating topography characterized by hills, hillocks (locally known dllah), wide plains and low-lying waterlogged areas (locally called beels). Most of the hills have a North-South spread interspersed by strips of plains. The region is flanked by the Southern belt of Barail range with an average width of 6 or 7 miles containing peaks between 3 and 6 thousand feet in height, on the Eastern frontier, lay the Bhuban range, a continuation of the Lusai hills.

The hills divisions consisting mainly of the Barail range from Jaintia hills to a point little to the west of Asalu range formed a continuous wall of mountains gradually increasing in height towards the East. The hill range entered Barak Valley at the place known as Kalangtam at which the hills become 4336 feet above the level of sea.

Most of these hills were rugged and precipitous into which innumerable rivers cut deep gorges as they descended upon the plains. The mountainous character of the region rendered inters communication extremely difficult.

Physiographically, the plain areas of the region can be divided into four classes, namely Undulating plains, Broad meander plains, Flood plains and Low-lying areas. The Undulating plain areas scattered across the region and mixed with low hills and meander plains. Barak River in large patches mixed with low hills and piedmonts. The Flood plains area chiefly covers the banks of the Barak River. While the low-lying areas consisted of the natural depressions and waterlogged areas. These are scattered in all three districts and occur mainly in the south of the Barak river.

The principal river of the region namely the “Barak” took its rise a little to the west of Maothana, on the northern boundary of Manipur. Taking a southwest turn from its source near Tipaimukh in Manipur, it then comes to the north and for considerable distances formed the boundary line between the region and the state of Manipur.

After its junction with the river Jiri, this too for a considerable area formed the border between the Barak Valley region and the Manipur. At Jiribun it turned again to the west and flowing to the heart of the Cachar district of the region and reached Badarpur town in the Karimganj district. From Badarpur to Haritikar, it provided the boundary between the Karimganj district and Bangladesh. At Flaritikar, the river became divided into two branches, namely, Surma and Kushiara.

The later branch entered Bangladesh while the former entered Karimganj town and continue to form the frontier of the Barak Valley region with Bangladesh. In addition to Jiri, the Barak river received numerous tributaries from the hills like Chiri, Barail, Madhura, Jatinga, Dalu, etc.

The other principal rivers of the region are Sonai, Daleswari, Katakhal, Longai, Singla and Kakra. Most of these rivers were dried up during winter and due to deposits of silt, the drainage capacity becomes ineffective. The rivers would remain unavailable even in the rainy season. As such in summer all these rivers rise up in high spate causing high floods visiting every year in the region.

The Karbi Anglong and North Cachar Hills

The Hills in Karbi Anglong is part of the Shillong plateau having an elevation of 300 to 400 meters with a moderate slope. The highest peak in this region is 1,360 meters high, the ‘Singhason’ peak located in East Karbi Anglong. More than 80% of the geographical area is steep to moderately slope, hilly land surface and undulating plains. The average altitude is 300-400m above MSL. West Karbi Anglong is dominated by steeper slopes except towards the extreme east. Whereas the northern part of East Karbi Anglong is steeper but the slope becomes gentle towards the south.

Physiographically, the district of Karbi-Anglong can be divided into the following two distinct divisions:

  1. The Plain Area which consists of valleys of Jamuna, Kapili and Dhansiri rivers bordering the districts of Nagaon and Golaghat,
  2. The Hill Area which covers 85% of the geographical area.
The hill zone of Assam can be broadly divided into the following three geographical tracts:

Plains:

It covers 40% area of Karbi Anglong (4,132.8 sq.km). The area located between the northern and the southern hills is the Diphu sub-division which is characterized by undulating plains of subdued relief. The minor streams include Kaliani, Barpani, Patradisa and Dikharu. The plain area of Karbi Anglong covers mainly Howraghat, Bokalia, Balipathar and Bokajan area. These plains are mainly formed by the rivers of Jamuna, Kapili and Dhansiri. Hills with Gentle Slope: This area comprises 60% of Karbi Anglong district. The slopes 15-40 percent steepness is considered as gentle slope. A negligible area of the N.C. Hills bordering Karbi Anglong and Nagaon district falls under this category.

Hills with Steep Slope: 

Comprises the hill tracts of the N.C. Hills covering 4156.5 sq. km. The hills with 40-80 percent slope come under this category

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