Physiography of Assam

 

Assam is a very important state of North-East India. It is located in between 24°8′N to 28°2′N latitude and 89°42′E to 96°E longitude. It has an area of 78,438sq.km. The state is surrounded by hills and mountains on the north, east and south and to the west it merges with West Bengal and Bangladesh Plains. Assam can be divided into three major physiographic divisions.

Physiographic divisions of Assam

1. The Brahmaputra Valley

2. The Barak Valley

3. The hills of Karbi Anglong and North Cachar.

 

1. The Brahmaputra Valley -The Brahmaputra valley is built up largely by fluvial aggradations. This valley has the Arunachal and Bhutan Himalayas to the north, the Patkai range, Arunachal Hills and Naga hills to the east, Karbi-Plateau and Meghalaya Plateau to the south and to the west it is open to the Ganga Plain. The total area of the valley is 54,315sq.km.  It is a flat plain with a length of 720 km and a width of 90km. The Brahmaputra valley is relatively wide in the eastern part between the Himalayas and the Naga hills where it is about 90km. The Karbi-Plateau which projects northward to the bank of the Brahmaputra restricts the width of the plain to about 40km-45km in its middle part near the Burhapar between Numaligarh and Jakhalabandha. The plain becomes wider westward with the Kalong-Kapili plain extending southward up to Meghalaya. Further west near Guwahati the plain becomes narrow about 70km again as the Meghalaya plateau projects northward and skirts the Brahmaputra. At Kokrajhar-Goalpara-Dhubri the plain is about 90km again.

The Brahmaputra has a large number of tributaries within Assam. Jia-Dhol, Subansiri, Ranga Nai, Jia Bharali, Jia Dhansiri, Buroi are the important north-bank tributaries. Major south bank-tributaries are Burhi-Dihing, Disang, Dikhou, Janji, Teok, Dibru, Kapili and Kalong.

2. The Barak Valley - Assam is occupied by the Barak Valley in the south. It is encircled by North Cachar Hills (Dima Hasao) to the north, to the east by Manipur Plains and to the south by Mizoram Hills. The plain is horse-shoe shaped with about 85 km of east-west extension. The total area of the Barak valley is 6962sq.km and is a low-lying flat plain with its altitude being 75 meter near its apex in Jiribam. It gently slopes westward to 73 meter, near Silchar and further to 51 km near Karimganj. The average gradient of the plain is 28 cm per km. Some of the important tributaries of Barak Valley are Jiri,Labak, Madhura,Dalu,Jatinga and Larang in the north –bank. The south bank tributaries are Sonai, Katakhal, Dhaleswari, Singla and Langla.

 3. The Hills of Karbi –Anglong and North Cachar (Dima Hasao)-  The hills of Karbi-Anglong and North Cachar divides the two valleys of Assam. The hills in Karbi Anglong are a part of Shillong Plateau. This region contains the highest peaks like Dambuksu with a height of 1363 meter and Singhasan   of about 1359 meters. More than 80% of the geographical area is steep to moderately slope, hilly land surface and undulating plains.

            The North-Cachar Hills are made of young tertiary folds; the ranges are high and alternate with valleys.  It covers an area of 4156.5sq.km.  The process of weathering and erosion are very active leading to the development of deep valleys, gorges and steep slopes. Dense forest is a very common feature of this region.