Physiography
Entering Assam, the Brahmaputra becomes a braided river, and, along with its tributaries, creates the flood plain of the Brahmaputra Valley. The Brahmaputra Valley in Assam is approximately 80 to 100 km wide and almost 1000 km long. The width of the river itself is 16 km at many places within the valley.
The hills of Karbi Anglong and Dima Hasao district and those in and around Guwahati and North Guwahati (along with the Khasi and Garo Hills) are originally parts of the South Indian Plateau system. These are eroded and dissected by the numerous rivers in the region. Average height of these hills in Assam varies from 300 to 400m.
The southern Barak Valley is separated by the Karbi Anglong and North Cachar Hills from the Brahmaputra Valley in Assam. The Barak originates from the Barail Range in the border areas of Assam, Nagaland and Manipur and flowing through the district of Cachar, it confluences with the Brahmaputra in Bangladesh. Barak Valley in Assam is a small valley with an average width and length of approximately 40 to 50 km.
Read more about this topic: Physical Geography Of Assam