Assam, situated at the foothills of the eastern Himalayas, is the largest State in northeast India and lies in the middle
reach of the river Brahmaputra and Barak. The State accounts for nearly 2.4% of India‘s total geographical area The
Brahmaputra basin covers an area of 5,80,000 sq. km out of which 70,634 sq. km falls within Assam. The land has uneven
topography, full of hills, plains and rivers. The State is bordering Arunachal Pradesh in the east, West Bengal, Meghalaya,
Bangladesh in the west, Arunachal Pradesh, Bhutan in the north and Nagaland, Manipur, Mizoram, Meghalaya, Tripura in the
south. Its longitude lies at 88.250E to 96.00E and latitude at 24.50N to 28.00N and temperature varies from 60C to 380C.
The humidity that is brought into Assam by the southwest monsoons, shower an average annual rainfall of 120 inches or more
on the Brahmaputra valley and the surrounding region. The monsoons are Assam's life line; creating a bio-diversity that can
compete with the equatorial rain-forests (State profile, Ministry of Health and Family Welfare, 2009). The topography and
the warm and humid climate are conducive to plant and vegetation growth. Assam is home to 51 forest and sub-forest types,
and the confluence of diverse patterns of vegetation (Assam Human Development Report, 2003).
The Brahmaputra River flows through Assam from east to west over a length of approximately 650 kilometers. Its main
branch originates in the Tibetan plateau, flowing from west to east as the Tsangpo River, and then turns south through
the eastern Himalaya as the Dihang River to enter Assam, where it is joined by other branches to form the Brahmaputra.
The Barak River rises in the Indian state of Nagaland at an elevation of approximately 2,300 meters and passes through
the Manipur Hills of Manipur state over a river length of nearly 400 kilometers. It then flows generally westward from
Lakhipur through the Cachar Plains region of Assam over a river length of approximately 130 kilometers to enter
Bangladesh near Bhanga (NHC, Background paper, 2006). Each flood season, the Brahmaputra and its tributaries forsake
their earlier channels to cut new swathes through the soil. As the water recedes, alluvial deposits remain in the river,
giving rise to sandy islands. Some of these islands are very large, and the annually enriched soil has attracted
cultivation and semi-permanent settlement. There is a distinct monsoon season in which a large part of the annual
rainfall is concentrated. There are also two months of cyclonic activity preceding the monsoon, and rainfall at other
times of the year as well.