Brahamaputra Basin

Brahamaputra Basin
1.4 Major rivers
The course of the Brahmaputra River can be divided into three reaches: Upper, middle, and lower. In
the upper reaches, the river is fed by the glaciers and in the lower reaches it is joined by a number of
tributaries.The three reaches are described briefly below:
a) Upper Reach: In its upper reach, the river flows 1,625 km from the source to the Indo- China
border through Tibetan plateau, mainly in the east direction almost parallel to the Himalayan
mountains and north thereof. In Tibet it is known as “Tsangpo”. After flowing for 80 km in an
easterly direction, Tsangpo meets two big rivers, viz; Mayum Chu and Chema Yung Dung.In the
eastern part of the Tibetan plateau, the Tsangpo River takes a hairpin bend around the Namcha
Barwa mountain ranges. Tsangpo arrives at the Indo-China border near Monku at an elevation of
660 m and flows for 5 km as the international boundary to arrive at Kobo in Arunachal Pradesh,
India. It enters India flowing south and is known as the Siang River. Upto this reach, the major
tributaries joining the Tsangpo are the Shap Chu, Nayang Chu, Rang Chu, Yarling Chu, Tong Chu,
Shang Chu, Kyi Chu and Po- Tsangpo.
b) Middle Reach: In the middle reach Brahmaputra, from the Indo China border to the Indo-
Bangladesh border, Brahmaputra flows 916 km through India.In Arunachal Pradesh the river is
known as Siang in the upper reach and Dihang in the lower reach. The river then flows almost in
Southern direction for another distance of about 226 km from the Indo-China border upto Passighat.
Dihang River enters into the plains of Assam at Kobo where it meets two major trans-Himalayan
tributaries, Dibong and Lohit, coming from northeast and east, respectively. The combined flow,
hereafter called the Brahmaputra, flows westward through Assam until near Dhubri, where it
abruptly turns south and enters Bangladesh and then falling into the Bay of Bengal. The river is
highly braided due to its low gradient. As a result, there are innumerable riverain islands.
˚E), the former biggest river island of the world,is the most
remarkable feature of the valley reach of the Brahmaputra.Owing to active bank erosion, the area of
the island has reduced from 1300 Sq.km as in 1950 to 900 Sq.km at present.
The river Brahmaputra receives a number of tributaries at its north and south banks (Map 2), in the
catchment area in India. Northern tributaries also receive considerable contribution from snow in
higher ranges of the Himalayas with peak contribution commences in August.The major tributaries
are as follows:
Tributaries from North bank: The Subansiri, the Manas, the Ranganadi, the Borgong, the Jiadhal,
the Sankosh, the Siang, the Kameng (Jiabharali in Assam), the Dhansiri (North), the Puthimari, the
Pagladiya, the Champamati, the Saralbhanga, the Aie and theSankosh.
Tributaries from South bank: The Noa Dehing, the Buridehing, the Debang, the Dikhow, the
Dhansiri, the Kopili, the Digaru, the Dudhnai, and the Krishnai.
The characteristics of the North bank tributaries are quite different than those of the south bank
tributaries. The north bank tributaries are flashy and flow through steepslopes.These rivers carry
heavy silt charge thus forming shallow braided channels, and coarsesandy beds. Rainfall in the north
bank tributary basin is much higher and the catchment areas of north bank tributaries are also much
bigger than the south bank tributaries. The South bank tributaries have flatter grades, deep
meandering channels, fine alluvial soils and comparatively low silt charge.
15