Brahamaputra Basin

Brahamaputra Basin
1.Introduction
1.1 Overview of basin
Brahmaputra basin forms a part of the major water division ‘the rivers draining into Bay of Bengal’.
Based upon the drainage outlet it is further included under the ‘Brahmaputra drainage’water
resources region.
The mighty Brahmaputra River originates in the great glacier mass north from Kailash ranges of
Himalayas at an elevation of 5,150 m just south of the lake called ‘Konggyu Tsho’. The Brahmaputra
River traverses a distance of 2,900 km, through four countries, namely Tibet (China), Bhutan, India
and Bangladesh, before joining the Bay of Bengal. It has an average annual discharge of 19,820
cumec, an average annual sediment load of 735 million metric tonnes, and a specific flood discharge
of 0.149 cumec / Sq.km.
Brahmaputra basin spreads over 580,000 Sq.km which covers China (50.5%), India (33.6%),
Bangladesh (8.1%) and Bhutan (7.8%). Although the main river does not flow through the kingdom of
Bhutan, 96% of Bhutan’s area falls under this basin.The basin is of irregular shape; the maximum
east-west length is 1,540 km and the maximum north-south width is 682 km.
Map 1 shows the geographical location of the basin with terrain features from DEM. The highlighted
blue boundary shows the basin extent overlaid on state boundary. The basin lies between 88°11’ to
96°57’ east longitudes and 24°44’ to 30°3’ north latitudes and covers an area of 1,94,413 Sq.km
which is nearly 5.9% of the total geographical area of the country. In India, the river flows for 916
km. Brahmaputra basin part in India, spreads over states of Arunachal Pradesh, Assam, West Bengal,
Meghalaya, Nagaland and the whole of Sikkim. Brahmaputra basin (in India) is bounded by the
Himalayas on the north, by the Patkai range of hills on the east running along the India-Myanmar
border, by the Assam range of hills on the south and by the Himalayas and the ridge separating it
from Ganga basin on the west. The distribution of the drainage area of Brahmaputra River in the
states of Arunachal Pradesh, Assam, West Bengal, Meghalaya, Nagaland, and Sikkim are 81,424
Sq.km, 70,634 Sq.km, 12,585 Sq.km, 11,667 Sq.km, 10,803 Sq.km and 7,300 Sq.km respectively as
shown through pie chart in Figure 1. Salient features of the basin are listed in Table 1. Map 2a is the
56 m resolution False Colour Composite AWiFS satellite imagery of the Brahmaputra basin. Map 2b
gives a detailed view of the Brahmaputra basin, its sub basins, drainage network and its pattern
across the basin. Major water resources structures (Dam/Barrage/Anicuts), major cities and major
hydro-meteorological observation sites and flood forecasting sites are also shown in the map. The
major hydrological observation sites of Brahmaputra basin are tabulated in Table 2.
The climate throughout the region is damp with humidity around 90%. Variation of atmospheric
temperature is considerably low unlike rest of India. The Brahmaputra catchment is the heaviest
rainfall region in the world. The Brahmaputra basin, particularly the portions in Assam, is notorious
for the annual flood hazards and river bank erosion that create mayhem every year, bringing misery
to the people and shattering the fragile agro-economic base of this region. This basin is seismically
very active falling in the ‘Seismic zone-V’ (except few parts of West Bengal and Sikkim falling in
seismic zone-IV). This sensitive zone is experienced several devastating earthquakes in the past. Part
of the Himalayan Mountains region of Sikkim and Arunachal Pradesh falling in Brahmaputra basin
experience snow cover. Brahmaputra basin represents the greenest part of India, accounting the
maximum 55.48% (107854.26 Sq.km) of forest cover.
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