<strong>Brahamaputra</strong> <strong>Basin</strong> 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. 1
<strong>Brahamaputra</strong> <strong>Basin</strong> Most interesting feature of the Brahmaputra River, in its middle reach is “Majuli”, the river island, in Assam, is marked as the largest mid river delta system in the world (UNESCO). Brahmaputra Board was established by the Govt.of India in 1980 with the objective of preparing a master plan for controlling the flood and bank erosion and improving the drainage of the Brahmaputra valley, simultaneously tapping the immense water potential for hydropower generation and possible irrigation. Figure 1. State wise <strong>Basin</strong> area 2
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