Brahmaputra basin, a part of the composite Ganga- Brahmaputra - Meghna basin extends over an area of 5,80,000 sq. km. And lies in Tibet (China), Bhutan, India and Bangladesh. The basin is enclosed by the Himalayas on the north, the Patkari range of hills on the east running along the Indo-Burma border, the Assam hills on the south and the ridge separating it from the Ganga basin on the west. In India it drains an area of 1,94,413 sq. km. in the states of Arunachal Pradesh, Assam, Nagaland, Meghalaya and West Bengal and Sikkim. The upper portion of the basin in Arunachal Pradesh and Nagaland is mostly mountainous and the portion in Assam, Meghalaya and West Bengal is covered by hills and forests. Lower part of the basin in West Bengal has fertile plains. The basin has a population of 29.1 million.

The Brahmaputra river known as the Tsangpo in Tibet, the Siang or Dihang in Arunachal Pradesh and the Jammu in Bangladesh is one of the largest rivers of the world. The 2880-km long Brahmaputra traverses its first 1,625 km in Tibet, the next 918 km in India and the remaining 337 km in Bangladesh. The average width of the Brahmaputra valley is about 86 km of which the river itself occupies 15-19 km. The river forms almost a trough receiving the flows of its tributaries both from north and south. Some of the important tributaries of the river in India are the Dibang, the Luhit, the Subansiri, the Manas, the Sankosh, the Tista, the Dhansiri and the Champamati. The annual rainfall in the Indian portion of the basin varies from 100 cm to 400 cm, most of which occurs during the monsoon months of June to September.

Throughout its course in India the Brahmaputra is highly braided with some well-defined and stable banks where the river width is narrow. All along it course, abandoned wet lands and back swamps are common. Because of friable nature of the hills in its catchment, high intensity of rainfall and seismicity of the area, the river carries heavy sediment load of the order of 735 million tones per annum.

The Barak basin lies in India, Myanmar and Bangladesh and drains an area of 41,723 sq. km in India. The basin is bounded on the north by the Barail range, on the east by the Naga and Lushai hills and on the south and west by Bangladesh. In India the basin lies in the states of Meghalaya, Manipur, Mizoram, Assam, Tripura and Nagaland with a total population of 6.2 million. The major portion of the basin is in the hilly terrain with thick tropical vegetation and only small portion of it is in the plain area.

The Barak river rises in the Manipur hills and enters the plains near Lakhipur. Down stream of Silachar town and before entering Bangladesh the river bifurcates into two streams called Surma and Kushiara. Further lower down the river is called Meghna and receives the combined flow of the Ganga and the Brahmaputra. The principal tributaries of the Barak in India are the Jirl, the Dhaleshwari, the Singla, the Longai, the Sonai and the Katakhal.

Most portion of the Brahmaputra - Barak basin consists of hills, forests cultivated lands and tea gardens. The most prominent soil types found are laterite, red and yellow soils and alluvial soils. The basin abounds in wide variety of flora and fauna. The famous wild life sanctuaries of Manas and Kaziranga, the Buxa tiger reserve the Phibsoo reserve forest (Bhutan) etc. provide glimpse of rare species of plant and animal life.

An average annual surface water potential of 585.6 km3 has been assessed in this basin. Out of this, 24.0 km3 is utilisable water. Culturable area of the basin is about 13.04 M. ha. which is 7.1% of the total culturable area of the country.

Live storage capacity in the basin has increased significantly since independence. From just about 0.1 km3 in the Third-plan period, the total live storage capacity of the completed projects has increased to 1.1 km3. In addition, a substantial storage quantity of over 2.4. km3 would be created on completion of projects under construction. An additional storage of the tune of over 63.4 km3 would become available on execution of projects under consideration. The hydropower potential of the basin has been assessed as 33,054 MW at 60% load factor.

Prior to independence there were no major projects in the basin. Most of the projects taken up during the various plan periods were medium and minor schemes. Some of important schemes are the Tista, Champamati and Dhansiri barrages. Floods are an annual feature in the Brahmaputra-Barak basin where the maximum flood prone area is of the order of 4.33 Million ha. Besides, a large number of towns and villages are affected by the erosive action of rivers. Since the inception of the flood control programme in 1954, 5108 km of flood embankments, 1127 km of drainage channels and 109 town protection schemes have been constructed. These measures have afforded reasonable protection to an area of 1.83 Million ha. Brahmaputra Board has been setup to look into the problems of floods, erosion and drainage congestion in the basin.

A network of 129 hydrological observation stations is maintained by the Central Water Commission in the basin for various purposes like flood forecasting, water quality monitoring, assessment of hydrological parameters like river discharge, water level, suspended sediments etc.

Source: MINISTRY OF WATER RESOURCES
GOVERNMENT  OF  INDIA