The Brahmaputra basin spreads over countries of Tibet (China), Bhutan, India and Bangladesh having a total area of 5,80,000 Sq.km. In India, it spreads over states of Arunachal Pradesh, Assam, West Bengal, Meghalaya, Nagaland and Sikkim and lies between 88°11’ to 96°57’ east longitudes and 24°44’ to 30°3’ north latitudes and extends over an area of 1,94,413 Sq.km which is nearly 5.9 % of the total geographical area of the country. It is bounded by the Himalayas on the north, by the Patkari 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 Brahmaputra River originates in the north from Kailash ranges of Himalayas at an elevation of 5,150 m just south of the lake called Konggyu Tsho and flows for about a total length of 2,900 km. In India, it flows for 916 km. The principal tributaries of the river joining from right are the Lohit, the Dibang, the Subansiri, the Jiabharali, the Dhansiri, the Manas, the Torsa, the Sankosh and the Teesta whereas the Burhidihing, the Desang, the Dikhow, the Dhansiri and the Kopili joins it from left. The major part of basin is covered with forest accounting to 55.48% of the total area and 5.79% of the basin is covered by water bodies. The basin spreads over 22 parliamentary constituencies (2009) comprising 12 of Assam, 4 of West Bengal, 2 of Arunachal Pradesh, 2 of Meghalaya, 1 of Sikkim and 1 of Nagaland.
|Basin Extent |
88° 11’ to 96° 57’ E
24° 44’ to 30° 3’ N
|Length of Brahmaputra River (Km)||916 (in India)|
|Catchment Area (Sq.km.)||194413|
|Average Water Resource Potential (MCM)||537240|
|Utilizable Surface Water Resource (MCM)||24000|
|Live Storage Capacity of Completed Projects (MCM)||1718|
|Live Storage Capacity of Projects Under Construction (MCM)||795.10|
|Total Live Storage Capacity of Projects (MCM)||2513.10|
|No. of Hydrological Observation Stations||108|
|No. of Flood Forecasting Stations||27|
The composite Ganga – Brahmaputra –Meghna basin covers nearly one-third of the land area of Indian Union. This basin is composed of the Ganga, the Brahmaputra and the Barak sub-basins. The Ganga joins the Brahmaputra in Bangladesh and continues its run under the name Padma or Ganga. It finally joins the Meghna river which outfalls into the Bay of Bengal. The basin extends to areas outside India.
Brahmaputra sub-basin extends over an area of 580,000 sq. km lying in Tibet (China), Bhutan, India and Bangladesh. The drainage area lying in India is 194413 sq. km which is nearly 5.9% of the total geographical area of the country. It is bounded on the north by the Himalays, on the east by the Patkari range of hills running along the Assam-Burma border, on the south by the Assam range of hills and on the west by the Himalayas and the ridge separating it from Ganga sub-basin. The Sub-basin lies in the States of Arunachal Pradesh, Assam, Nagaland, Meghalaya, West Bengal and Sikkim. The State-wise distribution of drainage area is given below :
|State||Drainage area (sq. km)|
The upper portion of the sub-basin lying in Arunachal Pradesh and Nagaland is mostly mountain ranges and narrow valleys. Most portion of the sub-basin lying in Assam, Meghalaya and West Bengal consists of hills, forests and tea gardens. The Cooch Bihar and West Dinajpur districts of West Bengal has fertile plains.
The most predominant soil type found in the sub-basin is the red loamy soil and alluvial soil. Other important soil types are sandy, loamy, clayey soils, their combinations and laterite soils. The culturable area of the sub-basin is about 12.15 M. ha which is 6.2% of the culturable are of the country.
Brahmaputa river originates from Kailash ranges of Himalayas at an elevation of about 5150 m and flows for abut 2900 km through Tibet (China), India and Bangladesh and joins the Ganga. The river Brahmaputra receives a number of tributaries at its north and south banks, in the catchment area in India. The major tributaries are as follow
|Tributaries from North bank||Tributaries from South bank|
|The Jiadhal||The Noa Dehing|
|The Subansiri||The Buridehing|
|The Siang||The Debang|
|The Kameng (Jiabharali in Assam)||The Dikhow|
|The Dhansiri(North)||The Dhansiri(S)|
|The Puthimari||The Kopili|
|The Pagladiya||The Digaru|
|The Manas||The Dudhnai|
|The Champamati||The Krishnai|
In addition, six tributaries namely the Tista, the Sankosh, the Raidak-I, the Raidak-II, the Torsa and the Jaldhaka flowing through the northern West Bengal also join the main stream of Brahmaputra but, in the plains of Bangladesh. The North bank tributaries are flashy and have steep slopes, shallow braided channels, coarse sandy beds, carry a heavy silt charge. The South bank tributaries have flatter grades, deep meandering channels, fine alluvial soils and comparatively low silt charge.
Some of the important rivers of Brahmaputra basin are narrated below:
(A) SIANG RIVER
The Siang is the principal constituent river of the Brahmaputra known as Yarlung Zangbo in China. It originates from the glacier mass of the Kailash Range of the Himalayas at an elevation of about 5300 m and flows through China. The river flows eastwards for about 1600 km through the Tibetan Plateau. Before entering India the river Siang or Dihang flows through a deep gorge across the eastern extremity of the Himalayas. The river then flows through Arunachal Pradesh in a south/ south easterly direction for about 230 km to reach Pasighat. Two other rivers viz. the Lohit and the Dibang join the Siang at about 30 km downstream of Pasighat to form the mighty Brahmaputra river.
(B) SUBANSIRI RIVER
The Subansiri rises in the mountains of Tibet. Near its source, a big "Chu" family of streams drain into the main valley. The principal stream belonging to this "Chu" group is the "Sikung chu" which may be considered as the main source of the subansiri. The total length of the subansiri is about 442 km. Out of which 192 km lie in NEFA now renamed as Arunachal Pradesh and 190 km in Assam and the rest part falls in Tibet.
(C) KAMENG OROrissa JIABHARALI RIVER
The Kameng rises from the unsurveyed hills of the Himalayas presumably in the territory of Tibet beyond the AKA & DUFFA Hills. The river kameng flows for 55 km in south westerly direction and then reach Bhalukpong where it ends its hilly journey. The river is nearly 250 km long(190 km in Arunachal Pradesh and 60 km in Assam)
(D) DHANSIRI (S) RIVER
The Dhansiri (S) rises in the south west corner of Nagaland below the laishiang peak. From its source upto Dimapur, the Dhansiri forms the boundary between the districts of Cachar, Nagaon and Nagaland. Beyond Dimapur, the river enters and flows through the Karbi-Along and Golaghat districts of Assam. The river is nearly 354 km long.
(E) BURIDEHING RIVER
The Buridehing is formed by the confluence of the Namphuk and the Namchik, which rises from the Patkai ranges and the Maganton river which is the southern branch of the Noadehing. The Namphuk which may be considered the principal source of the Buridehing. The plains of this sub-basin are very fertile. Almost the entire high land is covered by Tea gardens. The total length of the river Buridehing is 362 km .
(F) KOPILI RIVER
The river Kopili is one of the important major tributaries of the Brahmaputra on its left bank. It originates in the Saipong Reserve Forest situated in south east of Meghalaya and passes through the borders of Meghalaya, North Cachar hills and karbi anglong and enters the plains in Nagaon district of Assam and finally joins the Brahmaputra at Kopilimukh. Its total length is 256 km of which 78 km form the common border of Meghalaya and Assam and the remaining 178 km lie in Assam.
(GGuage) MANAS RIVER
The river Manas basin is bound by Bhutan range of hills on the North, Pohumara river basin on the East, Champamati river basin on the West and Brahmaputra river on the South. The catchment area extends over an area of 34,160 sq km upto N.H. Crossing. The river enters into plains of Assam near Mathanguri and flows through Manas reserve forest. At Mathanguri, this river bifurcates into two branches, the eastern branch is known as Beki and western branch is known as Manas. The river Manas meets the river Brahmaputra near Jogighopa.
(H) JALDHAKA RIVER
The Jaldhaka has its origin in Sikkim. It traverses a total distance of 186 km passing through Bhutan, Darjeeling, Jalpaiguri and Cooch Behar districts of West Bengal, before finally joining Brahmaputra near Kurigram district of Bangladesh. The Murti and the Diana are its main tributaries.
(I) TORSA RIVER
The Torsa takes its birth in the Chumbi valley of Tibet where it is called Machu. Its upper reaches fall in the territory of Bhutan. It enters Indian territory near Phuentsholling after travelling about 70 km in China and 78 km in Bhutan. It then flows through the districts of jalpaiguri and Cooech Behar in West Bengal and joins Brahmaputra in Bangladesh. The length of the river from its origin to Ghughumari (Cooch Behar) is 222km having a total catchment area of about 4530 sqkm. Therafter, it meets Raidak-I.
(J) TISTA RIVER
The Tista is the largest river of North Bengal. It rises in the Himalayas in North Sikkim. Running through narrow gorges for nearly 138 km, it debouches into the plains of the Jalpaiguri district at sevoke. It flows in a steady course upto Jalpaiguri town beyond which it records frequent changes. It joins the Brahmaputra near Rangpur town in Bangladesh after traversing a length of 309 km.
During the year, four distinct seasons occur in the Indian portion of the basin. These are (i) winter, (ii) summer, (iii) monsoon and (iv) autum or post-monsoon. The winter season begins in December and continues to the end of February. Light north-easterly winds blow down the Brahmaputra valley in Assam and light northerly to north westerly winds in West Bengal. The weather is occasionally changed by the passage of western disturbances across the region, light rainfall occurs in January and February along the hills, increasing towards North-east Assam. Thunder storms are rare in December and January and occur only on one or two days in February, these may occasionally be accompanied by a dust or hail storm. From March onwards, the hot weather starts and continues up to the last week of May. In this season the basin is under the sway of three air streams a deep north-westerly current from Uttar Pradesh and Bihar, a shallow southerly stream from the head of the Bay of Bengal over the Orissa and Bengal coasts, and a shallower current of North easterly to easterly winds from the Brahmaputra valley blowing over the plains of North Bengal and Bihar. With the interactions between these air streams, this is a season when marked instability develops in the atmosphere and severe thunderstorms occur extensively, sometimes preceded by dust-raising squalls. Rainfall increases both in amount and frequency as the season advances, being generally associated with after noon or evening thunderstorms and squalls. They are generally more concentrated in Upper Assam. Hail storms occur on one to three days in the season, especially in the Assam hills. The monsoon sets in by the last week of May or in early June, being usually ushered in by a depression in the Bay of Bengal. Subsequently, a series of such depressions, forming at the head of the Bay and moving inland, give spells of continuous and moderate to heavy rain generally over the region. The monsoon withdraws in the last week of September or the first week of October. July and August are the rainiest months. Rain is most frequent and heavy on the southern slopes of the khasi hills in the north-east corner of Assam, and in Northern Bengal. Much of the rainfall in June and September is associated with thunder-clouds, while thundery weather is less frequent in July and August. After the withdrawal of the monsoon winds, light unsteady winds are experienced by the middle of October. Occasionally, in October, cyclonic storms from the Bay cross the Bengal coast bringing clouds and rain with them. Almost all the rain in this season is associated with thunder.
During the post-winter months, the north-east monsoon finds its way into the Brahmaputra valley through a saddle in the high Himalayas, at their eastern end. The Assam range of hills gradually rise in height eastward from 300 m in the Garo hills to about 3,000 m in the Naga hills. The low clouds brought in by the south-west monsoon get interrupted on the southern face of the Khasi and Jaintia hills by a 1,830 m high ridge and cause extremely heavy rainfall along the Cherrapunji-Mawphlang-Pynursla belt. This is generally of the order of 11,000 mm per annum, the highest in the world. The clouds that pass over this 1,830 m ridge along this belt, precipitate in the Brahmaputra valley, their intensity increasing towards the foothills of the Himalayas. The rainfall in the Brahmaputra valley ranges from 2,125 mm in Kamrup to about 4,142 mm in Tirap Division of the Arunachal. The Lanka area in Nagaon district on the north of the Khasi and Jaintia hillis lies in the rain shadow region and in consequence, the annual rainfall there is only about 1,100 mm. The rainfall in the Tista valley varies from 1,635 mm in West Dinajpur district to 3,945 mm in Jalpaiguri district. During the monsoon months of May to October, about 85% of the precipitation in the basin occurs. About 12% of the annual rainfall occurs in March and April.
During the winter season in January, the mean temperature over the catchment varies from 15.0°C to 17.5°C. The higher elevations in the Himalayan ranges experience lower temperatures. During the summer season in April, the mean temperature in the lower part of the catchment varies from 25.0°C to 27.5°C. The temperatures are below 25°C in the upper parts of the basin notably in Arunachal. In the rainy season, in the month of July, the mean temperature varies from 27.5°C to 30.0°C. Towards the end of the monsoon season, in the month of October, the mean temperature over the basin varies from 25.0°C to 27.5°C. The Arunachal region experiences temperatures lower than 25.0°C.
Status of Surface Water Development
Prior to independence, little thought was given towards water resources development in Brahmaputra valley. For the low density of population in the sub-basin, the abundant rainfall and fertile soil could produce sufficient food grains to meet the requirements by traditional methods. Most of the projects taken up and completed in the plan periods were medium and minor schemes. Dhansiri, Champamati and Teesta barrage are three major projects in the sub-basins.
The Brahmaputra sub-basin has abundant hydropower potential. As per the latest assessment the hydropower potential of the sub-basin is 31012 MW at 60% load factor. This is almost 37% of the country’s total installed capacity of 196 MW are in operation and another 7 schemes with a total installed capacity of 1043 MW are under construction. These 14 schemes together amount for only 2.2% of the assessed potential. Therefore, a large chunk of the hydropower potential of the sub-basin remains to be tapped.
Urban Centres and Industries.
Guwahati, Shillong and Siliguri are the important urban centres. The sub-basin is rich in petroleum and coal. Digboi in Assam was the only source of petroleum in India until about 1953-54. Petroleum products, jute, drugs and pharmaceuticals are other industries in the sub-basin.
Hydrological observations in the sub-basin are carried out by the Central and State Governments. The Central Water Commission maintains 108 H.O sites in the basin. In addition, gauge data at 80 sites, gauge-discharge data at 15 sites and gauge, discharge and sediment data at 25 sites, maintained by the State Governments and the Brahmaputra Board, are also available. The Central Water Commission operates 26 flood forecasting stations in the sub-basin.
Brahmaputra Board was established by the Govt. of India in 1980 with the object 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. The Board has jurisdiction over the adjacent Barak valley also.
Floods, erosion and drainage congestion are the main problems of the valley. As mentioned above, the Brahmaputra Board has been set up to look into these problems.
Water Resources Projects
|Major Medium Projects in Brahmaputra||dams in Brahmaputra|