Brahmaputra River System - Facts for UPSC

The Brahmaputra river has been in the news in recent months. Apart from flooding, in the month of September 2021, a tragic boat mishap took place, taking several lives. 

It is an important river system, with one of the largest drainage capacities, after the Ganga, in India. It has been the lifeline of the north-east states on the foothills of eastern Himalayas, forming fertile floodplains, evolving geography and ecology and cultural landscape

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In this article, we shall be discussing various aspects of the Brahmaputra River System and issues, keeping in mind the requirements of the preliminary as well as main examination of the UPSC IAS Exam.

Brahmaputra River

• Brahmaputra River originates in the great glacier mass north of Kailash ranges of the Himalayas (elevation 5,150 m) & south of a lake called ‘Konggyu Tsho’.
• It is only next to Amazon with a  specific yield of  85 ha m / sq km in comparison to 87 ha m /sq km of the latter.
• Brahmaputra traverses a distance of 2,900 km through four countries – Tibet (China), Bhutan, India and Bangladesh before entering the Bay of Bengal.
• The source of this river lies in the Kanglung Kang Glacier near the Kailash range of the Himalayas located in the south-western part of the Tibetan plateau at an elevation of 5,300 m, near Konggyu Tso Lake
• Here, the river is called Tamchok Khambab Kangri. Many snow-fed streams join the river from the passes at about 60 km southeast of Mansarovar Lake.
• It has a catchment area of 580,000 sq. km, 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.
• The catchment area of the river falls in four countries.

Salient Features of Brahmaputra River

• The river system is on the landmass enclosed on the north by the Himalayas, on the east by the Patkai 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. 
• The Brahmaputra river system regions witness one of the heaviest rainfall patterns in the world,  particularly the portions in Assam,  and are prone to annual floods and riverbank erosion.
• Parts of the Himalayan Mountains region of Sikkim and Arunachal Pradesh, falling in the Brahmaputra basin, experience snow cover.
• Brahmaputra river systems regions collectively are one of the greenest parts of India, accounting for the maximum 55.48%  of the country’s forest cover.
• Majuli, an island, also a district of Assam, is known as the oldest and largest inhabited riverine island of the world, recognised by UNESCO.
• The hydroelectric potential of the Brahmaputra river systems has been assessed at 66065 MW.
• The Brahmaputra river, with a drop of elevation 4800 m, is achieved in a length of about 1700 Km in Tibet. This average slope of about 2.82 m/Km gets reduced to about 0.1 m/Km in Assam valley.
• Due to this sudden flattening of river slope, the river becomes braided in nature in the Assam valley. 
• During its course in Assam valley from Kobo to Dhubri the river is joined by about 20 important tributaries on its North bank and 13 (thirteen) on its South bank, bringing high sediment load that results in braiding.
• All the tributaries of the valley area are rain-fed and foam up with rain, experiencing a number of flood waves as per rainfall in respective catchments. 
• The precipitation here is mainly due to the South-West monsoon. Heavy precipitation occurs to the tune of 85% of total annual rainfall, only during the monsoon months from May to September.
• If the flood of the tributaries coincides with the flood of Brahmaputra, it causes severe problems and devastation. 
• The region gets a good amount of rainfall in the months of April and May due to thunderstorm events, which account for flooding during heavy rain in June when the soil is already saturated and the river is in spate.

Which are Tributaries of Brahmaputra?

The mighty Brahmaputra has many tributaries on the North and South banks, as illustrated in the following table.

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 mainstream of Brahmaputra but, in the plains of Bangladesh. 

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  Kailash Range, at an elevation of about 5300 m and 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. 
• Lohit and the Dibang join the Siang at about 30 km downstream of Pasighat to form the mighty Brahmaputra river.

Subansiri River

• The Subansiri rises in the mountains of Tibet. 
• The total length of the Subansiri is about 442 km. 
• Out of which 192 km lie in Arunachal Pradesh and 190 km in Assam and the rest fall in Tibet.

Kameng or Jiabharali River

• The Kameng rises from the unsurveyed hills of the Himalayas, presumably in the territory of Tibet.
• The river Kameng flows for 55 km in south-westerly direction and then reaches Bhalukpong where it ends its hilly journey. 
• The river is nearly 250 km long, 90 km in Arunachal Pradesh and 60 km in Assam.

Dhansiri (South) River

• The Dhansiri (S) rises in the southwest corner of Nagaland below the Laishiang peak.
• From its source up to 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.

Kopili River

•  It originates in the Saipong Reserve Forest situated in the southeast of Meghalaya and passes through the borders of Meghalaya, North Cachar hills and Karbi Anglong and enters the plains in Nagaon district of Assam before joining 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.

Manas River

• The river originates in Bhutan, enters into the 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 the western branch is known as Manas. 
• The river Manas meets the river Brahmaputra near Jogighopa.

Tista River

• The Teesta River rises in the Himalayas in North Sikkim. 
• Running through narrow gorges for nearly 138 km, it meets the plains of Jalpaiguri district.
• It joins the Brahmaputra near Rangpur town in Bangladesh after traversing a length of 309 km.

Characteristics of the Tributaries 

The North Bank Tributaries

• Have very steep slopes and shallow braided channels for a considerable distance from the foothills, and in some cases right up to the outfall.
• Have boulder, pebble and coarse sandy beds and carry a heavy silt charge.
• Generally have flashy floods.

The South Bank Tributaries

• Have comparatively flatter grades and deep meandering channels almost from the foothills.
• Have comparatively low silt charge.

Conclusion

The mighty Brahmaputra along with its tributaries are the lifelines of the north-east. Not only massive erosion but also heavy flooding coupled with the destruction of livelihood and siltation are major problems. The river assumes immense significance not only for water security but also for the possible impacts downstream, associated with events beyond the borders in China. Lack of mechanism and adherence to decisions for sharing crucial data on the flow of the river upstream, construction of dams are concerns. This jeopardises the region with the threat of flooding, which could be completely man-made, due to mismanagement of the flow of the river.

India must expeditiously put plans to work for controlling the flood and bank erosion and improving the drainage of the Brahmaputra, simultaneously tapping the immense water potential for hydropower generation and possible irrigation.

This article is relevant for the Geography section of the UPSC syllabus prescribed for Preliminary and Main Examination of UPSC Civil Service.

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