Brief Description

The source of this river lies in the Kanglung Kang Glacier near the Kailash range of Himalayas located in the south-western part of the Tibetan plateau at an elevation of 5,300m (82°10° E and 30°30’ N) near Konggyu Tso Lake. Here the river is called Tamchok Khambab Kangri. Many snowfed streams join the river from the passes at about 60 km southeast of Mansarovar Lake. The Brahmaputra River traverses a distance of 2,880 km through three countries, namely, China, India, and Bangladesh, before joining the Bay of Bengal. 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. 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. The basin lies between 23°N to 32°_N latitude and 82°E to 97°50’ E longitude. The part of the Tibetan plateau falling under the basin has an elevation varying from 3,000 to 5,000m and is dotted with numerous glaciers.

The Brahmaputra valley is long and narrow; it is 640 km long and the width varies from 64 km to 90 km. The valley is bounded in the north by high Himalayan mountain ranges, in the east by the Patkai hill ranges, in the south by the lower (Assam) hill ranges and in the west, it is contiguous with the plains of Bangladesh.

The southern (Assam) mountainous region under the basin is comprised of parts of Naga hills, Mikir hills, North Cachar hills, Khasi hills and Garo hills lying in continuity in the east-west direction from Patkai hill ranges up to the Bangladesh border.

In India, the Brahmaputra basin covers parts of six states: Arunachal Pradesh, Assam, Nagaland, Meghalaya and West Bengal and the whole of Sikkim.

The culturable area of the basin is 12.15 M-ha which is 6.2% of the culturable area of the country.

The numbers represents average flow in cumec.

Topography

The Brahmaputra basin covers 6 topographic regions falling in 4 countries.

Nature of Topography

Area under  Topography (sq. km)

Geographical Location

High Tibetan Plateau

293,000

Southern Part of the Tibet province of China.

High Himalayan mountains

137,050

Part of Himalayan kingdom of Bhutan and of 3 states of India: Arunachal Pradesh, West Bengal and Sikkim.

Brahmaputra Valley

56,200

Part of Assam State of India.

Lower (Assam) Mountainous Region

37,200

Part of 3 states of India: Nagaland, Assam and Meghalaya.

Plains

56,550

Part of the 2 plains districts of West Bengal (India) and part of Bangladesh.

Coastal Region

Negligible

Coastal region of Bangladesh.

Water potential

Surface Water potential (Km³)

537.2

Ground Water potential (Km³)

27.9

Total Water potential in the basin (Km³)

565.1

Hydropower Potential

The hydroelectric potential of the Brahmaputra basin has been assessed 66065 MW. Out of the identified schemes in the basin , schemes with a total installed capacity of 2120 MW are in operation as on 31.7.2014 and schemes with an installed capacity of about 5592 MW are in various stages of construction. (Source: www.cea.nic.in). The status as on 2010 is given below:

Sub-basin wise estimated hydro potential of Brahmaputra basin

Basin/Rivers

No. of schemes identified

Potential at 60% load factor  (MW)

Dihang-Dibang

28

13,615

Lohit

11

4,152

Subansiri

25

6,893

Upper Brahmaputra

19

789

Kameng

34

1,982

Kalang (Kopili)

16

510

Teesta

30

3,021

Lower Brahmaputra

03

50

Barak and neighboring rivers

60

3,908

Total

226

34,920

Water Utilization

Surface Water Utilization

Drinking purposes

Irrigation purposes

Ground Water Utilization

Drinking purposes

Irrigation purposes

Tributaries with drainage area in sq. km.

Name of the Tributary

Drainage area (Km²)

Jiadhol

77.3

Subansiri

4.3

Ranganadi

23.8

Borgong

36.4

Jia-Bharali

28.1

Gabharu

80.7

Belsiri

75.4

Dhansiri (N)

65.2

Noa-nadi

81.4

Nonoi

76.2

Barnadi

82.8

Puthimari

66.6

Pagladiya

75.8

Manas

14.1

Champamati

86.8

Gaurang

81.5

Tipkai

90.2

Sankosh

7.6

Major Projects

Doyang, Kopili, Khandong, Loktak, Rammam II, Ranganadi, Rangit III, Teesta Canal Power House I, II, III, Teesta Low Dam Stage – III Hydroelectric Project, Teesta Low Dam Stage - IV Hydroelectric Project, Umiam III, Umiam IV (Nongkhylle), Dhansiri + LBP, Karbi Langpi (Lower Borpani), Kopili Stage II, Likim- Ro, Loktak Downstream, Ranganadi, Teesta Stage V, Tuirial, Tuirini, Tuivall, Umiam- Umtru St-V, Dhansiri + LBP, Karbi Langpi (Lower Borpani), Kopili Stage II, Likim- Ro, Loktak Downstream, Ranganadi, Teesta Stage V, Tuirial, Tuirini, Tuivall

Water Quality of Basin

The major ion chemistry of the Brahmaputra is characterized by high bi-carbonate content and source rock influence. While higher values of TSM than TDS during monsoon indicate predominance of physical weathering over chemical weathering, chemical weathering is relatively more pronounced during the dry season. On average, 60% of the bicarbonates in the Brahmaputra water come from silicate weathering and the rest from the carbonates.

Surface suspended sediments range from fine sand to clay, the size fraction greater than 12 mm constituting an important size population. Surface suspended sediments are moderately to poorly sorted with greater amounts of finer material in the distribution, particularly during the rainy season. The detrital contribution in the form of Quartz, Feldspar and Mica make up more than 80% of the mineralogy. Chlorite, Illite, and Kaolinite constitute about 95% of the clay minerals.

Sediment chemistry does not reveal any marked spatial or temporal variation. However, spatial variation in the metal/aluminum ratio in some cases has been observed. This may be attributed to continuous addition of freshly eroded materials by a large number of tributaries at different points of the main stem. Since there is hardly any major industry in the catchment area and the amounts of sediment carried by the tributaries are enormous, there is not enough ground to link any occasional rise in metal concentration to any point source.

The major sources of carbon in the Brahmaputra basin are deforestation and fossil fuel consumption. In the case of nitrogen, precipitation, soil erosion, drainage and fertilizer application constitute the main sources. Phosphorous carried by the suspended load makes up a substantial part of the P loading in the Brahmaputra. A comparison of different forms of P between suspended and bed sediments indicates a decrease in organic-P, Fe-P and total-P after deposition. Since much of the suspended sediment-transported P is not available biologically, land management practices to minimize sediment input to the river should produce no significant reduction in the biological availability of P. The total flux of P from the Brahmaputra (150 - 270 10¹⁰ gm P/year) constitutes nearly 5% of the global flux and is about three times greater than that carried in dissolved form. Considering the mobilization of P by fertilizer use, it is reasonable to assume that the P concentrations will further increase.

Suspended sediments play a significant role on the overall solute and sediment biogeochemistry of the river. The biogeochemistry of Ganga and Brahmaputra is markedly different with respect to HCO₃, SO₄, Cl, SiO₂, Ca and a few heavy metals, such as Cu, Fe, and Zn. It may be possible that apart from the natural factors, such as geology, topography, vegetation, and precipitation, this is also owing to the difference in the intensity of utilization of the two rivers and anthropogenic impacts on their watersheds which may be different, having a direct reflection on their geochemical behaviour.

Mythology

Brahmaputra River has a male name whereas all other majors rivers of India have female names. According to legends, Brahmaputra is the son of Lord Brahma. It is said that Shantanu, a famous ancient sage began a long meditation in an ashram in this area along with his beautiful wife Amodha. Amodha was so beautiful that Lord Brahma himself became enchanted by the beauty of Amodha and requested her to make love with him. But Amodha did not accept the Brahma’s proposal. However, by that time Lord Brahma had become so excited that his semen discharged at that place. When Shantanu came to know about this, he inseminated the Brahma’s semen in the womb of Amodha. Subsequently, Amodha gave birth to a son and he was called Brahmaputra. The tank near the ashram of sage Shantanu is known as the Brahmkund. Another legend is that because Brahmaputra is the largest river in India, it carries a male name.