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Brahmaputra

'Note: National, provincial and district boundaries have changed considerably since 1908. Typically, old states, ‘divisions’ and districts have been broken into smaller units, and many tahsils upgraded to districts. Some units have since been renamed. Therefore, this article is being posted mainly for its historical value.

('Son of Brahma ').— River of Tibet and North- eastern India, which for its size and utility to man ranks among the most important in the world. Its total estimated length is about 1,800 miles, and its drainage area about 361,200 square miles, while during the rains the flood discharge at Goalpara is said to be more than half a million cubic feet of water per second. An element of romance hangs over the river, as a certain portion of its course has never been actually explored, though there is little doubt that the Tsan-po, or great river of Tibet, pours its waters through the Dihang into the river which is known as the Brahmaputra in the Assam Valley.

The source of the Tsan-po is in 31° 30' N. and 82° E., near the upper waters of the Indus and the Sutlej, and a little to the east of the Manasarowar Lake. It has been traced almost continuously for a distance of 850 miles eastwards to Gya-la-Sindong, which is barely 150 miles from the Assam frontier, but no explorer has yet succeeded in following the river right down to its junction with the Brahmaputra.

It was at one time thought that the Tsan-po might be identical with the great river of Burma, the Irrawaddy, but explorations which termi- nated in 1882 proved that the course of the Tsan-po could not lie east of a place called Sama in the Zayul valley. It was then suggested that the river that flowed past Sama was not identical with the stream that runs westward from the Brahmakund to Sadiya, but was a tributary of the Tsan-po, which flowed to the west of Sama into the plains of Burma. This theory was completely disproved by the explorations of Mr. Needham, who in 1885-6 marched from Sadiya up the so- called Brahmaputra to Rima, a village east of Sama, and proved that the river at Rima and the river that flowed past Sadiya were the same.

The Tsan-po having no outlet towards Burma in any direction, there is little room for doubt with regard to its identity with the Brahmaputra. Granted this premise, it seems probable that the chan- nel by which it makes its way through the Himalayas is the Dihang, which is by far the largest river that falls into the Brahmaputra from the north, and at the point of junction considerably exceeds in volume the river flowing from Jhe east, which, as it follows the same direction as the united stream in its passage down the valley, has been wrongly styled the Brahmaputra by the Assamese. In 1886-7 the Tsan-po was visited by a native explorer, who stated that he followed its course for nearly 100 miles south of Gya-la-Sindong to a place called Onlet, which is only 8 miles from Miri Padam and 43 miles from the Assam frontier.

At first sight, it may seem strange that a geographical problem of such interest as the identity of the Tsan-po and the Dihang should still remain unsettled, and that such a small strip of territory should be allowed to remain unexplored. The hills through which the Dihang makes its way present, however, great difficulties to the explorer, and are inhabited by fierce and hostile tribes of whom little is known. Activity in that region is politically undesirable ; and even if no opposi- tion was offered to the expedition, it is possible that an advance and subsequent retirement would be construed into a sign of weakness, which might embolden the hill tribes to make incursions on the frontier of Assam.

The Dihang at Pobha joins a river flowing from the east, which is sometimes styled the Brahmaputra, sometimes the Luhit. This river rises to the north-east of the hills inhabited by the Mishmis, and is known at Rima as the Zayul Chu. Near Sadiya, shortly above its junction with the Dihang, it receives the Noa Dihing from the southern, and the Dibang and Sesseri from the northern bank. The most important tributaries that fall into the river west of the Dihang are : on the north bank, the SubansirI, Bhareli, Dhansiri, Bar- nadI, Manas, Sankosh, Dharla, and Tista ; and on the south bank the Burhi Diking, Disang, Dikho, Jhanzi, Dhansiri Kulsi, and JiNjiRAM.

Below Dibrugarh the Brnhmaputra at once assumes the character- istics by which it is generally known. It rolls along through the plain with a vast expanse of water, broken by innumerable islands, and exhibiting the operations of alluvion and diluvion on a gigantic scale. It is so heavily freighted with suspended matter that the least impedi- ment in its stream causes a deposit, and may give rise to a wide- spreading almond-shaped sand-bank. On either side, the great river throws out large branches, which rejoin the main channel after a divergence of many miles. One of these divergent channels takes off from the main stream, under the name of the Kherkutia Suti, opposite Burhi Dihingmukh. It receives the great volume of the SubansirI, and is then called the Luhit, and thus reinforced, rejoins the main stream nearly opposite Dhansirimukh. The great island or char of Majui.i, with an area of 485 square miles, is enclosed between it and the main stream. Another large divergent channel is the Kalang, which takes off from the south bank opposite Bish- nath in Darrang District, and traverses the whole of Nowgong District west of that point, rejoining the Brahmaputra a short distance above Gauhati.

Unlike many rivers that flow through flat low-lying plains, instead of creeping along in a sluggish channel, the Brahmaputra in the Assam Valley has a comparatively swift current, and possesses no high permanent banks. At certain points in its course it passes between or by rocky eminences, which give a temporary fixity to its channel, as at Bishnath, Silghat, Tezpur, Singriparbat, Gauhati, Hathimura, Goalpara, and Dhubri. Where not so controlled, it sends its shifting channels over a vast extent of country, without forming any single continuous river trough.

After a course of 450 miles south-west down the Assam Valley, the Brahmaputra sweeps southward round the spurs of the Garo Hills, which form the outwork of the watershed separating it from the river system of the Surma in Sylhet. It enters Rangpur District in 25° 47' N. and 89° 49' E., and its southerly course continues thence for about 148 miles, under the name of the Jamuna, through the open plains of Eastern Bengal, as far as its confluence with the Padma, or main stream of the Ganges, at Goalundo in 23° 51' N. and 89° 46' E. The united rivers subsequently join the Meghna estuary opposite Chandpur, in 23° 13 N. and 90° 2>2>' E.

The main stream of the Brahmaputra formerly flowed south-east across the centre of Mymensingh District, and, after discharging its silt into the Sylhet swamps and receiving the Surma, united directly with the Meghna. This is the course shown on the maps of Rennell's survey of 1785; and it was not till the beginning of the nineteenth century that, having raised its bed and lost its velocity, the river was no longer able to hold its own against the Meghna, and, being forced to find another outlet for its banked-up waters, suddenly broke westwards and joined the Ganges near Goalundo. The old bed still retains its name, but has been steadily silting up, a process which was expedited by the great earthquake of 1897. The entire lower portion of the Brahmaputra may be described as an elaborate network of interlacing channels, many of which run dry in the cold season, but are filled to overflowing during the annual period of inundation. Numerous islands are formed by the river during its course, most of which are mere sandbanks deposited during one rainy season to be swept away by the inundation of the following year. The principal tributaries after leaving the Assam \^alley are the Dharla and TiSTA on its right bank ; the latter joins it a few miles to the south-west of ChilmarT in Rangpur District.

In agricultural and commercial utility, the Brahmaputra ranks next after the Ganges, and with the Indus, among the rivers of India. Unlike those two rivers, however, its waters are not largely utilized for artificial irrigation, nor are they confined within embankments. The natural overflow of the periodic inundation is sufficient to supply a soil which receives, in addition, a heavy rainfall ; and this natural overflow is allowed to find its own lines of drainage. The plains of Eastern Bengal, watered by the Brahmaputra, yield abundant crops of rice, jute, and mustard, year after year, without undergoing any visible exhaustion.

The Brahmaputra is navigable by steamers as high up as Dibrugarh, about 800 miles from the sea; and in its lower reaches its broad surface is covered with country craft of all sizes and rigs, down to dug-out canoes and timber-rafts. It is remarkable that there is comparatively little boat traffic in the Assam Valley itself. Goalpara is the great emporium of the boat trade, and Gauhati is ordinarily the extreme point reached by boats of large burthen. Nearly all the boats which resort to Goalpara and Gauhati come from Bengal or the United Provinces. Large cargo steamers with their attendant flats and a daily service of smaller and speedier passenger vessels ply on the Brahma- putra between Goalundo and Dibrugarh. The upward journey takes four and a half days to complete, the downward three. The principal places passed in the upward journey are, on the right bank, Sirajganj, a great emporium for jute and other agricultural produce, Dhubri, Tezpur, and Bishnath ; and on the left bank, Goalpara, Gauhati, vSil- ghat, and Dibrugarh. There are, however, eighteen other ghats at which steamers call, the most important being Shikarighat for Golaghat, Kakilamukh for Jorhat, and Disangmukh for Sibsagar. The down- ward trafific chiefly consists of tea, coal, oilseeds, timber, hides, lac, and raw cotton from Assam ; and jute, oilseeds, tobacco, rice, and other food-grains from Eastern Bengal.

Chinese control of the head waters

Why this affects India

Why China's hold on Brahmaputra bothers India
The Times of India

Why China's hold on Brahmaputra bothers India, The Times of India TNN | Updated: Oct 5, 2016

NEW DELHI: Within days of India announcing plans to assert its right within the Indus Water Treaty+ with Pakistan, China+ said it was building a dam+ on a tributary of the Yarlung Zangbo, as Brahmaputra is known in Tibet. This will be its 'most expensive hydel project'. Here's all about the project, the tributary and why India worries about the project.

Why India sees red

1. China's dam building overdrive is a concern because there are no bilateral or multilateral treaties on the water

2. China believes dam building on the Brahmaputra helps it assert claim over Arunachal Pradesh

3. India believes China's projects in the Tibetan plateau threaten to reduce river flows into India

4. Dams, canals, irrigation systems can turn water into a political weapon to be wielded in war, or during peace to signal annoyance with a co-riparian state

5. Denial of hydrological data becomes critical when the flow in the river is very high

6. China is contemplating northward re-routing of the Yarlung Zangbo+

7. Diversion of the Brahmaputra is an idea China does not discuss in public, because it implies devastating India's northeastern plains and Bangladesh, either with floods or reduced water flow

8. In 2013, India complained to China about its hydro projects on the Brahmaputra

9. India and China signed two pacts in 2008 and 2010 which facilitated India with data on water levels and rainfall twice a day from June 1 to October 15 at three hydrological stations in Tibet

10. In 2001, an artifical dam in Tibet collapsed and killed 26 people and damaged property of Rs 140 crore along the river Siang in Arunachal Pradesh

The Lalho project

• The Lalho project+ on the Xiabuqu River in Xigaze (close to Sikkim) is under way at an investment of $740 million. Xigaze is a few hours from the junction of Bhutan and Sikkim. It is also the city from where China intends to extend its railway towards Nepal

• China's first dam on the main upper reaches of the Brahmaputra was built at Zangmu in 2010

• Three more dams at Dagu, Jiacha, and Jeixu (small-scale projects) are under construction

• In 2015, China inaugurated the Zam Hydropower Station, largest in Tibet, the highest dam built on Brahmaputra

The Tributary that was blocked

• The Xiabuqu river, 195-km long, flows from Bainang in Tibet northwards and joins the Yarlung Zangbo near the region calledXigaze, also known as Shigatse

• This tributary was blocked for the Lalho hydel project that launched in June 2014, scheduled to be completed in 2019

• The river's mean discharge is 25.8 cubic metres per second (cumecs), less than 0.15 per cent of the Brahmaputra's mean discharge

• when it enters India

• Its reservoir was designed to store up to 295 cumecs and it will irrigate 30,000 hactares, control floods and generate power

Flood risk

As assessed in 2020

Chandrima Banerjee, December 26, 2020: The Times of India The trail of destruction the Brahmaputra leaves behind every monsoon is, in many ways, considered inevitable. What can be planned is the response, which depends on how bad the flood hazard is thought to be. But going over 700 years of river data, it turns out the already high flood hazard in the Brahmaputra basin has been underestimated by up to 38% — with the present assessment of flood risks based on some of the driest periods in the region.

For the study, published in ‘Nature Communications’ last week, Mukund P Rao from Columbia University and a team of 11 scientists used a new tree-ring reconstruction of the monsoon months — when river discharge is the highest — and studied how closely related (or not) these patterns were with flood years.

They found that the last six decades were much drier than the six and a half centuries preceding them. And since most flood risk estimates were based on more recent observations, they have been significantly off the mark. “The ‘simple’ number (by which they have been underestimated) … would be 24-38%. Though human policies could definitely mitigate or amplify this,” lead author Mukund P Rao told TOI.

The limitations come with a smaller dataset. The point in climate history when routine weather observations started being taken at fixed points is the beginning of the instrumental period, in the 18th century. For Brahmaputra discharge (volume of water flow), the longest instrumental record comes from the Bahadurabad gauging station in Bangladesh, spanning six decades from 1956 to 2011. “Such a short record makes it difficult to assess and put into perspective the magnitude of projected future changes relative to natural variability,” the paper says.

What threw estimates even further was the fact that half of that period — between 1956 and 1986 — was one of the driest in seven centuries. In fact, six of the 12 Brahmaputra floods before 1956 were in relatively dry years. This, of course, came up only when Rao and the team expanded the dataset that had formed the (misleading) baseline — by observing tree rings.

As trees grow they incorporate information about the environmental conditions they are living in in their annual growth rings. “Trees grow more and put on wide rings in wet monsoon years. Conversely, in dry monsoon years (or droughts) they grow less and put on narrow rings,” Rao said. “Some of these trees can live for a long time. By taking a small pencil-thin tree-core from them and measuring their rings under a microscope, we can learn about climate conditions for the past several centuries. These cores that we take are really small and do not injure or harm the trees. This field of study is known as dendrochronology.”

They arrived at a 48,800m3/s benchmark — any projected river discharge higher than this would qualify as flood hazard. And the most severe floods are those where there’s inundation for more than 10 consecutive days. The instrumental period, turned out, was “unusually dry”, with comparable periods only in the early 1400s, late 1600s, early 1800s and late 1800s. And the historical flood years (that is, before the instrumental period) did not always coincide with high discharge.

“Interestingly, we found a good match for a flood in the year 1787 CE. There was a major flood that year which caused the Teesta river to change its course eastward from flowing into the Ganga to the Brahmaputra instead,” Rao said. “It was unclear if this shift was earthquake-driven or monsoon-driven. We can’t say for sure, but our results suggest 1787 was a very wet year.”

And why is this important? Understanding how the river behaved before would inform projections of how it will behave in the future. The paper says, “The wetter reconstruction and projections relative to the instrumental period suggest that we may be currently underestimating the ... future frequency of high discharge in the Brahmaputra River watershed.” Climate model projections anyway suggest increasing flow and risk for flooding in the Brahmaputra watershed due to climate change, Rao said. “These trees are amazing natural archives. This just adds one more reason why we need to protect and preserve them.”