Brahmaputra River
The Brahmaputra is a trans-boundary river which flows through Southwestern China, Northeastern India, and Bangladesh. It is known as the Brahmaputra or Luit in Assamese, Yarlung Tsangpo in Tibetan, the Siang/Dihang River in Arunachali, and Jamuna River in Bangladesh. By itself, it is the 9th largest river in the world by discharge, and the 15th longest.
It originates in the Manasarovar Lake region, near Mount Kailash, on the northern side of the Himalayas in Burang County of Tibet where it is known as the Yarlung Tsangpo River. The Brahmaputra flows along southern Tibet to break through the Himalayas in great gorges and into Arunachal Pradesh. It enters India near the village of Gelling in Arunachal Pradesh and flows southwest through the Assam Valley as the Brahmaputra and south through Bangladesh as the Jamuna. In the vast Ganges Delta, it merges with the Ganges, popularly known as the Padma in Bangladesh, and becomes the Meghna and ultimately empties into the Bay of Bengal.
At long, the Brahmaputra is an important river for irrigation and transportation in the region. The average depth of the river is and its maximum depth is . The river is prone to catastrophic flooding in the spring when the Himalayan snow melts. The average discharge of the Brahmaputra is about ~, and floods reach about. It is a classic example of a braided river and is highly susceptible to channel migration and avulsion. It is also one of the few rivers in the world that exhibits a tidal bore. It is navigable for most of its length.
The Brahmaputra drains the Himalayas east of the Indo-Nepal border, south-central portion of the Tibetan plateau above the Ganga basin, south-eastern portion of Tibet, the Patkai hills, the northern slopes of the Meghalaya hills, the Assam plains, and northern Bangladesh. The basin, especially south of Tibet, is characterized by high levels of rainfall. Kangchenjunga is the highest point within the Brahmaputra basin and the only peak above 8,000 m.
The Brahmaputra's upper course was long unknown, and its identity with the Yarlung Tsangpo was only established by exploration in 1884–1886. The river is often called the Tsangpo-Brahmaputra river.
The lower reaches are sacred to Hindus. While most rivers on the Indian subcontinent have female names, this river has a rare male name. Brahmaputra means "son of Brahma" in Sanskrit.
Names
It is known by various names in different regional languages: Brôhmôputrô in Assamese; Yarlung Tsangpo; t=雅魯藏布江. It is also called Tsangpo-Brahmaputra and red river of India. In its Tibetan and Indian names, the river is unusually masculine in gender.Geography
Course
Tibet
The upper reaches of the Brahmaputra River, known as the Yarlung Tsangpo from the Tibetan language, originates on the Angsi Glacier, near Mount Kailash, located on the northern side of the Himalayas in Burang County of Tibet. The source of the river was earlier thought to be on the Chemayungdung glacier, which covers the slopes of the Himalayas about southeast of Lake Manasarovar in southwestern Tibet.From its source, the river runs for nearly in a generally easterly direction between the main range of the Himalayas to the south and the Kailas Range to the north.
In Tibet, the Tsangpo receives a number of tributaries. The most important left-bank tributaries are the Raka Zangbo, which joins the river west of Xigazê, and the Lhasa, which flows past the Tibetan capital of Lhasa and joins the Tsangpo at Qüxü. The Nyang River joins the Tsangpo from the north at Zela. On the right bank, a second river called the Nyang Qu meets the Tsangpo at Xigazê.
After passing Pi in Tibet, the river turns suddenly to the north and northeast and cuts a course through a succession of great narrow gorges between the mountainous massifs of Gyala Peri and Namcha Barwa in a series of rapids and cascades. Thereafter, the river turns south and southwest and flows through a deep gorge across the eastern extremity of the Himalayas with canyon walls that extend upward for and more on each side. During that stretch, the river crosses the China-India line of actual control to enter northern Arunachal Pradesh, where it is known as the Dihang River, and turns more southerly.
Arunachal Pradesh
The Yarlung Tsangpo leaves the part of Tibet to enter Indian state of Arunachal Pradesh, where the river is called Siang. It makes a very rapid descent from its original height in Tibet and finally appears in the plains, where it is called Dihang. It flows for about southward after which, it is joined by the Dibang River and the Lohit River at the head of the Assam Valley. Below the Lohit, the river is called Brahmaputra and Doima and Burlung-Buthur by native Bodo tribals, it then enters the state of Assam, and becomes very wide—as wide as in parts of Assam.The reason for such an unusual course and drastic change is that the river is antecedent to the Himalayas, meaning that it had existed before them and has entrenched itself since they started rising.
Assam
The Dihang, winding out of the mountains, turns towards the southeast and descends into a low-lying basin as it enters northeastern Assam state. Just west of the town of Sadiya, the river again turns to the southwest and is joined by two mountain streams, the Lohit, and the Dibang. Below that confluence, about from the Bay of Bengal, the river becomes known conventionally as the Brahmaputra. In Assam, the river is mighty, even in the dry season, and during the rains, its banks are more than apart. As the river follows its braided course through the valley, it receives several rapidly flowing Himalayan streams, including the Subansiri, Kameng, Bharali, Dhansiri, Manas, Champamati, Saralbhanga, and Sankosh Rivers. The main tributaries from the hills and from the plateau to the south are the Burhi Dihing, the Disang, the Dikhow, and the Kopili.Between Dibrugarh and Lakhimpur Districts, the river divides into two channels—the northern Kherkutia channel and the southern Brahmaputra channel. The two channels join again about downstream, forming the Majuli island, which is the largest river island in the world. At Guwahati, near the ancient pilgrimage centre of Hajo, the Brahmaputra cuts through the rocks of the Shillong Plateau, and is at its narrowest at bank-to-bank. The terrain of this area made it logistically ideal for the Battle of Saraighat, the military confrontation between the Mughal Empire and the Ahom Kingdom in March 1671. The first combined railroad/roadway bridge across the Brahmaputra was constructed at Saraighat. It was opened to traffic in April 1962.
The environment of the Brahmaputra floodplains in Assam have been described as the Brahmaputra Valley semi-evergreen forests ecoregion.
Bangladesh
In Bangladesh, the Brahmaputra is joined by the Teesta River, one of its largest tributaries. Below the Tista, the Brahmaputra splits into two distributary branches. The western branch, which contains the majority of the river's flow, continues due south as the Jamuna to merge with the lower Ganga, called the Padma River. The eastern branch, formerly the larger, but now much smaller, is called the lower or Old Brahmaputra. It curves southeast to join the Meghna River near Dhaka. The Padma and Meghna converge near Chandpur and flow out into the Bay of Bengal. This final part of the river is called Meghna.The Brahmaputra enters the plains of Bangladesh after turning south around the Garo Hills right below Dhuburi, India. After flowing past Chilmari, Bangladesh, it is joined on its right bank by the Tista River and then follows a course due south as the Jamuna River. Before its confluence with the Ganga, the Jamuna receives the combined waters of the Baral, Atrai, and Hurasagar Rivers on its right bank and becomes the point of departure of the large Dhaleswari River on its left bank. A tributary of the Dhaleswari, the Buriganga, flows past Dhaka, the capital of Bangladesh, and joins the Meghna River above Munshiganj.
The Jamuna joins with the Ganga north of Goalundo Ghat, below which, as the Padma, their combined waters flow to the southeast for a distance of about. After several smaller channels branch off to feed the Ganga-Brahmaputra delta to the south, the main body of the Padma reaches its confluence with the Meghna River near Chandpur and then enters the Bay of Bengal through the Meghna estuary and lesser channels flowing through the delta. The growth of the Ganga-Brahmaputra Delta is dominated by tidal processes.
The Ganga Delta, fed by the waters of numerous rivers, including the Ganga and Brahmaputra, is, one of the largest river deltas in the world.
Hydrology
The Ganges–Brahmaputra–Meghna system has the second-greatest average discharge of the world's rivers—roughly ~, and the river Brahmaputra alone supplies about 50% of the total discharge. The rivers' combined suspended sediment load of about 1.87 billion tonnes per year is the world's highest.In the past, the lower course of the Brahmaputra was different and passed through the Jamalpur and Mymensingh districts. In an 8.8 magnitude earthquake on 2 April 1762, however, the main channel of the Brahmaputra at Bhahadurabad point was switched southwards and opened as Jamuna due to the result of tectonic uplift of the Madhupur tract.
Climate
Rising temperatures significantly contribute to snow melting in the upper Brahmaputra catchment. The discharge of the Brahmaputra River is significantly influenced by the melting of snow in the upper part of its catchment area. This increase in river flow, caused by the substantial retreat of snow, leads to a higher downstream discharge. Such a rise in discharge often results in severe catastrophic issues, including flooding and erosion.Discharge
The Brahmaputra River is characterized by its significant rates of sediment discharge, the large and variable flows, along with its rapid channel aggradations and accelerated rates of basin denudation. Over time, the deepening of the Bengal Basin caused by erosion will result in the increase in hydraulic radius, and hence allowing for the huge accumulation of sediments fed from the Himalayan erosion by efficient sediment transportation. The thickness of the sediment accumulated above the Precambrian basement has increased over the years from a few hundred meters to over in the Bengal fore-deep to the south. The ongoing subsidence of the Bengal Basin and the high rate of Himalayan uplift continues to contribute to the large water and sediment discharges of fine sand and silt, with 1% clay, in the Brahmaputra River.Climatic change plays a crucial role in affecting the basin hydrology. Throughout the year, there is a significant rise in hydrograph, with a broad peak between July and September. The Brahmaputra River experiences two high-water seasons, one in early summer caused by snowmelt in the mountains, and one in late summer caused by runoff from monsoon rains. The river flow is strongly influenced by snow and ice melting of the glaciers, which are located mainly on the eastern Himalaya regions in the upstream parts of the basin. The snow and glacier melt contribution to the total annual runoff is about 27%, while the annual rainfall contributes to about and of discharge. The highest recorded daily discharge in the Brahmaputra at Pandu was August 1962 while the lowest was in February 1968. The increased rates of snow and glacial melt are likely to increase summer flows in some river systems for a few decades, followed by a reduction in flow as the glaciers disappear and snowfall diminishes. This is particularly true for the dry season when water availability is crucial for the irrigation systems.