Brahmaputra River

River, Central and South Asia.

From its headsprings in Tibet (as the Zangbo River), it flows across southern Tibet to break through the Himalayas in great gorges (where it is known as the Dihang). It flows southwest through the Assam Valley and south through Bangladesh (where it is known as the Jamuna). There it merges with the Ganges (Ganga) to form the Ganges-Brahmaputra delta. About 1,800 mi (2,900 km) long, the river is an important source for irrigation and transportation. Its upper course was long unknown, and its identity with the Zangbo was only established by exploration in 1884–86.

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▪ river, Asia

Introduction

Bengali  Jamuna,  Chinese (Wade-Giles)  Ya-lu-tsang-pu Chiang,  or  (Pinyin)  Yarlung Zangbo Jiang,  Tibetan  Tsang-po,  

 major river of Central and South Asia. It flows some 1,800 miles (2,900 kilometres) from its source in the Himalayas to its confluence with the Ganges River, after which the mingled waters of the two rivers empty into the Bay of Bengal. Along its course it passes through the Tibet Autonomous Region of China, the Indian (India) states of Arunāchal Pradesh (Arunachal Pradesh) and Assam, and Bangladesh. For most of its length, the river serves as an important inland waterway; it is not, however, navigable between the mountains of Tibet and the plains of India. In its lower course, the river is both a creator and a destroyer—depositing huge quantities of fertile alluvial soil but also causing disastrous and frequent floods.

Physical features

Physiography

      The Brahmaputra's source lies in the Chemayungdung Glacier, which covers the slopes of the Himalayas about 60 miles southeast of Ma-fa-mu (Mapam) Lake in southwestern Tibet. The three headstreams that arise there are the Kubi, the Angsi, and the Chemayungdung. From its source the river runs for nearly 700 miles in a generally easterly direction between the main range of the Himalayas to the south and the Nien-ch'ing-t'ang-ku-la (Nyenchen) Mountains to the north. Throughout its upper course the river is generally known as the Tsangpo (“The Purifier”); it is also known by its Chinese name and by other local Tibetan names at various points along its course.

      In Tibet the Tsangpo receives a number of tributaries. The most important left-bank tributaries are the Lo-k'a tsang-pu (Raga Tsangpo), which joins the river west of Jih-k'a-tse (Shigatse), and the La-sa (Kyi), which flows past the Tibetan capital of Lhasa and joins the Tsangpo at Ch'ü-shui. The Ni-yang (Gyamda) River joins the river from the north at Tse-la (Tsela Dzong). On the right bank the Nien-ch'u (Nyang Chu) River meets the river at Jih-k'a-tse.

      After passing P'i (Pe) 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 complex of Gyala Peri and Namcha Barwa (Mount Na-mu-cho-pa-erh-wa) in a series of rapids and cascades. Thereafter, the river turns south and southwest and forces its way through the eastern extremity of the Himalayas to enter the Assam Valley of northeastern India as the Dihāng River.

      Just west of the town of Sadiya, India, the Dihāng turns to the southwest and is joined by two mountain streams, the Lohit and the Dibāng. After the confluence, about 900 miles from the Bay of Bengal, the river is known as the Brahmaputra (“Son of Brahmā”). In Assam the river is mighty, even in the dry season, and during the rains its banks are more than five miles apart. As the river follows its braided, 450-mile course through the valley, it receives several rapidly rushing Himalayan streams, including the Subansiri, Kameng, Bhareli, Dhansiri, Mānas, Chāmpāmati, Saralbhānga, and Sankosh rivers. The main tributaries from the hills and from the plateau to the south are the Burhi Dihing, the Disāng, the Dikhu, and the Kopili.

      The Brahmaputra enters the plains of Bangladesh after turning south around the Gāro Hills below Dhuburi, India. After flowing past Chilmāri, Bangladesh, it is joined on its right bank by the Tīsta River and then follows a 150-mile course due south as the Yamuna River. (South of Gaibānda, the Old Brahmaputra leaves the left bank of the main stream and flows past Jamālpur and Mymensingh to join the Meghna River at Bhairab Bāzār.) Before its confluence with the Ganges, the Yamuna receives the combined waters of the Baral, Atrai, and Hurāsāgar 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 Burhi Ganga (“Old Ganges”), flows past Dhākā and joins the Meghna River above Munshiganj.

      The Yamuna joins with the Ganges north of Goalundo Ghāt, after which, as the Padma, their combined waters flow to the southeast for a distance of about 75 miles. The Padma reaches its confluence with the Meghna River near Chāndpur and then enters the Bay of Bengal through the Meghna estuary and lesser channels.

Climate

      The climate of the Brahmaputra valley varies from the harsh, cold, and dry conditions found in Tibet to the generally hot and humid conditions prevailing in the Assam Valley and Bangladesh. Tibetan winters are severely cold, with minimum temperatures below 32° F (0° C), while summers are mild and sunny. The river valley lies in the rain shadow of the Himalayas, and precipitation there is relatively light: Lhasa receives about 16 inches (400 millimetres) annually.

      In the Indian and Bangladeshi part of the valley, the monsoon climate is somewhat modified; the hot season is shorter than usual, and the average temperature ranges from 79° F (26° C) in Dhuburi, Assam, to 85° F (29° C) at Dhākā. Precipitation is relatively heavy, and humidity is high throughout the year. The annual rainfall of between 70 and 150 inches falls mostly between June and early October; light rains also fall from March to May.

Hydrology

      Constant changes of the river's course constitute a significant factor in the hydrology of the Brahmaputra; the most spectacular of these changes was the eastward diversion of the Tīsta River (Tista River) and the ensuing development of the new channel of the Yamuna, which occurred in 1787 with an exceptionally high flood in the Tīsta. The waters of the Tīsta suddenly were diverted eastward into an old abandoned course, causing the river to join the Brahmaputra opposite Bāhādurābād Ghāt in Mymensingh district. Until the late 18th century the Brahmaputra flowed past the town of Mymensingh and joined the Meghna River near Bhairab Bāzār (the path of the present-day Old Brahmaputra channel). At that time, the course of the Yamuna River (now the main Brahmaputra channel) was a minor stream called the Konai-Jenai, which was probably a spill channel of the Old Brahmaputra. After being reinforced by the Tīsta flood of 1787, the Brahmaputra began to cut a new channel along the Konai-Jenai and gradually converted it after 1810 into the main stream, now known as the Yamuna.

 Along the lower courses of the Ganges and Brahmaputra and along the Meghna, the land is subjected to constant erosion and deposition of silt because of the shifts and changes in these active river courses. Vast areas are subject to large-scale inundation during the monsoon months from June to September. The oscillations of the Yamuna since 1787 have been considerable, and the river is never in exactly the same place for two successive years. Islands and sizable newly deposited lands (chars) in the river appear and disappear seasonally. The chars are valuable to the economy of Bangladesh as additional cultivable areas.

      In Tibet the waters of the Brahmaputra are clear because little silt is carried downstream. As soon as the river enters the Assam Valley, however, the silt load becomes heavy. Because of the speed and volume of water in the northern tributaries that flow down from the rain-soaked Himalayan slopes, their silt load is much heavier than that carried by the tributaries crossing the hard rocks of the old plateau to the south. In Assam the deep channel of the Brahmaputra follows the southern bank closer than the northern. This tendency is reinforced by the silt-laden northern tributaries pushing the channel south.

      Another important hydrographic feature of the river is its tendency to flood. The quantity of water carried by the Brahmaputra in India and Bangladesh is enormous, discharge during the rainy season being estimated at 500,000 cubic feet (14,200 cubic metres) per second. The Assam Valley is enclosed by hill ranges on the north, east, and south and receives more than 100 inches of rainfall annually, while in the Bengal Plain heavy rainfall (70 to 100 inches) is reinforced by the huge discharge of the Tīsta, Torsa, and Jaldhāka rivers. Extensive flooding, aggravated by landslides associated with the Assam earthquake of 1950, is virutally an annual occurrence in the Brahmaputra valley. In addition, tidal surges accompanying tropical cyclones sweeping inland from the Bay of Bengal periodically bring great destruction to the delta region.

Plant and animal life

      Large areas in Assam are covered with forests of sal (valuable timber trees that yield resin), and tall reed jungle grows in the swamps and depressed, water-filled areas (jheels) of the immense floodplains. Around the settlements in the Assam Valley, the many fruit trees yield plantains, papayas, mangoes, and jackfruit. Bamboo thickets abound everywhere.

      The most notable animal of the swamps in Assam is the one-horned rhinoceros, which has become extinct in other parts of the world; Kaziranga National Park provides a refuge for the rhinoceros and for other wildlife in the valley, including elephants, tigers, leopards, wild buffalo, and deer. Numerous varieties of fish include the betki, pabda, ruhi, chital, and mrigal.

The people

      The people living in the different sections of the Brahmaputra valley are of diverse origin and culture. North of the Himalayan rampart, the Tibetans (Tibetan) practice Buddhism and speak the Tibetan language. They engage in animal husbandry and cultivate the valley with irrigation water taken from the river.

      The Assamese are a mixture of Mongolian-Tibetan, Aryan, and Burman ethnic origins. Their language is akin to Bengali, which is spoken in West Bengal state in India and in Bangladesh. Since the late 19th century a vast number of immigrants from the Bengal Plain of Bangladesh have entered the valley, where they have settled to cultivate the almost empty lands, particularly the low floodplains. In the Bengal Plain itself the river flows through an area that is densely populated by the Bengali people, who cultivate the fertile valley. The hilly margins of the plain are inhabited by the hill tribes of the Gāro, Khāsi, and Hajong.

The economy

Irrigation and flood control

      Flood-control schemes and the building of embankments were initiated after 1954. In Bangladesh the Brahmaputra embankment running west of the Yamuna River from north to south helps to control floods. The Tīsta (Tista River) Barrage Project is both an irrigation and a flood-protection scheme.

      Little power has been harnessed along the Brahmaputra or the Assam Valley, although the estimated potential is great—some 12,000 megawatts in India alone. Some hydroelectric stations have been completed in Assam, most notably the Kopili Hydel Project, and others are under construction.

Navigation and transport

      Near La-tzu (Lhatse Dzong) in Tibet, the river opens into a navigable channel for about 400 miles. Coracles (boats made of hides and bamboo) and large ferries ply its waters at 13,000 feet above sea level. The Tsangpo is spanned in several places by suspension bridges.

      Because it flows through a region of heavy rainfall in Assam and Bangladesh, the Brahmaputra is more important for inland navigation than for irrigation. The river has long formed a waterway between West Bengal and Assam, although, on occasion, political conflicts have disrupted the movement of traffic through Bangladesh. The Brahmaputra is navigable throughout the Bengal Plain and Assam upstream to Dibrugarh, 700 miles from the sea. In addition to all types of local craft, powered launches and steamers may easily ply up and down the river, carrying bulky raw materials, timber, and crude oil.

      The Brahmaputra remained unbridged throughout its course in the plains until the Saraighat Bridge—carrying both road and rail traffic—was opened in 1962 near Gauhāti, Assam. A second crossing, the Kalia Bhomora road bridge near Tezpur, was opened in 1987. Ferries, however, have continued as the most important—and in Bangladesh the only—means of crossing the Brahmaputra. Sadiya, Dibrugarh, Jorhāt, Tezpur, Gauhāti, Goālpāra, and Dhuburi are important towns and crossing points in Assam, while Kurīgrām, Rahumāri, Chilmāri, Bāhādurābād Ghāt, Phulchari, Sarishābāri, Jagannāthganj Ghāt, Nagarbāri, Sirājganj, and Goalundo Ghāt are important crossing points in Bangladesh. The railheads are located at Bāhādurābād Ghāt, Phulchari, Jagannāthganj Ghāt, Sirājganj, and Goalundo Ghāt.

Study and exploration

      The upper course of the Brahmaputra was explored as early as the 18th century, although it remained virtually unknown until the 19th century. The explorations of the Indian surveyor Kinthup (reported in 1884) and of J.F. Needham in Assam in 1886 established the Tsangpo River as the upper course of the Brahmaputra. Various British expeditions in the first quarter of the 20th century explored the Tsangpo upstream in Tibet to Jih-k'a-tse, as well as the river's mountain gorges.

Nafis Ahmad Deryck O. Lodrick

Additional Reading

Descriptions of the Brahmaputra are found in surveys of the corresponding regions, such as R.L. Singh (ed.), India: A Regional Geography (1971); and B.C. Law (ed.), Mountains and Rivers of India (1968). The Brahmaputra River and the Assam Valley are treated in H.P. Das, Geography of Assam (1970); The Brahmaputra Beckons (1982), a descriptive anthology; and Jere Van Dyk, “Long Journey of the Brahmaputra,” National Geographic, 174(5):672–711 (November 1988).Deryck O. Lodrick

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