BRAHMAPUTRA, a great river of India, with a total length of 1,800 miles. Its source is in a great glacier-mass of the north ernmost chain of the Himalayas, called Kubigangri, in the south west of Tibet, about 82° E. Tributaries join the infant river from the pass of Mayum La (15,5ooft.), which separates its basin from the Manasarowar lake district, in which two other great Indian rivers, the Indus and Sutlej, have their source. The river flows through southern Tibet for about loom., keeping a course roughly parallel to, and Loom. from, the main chain of the Himalayas. It is known as the Tsangpo, meaning in Tibetan "the purifier," but this is not a distinctive name, for it is applied to any large river; the Tibetans themselves call it by different names in different parts of its course. It receives many tributaries, of which the most im portant are :—on the left bank, the Raka Tsangpo, which joins it west of Shigatse, and the Kyi Chu, a river as broad as the Thames and twice as long, on which stands the sacred city of Lhasa; on the right bank, the Nyang Chu, which flows by the large trade cen tre of Gyantse. The principal place on the Tsangpo itself is Shi gatse, the second town of Tibet, with (half a mile away) the great monastery of Tashilhiinpo, the seat of the Tashi Lama.
From Lhatse near 88° E. to a day's journey below Tse-tang (II,85oft.) 5orn. south-east of Lhasa the Tsangpo has a wide navi gable channel. It is one of the most remarkable inland systems of navigation in the world, for boats go up and down it for 400m. at a height of 12,000f t. and more above sea-level. The boats are simply coracles made of hide stretched over withy frameworks. Large ferry boats, shaped like oblong boxes, ply in some places. Elsewhere there are suspension bridges made mainly of bamboos and in a few cases with heavy iron chains supporting the sides and narrow footway : some have a span of 30o ft.
At Tsela Dzong the Tsangpo is joined from the north by the Gyamda, 2m. wide at the point of junction. Further east at Pe (9,68oft.) the river is still a broad placid stretch of water, 66o yards wide. Then turning abruptly to the north-east and north it makes its way by a succession of stupendous gorges between the huge mountain masses of Gyala Peri (23, 740f t.) and Namcha Barwa (25,445ft.), which are in one place only 8m. apart. Through these deep narrow gorges the Tsangpo rushes tumultuously down in a series of cascades and rapids, turning the flank of the range in a hair-pin bend. It takes up from the north the Po Tsangpo, a swift torrent 8o yards wide, and then turning to the south and south-west emerges from the foothills under the name of the Di hang and flows past the frontier station of Sadiya (44oft.) into the Assam valley. Near Sadiya it receives from the north the Dibang and from the east a stream, which, as it flows in the same direction as the main river, is wrongly called by the Assamese the Brahma putra. From the point of junction the mighty river, which is now for the first time known by the Indian name of Brahmaputra, i.e., the son of Brahma, rolls majestically down the Assam valley for a length of 450 miles. Its channels oscillate from side to side over a bed some 6m. wide and it forms many islands, one of which, Ma juli, has an area of 485 square miles. In times of flood it overflows its banks and, spreading over the sandy grass-covered flats on either side, resembles an inland sea.
Sweeping round the spurs of the Garo hills, the river enters the alluvial plains of Bengal, through which it flows for another Isom. until it joins the Ganges at Goalundo. The united stream of the two rivers flows south-east under the name of the Padma and makes its exit into the Bay of Bengal by the broad estuary of the Meghna. Till the end of the 18th century the Brahmaputra flowed through the centre of the district of Mymensingh to join the Gan ges near Bhairab Bazar, but in the early part of the next century, as this channel became choked with silt, the stream deserted it moving westward across the friable soil of the delta cut out its present channel along the western boundary of Mymensingh.
It has well been said that the Brahmaputra for its size and utility ranks among the most important rivers in the world. It is 250m. longer than the Ganges. It drains an area of 361,000sq.m. and its flood-discharge during the rainy season, when its level rises 3o to 4oft., has been estimated at 50o,000cu.ft. per second. It not only builds up land, but also fertilizes it and distributes its prod uce. It is the highway of commerce between Assam and Bengal. Unbridged throughout its length in British territory it is navigable by steamers as far as Dibrugarh, Boom. from the sea. Its value in irrigating and fertilizing the land of the delta cannot be estimated. During the rains a turgid volume of water spreads over the coun try; the silt with which it is loaded is left behind; and the soil, enriched without labour to the cultivator, yields rich crops.
The upper course of the Brahmaputra was long air unsolved mystery ; it was even thought at one time that the Tsangpo might be the upper channel of the Irrawaddy and might thus have no connection with the Brahmaputra. Full and certain knowledge of its course has been gained only during the present century. The explorations of Kinthup, an Indian surveyor, along the Tsangpo as far as Pemakochung in 1884 and of Needham up the Dihang in 1886 first established the identity of the Tsangpo and Brahmaputra beyond reasonable doubt. Capt. C. G. Rawling, with Capt. C. H. D. Ryder, Capt. H. Wood and Lieut. F. Bailey marched up the Tsangpo from Shigatse to its source in 1904-05 ; but its course from Pemakochung through the Himalayas to its debouchment in the Abor hills of Assam remained a mystery. It was known that after flowing at a level of 12,000f t. on one side of the range it reappeared at 1,000f t. on the other ; and it was thought that there might be tremendous waterfalls hidden away in the mountains. Exploration was barred by the hostility of savage tribes, but in 1913, after the Abor expedition had inspired them with wholesome respect, Capt. F. M. Bailey and Capt. H. T. Morshead explored mom. of the river and found marvellous gorges and rapids but no falls of over 3oft. A gap of 5om. still remained, but the last ves tiges of doubt were removed in 1924 by Capt. Kingdon Ward, who found that in this part of its course also the river descends not by great waterfalls but by rapids and cascades pent in towering cliffs and narrowing down in one place to a width of 3o yards.