INDUS, one of the three greatest rivers of northern India. Its sources are in the glaciers of the Himalayan peaks of the Kailas group, which overlook the Mansarowar lake and the sources of the Brahmaputra, the Sutlej and the Gogra to the south-east. Three affluents, flowing north-west, unite about 80° E. to form the main stream. At Leh, the Ladakh capital, the river has already run north-westerly for 30o m., except for a divergence to the south-west, which carries it through the Ladakh range, about ioo m. above Leh, to follow the same course on the southern side that had been maintained on the north. For another 23o m. the Indus pursues a comparatively placid north-western course over its sandy bed between the giant chains of Ladakh to the north and Zaskar (the main "snowy range" of the Himalaya) to the south, through magnificent mountain scenery. Then the river receives from the north the waters of the Shyok (a tributary nearly as large as itself), having already been augmented by the Zasvar from the south, together with innumerable minor glacier-fed streams.
The Shyok rises near the southern foot of the Karakoram pass on the high road between Ladakh and Kashgar, drains the southern slopes of the Karakoram range and then breaks across the axis of the Murtagh chain, before bending north-westward to run parallel to the Indus for iso m. before its junction with that river. The combined stream still flows north-west for an other 10o m., under the shadow of a vast array of snow-crowned summits, until it arrives within sight of the Rakapushi peak, mid way between Gilgit and Hunza. Here occurs a change of direction to the south-west, which is thereafter maintained till the Indus reaches the ocean. At this point it receives the Gilgit river from the north-west, having dropped from 15,00o to 4,00o ft. (at the junction of the rivers) after about soo m. of mountain descent through the northern Kashmir. It continues through mountainous country till it emerges into the plains of the Punjab below Dar band, in 34° I o' N.
There are a few native bridges in the upper course, and a wooden bridge at Leh. There are iron bridges above Bunji and at Attock, where the valley narrows almost to a gorge, 90o ft. above sea level. Twenty miles below Attock the river has carved out a central trough believed to be 18o ft. deep. Forty miles below Attock a bridge carries the railway to Kohat and the Kurram valley; and at Mari, beyond the series of gorges which continue from Kushalgarh to the borders of the Kohat district there is a boat-bridge. Another boat-bridge opposite Dera Ismail Khan connects that place with the railway. The Lansdowne bridge at Sukkur is one of the greatest triumphs of Indian bridge-making. Kotri is connected with Hyderabad in Sind, and the Indus is now one of the best-bridged rivers in India. The river is navigated in the plain by high-sterned flat native boats.
In Sind there is much variation in the channel beds within the outside banks of the river. In prehistoric days a branch found its way to the Runn of Cutch, and the gradual shift of the river westward led later to the disappearance of many populous places which were more or less dependent upon it for their water supply. The greatest change was caused when the stream broke through the limestone ridges of Sukkur and assumed a course which has been fairly constant for nearly two centuries. These variations are due largely to the fact that the Indus carries down sufficient detritus to raise its own bed above the general level of the sur rounding plains. At present the bed of the river is stated to be 7o ft. above the plains of the Sind frontier, some 5o m. W. of it.
The total length of the Indus, measured directly, is about 1,5oa m., and the area of its basin is computed at 372,00o sq.m. Even at its lowest in winter it is 50o ft. wide at Iskardo (near the Gilgit junction) and 9 or Io ft. deep. At Attock, where the river nar rows between rocky banks, a height of 5o ft. in the flood season above lowest level is common, with a velocity of 13 m. per hour. At its junction with the Panjnad (the combined rivers of the Punjab east of the Indus) the Panjnad is twice the width of the Indus, but its mean depth is less, and its velocity little more than one-third. Below the junction the united discharge in flood season is 380,00o cu. ft. per sec., rising to 460,000 (record in August). Unusual floods, owing to landslips or other exceptional causes, are not infrequent.
The naturally arid lands of Sind depend largely for their pros perity upon the waters of the Indus. Canals from the river irri gated nearly 3,000,00o acres in 1926, but their water-supply fluctuates with the rise and fall of the river. A vast scheme was therefore undertaken to ensure a continuous supply; it includes a barrage in the gorge below Sukkur, three weirs on the Sutlej, and one on the Panjnad. The scheme is designed to command an area of 7,500,00o acres, and to irrigate over s,000,000 in British territory, Bikaner and Bahawalpur. The Thal irrigation project, also in hand, is intended to irrigate nearly 2,000,000 acres from the Indus on and about the watershed between that river and the Jhelum.