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Irtysh(ĭrtĭsh`), river, c.2,650 mi (4,260 km) long, W Siberian Russia and Kazakhstan. It is the chief tributary of the Ob and one of the two major rivers of W Siberia. As the Ertix, it rises in Xinjiang, China, in the Mongolian Altai Mts., flows NW through Lake Zaysan in Kazakhstan (where it is known as the Ertis), and enters W Siberia. There it receives the Ishim and Tobol rivers, its chief tributaries. The Irtysh flows past Semey in Kazakhstan and Omsk and Tobolsk in Russia and joins the Ob near Khanty-Mansiysk. Major hydroelectric stations are at Öskemen and Zhana Buktyrma, Kazakstan. The river banks were occupied by Chinese, Kalmyks, and Mongols until the Russians arrived in the late 16th cent. The Russian conquest of the basin was completed by the early 19th cent.
a river in the Kazakh SSR (Vostochnyi Kazakhstan, Semipalatinsk, and Pavlodar oblasts) and the RSFSR (Omsk and Tiumen’ oblasts); left-bank tributary of the Ob’. Length, 4,248 km. Basin area, 1,643,000 sq km.
The Irtysh rises in China in the Mongolian Altai Mountains and bears the name Chernyi Irtysh until it discharges into Lake Zaisan. In its upper course, as far as the city of Semipalatinsk, it has the features of a plain-and-mountain river. Owing to the construction of the Ust’-Kamenogorsk and the Bukhtarma hydroelectric power plants, the Irtysh has been transformed into large reservoirs up to the city of Ust’-Kamenogorsk; Lake Zaisan has become part of the Bukhtarma Reservoir. Below Ust’-Kamenogorsk the valley of the Irtysh widens. In this section the Kal’dzhir, Kurchum, Narym, Bukhtarma, Ul’ba, and Uba rivers empty into the Irtysh and its reservoirs from the right, and the Kyzylsu and Char enter from the left. Below Semipalatinsk the Irtysh emerges onto the West Siberian Plain and flows northwest amid dry steppes, without receiving any significant affluents as far as Omsk. Undrained land and areas of internal drainage are located here. The channel is unstable: one moment it is very tortuous, the next it divides into branches; it has numerous sandy shoals. Below Omsk the Irtysh forms large meanders. The valley is wide, up to 20 km across and as much as 35 km near the mouth. At the mouth of the Tobol the Irtysh veers sharply north and flows through the most marsh-ridden part of the West Siberian Plain, the channel becoming even more winding. The tributaries here are the Om’ on the right and the Ishim and Tobol on the left.
The Irtysh is fed by various sources: in its upper course by snow and glaciers, and, to a lesser degree, by rain, and in its lower course by snow, rain, and groundwater. The character of its stream-flow regime also changes considerably. In the upper course the high-water period begins in April, the peak water level extends from April to June, and the lowering of the water level lasts until October; the river’s flow is regulated. In the lower course high water lasts from the end of May until September, attaining its maximum level in June. Fifty percent of the annual discharge runs through in the spring; in the upper course the proportion of the discharge in summer and fall is 20 percent in each of these seasons and 10 percent in winter; at Tobol’sk the figures are 27, 19, and 7 percent, respectively. The average discharge (in cu m per sec) is 628 at Ust’-Kamenogorsk, about 960 at Semipalatinsk, 917 at Omsk, and 2,150 at Tobol’sk; at the mouth the annual discharge is approximately 95 cu km. The range of water-level fluctuation above Lake Zaisan is 4.4 m, at Omsk it is 7m, and at Ust’-Ishim it is 12.7 m; the range diminishes toward the mouth. Before becoming icebound the Irtysh has a period of floating ice lasting 20 days in the upper course and six to ten days in the lower course. The Irtysh freezes over in late November in its upper course and in early November in its lower course; ice breaks up in April.
The river is rich in fish—nelma, pike, perch, sturgeon, sterlet, burbot, ide, and bream. The waters of the Irtysh are used to feed the Irtysh-Karaganda Canal (intake of Irtysh water into the canal averaging 75 cu m per second), as a water supply, and for irrigation. There is regular navigation on the Irtysh from the tail water of the Ust’-Kamenogorsk Hydroelectric Power Plant to the mouth. The principal landings are Ust’-Kamenogorsk, Semipalatinsk, Pavlodar, Omsk, Tara, Tobol’sk, and Khanty-Mansiisk.
K. G. TIKHOTSKU