Tarim River - Geography and Hydrology

Geography and Hydrology

The name Tarim is applied to the river formed by the union of the Aksu River, flowing from the north, and Yarkand River, coming from the southwest, near the Aral City in western Xinjiang. The third river, the Khotan River comes to the same junction area from the south, but it is usually dry at this location, as it has to cross the Taklamakan Desert to get here.

Another river of western Xinjiang is the Kashgar River, which falls (at least theoretically, i.e., when it has water in it) into the Yarkand River some 37 km (23 mi) upstream from the Yarkand's merger with the Aksu. By another definition, however, Tarim starts at the Kashgar/Yarkand merger, and Aksu, then, is considered just a tributary of the Tarim.

The Tarim flows in an eastward direction around the northern edge of the Taklamakan Desert. It receives another tributary, the Muzat River from the north; however, out of these four rivers (Aksu, Yarkand, Khotan, and Muzart), only the Aksu flows into the Tarim year-round It is the Tarim's most important tributary, supplying 70–80 percent of its water volume.

The word 'tarim' is used to designate the bank of a river that flows into a lake or that is not able to be differentiated from the sands of a desert. This is a characteristic hydrographic feature of many rivers that traverse the sands of the Taklamakan Desert.

Another characteristic of the rivers of the Tarim Basin, including the Tarim River itself, is their active migration, that is, the shifting of their beds and banks.

The total length of the Yarkand-Tarim river system is 2,030 km (1,261 mi), although, as the Tarim frequently changes its channel, the length tends to vary over the years. It is shallow, unsuitable for navigation, and because of its heavy silt load, forms a braided stream near its terminus. Prior to the completion of reservoirs and irrigation works in the mid-20th century, the Tarim's waters eventually reached Lop Nur (now a salt-encrusted lake bed). The river's waters now drain intermittently into Taitema Lake, which is located about 160 km (100 mi) southwest of Lop Nur. The area of the Tarim River Basin is about 557,000 square km (215,000 square mi). A considerable part of the Tarim's course is unformed, following no clearly defined riverbed. The water volume of the lower course of the river diminishes as a result of extensive evaporation and water-diversion schemes.

The Tarim's low-water period is from October through April. The spring and summer high waters begin in May and continue through September as the snows melt on the distant Tian Shan and Kunlun mountains.

The Lower Tarim Basin is an arid plain composed of alluvium and lake sediments and is bordered by massive mountain ranges. The basin is the driest region of Eurasia. The predominant part of it is occupied by the Taklamakan Desert, whose sand area exceeds 270,000 square km (105,000 square mi). In addition, there are several comparatively small sand massifs with areas of from 780 to 4,400 square km (300 to 1,700 square mi). Sand dunes are the predominant relief.

Precipitation in the Tarim Basin is extremely scanty, and in some years it is nonexistent. In the Taklamakan Desert and in the Lop Nur basin, the average annual total of precipitation is about 12 mm (0.5 in). In the foothills and in several other areas of the river's basin, the precipitation amounts to from 50 to 100 mm (2 to 4 inches) a year. In the Tian Shan it is much wetter, precipitation often exceeding 20 inches (500 mm). Maximum temperatures in the Tarim Basin are about 40°C (104°F). The Tarim River freezes over every year from December through March.