Fergana Basin

(also Fergana Valley, Fergana), an intermontane basin in Middle Asia, between the mountain systems of the Tien-Shan in the north and the Gissar-Alai in the south. Most of it is located in the Uzbek SSR; part of it lies in the Kirghiz and Tadzhik SSR’s. The basin forms a triangle, with the northern slopes of the Turkestan and Alai ranges forming a wide base. It is bordered by the Kuram and Chatkal ranges on the northwest and the Fergana Range on the northeast. In the west, a narrow pass connects it with the plain of the Golodnaia Steppe. The basin is approximately 300 km long and up to 170 km wide and has an area of 22,000 sq km.

The tectonic trough of the Fergana Basin is filled with loose deposits that come from the surrounding mountains. The surface of the flat aggradational floor is composed of Anthropogenic (Quaternary) alluvial and proluvial-alluvial sediments. The elevation increases from 320 m in the west to 500–1,000 m in the east. On the flat terraces, the Sokh, Isfara, and other rivers terminate in alluvial fans, along which the river channels disperse. The southeastern part of the basin is separated from the rest of the basin by a belt of adyry (low foothills) composed of Neogenic and Anthropogenic (Quaternary) loess and pebble beds; in the northwest, low ridges of Paleogenic and Neogenic variegated rocks, reaching elevations of 854 m at Okbel’ and 1,009 m at Mekhautauk, stretch along the Syr Darya. The belt of adyry gives way to foothills, composed of Mesozoic, Cenozoic, and Paleozoic limestones and shales. The Fergana Basin is a highly seismic region. The periphery of the floor and the surrounding foothills and mountains contain deposits of petroleum, coal, iron, copper, and complex-metallic ores, as well as mercury, antimony, sulfur, rock salt, and other minerals.

The climate is dry and continental. Summers are very warm, with an average July temperature of 24°—27°C and a maximum of nearly 40°C. Winters are mild, with an average January temperature of –2° or –3°C. Annual precipitation in the central basin floor is 100–120 mm, increasing to 500 mm in the east.

The Syr Darya, which originates in the eastern part of the basin by the confluence of the Naryn and Karadar’ia rivers, is the principal river and is used for irrigation. Most of the rivers flowing from the mountains are almost entirely diverted for irrigation. Most of the rivers are fed by mixed sources, primarily glaciers and snow; in the northwest they are fed mainly by groundwater. The Great Fergana and Southern Fergana canals have been built on the southern periphery of the basin floor, and in the west, the Kairakkum Reservoir has been created on the Syr Darya. A virtually continuous strip of oases, which includes the Fergana Oasis, stretches along the perimeter of the basin floor, which consists of solonchaks and deflation sands; it is interrupted only in the northwest, where the slopes of the Kurama Range have no copious rivers.

The Fergana Basin is a center for cotton growing, sericulture, and viticulture. The oases contain cotton fields and some rice paddies, as well as orchards, vineyards, and plantings of melons, gourds, and vegetables. The virgin desert lands of the central part of the basin are being brought under cultivation. Tracts of desert plains are used for pasture throughout the year, and the adyry, with their ephemeral vegetation, are used for spring grazing. Grain crops are raised by dry farming. Forests of walnut, apple, and cherry plum trees are found on the slopes of the Fergana and Chatkal ranges.

The Fergana Basin is one of the most heavily populated regions of Middle Asia and contains the cities of Leninabad, Kokand, Fergana, Andizhan, Namangan, and Osh.