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a land area, together with the network of canals and other hydraulic-engineering and operating structures that ensure its irrigation. In addition to the land, systems for regular irrigation include a main water-intake unit, which draws water from a source (river, reservoir, canal, or well) and protects the system from debris, slush, and trash; an irrigation network; a runoff network; a collector-drainage network, which lowers the level of groundwater and carries water and salts away from the territory being irrigated; hydraulic-engineering structures, which regulate water intake (regulator sluices, water-lifting structures, and so on) and its distribution over the area being irrigated; operating structures, such as roads and devices for observing the condition of the land being irrigated; and wooded strips.
Irrigation systems may have gravity-flow water intake, in which the water enters the canals from the source under natural flow, or systems with mechanical water-lifting, in which the water is supplied by a pumping station. In terms of design, systems are subdivided into open, closed (pipeline), and combination systems. Open irrigation systems are the most common; they have chute canals or canals in earthen channels (usually with concrete, reinforced-concrete, asphalt, and synthetic materials used to protect against seepage). Among the open systems are rice systems, in which the entire area is divided by earthen ridges into fields, and the fields are divided into smaller sectors called paddies (4–10 hectares [ha]).
Closed irrigation systems may be permanent, semipermanent, or mobile; they use pipes (ordinarily underground) instead of canals. In permanent systems, all the elements are permanent. Irrigation is done by the sprinkling method (long-stream or medium-stream sprinklers attached to the irrigation pipes). The system for irrigating perennial crop pastures may consist of a well or a pumping station on a river and a sprinkler (for example, the Fregat sprinkler). Semipermanent irrigation systems usually have permanent distribution pipes and sectional irrigation pipes, which are connected to irrigation hoses or sprinkler vanes. In mobile systems, all the pipes are sectional. Closed irrigation systems ensure high system efficiency (ratio of the flow of water supplied to the discharge from the source), do not cause deterioration of the reclamation condition of the irrigated area, make possible economizing of water use, provide a high coefficient of land use and use of machinery and mechanisms in the fields, and facilitate automation of water distribution by sections (program control), including sections with complex terrain. At the same time, closed irrigation systems typically are very expensive to build and operate and are more complex in operation.
Large combination irrigation systems usually consist of open main canals and interfarm distribution canals, often with concrete channels and piped intrafarm irrigation networks; the irrigation technique varies (sprinkling, furrows, and so on). The Verkhniaia Samgori system in Georgia (irrigated area, 100,000 ha) is an example of a combined system. In addition to irrigation systems for regular irrigation there are systems of catchwork irrigation and irrigation-flooding systems. Irrigation systems are designed on the basis of technical and economic comparison of various versions for the specific planning conditions. In the USSR, interfarm systems are operated by basin and oblast regional administrations and administrations for interregional canals, and intrafarm systems are operated by the hydraulic-engineering departments of sovkhozes and the irrigation sections of kolkhozes.
During the years of Soviet power, irrigation systems that cover millions of hectares have been built and restored in the USSR. Some examples are the Kuban’-Kalaus system (irrigated area, 200,000 ha; water supply for 3 million ha), the Terek-Kuma system (irrigates and waters 2.2 million ha), and the Northern Crimean system (irrigates 165,000 ha) and the irrigation systems in the Amu Darya River basin (1.3 million ha) and the Golodnaia Steppe (more than 500,000 ha). Large modern irrigation systems are under construction—for example, the Karshi system (irrigated area, 900,000 ha; 25 percent of the area will have closed irrigation, and 75 percent will have a chute network; plans call for 350,000 ha to be in operation by 1985; see Figure 1), the Southern Golodnaia Steppe system (787,000 ha, including 504,000 by 1975 in the zone of new irrigation), and the Kakhovka system (600,000–650,000 ha; construction to be completed by 1985).
REFERENCESKostiakov, A. N. Osnovy melioratsii, 6th ed. Moscow, 1960.
Zaitsev, V. B. Risovaia orositel’naia sistema, 2nd ed. Moscow, 1968.
Bagrov, M. N., and I. P. Kruzhilin. Orositel’nye sistemy i ikh ekspluatatsiia. Moscow, 1971.
Natal’chuk, M. F. Ekspluatatsiia orositel’nykh sistem. Moscow, 1971.
N. G. RAEVSKAIA