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drainage system[′drān·ij ‚sis·təm]
an excessively wet land area with a network of channels, drains, and hydraulic engineering and other structures that provide for drainage. The main elements of a drainage system are the regulating, protective, and conducting networks, which make up the drainage network; the water relief system, that is, the body of water, such as river, lake, or sea, receiving the drained water; the hydraulic engineering structures (overfalls, channel openings, sluices, manholes, and pumping stations); the road network (roads, bridges, culverts, and livestock crossings); and the operating structures (benchmarks, observation shafts).
Drainage systems may be open or closed (subsurface), depending on the drainage method. In the open system, open channels are used as the regulating network, whereas in the closed system, the regulating network is made up of closed collectors and has underground drains and small channels. In both systems, the main conducting and protective channels are open. Open drainage systems are used for the initial drainage of marshes and forests and sometimes also of hayfields and pastures. Their drawbacks include a reduction in land available for cultivation, interference with mechanized farming operations, and overgrowth with weeds and other types of interference in the channels. Closed drainage systems are technically more advanced and long-lasting. They do not have the shortcomings of open systems, and they offer great potential for irrigation of drained lands during dry periods of the growing season. Such systems are built for intensive use of drained lands (vegetable, fodder, and field crop rotations; orchards; crop pastures).
The water relief system is an essential part of the drainage system, and it is usually a river or reservoir that can accept the excess water from the drainage network without backing up. In rare cases where the hydrogeological conditions are favorable, water is discharged into underground water-bearing horizons in which inverted drainage wells have been installed. If the characteristics of the water relief system are unsatisfactory (inadequate capacity, high water levels during periods of drainage network operation, unstable channel), the system is regulated by cleaning, straightening, deepening, and widening or narrowing the channel.
In terms of the method of removing water from the drainage network, drainage systems are subdivided into gravity systems, in which the water flows out of the drainage system by gravity, and pump systems, in which water is pumped from the main channels. Pump outlets are usually used for draining coastal lowlands (the reclamation of polders in Kaliningrad Oblast and elsewhere), low-lying river and lake floodplains (for example, the Neman and Lielupe rivers, and the widening of the Moskva River floodplain near Ramenskoe), and marshy river flats (the Kuban’ and Dnestr rivers), where gravity systems are virtually impossible. Water is also pumped to drain lands in national parks and forest preserves in zones of inadequate moisture, where regulation of the rivers can reduce their natural attractiveness and recreational value. The construction and operation of pump systems are more expensive than gravity systems, but pump systems are economically more efficient for intensive agricultural production.
In terms of the nature of influence on the water regime of the area being drained, drainage systems are subdivided into systems with one-way action (channels and other structures that provide only water removal) and two-way systems (drainage-irrigation systems), in which the water regime is regulated by retention and redistribution during periods of excessive water supply and then by supplemementing soil reserves during dry periods. Moisture is added to the soil by sprinkling or subsoil irrigation with sluices and drains. Water can be removed and added by the same elements of the drainage system; for example, the main drainage channels and water relief channels are both the source of water and conducting irrigation canals; the drains also operate to supply moisture to the area. The use of two-way systems makes it possible to maintain throughout the growing season a close to optimum water regime for agricultural plants in the root zone of the soil.
The design of a drainage system depends on the soil and on the hydrogeological, economic, and other conditions of the terrain. In the USSR, drainage systems are operated by system administrations, regional land-reclamation services, and the land users to whom the drained lands are assigned.
During the years of Soviet power, drainage systems have been built and modernized on millions of hectares in the USSR. The Oressa Drainage System, which is located in the Oressa River basin (Byelorussia), covers 98,500 hectares (ha), of which 51,500 ha is moistened by drains during dry periods using water from a reservoir with a volume of 39.5 million cu m that was constructed in the upper part of the system. Vegetables, grains, and grasses are grown on drained lands. The Trubezh Drainage System (natural flow, two-way) in the floodplain of the Trubezh River and its tributaries in the Ukraine has a drainage area of 32,500 ha. The main crops are vegetables (including potatoes), silage corn, grasses, and root crops for fodder. The Iakhroma Drainage System, in the floodplain of the Iakhroma River (Moscow Oblast), covers about 10,000 ha; most of the system operates two ways (irrigation by sprinkling), and vegetables and fodder crops are raised.
B. S. MASLOV
a ship’s system that is used to remove small quantities of water that enter the vessel. Independent drainage systems service individual compartments or groups of compartments, such as the engine room, the holds (on dry-cargo vessels), the pump compartments (on tankers), and the magazines (on warships). A drainage system consists of pipelines with inlet and discharge pipes, pumps, and accessories, together with separators that cleanse the bilge water of polluting petroleum products. On modern vessels the pumps in the drainage systems start automatically according to the water level in the bilge.