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reservoir (rĕzˈəvôr, –vwär), storage tank or wholly or partly artificial lake for storing water. Building an embankment or dam to preserve a supply of water for irrigation is an ancient practice; India and Egypt have many old and large reservoirs. In building artificial lakes for a municipal water supply it is necessary to consider all the aspects of a catchment area, including the amount and distribution of rainfall, evaporation, runoff, soil or rock conditions, and elevation (for its effect upon precipitation and upon the pressure in the conducting pipes). The ground of the reservoir may be naturally impervious enough to prevent excessive seepage, or a clay or other lining may have to be built. The embankments or retaining walls may be of earth, loose rock, or masonry. Earth forms a good embankment but must be sealed by a core of clay, and the face must be covered with masonry or a similar substance to prevent erosion. Distributing reservoirs in towns are sometimes built of masonry or of reinforced concrete. They serve to cope with fluctuations of demand and with interruptions of supply from the source. Reservoirs are also built on the headstreams of or along the courses of rivers to aid in flood control, on canals to maintain water level for navigation, and to ensure water supply for hydroelectric plants. Some reservoirs are built on the tributaries of large rivers to act as catch basins for silt. In addition to seepage, the major loss of water from a reservoir is by evaporation; chemicals that form a film on a water surface are used to minimize such losses. Covered tanks made of prestressed concrete are used for limited local water supply.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



in hydroelectric power engineering.

Pressure reservoir of a hydroelectric power plant. A structure that connects the nonpressured water supply of the power plant with the turbine conduits and serves to eliminate litter, sludge, and ice from the flow and also to discharge excess water in case of sudden cutting off of the hydraulic units from the power system. In terms of construction, a pressure reservoir is a part of the channel that is smoothly increasing in plan and elevation, ending in a retaining structure where intake basins for the turbine water pipelines are located.

Daily regulation reservoir. The daily regulation reservoir of a hydroelectric power plant is an artificial reservoir that is built at the plant with nonpressured supply to regulate the diurnal water flow required by the station; it is located in the immediate vicinity of the pressure reservoir and is connected to it by a short canal. Depending on the local conditions, the diurnal regulating reservoir can adjoin the supply or be placed on its route. Reservoirs are built in the form of an excavation in the ground, a partial excavation, or a partial embankment; the perimeter is enclosed by earthen dikes or reinforced-concrete walls. A dip in the local topography is usually utilized in its construction.

Equalizing reservoir. The equalizing reservoir of a hydroelectric power plant is an artificial reservoir in the after-bay of the plant that serves to equalize the nonuniform discharges of water (as a result of the diurnal regulation) coming from the turbines.


Argunov, P. P. Gidroelektrostantsii. Kiev, 1960.
Sokolov, D. la. Ispol’zovanie vodnoi energii, part 2. Moscow, 1965.




an artificial body of water that is formed, as a rule, in a river valley by hydrostatic structures; water is collected and stored in it for use in the national economy. Reservoirs are characterized by increased depth toward the dam, with the exception of those that include deep lakes; extremely slow water exchange and flow velocity compared to rivers; instability of summer thermal and gas stratification; and certain other peculiarities of the hydrological regime.

Reservoirs are created to redistribute the flow of rivers with respect to time and, with canals and other water-conveying structures, to area. They form the base of a comprehensive utilization of water resources. The need for reservoirs is caused by the great unevenness in the distribution of river discharge during the course of the year, as well as its unequal territorial distribution. Reservoirs may have diurnal, weekly, seasonal (or yearly), and even longer periods of regulation.

The volume of a reservoir’s water mass—and consequently its surface area, depth, and so on—is subject to seasonal changes associated with the irregularity of the natural water flow, as well as of the consumption of water for the needs of the national economy. Reservoirs are built in widely diverse sizes, ranging from several dozen hectares to several thousand square kilometers in area and from hundreds of thousands of cubic meters to hundreds of cubic kilometers in volume (see Table 1). According to data of the Institute of Water Problems of the Academy of Sciences of the USSR, the total volume of reservoirs in operation or under construction as of Jan. 1, 1971, was approximately 5,000 cu km. The total usable reservoir volume of the entire world at the beginning of the 1%0’s was 2,050 cu km, including 755 in America, 525 in Asia, 460 in Africa, 280 in Europe, and 30 in Australia (according to calculations made by M. A. Fortunatov).

The following levels are distinguished in a reservoir: the normal affluent level (or horizontal affluent level)—the highest affluent level the dam can support over a long period while ensuring the normal operation of all installations; the forced affluent level—the highest level that can be supported for a relatively brief time during the passage of floodwaters, ensuring the maintenance of the installations; and the level of stagnant volume—the minimum allowable level under conditions of normal operation.

The creation of reservoirs causes essential changes in the terrain of river valleys, and their regulation of the river’s flow transforms the natural hydrological regime within the back-water. Changes in the hydrological regime caused by the creation of reservoirs also occur in the tail waters of hydraulic-engineering complexes, sometimes for dozens and even hundreds of kilometers. The decrease in high-water periods, as a result of which the conditions for the spawning of fish and the growth of grasses in the river marshes deteriorate, is of great importance. A decrease in the flow velocity causes the precipitation of alluvium and the silting-up of reservoirs; the temperature and ice cycles change, and in winter a polynya, which is sometimes dozens of kilometers long and which does not freeze over, forms in the tail water. The height of wind waves on reservoirs is higher than on rivers (3 m and more). The hydrobiological regime of reservoirs differs essentially from the regime of rivers; the biomass in a reservoir forms more intensively, and the variety of flora and fauna changes. Floating islands of peat mold ranging from several square meters to hundreds of hectares appear in a number of reservoirs during their first few years of operation.

Depending on their configuration, intensity of water exchange, and, consequently, their hydrological regime, reservoirs are divided into lake and river types. Lake reservoirs (for example, Rybinsk) are characterized by the formation of water masses whose physical properties differ essentially from those of the tributary waters. The currents in these reservoirs are primarily governed by the winds. River reservoirs (Dubossary and others) are smaller; their currents are governed by gravity, and their water masses closely resemble river waters.

The creation of a reservoir brings about many changes in the terrain and economy of the surrounding region. There is flooding, partial flooding, and washing out of the lands along the banks, on which fallow and cultivated lands, populated areas, industrial enterprises, and transportation routes were located; economic and transportation links, as well as conditions in public health, hygiene, and the fishing industry, change. The effect of a reservoir on the climate increases with the size of its water mass. Large reservoirs exert a relatively noticeable influence on the climate within a fairly narrow zone (3-10 km wide) along the banks, resulting in less abrupt diurnal and annual temperature variations and increased atmospheric humidity.

After 1950 certain regions with well-developed industry

Table 1. Largest reservoirs of the world
 RiverCountryTotal volume
(cu km)
Water surface
area (sq km)
1 With Lake Victoria as a backwater 2 With Lake Baikal as a backwater 3 Planned for 204.8 cu km
Bratsk . . . . . . . .AngaraUSSR169.35,470
Kariba . . . . . . . .ZambeziZambia, Southern Rhodesia160.44,450
Nasr . . . . . . . .NileEgypt, Sudan157.05,120
Volta . . . . . . . .VoltaGhana148.08,480
Manicouaoane–5 . . . . . . . .ManicouaganeCanada142.01,940
Krasnoiarsk . . . . . . . .EniseiUSSR73.32,000
Portage Mountain. . . . . . . .PeaceCanada70.11,760
Owen Falls’ . . . . . . . .Victoria NileUganda, Kenya,Tanzania68.03
Wadi Tartar . . . . . . . .TigrisIraq67.02,000
Sanmin hsia. . . . . . . .Hwang HoChinese People’s Republic65.03,500
Kuibyshev . . . . . . . .VolgaUSSR58.06,448
Bukhtarma . . . . . . . .IrtyshUSSR53.05,500
Irkutsk2 . . . . . . . .AngaraUSSR48.5
Lake Mead. . . . . . . .ColoradoUSA36.7631
Glen Canyon. . . . . . . .ColoradoUSA33.3646
Volgograd . . . . . . . .VolgaUSSR31.53,117

this has affected not only regions of small and even discharge but also those where the natural discharge was sufficient while industry was still poorly developed. A radical method —in many cases the only method—of eliminating the unevenness in the flow distribution of rivers is the construction of a reservoir. Most reservoirs are created in the interests of several branches of the economy—that is, for complex utilization.

There are about 1,000 reservoirs with a volume of more than 1 million cu m each in use or in preparation in the USSR; of this number, 150 have a volume of over 100 million cu m. In the USSR reservoirs are needed for irrigation and for water supply (most of the reservoirs in the southern regions—Kaira, Chardara, Minchegaur, and Toktogul); for water supply to cities and industrial enterprises (Ivan’kovskii, Mozhaisk, Iriklinskii, Magnitogorsk, Krasnyi Oskol, and others), and for hydroelectric power engineering (Bratsk, Krasnoiarsk, and many others). In addition to regulating the flow of water in the interests of hydroelectric power production, the reservoirs of the Volga-Kama and Dnieper power grids have improved irrigation, navigation, flotation of logs, flood control, and recreation. In the Far East, the Caucasus, the Carpathians, and other regions, reservoirs are of great importance in combating floods (Zeia, Minchegaur, and others). The composition and importance of individual sections of a water-management complex change not only with regard to the region of the country but also over time in connection with the development of the economy and hydraulic-engineering construction.

Abroad the greatest number of reservoirs are in the USA, India, Brazil, Spain, Mexico, Canada, Australia, and Japan. The USA has more than 1,500 reservoirs with a volume of over 6 million cu m, of which 468 have a volume exceeding 100 million cu m. In countries with water shortages, reservoirs are being created to improve water supply and irrigation. In the mountainous regions of many countries a large number of reservoirs have been formed by the dams of hydroelectric power plants.

In the head races and tail waters of hydraulic-engineering complexes, steps taken in conjunction with the creation of reservoirs include protection of areas on which important installations and valuable farmlands are located (embanking, drainage, shore reinforcement, and so on); organization of land use under the new conditions; resettlement of inhabitants; transfer, reconstruction, new construction, or demolition of structures and installations; felling of timber; and transfer of archaeological and other monuments.


Sanitation and public health measures. In preparing the bed of a reservoir, refuse and waste products from enterprises are either removed from the area to be flooded or are disinfected in place, plowed under, and so on. Forests are cleared, and the graves are moved. Public health agencies supervise the transfer of people from the zone to be flooded and select the place where they will be resettled. Basic measures for the protection of public health once the reservoir is in use include control over the location of cities and industrial installations on the banks of the reservoir, regulation of sewage discharge, and the equipping of boats that sail on the reservoir with holding tanks. In connection with any possible change in the epidemiology of the reservoir zone, public health agencies undertake measures to prevent malaria, tularemia, and other diseases. Sanitation requirements in the construction of reservoirs are regulated by the Sanitation Rules for the Preparation, Flooding, and Sanitary Protection of Reservoir Beds (1957).



Kritskii, S. N., and M. F. Menkel’. Vodokhoziaistvennye raschety, Leningrad, 1952.
Bogatyrev, V. V.Inzhenernaia zashchita v zonakh vodokhranilishch krupnykh gidroelektrostantsii. Moscow-Leningrad, 1958.
Grishin, M. M. Gidrotekhnicheskie sooruzheniia. Moscow, 1968.
Fortunatov,, M. A. Problema sooruzheniia vodokhranilishch i predvaritel’nye itogi ikh ucheta v razlichnykh chastiakh sveta: Materialy I nauchno-tekhnicheskogo soveshchaniia po izucheniiu Kuibyshevskogo vodokhranilishcha, part 1. Kuibyshev, 1963.
Kibal’chich, I. A. Sanitarnye voprosy gidrostroitel’stva. Moscow, 1965.
Rumiantsev, A. M. Regulirovanie ispol’zovaniia vodnykh resursov vodokhranilishch. Moscow-Leningrad, 1966.
Gidroenergeticheskie resursy. Moscow, 1967. (Energeticheskie resursy SSSR.)
Avakian, A. B., and V. A. Sharapov. Vodokhranilishcha gidroelektrostantsii SSSR. Moscow-Leningrad, 1968.
Rol’ vodokhranilishch v izmenenii prirodnykh uslovii. Moscow, 1968.
Kalinin, G. P. Problemy global’noi gidrologii. Leningrad. 1968.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

What does it mean when you dream about a reservoir?

A dream about a reservoir may indicate that the dreamer has stored up emotional energy, especially if the reservoir is full. If it appears to be empty, the dreamer may have expended all available emotions on others.

The Dream Encyclopedia, Second Edition © 2009 Visible Ink Press®. All rights reserved.


(civil engineering)
A pond or lake built for storage of water, usually by the construction of a dam across a river.
A subsurface accumulation of crude oil or natural gas under adequate trap conditions.
An area covered by névé where snow collects to form a glacier.
A space within the earth that is occupied by magma.
(science and technology)
A container for storage of a liquid material, for example, a tank.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


A place or containment area where water is stored. Where large volumes of water are to be stored, reservoirs usually are created by the construction of a dam across a flowing stream. When water occurs naturally in streams, it is sometimes not available when needed. Reservoirs solve this problem by capturing water and making it available at later times. See Dam

In addition to large reservoirs, many small reservoirs are in service. These include varieties of farm ponds, regulating lakes, and small industrial or recreational facilities. In some regions, small ponds are called tanks. Small reservoirs can have important cumulative effects in rural regions

Reservoirs can be developed for single or multiple purposes, such as to supply water for people and cities, to provide irrigation water, to lift water levels to make navigation possible on streams, and to generate electricity.

Another purpose of reservoirs is to control floods by providing empty spaces for flood waters to fill, thereby diminishing the rate of flow and water depth downstream of the reservoir.

Reservoirs also provide for environmental uses of water by providing water to sustain fisheries and meet other fish and wildlife needs, or to improve water quality by providing dilution water when it is needed in downstream sections of rivers. Reservoirs may also have esthetic and recreational value, providing boating, swimming, fishing, rafting, hiking, viewing, photography, and general enjoyment of nature. See Pumped storage, River engineering, Water supply engineering

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.


A receptacle or enclosed space for the collection or retention of water, which is supplied to it by natural springs, drainage, or artificial means.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.


As the temperature rises the bimetallic strip makes the contact and the warning light comes on. As soon as fire goes out the temperature drops and the contact is broken putting the light off.
A tank in which fluid is stored for a system. The term is usually used for a hydraulic reservoir.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved


1. a natural or artificial lake or large tank used for collecting and storing water, esp for community water supplies or irrigation
2. Biology a vacuole or cavity in an organism, containing a secretion or some other fluid
3. Anatomy another name for cisterna
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005