canal(redirected from central brain canal)
Also found in: Dictionary, Thesaurus, Medical, Legal.
canal,an artificial waterway constructed for navigation or for the movement of water. The digging of canals for irrigation probably dates back to the beginnings of agriculture, and traces of canals have been found in the regions of ancient civilizations. Canals are also used to provide municipal and industrial water supplies. The drainage of wet lands may be accomplished by means of a canal; by this method the FensFens, the,
district, E England, a flat lowland, W and S of The Wash. Extending c.70 mi (110 km) from north to south and c.35 mi (60 km) from east to west, it is traversed by numerous streams.
..... Click the link for more information. of England and the Zuider ZeeZuider Zee
, former shallow inlet of the North Sea, c.80 mi (130 km) long, indenting NE Netherlands. In ancient times Lake Flevo, it was joined to the North Sea by a great flood in the 13th cent.
..... Click the link for more information. in the Netherlands were drained. Canals can be used for flood control by diverting water from threatened areas into storage basins or to other outlets. In some cases canals are used to generate electricity; the Moscow-Volga Canal is used for this purpose.
Navigation canals developed after irrigation canals and for a long time were level, shallow cuts or had inclined planes up which vessels were hauled from one level to the next; locks (see lock, canallock, canal,
stretch of water enclosed by gates, one at each end, built into a canal or river for the purpose of raising or lowering a vessel from one water level to another. A lock may also be built into the entrance of a dock for the same purpose.
..... Click the link for more information. ) developed separately in China (10th cent.) and Europe (Holland; 13th cent.). Over the years canals have been expanded in width and depth in order to accommodate larger craft, and they have, in some cases, been constructed to form bridges or to pass through tunnels to overcome topographic difficulties. Movement on canals was long accomplished by animal tows or by poling; in the 20th cent. mechanized tows and self-propelled barges appeared.
The Grand CanalGrand Canal,
Chinese Da Yunhe [large transit river], longest in the world, extending c.1,000 mi (1,600 km) from Beijing to Hangzhou, E China, and forming an important north-south waterway on the North China Plain. The canal was started in the 6th cent. B.C.
..... Click the link for more information. of China (the longest in the world) was completed in the 13th cent. and is the most notable of the early canals. France, Belgium, Holland, and Germany were the first in Europe to develop inland waterway systems by using canals to connect rivers; these countries now have a dense network of waterways (see Rhine CanalsRhine Canals.
Among the chief canals linking the Rhine with other river systems are the Rhine-Rhône Canal, 217 mi (349 km) long (built 1784–1833, now unimportant), connecting with the Rhône River through the Saône River; the Rhine-Marne Canal, 195 mi (314
..... Click the link for more information. ; Midland CanalMidland Canal,
Ger. Mittelland Kanal, artificial waterway system of Germany, extending eastward c.200 mi (320 km) along the North German plain from the Dortmund-Ems Canal, Germany, to Magdeburg, Germany, on the Elbe River.
..... Click the link for more information. ). Canal building was widespread in the 18th and 19th cent. During that period England developed an elaborate canal network, and there was also a canal-building boom in the United States in the 19th cent., especially after the completion of the Erie CanalErie Canal,
artificial waterway, c.360 mi (580 km) long; connecting New York City with the Great Lakes via the Hudson River. Locks were built to overcome the 571-ft (174-m) difference between the level of the river and that of Lake Erie.
..... Click the link for more information. . However, the rise of railroads brought a decline in the building and use of canals as inland waterways. Canals have been built to shorten sea voyages or to make them less hazardous, e.g., the Suez CanalSuez Canal,
Arab. Qanat as Suways, waterway of Egypt extending from Port Said to Port Tawfiq (near Suez) and connecting the Mediterranean Sea with the Gulf of Suez and thence with the Red Sea. The canal is somewhat more than 100 mi (160 km) long.
..... Click the link for more information. , the Panama CanalPanama Canal,
waterway across the Isthmus of Panama, connecting the Atlantic (by way of the Caribbean Sea) and Pacific oceans, built by the United States (1904–14, on territory leased from the republic of Panama) and expanded by Pamana (2007–16).
..... Click the link for more information. , and the Kiel CanalKiel Canal,
artificial waterway, 61 mi (98 km) long, in Schleswig-Holstein, N central Germany, connecting the North Sea with the Baltic Sea. At sea level, the canal extends from Kiel on the Baltic to Brunsbüttelkoog at the mouth of the Elbe River.
..... Click the link for more information. . Canals improve conditions on natural waterways by bypassing falls (the Welland Ship CanalWelland Ship Canal,
27.6 mi (44.4 km) long, SE Ont., Canada, connecting Lake Ontario with Lake Erie and bypassing Niagara Falls. Built between 1914 and 1932 by Canada to replace a canal opened in 1829, it can accommodate (minimum depth 27 ft/8 m) the largest lake ships.
..... Click the link for more information. ), shallows, or swift currents (the Sip Canal in the Danube River's Iron Gate gorge). Canals may provide inland cities with direct access to the sea (the Manchester Ship CanalManchester Ship Canal,
35.5 mi (57 km) long with a minimum depth of 28 ft (8.5 m), connecting Manchester, W England, with the Mersey estuary at Eastham, above Birkenhead. Begun in 1887, it was opened in 1894 and changed Manchester from a river port to a seaport.
..... Click the link for more information. ), or shorten the distance between cities (the Albert CanalAlbert Canal,
waterway, c.80 mi (130 km) long, N Belgium, from the Meuse River to the Scheldt River; constructed 1930–39. The canal connects the important industrial region around Liège with the port of Antwerp, Belgium.
..... Click the link for more information. ). In the 20th cent. canals regained importance, as modern technology provided the means to overcome greater topographic obstacles and facilitated the construction of larger canals and the expansion of existing ones. The Great LakesGreat Lakes,
group of five freshwater lakes, central North America, creating a natural border between the United States and Canada and forming the largest body of freshwater in the world, with a combined surface area of c.95,000 sq mi (246,050 sq km).
..... Click the link for more information. –Saint Lawrence SeawaySaint Lawrence Seaway,
international waterway, 2,342 mi (3,769 km) long, consisting of a system of canals, dams, and locks in the St. Lawrence River and connecting channels between the Great Lakes; opened 1959.
..... Click the link for more information. system, opened to navigation in 1959, is the world's longest deep-draft inland waterway. Including six short canals with a total length of less than 60 nautical mi (110 km), it extends from the Atlantic Ocean to Duluth, Minn. on Lake Superior, a distance of more than 2,340 mi (3,700 km), providing large oceangoing vessels passage into central North America.
See C. Hadfield, World Canals (1986); R. Spangenburg and D. Moser, The Story of America's Canals (1992); R. E. Shaw, Canals for a Nation: The Canal Era in the United States, 1790–1860 (1993); J. M. Bracken, American Waterways: The Role of Canals in America (1997).
in hydraulic engineering, a regularly shaped man-made channel (waterway) built in the earth, with nonpressured movement of the water. Canals are built in open excavations or in embankments (when crossing gorges or ravines) and sometimes half in excavations and half in embankments (a canal on a slope). According to purpose, a distinction is made among navigation canals (man-made waterways), power-engineering canals (diversion channels), irrigation canals, water-supply canals, drainage canals, lumber-flotation canals, fish-ladder canals, and general-purpose canals.
Connecting navigation canals join navigable rivers, lakes, and seas (for example, the V. I. Lenin VolgaDon Ship Canal, the Moscow Canal, the Dnieper-Bug Canal, and the Panama Canal). Bypass canals are built to improve navigation conditions and to avoid rapids in rivers and turbulent sections of large lakes and seas (the Ladoga canals, the Onega Canal, and the Gulf Intracoastal Canal). Straightening canals eliminate meandering of a navigation route and reduce the length of the waterway (the Khoroshevo Canal on the Moscow River and the canal on the Don River below the Tsimliansk Hydroelectric Power Plant). Approach canals provide an approach to large cities, inland port areas, and industrial enterprises from a sea, lake, or river (the Leningrad and Astrakhan sea canals and the Manchester Ship Canal).
Navigation canals are also divided into open and lock canals. Open canals are built by joining waterways whose water levels are almost the same; canals with locks are used when there is a difference in levels or when the route of the canal crosses a high water divide. Lock canals usually consist of several sections, called races, on different levels; locks or ship hoisters are installed between them. Bypass and approach canals are generally open; connecting canals have locks. The water in navigation (lock) canals may move by gravity flow (free-flowing canals), or it may be pumped by pumping stations (machine canals). Navigation canals are characterized by great length (for example, the coastal canal from New York to Florida in the USA is about 1, 800 km long, the Baltic-White Sea Canal is 227 km long, and the Dnieper-Bug Canal is 196 km long; among sea canals, the Suez Canal is 171 km long and the Panama Canal is 81.6 km long) and by broad transverse dimensions (the Suez Canal is 120–150 m wide across the top and 12–13 m deep).
Diversion channels take water from a river, reservoir, or lake to a hydroelectric power plant or draw off water that has passed through the turbine. Such canals are typically very short; delivery canals are usually not more than 5–10 km long (maximum of 30 km), and return canals are seldom more than a few kilometers long. The water flow (carrying capacity) of diversion channels varies; in some cases it is more than 1,000 m3/sec (for example, the carrying capacity of the diversion channel of the Montélimar Hydroelectric Power Plant in France is 1, 860 m3/sec). In the USSR the Zemo-Avchala, Rioni, and Kondopoga hydroelectric power plants and the Sevan grid have diversion channels.
Irrigation canals are designed to supply water to irrigated lands. They usually form a system of main canals, distribution canals, the irrigation canals themselves, and drainage canals. Water enters irrigation canals by gravity flow or is fed by pumps. In large irrigation systems the length of the main canals may be several hundred kilometers (the Karakum Canal’s first section, up to the city of Ashkhabad, is more than 800 km long, the North Crimean Canal is more than 400 km long, and the Bol’-shoi Fergana Canal is about 300 km long). The water flow at the head of these canals is 250–500 m3/sec.
Agricultural water-supply canals deliver water to waterless and arid regions for the needs of agriculture (primarily for livestock raising). Examples are the agricultural water-supply canals in the lower regions of the Volga and the canals of the Terek-Kuma Water-Supply System. Since small, oasis-like irrigated areas are usually formed when water is supplied to arid lands, agricultural water-supply canals are often at the same time irrigation canals (for example, the Nevinnomyssk and Kuban’-Kalaus canals).
Drainage canals collect water that comes from a drainage network (on swampy or overly moist terrain) and conduct it to a river, lake, or sea by gravity flow or through the use of pumping stations. Drainage canals are usually routed along the lowest points of the territory being drained (along thalwegs).
Water-supply canals deliver water from the source of supply to the place of consumption (an industrial region, city, or community). Among the large water-supply canals in the USSR are the Irtysh-Karaganda Canal, with a total length of about 460 km and a carrying capacity of 75 m3/sec at its head, and the Severskii Donets-Donbas Canal, which is about 130 km long, with a water flow of 25 m3/sec at its head. Operating conditions and public-health requirements sometimes necessitate the covering of water-supply canals (for example, the canal—about 30 km long—that delivers water from the Ucha Reservoir to Moscow).
Timber-flotation canals are built to float timber (as individual logs or in rafts), usually from the place where it is cut to a river that is suitable for flotation or to a sawmill. Flotation canals are also built in the area of hydraulic-engineering complexes to direct floating timber around hydraulic-engineering structures.
Fish-ladder canals supply water to man-made breeding grounds, provide a connection between rivers and isolated bodies of water (lakes) in which fish are found, and supply fresh water to estuaries (for example, in the lower course of the Kuban’ River).
General-purpose canals are built to accomplish several water-management tasks simultaneously. Such canals have been developed on a particularly large scale in the USSR in connection with multiple use of river resources. For example, the Moscow Canal delivers water for navigation and water supply for the city of Moscow, the V. I. Lenin Volga-Don Canal (together with the Tsimliansk Hydroelectric Power Plant) is a navigation-irrigation-water-supply and power complex, and the Irtysh-Karaganda Canal solves irrigation problems in Central Kazakhstan, in addition to its primary task of water supply.
The cross section of a canal depends on the purpose of the canal, the structural features of the ground, and the conditions for earthwork. The most common shapes of canal cross sections built in soft soils are trapezoidal and polygonal. The latter is usually used in building large navigational canals. A rectangular profile is advisable when canals are built in rock excavations. Sometimes (for example, when a canal route passes through populated areas or in sloping sectors) the rectangular cross section in soft soils is reinforced by constructing vertical retaining walls.
The dimensions of a canal’s cross section are determined by hydraulic calculations for a given water flow and the current velocity that is permissible for the particular conditions; for navigation and timber-flotation canals the size of ships and rafts that will be passing through must also be taken into account. The ratio between the area of the clear section of navigation canals and the area of the midship section of the hypothetical ship should not be greater than 4:1 for canals on first-category waterways, 3.5:1 for second-category waterways, and 3:1 for the third and fourth categories. If the ratio is smaller, resistance to the movement of ships increases substantially.
The slope of canal walls is determined by the nature of the soil. Where excavations are very deep, and also under difficult geological conditions, the strength of the walls is checked through calculations.
The velocity of water current in canals has maximum and minimum values: the maximum, to avoid erosion of the bed of the canal, and the minimum, so that the bed does not become silted or overgrown with vegetation. For example, for canals in soft ground (sand and sandy loam), with a water depth of more than 3 m, current velocities of 0.4−1.5 m/sec present no danger of erosion; in hard rock (marl or sandstones), the velocities may be 3.1−5.6 m/sec. Formulas based on the principle of the so-called alluvium-transporting capability of a current are used to determine silt-free water velocities. Minimum canal velocities for preventing overgrowth with vegetation are 0.3 m/sec for small canals and 0.5 for large canals.
The bed of the canal is lined to protect it against erosion by the current and waves, to reduce water losses from seepage into the soil, and to decrease the roughness of the bottom and walls (to increase the carrying capacity of the canal). Lining that serves only to protect the walls of the canal against erosion is made of rock paving, fill, and laying and of concrete and rein-forced-concrete slabs. This kind of lining is usually used on navigation canals. For irrigation, agricultural water-supply, and drainage canals, sod-brushwood, wicker, and other types of rein forcements are sometimes used. Antiseepage lining (screens) is usually made of clay, sandy loam, and well-decomposed peat. The screens are covered with a layer of sand or gravel to protect them against mechanical damage and the effects of temperature. Concrete, reinforced-concrete, and asphalt-concrete linings are the most versatile; they provide reliable protection against erosion for the canal bed, ensure its watertightness, increase its carrying capacity and, at the same time, make possible complete mechanization of construction work. In addition to installing lining or screens, silt deposition, mechanical packing of the soil, and films made of synthetic materials are used to combat seepage in canals.
Structures on canals. In addition to special structures related to the operation of canals, such as locks (on navigation canals), pumping stations (on machine canals), and flood gates, many other hydraulic-engineering structures for various purposes are also erected along all canals. Among them are structures in places where the canal intersects streams (pipes, inverted siphons, and aqueducts), at intersections with transportation routes (viaducts, tunnels, bridges, and ferry crossings), and in places where there is a sharp break in the relief of the terrain (knickpoints and races).
Historical survey. Long before the Common Era, in the ancient states of the Southeast and East, the development of irrigation and water-supply canals became necessary as farming developed. For example, irrigation was known in the valley of the Nile River in Egypt in 4400 B.C. and in China (on the Yangtze River) in the third millennium B.C. The construction of navigation canals—for example, the canal from the Nile to the Red Sea, sixth century B.C., and the Chinese Grand Canal—also began in ancient times.
In the Middle Ages navigation canals were constructed primarily in Holland, France, and England. The invention of the chamber lock in Holland in the 15th century was of great importance for the construction of navigation canals. In the 16th and 17th centuries the development of trade and early industrial manufacture required an improvement in transportation routes and the design of navigation canals. In the 17th and 18th centuries and the first half of the 19th century, waterways were the primary and most economical transportation arteries. Among the most important structures of that period are the navigation canals in France (the Seine-Loire, Languedoc and Central canals), Germany (Vinow, Oder-Spree, Oder-Vistula, and Elbe-Havel), and England (Bridgewater and Caledonian). Sea canals (Suez, Kiel, and Panama) were built in the second half of the 19th century and in the 20th century in connection with the extensive development of world trade and for strategic purposes.
Canals for irrigation were built on the territory of the USSR as early as the eighth to sixth centuries B.C., in the ancient states of Khwarizm and Urartu. Irrigation canals were built in the 12th and 13th centuries A.D. in Georgia (Alazani and Samgori). Later canal building developed primarily for purposes of improving river navigation (for example, the navigation canal on the Sukhona River, 13th century), for hydraulic-engineering purposes (for supplying water to water-powered mills), and sometimes for drainage of land. Intensive construction of canals developed during the reign of Peter I. The Oka River was linked to the headwaters of the Don by the Ivanovskii Canal, the Vyshnii Volochek Water System was built to connect the Volga with the Msta River and the Baltic Sea, the Ladoga canals were built, and later, various connecting navigation canals, such as the Mariinskii, Tikhvin, Oginskii, and Severnaia Dvina, were added.
A new stage in the construction of navigation and irrigation canals and diversion channels in the USSR began after the Great October Socialist Revolution. Surveying for the Volga-Don Canal was under way as early as 1918. In the period of reconstruction—and especially during the prewar five-year plans— extensive construction of canals that were of great general importance to the national economy of the USSR was carried on. The plan of GOELRO (State Commission for the Electrification of Russia) played a large role in the construction of power-engineering canals; a number of hydroelectric power plants with diversion channels (for example, the Zemo-Avchala and Kondopoga plants) were built on the basis of this plan. The largest irrigation complex of the prewar five-year plans was the Bol’shoi Fergana Canal. The Baltic-White Sea and Moscow canals, as well as a number of irrigation canals in Middle Asia and the Caucasus, were built during the 1930’s.
After the Great Patriotic War (1941–5) canal construction was even more extensive. The following canals were built and put into operation: the V. I. Lenin Volga-Don Canal, the Karakum Canal (up to Ashkhabad), the Golodnaia Step’ Canal, the Don Main Canal, the Northern Crimean Canal, the Severskii Donets-Donbas Canal, the Dnieper-Krivoi Rog Canal, and the Amu-Bukhara Canal.
REFERENCESUginchus, A. A. Kanaly i sooruzheniia na nikh. Moscow, 1953.
Askochenskii, A. N. Oroshenie i obvodnenie v SSSR. Moscow, 1967.
Grishin, M. M. Gidrotekhnicheskie sooruzheniia. Moscow, 1968.
P. N. KORABLINOV
What does it mean when you dream about a canal?
As a waterway that must be constructed (in contrast to a stream or a river), dreaming about a canal might be about channeling or directing our feelings. It could also be emblematic of our goals.
An artificial open channel usually used to convey water or vessels from one point to another. Canals are generally classified according to use as irrigation, power, flood-control, drainage, or navigation canals or channels. All but the last type are regarded as water conveyance canals.
Canals may be lined or unlined. Linings may consist of plain or reinforced concrete, cement mortar, asphalt, brick, stone, buried synthetic membranes, or compacted earth materials. Linings serve to reduce water losses by seepage or percolation through pervious foundations or embankments and to lessen the cost of weed control. Concrete and other hard-surface linings also permit higher water velocities and, therefore, steeper gradients and smaller cross sections, which may reduce costs and the amount of right-of-way required.
Navigation canals are artificial inland waterways for boats, barges, or ships. A canalized river is one that has been made navigable by construction of one or more weirs or overflow dams to impound river flow, thereby providing navigable depths. Locks may be built in navigation canals and canalized rivers to enable vessels to move to higher or lower water levels. A lock is a chamber equipped with gates at both upstream and downstream ends. Water impounded in the chamber is used to raise or lower a vessel from one elevation to another. The lock chamber is filled and emptied by means of filling and emptying valves and a culvert system usually located in the walls and bottom of the lock. See Transportation engineering, Water supply engineering