canal

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 Fens of England and the Zuider Zee 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, canal) 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 Canal 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 Canals; Midland Canal). 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 Canal. 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 Canal, the Panama Canal, and the Kiel Canal. Canals improve conditions on natural waterways by bypassing falls (the Welland Ship Canal), 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 Canal), or shorten the distance between cities (the Albert Canal). 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 Lakes–Saint Lawrence Seaway 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).

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