CANAL

artificial waterway built for navigation, crop irrigation, water supply, and drainage. Canals are usually connected with natural bodies of water or other canals. The early civilizations of the Middle East probably built canals to satisfy their need for drinking and irrigation water; navigation was of lesser importance. In the 7th century BC the Assyrian king Sennacherib had a stone canal 50 miles (80 km) long built to bring fresh water to the city of Nineveh. About 510 BC Darius I, the king of ancient Persia, undertook the construction of a canal linking the Nile River and the Red Sea, a forerunner of the modern Suez Canal. Phoenicia, Sumeria, and Babylonia, were all sites of canal systems, the most ambitious project being a navigation canal that extended 200 miles (320 km) between Samarra' and Al-Kut, both now in modern Iraq. In the 3rd century BC the Chinese began building a series of canals to tie together the inland regions around their major rivers. The greatest of these projects was the Grand Canal. With a total length of more than 1,000 miles (1,600 km), it is the longest artificial waterway in the world. The first section was opened in AD 610, and later dynasties added to it until it ran from the Yangtze River to Peking. Romans built extensive canal systems throughout northern Europe and Britain that were used primarily for military transport. Some, such as those constructed in southeastern Britain, were designed for drainage. The decline of Rome led to a lapse in European waterway development for a time. By the 12th century, however, commercial expansion started a revival of their use, and eventually about 85 percent of medieval Europe's transport went by inland waterway. Canals from this period still dominate the transportation system of Venice, which was built on marshy islands in a lagoon of the Adriatic. About 1373 the Dutch developed the pound lock, an innovation that remains the most significant in canal construction. The tightly closed chamber, or pound, of a lock is flooded with or drained of water so that a vessel within it is raised or lowered with the water level. The vessel is thus able to pass between bodies of water at different elevations. With the perfection of the pound lock, canals could be built through terrain where the changes in elevation, or gradient, had previously made their construction difficult or impossible. The great modern era of the canal was the period between the start of the Industrial Revolution and the rise to predominance of the railroad in the mid-19th century. During this time canal-building activity was most dramatic in the United States, where territorial expansion had opened up a vast interior that was hard to reach. At the beginning of the 19th century the United States had only about 100 miles (160 km) of canals, but by the end of the century more than 4,000 miles (6,500 km) had been constructed. Among the most important waterways were the several linking the Great Lakes and one, the Illinois and Michigan Canal, that connected the Great Lakes to the Mississippi River. Railroads and, later, motor vehicles brought an end to the canal boom, but inland-waterway transportation has remained important. With their network of transnational rivers and canals, Europeans have continued to rely heavily on waterway commerce. Russia has been a significant beneficiary. Not only have inland waterways opened vast areas of its interior to development, but Moscowlinked to the White, Baltic, Black, Caspian, and Azov seas by canals and rivershas become a major inland port. Transoceanic shipping boomed with the construction of several inland-waterway projects in the 19th and 20th centuries. The Kiel Canal, dug through a spit of land in northern Germany, cut travel distance between the North and the Baltic seas by several hundred miles. The efforts begun by Darius I in the Suez some 2,300 years earlier were finally realized in 1869 with the opening of the Suez Canal. In the Western Hemisphere the 51-mile (82-kilometre) Panama Canal, cut through the Isthmus of Panama and completed in 1914, allowed ships to move between the Atlantic and Pacific oceans without having to go around South America. In addition, the St. Lawrence Seaway, which utilizes several canals and sets of locks, was opened in 1959; its completion provided the link between the North Atlantic and the Great Lakes and turned such cities as Toronto and Chicago into ocean ports. The pound lock solved the most fundamental problem of the canal buildermaintaining a gradient that was level enough to hold water over varied terrain. Two major innovations, the mitre gate and the side pound (or side pond), have further improved its working capabilities. A mitre gate consists of two leaves that close to form an angle upstream. It can withstand much higher water pressures than can be withstood by a gate that closes flat, thus making possible deeper and longer locks that can accommodate larger ships. With the use of side pounds, scarce water can be reused; it is pumped out and stored in the pounds when the water level in the lock is lowered, then pumped back in when the level is raised. Modern waterway engineering is directed toward providing channels suitable for larger vessels to travel faster by reducing delays at locks or from darkness and other natural hazards. One way of making these improvements is by selecting a canal site in an area that presents few natural obstacles. The Kiel Canal crosses fairly level terrain, which minimized the excavation work; it has locks only at either end. By utilizing existing lakes and marshes, engineers were able to build the Suez Canal without using locks. Where physical features make locks a necessity, efforts are made to improve their efficiency or keep their use to a minimum. On the Welland Canal of the St. Lawrence system, for example, the locks are arranged in pairs, and ships can move both up and down the river simultaneously. Engineers on the Panama Canal reduced the need for locks by cutting a deep channel through the continental divide and by damming a river to create a long, navigable lake. Even with the help of locks, canal builders occasionally encounter gradients that are too steep and abrupt to be approached in gradual steps. One solution is to haul vessels up inclined planes. One such structure built in Brussels in 1968 can lift a 1,350-ton barge up a 5 percent incline. Another device is the vertical lift, which is necessary when the change of level occurs within an extremely short distance. Operated by high-pressure hydraulic lifts, submersible floats, or geared counterweights, lifts can also replace several locks. One lift completed at Henrichenburg, Germany, in 1962 can lift a 1,000-ton vessel 60 feet (18 m).