The Development of Canal Locks
The Development of Canal Locks
Canals have been used since ancient times to carry water where it is needed or allow transportation where natural waterways do not go. The canal lock was developed in China, and first used in Europe during the Middle Ages. Locks enable ships to go from one water level to another, thus making many more transportation routes possible.
Canals are artificial inland waterways. They are built for water supply, sewage removal, crop irrigation, drainage, and transportation. The first known canals were dug in the Middle East thousands of years ago. King Sennacherib, who ruled Assyria in 704-681 b.c., had a 50-mile (80-km) long stone canal built to supply the city of Nineveh with fresh water. Several additional canals were built elsewhere in the Mesopotamian region, as well as in Egypt and Phoenicia. In about 510 b.c. the Persian king Darius I (550-486 b.c.) even attempted to connect the Nile with the Red Sea.
The ancient Romans embarked on major public works projects throughout their empire, and these included canals. Roman canals were used primarily for military transportation, although some were built to provide drainage. With the decline of Rome, the European canals fell into disrepair. In the late Middle Ages, however, as trade expanded, many were reclaimed and the system was enlarged, until it carried as much as 85% of Europe's commercial traffic. This was the period in which the extensive canal network of Venice was built.
The Chinese began building canals about 2,300 years ago to provide easier access to their major rivers and the ability to transport grain from the rich river valleys to the cities of the north. The Grand Canal, which was begun in 540 b.c. and opened in sections over the next 1,800 years, remains the longest artificial waterway in the world as well as the oldest still in use. It travels approximately 1,000 miles (1,600 km) between the Chang (Yangtze) River and Beijing (Peking). The Grand Canal is a summit canal; that is, it follows the contour of the landscape. The changing terrain required boats to go up and down hills, which they cannot normally do. The Chinese solved this problem with water traps called locks.
Locks are used to move ships from one water level to another, for example, in a canal between two lakes that are at different heights above sea level. The earliest locks, called flash locks, were simple movable barriers across the canal or river. The barriers, or lock-gates, slowed the water flow and allowed water to build up behind the gate. When the gate was opened, a boat going downstream would be carried smoothly over any downhill drops or shallow areas by the surge of water. However, a boat heading upstream would have to be hauled through the gate against the flow. Flash locks were used in China by the first century b.c. in canals near Nanyang. In a.d. 983, the provincial transportation commissioner Chaio Wei-Yo built the first recorded chamber or pound lock on the Grand Canal. A pound lock consists of a section of the canal that is enclosed with watertight gates at both ends so that the water level inside can be raised or lowered. A ship that needs to move to the lower water level would enter through the upper gate. When the gate closes behind the ship, water is allowed to drain into the canal below the lock by opening ports or sluices in the lower gate. When the water within the lock is at the same level as the water below the lock, the lower gate is opened and the ship goes on its way.
To go from a lower level to a higher one, the process is reversed. The ship enters through the gate at the lower end of the lock, and sluices in the upper gate are opened to allow water in from the upper level to raise the water level in the lock. When the two levels are equal, the upper gate is opened and the ship moves on.
The pound lock provided a way to get a ship from a lower water level to a higher level without dragging it. Since most of the water in a pound lock is held between the gates at any given time, it was much quicker to use than the flash lock, and required much less water flow to operate. Despite this improvement, water supply in canal operation was always a consideration. Side pools intermediate between the two water levels were sometimes used to store water when the lock was being emptied, and serve as a reservoir from which to fill it again. The Grand Canal had side pools as well as large holding tanks to ensure that water would be available to operate the locks.
In the eleventh and twelfth centuries, single locks began to be used in the Low Countries (today's Belgium, Netherlands, and Luxembourg) and in Italy. The first pound lock in Europe was built by the Dutch in 1373, at the junction of the Utrecht Canal with the River Lek at Vreeswijk. It used guillotine gates, which move up and down to open and close. Around 1500, miter gates began to appear in Italy. These open like double-leaf doors and close to form a V-shape, held shut by the pressure of the water pushing against them. The invention of miter gates is often attributed to Leonardo da Vinci because the earliest drawings of them are found in his notebooks. Miter gates can withstand the forces of water pressure better than guillotine gates, allowing locks to be made wider than they had been before.
Canal locks must often be built in a series so that a large water level difference can be handled gradually. For example, the modern Welland Canal must raise ships 325 feet (99 m) between Lakes Ontario and Erie. It does this using a series of eight locks. The pound lock enabled most of the world's canals to be built, because without it changes in elevation would have made canals impractical.
Canals have had a major impact on trade and politics by providing significant transportation short cuts. In eighteenth century England, canals improved transportation between the factories in the north, their raw materials, and their markets, thereby helping to foster the Industrial Revolution. This in turn provided the improved technological capabilities that allowed massive canal projects to be undertaken in the early 1800s.
Many canals were built in the interior of the United States to link the Great Lakes and the Mississippi River. Canal-building in the United States tapered off when railroads and eventually cars and trucks provided alternate means of transportation.
The vast country of Russia has also benefited greatly by building canals. Canals have made transportation easier across Russia's large expanse. By providing access to the White, Baltic, Black, Caspian, and Azov Seas from Moscow, canals have made the Russian capital into a major port despite its inland location.
Internationally, two canals have been particularly important. The Suez Canal in Egypt, dating from 1869, connects the Mediterranean and Red Seas, and was the belated realization of the project envisioned by Darius I. It provides European ships with a passage to India that avoids a 6,000-mile (9,660-km) trip around Africa. The path of the Suez Canal through Egypt's lakes and marshes allowed engineers to avoid using locks, which despite their advantages do cause delays. Other modern alternatives to locks include engineering the terrain itself or installing hydraulic lifts.
The Panama Canal, with its 12 locks, opened in 1914. It links the Atlantic and Pacific Oceans across the narrow Isthmus of Panama. Ships can travel between the East and West Coasts of North America through the Panama Canal without circumnavigating the entire continent of South America, a difference of almost 8,000 miles (12,900 km).
SHERRI CHASIN CALVO
Needham, Joseph. Science and Civilisation in China. Cambridge: Cambridge University Press, 1962.
Temple, Robert. The Genius of China: 3,000 Years of Science, Discovery and Invention. New York: Simon and Schuster, 1986.
Williams, Suzanne. Made in China: Ideas and Inventions from Ancient China. Berkeley, Calif.: Pacific View Press, 1997.