Canal

Canal, Antonio: see Canaletto.

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.

lock, 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. When the ship is to be raised to a higher level, it enters the lock and a gate is closed behind it. Water is let into the lock until its level equals that of the water ahead. The forward gate is then opened, and the ship progresses on the higher level. The procedure is reversed when the vessel is to pass from a higher to a lower level. As many locks as necessary are used in a given waterway. Most modern locks are made of concrete, although some have walls of steel-sheet piles or floors of natural rock or sand. The mitre gate, frequently used in the United States, consists of two swinging sections forming an arc or shallow V, with the apex pointed toward high water so that water pressure keeps both sections tightly sealed when closed. Another type of gate in common use consists of one piece of sheet steel that slides across the entrance to the lock on rollers or is lifted into the air or sunk underwater. The gates of most locks are operated by hydraulic or electric power. Water is poured into or out of locks through culverts built into the masonry structure of the lock walls. Among well-known locks are those of the Panama Canal.

Artificial waterway built for transportation, irrigation, water supply, or drainage. The early Middle Eastern civilizations probably first built canals to supply drinking and irrigation water. The most ambitious navigation canal was a 200-mi (320-km) construction in what is now Iraq. Roman canal systems for military transport extended throughout northern Europe and Britain. The most significant canal innovation was the pound lock, developed by the Dutch c. 1373. The closed chamber, or pound, of a lock is flooded or drained of water so that a vessel within it is raised or lowered in order to pass between bodies of water at different elevations. Canals were extremely important before the coming of the railroad in the mid-19th century. Among the significant waterways in the U.S. were the Erie Canal, several canals linking the Great Lakes, and one connecting the Great Lakes to the Mississippi River. Modern waterway engineering enables larger vessels to travel faster by reducing delays at locks. See also Grand Canal, Panama Canal, Suez Canal.

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End portion of the alimentary canal, distinguished from the rectum by the transition from an internal mucous membrane layer to one of skinlike tissue and by its narrower diameter. Waste products move from the rectum to the anal canal. The human anal canal is 1–1.5 in. (2.5–4 cm) long and has three parts: upper, with longitudinal folds (rectal columns); lower, with involuntary and voluntary constrictive muscles (sphincters) to control discharge of feces; and the anal opening itself. Enlargements of the ends of rectal and anal veins are called hemorrhoids.

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Canal, southeastern Ontario, Canada. Linking Lake Huron with Lake Ontario, the canal extends from the southeastern shore of Georgian Bay up the Severn River to Lake Simcoe, connects several lakes of the Kawartha Lake region to Rice Lake, and passes down the Trent River to the Bay of Quinte and Lake Ontario. Its 242-mi (389-km) main course consists of 33 mi (53 km) of man-made channels and 42 locks. Construction began in 1833. The waterway once served a busy lumber trade; it is now a popular tourist attraction.

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Ship canal, Isthmus of Suez, Egypt. Connecting the Red Sea with the eastern Mediterranean Sea, it extends 101 mi (163 km) from Port Said to the Gulf of Suez and allows ships to sail directly between the Mediterranean and the Indian Ocean. Built by the French-owned Suez Canal Co., it was completed in 1869 after a decade of construction. Its ownership remained largely in French and British hands until Egypt nationalized it in 1956, setting off an international crisis (see Suez Crisis). It has a minimum width of 179 ft (55 m) and a depth of about 40 ft (12 m) at low tide. Though protected by international treaty, the canal has been closed twice. The first closing was during the Suez Crisis. The canal was closed again by the Six-Day War (1967) and remained inoperative until 1975. It is one of the world's most heavily used shipping lanes.

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or Panama Canal Zone

Strip of territory, a historic administrative entity in Panama over which the U.S. formerly exercised jurisdictional rights (1903–79). The zone came into being in 1904 when Panama granted the U.S., in return for annual payments, sole right to operate and control the Panama Canal, including a strip of land 10 mi (16 km) wide along the canal extending from the Atlantic to the Pacific Ocean and bisecting the Isthmus of Panama. The zone was abolished by treaty in 1979, and civil control of the territory was returned to Panama. By the same treaty a commission under joint U.S.-Panamanian ownership was established to operate the canal until the year 2000, when Panama assumed full control.

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Lock-type canal, Panama. Extending across the Isthmus of Panama, it connects the Atlantic and Pacific oceans. It is about 50 mi (82 km) long from deepwater to deepwater, with an average depth of 43 ft (13 m). The width varies between 500 to 1,000 ft (150 to 300 m). In 1881 a French company began constructing the canal, but the enterprise collapsed in 1889. Under a 1903 treaty Panama granted the U.S. the Panama Canal Zone and the rights to build and operate a canal. Work began in 1904; facing enormous obstacles, George Washington Goethals directed the construction from 1907, and the canal opened on Aug. 15, 1914. The canal enabled ships traveling between the two oceans to avoid the lengthy circumnavigation of South America and was a boon to world commerce. After disputes over sovereignty, a 1977 treaty provided for Panama to take control of the canal by 2000; it did so in 1999. Except for small craft, no vessel can pass through the canal under its own power. Ships are towed by electric locomotives, and it generally takes 15–20 hours to complete the passage (including waiting time). Sets of double locks enable ships to pass in opposite directions simultaneously.

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Deep fjord, southeastern Alaska, U.S. An important gateway to the Klondike region, it is 80 mi (129 km) long and 6 mi (10 km) wide. The northernmost fjord to penetrate the Coast Mountains, it was named in 1794 by Capt. George Vancouver for his birthplace, King's Lynn, Eng.

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Neighbourhood in Niagara Falls, N.Y., the site of the worst environmental disaster involving chemical wastes in U.S. history. Originally the site of an abandoned canal, it became a dumping ground for nearly 22,000 tons of chemical waste in the 1940s and '50s. The canal was later filled in, and housing was built on it. The leakage of toxic chemicals into these homes was detected in 1978, and residents were discovered to have a high incidence of chromosome damage. After their evacuation, 1,300 former residents obtained a $20 million settlement from the dumping company and the city. In the early 1990s New York state ended its cleanup and declared parts of the area safe for residence.

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Series of waterways in northern China that link Hangzhou with Beijing. Some 1,085 mi (1,747 km) in length, it is the world's longest man-made waterway. It was build to enable successive Chinese regimes to transport surplus grain from the agriculturally rich Yangtze (Chang) and Huai river valleys to feed the capital cities and large standing armies in the north. The oldest portion, in the south, may date from the 4th century BC. Expanded over the centuries, it continues to be used today for shipping and irrigation.

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Historic waterway, northern U.S. It stretches from Buffalo, N.Y., on Lake Erie to Albany, N.Y., on the Hudson River. Commissioned by Gov. DeWitt Clinton of New York, it opened in 1825. It connected the Great Lakes with New York City and contributed greatly to the settlement of the Midwest, allowing for the transport of people and supplies. Enlarged several times, the canal is 363 mi (584 km) long, 150 ft (46 m) wide, and 12 ft (3.6 m) deep. Now used mainly for pleasure boating, it is part of the New York State Canal System.

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Park, eastern U.S. It consists of the former Chesapeake and Ohio Canal, a waterway running along the Potomac River between Washington, D.C., and Cumberland, Md. The canal, which extends 185 mi (297 km), was built beginning in the 1820s. Competition from the railroads later caused its economic decline. The canal was purchased in 1938 by the U.S. government; it was restored and established as a historical park in 1971.

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Canals are artificial channels for water. There are two types of canals: water conveyance canals, which are used for the conveyance and delivery of water, and waterways, which are navigable transportation canals used for passage of goods and people, often connected to existing lakes, rivers, or oceans. For canals used for water supply, see Aqueduct.

Types of artificial waterways

Some canals are part of an existing waterway. This is usually where a river has been canalised: making it navigable by widening and deepening some parts (by dredging and/or weirs), and providing locks with "cuts" around the weirs or other difficult sections. In France, these are called lateral canals and in the UK they are generally called navigations, and the length of the artificial waterway often exceeds the natural. Smaller transportation canals can carry barges or narrowboats, while ship canals allow seagoing ships to travel to an inland port (eg Manchester Ship Canal, or from one sea or ocean to another (eg Caledonian Canal, Kiel Canal).

Features

At their simplest, canals consist of a trench filled with water. Depending on the stratum the canal passes through, it may be necessary to line the cut with some form of watertight material such as clay or concrete. When this is done with clay this is known as puddling.

Canals need to be flat, and while small irregularities in the lie of the land can be dealt with through cuttings and embankments for larger deviations, other approaches have been adopted. The most common is the pound lock which consists of a chamber within which the water level can be raised or lowered connecting either two pieces of canal at a different level or the canal with a river or the sea. When there is a hill to be climbed, flights of many locks in short succession may be used.

Prior to the development of the pound lock in 984AD in China by Chhaio Wei-Yo and later in Europe in the 15th century, either flash locks consisting of a single gate were used, or ramps, sometimes equipped with rollers, were used to change level. Flash locks were only practical where there was plenty of water available.

Locks use a lot of water, so builders have adopted other approaches. These include boat lifts, such as the Falkirk wheel, which use a caisson of water in which boats float while being moved between two levels; and inclined planes where a caisson is hauled up a steep railway.

To cross a stream or road, the solution is usually to bridge with an aqueduct. To cross a wide valley (where the journey delay caused by a flight of locks at either side would be unacceptable) the centre of the valley can be spanned by an aqueduct - a famous example in Wales is the Pontcysyllte aqueduct across the valley of the River Dee.

Another option when dealing with hills is to tunnel through them. An example of this approach is the Harecastle Tunnel on the Trent and Mersey Canal. Tunnels are only practical for smaller canals.

Some canals attempted to keep changes in level down to a minimum. These canals known as contour canals would take longer winding routes, along which the land was a uniform altitude. Other generally latter canals took more direct routes requiring the use of various methods to deal with the change in level.

Canals have various features to tackle the problem of water supply. In some cases such as the Suez Canal the canal is simply open to the sea. Where the canal is not at sea level a number of approaches have been adopted. Taking water from existing rivers or springs was an option in some cases, sometimes supplemented by other methods to deal with seasonal variations in flow. Where such sources were unavailable, reservoirs, either separate from the canal, or built into its course, and back pumping were used to provide the required water. In other cases water pumped from mines was used to feed the canal.

History

Ancient canals

The oldest known canals were built in Mesopotamia circa 4000 BC, in what is now modern day Iraq and Syria. The Indus Valley Civilization in Pakistan and North India (from circa 2600 BC) had a sophisticated canal irrigation system. Agriculture was practised on a large scale, and an extensive network of canals was used for the purpose of irrigation. Sophisticated irrigation and storage systems were developed, including the reservoirs built at Girnar in 3000 BC.

In Egypt, canals date back at least to the time of Pepi I Meryre (reigned 2332 – 2283 BC), who ordered a canal built to bypass the cataract on the Nile near Aswan.

In ancient China, large canals for river transport were established as far back as the Warring States (481-221 BC), the longest one of that period being the Hong Gou (Canal of the Wild Geese), which according to the ancient historian Sima Qian connected the old states of Song, Zhang, Chen, Cai, Cao, and Wei. By far the longest canal was the Grand Canal of China, still the longest canal in the world today. It is long and was built to carry the Emperor Yang Guang between Beijing and Hangzhou. The project began in 605 and was completed in 609, although much of the work combined older canals, the oldest section of the canal existing since at least 486 BC. Even in its narrowest urban sections it is rarely less than wide.

Canals in the Middle Ages

The Naviglio Grande near Milan was the first artificial canal in Medieval Europe and the most important of the lombard “navigli”; started in 1127 and opened in 1257, allowing development of commerce, transport and agriculture. Canal building was revived in this age because of commercial expansion from the 12th century AD. River navigations were improved progressively by the use of single, or flash locks. Taking boats through these used large amounts of water leading to conflicts with watermill owners and to correct this, the pound or chamber lock first appeared, in 10th century AD in China and in Europe in 1373 in Vreeswijk, Netherlands. Another important development was the mitre gate which was probably introduced in Italy by Bertola da Novate in the sixteenth century. This allowed wider gates and also removed the height restriction of guillotine locks.

To break out of the limitations caused by river valleys, the first summit level canals were developed with the Grand Canal of China in 581-617 AD whilst in Europe the first, also using single locks, was the Stecknitz Canal in Germany in 1398. The first to use pound locks was the Briare Canal connecting the Loire and Seine catchment areas in France (1642) followed by the more ambitious Canal du Midi (1683) connecting the Atlantic to the Mediterranean. This included a staircase of 8 locks at Béziers, a tunnel and three major aqueducts.

Canal building progressed steadily in Germany in the 17th and 18th centuries with three great rivers, the Elbe, Oder and Weser being linked by canals. In post-Roman Britain, the first canal built appears to have been the Exeter Canal, which opened in 1563. The oldest canal built for industrial purposes in North America is Mother Brook in Dedham, MA. It was constructed in 1639 to provide water power for mills. In Russia, the Volga-Baltic Waterway, a nationwide canal system connecting the Baltic and Caspian seas via the Neva and Volga rivers, was opened in 1718.

The greatest stimulus to canal systems came from the Industrial Revolution with its need for cheap transport of raw materials and manufactured items.

Industrial revolution

In Europe, particularly Britain and Ireland, and then in the young United States and the Canadian colonies, inland canals preceded the development of railroads during the earliest phase of the Industrial Revolution. The opening of the Bridgewater Canal in 1761, which halved the price of coal in Manchester, triggered a period of "canal mania" in Britain so that between 1760 and 1820 over one hundred canals were built.

In the United States, navigable canals reached into isolated areas and brought them in touch with the world beyond. By 1825 the Erie Canal, long with 82 locks, opened up a connection from the populated Northeast to the fertile Great Plains. The Blackstone Canal in Massachusetts and Rhode Island fulfilled a similar role in the early industrial revolution between 1828-1848. The Blackstone Valley was considered the 'birthplace' of the American Industrial Revolution where Samuel Slater built his first mill.

In addition to their transportation purposes, parts of the United States, particularly in the Northeast, had enough fast-flowing rivers that water power was the primary means of powering factories (usually textile mills) until after the American Civil War. For example, Lowell, Massachusetts, considered to be "The Cradle of the American Industrial Revolution," has of canals, built from around 1790 to 1850, that provided water power and a means of transportation for the city. The output of the system is estimated at 10,000 horsepower. Other cities with extensive power canal systems include Lawrence, Massachusetts, Holyoke, Massachusetts, and Manchester, New Hampshire.

The 19th century

Competition from the railway network from the 1830s, and later the roads, made the smaller canals obsolete for commercial transportation, and most of the British canals fell into decay. Only the Manchester Ship Canal and the Aire and Calder Canal bucked this trend. But in other countries canals grew in size as construction techniques improved. During the 19th century in the US, the length of canals grew from to over 4,000, with a complex network making the Great Lakes navigable, in conjunction with Canada, although some canals were later drained and used as railroad rights-of-way.

In France, a steady linking of all the river systems—Rhine, Rhône, Saône and Seine—and the North Sea was boosted in 1879 by the establishment of the Freycinet gauge which specified the minimum size of locks so that canal traffic doubled in the first decades of the 20th century.

Many notable sea canals were completed in this period, starting with the Suez Canal (1869), and the Kiel Canal (1897), which carries tonnage many times that of most other canals, though the Panama Canal was not opened until 1914.

In the 19th century, a number of canals were built in Japan including the Biwako canal and the Tone canal. These canals were partially built with the help of engineers from the Netherlands and other countries.

Modern uses

Large scale ship canals such as the Panama Canal and Suez Canal continue to operate for cargo transportation; as do European barge canals. Due to globalization, they are becoming increasingly important, resulting in expansion projects such as the Panama Canal expansion project.

The narrow early industrial canals however have ceased to carry significant amounts of trade and many have been abandoned to navigation, but may still be used as a system for transportation of untreated water. In some cases railways have been built along the canal route, an example being the Croydon Canal.

A movement that began in Britain and France to use the early industrial canals for pleasure boats has spurred rehabilitation of stretches of historic canals. In some cased abandoned canals such as the Kennet and Avon Canal have been restored and are now used by pleasure boaters. In Britain canalside housing has also proven popular in recent years.

The Seine-Nord Europe Canal is being developed into a major transportation waterway, linking France with Belgium, Germany and the Netherlands.

Canals have found another use in the 21st century, as wayleaves along the towing paths for fibre optic telecommunications networks.

Cities on water

Canals are so deeply identified with Venice that many canal cities have been nicknamed "the Venice of..." The city is built on marshy islands, with wooden piles supporting the buildings, so that the land is man-made rather than the waterways. The islands have a long history of settlement; by the 12th century, Venice was a powerful city state.

Amsterdam was built in a similar way, with buildings on wooden piles. The pace of draining of fenland and polder in the Low Countries quickened in the 14th century and canalization made the village of Amsterdam a port. It became a city around 1300.

Other cities with extensive canal networks include: Brugge in Flanders, Birmingham in England, Saint Petersburg in Russia, Hamburg in Germany, and Fort Lauderdale, Florida in the United States.

Canal estates are a form of subdivision popular in cities like Miami, Florida and the Gold Coast, Queensland; the Gold Coast has over 700 km of residential canals. Wetlands are difficult areas upon which to build housing estates, so dredging part of the wetland down to a navigable channel provides fill to build up another part of the wetland above the flood level for houses. Land is built up in a finger pattern that provides a suburban street layout of waterfront housing blocks. This practice is not popular with environmentalists.

Boats

Inland canals have often have had boats specifically built for them. An example of this is the British narrowboat which is up to long and wide and was primarily built for British Midland canals. In this case the limiting factor was the size of the locks. This is also the limiting factor on the Panama canal where Panamax boats are limited to a length of 294.1 metres and a width of 32.3 metres. For the lockless Suez Canal the limiting factor for Suezmaxes is generally draft which is limited to 16 metres. At the other end of the scale, tub-boat canals such as the Bude Canal were limited to boats of under 10 tons for much of their length due to the capacity of their inclined planes or boat lifts. Most canals have a limit on height imposed either by bridges or tunnels.

Gallery

Lists of Canals

• List of waterways
• Americas
• Canals of Canada
• List of canals in the United States
• Europe
• List of canals in France
• List of canals in Germany
• Canals of Ireland
• Canals of Great Britain

See also

• Barge (includes canal boats)
• Canal tunnel
• Channel
• Horse-drawn boat
• List of navigation authorities in the United Kingdom
• List of waterway societies in the United Kingdom
• Lock
• Navigation authority
• Volumetric flow rate
• Water bridge
• Waterway restoration
• Water transportation
• Weigh lock

Notes

Bibliography

External links

• Leeds Liverpool Canal Photographic Guide
• Information and Boater's Guide to the New York State Canal System
• "Canals and Navigable Rivers" by James S. Aber, Emporia State University
• National Canal Museum (USA)
• Canals in Amsterdam
• Canal du Midi
• Canal des Deux Mers
• Canal flow measurement using a sensor