Canal



s or artificial waterways are or   built for  management (e.g.  and ) or for conveyancing   (e.g. ). They carry free, calm surface flow under }}, and can be thought of as artificial {{river]]s.

In most cases, a canal has a series of {{w|dam|dams}} and {{w|lock (water transport)|locks}} that create {{w|reservoir|reservoirs}} of low speed current flow. These reservoirs are referred to as slack water levels, often just called levels. A canal can be called a navigation canal when it parallels a natural river and shares part of the latter's {{w|discharge (hydrology)|discharges}} and {{w|drainage basin}}, and leverages its resources by building dams and locks to increase and lengthen its stretches of slack water levels while staying in its {{w|valley}}.

A canal can cut across a {{w|drainage divide}} atop a {{w|ridge}}, generally requiring an external water source above the highest {{w|elevation}}. The best-known example of such a canal is the {{w|Panama Canal}}.

Many canals have been built at elevations, above valleys and other waterways. Canals with sources of water at a higher level can deliver water to a destination such as a city where water is needed. The {{w|Roman Empire}}'s {{w|aqueduct (bridge)|aqueducts}} were such {{w|water supply}} canals.

Types of artificial waterways
A navigation is a series of channels that run roughly parallel to the valley and of an unimproved river. A navigation always shares the of the river. A vessel uses the calm parts of the river itself as well as improvements, traversing the same changes in height.

A true canal is a channel that cuts across a, making a navigable channel connecting two different.

In gardening and landscaping, especially historically, a is an artificial piece of water, typically long, thin, and straight-sided, fed by a stream that is diverted and dammed. They are typical of the style of the 17th century, and the  variant which was influential in England. The example in the restored, of c. 1700, is 137 m long.

Most commercially important canals of the first half of the 19th century were a little of each, using rivers in long stretches, and divide crossing canals in others. This is true for many canals still in use. Canals are an efficient way of traveling as it was easier for people to get to areas faster than horse wagons.

Structures used in artificial waterways
Both navigations and canals use structures to improve navigation:
 * and to raise river water levels to usable depths;
 * looping descents to create a longer and gentler channel around a stretch of rapids or falls;
 * to allow ships and barges to ascend/descend.

Since they cut across drainage divides, canals are more difficult to construct and often need additional improvements, like and  to bridge waters over streams and roads, and ways to keep water in the channel.

Types of canals
There are two broad types of canal:
 * : canals and navigations used for carrying vessels transporting goods and people. These can be subdivided into two kinds:
 * Those connecting existing s, s, other canals or seas and s.
 * Those connected in a city network: such as the ' and others of ; the ' of or, and the waterways of.


 * : canals that are used for the conveyance and delivery of  water for human consumption,  uses,  and.

Importance
Historically canals were of immense importance to commerce and the development, growth and vitality of a civilization. In 1855 the carried over 1.2 million tons of anthracite coal; by the 1930s the company which built and operated it over a century pulled the plug. The few canals still in operation in our modern age are a fraction of the numbers that once fueled and enabled economic growth, indeed were practically a prerequisite to further urbanization and industrialization. For the movement of bulk raw materials such as coal and ores are difficult and marginally affordable without water transport. Such raw materials fueled the industrial developments and new resulting of the spiral of increasing mechanization during 17th–20th century, leading to new research disciplines, new industries and economies of scale, raising the standard of living for any industrialized society.

Construction
Canals are built in one of three ways, or a combination of the three, depending on available water and available path:
 * Human made streams
 * A canal can be created where no stream presently exists. Either the body of the canal is dug or the sides of the canal are created by making by piling dirt, stone, concrete or other building materials. The finished shape of the canal as seen in cross section is known as the canal prism. The water for the canal must be provided from an external source, like streams or reservoirs. Where the new waterway must change elevation engineering works like locks, lifts or elevators are constructed to raise and lower vessels. Examples include canals that connect valleys over a higher body of land, like,  and the.
 * A canal can be constructed by dredging a channel in the bottom of an existing lake. When the channel is complete, the lake is drained and the channel becomes a new canal, serving both drainage of the surrounding and providing transport there. Examples include the Lage Vaart. One can also build two parallel dikes in an existing lake, forming the new canal in between, and then drain the remaining parts of the lake. The eastern and central parts of the  were constructed in this way. In both cases pumping stations are required to keep the land surrounding the canal dry, either pumping water from the canal into surrounding waters, or pumping it from the land into the canal.
 * Canalization and navigations


 * A stream can be  to make its navigable path more predictable and easier to maneuver. Canalization modifies the stream to carry traffic more safely by controlling the flow of the stream by dredging, damming and modifying its path. This frequently includes the incorporation of locks and spillways, that make the river a navigation. Examples include the in 's, , , and .  may be required.


 * Lateral canals
 * When a stream is too difficult to modify with canalization, a second stream can be created next to or at least near the existing stream. This is called a , and may meander in a large horseshoe bend or series of curves some distance from the source waters stream bed lengthening the effective length in order to lower the ratio of rise over run (slope or pitch). The existing stream usually acts as the water source and the landscape around its banks provide a path for the new body. Examples include the, , , and.

Smaller transportation canals can carry s or s, while allow seagoing ships to travel to an inland port (e.g., ), or from one sea or ocean to another (e.g.,, ).

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

Canals need to be level, 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, 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 984 AD in China by Chhaio Wei-Yo and later in Europe in the 15th century, either consisting of a single gate were used or ramps, sometimes equipped with rollers, were used to change the 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 for situations where little water is available. These include, such as the , which use a of water in which boats float while being moved between two levels; and  where a caisson is hauled up a steep railway.

To cross a stream, road or valley (where the delay caused by a flight of locks at either side would be unacceptable) the valley can be spanned by a – a famous example in Wales is the  (now a  ) across the valley of the.

Another option for dealing with hills is to tunnel through them. An example of this approach is the on the. Tunnels are only practical for smaller canals.

Some canals attempted to keep changes in level down to a minimum. These canals known as would take longer, winding routes, along which the land was a uniform altitude. Other, generally later, 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 cases, like 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, – either separate from the canal or built into its course – and  were used to provide the required water. In other cases, water pumped from mines was used to feed the canal. In certain cases, extensive "feeder canals" were built to bring water from sources located far from the canal.

Where large amounts of goods are loaded or unloaded such as at the end of a canal, a may be built. This would normally be a section of water wider than the general canal. In some cases, the canal basins contain s and cranes to assist with movement of goods.

When a section of the canal needs to be sealed off so it can be drained for maintenance are frequently used. These consist of planks of wood placed across the canal to form a dam. They are generally placed in pre-existing grooves in the canal bank. On more modern canals, "guard locks" or gates were sometimes placed to allow a section of the canal to be quickly closed off, either for maintenance, or to prevent a major loss of water due to a canal breach.

History
The transport capacity of s and s is limited. A mule can carry an eighth-ton [250 lb] maximum load over a journey measured in days and weeks, though much more for shorter distances and periods with appropriate rest. Besides, carts need roads. Transport over water is much more efficient and cost-effective for large cargoes.

Ancient canals
The oldest known canals were canals, built in  circa 4000 BC, in what is now. The, , (circa 3000 BC) had sophisticated irrigation and storage systems developed, including the built at  in 3000 BC. This is the first time that such planned civil project had taken place in the ancient world. In, canals date back at least to the time of (reigned 2332–2283 BC), who ordered a canal built to bypass the  on the Nile near. In, large canals for river transport were established as far back as the (8th–5th centuries BC), the longest one of that period being the Hong Gou (Canal of the Wild Geese), which according to the ancient historian  connected the old states of Song, Zhang, Chen, Cai, Cao, and Wei. The of canals was essential for imperial taxation, which was largely assessed in kind and involved enormous shipments of rice and other grains. By far the longest canal was the, still the longest canal in the world today and the oldest extant one. It is 1794 km long and was built to carry the between Zhuodu  and Yuhang. 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 30 m wide.

were also among the first to use, by which they regulated the water flow in the as early as the 3rd century BC.

""There was little experience moving bulk loads by carts, while a pack-horse would [i.e. 'could'] carry only an eighth of a ton. On a soft road a horse might be able to draw 5/8ths of a ton. But if the load were carried by a barge on a waterway, then up to 30 tons could be drawn by the same horse." — technology historian referring to transport realities before the industrial revolution and the."

was a society in the in what is now part of, United States, and , Mexico. Their irrigation systems supported the largest population in the Southwest by 1300 CE. Archaeologists working at a major archaeological dig in the 1990s in the Tucson Basin, along the Santa Cruz River, identified a culture and people that may have been the ancestors of the Hohokam. This prehistoric group occupied southern Arizona as early as 2000 BCE, and in the Early Agricultural Period grew corn, lived year-round in sedentary villages, and developed sophisticated irrigation canals. The large-scale Hohokam irrigation network in the was the most complex in ancient North America. A portion of the ancient canals has been renovated for the and now helps to supply the city's water.

Middle Ages
In the, water transport was several times cheaper and faster than transport overland. Overland transport by conveyances was used around settled areas, but unimproved roads required pack animal trains, usually of s to carry any degree of mass, and while a mule could carry an eighth ton, it also needed teamsters to tend it and one man could only tend perhaps five mules, meaning overland  was also expensive, as men expect compensation in the form of wages, room and board. This was because long-haul roads were unpaved, more often than not too narrow for carts, much less wagons, and in poor condition, wending their way through forests, marshy or muddy quagmires as often as unimproved but dry footing. In that era, as today, greater cargoes, especially bulk goods and s, could be transported by ship far more economically than by land; in the pre-railroad days of the industrial revolution, water transport was the gold standard of fast transportation. The first artificial canal in Western Europe was the built at the end of the 8th century under personal supervision of.

In Britain, the   is believed to be the first post-Roman canal and was built in the middle of the 10th century to link the at Northover with, a distance of about 1.75 km. Its initial purpose is believed to be the transport of building stone for the abbey, but later it was used for delivering produce, including grain, wine and fish, from the abbey's outlying properties. It remained in use until at least the 14th century, but possibly as late as the mid-16th century. More lasting and of more economic impact were canals like the built between 1127 and 1257 to connect  with the. The Naviglio Grande is the most important of the "" and the oldest functioning canal in Europe. Later, canals were built in the and  to drain the  and assist transportation of goods and people.

Canal building was revived in this age because of commercial expansion from the 12th century. River navigations were improved progressively by the use of single, or. Taking boats through these used large amounts of water leading to conflicts with owners and to correct this, the  or chamber lock first appeared, in the 10th century in China and in Europe in 1373 in, Netherlands. Another important development was the, which was, it is presumed, introduced in Italy by Bertola da Novate in the 16th century. This allowed wider gates and also removed the height restriction of.

To break out of the limitations caused by river valleys, the first were developed with the  in 581–617 AD whilst in Europe the first, also using single locks, was the  in Germany in 1398.

Africa
In the of West Africa, several canals were constructed under  and  between  and  in the 15th century. These were used primarily for irrigation and transport. Sunni Ali also attempted to construct a canal from the to  to facilitate conquest of the city but his progress was halted when he went to war with the.

Cities on water
Canals are so deeply identified with 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.

was built in a similar way, with buildings on wooden piles. It became a city around 1300. Many Amsterdam canals were built as part of fortifications. They became  when the city was enlarged and houses were built alongside the water. Its nickname as the "Venice of the North" is shared with of Germany,  of Russia and  of Belgium.

was dubbed the "Venice of the East" by Marco Polo during his travels there in the 13th century, with its modern canalside and  becoming major tourist attractions. Other nearby cities including, , , , , , , , and are located along the lower mouth of the  and , yet another source of small rivers and creeks, which have been canalized and developed for centuries.



Other cities with extensive canal networks include:, , , , , , , , , , , , , , , and  in the Netherlands;  and  in Flanders, Belgium;  in England;  in Russia; , ,  and  in Poland;  in Portugal;  and  in Germany;  and  in , United States,  in China,  in Vietnam,  in Thailand, and  in Pakistan.

was a near the centre of, England, where a system of intertwining waterways and docks is now being developed for mainly residential and leisure use.

(sometimes known as bayous in the United States) are a form of popular in cities like,  and the ; the Gold Coast has over 890 km of residential canals. are difficult areas upon which to build housing estates, so part of the wetland down to a  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.

Boats
Inland canals have often had boats specifically built for them. An example of this is the British, which is up to 72 ft long and 7 ft 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 ships were limited to a length of 289.56 m and a beam of 32.31 m until 26 June 2016 when the opening of larger locks allowed for the passage of larger New Panamax ships. For the lockless Suez Canal the limiting factor for ships is generally draft, which is limited to 16 m. At the other end of the scale, tub-boat canals such as the  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 by tunnels.

Lists of canals

 * Africa
 * Egypt
 * Egypt
 * Egypt
 * Egypt
 * Egypt


 * Asia
 * see
 * see


 * Europe


 * North America

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