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Aqueduct (structure)

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For other uses, see Aqueduct (structure) (disambiguation).
Pont du Gard, France, a Roman aqueduct built circa 19 BC. It is one of France's top tourist attractions and a World Heritage Site.
Aqueduct of Pegões, Tomar, Portugal. It was built between 1593 and 1614, to serve the Convent of Christ

An aqueduct is a water supply or navigable channel (conduit) constructed to convey water. In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose.[1]

In a more restricted use, aqueduct (occasionally water bridge) applies to any bridge or viaduct that transports water —instead of a path, road or railway —across a gap. Large navigable aqueducts are used as transport links for boats or ships. Aqueducts must span a crossing at the same level as the watercourses on each side. (Alternative solutions involving a change of water level are a water pump or siphon for water transport, or a boat lift, pound lock, or canal inclined plane for boat movement.) The word is derived from the Latin aqua ("water") and ducere ("to lead").

Ancient aqueducts

View from inside a Roman aqueduct from the Pools of Solomon to Jerusalem
Ancient Indian aqueduct in Hampi
An entrance to the ancient Puquios, near Nazca, Peru

Although particularly associated with the Romans, aqueducts were devised much earlier in the Near East and Indian subcontinent, where peoples such as the Egyptians and Harappans built sophisticated irrigation systems. Roman-style aqueducts were used as early as the 7th century BC, when the Assyrians built a 50 mile (80 km) long limestone aqueduct, 30 feet (10 m) high and 900 feet (300 m) wide, to carry water across a valley to their capital city, Nineveh.

In the new world, when the Aztec capital of Tenochtitlán was discovered in the middle of the second millennium, it was watered by two aqueducts.

India

The Indian subcontinent had some of the earliest aqueducts. Evidence can be found at the sites of present day Hampi. The massive aqueducts near river Tungabhadra supplying irrigation water were once 15 miles (24 km) long[2]. The water ways supplied water to royal bath houses.

Persia

Main article: Qanat

In Persia from early times [vague] a system of underground aqueducts called Qanat were constructed, a series of well-like vertical shafts, connected by gently sloping tunnels. This technique:

  • taps into subterranean water in a manner that delivers water to the surface without need for pumping. The water drains relying on gravity, with the destination lower than the source, which is typically an upland aquifer.
  • allows water to be transported long distances in hot dry climates without losing a large proportion of the source water to seepage and evaporation.

Roman

Main article: Roman aqueduct

Roman aqueducts were built in all parts of the Roman Empire, from Germany to Africa, and especially in the city of Rome, where they totalled over 260 miles (416 km). The aqueducts supplied water to large cities across the empire, and set a standard of engineering that was not surpassed for more than a thousand years.

South America

Near the Peruvian town of Nazca, an ancient pre-columbian system of aqueducts called Puquios were built and are still in use today. They are made of intricately placed stones, a construction material widely used by the Nazca culture. The time period in which they were constructed is still debated, but some evidence supports circa A.D. 540-552, in response to drought periods in the region.[3]

Modern aqueducts

In modern times, the largest aqueducts of all have been built in the United States to supply the country's biggest cities. The Catskill Aqueduct carries water to New York City over a distance of 120 miles (190 km), but is dwarfed by aqueducts in the far west of the country, most notably the Colorado River Aqueduct, which supplies the Los Angeles area with water from the Colorado River nearly 250 miles (400 km) to the east, and the 444 mile (714.5 km) California Aqueduct, which runs from the Sacramento-San Joaquin River Delta to Lake Perris.

Uses

Historically, agricultural societies have constructed aqueducts to irrigate crops. Archimedes invented the water screw to raise water for use in irrigation of croplands.

Another use for aqueducts is to supply large cities with drinking water. Some of the Roman aqueducts still supply water to Rome today. In California, USA, three large aqueducts supply water over hundreds of miles to the Los Angeles area. Two are from the Owens River area and a third is from the Colorado River.

In more recent times, aqueducts were used for transportation purposes to allow canal barges to cross ravines or valleys. During the Industrial Revolution of the 18th century, aqueducts were constructed as part of the boom in canal-building.

In modern civil engineering projects, detailed study and analysis of open channel flow is commonly required to support flood control, irrigation systems, and large water supply systems when an aqueduct rather than a pipeline is the preferred solution.

In the past, aqueducts often had channels made of earth or other porous materials but significant amounts of water are lost through such unlined aqueducts. As water gets increasingly scarce, these canals are being lined with concrete, polymers or impermeable soil. In some cases, a new aqueduct is built alongside the old one because it cannot be shut down during construction.

Notable aqueducts

Ancient Greek aqueducts

Roman aqueducts

See also: List of aqueducts in the Roman Empire
Segovia, Spain. Roman aqueduct
Roman aqueduct supplying Carthage, Tunisia
File:Valens Aqueduct in Istanbul.jpg
Valens Aqueduct, Istanbul, Turkey
Aqueduct near Tokatee Falls in Oregon
Roman-era aqueduct near Skopje.

Other aqueducts

See also: List of canal aqueducts in Great Britain
The Longden-on-Tern aqueduct
Pontcysyllte Aqueduct on the Llangollen Canal, Wales. Built for the transport of goods, the canal is now used for leisure
A canal boat traverses the Pontcysyllte Aqueduct

Navigable aqueducts are bridge structures which carry canals over other rivers, valleys or railways or roads. They are primarily distinguished by their size, carrying a larger cross-section of water than most water-supply aqueducts. Although Roman aqueducts were sometimes used for transport, aqueducts were not generally used until the 17th century when the problems of summit level canals had been solved and the modern canal system started to appear.

Early aqueducts such as the three on the Canal du Midi (1683) were stone or brick arches, the longest span being 18.3 m on the Cesse Aqueduct (1686). However the weight of the construction to support the trough with the clay or other lining to make it waterproof made these structures clumsy and it was not until 1796 that the first large cast iron aqueduct was built at Longdon-on-Tern by Thomas Telford on the Shrewsbury Canal. It has a total length of 57 m with 3 intermediate piers. Within 10 years he had completed the far more ambitious Pontcysyllte Aqueduct over the Dee valley on the Llangollen Canal which has a total length of 307 m. Other cast iron aqueducts followed such as the single span Stanley Ferry Aqueduct on the Calder and Hebble Navigation in 1839 with its innovative 50 m through arch design.

The impact of new materials can be seen in the experience of the Canal latéral à la Loire in France. It had two substantial arch aqueducts on the higher stretches of the Loire, the longest being 470 m completed in 1838, but a river-level crossing was used to cross the Loire to the Canal de Briare because the consequent obstruction to the river during flooding was considered unacceptable. This proved troublesome until the 662 m long steel Briare aqueduct was built in 1896, which remained the longest aqueduct in the world until the 21st century when the Magdeburg Water Bridge in Germany took the title.

Notable navigable aqueducts

File:Nanzenji aqueduct channel.jpg
Water channel of the Nanzen-ji aqueduct, Kyoto, Japan
The Magdeburg Water Bridge seen from the shores of the Elbe.

See also

References

  1. ^ "aqueduct", Britannica CD 2000
  2. ^ http://books.google.ca/books?id=_kc3LKI_slEC
  3. ^ http://www-unix.oit.umass.edu/~proulx/online_pubs/Zurich_Puquios_revised_small.pdf
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