Aqueduct edit
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Aqueduct edit
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It has been suggested that this article be split into articles entitled Aqueduct (pipeline), Aqueduct (bridge), Navigable aqueduct and Cerebral aqueduct, accessible from a disambiguation page. (Discuss) |
An aqueduct is a water supply or navigable channel (conduit) that is constructed to convey water from one location to another. 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. Sufficiently 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 are water pumps or siphons). The word is derived from the Latin aqua ("water") and ducere ("to lead").
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Although famously 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 limestone aqueduct 30 feet (10 m) high and 900 feet (300 m) long to carry water across a valley to their capital city, Nineveh. The full length of the aqueduct ran for 50 miles (80 km).
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.
The Indian subcontinent witnessed the construction of some of the earliest aqueducts. Prominent 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) long2. The elegant water ways were designed to supply water to royal bath houses.
In Persia from early timesvague a system of underground aqueducts called Qanat were constructed, a series of well-like vertical shafts, connected by gently sloping tunnels. This technique:
Roman aqueducts were built in all parts of the Roman Empire, from Germany to Africa, and especially in the city of Rome itself, where they totalled over 260 miles (416 km). The aqueducts were important for supplying water to large cities across the empire, and they set a high standard of engineering that was not surpassed for more than a thousand years.
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 familiar construction material widely used by the Nazca culture. The exact time period in which they were constructed is still debated, but some evidence supports that they may have been built circa A.D. 540-552, in response to several drought periods in the region.3
In modern times the largest aqueducts of all have been built in the United States to supply that country's biggest cities. The Catskill Aqueduct carries water to New York over a distance of 120 miles (190 km), but it 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 Delta to Lake Perris.
Historically, many agricultural societies have constructed aqueducts to irrigate crops. Archimedes invented the water screw to raise water for use in irrigation of croplands.
Another widespread use for aqueducts is to supply large cities with clean drinking water. Some of the famed 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, many aqueducts were constructed as part of the general 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. The aqueduct is a simple way to get water to other ends of a field.
In the past, aqueducts often had channels made of earth or other porous materials. 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.
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 2 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.
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