Aqueduct

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This article is about the structure aqueduct, for the racecourse see Aqueduct Racetrack.

An aqueduct is an artificial (man-made) channel that is constructed to convey water from one location to another. The word derives from the Latin words aqua, "water", and ducere, "to lead". Many aqueducts are raised above the landscape, resembling bridges rather than rivers. Sufficiently large aqueducts may also be usable by ships. They are a kind of viaduct, carrying water instead of a road or railway. While a road bridge often carries the roadway at a more elevated level than the rest of the road, such a variation of height is not possible for an aqueduct.

1 History
2 Uses of aqueducts
3 Notable aqueducts
4 See also
5 External links and references

History

Although most famously associated with the Romans, aqueducts were devised centuries earlier in the Middle East, where peoples such as the Babylonians and Egyptians 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).

The Romans constructed numerous aqueducts to supply water to cities and industrial sites. The city of Rome itself had the largest concentration, with water being supplied by eleven aqueducts constructed over a period of 500 years. Their combined length was nearly 260 miles (350 km). However, only 29 miles (47 km) were above ground, as most Roman aqueducts were constructed below the surface. The Eifel Aqueduct in Germany provides a very well-preserved example of this type. This method of conveyance helped to keep the water free from disease (the carcasses of animals would not be able to get into the aqueduct) and helped protect them from enemy attack. The longest Roman aqueduct, 87 miles (141 km) in length, was built in the 2nd century AD to supply Carthage in what is now Tunisia.

Roman aqueducts were extremely sophisticated constructions. They were built to remarkably fine tolerances, and of a technological standard that was not to be equaled for over 1000 years after the fall of the Roman Empire. For example, the aqueduct of Pont du Gard in Provence had a gradient of only 34 cm per km (1:3,000), descending only 17 m vertically in its entire length of 31 miles (50 km). Powered entirely by gravity, they transported very large amounts of water very efficiently (the Pont du Gard carried 20,000 cubic meters {44 million gallons} a day). Sometimes, where depressions deeper than 50 m had to be crossed, gravity pressurised pipelines called inverted siphons were used to force water uphill (although they almost always used venter bridges as well). Modern hydraulic engineers use similar techniques to enable sewers and water pipes to cross depressions.

Image:Arizona cap canal.jpg

Much of the expertise of the Roman engineers was lost in the Dark Ages, and in Europe the construction of aqueducts largely ceased until the 19th century. Water was instead usually supplied through the digging of wells, though this could cause serious public health problems when local water supplies became contaminated. One notable exception was the New River, a man-made waterway in England, opened in 1613 to supply London with fresh drinking water over a distance of 38 miles (62 km). The development of canals provided another spur to aqueduct building. However, it was not until the 19th century that aqueduct building resumed on a large scale to supply fast-growing cities and water-hungry industries. The developments of new materials (such as cast iron) and new technologies (such as steam power) enabled significant improvements to be made. For instance, cast iron permitted the construction of larger, more highly pressurised inverted siphons, while steam- and electrically-powered pumps enabled a major increase in the quantity and speed of water flow. England led the world in aqueduct construction, with notable examples being built to convey water to Birmingham, Liverpool and Manchester.

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. Although such aqueducts are undoubtedly great engineering achievements, the huge quantity of water that they transport has resulted in serious environmental damage from the depletion of river water.

Uses of aqueducts

Image:Nanzenji aqueduct channel.jpg

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.

Notable aqueducts

Navigable aqueducts

aqueduct near Roelofarendsveen, Netherlands: carries the Ringvaart canal over the A4 highway and the HSL being constructed, which are situated on land below the level of the canal (and below sea level)
Gouwe aqueduct, near Gouda, Netherlands: carries the Gouwe river over the A12 highway, which is on land below the level of the river
Benjamin Outram's 44ft-long single-span Holmes Aqueduct on the Derby Canal in Derby was the world's first navigable cast iron aqueduct, narrowly predating Thomas Telford's 186ft-long Longdon-on-Tern Aqueduct on the Shrewsbury Canal, sometimes described as the world's first large-scale navigable cast iron aqueduct.
the Pontcysyllte Aqueduct carries the Llangollen Canal over the River Dee in north Wales, and was designed by Thomas Telford and opened in 1805.
the Union Canal in Scotland has many aqueducts, including the Slateford Aqueduct that takes the canal over the Water of Leith, the Almond Aqueduct over the River Almond at Ratho and the very impressive Avon Aqueduct over the River Avon. This is the second longest aqueduct in the United Kingdom.
in recent years the building of the Lichfield Aqueduct prompted the UK government to pass legislation preventing a road being built in the path of a canal being renovated without providing a tunnel or aqueduct for it to pass.
The Bridgewater Canal is carried across the lower Manchester Ship Canal by the Barton Swing Aqueduct - a form of swing bridge. A 234ft section of the aqueduct rotates through 90 degrees to allow vessels to pass along the Ship Canal.