- 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 road at a more elevated level than the rest of the road, such a variation of height is not possible for an aqueduct.
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 of aqueducts, with water being supplied by eight aqueducts constructed over a period of 500 years, with a combined length of nearly 220 miles (350 km). Only 29 miles (47 km) of these were above ground, however; most Roman aqueducts were constructed underground (the Eifel Aqueduct in Germany provides a very well-preserved example). The longest Roman aqueduct was the one built in the 2nd century AD to supply Carthage in what is now Tunisia, which ran for 87 miles (141 km).
Roman aqueducts were extremely sophisticated constructions, of a technological standard which was not to be equalled for over 1000 years after the fall of the Roman Empire. They were built to remarkably fine tolerances: the aqueduct of which Pont du Gard in Provence was a part 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). They were powered entirely by gravity, transporting very large amounts of water very efficiently (the Pont du Gard carried 20,000 cubic meters (44 million gallons) a day). Sometimes, where deep depressions had to be crossed, pressurised pipelines called inverted siphons were used to force water uphill. Modern hydraulic engineers use similar techniques to enable sewers and water pipes to cross depressions.
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 concrete and 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 led to serious environmental damage resulting from the depletion of rivers.
Uses of aqueducts
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 elevations. 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.
Navigable aqueducts include
Roman aqueducts include
Other aqueducts include
External links and references
Last updated: 07-31-2005 23:22:07
Last updated: 08-18-2005 09:51:25