aqueduct

The Pont du Gard that spans the River Gard near Nîmes in southern France. With a height of 48 m/160 ft, it is one of the highest Roman bridges built to carry an aqueduct.

The Aqueducte de les Farreres near Tarragona, in Catalonia, Spain. This is named after the local rust-red water, and is also known as the Ponte del Diable (‘Devil's Bridge’).

Any artificial channel or conduit for water, originally applied to water supply tunnels, but later used to refer to elevated structures of stone, wood, or iron carrying navigable canals across valleys. One of the first great aqueducts was built in 691 BC, carrying water for 80 km/50 mi to Ninevah, capital of the ancient Assyrian Empire. Many Roman aqueducts are still standing, for example the one carried by the Pont du Gard at Nîmes in southern France, built about 8 BC (48 m/160 ft high).

The largest Roman aqueduct, at Carthage in Tunisia, is 141 km/87 mi long and was built during the reign of Publius Aelius Hadrianus between AD 117 and 138. A recent aqueduct is the California State Water Project taking water from Lake Oroville in the north, through two power plants and across the Tehachapi Mountains, more than 177 km/110 mi to southern California.

Roman period The Romans went to great lengths to provide supplies of water to towns and cities for domestic and industrial uses. Rome was supplied by eight aqueducts with a combined length of nearly 350 km/220 mi (only 47 km/29 mi above ground) and long aqueducts were built elsewhere in Italy, in France and Spain, and in North Africa. Usually Roman aqueducts were open channels following a gentle upward gradient (generally 1:200-1:1,000) but occasionally pressurized pipelines, called inverted siphons, were used to cross deep depressions. Roman engineers fabricated such pipes from lead notably at Lyon, where four aqueducts featured no less than nine siphons. Examples of surviving aqueducts which bear striking testimony to the engineering skill of the Romans occur in and near Rome, at Cherchel in Algeria, and at Mérida and Segovia in Spain, which was in daily use until early in the 20th century. One of the highest of all Roman bridges, the Pont du Gard, was built to carry the aqueduct which conveyed water to Nîmes in southern France.

17th century Subsequent to the Roman period and prior to the 19th-century, water-supply aqueducts were rarely built. A notable exception, however, was the New River in England, authorized by an act of Parliament in 1606, between Amwell in Hertford to Camberwell in London; it was 62 km/38.5 mi long.

The first major canal to use aqueducts for river crossings was the Languedoc Canal in France, with its first single-arched aqueduct completed c.1680.

19th century In the 19th century aqueducts were built in increasing numbers, to larger sizes and over longer distances. Brick and later on concrete were used to fabricate both open channels and closed conduits and the increasing availability of cast iron prompted a much greater reliance on inverted siphons under high pressure. Steam- and electrically-driven pumps were introduced to increase quantities and speeds of flow. Notable 19th-century aqueducts in England were built to convey water to Manchester, Liverpool, and Birmingham.

Modern aqueducts The largest modern aqueducts are in the USA. New York's Catskill Aqueduct is 190 km/120 mi long and able to deliver 32 m3/s; in southern California the Colorado River Aqueduct supplies Los Angeles and its adjacent communities with 53 m3/s from the Colorado River nearly 400 km/250 mi to the east.