Aqueduct (water supply)

An aqueduct is a watercourse constructed to carry water from a source to a distribution point far away. In modern engineering, the term aqueduct is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose. The term aqueduct also often refers specifically to a bridge carrying an artificial watercourse. Aqueducts were used in ancient Greece, ancient Egypt, and ancient Rome. In modern times, the largest aqueducts of all have been built in the United States to supply large cities. The simplest aqueducts are small ditches cut into the earth. Much larger channels may be used in modern aqueducts. Aqueducts sometimes run for some or all of their path through tunnels constructed underground. Modern aqueducts may also use pipelines. Historically, agricultural societies have constructed aqueducts to irrigate crops and supply large cities with drinking water.

Etymology
The word is derived from the Latin aqua (water) and ductus (led, guided).

Ancient aqueducts
Although particularly associated with the Romans, aqueducts were devised much earlier in Greece and 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 an 80 km long limestone aqueduct, which included a 10 m high section to cross a 300 m wide valley, to carry water to their capital city, Nineveh.

India
The Indian subcontinent is believed to have some of the earliest aqueducts. Evidence can be found at the sites of present-day Hampi, Karnataka. The massive aqueducts near river Tungabhadra supplying irrigation water were once 15 mi long. The waterways supplied water to royal bath tubs.

Oman
In Oman from the Iron Age, in Salut, Bat, and other sites, a system of underground aqueducts called falaj or qanāts were constructed, a series of well-like vertical shafts, connected by gently sloping horizontal tunnels.

There are three types of falaj:
 * Daudi (داوودية) with underground aqueducts
 * Ghaili (الغيلية ) requiring a dam to collect the water
 * Aini (العينية ) whose source is a water spring

These enabled large scale agriculture to flourish in a dry land environment.

Persia
In Persia from early times a system of underground aqueducts called qanāts 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.

Petra, Jordan
Throughout Petra, Jordan, the Nabataean engineers took advantage of every natural spring and every winter downpour to channel water where it was needed. They constructed aqueducts and piping systems that allowed water to flow across mountains, through gorges and into the temples, homes, and gardens of Petra's citizens. Walking through the Siq, one can easily spot the remains of channels that directed water to the city center, as well as durable retention dams that kept powerful flood waters at bay.

Greece
On the island of Samos, the Tunnel of Eupalinos was built during the reign of Polycrates (538-522 BC). It is considered an underground aqueduct and brought fresh water to Pythagoreion for roughly a thousand years.

Roman


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 415 km. The aqueducts supplied fresh water to public baths and for drinking water, in large cities across the empire, and set a standard of engineering that was not surpassed for more than a thousand years. Bridges, built in stone with multiple arches, were a distinctive feature of Roman aqueducts and hence the term aqueduct is often applied specifically to a bridge for carrying water.

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 were 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.

The Guayabo National Monument of Costa Rica, a park covering the largest archaeological site in the country, contains a system of aqueducts. The complex network of uncovered and covered aqueducts still functions well. The aqueducts are constructed from rounded river stones, which are mostly made of volcanic rock. The civilization that constructed the aqueduct system remains a mystery to archaeologists; it is suspected that Guayabo's aqueducts sat at a point of ancient cultural confluence between Aztecs, Mayans, and Incas.

North America
When Europeans saw the Aztec capital Tenochtitlán, early in the 16th century, the city was watered by two aqueducts. One of these, Chapultepec Aqueduct, built circa 1420, was rebuilt by the Spanish almost three hundred years later. Originally tracing part of its path over now-gone Lake Texcoco, only a fragment remains in Mexico City today.

Sri Lanka
Extensive usage of elaborate aqueducts have been found to have been used in ancient Sri Lanka. The best example is the Yoda Ela or Jaya Ganga, an 87 km long water canal carrying excess water between two artificial reservoirs with a gradient of 10 to 20 cm per kilometer during the fifth century AD. However, the ancient engineering methods in calculating the exact elevation between the two reservoirs and the exact gradient of the canal to such fine precision had been lost with the fall of the civilization in 13th Century.

Modern aqueducts
Modern aqueducts are a central part of many countries' water distribution infrastructure.

The United States' aqueducts are some of the world's largest. 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 242-mile (389-km) Colorado River Aqueduct, which supplies the Los Angeles area with water from the Colorado River nearly 250 miles to the east and the 701.5 mile California Aqueduct, which runs from the Sacramento-San Joaquin River Delta to Lake Perris. The Central Arizona Project is the largest and most expensive aqueduct constructed in the United States. It stretches 336 miles from its source near Parker, Arizona to the metropolitan areas of Phoenix and Tucson.

An aqueduct in New Zealand, "the Oamaru Borough Race", was constructed in the late 19th century to deliver water (and water-power) about 50 km from the Waitaki River at Kurow to the coastal town of Oamaru.

In Spain, the Tagus-Segura Water Transfer system of aqueducts opened in 1979 and transports water 286 km from north to south.

In China, the South–North Water Transfer Project aims to connect the Yangtze River basin to Beijing through three separate systems. The project will reuse part of the Grand Canal of China.

Open channels
The simplest aqueducts are small ditches cut into the earth. Much larger channels may be used in modern aqueducts, for instance the Central Arizona Project uses 24 ft wide channels. A major factor in the design of all open channels is its gradient. A higher gradient allows a smaller channel to carry the same amount of water as a larger channel with a lower gradient, but increases the potential of the water to damage the aqueduct's structure. A typical Roman aqueduct had a gradient of about 1:4800.

Artificial rills


A constructed functional rill is a small canal or aqueduct of stone, brick, concrete, or other lining material, usually rectilinear in cross section, for water transportation from a source such as a river, spring, reservoir, qanat, or aqueduct for domestic consumption or agricultural irrigation of crop land uses.

Rills were traditionally used in Middle Eastern and Mediterranean climate cultures of ancient and historical eras; and other climates and continents worldwide. They are distinguished from a 'water ditch' by being lined to reduce absorption losses and to increase durability. The Falaj irrigation system at the Al Ain Oasis, in present-day Abu Dhabi Emirate, uses rills as part of its qanat water system. Sometimes in the Spanish language they are called Acequias.

Rills are also used for aesthetic purposes in landscape design. Rills are used as narrow channels of water inset into the pavement of a garden, as linear water features, and often tiled and part of a fountain design.

The historical origins are from paradise garden religious images that first translated into ancient Persian Gardens. Rills were later exceptionally developed in the Moorish (Spanish) Gardens of Al-andalus, such as at the Alhambra in Granada; and also in other Islamic gardens, cultures, and countries. Early 20th century examples are in the Maria Louisa Park gardens in Seville, Spain; and at the Casa del Herrero gardens in Montecito, California.

Tunnels
Aqueducts sometimes run for some or all of their path through tunnels constructed underground. A version of this common in North Africa and Central Asia that has vertical wells at regular intervals is called a qanat. One historic example found in Syria, the Qanat Firaun, extends over 100 kilometers.

Pipes


Modern aqueducts may also make extensive use of pipelines. Pipelines are useful for transporting water over long distances when it needs to move over hills, or where open channels are poor choices due to considerations of evaporation, freezing, pollution, or environmental impact. They can also be used to carry treated water.

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. It also help drought prone areas with water supply. Some of the Roman aqueducts still supply water to Rome today. In California, United States, 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 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.

Ancient Greek aqueducts

 * The Eupalinian aqueduct on the Greek island of Samos

Roman aqueducts

 * The Pont du Gard, constructed in the 1st century, in southern France.
 * The Aqueduct of Segovia, an aqueduct bridge is one of the most significant and best-preserved ancient monuments left on the Iberian Peninsula, Segovia, Spain
 * The Valens Aqueduct. a Roman aqueduct in the Eastern Roman capital of Constantinople, now Istanbul, Turkey.

Other aqueducts

 * Ponte Mantible Aqueduct in Santiago de Compostela, Spain, 12th century.
 * The Jerwan Aqueduct built by the Assyrian king Sennacherib dated to 688 BC, as part of the water supply system to the city of Nineveh
 * Wignacourt Aqueduct, Malta; built in the 17th century to transport water from Dingli and Rabat to the new capital city Valletta; today, most of its arches still survive in the localities of Attard, Balzan, Birkirkara, Fleur-de-Lys and Santa Venera
 * St-Clément Aqueduct, Montpellier, France, 17th century
 * Bar Aqueduct, Montenegro, 16th century
 * Águas Livres Aqueduct, in Lisbon, Portugal (built 1731–1748)
 * Acueducto de Albear Havana, Cuba. (Inaugurated January 22, 1893)
 * Óbidos Aqueduct, in Óbidos, Portugal (built 1570)
 * Setúbal Aqueduct in Setúbal, Portugal (built 1696)
 * Pegões Aqueduct in Tomar, Portugal (built 1593)
 * Água de Prata Aqueduct, in Évora, Portugal (built 1531–1537)
 * Santa Clara Aqueduct, in Vila do Conde, Portugal
 * Carioca Aqueduct in Rio de Janeiro, Brazil (built 1744–1750)
 * Teruel Aqueduct, Spain
 * Roquefavour Aqueduct, France, built between 1842 and 1847
 * Greater Winnipeg Water District Aqueduct, Manitoba, Canada, built between 1915 and 1919
 * Canal de l'Aqueduc, Quebec, Canada
 * Päijänne Water Tunnel, a 120-kilometer long underground aqueduct (continuous tunnel) connecting lake Päijänne to Greater Helsinki
 * Wan Mat Saman Aqueduct, Kedah, Malaysia, built between 1900 and 1909
 * Surviving Spanish aqueducts in Mexico:
 * Aqueduct of Querétaro, Mexico, built between 1726 and 1738, 1.3 km long and featuring 74 arches
 * Aqueduct of Morelia, Michoacán, built between 1735 and 1738
 * Aqueduct of Acámbaro, Guanajuato, built in 1528
 * Chapultepec aqueduct, Mexico D.F.
 * Kavala aqueduct, 16th-century Ottoman aqueduct in Kavala, Greece
 * Levadas, 1350 mi of 17th century aqueducts on the Portuguese island of Madeira
 * Skopje Aqueduct is located 2 km from the capital of North Macedonia.
 * Espada Aqueduct, built 1735, in San Antonio, Texas, United States
 * Quabbin Aqueduct, 24.6 mi long tunnel, in Massachusetts, United States
 * Chicopee Valley Aqueduct, 13.1 mi long, in Massachusetts, United States
 * Central Arizona Project Aqueduct
 * California Aqueduct, a 715 mi (1,151 km) combination of canals, pipelines, and tunnels, United States
 * Aqueducts in the New York City water supply system (all in New York State):
 * Croton Aqueduct, a large and complex water distribution system constructed between 1837 and 1842. Decommissioned in 1955 following improvements in the city's water system.
 * New Croton Aqueduct, built largely parallel to the original Croton Aqueduct and opened in 1890, supplementing the original Croton Aqueduct. Supplies about 10% of the city's water today.
 * Catskill Aqueduct, considerably larger than either Croton Aqueduct; built between 1907 and 1916, with construction on related infrastructure lasting through 1924. Carries water from watersheds in the Catskill Mountains, today supplying about 40% of the city's water.
 * Delaware Aqueduct, built between 1939 and 1945 to carry water from three reservoirs in the Delaware River watershed and one in the Hudson River watershed, supplying about half of the city's water. At 85 miles (137 km) long, it is the world's longest continuous tunnel.
 * Sooke Flowline located on Vancouver Island, Canada, is a 44 kilometres long, gravity-fed concrete pipe which provided water to the City Of Victoria for 55 years
 * Boothtown Aqueduct, in Sydney, Australia, completed in 1888
 * National Water Carrier of Israel located in Israel, is a 130 km long system of giant pipes, open canals, tunnels, reservoirs, and large scale pumping stations to transfer water from the Sea of Galilee in the north of the country to the highly populated center and arid south, built between 1953 and 1964
 * Kamares, Larnaca, Cyprus
 * Apulia Aqueduct, Apulia, Italy