How Aqueduct works and the history surrounding the system.

How Aqueduct works and the history surrounding the system.

A large-scale system for carrying water from one place to another is called an aqueduct. The word aqueduct comes from two Latin words: aqua, meaning ‘water', and ducere, meaning ‘to lead'. An aqueduct can take various forms. The water can be carried underground through a tunnel or pipe. It can be carried at ground level through a canal. Or it can be carried above ground level over a bridge. Sometimes the word aqueduct is used specifically to refer to the last type.

People have built aqueducts since ancient times. Even then, some cities grew too large for their freshwater supply or polluted it with wastes. Other places had good soil but too little rain to grow good crops. The solution to these problems was to build an aqueduct that connected the city or farmland to another source of freshwater.

How an Aqueduct Works

Early aqueducts depended on gravity to create the flow of water. The water source had to be higher than the destination so the water would flow downhill through the aqueduct's water channel.

Because these aqueducts needed a continuous downward flow, variations in the height of the land caused problems. A simple channel at ground level was rarely possible because of changes in elevation from mountains and hills to valleys. Sometimes people built aqueducts around mountains and through hills. To move water across valleys people sometimes built aqueducts in the form of arched bridges with two or three layers of arches on top of each other. The water flowed through a channel in the top of the uppermost layer.

Aqueducts that depend on downward flow are still built in some places, such as Iran and Afghanistan. However, most engineers today use powerful pumps to force water upwards when necessary. This advancement allows modern engineers to design aqueducts in ways that ancient engineers could not. Instead of building a bridge over a valley, for example, modern engineers can simply run pipes down one side of the valley and up the other.

History

Aqueducts were built by the people of ancient Greece, Babylonia, Assyria, Persia (now Iran) and India. Many of these aqueducts were tunnels dug into hillsides to carry water to farm fields for irrigation or to cities. The Assyrians used 2 million stone blocks to build an aqueduct to carry water to their capital, Nineveh.

The most popular system of ancient aqueducts was built by the ancient Romans. The city of Rome was served by 11 aqueducts that were built over a period of more than 500 years, from 312 BC to AD 226. The Romans also built aqueducts in other parts of their empire. Perhaps the finest Roman aqueduct bridge still standing is the Pont du Gard near the city of Nîmes in southern France. It consists of three rows of stone arches, one on top of the other, and is 49 metres (160 feet) high and almost 270 metres (900 feet) long.

In the Middle Ages most of the Roman aqueducts fell out of use. Some new aqueducts were built during this period in Western Europe, Asia and Africa, but they did not improve much on the Roman ones. In South America the Inca people built a system of aqueducts to carry water down from rivers in the Andes Mountains.

Pumps powered by steam were first used in the late 1700s. Later pumps were powered by electricity.