A reservoir is an artificial (man-made) lake. It is created by flooding the land behind a dam. Some of the world's largest lakes are reservoirs.

Lake Eucumbene in Australia

Construction of a reservoir

• A suitable site has to be found to build a reservoir. Surveyors (people who look at buildings and land) have to study river valley sites. A suitable site is a deep, narrow river valley, where water is trapped between the valley sides. The valley sides act as natural walls.

• The surveyors and engineers now have to decide the best place for building the dam.

• If the river valley is inhabited (people live there), then the inhabitants will have to be moved to other places. Sometimes people do not want to move house.

• If there are historic sites or places of interest in the river valley, these have to be either photographed or moved to other locations. The two temples of Abu Simbel in Egypt had to be moved to a new site. Otherwise they would have been under water when Lake Nasser flooded.

• Houses, hedges and trees have to be destroyed before the reservoir can be built. They would be dangerous to people swimming in the reservoir.

• The grass in the valley is removed by JCB's. The valley is then lined with sand, followed by a layer of clay. The clay stops the water from leaking out of the reservoir.

• Construction starts on the dam about half a mile upstream of the reservoir site.

• Once the dam has been built, the holes or gates in the dam are closed so that water can build up behind the dam and flood the land.

• Once the reservoir is filled, the people who look after the dam and reservoir open some of the holes or gates so that the river maintains a normal water level.

• Sometimes a Visitors' Centre is built.

The construction of a new dam and reservoir in Panama

Uses of a reservoir

Reservoirs are used for many purposes:-

• Domestic: water from a reservoir is pumped into the Water Supply Works for cleaning and treatment so that it is suitable for drinking and use by the public.

• Industrial: water is pumped into factories and is used for cooling down machinery.

• Irrigation: water is pumped into irrigation channels (sometimes called aqueducts) to water crops.

• Recreational: a reservoir is sometimes used for water sports and as a wildlife area.

Examples of reservoirs

There are many reservoirs in the World. The most famous is Lake Nasser, behind the Aswan Dam in Egypt. Reservoirs are found behind all of the world's dams. Many reservoirs don't have a name. Bewl Water is an example of a reservoir in Kent.

Bewl Water in Kent

The frozen reservoir in Central Park, New York