Dam

A dam is a structural barrier designed to stop or restrict the flow of water. This water may come from surface streams or underground sources.

By holding water back, dams create reservoirs, which are large bodies of water. These reservoirs serve many vital purposes for human civilization. They help suppress floods to protect nearby land from rising water. They also provide a steady supply for irrigation to help crops grow. Humans use this stored water for drinking, industrial processes, and aquaculture, which is the farming of aquatic organisms.

Dams function by managing the movement and distribution of water. While a dam primarily retains water, other structures like floodgates or levees manage specific flows. Levees, also known as dikes, prevent water from entering certain land regions. Many dams are used for hydropower to generate electricity. This process often uses the energy of moving water to power turbines.

Dams allow water to be collected and then distributed evenly between different locations. This controlled release ensures that water is available even during dry periods.

Engineers use many different designs depending on the environment and purpose. Roman engineers were particularly innovative in this field. They introduced reservoir dams to secure water supplies for cities during dry seasons. They also developed arch-gravity dams and arch dams. An arch dam uses the reaction forces from the abutments, which are the sides of the valley, to stabilize the structure against hydrostatic pressure.

Other designs include buttress dams and multiple arch buttress dams. In Iran, engineers even built bridge dams, such as the Band-e Kaisar, to combine water management with transportation.

The history of dam building stretches back thousands of years to ancient civilizations. The Jawa Dam in Jordan is possibly the earliest known dam, dating to 3,000 BC. It was a gravity dam featuring a stone wall and an earthen rampart. In Egypt, the Sadd-el-Kafara Dam was built around 2800 or 2600 BC for flood control. The Great Dam of Marib in Yemen was an engineering wonder built between 1750 and 1700 BC. It used packed earth and substantial stonework to manage water.

In China, the Dujiangyan irrigation system was finished around 251 BC to direct water flow.

Roman engineering changed how large structures were built. They used advanced materials like hydraulic mortar and Roman concrete. These materials allowed them to build much larger barriers, such as the Lake Homs Dam in Syria. The Subiaco Dam near Rome reached a record height that was not surpassed until 1305. In the Middle Ages, the Netherlands used dams to regulate water levels and prevent the sea from entering marshlands. This influenced the names of major cities. Amsterdam began with a dam on the Amstel River, and Rotterdam began with a dam on the Rotte.

The 19th century saw significant advances in engineering techniques and materials. Large-scale arch dams were constructed throughout the British Empire. For example, the Mir Alam dam in India was completed in 1804. In Canada, the Rideau Canal system included curved masonry dams like the Jones Falls Dam, completed in 1832. Australia also saw early progress with the Hunts Creek dam in 1856. This was the first engineered dam in Australia and the second arch dam in the world built to mathematical specifications.

The modern era of large-scale dam construction began in the early 20th century. The Aswan Low Dam in Egypt was constructed in 1902. One of the most famous examples is the Hoover Dam in the United States. It is a massive concrete arch-gravity dam built on the Colorado River between 1931 and 1936.

The scale of dam construction has grown immensely over time. By 1997, there were an estimated 800,000 dams worldwide. Of these, approximately 40,000 dams were over 15 meters high. This widespread use of dams continues to shape how humans interact with the Earth's water systems.