dammen

A dam is a barrier constructed across a river or valley to hold back water and form a reservoir. Dams are built to manage water resources, reduce flood risk, generate hydroelectric power, supply irrigation and drinking water, support navigation, and provide recreational opportunities. The term is used for both the barrier itself and the structure that contains the reservoir.

There are several dam types. Gravity dams rely on their weight to resist water pressure; arch dams transfer pressure to the canyon walls; buttress dams use reinforced supports on the downstream side; embankment dams are built from earth or rock fill. Many modern dams combine elements of these types and rely on reinforced concrete.

Common components include the reservoir, intake structures and gates, spillways to release excess water, a powerhouse for electricity generation, and a foundation and outlet works for maintenance and environmental flow.

Dams have a long history, with some of the earliest examples built in ancient Mesopotamia and Egypt. In the modern era, large-scale projects such as the Hoover Dam on the Colorado River, the Aswan High Dam in Egypt, the Three Gorges Dam in China, and Itaipu on the Paraná River have shaped regional development and energy policy.

Dams can have significant environmental and social impacts, including habitat alteration, changes in sediment transport, disruption of fish migrations, displacement of communities, and increased evaporation losses. Proper design, operation, and decommissioning practices aim to mitigate these effects and enhance safety, with regulatory oversight and dam safety evaluations.

Related topics include hydroelectric power, reservoir management, dam safety, spillways, and irrigation.