reservoirs

A reservoir is a large storage space for water, typically created to meet human needs such as water supply, irrigation, hydropower, flood control, and recreation. Most reservoirs are artificial lakes formed by damming rivers or streams, though natural lakes and basins can be used as reservoirs when water storage is managed for public use. Reservoirs are defined by their storage capacity, surface area, and the water level that can be reliably withdrawn for use.

Dams and associated structures (spillways, outlet works, intakes) form reservoirs. Storage is described in terms of total (gross) storage and active (live) storage, with a portion of the water held as dead storage that cannot be easily withdrawn. Pumped-storage reservoirs exist to store energy by pumping water uphill during low-demand periods and releasing it through turbines during peak demand.

Typical uses include municipal and industrial water supply, agricultural irrigation, generation of hydropower, flood management, navigation support, and recreational activities such as boating and fishing. Reservoir operations depend on inflows from catchments, evaporation losses, sedimentation, and ecological considerations. Sedimentation can reduce capacity and alter water quality, while evaporation can be significant in hot climates.

Environmental and social impacts may include displacement of communities, changes to aquatic and terrestrial ecosystems, sediment transport disruption, and water-quality changes. Reservoir management often involves balancing water rights, environmental protections, dam safety, and long-term infrastructure maintenance.

Notable examples include Lake Mead and Lake Powell on the Colorado River in the United States, the Three Gorges Reservoir in China, and Lake Nasser in Egypt. Reservoirs continue to be central to water security and energy systems, while requiring careful planning and stewardship to mitigate adverse effects.