Reservoirs are predominantly artificial bodies of water, created through human engineering to store water for various uses. They function as artificial lakes, collecting and holding water for specific purposes. While the term “reservoir” can sometimes refer to natural storage areas, the vast majority serving human communities are constructed by modifying the landscape. These structures play a significant role in global water management.
Creating a Reservoir
A reservoir is created by constructing a dam across a river or stream, which impounds water upstream to form a large body of water. Site selection for a dam is a complex process, considering topography, underlying geology, and sufficient water supply from the catchment area. Ideal locations often feature narrow river valleys or gorges, which naturally maximize water storage capacity for a given dam height.
Dam structures vary widely in material and design. Embankment dams, commonly made from compacted earth or rockfill, are prevalent and can be adapted to diverse terrains. These dams rely on their sheer mass to resist water pressure.
Concrete dams, including gravity dams, arch dams, and buttress dams, are another type. Gravity dams use their weight for stability, while arch dams transfer water forces to the valley sides. Once the dam is complete, the area behind it is flooded. The basin fills naturally over months or even years, often after diverting river flow during construction.
Why Reservoirs Are Built
Reservoirs serve multiple purposes for human societies, providing essential water management functions. A primary use is supplying drinking water to communities, storing it during wetter periods for continuous supply. This water undergoes treatment before distribution. Reservoirs also provide water for agricultural irrigation, supporting crop growth, especially in arid regions.
Beyond direct water supply, reservoirs are instrumental in flood control, impounding excess water during heavy rainfall to prevent downstream flooding. They then release this water gradually, regulating river flow. Many reservoirs are also built to generate hydroelectric power, utilizing falling water to drive turbines. Additionally, reservoirs often support recreational activities like fishing and boating, contributing to local economies.
Reservoirs Versus Natural Lakes
The distinction between reservoirs and natural lakes lies in their origin. Reservoirs are intentionally engineered and constructed by humans, typically by building a dam. In contrast, natural lakes form through geological processes over long periods, such as glacial erosion, tectonic activity, or volcanic eruptions.
Due to their man-made nature, reservoirs often exhibit different physical characteristics compared to natural lakes. They typically follow river valley contours, resulting in an elongated or branching shape, with the deepest section behind the dam. Natural lakes, formed by diverse geological events, have more varied shapes. Reservoirs are managed for specific utilities, leading to controlled water level fluctuations, unlike natural lake levels influenced by rainfall and evaporation. Their creation and management reflect their distinct origins.