A reservoir is a natural or artificial lake used for the storage, regulation, and controlled release of water. Reservoirs are critical components of water supply, flood control, and hydropower systems.
A reservoir is a body of water, typically created by constructing a dam across a river, used to store water for municipal supply, agricultural irrigation, industrial use, hydroelectric power generation, flood control, navigation, recreation, and environmental flow management. Reservoirs can also be natural lakes modified by outlet control structures or purpose-built off-channel storage facilities. Reservoir design involves balancing storage capacity against inflow variability, downstream demand, flood risk, and environmental requirements using techniques such as mass curve analysis, stochastic hydrology, and operations optimization models. Key operational parameters include conservation storage (the volume held for water supply), flood control storage (empty volume reserved to capture flood peaks), and dead storage (volume below the lowest outlet that cannot be released). Reservoir sedimentation is a major long-term challenge, as trapped sediment gradually reduces storage capacity; globally, reservoirs lose an estimated 0.5-1 percent of their storage capacity annually to sedimentation. Evaporative losses from reservoir surfaces can be substantial, particularly in arid and semi-arid regions, sometimes exceeding 10 percent of stored volume annually. Reservoirs alter downstream hydrology, water temperature, sediment transport, and aquatic habitat, requiring careful environmental management of releases. The world's total reservoir storage capacity is estimated at approximately 8,300 cubic kilometers, equivalent to about 20 percent of mean annual global river runoff.