Dams, Reservoirs, and Water Storage

Large dams and their reservoirs are the primary engineered tool societies use to convert an unreliable, seasonal river flow into a stored, controllable water supply for irrigation, drinking water, flood control, and hydroelectric power. According to the register maintained by the International Commission on Large Dams (ICOLD), the world now holds more than 58,000 large dams, a category ICOLD defines by height and reservoir capacity thresholds, with construction concentrated especially in the mid-twentieth century and, more recently, in China. The Three Gorges Dam on the Yangtze River in China, completed structurally in 2006 with its final generating units brought online in 2012, is the world's largest hydropower station by installed generating capacity, at roughly 22,500 megawatts, and its reservoir required the resettlement of an estimated 1.3 million people, making it one of the largest dam-related displacements in history.