Posted: 23 January 2001

Structures designed to restrict the flow of surface runoff, usually to control flooding or to provide water for irrigation or the production of hydroelectricity. They range from relatively small earth-fill features, pounding back thousands of cubic metres of water, to massive reinforced concrete structures which create reservoirs containing several billion cubic metres of water. All dams, large or small, have an environmental impact on the area in which they are built. The obvious change is in the hydrological cycle, but environmental interrelationships ensure that the effects are felt in the local climatology and in the flora and fauna of the region.