Spillway(redirected from wasteweir)
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a hydraulic structure for the discharge of excess (flood) water from a reservoir and for the useful release of water into tailwater. A spillway may have openings: surface openings on the crest of a dam, openings sunk below the level of the headwater, other types of deep openings, or two kinds of openings, as in a two-stage spillway. The flow of water is regulated by locks. Some automatic spillways (for example, those working by means of siphons or shafts) are not equipped with locks. Spillways that are built in the bypass of concrete and earthen dams are called coastal spillways.