Overflow Dam

a dam designed for raising the water level of rivers or for creating a reservoir; it permits the overflow of water during the passage of excess (flash-flood) discharges over the entire length of the dam crest or through drain openings. The operation of the drain openings is regulated by gates depending on the quantity of the discharge and the water level in front of the dam. Drain openings can also be used for the passage of floating timber, ice floes, alluvium (in cases of low rapids), and ships (when current speeds permit). Intermediate drain openings are separated by piers, and the extreme openings are bounded by abutments, which also serve to link the spillway with the shores or with various components of the hydraulic power complex.

An overflow dam on a nonrocky bed also consists of a foreapron, a water apron, and a rear apron; on a rocky bed it is usually built without these structures. Overflow dams are made of concrete, reinforced concrete, stone, or wood. Those made of concrete and reinforced concrete may be as much as 300 m high, and the discharge of overflow water reaches several tens of thousands of cubic meters per second.