Volume XV Issue 3

Recent advances in technology have permitted the construction of large high dams and large storage reservoirs. These advances have necessitated the development of new design and construction techniques, particularly pertaining to provision of adequate flood release facilities. Chutes and spillways are designed to spill large water discharge over a hydraulic structure without causing major damage to the structure itself and its environment.

Overflow spillways enable flood release over the dam. The water flows as open channel flow or as free falling jet and it is necessary to dissipate the major part of its kinetic energy. Otherwise the overflowing water could endanger the downstream toe, the surroundings and eventually the dam itself. Energy dissipation is usually achieved by:

• High velocity water jet taking off from a flip bucket and impinging into a downstream plunge pool acting as water cushion.

• A standard stilling basin downstream of the spillway where a hydraulic jump is created to dissipate a large amount of flow energy.

• The construction of steps on the spillway to assist energy dissipation of water flowing over a rough or stepped channel can dissipate a major proportion of its energy. In a stepped chute, the steps increase significantly the rate of energy dissipation taking place along the spillway face and thus eliminate or reduce greatly the need for a large energy dissipater at the toe of the spillway.

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