ENERGY DISSIPATION DUE TO STEPPED SPILLWAYS

Abstract

A spillway is a structure for effectively disposing of the surplus water from the dam. The water flowing over the spillway acquires a lot of kinetic energy by the time it reaches near the toe. If arrangements are not made to dissipate this huge kinetic energy of the water, large scale scour can take place on the downstream side near the toe of the dam and away from it. In general, the kinetic energy of this supercritical flow can be dissipated in two ways : (i) By converting the supercritical flow into sub-critical flow by hydraulic jump. (ii) By directing the flow of water into air before its impact against a solid body or a water cushion. Some of the energy dissipating devices which use the above mentioned mechanisms are briefly described below : 1.2 Energy Dissipators 1.2.1 Friction Blocks The high velocity flow is allowed to impinge against solid blocks of masonry of various shapes and sizes. This impact causes turbulence and energy is dissipated in the form of heat and sound. This may also result in formation of hydraulic jump, thus further reducing the velocity and hence the kinetic energy of the flow.