Abstract
A stepped spillway is a hydraulic structure built at storage and detention dams to discharge flood water that cannot be safely kept in the reservoir. It was created to minimize the kinetic energy that would have otherwise produced dangerous scour at the natural river bed beneath the spillway. They discharge this energy in floodwater using their stepping nature. Several studies show the detrimental consequences of falling water's kinetic energy on the river bed underneath the structure. Only a handful of these studies, however, have evaluated the impact of energy losses caused by stepped spillways with channel slopes 26.6° or less. As a result, there are gaps in the rules and recommendations for designers of stepped spillways with channel slopes below 26.6°. Furthermore, the existing models for forecasting energy dissipation in stepped spillways for channels of all slopes include a parameter, the friction factor, f, which is difficult to estimate with precision, leading to its subjective estimation by those involved in the stepped spillway design. The goal of this study is not only to provide designers with design recommendations and information for stepped spillways with channel slopes below 26.6°, but also to eliminate the 'troublesome' frictional factor; f. Using phase-detection intrusive probes, air-water flow tests were carried out in nappe, transitional, and skimming flows on a stepped spillway with channel slope below 26.6° in a large facility. New expressions for evaluating energy losses in stepped spillways with slopes 26.6° or less are developed. Regarding energy dissipation, the data from the latest models compare well with the measured data, with high coefficients of correlation that range between 0.95 and 0.99. All of the measured data and the estimated data are in good agreement. The models are simple to use.
Published Version
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