Journal of Engineering Research and Reports

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 produced dangerous scour at the natural river bed beneath the spillway. It discharges this energy in floodwater using their stepping nature. Several studies in the literature 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 slope of 8.9^o. As a result, there are gaps in the rules and recommendations for designers of stepped spillways with a channel slopes of 8.9^o. Additionally, the existing models for estimating energy losses in stepped spillways with channels of all slopes contain a parameter, the friction factor, f, which is difficult to estimate with certainty, thereby to leading their subjective provision by the designers involved in stepped spillways design.

The goal of this study is not only to provide designers with design recommendations and information for stepped spillways with a channel slope of 8.9^o, but also to eliminate the 'troublesome' frictional factor; f. Using phase-detection intrusive probes, air-water flow tests were carried out in transitional and skimming flows on a stepped spillway with channel slope of 8.9° in a large facility. Three new expressions for evaluating energy losses in stepped spillways with slopes of 8.9^o are developed. In terms of energy dissipation, the data from the new models compared well with the measured data, with high coefficients of correlation that range between 0.87 and 1.00. All of the measured data and the estimated data are in good agreement. The models are simple to use.