Flow Resistance in Skimming Flows and its Modelling

Dams and weirs must be equipped with adequate flood release facilities for a safe dissipation of the kinetic energy of the flow. With stepped spillway design, it is essential to predict accurately the flow resistance associated with the steps. The authors investigate the flow resistance of skimming flows and associated form losses. Recent experiments were systematically performed with channel slopes ranging from 5.7 deg. up to 55 deg.. The results provide a better understanding of the basic flow patterns and flow resistance mechanisms. They emphasise that form loss is dominant. Simple analytical models provide a reasonable order of magnitude of the pseudo-boundary shear stress and of the cavity ejection mechanism. Altogether more than 38 model studies and 4 prototype investigations (totalising more than 700 data points) are re-analysed.

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