Energy Loss Evaluation of Two Phase Over- Flow of Stepped Spillway with Downstream Scour Depth Method

Document Type : Research Article


Assistant Professor, Water Department, Shiraz University, Shiraz, Iran


Stepped spillways with high roughness initiate the formation of vertical turbulence with high intensity. This turbulence causes air entrainment and as a result a two phase flow is formed. Energy dissipation under this condition is one of the most important aspects of the complicated nature of stepped spillways. In this study, energy loss was determined by the method of downstream scour depth measurement. Two slope angles of 18.8 and 28 degrees with four step heights of 3, 5, 8 and 12 centimeters and five discharges of 6, 10, 15, 20 and 25 liters per second were implemented (total of 40 runs). The results showed that when the above method was compared to the method of air concentration measurement, the scour depth method was simpler and more practical. The analysis also showed that a strong correlation exists between roughness Froude number and flow condition for the three different cases. This is an indication of the significance of this dimensionless number in stepped spillway studies. Finally the method used in this study for residual energy measurements under a wide range of flow condition, yielded a new empirical formula. Roughness Froude number, number of steps and slope of the spillway are the main parameters of this formula.