The Effects of Modifying the Geometric Shapes of steps in Stepped Spillway on Hydraulic Parameters and Energy Dissipation

Stepped spillways are a common structure for energy dissipation since they create turbulence and frictional resistance to flow through the steps, which increases energy dissipation along the structure. In this study, by performing a series of tests, the effect of modifying the shape of steps by simultaneously applying elements on the steps and their edge on the flow pattern, inception point on the spillway, hydraulic jump characteristics in the downstream, and energy dissipation were investigated. The pool edge elements were of two types (height and notch), and the elements placed on the steps were different arrangements. Their results were compared to the flat stepped spillway. Finally, by applying these elements on an operational spillway, the effect of step modifications on the flow characteristic was evaluated. The results showed that the simultaneous application of elements on the steps and the edge caused some turbulence and instabilities on the flow surface with fluctuations and had little effect on the flow regime. Turbulence flow due to colliding with elements affects the inception point, causing it to be transferred upstream of the stepped spillway. Step modification reduces the sequent depth and jump length by 26.29 and 34.24%, respectively, and increases the energy dissipation rate by 14.38%. The effect of additional elements on the performance of the stepped spillway is high at low discharges. Modification of Siah-Bisheh stepped spillway by applying elements on the steps reduces the flow velocity by 9.8% downstream of the spillway, increases turbulent kinetic energy (TKE) by 63%, and enhances the energy dissipation rate by 11.32%.