Investigation the Energy Dissipation on Gabion Stepped Weirs and Downstream Hydraulic Jump Characteristics

Net-Stone water structures, in particular gabion stepped weirs, have become more prevalent due to their significant impact on reducing energy dissipation, proper stability, cost-effectiveness, ease of construction, and increasing the level of oxygen in the mixed water. Furthermore, due to air entrainment, the flow rate passing through the structure can prevent a considerable amount of cavitation, which is one of the problems in the design of hydraulic structures such as weirs (Shamsayi and Paknahal, 2005). One of the important characteristics of this structure is the internal flow through the permeable body of the weir, which creates complexities in the flow behavior. The energy dissipation of gabion stepped weirs is a function of the upstream and downstream slope of the weir, the number of steps, porosity, and the Froude number. Changing the porosity leads to a change in the ratio of the internal flow to the overtopping flow, and consequently, the amount of energy dissipation changes.Wüthrich and Chanson (2014) and Pallavi and Harshith (2018) conducted experiments to investigate the flow characteristics of the overtopping and internal flow of gabion weirs and compared the hydraulic characteristics of this type of weir with a solid weir. The results showed that the energy dissipation in the gabion weir is higher than the solid weir due to the division of the overtopping and internal flow.The aim of this study is to investigate the effect of the number of steps in gabion stepped weirs with a fixed slope on the energy dissipation of the structure. It should be noted that in the case of a small number of steps, the flow conditions on the steps are often in a cascading form, which leads to more energy loss. Certainly, increasing the energy loss of the structure is affected by the downstream hydraulic jump conditions and the length of the calm pool.