Characteristics of hydraulic jump and energy dissipation in the downstream of stepped spillways with rough steps

Stepped spillways are used to improve the hydraulic performance of a water-flow structure. This research describes the study of two types of physical models to investigate the impacts of rough steps on stepped spillways in terms of energy dissipation and hydraulic jumps. To this end, six stepped spillway models, including a flat spillway with smooth steps and five models with rough steps using gravel with a given grain size (i.e., d50 = 18.9 mm), were made with different step arrangements. The results showed that stepped spillways with rough steps and in the nappe flow regime show a better performance regarding energy dissipation of about 20.97 % compared to smooth steps. On the smooth stepped spillway, the non-dimensional residual head was 4.65, and for similar operating conditions, the average dimensionless residual head on the rough steps was 2.92. Furthermore, when rough steps are placed on all steps, the hydraulic jump characteristics, including sequent depth ratio, jump length, and roller length, decrease by 3.34, 8.61, and 8.14 %, respectively, compared to smooth steps.