Experimental Study of Variation Sediments and Effective Hydraulic Parameters on Scour Downstream of Stepped Spillway

Stepped spillways are considered one of the most significant energy-dissipating structures; however, the most complicated problem that threatens the overall stability of the spillway is local scour downstream of the stepped weirs due to hydraulic jumps in the skimming flow. In this study, a series of experiments were conducted under five discharges, three tail-water depths and two sediment sizes to investigate the scour downstream of a stepped spillway to reduce scour and increase the stability of hydraulic structure. Moreover, the optimal design of parameters, including type, crest and slope of chute, step height and type of stepped spillway flow, was determined considering the economic reasons and criteria that lead to more energy dissipation. Generally, the scour dimensions decreased as the sediment size and tail-water depth increased or the particle Froude number (Fr_d) and critical depth reduced. With the reduction in Fr_d, the relative scour depth, the relative distance of maximum scour depth and the relative scour length decreased by 68.6%, 75.6% and 73.4%, respectively. Empirical equations of regression analysis were developed to estimate scour depth compared to other studies. The final equations in this study can provide good estimates of the scouring parameters downstream of the stepped weir.