The Effect of Stilling Basin Slope of Bed Scour at Downstream of Stepped Spillway

Stepped spillways and stilling basins are the most important energy dissipation structures. Even though most part of energy would be dissipated by these two structure, the remaining part of energy of flow may be capable to grave the bed scour and to create the scour hole downstream of them. Structures could be destroyed if this part of energy is high. In this study, the effects of stilling basin slopes on bed scour at downstream of stepped spillway were investigated experimentally. Experiments were conducted in the laboratory of hydraulic structures at University of Kerman with six different discharges and five various stilling basin slopes. The following parameters were measured: maximum scour depth (ds), flow velocity (in three point), water depth in upstream and downstream stepped spillway and stilling basin, the distance from where  the maximum scour depth happened to sill (Ls), and the geometry of scour hole. Results showed 47 percent increase and 52.2 percent decrease in average of maximum relative scour depth when stilling basin slopes were 0.02 and -0.02, respectively. Also, it was shown that the distance between the point where maximum scour depth had happened to the end of stilling basin increased when Froude number increased and decreased when stilling basin slope decreased.