Experimental Study of Effect of Flow Drop Height on Downstream Bed Topography of Type-A Trapezoidal Piano Key Weir

Predicting the extent of local scouring downstream of hydraulic structures has been one of the topics of interest to researchers in recent years. In this research, downstream scouring of a trapezoidal piano key weir under changes in the hydraulic conditions of the flow and the height of the flow drop passing through the weir in a channel with a length of 10 meters and a width and height of 0.75 and 0.80 meters in the hydraulic laboratory of Water Engineering Group. And hydraulic structures of Tarbiat Modares University of Tehran have been studied. Uniform and non-sticky sediments with an average diameter of 2 mm in length and width of 3 and 0.75 m downstream of the piano key weir were used. All experiments were performed under free flow conditions. The results showed that the maximum occurrence of scour depth with increasing flow drop height is farther away from the weir. The maximum scour depth increases with increasing flow drop height. Scouring in the transverse middle of the bed is less than its walls. Increasing the height of the flow drop is accompanied by more changes in the topography of the bed.