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Grade control structure (GCS) can be used to reduce erosion in river beds. They decrease the river bed scour by changing the flow regime and reducing its velocity. It is required to maintain the stability of these structures against the scour hole that generates downstream of them, so investigating the scour hole characteristics downstream of the GCS is inevitable. In the present research, the equilibrium scour holes downstream of GCS were investigated under three discharges (q=0.00467, 0.00583, 0.00700 m3/s.m) and two different sedimentation conditions (d50=0.082, 1.6 mm). The results show that in the constant GCS geometry and finer sediment, the maximum scour depth (ds) and maximum scour hole length (ls) increase. In the same sedimentary conditions and different geometry, when the slope of the GCS downstream face varied from 90° to 60°, ds increases, but ls decreases. Also, the hydraulic jump forms on the scour hole at high flow intensity, which has an essential influence on the geometry of the equilibrium scour hole. Comparison of ds/Hc between the present study and Ben Meftah and Mossa (2020) has R2=0.891 and RE=10.66%, which reveals acceptable compatibility between the present study results and previous ones.

Debris upstream of the bridge pier and through the flow variations, changes scour hole and river morphology. Dune forms downstream of the pier as a result of sediment movement in the pier scour phenomenon. The present study investigates the dune characteristics and geometrical parameters in experimental models. Experimental models are categorized into four cases including the pier, pier with buried debris, pier with free debris, and pier with free debris which was protected by bed sill at four various distances from the pier downstream face. It was concluded that debris submergence, densimetric particle Froude number, flow intensity, and bed sill affect dune geometrical parameters such as dune height (hd), dune crest position (xd), and dune length (ld). Results show dune height increases with debris accumulation up to almost 150% and its crest distance from the pier reduces up to approximately 100%. Also, in higher Fd, the dune height and its crest distance reduce with bed sill up to 50%, and in lower Fd, hd, and xd increase by up to 80% by using bed sill. Based on these effective parameters, three separate equations were proposed for hd, xd, and ld in pier scour with debris accumulation protected by bed sill.

Sluice gates are utilized in dams and irrigation channels as regulating structures in the channel have the role of regulating the water level for proper water intake of upstream intakes. As high velocity and energy of the flow issuing from these hydraulic structures scour occurred in erodible downstream beds. Occurrence of the hydraulic jump is very possible, and when it forms, therefore the necessity of investigating the flow condition increases. The scouring phenomenon is a time evolution and a long-time procedure. This research focused on time effects on experimental data received by a sediment bed profiler at different times from the experimental setup conducted in a laboratory. The maximum scour depth (dse), the maximum dune height (hd), the horizontal distance of the maximum scour depth from the beginning of the sedimentary bed (xse), and the horizontal distance of the maximum dune height from the beginning of the sedimentary bed (xd) were investigated. Laboratory observations show that the extension of the location of the maximum scour depth and the maximum height of the dune formed with time is evident. The laboratory data for the dimensionless conditions of 4 scour profiles characteristics including dse/b0, hd/b0, xse/b0, and xd/b0 were analyzed by the nonlinear regression method, and separate equations were proposed for each characteristic. RMSE=0.045, 0.0677, 0.358, and 2.146 respectively, and the R2 =0.996, 0.975, 0.974, and 0.977 respectively.