Abstract
Due to the lack of any specific study about the sidewalls and other blocks’ changes in the case of hydraulic and scour downstream, the present study was conducted to investigate this issue. For this purpose, drainage projects and spillway chutes, as well as many baffle block chutes, were designed and constructed with the parallel sidewalls and trapezoidal shape using the U.S. Bureau of Reclamation (USBR) instructions. Three divergence ratios of b 1 / b 2 = 1.45 , 1.75 , and 2.45 , a parallel sidewall of b 1 / b 2 = 1 , and also three geometry blocks including trapezoidal USBR, trihedral, and semicircle blocks were applied and tested in the hydraulic laboratory using a baffle chute with the slope of (2 : 1), (H : V). The material used in this study was sediment sand with a uniform grain size of d50 = 1.2 mm, 15 cm of thickness, and 2 m of length. The experiment was conducted with seven different discharges in lasting condition, and the flow characteristic and scour hole dimensions were measured. The results revealed that in comparison with the USBR blocks, changes in the baffle sidewall and block shape made an approximate 50% reduction in the maximum depth of the scour hole. Thus, increasing the divergence ratio from 1 to 2.45 had a significant effect on reducing the maximum depth and the topographic shape of the scour hole. According to the range mentioned in the literature for the Weber number, the scale effect was negligible for the chute with baffle blocks. Generally, it can be concluded that the sidewall changes also can make a reduction in the number of overbaffle blocks, causing a reduction in the construction cost.
Highlights
Erosion and scour downstream of the hydraulic structures have always been a matter of concern for the hydraulic engineers and researchers in this field
According to the range mentioned in the literature for the Weber number, the scale effect was negligible for the chute with baffle blocks
Semicircular and trihedral blocks were proposed as alternatives to the standard U.S. Bureau of Reclamation (USBR) blocks and the effect of blocks of different geometries on the scour downstream of the chute was investigated. e effect of three divergence ratios (b2/b1) of 1, 1.45, and 2.45 at chute inlet was studied
Summary
Erosion and scour downstream of the hydraulic structures have always been a matter of concern for the hydraulic engineers and researchers in this field. Numerous studies have been conducted on the scour and its various aspects, such as energy dissipation downstream of the structures [1,2,3]. Dargahi [5] experimentally studied the scour downstream of a spillway with an apron installed at the end of the spillway on the surface of the sediments. According to their results, secondary flows downstream of the spillway formed several scour holes, which were gradually developed and incorporated. Zare and Doering [3] studied the effect of adding the baffles and end sills on the energy dissipation of flow over stepped spillways with sharp or round edges and an ogee inlet. ey concluded that the energy dissipation ratio for baffle-edged chutes was higher than the still-edged chutes
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