Scour depth downstream weir with openings

Local scour downstream hydraulic structures may cause damage or complete failure of this structures. Weir may be used for measuring of discharge, decreasing the water slope in canals and distribution of water between canals for irrigation etc. Most of the past studies concentrate on discharge coefficient of combined flow, little information available on scour downstream of this flow. So, the objective of this research is to investigate the influence of using openings in weirs on scour hole depth downstream of this structure. The study was based on an experimental program included 171 runs. These runs were carried in a rectangular flume with openings fixed in the body of weirs. Three cases of opening arrangements were included, no opening, one opening and three openings. Different diameters of openings 1.27 cm, 1.9 cm and 2.54 cm, different heights at 0, 0.25 and 0.5 of weir height were tested under different flow conditions. The experiments showed that for most considered values of openings diameter either case of one opening or three openings, the value of hlp =0.25 gave the smaller values of scour depth, while the value of hlp =0.5 gave the higher values of scour depth. Also, it was noticed that for most considered values of openings height, the value dip =0.149 gave the smaller values of scour depth for case of one opening but for case of three openings, the value dip =0.075 gave the smaller values of scour depth. Finally empirical formula was developed for estimating scour hole depth in terms of downstream flow conditions, Froude number, height of the weir, number of openings, area of openings, diameters and heights of the openings.