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 h/p = 0.25 gave the smaller values of scour depth, while the value of h/p = 0.5
gave the higher values of scour depth. Also, it was noticed that for most considered values of
openings height, the value d/p = 0.149 gave the smaller values of scour depth for case of one
opening but for case of three openings, the value d/p = 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. |
