Hydraulic charateristics over weirs with circular openings

Abstract

Weirs may be used to control the discharge, decrease the water slope in canals and to distribute water between canals for irrigation etc. The objective of this research is to investigate the influence of using one opening or more in weirs on discharge coefficient (Cd), the hydraulic jump characteristics and velocity distribution downstream of these structures. This study is based on an experimental program. Three cases of openings arrangements were included, one, two and three openings. Different diameters of openings (D) and different heights from the bed (Z) were tested. The experiments showed that decreasing (D/Z) for weirs which have the same openings numbers and diameters decreases the discharge coefficient (Cd) and the ratio between the length of the submerged hydraulic jump (Lj) and the water tail depth (yt). Also, decreasing (D/Z) leads to make the maximum velocity near the bed tends to be lifted upward. Moreover, Comparing weirs with different openings numbers but have the same openings area leads to that, weirs with one opening have a bigger (Cd) than weirs with two or three openings but the maximum velocity near the bed of the weir with three openings is less than this with one opening. Also, the ratio (Lj/yt) for the weir with three openings is decreased approximately compared with the same ratio for the weir with one opening. Finally, equations were developed to deduce the value of the coefficient of discharge for the composite structure.