عنوان مقاله [English]
Bridge abutments cause constriction in river section and change the pattern of river flow. Due to presence of a bridge abutment in a river, velocity and bed shear stress increase, vortices are formed and finally local scouring around structure commences leading to a scour holes development. In order to reduce scouring around bridge abutments, one method is to implement collars. They mitigate scour and produce a time delay in scour holes development process by deflecting the down flow. In this research, the effect of a collar on scour reduction around vertical semicircular bridge abutments was investigated experimentally. Experiments were conducted in a flume 6 m long, 0.8 m wide under clear water condition (0.85). The results showed that collars reduced the scour depth significantly, and 63.5 to 100 percent reduction on the scour depth and delay on the time of scouring were observed using different collars. Maximum scour depth also moved downstream of the bridge abutment.