Effects of collars on local scour around semi-circular end bridge abutments

The occurrence of scour around bridge elements by the transportation of bed material during flood events can cause serious structural damages and loss of lives. Furthermore, increased uncertainty of precipitation and runoff prediction due to climate change makes this phenomenon more complex and dangerous nowadays. So, bridge scour countermeasures should be more focused on decreasing scour formation around bridge elements. In this study, abutment scour under clear-water conditions with constant flow intensity was conducted and collars were tested as scour countermeasures around semi-circular end bridge abutments. The experimental study was performed in a rectangular channel with an almost uniform cohesionless bed material for 3 h with and without collars. Collars of various lengths located at different elevations around the abutments were tested to investigate the effect of collars on scour development. Based on the experimental results of the study, it was concluded that scour depths decreased with increasing collar width and the collar was placed below the bed level for a given abutment length. The results of this study were compared with those of similar earlier studies to show the effect of abutment shape, size of the bed sediment and test durations on the development of scour depth around the abutments.