Simultaneous effects of submerged vanes and collar on scour reduction around rectangular piers with rounded nose

In this research، the influences of submerged vanes and collar on scour reduction around rectangular bridge piers with circular nose were investigated. Vanes are used as protective structures against bank erosion، exclusion of sediment from water intake structures and increasing navigational depth. Vanes change the regime of bed load movement that lead to control place of deposition and erosion. Collar prevents the direct impact of down flow with the bed that leads to decreasing the scour depth. Experiments were carried out with different piers and submerged vanes at various arrangements. The width of the collar was three times greater than the pier width and was installed on the bed. It was found that effectiveness of submerged vanes reduces by increasing the skewness of the pier. Maximum reductions of scouring were 45. 57، 39. 76 and 27. 78% for submerged vanes with 2. 5cm heights on the bed and skewed at to the flow when the angle of pier was and skewed at and to the flow، respectively. Results showed that the performance of collar decreased with increasing of pier angle with flow direction. Also maximum reductions of scouring were 69. 62%، 49. 4% and 7. 78% for pier with submerged vanes and collar when were aligned and skewed at and to the flow، respectively.