combined effect of bed sill and collar in reduction of scour depth around cylindrical bridge piers

in this paper the effectiveness combination of bed sill and collar in reduction of local scour depth at cylindrical piers under clear water flow condition was investigated (v/vc=0.9). in the first of experiments, the bed sill was located in downstream and different distances from the piers. results indicated that minimum distance of the bed sill from the piers in downstream has maximum reduction of scour depth in front of the piers. the percent reduction of scour depth is about 30% in this case. in continuing the tests, used the collar and bed sill simultaneous. when using the combined of collar (2d) and bed sill (l=0), the percent reduction of scour depth in front of piers is about 42% and more than 98% when using the combined of collar (3d) and bed sill (l=0). the results show that using combined of collar and bed sill have more effect in reduction of local scour around bridge piers.