effect of collar- slot combination on the local scouring around the bridge piers

scoure is the removal of particle sediment which results variation of flow pattern. local scour is considered as one of the reasons of instability and ultimately failure of bridges.therefore, proposing some controlling methods to reduce this phenomenon is essential. in the study, effects of two types of squar and circular collar on a single cylindrical model have been investigated. in the next step by providing a slot through the pier and combination of collar and slot was used to investigate the scouring reduction. the results showed that use of both collar, specically below bed level decreased the scour depth. square collar was more effective than circular in decreasing the scour depth. combination of slot and collar on the pier could further reduce the scouring depth in which a square collar with w/d=2.5 in the bed with a slot near the bed reduce scouring depth up to 80 percent consequence