%0 Journal Article %T Effect of Collar on Time Development of Scouring Around Rectangular Bridge Piers %J Journal of Hydraulics %I Iranian Hydraulic Association %Z 2345-4237 %A B. Mashahir, M. %A Zarrati, A.R. %A Mokallaf Sarband, E. %D 2008 %\ 08/22/2008 %V 3 %N 2 %P 19-11 %! Effect of Collar on Time Development of Scouring Around Rectangular Bridge Piers %R 10.30482/jhyd.2008.85463 %X Collars acts as a barrier to the down flow and prevent its direct impingement to the streambed. In thepresent work collars with 3 different lengths (5B, 7B and 9B, B=pier width) and constant width equalto 3B were installed around a rectangular pier with aspect ratio equal to 1:3. Also, collars wereattached at the streambed level and all tests were conducted at the threshold of bed material motionwhere maximum depth of scour hole is expected. Piers aligned with the flow and skewed at 10o and20o to the flow were tested. Long time tests were carried out to study the development of the scourhole around the pier and efficiency of the collar. Based on experiment results with 9B collar, flowcould not penetrate below the upstream edge of the collar after 185 hours. Therefore, scouring at theupstream region of the pier will not occur. In this test maximum depth of scouring occurred at thesides of the collar with 60% reduction of local scouring compared with an unprotected pier. Withskewed pier performance of the collar on reducing the rate of scouring was decreased. Results of theexperiments showed that at skewed piers, after 50 hours depth of scouring reduced about 30%compared with an unprotected pier. In addition the rate of scouring decreased with 9B collar. %U https://jhyd.iha.ir/article_85463_573934268023eb89f23f8ae2972fb03e.pdf