Evaluation of Flow-altering Countermeasures against Bridge Pier Scour

In this study, six different types of flow-altering countermeasures against pier scour were evaluated experimentally. The selected countermeasures were submerged vanes, bed sill, transverse sacrificial piles, collar, threading and pier slot. Laboratory tests were performed in clear-water conditions with flow intensity slightly below the threshold of sediment motion. Tests were designed on the basis of the best configurations recommended in previous studies by different authors in order to obtain the maximum efficiency in terms of scour depth reduction. Results showed that some countermeasures, which were recommended as highly efficient in the literature, do not perform well under other test conditions; in particular, literature tests carried out with low flow intensity or short duration or in narrow channel conditions are criticized. The efficiency of bed sill, submerged vanes and threading was found to be less than 20%, whereas collar, pier slot and transverse sacrificial piles reduced the maximum scour depth of about 35% or less. Design of a pier slot is finally discussed and an optimum configuration is proposed.