Bridge failure is a common phenomenon all around the world. The reason of the failure is not just the construction, but ignoring hydraulics’ roll in designing. Therefore, finding ways to reduce scouring is essential. There are two fundamental ways to protect bridges from scouring; increasing the resistant of bed materials and decreasing the power of erosion factors. A new method of decreasing pier scouring is to create roughness around the pier. In this study, the efficiency of using submerged plates and roughness around the piers to decrease scouring is investigated. Results show that by increasing the size of roughness, scouring will decrease. In fact, increasing the size of roughness will decrease the power of down flow, horseshoe and wake vortexes. By using roughness and submerged plates simultaneously, a delay on start of scouring was observed and this delay was more at back of the pier in comparison with sides and front of it. Besides, final scouring depth reduces dramatically in this situation. The experiments were conducted under clear water scouring and with a constant discharge during 8 hours in hydraulic laboratory of Isfahan University of Technology using a flume of 7 m length, 0.32 m width and 0.36 depth. Sands with median diameter of 0.75, special gravity of 2.65 grams per cubic centimeters and geometric standard deviation of 1.2 are used in the experiments. The number of experiments was 15 including simple pier, piers with roughness and piers with submerged vanes. An ADV was used to measure velocity distribution, Reynolds stress and turbulence intensity. Investigation of velocity and shear profiles around the piers shows the existence of horseshoe vortex and downward flow simultaneously at upstream of piers. In downstream, existence of wake vortex causes fluctuations in flow structure. Velocity fluctuations in upstream of flow increases by entering scour hole, so inside the hole, there is a core with high intensity of turbulence in front of piers which is the result of flow separation in that region. Turbulence intensity longitudinal profiles and velocity profiles at the back of pier show that wake vortex causes fluctuations of velocity and reduction of it at back of the pier. Using quadrant analysis shows that Ejection and Sweep are common phenomenon in bursting cycles. Keywords: Bridge piers, Local scour, Submerged vanes, Flow structure, Quadrant analysis
