Bridges are one of the important hydraulic structures and have strategic importance in terms of political, social, economic and military. All years, broke and destroyed many bridges in the world and in our country. One of the major reasons for the destruction of bridges is underestimated the depth of foundation without considering the problem of erosion caused undermining by water. There are direct and indirect methods to protect bridges undermining by water. Increasing the resistant of subgrade materials in direct method and changing the flow structure around the bridge pier in indirect method caused controlling and decreasing the undermining by water. A new indirect method in the bridge pier undermining by water is to create surface roughness around the bridge pier when depositing concrete. In this research the number of concrete roughness effect with sharp edges in decrease undermining by water investigated in two models (with assumption constant roughness parameters). In first model, the roughness including all around the bridge pier (whole roughness) and in second model, the roughness including half around the bridge pier that was in front of the flow. The experiments were conducted in hydraulic laboratory of Isfahan University of Technology using a flume of 7 (m) length, 0.32 (m) width and 0.36(m) depth with clear water scouring and a constant discharge during 8 hours. Sands with median diameter of 0.7(mm), special gravity of 2.65(grams per cubic centimeters) and geometric standard deviation of 1.23 are used in the experiments. The number of experiments was 13 including simple pier (without roughness), piers with whole roughness and piers with half roughness. The results show that by increasing the number of roughness from bottom to top of the pier in both whole roughness and half roughness models and constant other roughness parameters (The distance between two consecutive roughnesses, Thickness and protrusion), in pier with whole roughness, undermining by water depth will decrease in front, side and back of the pier and in pier with half roughness, scouring depth will decrease in front and side of the pier. In fact roughness creating will decrease the power of down flow and horseshoe vortex in front of the pier and will decrease the power of wake vortex in back of pier. Results show that whole roughnesses and half roughnesses decrease undermining by water depth in front of the pier amount 21% and 10% respectively. In this study an ADV was used to obtain velocity database at a certain distances from the simple pier and optimal piers between piers with whole roughness and piers with half roughness. By using this data the structure parameters including velocity distribution, Reynolds stress and turbulence intensity were analyzed. The results shows in upstream of all the three piers and the bottom of hole existing the negative horizontal velocity and positive vertical velocity indicates the presence of horseshoe vortex in this area. In downstream of all the three piers, power of wake vortex caused high value of turbulence intensity in horizontal, transverse and vertical direction. The results of quadrant analysis show that Ejection and Sweep have high probable in bursting cycles. Keywords : Local scour, Bridge pier, Sharp edge roughness, Whole roughness, half roughness, Flow structure, Quadrant analysis