Bridges are one of the most important structures which are under attention from many years ago. Bridge is a structure to cross over obstacles such as rivers or valleys. In recent decades, despite using modern materials and technology and spending a lot of costs for designing and building bridges, failure of them is commonly reported due to flood and local scouring. Local scouring occurs by placing obstacles such as abutments in flow direction. Increasing the resistance of bed materials and decreasing the power of erosion factors are the ways to stand against local scouring. To decrease the power of erosion factors (horseshoe and wake vortex), equipment such as collars, submerged vanes and etc. are being used. One of the ways of controlling and reducing local scouring, is to create roughness on abutments which are prominences that made while concreting spherical and angled rings. In this study, by creating roughness on semi-circular abutment, their effects on reducing scour depth are investigated and also flow structure is being compared around simple abutment and abutment with roughness. Experiments were conducted in a traarent rectangular Plexiglas flume with length of 7 m, width of 0.32 m, depth of 0.35 m and discharge of 10.5 liters per second. The experiments were dune under clear water scouring and with bed materials sizing 0.75 mm. The 3-D instantaneous flow velocity in different cross sections was measured using an Acoustic Doppler Velocimeter (ADV). Results revealed that the best condition of placing roughness, with descriptions of depth of roughness (c=0.1L), roughness intervals (b=0.45L) and with constant height of (a=0.05L), the roughness has reduced the intensity of scouring and decreased the final scour depth by 47%. L is the length of abutment. Also by increasing roughness intervals, scour depth is reduced and this reduction continues till a specific value and after that the efficiency of roughness was reduced. It means that there is an optimum value for placing roughness on abutment to reach the best performance. By doing experiments and finding the optimum value of roughness intervals, the bigger the size of roughness, the more performance they have. Also velocity profiles, shear stress and turbulence were investigated and quadrant analyses were done to study flow structure. Results of shear and velocity profiles around abutment reveal the existence of downward flow and horseshoe vortex in upstream, and downstream, profiles show wake vortex and turbulence behind the abutment. But the main result of this study is the effect of roughness on flow structure around the abutment which reduces the power of scouring elements. Also quadrant analysis shows that the most common phenomenon around the abutment and near bed is sweep and ejection. Keywords : Abutment, Local scour, Local roughness, Flow pattern, Quadrant analysis