Bridges are structures in danger of destruction due to being subjected to flood river bed. Local scour around piers across the flood flow is one of the threatening factors of their stability. Water stream cause digging hole around pier and leaching river bed that consequently may result in hollowing under the foundation and finally destroying the bridge. Many studies have been done presenting methods for controlling scour around piers. Generally there are two base methods for protection of bridges against scour phenomenon that first one is increasing resistance of bed materials and second is decreasing erosion factors. In direct methods, riprap, and cement blocks are used to increase bed resistance. Riprap, collar, pile are the tools that use for decreasing downward scour and horse-shoe vortex in indirect methods. Using piers with concrete-roughness is one of the economical methods easy to implement. Considering the results of cable method, the lower the twisting angle of cable the higher efficiency of pier in reducing scour can be obtained. Ability of reducing concrete roughness angle to zero degree is counting as an advantage of this method compared to cable method. Another advantage of concrete-roughness than cable is their inability of displacement by human factors. In this study, effect of concrete-roughness in decreasing scour factors is investigated. For achieving this goal, 17 piers with different roughnesses in two base states with presence of angular and rounded roughnesses are used. Experiments of angular roughnesses are done by 11 piers with constant roughness width of 0.06 of diameter. Increasing in protrusions leads to increasing in their performance. However, in particular conditions that distance between roughnesses is less than optimum value; increase in width of pier is a factor to decrease the efficiency of roughnesses. Performance of pier has a direct relation with protrusions of roughnesses and effective area across the downward stream path, with respect to increase in width of pier restriction. Performance of pier in reducing scour is increased and length and width of final digged hole are decreased, as protrusion of roughnesses is increased. Designed diagram and equations that are presented in this study can be used for selecting optimum distance between roughnesses. In constant C/D=0.06 and protrusions of 0.06 and 0.07 of pier diameter, optimum distance of roughnesses is estimated to be 0.51 of pier diameter. Best performance in presence of angular pier and protrusion 0.07of pier diameter is about 34%. Finally it seems that for every roughness with particular protrusion there is an optimum value for distance between roughnesses. Experiments of pier with presence of rounded roughnesses are done with this consideration that in long periods angular roughnesses are turned to rounded roughnesses. These experiments in addition to representing another form of roughnesses are proofs to performance of angular roughnesses in long periods. For this goal, large diameter of semi ellipse and small radius of semi ellipse is considered to be less than 0.11 and 0.06, respectively. Thus with considering distances between roughnesses, 22% improvement in performance for increasing scour can be achieved. With reducing number of roughnesses it could be seen that presence of roughnesses in all of piers is not necessary. Consequently considering effectiveness of roughnesses in scour factors, their location has a particular range.