In this paper, the flow and local scour variation around single pier and by interaction between bridge piers are studied using 3D flow model. The model uses a finite-volume method to solve the non-transient NavierStokes equations for three dimensions on a general non-orthogonal grid. The k   turbulence model is used to solve the Reynolds-stress term. The numerical model solves the sediment continuity equation in conjunction with van-Rijn's bed-load sediment transport formula to simulate the bed evolution. The 3D flow model is verified through experimental study in a non cohesive bed material in an experimental flume. The different causes of local scour around the pier are simulated well, such as bow flow, down flow, horseshoe vortex, pressure variation and lee-wake vortex. It is found from this study that the local scour depth by interaction between bridge piers depends on the Froude number, the longitudinal distance between piers and the ratio of pier diameter to channel bed width. The maximum scour depth for double piers is higher than that for single pier. Furthermore, the effect of pier shape on the scour process is studied and it is found that the maximum scour depth for circular pier is less than that for rectangular one for both single and double piers. The effect of double piers on scour hole depth is diminished at L/D= 7 for circular piles and at L/D= 15 for rectangular ones. The results show good agreement between simulation and experimental results. Also, empirical equations are developed for computing the maximum scour depth due to the interaction between bridge piers at rectangular and circular shapes. Moreover, empirical equations are developed for computing the length of scour hole at single circular and rectangular piers respectively.