In this paper, the flow and local scour variation around single pier and introducing interaction effect between bridge piers were studied using 3D flow model. The model used a finite-volume method to solve the non-transient Navier-Stokes equations for
three dimensions on a general non-orthogonal grid. The k -e 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 was verified through experimental study in the non cohesive bed material in an experimental flume. The different causes of local scour around the pier were simulated well, such as bow flow,
down flow, horseshoe vortex, pressure variation and lee-wake vortex. It was found from this research study that the local scour depth by interaction process between bridge piers depends on the Froude number, the distance between piers and the
diameter of piers. The maximum scour depth for double piers is higher than that for single pier. Furthermore, the effect of pier shape on the scour process was studied and it was found that the maximum scour depth for circular pier is less than that for
rectangular one for both single and double piers cases. The results show good agreement between simulation and experimental results. Also, empirical equation was developed from the experimental data for computing the maximum scour depth due to
the interaction between bridge piers.