Using time invariant flow condition for simulation of local scour depth around circular piers under time varying flow

Local scouring around bridge piers had been considered as an undesirable event and against the bridge safety. In this process, the 3D flow patterns in the vicinity of bridge pier have important role and cause the bed material erosion around bridge pier. Embedment of the foundation in the depth deeper than the maximum local scour depth according to the design flood has been proposed as a conservative solution. However, implementation of the pier foundation in a deep depth from the original bed level is not an economic solution in practical cases. In real cases, the variant stream flow of floods is the main reason of bridge failures. In this study the evolution of local scour depth around circular bridge piers under unsteady flow condition of hydrographs has been numerically simulated using steady flows. The results showed that during the rising period of hydrograph, the scour depth increased steadily and more than 70% of final scour depth occurred at the rising limb of hydrograph. The results also show that by using the SSIIM program, it will be possible to evaluate the local scour depth in the end of rising limb of hydrograph with a satisfying accuracy.