With the collision of the water flow to the bridge pier, which is associated with the flow separation phenomenon and vortex formation around the bridge pier, local scouring occurs in the bed around the pier location. This phenomenon is one of the major reasons for bridge failure, and various flow structures formed around the bridge pier include down flows and the horseshoe vortex at the front side of the pier and the rising vortices caused by the separation of flow from the sides and the upstream face of the piers. Experimental observations have shown that due to these flow structures, bed materials around bridge foundations are highly subjected to the forces generated by the flow and the vortices. The shape of the pier is one of the influential parameters in changing the flow pattern. Reduction of scour around the bridge pier by protective structures has always been considered by engineers. Collar is one of these protective structures that has an effective role in reducing scouring by diverting currents. In the present study, the effect of peak occurrence time and flood on the scour around the bridge pier installed in a sharply bended channel was investigated. The effect of peak occurrence time, hydrograph duration and pier installing position on scouring around different shapes of single bridge pier with and without collar, installed in a sharply bended channel under unsteady flow conditions was investigated. The flow velocity range began from incipient motion conditions and steeply increased to live bed conditions. In each experiment, the temporal variations of the maximum local scour depth were measured. The results showed that for a hydrograph with a constant duration, the rising limb time of hydrographs has little effect on the local maximum scour depth, However, the difference in the ratio of the rising and falling limb time of hydrographs, is effective on the temporal development of the maximum local scour depth and sediment exit from the bend.Comparing the