ABSTRACT
Studies dealing with time dependent scour under unsteady flows are limited. In the present work the temporal variation of scour depth at cylindrical bridge piers under a hydrograph event is studied experimentally. Conducting experiments with 8 different hydrographs, the time development of scouring at the upstream face of the pier was recorded by small cameras which were installed inside the hollow pier. Experimental results showed that the scour depth increases during the rising period of the hydrograph, and changes slightly during the recession period. In addition, results indicated that the peak discharge is more effective on the development of scour depth than other hydrograph characteristics such as time to the peak. By analyzing the present experimental results as well as data presented by previous studies, an empirical relationship is proposed for calculating time evolution of scour hole at the pier nose under hydrograph events. Comparison of the present relationship with experimental data in predicting scour time evolution showed good agreement with maximum discrepancy of 10%.
