Effect of Hydrograph Peak Time on Local Scour around Bridge Pier

In the present study effect of hydrograph peak time on local scour around bridge pier is studied. Hydrographs with one discharge peak as well as double discharge peaks were generated in the labaratory. The duration time for some of these hydrographs were so short that could be considered as flash flood occuring in arid or semi-arid zone rivers. In each experiment، development of scour depth with time was measured by small cameras. Results showed that for hydrogaphs with similar duration، parameter of peak time or sequence of peaks in double discharge peak has negligible effect on final scour depth but considerable effect on time development of scour depth. Furthermore، time developmet of scour depth for present hydrographs are calculated by stepped- hydrograph model and empirical equations presented in the literature for steady flow. Results also showed high descrepancy between calculated and measured data for time development of scour depth and all of the final calculated scour depths are larger than experimental ones. In the best case، the average error for final calculated scour depth is about 10%.