Effect of Duration and Pattern of Hydrographs on Scour Around Pier in Sharp Bend Under Incipient Motion and Live Bed Conditions

In the present study, the effect of peak occurrence time and flood duration on the scour around the bridge pier installed in a sharply bended channel was investigated. For this purpose, several simple single-peaked hydrographs with the same durations and different peak occurrence times were produced in laboratory. In addition, hydrographs having two consecutive peaks with a steady flow discharge at the first peak and an unsteady-flow discharge at the second peak and vice versa were 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. In single-peaked experiments, by increasing hydrograph duration from 25 to 100 min, the maximum scour depth increased by 20%, and the progression of sediments along the downstream straight path increased by 150%. For hydrographs with two non-equal and the same duration peaks, at a constant discharge for the first peak and a decrease in the second peak discharge from 70 to 60, 50, and 45 (L s(-1)), the volume of the scour hole around the pier was decreasing 15, 40, and 60%. Its area fell by 10, 40, and 55%, respectively. When the rising and falling limb time of hydrographs were equal, the maximum sedimentation height increased by 2.7, 3.5, and 5 times, respectively by increasing test duration from 25 to 50, 75, and 100 min.

Automated summary

This study investigated the effects of peak occurrence time and flood duration on scour around bridge piers in sharply bended channels. Results showed that different peak occurrence times and durations had varying impacts on maximum scour depth and sediment progression around the bridge piers.