Clear-water bridge scour under triangular-shaped hydrographs with different peak discharges

In this study, two triangular-shaped hydrographs with identical rising and falling durations but different peak discharges were generated so as to investigate the time variation of instantaneous velocities at a point upstream of a bridge pier and the evolution of scour depths at clear-water conditions under unsteady flow conditions. The circular bridge pier of 6 cm diameter was located 9 m downstream from the flume entrance inside a mobile bed zone 3.35 m long. The base approach flow depth was 12.2 cm and the peak approach flow depths were 19.1 cm and 21.8 cm for the two experiments. The obtained time series were averaged by a smoothing algorithm to obtain the time varying mean point velocity and the fluctuating components. The turbulence intensities at the rising and falling limbs were calculated. The maximum scour depths were recorded to 0.8 cm and 2.9 cm at about 70° downstream from the channel axis. © 2014 Taylor & Francis Group, London.