Assessment of Sediment Hazards by Bed Level Variations Around the Bridge Pier

Abstract

Local scour around the hydraulic structure is one of the prime responsibilities for the sediment hazards. The present study investigated the bed level variations around the bridge pier on uniform sediments under varied flow intensities (U/Uc = 0.66, 0.82, and 0.98) to assess the sediment hazard around the hydraulic structures, viz., bridge pier. A single pier of diameter (d = 8.8 cm) was positioned on a sediment bed of 15 cm thick, having mean sediment size, d50 = 0.75 mm, standard deviation, σg = 1.29, specific gravity of 2.65 were used during the experimentation. The SeaTek 5 MHz Ultrasonic Ranging System (URS) has been used to measure the instantaneous bed levels at different grid points around the pier during the experiments. The scour hole structure was quantified during its evolution, i.e., at 25%, 50%, 75%, and 100% scour depth. The quantities of scour hole in terms of areal and volume studies, temporal variations at different time intervals, three-dimensional scour depths are computed from measured bed levels. From the analysis, the scour depths are observed 20% more at vicinity of bridge pier at U/Uc = 0.98, vis-à-vis U/Uc = 0.66. The present study suggested that the volume and areal extent of local scour, though challenging, is also essential along with scour depth computations to assess sediment hazards around the bridge piers.