Local scour at the bridge pier is the main reason for the collapse of bridge pier founded in alluvial sediments (Melville and Coleman 2000). This process involves two complexities, the three-dimensional flow pattern and the sediment transport. The determination of the scour characteristic is the main topic of interest for the hydraulic engineers. By underestimation of scour depth, it will result in exposure of foundation and ultimately lead to endangering safety of the structure. By overestimation of scour depth, it will lead to uneconomical design.
Due to the presence of the bridge piers and abutments the three dimensional flow around obstruction would cause vortices and this will lead to deep scour hole around piers. The basic mechanism causing local scour at piers is the formation of vortices (known as the horseshoe vortex) at their base.
No study has been conducted so far to find maximum scour depth in non-uniform cohesionless sediment mixed in various proportions as in our study. To obtain this several experiments have been conducted in non recirculating tilting flume, 6.0 m long, 0.250 m wide and .750 m deep located at LDRP ITR Gandhinagar, Gujarat. Three different sizes of sediment having median size 4.75mm, 0.16 and 1.18 mm are mixed in various proportions.