Application of Quadrant Analysis in Determination of Bursting Values in Scouring around Bridge Pier

In order to protect hydraulic structures against scour, it is necessary to know what causes scouring. Local scour is the process whereby sediment is removed from the base or toe of a structure due to change of local flow patterns. Local scour at a bridge pier principally results from the down flow that forms along the upstream face, and the resulting horseshoe vortex at the base of the pier wich cause an increase in sediment movement leading to scour. The studies showed that sediment transport near the bed depends on bursting event. Quadrant analysis is a method to quantify the contribution to the Reynolds shear stress production by the coherent eddies during the events involved near-bed bursting in the turbulent boundary layer. In this study, the instantaneous velocities of flow in three directions were measured using a Micro ADV in an equilibrium pier-scour hole around a circular bridge pier in a rectangle experimental flume. The results reveal that the dominant event is sweep (Q4), followed by ejection (Q2), then outward (Q1) and inward (Q3) in the entire flow depth except at some points close to the bed level and within the scour hole (z/h< 0) where the contribution of ejection is more important than that of the sweep and Q2 events gradually exceed Q4 events with an increase in z. Also, the contribution of sweep and ejection event diminishes away from the bed level and in contrast, the contribution of outward and inward (Q1 and Q3 events) continues to have insignificant contributions and increase close to water surface becoming approximately equal in the water level. Furthermore, it is also found that the difference in distances from the pier have no significant effect on contributions of events.