Pier scours in fine-grained non-cohesive sediment and downstream siltation, an experimental approach

Scour is a natural phenomenon involving the removal of bed sediments by the perturbation of flow field with the erection of hydraulic structures such as guide bank, abutments and bridge piers. Removal of sediment at the base of the pier due to scouring not only undermines its foundation support considerably but also leads to deposition and siltation downstream due to lower flow velocities. This deforms the river bed configuration and thereby flow kinematics. While there have been numerous studies of scouring in gravel and sand beds, there are few studies involving fine sand to silt beds. In the present flume-based study, an attempt was made to study the effect of pier size, shape and flow velocity on scouring process, scour depth for piers in fine sand to silt bed. Results reveal that scouring process significantly differs for different pier shapes and sizes. Equilibrium scour depth and downstream bed deformations show considerable correlation with turbulent flow characteristics. Empirical equations have been proposed to predict the maximum equilibrium scour depth. Outcomes of the investigation support and assist engineering practices related to site-specific, cost-effective designs of bridge pier foundations and the consequence on streambed modifications at the lower reach of rivers.