Characteristics of intermittent turbulent structures for river bank undercut depth increment

The complex interplay between the resistive forces of the bank material and Reynolds shear stress of the turbulent flow field control the fluvial bank erosion. In-depth knowledge on the interactions of the flow-form at the river bank is a prerequisite to understand erosion mechanism and quantification of the erosion rate. Measurement at 1.5 m from the bank face as reported in the literature revealed that turbulent lateral flux of stream-wise momentum propagated towards the bank face that was held responsible for the removal of material from the bank face. Further experimental results from the literature depict that the stream-wise and lateral fluctuating velocity components deploy a random forcing effect on the river bank face which may be one of the primary agents for sediment particle entrainment from the bank face. It is gestated from these previous studies that the momentum flux and turbulent structures of the flow field has a great impact on the river bank erosion. Nevertheless, the previous field and experimental studies do not focus on the flow turbulence and sediment interaction that extracts information on the detailed temporal features of sediment entrainment process. Thus, the present study was carried out to understand the coupled dynamics of the effect of intermittent flow structures on the intermittent removal of river bank materials, and for advancing the knowledge on river bank erosion process. The present experimental study focuses on the evaluation of the turbulent flow characteristics when the undercut mechanism initiates in a cohesive river bank. Based on the results it is evident that moderate scale intermittent stream-wise flow structures probably imposes a periodic loading on the cohesive aggregates of the bank face. This accelerates the entrainment of aggregates from the bank face. The study also reveals that the undercut increment is a small scale intermittent process. Findings of the present study may be helpful for the improved design of bank protection measures.