Near bank turbulence of a river bend with self similar morphological structures

Abstract

The shapes of a meandering river at the different stages of its evolution forming meander loops result from the interaction of the turbulent flow structures and channel planform. Based on field investigations and analysis of Google Earth (aerial) images, series of self-similar lobed-shaped patterns of different scales evolving in both space and time were observed at the outer curved bank of large rivers such as Hooghly River (India), Yamuna River (India), Madhumati River (Bangladesh) and in the White Nile (Africa). The present study attempts to develop insight into the turbulence characteristics of the flow leading to the formation, growth and migration of these self-similar lobed-shaped patterns. Measurements of turbulent flow characteristics were carried out at five different locations within a distinct dynamic lobe of an outer bend of the River Hooghly. Results show that the outer bank of a curved channel is under the action of strong secondary currents, turbulent burst-sweep cycles, flow separation and strong intermittent turbulent shear stress at different scales leading to enhanced bank erosion activity. The results from the present study form the basis for a conceptual representation of the bankline retreatment process through the formation, growth and evolution of dynamic lobed-shaped erosive patterns.