Evaluation of boundary shear distribution in a meandering channel

Abstract

Information on the nature of boundary shear stress distribution in simple and meandering open channel are required to solve a variety of river hydraulics and engineering problems so as to get a basic understanding of the flow resistance relationship, calculation of energy losses, understanding the mechanism of sediment transport, design of stable channels, revetments etc. Distribution of boundary shear stress depends mainly on the channel geometry and the structure of the secondary flow cells. In a meandering channel, the complex flow mechanism causes significant variation in the distribution of shear around its wetted perimeter. Therefore, evaluation of boundary shear stress distribution at various locations of the wetted perimeter gives a better insight into the problem. Literature shows that the investigators have studied the boundary shear distribution mostly for shallow channels having low sinuosity. Reports on boundary shear distribution for deep and highly meandering channels are limited. The work presented in this paper is based on series of highly meandering channels having distinctly different sinuosity and geometry. The three dimensional flow velocities at a number of pre defined grid points across the channel section close to the surface are measured using 16-Mhz Micro ADV (Acoustic Doppler Velocitymeter). Using these velocity data, the shear stress at various points on the channel boundaries are evaluated from semi log plot of velocity distribution as well as by Preston tube technique. Based on the experimental results, this paper predicts the distribution of boundary shear in meandering channels thus showing the interrelationship between the boundary shear, sinuosity and geometry parameters. The models are also validated using the well published data of other investigators.