Meandering Effect for Evaluation of Roughness Coefficients and Boundary Shear Distribution in Open Channel flow

Abstract

Almost all the natural channels meander. During uniform flow in an open channel the resistance is dependent on a number of flow and geometrical parameters. The usual practice in one dimensional flow analysis is to select an appropriate value of roughness coefficient for evaluating the carrying capacity of natural channel. This value of roughness is taken as uniform for the entire surface and for all depths of flow. The resistance coefficients for meandering channels are found to vary with flow depth, aspect ratio, slope and sinuosity and are all linked to the stage-discharge relationships. Although much research has been done on Manning's n for straight channels, less works are reported concerning the roughness values for meandering channels. An investigation concerning the variation of roughness coefficients for meandering channels with slope, sinuosity and geometry are presented. The loss of energy in terms of Manning’s n, Chezy’s C, and Darcy-Weisbach coefficient f are evaluated. A simple equation for roughness coefficient based on dimensional analysis is modeled and tested with the recent experimental data. The method gives discharge results that are comparable to that of the observed values as well as to other published data. Knowledge on wall shear stress distribution in open channel flow is required to solve a variety of engineering and river hydraulic problems so as to understand the mechanism of sediment transport, and to design stable channels etc. The study on boundary shear and its distribution also give the basic idea on the resistance relationship. Good many works have been reported on the distribution of wall shear for straight channels, but only a few studies are reported on the works involving meandering channels. Experiments are conducted to evaluate wall shear from point to point along the wetted perimeter of the meandering open channel flow. The wall shear distributions in meandering channel is found to be dependent on the dimensionless parameters such as sinuosity, aspect ratio, and channel roughness. Equations are developed to predict the wall shear distribution in meandering channel which is adequate for the present data and other published data.