Determination of Manning’s Roughness Coefficient and Chezy’s Coefficient for Different Bed Materials

Abstract

The present study is aimed at investigating the effect of bed roughness on various hydraulic flow parameters. The study primarily revolves around determination of Manning‟s roughness co-efficient (n) and Chezy‟s co-efficient (C) for three different conditions of bed roughness. Bed roughness was simulated and changed using two different materials as the bed form, i.e. sunboard and plastic fibre mat. The experimental work has been performed in a re-circulating tilting flume. Three sections, 1 m apart are chosen as test sections and longitudinal velocity readings are recorded for whole flow depth at the centre of flume width. Two governing flow conditions are kept constant alternatively i.e., slope and discharge, and three runs of experimental investigations were carried out for each of these flow conditions.. All required geometrical and hydraulic parameters are calculated and thus, the values of roughness co-efficients n and C are determined. Velocity profiles have been plotted and the variations of velocity and other hydraulic parameters with the roughness co-efficients has been studied. Velocity is found to increase with increase in discharge and slope for all the bed roughness conditions. Also, increase in roughness leads to increase in flow depth and a decrease in velocity. Plastic fibre mat has been found to have the highest value of n and the lowest value of C while sunboard being the smoothest of all bed forms boasts the lowest value of n and highest C value.