Effect of bed roughness on grain-size distribution in an open channel flow

Grain-size distributions of suspended load were studied in a laboratory flume over five sediment beds having different values of bed roughness at three different flow velocities. The experiments had been performed to investigate the influence of bed roughness, flow velocity and suspension height on the grain-size distribution in suspension. This study focuses on the determination of the proportionality parameter beta(n) in suspension which is the ratio of sediment diffusion coefficient to the momentum diffusion coefficient of the nth grain-size class. An empirical equation for beta(n) has been proposed which is valid for a wide range of normalizing settling velocity of sediment particles and bed roughness. Also, the bed roughness effect is studied on the parameter beta for total concentration in suspension and on the reference concentration, which is very important in suspension studies. The Rouse equation with modified beta(n) and beta was surveyed to know the grain-size distribution and total concentration in suspension that agreed well when compared with the experimental data. (C) 2013 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. Published by Elsevier B.V. All rights reserved.