Grain-size distribution in suspension over a sand-gravel bed in open channel flow

Grain-size distributions of suspended load over a sand-gravel bed at two different flow velocities were studied in a laboratory flume. The experiments had been performed to study the influence of flow velocity and suspension height on grain-size distribution in suspension over a sand-gravel bed. The experimental findings show that with an increase of flow velocity, the grain-size distribution of suspended load changed from a skewed form to a bimodal one at higher suspension heights. This study focuses on the determination of the parameter βn which is the ratio of the sediment diffusion coefficient to the momentum diffusion coefficient of n th grain-size. A new relationship has been proposed involving βn, the normalizing settling velocity of sediment particles and suspension height, which is applicable for widest range of normalizing settling velocity available in literature so far. A similar parameter β for calculating total suspension concentration is also developed. The classical Rouse equation is modified with βn and β and used to compute grain-size distribution and total concentration in suspension, respectively. The computed values have shown good agreement with the measured values of experimental data.