Mechanisms of particle vertical diffusion in sediment-laden flows

Diffusion coefficient of natural sediments andeffects of lift force and gradient in particle velocity fluctua-tions were investigated through using a closed kinetic model.Comparison against experimental data of Einstein & Chien(1955) validated the model. The diffusion coefficient εofmedium and large sediments distinctly exceeds fluid eddyviscosity v~t, while εof fine sediments approximately equalsv~t.In the measured region of 0.03<y/H<0.4, ε/v~t increaseswith the distance from the wall decreasing. Combined effectsof lift force and gradient in particle velocity fluctuationschange sediment gravitational settling remarkably belowy/H=0.2, and need to be accounted for describing sedimentdiffusion in this region.