Author(s): B.S. Mazumder; K. Ghoshal; D.C. Dalal
Keywords: Bed roughness; flow velocity; suspension concentration; grain-size distributions; diffusion coefficients; settling velocity; mathematical model
Abstract: Flume experiments with five beds of heterogeneous sediment mixtures having different values of bed roughness show that for fixed height and velocity the amount of suspension concentration increases up to a certain value with increase of bed roughness and then decreases with further increase of bed roughness. This indicates depletion of concentration in suspension due to increase of coarse sediment in the bed. Some sort of “critical bed roughness” together with sediment entrapment acting on the sediment beds due to further increase of bed roughness prevent grain sizes from lifting into suspension from the beds. Mathematical models for computation of actual amount (g/l) and size distribution of suspended materials over different sediment beds, based on Hunt's diffusion equations for sediments and water, have been developed in this work. Models give results which compare well with the observed values of actual amount and grain-size distributions comprising the wide range of grain sizes. In this study, the parameter γ, the ratio of sediment diffusion coefficient to the momentum diffusion coefficient, has been shown to be a function of normalized settling velocity of particle, and the relation has been used to estimate sediment suspension distribution.