Modeling Suspended Sediment Transport in Nonequilibrium Situations

Abstract

A mathematical model is presented for calculating suspended sediment transport in unidirectional channel flow under general, non-equilibrium conditions. The model consists of a flexible hydrodynamic component for calculating the flow field and the turbulence characteristics and a scalar transport model. The former employs the \Ik\N-e turbulence model and provides, as input to the latter, the distribution of velocity and eddy diffusivity as well as the friction velocity. The settling process is simulated with an empirical settling velocity appearing in the particle concentration equation. As a boundary condition for this equation, the net flux of sediment to and from the bed is prescribed with a new model which covers both fixed-bed and erodable-bed situations. The net flux is expressed as the difference between deposition to and entrainment from the bed and, while the deposition rate is known from the local concentration and settling velocity, the entrainment is assumed to occur at the same rate as it does under equilibrium conditions, provided sufficient sediment material is available. With the aid of a finite volume procedure, the combined hydrodynamic sediment transport model is applied to a variety of flume experiments involving zero net flux, net-deposition, and net-entrainment situations. The predicted development of the vertical concentration profiles is compared with the measurements and generally good agreement is obtained.