A theoretical model for suspended sediment transport in river bends

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ABSTRACT

A two dimensional depth-averaged model for the concentration field of suspended sediment in river bend flow is formulated. Transport of suspended sediment in horizontal and vertical directions is modelled. Convection by the main and secondary flow and turbulent diffusion are incorporated. The model is capable of computing the exchange of sediment with the bed-load layer adjacent to the bed.

The model is based on the three dimensional convection-diffusion equation formulated in a cylindrical bed following coordinate system. Non-orthogonality of the coordinate system is included.

The concentration field is modelled by a first order asymptotic solution of the convection-diffusion equation. The zeroth order contribution to the solution is given by equilibrium shape concentration verticals, the first order contribution is due to the convection by the flow. The result is formulated in depth-averaged variables.

The time and length scales of the model are computed. These scales are significantly affected by the choice of reference level, the choice of boundary condition at this level, the suspension parameter and the Chezy coefficient.

The model will have to be calibrated and verified by measurements and numerical computations.

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