Modeling of Riverbed Evolution for Bedload Sediment Mixtures

Abstract

A new computational methodology for fully coupled simulation of unsteady water and sediment movement in mobile‐bed alluvial rivers has been developed and tested. The one‐dimensional approach treats bedload transport of nonuniform sediment mixtures with sorting and armoring effects considered. Spatial lag effects in nonequilibrium bedload transport are taken into account through innovative use of the recently developed notion of a loading law. The new system of equations for water and sediment movement is solved in a fully coupled, implicit manner using the Preissmann finite difference scheme implemented to allow for either upstream‐ or downstream‐induced mobile‐bed perturbations. Formal analysis of the coupled system sheds new light on boundary‐condition requirements for the multiple‐size‐class problem. The fully coupled implicit solution has proven to be robust and stable, and it respects the underlying volumetric conservation laws remarkably well, as demonstrated in continuity analyses of computed bed evolution for systematic test runs. Implementation of the new code is demonstrated through application to a schematic river reach resembling a portion of the lower Rhone River in France.