River morphodynamics with creation/consumption of grain size stratigraphy 2: Numerical model

As a river-carrying sediment mixture aggrade, it creates a stratigraphic signature that records this evolution. This stratigraphy is characterized by the vertical/horizontal variation of substrate grain size distribution. If a river degrades, it mines this stratigraphy, and transfers the sediment so accessed farther downstream. Although several numerical models tracking the creation/consumption of stratigraphy are available, none has been tested against experiments under plane bed regime conditions. Here nine physical experiments modelling the creation/consumption of stratigraphy are described. These are compared with nine corresponding numerical experiments using a model that tracks stratigraphy. The results justify the numerical model, and in particular the scheme to track stratigraphy. This scheme can be used at field scale to characterize e.g. the response of a river to an increased/decreased sediment supply. The numerical model shows a discrepancy with the experiments, however, whenever a distinct delta front forms, because the model does not describe sediment sorting across an avalanche face.