A numerical model to store and access the stratigraphy of non-cohesive sediment as an alluvial bed aggrades and degrades in a flume

A one-dimensional model describing bed evolution in a water-feed flume is presented. The model considers conditions of lower-regime plane bed. Sediment transport can be modeled as uniform in size or as a mixture of different grain sizes. As in some previous morphodynamic models with sediment mixtures, the active layer approximation has been introduced to describe how sediment is exchanged between the bed and the bedload. The innovative characteristic of the present model is a procedure to store the stratigraphy created by deposition, and to access this stratigraphy when the bed erodes into it. Stratigraphy is stored in a grid, and a set of grain size distributions, each associated with a different vertical position in the bed, is associated with each node in the downstream direction. When the bed degrades, the upper part of the substrate is transferred to the active layer and the number of storage sites on the vertical decreases. If the bed aggrades, part of the active layer is transferred to the substrate and the number of storage sites increases. In the present paper numerical results are presented and discussed so as to compare the approach to mobile-bed equilibrium in sediment-feed and sediment recirculating flumes. Physical experiments are currently in process in order to test the model.