The first part of the modelling study focuses on the reproduction of erosion rates of sand-mud mixtures in long bed experiments, in which an inverse relation was found between the erosion rate and the mud content in the sediment bed. We have reproduced these experiments in a Delft3D model that we refer to as the digital flume. Our model results show that to correctly reproduce the observed erosive behavior, we must account for sand-mud erosion interaction (as defined in van Ledden’s (2003) model) in the model set-up. Moreover, we have seen that suspended sand concentrations reach an equilibrium concentration within a short time span, while suspended mud concentrations build up over time. The timing and sequence at which measurements of absolute suspended mud concentrations are taken therefore largely influences the results, and erosion rates should be derived from continuous measurements.

The second part of this study focuses on the dependency between the dry bulk density of sediment mixtures and their critical shear stress for erosion. In general, it is very difficult to model long-term morphodynamic development including mudflat formation with mudflats that are capable of surviving episodic storms. However, when applying the new density-erodibility formulation, which results in a space- and time varying mobility of mud, we are able to reproduce this behavior in a Delft3D model. To support applications of sand-mud formulations in Delft3D, we have included instructions on practical aspects of working with these formulations in this report. Besides, we discuss in which engineering applications these formulations may be of crucial importance.

The sand-mud modelling in Delft3D is discussed in this report: 11204950_TKI-MUSA_04_Modelling sand-mud dynamics in Delft3D.pdf

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