A pragmatic framework for the erosion threshold of sand-silt-clay mixtures

The morphodynamic development of estuaries and deltas is strongly governed by the sediment composition of the bed. Predicting the evolution of these systems depends on accurate estimates of sediment transport. A key concept in the sediment dynamics of sand-mud systems is the erosion threshold or critical bed shear stress ( ). Previous studies have typically classified sand-mud regimes based on a single bulk parameter such as mud content, despite mud consisting of both silt and clay, which affect the erosion threshold in a different manner. In this study, a dataset of erosion experiments with sand-silt-clay mixtures was compiled and categorized using the Van Ledden et al. (2004) bed type framework. This approach highlights the different effects of silt and clay fractions on the erosion threshold. For each bed type, new, empirical formulations were derived that provide a better fit to experimental data than previously proposed equations, while also highlighting the controlling factors of initiation of motion in different sediment mixtures. The results offer a practical method to estimate from sediment properties that are commonly available or relatively easy to obtain. These findings inform the design of future sand-silt-clay erosion experiments and provide first approximations of initiation of motion to improve the parameterization of sediment dynamics in morphodynamic numerical modeling.