A Dynamic Model for Coastal Mud Flocs with Distributed Fractal Dimension

Suspended sediments entrained from muddy estuarine and coastal areas usually contain a large amount of mud flocs of various sizes and densities. The size and settling velocity of these mud flocs are unsteady and may vary over a large range. In most theoretical descriptions the mud flocs are treated as self-similar fractal entities with the fractal dimension being considered as either a constant or a simple function of the mean floc size. This deterministic description of fractal dimension has recently been found to be inadequate as for a given size class; fractal dimension of the mud flocs is not a single value but is distributed over a certain range. To address this problem this paper proposes a new flocculation model for the temporal evolution of floc size by considering the fractal dimensions for a given floc size class D to be normally distributed and validates the model with available experimental data. The proposed model is found to perform better in predicting the temporal evolution of floc size than that based on a single fixed floc-size-dependent fractal dimension, especially under high shear conditions and with large equilibrium floc size.