The anatomy and propagation dynamics of non-Newtonian fluid mud gravity currents through emergent aquatic vegetation were investigated experimentally. The motivation of this study was related to the pipeline disposal of the dredged fluid mud into vegetated wetlands and near-shore areas, during which bottom gravity currents form. Our experimental observations showed that the presence of vegetation affects the propagation dynamics, hence the anatomy, of the gravity currents significantly. Vegetation-induced drag force dominated the resisting forces acting on the gravity current, forcing the current to transition into a drag-dominated propagation phase. During this transition, the gravity current profile evolved into a well-defined triangular/wedge shape. The onset of the fully established drag-dominated propagation phase was marked by the establishment of an equilibrium slope angle for the upper interface of the current with the ambient fluid. This equilibrium/terminal slope angle value remained constant throughout the rest of the drag-dominated propagation phase. Parameterizations for the required propagation distance for the onset of the fully established drag-dominated propagation phase, the array-averaged drag coefficient at the onset of this propagation phase, and the value of the terminal slope angle were proposed. Our experimental observations on the anatomy of gravity currents during the drag-dominated propagation phase were discussed in detail. This study documented significant effects of the vegetation in the propagation dynamics and anatomy of gravity currents, which warrants future detailed studies.

This study elucidates a relationship between the Fanning friction factor and the Reynolds number for the laminar propagation of constant-flux gravity currents. The particular motivation for this study was related to the pipeline disposal of dredged fluid-mud where non-Newtonian bottom gravity currents form. The power-law rheology model, which has been shown to model fluid-mud rheology well, was incorporated in the theoretical analysis. The proposed Fanning friction factor-Reynolds number relationship includes a proportionality constant (henceforth, the shape factor) that considers the shape of the current. For non-Newtonian fluid-mud gravity currents, a relationship for the shape factor was developed through laboratory experiments. Different potential applications of the developed friction factor-Reynolds number relationship are discussed. In this regard, a new viscous propagation model was developed and evaluated through comparisons with laboratory experimental data for fluid-mud gravity currents. The approach presented in this manuscript can be extended for currents of different fluids propagating over smooth and rough bottoms.