On modeling boundary layer and gravity‐driven fluid mud transport

A model for fine sediment transport processes in the fluvial and coastal environment is proposed based on a simplified two‐phase formulation. This simplified approach for fine‐sediment transport is essentially single‐phased; however, it retains several critical mechanisms originated from the complete two‐phase formulation. By incorporating closures of carrier fluid turbulence and turbulent suspension and rheology of the sediment, the model is first tested with laboratory measurements of flow velocity and concentration for fine‐sand transport driven by steady currents. Next, particle diameter and density are prescribed in the model according to fractal dimensions of typical flocs for fluid mud observed on the continental shelf. The model is able to predict the dynamics of tidal‐driven lutocline behavior observed on the Amazon shelf and wave‐supported gravity‐driven fluid mud transport measured at the Po prodelta. Model results also indicate strong interplay between flow turbulence and fluid‐mud concentration, suggesting that the mechanism of sediment‐induced stratification on damping the carrier fluid turbulence is crucial in determining the fluid mud behavior. Results are encouraging for incorporation in the future of more comprehensive descriptions on floc dynamics, mud‐bed consolidation and various mud rheology closures.