Bottom turbulence on the muddy Atchafalaya Shelf, Louisiana, USA

[1] Wave, current, and sediment observations collected in approximately 5 m depth on the muddy Atchafalaya clinoform, LA, USA, are used to study the interaction between near-bed wave-induced turbulent flows and suspended sediment characteristics in a muddy environment. Low wave-bias estimates of near-bed Reynolds stresses are strongly correlated with flow accelerations and suspended sediment concentration, as previously observed on sandy beaches, where accelerations have been associated with bed fluidization and sediment transport. A detailed numerical analysis of the observations is performed, based on a uni-dimensional boundary layer model that accounts for the coupling between the fluid and the cohesive sediment phases. The numerical simulations suggest that sediment-induced stratification effects are of the same order of magnitude as turbulent dissipation, and thus play a significant role in the turbulent kinetic energy balance within the tidal boundary layer. However, inside the wave boundary layer, the ratio of stratification to shear-induced turbulence production (i.e., gradient Richardson number) decreases significantly, and shear-induced turbulence production dominates. For these observations, the vertical structures of currents and Reynolds stresses are relatively insensitive to the exact floc size.

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