Coupled Wave-Bed Dynamics, Atchafalaya Shelf, Louisiana

摘要

Recent work that studied the coupling between hydrodynamics and themuddy sea-floor on the Atchafalaya Shelf suggests that the amount ofsediment in the water column is controlled by bottom shear stress, theerosion threshold of which is within 0.3-0.5 Pa. However, these resultsare based on the analysis of a small number of events. In this study, weinvestigate the applicability of these conclusions for a larger populationof storms, as well as for different observation locations (e.g., near 7.5-m to 4-m isobaths), using observations of suspended sedimentconcentration and acoustic backscatter intensity collected in 2008 onthe Atchafalaya inner shelf. The suspended sediment concentrationprofile is estimated based on the acoustic backscatter of the PC-ADP,and calibrated using independent OBS observations within the first 50-cm above the bed. A uni-dimensional bottom boundary model is usedto reconstruct the vertical structure of the flow characteristics, andestimate parameters difficult to observe directly, such as bottom shearstress. The results generalize previous estimates of bed yield stress,allow for building a statistical model for the bed-reworking cycle(liquefaction, erosion, fluid-mud formation and consolidationprocesses) and represent a first step towards a forecasting model forwave-bed coupling in muddy environments.