Coupled wave-bed dynamics, Atchafalaya shelf, Louisiana

Abstract

Recent work that studied the coupling between hydrodynamics and the muddy sea-floor on the Atchafalaya Shelf suggests that the amount of sediment in the water column is controlled by bottom shear stress, the erosion threshold of which is within 0.3-0.5 Pa. However, these results are based on the analysis of a small number of events. In this study, we investigate the applicability of these conclusions for a larger population of storms, as well as for different observation locations (e.g., near 7.5- m to 4-m isobaths), using observations of suspended sediment concentration and acoustic backscatter intensity collected in 2008 on the Atchafalaya inner shelf. The suspended sediment concentration profile 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 used to reconstruct the vertical structure of the flow characteristics, and estimate parameters difficult to observe directly, such as bottom shear stress. 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 consolidation processes) and represent a first step towards a forecasting model for wave-bed coupling in muddy environments. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE).