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The Louisiana coast is generally characterized as a low wave-energy environment where sediment transport is dominated by the influence of the Mississippi and the Atchafalaya Rivers. Winter cold fronts, however, generate waves and currents that have a significant impact on a variety of Louisiana’s coastal environments, although field data regarding their influence on the inner shelf are extremely sparse. During a 12-d period that included the passage of two cold fronts, waves and near-bed currents were measured on the Louisiana inner-shelf (depth-8 m) using a sophisticated bottom-mounted instrumentation system. Bottom boundary layer parameters were then calculated using wave-current interaction models, and sediment transport was predicted by assuming steady state turbulent diffusion within and above the wave boundary layer.

Results indicate that the second front (Front 2) was the more energetic of the two. A maximum significant wave height of 1.33 m and maximum current speed of 0.21 m s-1 occurred during this event. Additionally, mean current-induced shear velocity (2.95 cm s-1) and wave-current shear velocity (4.99 cm s-1) were highest during this event’s frontal and prefrontal stages, respectively. During the postfrontal stage, currents were strong and well organized, although combined shear velocities were low as a result of reduced wave height. Predicted sediment transport varied considerably in direction and magnitude throughout the deployment, but was highest (12.7-16.2 mg cm-1 s-1 towards the southeast) during the prefrontal and frontal stages of Front 2. Fair weather transport was low and to the west. Thus, winter cold fronts are likely an important mechanism for sediment movement on the Louisiana inner shelf, although the associated transport direction and magnitude require further quantification.

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Recent Research in Coastal Louisiana: Natural System Function and Response to Human Influence, p. 35-45

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