Hydrodynamics and Sedimentary Responses Within the Bottom Boundary Layer: Sabine Bank, Western Louisiana

Daijiro Kobashi, Felix Jose, and Gregory Stone
Coastal Studies Institute and Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, Louisiana 70803

To determine the wave-current interactions and bottom boundary layer characteristics of eastern Sabine Bank, off the southwestern Louisiana coast, an extensive array of bottom mounted equipment was deployed for a period of 44 days (11 March - 23 April, 2004). The instrument array mainly consisted of Acoustic Doppler Velocimeters (ADV's), Electromagnetic current meters (ECM's), Optical Backscatters (OBS's) and pressure sensors deployed at three locations (on the crest along the eastern flank of the bank, offshore and onshore of the bank). The results show thatwaves were generally from south-east with a mean peak period of 5.2 s. The highest significant wave height obtained was 1.8 m. Velocities parallel to the coast prevailed during fair-weather wave conditions. However, during cold fronts and strong wind regimes, cross-shore velocity components dominated. The significant wave height and the corresponding shear stress and shear velocity, all show higher values associated with the passage of cold fronts and during strong southerly/southeasterly wind regimes, when larger than the threshold for sediment re-suspension velocities were estimated from grain-size data. Hence it is inferred that waves during fair weather are too weak to re-suspend bottom sediments. However, waves during the cold fronts can effectively re-suspend and re-distribute sediments along the bank. It is also suggested that the strong wind regimes which usually occur during this period of the year can strongly affect sediment transport as effectively as the cold fronts do.

AAPG Search and Discovery Article #90080©2005 GCAGS 55th Annual Convention, New Orleans, Louisiana