Degree

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

The Barataria Basin is a large estuarine system in Southeastern Louisiana, connected to the Gulf of Mexico through a number of inlets, the most important of which is the Barataria Pass. This research examines, during April-June 2010 including both cold front passage and calm summer-time wind regimes, the wave dynamics in this basin and in its major inlets, morphological evolution near the Barataria Pass, and the budgeting and dispersal of the Mississippi River sediment in the birdfoot delta region. An unstructured grid, terrain following, high resolution coupled FVCOM-SWAVE-SED model is employed and validated in this study. The numerical model results reveal that locally generated wind-seas are the main source of the wave field inside the Barataria Basin, especially for waves with significant wave height greater than 0.1 m and during cold front passage events. Moreover, the model predicts an almost instantaneous response of the wave field to the change in the wind direction. The impact of cold front passage on shoreline erosion is also attested by wave exposure analysis, i.e. frequency of occurrence of wind waves with significant wave height greater than 0.1 m.

In tidal inlets, an analysis indicates a dual nature of the wave field: locally generated seas and swells from the Gulf of Mexico. We assessed the contribution of hydrodynamic forces and found them to be more important in the inlets rather than inside the basin. FVCOM-SWAVE predicts a decrease in significant wave height inside the Louisiana Bight due to current-induced refraction and wave stretching effects caused by the clockwise gyre from the Mississippi River plume. The modulation of significant wave height at the Barataria Pass due to partial wave blocking from the opposing current, and wave stretching for the following current can be up to 20%. The effect of depth-induced breaking and bottom friction overshadows that from wave-current interaction at other shallower inlets.

The analysis of the water and suspended sediment concentration fluxes among six major outlets of the Mississippi birdfoot delta indicates that 64% and 40% of the flow and SSC passes through the Southwest Pass during the three-month simulation time, respectively. Due to the more energetic flow field at this pass, the sediment dispersal and deposition is more elongated and large suspended sediment concentration (> 10-2 kg/m3) is retained in the upper four meters of the water column for ~ 8 km offshore of the Southwest Pass.

A study on morphological evolution near the Barataria Pass demonstrates an erosional area mainly located at the shelf side of the Barataria Pass, and two depositional regions at the shelf and the bay side of the pass. Tidal forcing is shown to be the dominant forcing during the modeling period. Because the location of the transect across the pass is located almost on the northern edge of the erosional area, the net sediment flux is bayward while the net water flux in this ebb-dominated inlet is seaward. The largest sediment flux into the bay occurs during the pre-frontal phase of cold front events.

Committee Chair

Huang, Haosheng

Available for download on Sunday, August 14, 2022

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