Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Dag Nummedal

Abstract

At least three delta progradations have contributed to the Barataria geologic framework since 5000 ybp. The Bayou des Families lobe was first (4600 to 3600 ybp) followed by Bayou Blue (2600 and 1900 ybp) and then the Mississippi lobe (1000 ybp to the present). A flooding surface separates the (lower) Bayou des Families from the Bayou Blue progradation (above). The shoreface of the Bayou des Families transgression lies seaward of the present Barataria shoreline. This transgression lasted approximately one thousand years. A flooding surface also separates the Bayou Blue progradation from the Mississippi Delta lobe. This (Bayou Blue) transgression lasted 900 years, was halted near the present shoreline, and can be traced from the Caminada headland to the meander bend of the Mississippi River at Nairns, Louisiana. Rates of relative sea level rise recorded in the subsurface of the Mississippi River delta plain decrease from 1.0 cm/yr in the top meter to less than 0.20 cm/yr at three meters. In recently abandoned delta lobes the high initial rate of subsidence contributes to rapid increases in bay area and tidal prism. This increase has caused the Barataria tidal inlets to evolve from wave-dominated to tide-dominated inlets within the past 150 years. In the late stages of delta lobe abandonment sediment supply to barriers islands becomes critically low. The inlets widen causing tidal currents to decrease. This causes the once tide-dominated inlets to become wave influenced. Dynamic coastal processes in the bays, inlets, and on the shoreface all contribute to the low preservation potential for Barataria shoreline sediments following the present transgression. Preservation, if any, will be limited to inlet channels scoured beneath the shoreface depth. The processes occurring along the Barataria shoreline are probably similar to those that occurred during past Holocene delta plain transgressions. By understanding the links between landloss and tidal inlet evolution during delta lobe abandonment the success of future Barataria barrier shoreline preservation programs may be improved. Bay area reduction by wetland restoration may reduce tidal currents through an inlet/barrier system. This activity combined with sand nourishment of the barrier shoreline should help save the Barataria Bay ecosystem.

Pages

468

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