Identifier

etd-01202006-163647

Degree

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

The balance between river and marine influences is important in governing landscape sustainability in river deltas. River- and atmospherically driven sea level variability, sediment loading, and estuary-ocean exchange in the Mississippi River delta are examined in this study. Subtidal estuarine sea level variability in the Breton Sound estuary was driven by a combination of remote atmospheric forcing outside the estuary over the continental shelf and controlled river inputs through a gated diversion structure at the estuary head. The highly-frictional deltaic landscape acted as a low-pass filter to coastal fluctuations near the estuary mouth. When substantial quantities river water were discharged into the estuary, upper estuary sea levels responded to a combination of river and atmospheric forcing, while sea levels in the lower estuary responded only to coastal forcing. Annual sediment loading into Breton Sound through a Mississippi River diversion was approximately 1 × 105 metric tons yr-1. Four pulsed, high-discharge diversions were conducted during the study, and sediment loading across each pulse was highly variable and was greatest during rising limbs of Mississippi River floods. Overland flow was induced when diversion discharge exceeded 100 m3 s-1. These results indicate timing and magnitude of diversion events are both important factors governing marsh sediment deposition in river diversion receiving basins. Sediment inputs measured during this study were negligible compared to historical loading through crevasses in the region. An investigation of estuary-shelf exchanges through Barataria Pass revealed that tidal exchange accounted for approximately 80% of the observed flow variability. Two dominant vertical subtidal exchange modes were identified. A barotropic mode, which accounted for most of the flow variance, was most coherent with cross-shelf wind stress. A second mode resembling baroclinic estuarine circulation recurred over fortnightly timescales, apparently in response to variations in tidal stirring. The baroclinic mode also appeared to be modulated by variability in freshwater inputs to the estuary. These findings provide a greater understanding of the physical dynamics that govern landscape sustainability in microtidal river deltas

Date

2006

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Jaye E. Cable

Share

COinS