Date of Award

1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

First Advisor

Harry H. Roberts

Abstract

Contamination of oyster-rich waters in south Louisiana by sewage-related wastes is believed to occur on a seasonally varying basis, and pose a serious threat to both human welfare and the local economy. Fluctuations in the meteorologic and oceanographic conditions in the region are believed to be responsible for the variability observed in bacterial concentrations. To gain a better understanding of the relationship between transport processes, environmental forcing, and the potential for contamination, a combined program of in situ measurements and numerical modeling techniques was conducted in the nearshore waters of Terrebonne Bay, Louisiana. A finite element model based on the vertically integrated equations of motion and continuity was used to simulate flow under various environmental regimes. Wind, tides, and runoff were incorporated based on real-time measurements within the study area. Observations of large-scale circulation were used to calibrate and verify the ability of the model to realistically simulate flow. Lagrangian-type particle tracking was employed to specifically examine tidal advection and residual transport in the pollution-prone northwestern region of the bay. Results indicate that the patterns of transport within the nearshore waters of Terrebonne Bay are highly complex and depend on the interactions of tides, wind, runoff, and changes in mean sea level within the bay. Residual flow of particulate materials within the bay is commonly seaward at a rate of 0.8 to 5.0 cm/s depending on location and environmental conditions occurring during the time of release. Even under the strongest of transport regimes, the residence time within the oyster-rich upper reaches of the bay appears to be on the order of 2 or more days. Rising sea level within the bay, daily landward advection by the incoming tide, and several wind/tide combinations produce transport patterns conducive to contamination. Consequently, the likelihood for contamination of oyster-rich waters is not a function of season or any one environmental parameter. Present management strategies for oyster harvesting are not supported by these results, and efforts towards more effective treatment of wastewater prior to discharge, and the use of depuration processes post-harvest are recommended.

Pages

158

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