Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Nicholas C. Kraus

Second Advisor

James M. Coleman

Abstract

East Pass, a tidal inlet located in the Florida Panhandle between Pensacola and Panama City, connects Choctawhatchee Bay to the Gulf of Mexico. A three-phase model has been developed which describes the behavior of East Pass inlet during the last 120 years, based on wave, current, tide, bathymetric and shoreline data, and on historical records. The first phase (pre-1928) is of spit development and breaching. This phase covers the period when the pass was oriented in a northwest-southeast direction between Choctawhatchee Bay and the Gulf. From 1928 to 1968, the second phase was characterized by a stable throat position but with a main ebb channel that migrated over a developing ebb-tidal delta. This phase covers the time after the inlet breached Santa Rosa Island in a north-south direction and began to migrate east. The third phase, spanning 1968, when rubblemound jetties were built, to the present, is characterized by a stable inlet throat and ebb channel, and ebb-tidal shoal growth. Despite the jetties, East Pass has attempted to continue moving eastward, resulting in continued maintenance problems and erosion. The eastward migration is caused by: (1) Wave forces. The predominant local wave direction is from the southwest, while the shoreline trends east-west. (2) Backbay tidal channel and flood-tidal shoal geometry direct ebb currents towards the eastern shore of the inlet. Tide and meteorological data reveal that water levels in Choctawhatchee Bay fluctuate rapidly during the winter months in response to the passage of winter cold fronts. Northwest winds that follow fronts cause a setdown of offshore water, leaving Choctawhatchee Bay perched. The resulting outflow can account for as much as a 50 percent increase in the water that flows through East Pass over that due to astronomical tides alone. It is likely that the greatest erosion and sediment transport in the inlet occur during these episodes when current velocities are higher. The large number and regularity of fronts (261 between 1979 and 1991) suggest that they may be a more important factor causing long-term geological changes than are the infrequent hurricanes that pass through the area.

Pages

340

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