Graduation Year

2004

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

Richard A. Davis, Jr.

Keywords

sedimentology, microtidal, hydrodynamics, ebb-tidal delta

Abstract

Bunces Pass is an unstructured tide-dominated inlet just north of the main entrance to Tampa Bay, Florida. The inlet has been stable for at least 130 years, as the size, shape, and orientation have remained unchanged. The morphological evolution of the Bunces Pass ebb-tidal delta is influenced by adjacent inlets. Historically, the ebb tidal delta was extremely large, due to the presence of the south channel of Pass-A-Grille Pass. As the tidal prism decreased through the south channel, the sheltering effect produced by the large ebb tidal delta diminished, and large volumes of sand began migrating shoreward. Sediment from the ebb tidal delta accreted along "the Reefs", formed both North Bunces Key and South Bunces Key, and accreted on Mullet Key south of the inlet. Tidal currents at Bunces Pass are primarily ebb-dominant during both summer and winter seasons, though there is flood dominance for several days during neap tides.

The ebb dominance is primarily due to the large back-barrier embayment of Tampa Bay, which results in a spring ebb tidal prism of 2.02 x 10⁷ m³. This tidal prism is more than 400 times the corresponding littoral drift. It is primarily responsible for maintaining the inlet's stability, as well as the development of its large ebb-tidal delta. Sediments from the ebb tidal delta at Bunces Pass reflect different degrees of wave versus tidal energy. The strongest tidal currents present throughout the entire ebb tidal delta complex mechanically weather shell gravel in the main channel, producing a shelly, fine quartz sand with relatively high amounts of shell gravel and carbonate sand. This sub-facies is also present on the north channel margin linear bar, due to the interaction of waves, tidal currents, and a southerly littoral drift along this coastal reach. Fine, quartz sand dominates the off shore and swash platform environments.

The present situation at Bunces Pass shows a stabilized, tide-dominated inlet with a large, elongate ebb delta that is unlikely to change significantly in the future if present conditions are maintained. The prevalent ebb-dominance suggests that the inlet is hydraulically connected to the adjacent and much larger Egmont Channel inlet system, which also serves Tampa Bay. Strong ebb-tidal currents have kept Bunces Pass in dynamic equilibrium with its surrounding environment. The large ebb tidal prism is responsible for explaining how a tide-dominated inlet is maintained in a microtidal environment.

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