Master of Science (M.S.)
Degree Granting Department
Ping Wang, Ph.D.
Jun Cheng, Ph.D.
Lori Collins, Ph.D.
John E. Bishop, Ph.D.
coastal morphodynamics, ebb shoal, nearshore sediment transport, swash bar, West Central Florida
Shell Key and Mullet Key are two sandy barrier islands on the West Central Florida coast near the mouth of Tampa Bay. These islands are part of an interconnected barrier-inlet system that includes Pass-a-Grille (PAG) and Bunces Pass. Shell Key is a relatively new island about 40-years of age that formed in between the two inlets of Bunces Pass and PAG. Mullet Key is an island to the south of Shell Key situated between Bunces Pass and the main Tampa Bay channel that has demonstrated large scale upward shoaling events. Using numerical modeling, the wave and tidal conditions at the dual-inlet system were investigated in order to understand the hydrodynamic conditions that drive the morphology change. Historical aerial imagery and historical nautical charts were analyzed to determine the large scale accretionary and erosive changes that happened in the study area from 1873 to 2018. Four historical nautical charts, from 1873, 1928, 1966, and 1996 were digitized to create bathymetry maps of the two islands, their adjacent inlets, and the ebb shoals. These historical bathymetry maps were compared with the bathymetry survey by this study in 2016. The research goal of this thesis is to investigate the mechanism of origin and development of two barrier islands along the coast of West Central Florida through a time series of photos combined with numerical modeling.
Based on aerial photos from 1984 to 2018, the overall shape and orientation of ebb shoals at both Bunces Pass and PAG were analyzed in order to examine the effect that the 30 year swash bar cycle at Bunces Pass has on a connected inlet system. The ebb shoal orientations were compared to see how swash bar initiation would affect the two ebb shoals; most notably Bunces Pass ebb shoal. A bending of the entire Bunces Pass ebb shoal was identified over the 2002-2018 time span corresponding to the development of a large sand feature located here.
Further numerical modeling was conducted at PAG to determine the factors controlling the formation of Shell Key. Before the 1970s, the PAG inlet included two branches, the North PAG Channel and the South PAG Channel. A major dredging event took place at the North PAG Channel in 1966 causing significant widening and deepening of the channel. This dredging event was simulated to quantify the impact to the natural flow pattern. The 1966 dredging project had a significant impact to the overall flow pattern, increasing the ebb jet flow velocity by 0.8 m/s over the dredged area and significantly decreasing flow velocity by -0.4 m/s over a large area where the South PAG Channel was previously located. This artificially induced change of flow pattern resulted in the closure of South PAG Channel and the corresponding development of Shell Key.
Scholar Commons Citation
Westfall, Zachary J., "Morphodynamics of Shell Key and Mullet Key Barrier Islands: Their Origin and Development" (2018). USF Tampa Graduate Theses and Dissertations.