Mullet Key is a right angle barrier island located at the mouth of Tampa Bay, west-central Florida. Based on historical shoreline data from 1873, the Gulf (west)-facing section of the beach has been dynamic illustrating large beach advances and retreats of up to 500 m on a decadal scale, while the south (channel)-facing section of the beach has shown to maintain a stable shoreline. This study focuses on the morphodynamics of the Gulf-facing beach. Since the 1920s, most of the Gulf-facing beach has been accreting except at the southern end near the Tampa Bay main channel. However, over the past 17 years, severe beach erosion has occurred along the northern portion of the island while accretion occurred along the middle portion. The southern end of the island has been maintained through artificial beach nourishments. Analysis of 27 aerial images from 1942 to 2014 revealed that the above large shoreline variations can be explained by the initiation, emergence, landward migrating, shoreline attachment, and post-attachment beach adjustment of the swash-bar complex on the Bunces Pass ebb delta. Two cycles of the swash-bar complex attachments with a period of approximately 30 years were identified from the aerial photos spanning 72 years. Twenty-eight beach-profiles spanning the 4 km Mullet Key Gulf-facing beach were surveyed 7 times on a bi-monthly basis from March 2014 to February 2015 to quantify the recent rapid changes, and to assess a yearly rate of shoreline change. Beach-profile analyses showed that the 120 m beach at the north-most tip in the immediate vicinity of Bunces Pass has lost a small amount of sediment. The 360 m beach to the south has gained some sediment. The 670 m stretch of beach further south has had significant shoreline retreat at a rate of 10-15 m/year. The 2,400 m section southward has experienced some gain of sediment, while the 370 m nourished beach at the southernmost tip has had slight retreat. This beach change pattern illustrates a diverging longshore sediment transport. Nearshore wave and current conditions were measured during a cold front passage in December 2014 to quantify the hydrodynamic processes that induced the diverging longshore transport. Three wave and current gauges were deployed along the eroding and accreting sections. The hydrodynamic data reveal that the longshore transport divergence is caused by diverging flood tidal flow into Bunces Pass to the north and Tampa Bay channel to the south. Furthermore, the waves in front the eroding beach were higher than the adjacent accreting beach.

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.