John’s Pass is a stable mixed-energy inlet located on a microtidal coast in Pinellas County, Florida. It is hydraulically connected to the northern portion of Boca Ciega Bay. Morphological analysis using a time-series of aerial photographs indicated that anthropogenic activities have influenced the evolution of the tidal deltas and adjacent shorelines at John’s Pass. Previous studies have documented the channel dimensions at the location of the existing bridge and calculated the tidal prism. A chronological analysis of these data yielded an increasing trend in the cross-sectional area at John’s Pass from 1873 to 2001. Anthropogenic activities occurring in Boca Ciega Bay impacting this trend begin in the 1920’s when Indian Pass, approximately 7 km north of John’s Pass, was artificially closed. Other significant events causing an increase or decrease in the crosssectional area at John’s Pass include dredging and filling in the bay, channel dredging at John’s Pass, and jetty construction. More recent data collected from a simultaneous current meter deployment at John’s Pass and Blind Pass were used to calculate the bay area serviced by each inlet resulting in an area serviced by John’s Pass being 1.8x104 km2 and 0.33x104 km2 serviced by Blind Pass. In comparison, Blind Pass captures 14 percent of the tidal prism that John’s Pass captures and John’s Pass captures 87 percent of the bay prism while Blind Pass captures 13 percent. Using the discharge equation and assuming the channel area was largely constant the tidal prism at John’s Pass was 1.07x107 m3 during the twenty-one day deployment. Based on a historical analysis of the tidal prism this study is within 40 percent of the tidal prism calculated by Mehta (1976) and Becker and Ross (2001) and within 20 percent of the tidal prism calculated by Jarrett (1976) and Davis and Gibeaut (1990). An analysis of the current meter time-series indicated that flood velocities in the channel were influenced by a frontal system passing through the study area during the deployment increasing the amount of potential sediment being deposited in the channel thalweg. The maximum ebb and flood-tidal velocities during the deployment were 143 cm/s and 115 cm/s, respectively. Morphological analysis of cross-sectional data from 1995 to 2004 indicated that sediment tends to accumulate along the northern portion of the channel. The channel thalweg tends to accumulate more sediment east of the bridge where wave energy is lower and currents are not as strong. An average net accumulation of 0.5 m per year was estimated along all seven cross-sections. Given the length and width of the surveyed channel, 610 m by approximately 150 m, the sediment flux through the inlet is approximately 45,800 m3 /yr along the channel thalweg. A small amount of sediment accumulation has occurred southwest of the bridge in response to channelized flood flows along the newly constructed jetty. An annual sediment budget was estimated for the John’s Pass inlet system using the beach profiles and inlet bathymetry data between 2000 and 2001. Overall, the inlet system has accumulated more sediment than it has lost during this time period.

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.

West-central Florida has supplied much of the national and global demand for phosphate for over 100 years. The two main tributaries of the Alafia River, the North and South Prongs, have been extensively modified by the strip mining, benefaction, and chemical processing activities associated with the phosphate mining industry. Using aerial photos, an analysis of landscape change in the South Prong Alafia River drainage basin (357.4 km2) between 1940, 1970, and 2004 was conducted. A modified Florida Land Use, Land Cover, and Forms Classification System code (FLUCCS) was used to classify and measure change through the study period. Change in the study area is characterized by a dramatic decline in the area covered by natural lands and an increase in the area covered by anthropogenic activity. Increasing 43.8 km2 from 1940 -- 1970 and 199.96 km2 from 1970 -- 2004, phosphate mining activity is the primary force of landscape alteration in the study area. The historic headwaters of the main stream, Hooker's Prairie, is completely replaced by mining-induced landforms in 2004. Net change in landscape composition from 1940 -- 2004 is 1) phosphate mining (+243.76 km2), 2) surface hydrology (-113.13 km2), 3) urban (+2.42 km2), agriculture (+19.76 km2), and undisturbed / other (-139.66 km2). The results of this study indicate that the regional environment and hydrology have been heavily impacted by phosphate mining activity. The critical management of the industry's environmental impacts and reclamation practices is essential for the current and future health of the local environment and its inhabitants.

A new methodology is proposed for estimation of evapotranspiration (ET) flux at small spatial and temporal scales. The method involves simultaneous measurement of soil moisture (SM) profiles and water table heads along transects flow paths. The method has been applied in a shallow water table field site in West-Central Florida for data collected from January 2002 through June 2004. Capacitance shift type moisture sensors were used for this research, placed at variable depth intervals starting at approximately 4 in. (10 cm) below land surface and extending well below the seasonal low water table depth of 59 in. (1.5 m). Vegetation included grassland and wetland forested flatwoods. The approach includes the ability to resolve multiple ET components including shallow and deep vadose zone, surface interception capture and depression storage ET. Other components of the water budget including infiltration, total and saturation rainfall excess runoff, net runoff, changes in storage and lateral groundwater flows are also derived from the approach. One shortcoming of the method is the reliance on open pan or other potential ET estimation techniques when the water table is at or near land surface. Results are compared with values derived for the two vegetative covers from micrometeorological and Bowen ratio methods. Advantages of the SM method include resolving component ET.

A generalized non-dimensional mathematical expression has been developed to describe the rating relation of depth and discharge for intermediate and high streamflow of natural and controlled streams. The expressions have been tested against observations from forty-three stations in West-Central Florida. The intermediate-flow region model has also been validated using data from thirty additional stations in the study area. The proposed model for the intermediate flow is a log-linear equation with zero intercept and the proposed model for the high-flow region is a log-linear equation with a variable intercept. The models are normalized by the depth and discharge values at 10 percent exceedance using data published by the U.S. Geological Survey. For un-gauged applications, Q10 and d10 were derived from a relationship shown to be reasonably well correlated to the watershed drainage area with a correlation coefficient of 0.94 for Q10 and 0.86 for d10. The average relative error for this parameter set shows that, for the intermediate-flow range, better than 50% agreement with the USGS rating data can be expected for about 86% of the stations and for the high-flow range, better than 50% for 44% of the stations. Testing the model outside West Central Florida, in some stations at North Florida, and South Alabama and Georgia, show some reasonable relative errors but not as good as the results obtained for West Central Florida. Using a model with a different slope, developed specific for those particular stations improved the results significantly.

The morphodynamics of an inlet channel draining an estuary or bay are governed by a complex system of temporally and spatially varying physical processes, including wind, waves, tides, sediment transport, and both tide and wave driven currents. In addition, sediment availability and characteristics in conjunction with underlying geologic framework bear on the morphology and morphologic behavior of an inlet system. This study examines the morphodynamics, sediment transport patterns and time-series morphologic change of John’s Pass and Blind Pass, two structured tidal inlets that collectively make up a dual-inlet system sharing the tidal prism of northern Boca Ciega Bay, in Pinellas County, Florida. To quantify wave and tidal forcing and response mechanisms an array of hydrodynamic sensors were deployed over a 12 month period at both inshore and offshore locations. In order to capture morphologic changes and quantify volumetric changes within the inlets, bathymetric surveys of the inlets were conducted in 2010, 2011, 2012, and 2014. Similarly, bi-monthly beach survey data for the same range of time was acquired in order to quantify volumetric changes along adjacent stretches of beach. In addition to gaining insights into sediment pathways based on morphologic and volumetric variability, those data were also used to develop a regional sediment budget along the studied stretch of coast. To gain insights into the morphodynamics of the dual-inlet system, bathymetric and hydrodynamic data was used to develop a numerical model of the dual inlet system. Numerical model simulations based on existing or baseline conditions were compared with numerical simulations employing synthetic bathymetric and hydrodynamic conditions in order to examine inlet behavior under a range of different morphological and hydrodynamic conditions. John’s Pass is the dominant of the two inlets. It exhibits mixed-energy straight morphology and captures ca 81% of the available tidal prism. The inlet has a well-developed mature ebb shoal, and actively bypasses sediment from one side of the inlet to the other supplying sediment to the downdrift littoral system. Blind Pass captures less than 20% of the available tidal prism, and while also exhibiting mixed-energy morphologic characteristics has a less well developed ebb shoal that currently has not fully established a sediment bypassing system. Both inlets channels and ebb shoals have been dredged on multiple occasions to provide sediment for the nourishment of nearby chronically eroding stretches of beach. Dredge pits excavated along the distal margins of the ebb shoals are infilling at rates substantially slower than expected due to limited sediment transport along those regions of the ebb shoal, while inlet channel dredge pits infill at rapid and expected rates. The objective of this study was to characterize the morphodynamics of the dual-inlet system with the aim of identifying sediment pathways and bypassing mechanisms, and quantify a balanced regional sediment budget in order to design more sustainable approaches to inlet management.