Fact Sheet - Limited Sand Resources for Eroding Beaches
Under natural conditions, barrier islands shift in response to storms, sediment supply, and changes in sea-level. Manmade structures such as sea walls, jettys, and even buildings and roads can alter the influence of these natural processes. Consequently, some areas have experienced rapid beach erosion, resulting in narrow beaches that are insufficient for recreational use or protection of upland properties.
In 1992, Congress directed the U.S. Geological Survey (USGS) to initiate a 5-year study of this region in order to better understand the recent geologic history of the barrier island system and the processes that control the distribution and transport of sediment on the inner shelf. The West-Central Florida Coastal Studies Project is a cooperative effort between the USGS, the University of South Florida, and Eckerd College.
The west-central Florida coast barrier-island chain sits near the center of a broad, gently sloping carbonate platform. The continental shelf is underlain by limestone bedrock with a thin, discontinuous cover of sand deposits of both quartz and carbonate origin. Prior to the initiation of this project, it was generally believed that sand resources were evenly distributed on the continental shelf. Early results, however, have demonstrated that sand is concentrated in specific, nearshore areas and is of limited thickness.
In addition to the reconnaissance mapping, USGS scientists and collaborators have completed detailed studies in two localities, one north and one south of the entrance to Tampa Bay. Detailed sidescan-sonar maps were made of localized areas which are being used to understand the variability in sediment distribution of beach-quality sand, carbonate shell material, and hardgrounds and to shed new light on the processes that shape the inner shelf.
Coastal Processes and Morphodynamics
The west-central Florida barrier island and inlet system is among the most varied in the world. The combination of low wave energy and microtidal conditions produces a wide range of barrier and inlet morphologies. Barrier islands and inlets in this region are affected by a complex suite of processes including sediment availability, impacts of storms and hurricanes, circulation, and underlying geologic control. For example, analysis of core samples and seismic data indicate that, in some areas along the coast, the underlying limestone bedrock exerts a significant control on the location of the barrier islands. Processes affecting the barrier island and inlet system have been active throughout recent geologic history, evidenced by the range in ages of barrier islands, from greater than 4,600 years at Siesta Key in the southern part of the study area to less than a decade at 3-Rooker Bar in the north. There is also evidence that the location of some islands have shifted considerably landward over thousands of years.
Researchers are also examining dominant oceanographic processes, how they influence sediment transport, and how they affect sand distribution in this region. Several methods are being utilized to examine circulation patterns on the inner shelf including deploying instruments that measure winds, currents, temperature, and salinity. Early results have demonstrated the importance of seasonal variations in the mean circulation and in sea level and have identified coastal upwelling of colder, deeper water following storms.
Data collected by current meters and satellite imagery are being utilized in the development of three-dimensional numerical circulation models. These models help to describe the responses of the entire west Florida continental shelf circulation and sea level to storms and seasonally varying conditions.
The west-central Florida coast is a highly populated region with an economy closely tied to its natural resources. The results of this project will allow planners and managers to better understand the effects of land-use decisions based upon a scientific understanding of the natural coastal processes.