Graduation Year

2007

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

Ping Wang Ph.D.

Keywords

Mangroves, Estuary, Oysters, Sedimentation, Stratigraphy, Vibracore

Abstract

The Dona and Roberts Bay watershed comprises one of the five major watersheds in Sarasota County, Florida. It is connected to the Gulf of Mexico via Venice Inlet. Like many estuaries in the Florida, significant modifications have been made to the drainage basins, principally to the main tributaries. The system has undergone several anthropogenic modifications to enhance water management efforts. Creeks that comprise fresh water input into the system have been dammed in order to inhibit the upstream flow of salt water during the dry season. They are also deepened or lengthened to allow for better drainage. In addition, biogenic activity has also had morphological effects on the system. There are numerous oyster bars, and mangrove forests that impose obstruction to the tidal and river flows. This has resulted in a highly complicated estuary system in terms of flow velocities and sedimentation patterns.

The objectives of this study are to quantify the sediment characteristics and deposition-erosion trends and their relationship to flow patterns and other natural and anthropogenic factors within the system. A detailed sedimentary analysis was conducted based on 149 surface sediment samples and 29 drill cores. Spatial distribution of the sediment properties is quite complex, controlled by several interactive factors including; local sediment supply, intensity of the hydrodynamic processes, distribution of oyster bars and mangrove islands, and artificial structures. Sedimentation and erosion is significantly influenced by flood events. In some locations, such as the mouth of the fluvial channels, or the confluence of two creeks, the core data suggest that rapid sedimentation, driven by flood events, is responsible for the development of some of the large shoals. A 2-D depth-averaged circulation model was established for the study area.

Many of the natural structures and artificial modifications to the watershed system are incorporated into the model. A close relationship between the flow intensity and sediment characteristics, and therefore, sedimentation-erosion tendency is identified. Remotely sensed data is also incorporated into the study in order to gain an understanding of the development of the estuary system over a ten-year period. Data suggests that the maturation of biogenic organisms that inhabit the system coincides with the development of complex sedimentation patterns.

Download

Share

COinS