Detailed, high-resolution sea-floor maps of Florida Bay basins and mudbanks are needed to understand sediment dynamics and provide input into circulation model. The sea-floor of Florida Bay has not been systematically mapped in nearly 100 years, and some shallow areas have never been mapped. Because Florida Bay morphology is an intricate network of basins and mudbanks combined with extremely shallow water depths, an updated bathymetric grid is critical for implementing an accurate circulation model of the Bay. Additionally, an updated bathymetric survey of the Bay will provide a baseline for assessing future sedimentation rates and a foundation for developing a sediment budget.

The main objective of this 5-year project is to collect modern bathymetric data of Florida Bay and any other areas that have not been previously mapped. Hydrographic surveying is being conducted using the GPS based SANDS bathymetric system which has an average vertical accuracy +/- 10 cm and can collect data in water depths as shallow as 50 cm. Sounding trackline spacing for the majority of the Bay is 500 meters. All mudbanks and islands have been outlined and have closer line spacing because of the detailed intricatenature of the mudbank and island morphology. Surveying is near completion with data collected from Blackwater Sound to a line from Cape Sable to Grassy Key. Historical horelines and hydrographic data from the 1890’s has been digitized and registered to a modern datum using a unique set of survey control data points provided by the National Ocean Service (NOAA/NOS). The historical data will serve as the basis for comparison to the modern bathymetry and shorelines of Florida Bay.

A preliminary comparison of historical bathymetric data to modern data suggests that water depths in the eastern part of the Bay have not significantly changed; although, westward from Calusa Keys (middle Bay) it appears that modern depths differ depths often by as much as +/-0.75m. The overall size and shape of the major mudbanks, e.g. Cross Bank, Ninemile Bank, have not changed since the 1890’s. However, the channels and cuts through the banks are often in different locations and appear to have been extensively dynamited in some areas. In general, the submerged portions of the mudbanks recently mapped do not have "smooth" contours as depicted on some maps, but often have undulating or "finger" shaped contours. Some "fingers" extend perpendicular to the mudbanks 50 to 100m. A detailed comparison of historical data to modern sea-floor maps will be performed when the digital maps are completed. This comparison will aid in assessing sedimentation rates and possibly gather some insight or conclusions to effects of sea-level rise on Florida Bay. Final products for this project will be historical and modern shorelines and bathymetry, digital bottom grids, and USGS 7.5 minute ortho-photo quadrangle maps overlaid with modern bathymetry.

(This abstract was taken from "Programs and Abstracts - 1999 Florida Bay and Adjacent Marine Systems Science Conference". (PDF, 1 MB))

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