Continuing Project Work plan - FY 1999

IDENTIFYING INFORMATION
Project Title: HIGH-RESOLUTION BATHYMETRY OF FLORIDA BAY
Geographic Area: Florida Bay
Project Start Date: FY95
Project End Date: FY99
Project Number: 7242-37650

Project Chief: Mark Hansen
Region/Division/Team/Section: Eastern/Geologic/St. Petersburg
E-mail: mhansen@usgs.gov
Phone: 813-893-3100 Extension 3036
Fax: 813-893-3333
Mail Address: 600 4th St. South., St. Petersburg, Florida 33701
Program: Integrated Natural Resource Science Program
Program Element(s)/Task(s): 7.1
 

BACKGROUND NARRATIVES
Project Summary: Detailed, high-resolution maps of Florida Bay mudbank elevations are needed to understand sediment dynamics and provide input into water quality and circulation models. The bathymetry of Florida Bay has not been systematically mapped in nearly 100 years, and some shallow areas of the bay have never been mapped. An accurate, modern bathymetric survey will provide a baseline for assessing future sedimentation rates in the Bay, and a foundation for developing a sediment budget. Due to the complexity of the Bay and age of existing data, a current bathymetric grid (digitally derived from the survey) is critical for numerical models.
 

 The objective of this research is to collect new bathymetry for all of Florida Bay, digitize the historical shoreline and bathymetric data, compare previous data to modern data, and produce maps and digital grids of historical and modern bathymetry. This information will be provided to other researchers involved in the South Florida Ecosystem Restoration Program so they can better address the water quality issues of Florida Bay.

The strategy is to systematically map the bathymetry in Florida Bay in order to aid in the assessment of Bay sedimentation rates and to provide an accurate seafloor surface for numerical models. The Bay will be mapped using a shallow draft boat equipped with a high-precision GPS receiver coupled with a high-precision depth sounder. Data will be collected on a USGS 7.5 mm quad-by-quad basis proceeding westward from Blackwater Sound. Sounding trackline spacing will vary depending upon the relief of the seafloor, i.e. closer spacing and outlining near the mud banks - wider spacing in the basins.

Potential Impacts and Major Products: Numerical circulation and sediment transport models being developed for the South Florida Ecosystem Restoration Program will be used to address water quality issues in Florida Bay. Application of these models is complicated due to the complex seafloor topography (basin/mudbank morphology) of the Bay. The only complete topography data set of the Bay is 100 years old. Consequently, an accurate, modern seafloor bathymetry map of the Bay is critical for numerical modeling research. A modern bathymetry data set will also permit a comparison to historical data in order to help access sedimentation rates within the Bay. Previous research suggests that the mudbanks are dynamic features that migrate, accrete and erode. Less is known about the sedimentation rates in the basins. Some experts suggest the basins are filling, in association with sea level rise, while others suggest the basins are deepening relative to sea level. This study will provide modem detailed bathymetry data for Florida Bay necessary to help assess sedimentation rates and provide numerical modelers with the accurate bathymetric maps needed for modeling. Digital seafloor grids will be produced from the trackline data for use in numerical models. Historical bathymetric data (1890s) will be obtained from NOS archives, digitized, and entered into a GIS. Digital comparisons of mudbank basin morphology changes will be created using the historical data and the modern data. The project will produce hardcopy maps, digital maps, comparison maps and professional papers for both the historical and modern data sets. Digital maps will be available on the Internet and distributed on CD-ROM. CD-ROM format will conform to ARC/View and SDTS standards.

Collaborators, Clients: The primary users of the data will be researchers who are applying numerical models to the Bay to understand water circulation patterns and gradients in sediment transport. These efforts are directly related to water quality issues in the Bay. Circulation models are being developed and applied by WES and sediment transport models are being applied by USGS researchers. The updated bathymetry will also serve as a reference for future research in the Bay.

Clients:   US Army Corps of Engineers - Numerical modeling
                NOAA - Mapping

WORK PLAN
Time Line (FY1999 to project end):

• Complete collection of bathymetric data including establishing new ground control points when necessary. - M. Hansen/N. Dewitt
• Process bathymetric data. - N. Dewitt
• Produce final maps and digital grids of modern data. - M. Hansen/L. Thornton
• Produce final maps of historical data.- M. Hansen/L. Thornton
• Produce final maps of seafloor change.- M. Hansen/L. Thornton
• Produce an USGS Atlas of historic and modern bathymetry in Florida Bay. - M. Hansen/L. Thornton

FY1999 Deliverables/Products:

We plan to produce an atlas this year as a final map product of this project. The atlas will be in both printed and CD-ROM formats. The atlas will have the following sections: methodology, historic and modern data trackline maps, historic bathymetric contour maps, modern bathymetric contour maps on a DOQ image backdrop (see Accomplishments section), bathymetric change maps, and digital grids (for use in numerical modeling software). Maps will be presented at 1:100,000 and 1:24,000 scale.

In summary, the major products for FY1999 which will be presented in the atlas are:

• Modern seafloor maps of Florida Bay overlaid on DOQs
• Digital grids of modern seafloor bathymetry
• Historical (1890ís) seafloor maps of Florida Bay
• Seafloor change maps (1 890s-1998) of Florida Bay

ACCOMPLISHMENTS, OUTCOMES, PRODUCTS, OUTREACH
FY 1998 Accomplishments and outcomes, including outreach:
To survey areas not accessible by boat, e.g. mudbank tops and sensitive sea-grass areas, other non-intrusive (remote sensing based) methods must be employed to fully map the bathymetry of the Bay. Previously, we proposed using either the US Army Corps of Engineers (US COE) SHOALS helicopter LIDAR bathymetry system or photographic/satellite techniques to determine mudbank elevations. This year we assisted NOAA in the evaluation of the SHOALS system near Black Betsy Keys to determine if the system could be used to map mudbank tops in all of Florida Bay. According to the USCOE, the SHOALS system was unable to resolve the bottom due to a combination of the grassy bottom and shallow water depths. Consequently, the SHOALS system will probably not be utilized for mapping mudbank tops due to system and financial constraints. The alternate method, known as the ìbath tub ringî method, utilizes vertical photography or imagery in combination with water stage data to determine the elevations of the mudbanks. Procedures have been developed this past year by Rick Stumpf to extract mudbank elevations from LANDSAT imagery. Preliminary results are encouraging suggesting this method will be capable of mapping needed mudbank tops. Utilizing the ìbath tub ringî method in conjunction with boat sounding data will provide basin and mudbank elevations for the entire Bay.

Historical shorelines and bathymetric data from the 1890ís and 1930ís have been obtained from NOS historical archives; however, the only complete historical bathymetric data of the Bay is from the 1890ís time period. All shorelines and soundings from the 1890ís have been digitized using standard digitizing practices and projected to a modern datum (NAD83) with an overall RMS error of < 10 meters.

This past year, we have purchased USGS DOQs (1/4 quads) with 1-meter resolution for all of Florida Bay. For demonstration purposes, we requested Brevard Teaching Lab to mosaic 4 DOQs into one seamless 7.5 minute quad in order to create a color background image of land features on which color filled bathymetric contours were placed. An example of the Blackwater Sound quad was presented and well received at the Florida Bay Science Conference in May. We plan as final map products to present the recently collected bathymetric data as color fill contours overlaid on the DOQ mosaics.

In FY1998, we have completed/provided the following:

• Florida Bay has been systematically surveyed from Buttonwood Sound to Whipray Basin.
• Seven new ground control points were established.
• All historical shoreline and bathymetric data of Florida Bay has been digitized and registered to a modern datum.
• Eric Swain has been provided bathymetric data for numerically modeling the Joe Bay area.
• University of Miami was provided historical shoreline data and GIS conversion techniques.

• Modern seafloor maps of Florida Bay at 1:24000 (7.5 mm USGS Quadrangle) for the area from Blackwater Sound to Whipray Basin.
• Digital grids of modern seafloor bathymetry
• Historical (1890ís) seafloor maps of Florida Bay at 1:24000 (7.5 mm USGS Quadrangle).