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St. Petersburg Field Center Hosts Workshop on Ordnance Mine Burial

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The Office of Naval Research (ONR), Marine Geology and Geophysics Program held its "Coastal Processes Driving Mine Burial" workshop at the St. Petersburg Field Center (SPFC) on January 30th-February 1st. Peter Howd of the University of South Florida St. Petersburg campus was the local contact. Objectives of this ONR 6.2 program are to use both field and laboratory measurements in conjunction with numerical models to increase prediction of the fate of mines placed on the seabed in shallow marine environments. Approximately 40 researchers from six countries representing academia, the private sector and government agencies attended the workshop. The SPFC (Terry Kelley) receives funding from ONR to help support field operations associated with this program.

The objectives of the workshop were to begin establishing experimental designs for the program through discussion as a collected group of modelers, and laboratory and field investigators. During the workshop, two field sites were selected for extensive measurement programs in the coming years. The sites are the west Florida inner continental shelf (WFS), and the new WHOI coastal observatory based on Martha's Vineyard. The selection of the WFS site was helped in part by the extensive background information resulting from the 1990s USGS study headed by Guy Gelfenbaum, now at the Menlo Park office.

For the coming year, USF College of Marine Science investigators have been funded by ONR to:

  • Conduct detailed geoacoustic and sedimentological surveys of the Indian Rocks Beach inner shelf (IRB) area to obtain baseline geological information, such as, high-resolution bathymetry, sediment thickness, surficial variability in sediment acoustic patterns and textures, and the shallow subsurface (1-2 m) sedimentary facies patterns. A boomer seismic system or a CHIRP profiler will be used for mapping sediment thickness. A 100-kHz EG&G Model 272 TD side-scan sonar system will be deployed concurrently with a subbottom profiler to acquire backscatter data using a 300-m-swath coverage. This backscatter coverage is appropriate for detecting major surficial-sediment facies changes and the presence of bedforms as small as 0.5 m in wavelength. In addition, 300-kHz multibeam bathymetry and backscatter data will be collected in reconnaissance mode using a Kongsberg Simrad EM3000 (300 kHz) multibeam sonar system. Seabed textural changes will be assessed using backscatter data sets from the side-scan and multibeam systems and vertical-beam bottom classification techniques using QTC-IMPACT software designed to classify seafloor sedimentary facies based on bottom-sampling calibrations.

  • Integrate these geophysical techniques into the quantitative process studies. We will conduct an assessment of the calibration and repeatability of the various acoustic systems as we transition from qualitative to quantitative applications of these geophysical tools. A key component of the study will include ground-truthing of the geophysical data sets with sedimentary data. Sediment samples will be obtained using grab-sampling techniques and diver-deployed push cores. Correlation analysis will be run between textural components, acoustic classification of bottom types based on vertical beam wavelet analysis, and zonation of bottom types based on side-scan sonar imagery.

  • Measure the hydrodynamic conditions that produce and maintain bedforms and shallow stratigraphy. We will make detailed measurements of the combined-flow bottom boundary layer using a combination of current meters. An upward-looking ADP will measure mean flows from approximately 80 cm above the bed to near the surface. A tripod-mounted, downward-looking PC-ADP will measure the instantaneous flows in roughly the bottom 75 cm (in 2.5-cm bins). A downward-looking ADV will measure instantaneous flow at a point at rates of up to 25 Hz, allowing burst estimates of turbulence and accurate calculation of higher moments (skewness and asymmetry) of the flow. The downward-looking instruments will also function as altimeters. These spot measurements will be put in context of local (~102 m2) changes using high-resolution rotary fan-beam and scanning pencil beam sonars. Suspended sediment characteristics will be measured using acoustics and optical sensors (OBS, LISST-100).

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Leaky Coastal Margins / Karst Interest Group

Nat'l Sand & Gravel

Ordnance Mine Burial

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