PREDICTIVE MODELING OF MODERN SEDIMENT TRANSPORT DYNAMICS ON THE NORTHEASTERN FLORIDA CONTINENTAL SHELF

This investigation calculates modern sediment transport processes along the northeastern Florida continental shelf. The work uses numerical predictions, which are constrained by data from the published literature and from unanalyzed seafloor surveys previously performed by government agencies, to explore end-member scenarios for sediment transport. The work also specifically examines extreme oceanographic cases appropriate to hurricane conditions. The modern east Florida shelf is the southern extension of a gently sloping, continuous platform that lies off the entire US east coast. In general, the northeastern Florida coast is wave dominated, having a winter mean significant wave height of 1.2 m and receiving a long-period (8-9 s) swell from the open Atlantic. The tidal range for the region is historically less than 3 m. The study area is located on the inner-mid shelf, 15 km off the coast of Jacksonville, and has an average water depth of 20 m. Shallow seismic and vibracore data are available over the area of 81.5-81.0°W, 29.9-30.8°N. The vibracore and shallow seismic data are used to characterize sediment lithology, grain size, and the lateral extent of sediment facies. The most important aspects of the observational data have been synthesized into a three-dimensional model of sediment type distribution. Oceanographic conditions in the area are constrained by NOAA offshore buoy data. Calculations of transport focus on the physical forces responsible for sediment motion on the seafloor. For the calculations, it is assumed that sediment grains are spherical and non-cohesive, that conditions are steady-state, and that the area only experiences unidirectional flows. A series of model runs are performed using the same surface sediment distributions, but different end-member oceanographic conditions to force sediment motion. Thus, this forward-predictive study produces a series of maps showing anticipated sediment transport along the shelf under a variety of forcing conditions. The model predicts that there is not a significant amount of sediment movement on a day-to-day basis, but that most sediment transport occurs during hurricane-like storm events, followed by some significant seasonal variation in the winter due to strong winter storms.