Area of Operations: Puerto Real, off Villa Esperanza, south coast of Vieques, Puerto Rico, Caribbean Sea, United States, North America, North Atlantic
Dates: May 21, 1988 to May 25, 1988
Chief scientist: Juan Trias
Objectives: Locate offshore sand supply that might possibly be suitable for nourishing the eroding beach along Villa Esperanza shoreline. This study is part of the coastal erosion study of Puerto Rico presently in its beginning stages.
Type of Activity: Seismic profiling; Sampling;
Information to be derived: Grain size analysis; Sea floor map; Morphology;
Summary: The hard-earned seismic coverage was of sufficient quality and quantity to identify sand deposits and to infer their composition. Just outside (to the south) of Puerto Real, about even with the two small islands, Cayo de tierra and Cayo Afuera, there is a shore-parallel feature whose seismic signature suggests rock. This is most likely a reef, probably a flourishing reef. The feature is at about 10 meters water depth. Seaward of that feature is a wedge of sand, lapping landward onto the previously inferred reef. The sand wedge extends seaward about 200 or so meters and terminates behind another shore-parallel feature at about 20 meters water depth. This feature is also inferred to be a reef. Diver observations were not made because of weather conditions. Seaward of this second feature is another wedge of sand that extends for a few hundred meters until it terminates just landward of what is inferred to be a drowned Pleistocene (?) reef at the present shelf edge. In addition to these sand deposits, there are numerous Pleistocene (?) channels on the shelf, inside the islands, that are filled with sediment. These are also potential sources of sand for beach replenishment. Unfortunately, the weather was at all times too rough for vibracoring. Even a larger vessel, such as the DNR's JEAN A, would not have helped in this regard. Thus, it will be necessary to return to Vieques to obtain a few vibracores and a handful of grab samples outside of the bay. With good weather, all the samples could be obtained in just two days of field work. It is critical for beach replenishment that the mud content of the snad not exceed a value of more or less 2%, thus the composition and texture of the sediment need to be known in some detail. A larger vessel would have allowed us to obtain more seismic and more grab samples. More seismic is not really necessary, but more grab samples could, perhaps, take the place of vibracores. More serious than sampling limitations of the small vessel were the logistical problems caused by not enough equipment storage space and crew housing/feeding facilities. Uniboom lines: 27; Beach samples: 5; Shipek samples: 12; Vibracore: 0; several beach profiles and observations.
Contact: Juan Trias ()
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