U.S. Geological Survey (USGS) scientists in St. Petersburg, Fla., have developed a new computer model to help track, manage and predict the spread and path of oil spills, sometimes years into the future.
The study, published last week in the Marine Pollution Bulletin, looked at conglomerates of sand and oil several centimeters thick known as surface residual balls (SRBs) found in the surf zones of the Gulf of Mexico after the Deepwater Horizon oil spill. SRBs can float to surf zones, where waves break, and beaches, more than three years after the spilled oil first touched the shoreline.
"SRBs are dense enough to rest on the seafloor, rather than floating,” P. Soupy Dalyander, lead author of the study and a research oceanographer, said in a statement. “Because sand grains are smaller and more mobile than the larger SRBs, under nonstorm conditions when the SRBs themselves are not moving, they can be buried and exhumed by mobilized sand.”
USGS scientists applied their numerical model to the movement of SRBs along the coast of Alabama and western Florida and found that normal wave conditions of less than 1.5 to 2 meters will not move centimeter-sized SRBs along the shore. But tropical storms and winter storms would mobilize and redistribute the SRBs.
The model also indicates that inlets trap SRBs, allowing them to accumulate, and that larger SRBs found on shore are likely to have formed when the oil floated ashore rather than while the oil traveled from its original location. Another highlight in the report is that SRBs were found likely to be covered and uncovered by sand moved by waves and currents in surf zones.
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"The techniques developed here can be applied to evaluate the potential alongshore movement of SRBs in other locations or from any future spill where large quantities of oil and sand mix in the surf zone,” Dalyander said.