TYBEE ISLAND, Ga. – Members of the U.S. Army Corps of Engineers, Savannah District, and the Engineer Research and Development Center reported the findings from their ship wake study to the Tybee Island city council on Tybee Island, Ga. on Jan. 26, 2023.
Jared Lopes, water resources planner for the Savannah District, led the overview of the study before handing it over to Dr. Richard Styles, research oceanographer from the ERDC Coastal and Hydraulics Laboratory, for a more detailed analysis. After the presentation, they fielded questions from Tybee Island Mayor Shirley Sessions and the six-member city council. Dr. Rachel Bain, research physical scientist also from the Coastal and Hydraulics Laboratory, coauthored the study, but wasn’t present at the council meeting.
The study was set into motion amid concerns regarding the ongoing risk to beachgoers from vessel-generated wakes on Tybee Island’s northern shore, said Lopes. The goal of the study was to develop a better understanding of vessel traffic patterns and associated boat wakes generated by large commercial vessels.
“It was a rewarding experience being able to work closely with Dr. Bain and Dr. Styles from ERDC and the City of Tybee Island on this study,” said Lopes. “I was eager to present the final briefing at the Tybee City Council meeting, as the results of this study hold ample potential for helping mitigate the impacts of ship wake on the northern shore of Tybee Island.”
Vessel operations and environmental conditions were monitored between late July and early December 2021, where such factors as size, speed, type, and heading of each ship, the types of waves created by those ships, and tidal currents were observed.
The study findings discovered that the largest vessel wakes were generated from container ships and vehicle carriers, ships that traveled faster than 12 knots, and ships that were longer and wider than average. Other lesser influences included tidal currents, wind waves, and vessel direction.
“Despite the fact that wakes generated by commercial vessels tend to be larger than those created by wind, wind waves constitute a more considerable source of continuous energy for moving sediment in the area,” said Lopes. “This is because large vessels pass the beach infrequently, an average of 12 passages per day, whereas wind waves break on the beach continuously.”
Instruments used to record this data included the sensors mounted on U.S. Coast Guard navigation ranges, pressure sensors mounted below water, near-shore sensors, and information commercial vessels submitted to the Coast Guard’s Automated Information System.
The study concluded that the next steps should explore the best approaches of reducing vessel-generated wave impacts. Two options were suggested: Modify navigation conditions to reduce wave heights near the source; or reduce the height of the waves near the shoreline.
Several strategies were recommended to achieve those two suggestions, including reducing maximum ship speed, refurbish and extend the south jetty, install nearshore breakwaters, channel modifications, channel realignment, and active warning system. However, the study observed that those recommendations do not address the potentially substantial engineering requirements needed to implement those strategies.
The cost of the study was $350,000 and was split equally between the Corps and the City of Tybee Island, whose cost-share was supported by a Georgia Department of Community Affairs grant.
The 90-page study was published on Dec. 1, 2022, and can be read here: https://erdc-library.erdc.dren.mil/jspui/handle/11681/46140