RAPID: Examining Seafloor Dynamics offshore Bogue Banks, North Carolina, Related to Hurricane Florence

University Of Rhode Island, Kingston RI

Investigators

Abstract

Many communities along the East and Gulf Coasts of the United States are experiencing moderate to severe erosion. Decadal shoreline erosion rates determined by the North Carolina Division of Coastal Management indicate that less than 65 percent of the North Carolina shoreline is eroding. Chronic long-term erosion and episodic impacts from storms have encouraged most coastal communities in this state to conduct beach nourishments using local off shore sand sources. One concern is present limited knowledge of how offshore sand shoals (potential borrow areas for replenishment of coastal dunes and beaches) are evolving in response to storm conditions and dredging activity. In September, 2018, Hurricane Florence severely impacted southern North Carolina and northern South Carolina, causing coastal erosion and flooding. As a result, significant erosion mitigation efforts are anticipated due to these impacts. This project will collect seafloor measurements from an offshore sand shoal which can be used to evaluate hurricane-driven changes. Broader impacts of the work include student training and information that can be used by coastal land managers and policy makers. Hurricane Florence made landfall as a Category 1 storm near Wilmington, North Carolina on the morning of September 14, 2018 but, just prior to making landfall, the storm was a powerful Category 2 hurricane, down from Category 4 status days prior. Hurricane-force winds were experienced over a large region, and these yielded significant storm surges as well as powerful waves along the central East Coast. Subaerial and subaqueous geomorphic changes likely resulted due to sediment movement resulting from forceful wave and tidal activity. This research is a rapid response to collect seafloor mapping data (i.e., multibeam bathymetry) over a portion of a previously surveyed area near Wilmington, North Carolina, known as the Morehead City Ocean Dredged Material Disposal Site. Work will involve the collection and interpretation of sub-bottom (CHIRP seismic) profiles, Samples of surface sediments will also be collected and analyzed for grain-size to determine clast size and sand transport parameters. These data will inform the nature of shelf sediment transport associated with Hurricane Florence and provide essential ground-truthing for interpretations of sediment transport and redistribution during a strong storm event. Surveys and sampling will take place along the inner continental shelf, within 16 kilometers of the North Carolina shore and water depths generally less than 20 meters. This is the region where offshore sand borrow sites used for beach nourishment are often located. It is also a coastal area that has been relatively understudied due to its shallow and energetic nature. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.