Impact of Human vs Natural Processes: Insights from the North Carolina
Shelf following Hurricane Florence
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 >65% of the NC shoreline is eroding, with 20% losing
shore at ~1 m per year. Chronic long-term erosion and
episodic rapid impacts from storms have encouraged most coastal NC
communities to conduct beach nourishments for mitigation. One concern is
that there is limited knowledge of how offshore sand shoals – often
sources for nourishments – are evolving in response to storm conditions
and dredging activity. In September 2018, Hurricane Florence impacted
southern NC and northern SC, and many communities experienced enhanced
erosion. Future offshore sand removal for beach nourishment is
inevitable here and elsewhere along the East Coast. A borrow area on the
continental shelf seaward of Bogue Inlet (NC) offers an opportunity to
see how the seabed is changing as a result of anthropogenic and
oceanographic processes. Hurricane Florence made landfall as a Category
1 near Wilmington, NC on the morning of September 14, 2018. 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, yielding powerful storm surge and waves over 8 m
near the study area. Given the water depths of the ODMDS, seabed
reworking was anticipated. The project collected geophysical data and
sediment samples over a portion of the ODMDS offshore of Bogue Banks, NC
in February 2019. Multibeam bathymetry, backscatter and seismic
reflection data were obtained along with 24 sediment samples. These data
add to previously collected data over the same area in 2013 and 2018.
Grain-size analysis has been completed on all collected samples.
Preliminary analysis of the post-hurricane data in comparison to earlier
results indicate that the seabed has been reshaped since the last survey
in March 2018, likely in response to Hurricane Florence. The broad
dome-shape of the ODMDS remains, however, there is conspicuous
morphological change. In shallower areas large sand waves (crests
oriented roughly N-S, wavelength 20-30 m) differ from earlier mapping.
Despite notable reworking, the anthropic signature of dredging in 2013
remains on the seascape.