Even without direct landfall by a major storm, a wealth of data was collected on the Outer Banks of North Carolina this hurricane season.
Hurricane or Bust: How DUNEX Found Consolation in the Middle
This article is part of the November-December 2021 issue of the Sound Waves newsletter.
Few things are more costly than past ravages of the Atlantic hurricane season, and the inevitability of future storms keeps coastal communities in a constant state of unease. Accurate forecasting and mitigation of storms has been a goal for decades and as technologies and computing power have taken off, there is new energy towards predicting, modeling, and understanding these forces of nature. The During Nearshore Event Experiment (DUNEX), one of the biggest collaborative scientific studies seeking to capture the before, during, and aftereffects of hurricanes on coastal communities, is almost at its end. Staged along the Outer Banks of North Carolina at the Duck Field Research Facility (FRF), Jeanette's Pier, and at the Pea Island National Wildlife Refuge, over thirty research teams from federal agencies and universities across the country deployed hundreds of sensors and retrieved hundreds of terabytes of data despite an ongoing pandemic this summer and fall. Only one tiny hiccup occurred—be it highly specific to this scientific community—a lack of hurricanes.
As the first storms of the 2021 season were forming, USGS scientists in Woods Hole, MA, and St. Petersburg, FL, were mobilizing a large team. After multiple pandemic postponements, the 2021 DUNEX season was given the go-ahead. Equipment was ordered, boats were tested, and permits were obtained. However, organizing schedules of 18 staff members over a two-month period spanning a fiscal-year transition was quite possibly the hardest part. Our goal, in the larger context of DUNEX, was to instrument the undeveloped low-lying dunes, beach, and nearshore of Pea Island with various sensors and measure the passage of a storm and its effects. Sensors were attached to poles stretching from the backside of the dune into the surf zone and out to an offshore sand bar. They measured waves, water-levels, currents, and beach and seafloor elevations–particularly during an event where the water would make it over the dunes, a process known as overwash. Indirectly, geomorphological change and wave runup at the site were to be captured from three systems: a helium filled balloon-kite (heli-kite), a remote controlled/autonomous surf vehicle (ASV), and cameras mounted high above the dunes.
The first crew arrived at Pea Island on Labor Day weekend as Hurricane Larry was sending an incredible swell towards the field sites with an ~18 second wave period. High water marks went up the dune and traces of overwash were visible at the beach access point—all very exciting—if this was just a distantly-driven swell, imagine what a hurricane coming up the coast would bring! We conducted pre- and post-Larry surveys with the camera-equipped heli-kite to see how the beach and sand reorganized and whether it accreted on the upper part of the beach and up to the dunes. This footage allows the beach to be reconstructed in 3-D with structure-from-motion technology.
A lull in the weather afterwards made for a glass-like Atlantic, perfect for launching the ASV to collect bathymetry data and for installing the offshore instruments… yet terrible for the poor souls onshore being eaten alive by black flies. By the end of the first two weeks, all the poles were installed, the stationary cameras were live, and collaborators from the University of North Carolina (UNC) Wilmington, UNC Chapel Hill, and North Carolina State University had placed their instruments. Most of the crew rotated home as Tropical Storm Odette headed north toward the Carolinas, and it was a skeleton crew that reported that two sensors cracked off their welding mounts in the pounding surf. Dismay became more widespread as storms Peter, Rose, Sam, Teresa, and Victor all formed and then either swung eastward or fizzled out early into a quiet October. Alas, the cooperation of mother nature for one perfect storm cannot be coerced, no matter the number of times you refresh the National Hurricane Center page and mutter encouraging words.
Not all hope for data was lost, however; a local storm provided two days of elevated water levels, and in the end our team managed to capture nine heli-kite surveys, four bathymetric surveys, almost two months of continuous hourly imagery, and five weeks of ADCP (acoustic doppler current profiler; which measures the speed and direction of water currents) data at two nearshore sites. The instruments at the offshore bar were recovered intact, and even if most of the instruments on the beach hoping for overwash did not get their ‘feet’ wet, the proof-of-concept design was a success.
Perhaps high on the list of accomplishments was, after a year of virtual meetings, finally being able to meet and work together in person. Many teams benefitted from exchanging ideas, expertise, and personnel, but we also look forward to the exchange of data collected by the many groups at the FRF.
This DUNEX dataset will be a rare gem in the coastal field because it includes almost every possible in situ measurement having been made at the same time in multiple places. By capturing data from great heights to great depths, we are closer to capturing a more complete understanding of how coastal land and seascapes change under changing conditions.
Hurricane or no hurricane, these data will help us make progress towards a safer, smarter coast.