Beach response, shoreline water levels, and surf-zone hydrodynamics measured during Hurricane Dorian in Duck, NC

Hurricane Dorian made landfall on Cape Hatteras, NC at 0935 EDT on September 6^th, 2019 as a category 1 hurricane, 70 miles south of the U.S. Army Engineer Research and Development Center’s Field Research Facility (FRF) in Duck, NC. Continuous observations from long-term gauges and rapidly deployed supplemental sensors quantified surf-zone hydrodynamics, morphology change, and meteorological conditions at the FRF. Sustained winds at the end of the 600-m long pier exceeded category 1 strength for 1.75 hours, peaking at 36.5 m/s from the north at 1050 EDT with a maximum gust of 43.8 m/s. Offshore significant wave heights measured in 26-m depth peaked at 6.9 m at 1133 EDT, making Dorian the 4^th largest wave event at the FRF since 1985. Wave heights peaked 3 hours before high tide (1414 EDT), 4 hours before the peak surge of ~ 1 m (1542 EDT), and exceeded 4 m for 8 hours (0830-1630 EDT). Shoreline water levels were measured with terrestrial lidar, stereo imagery, and in-situ pressure sensors on four cross-shore transects on the 1-km-long FRF property. At the northern transect, total water level (wave runup, tide, and surge) peaked near 4 m NAVD88 between 1200-1330 EDT. Morphological response was measured with vessel-based GPS and sonar 2 days before and 3 days after the storm, and with fixed terrestrial lidars continuously during the storm. Despite the large offshore waves, impacts to the dunes at the FRF were minimal. Beach response varied spatially, with erosion of 1 m vertically on the summer berm and accretion of 0.1 m near the dune toe. Initial recovery of the lower beach (0.5 m accretion) at the northern transect was rapid, occurring within 48 hours of the storm peak. Regional mobile terrestrial lidar surveys were performed 2 days before and 4 days after the storm along 40-km surrounding the FRF. Further analysis will explore the scales of spatial variability in storm-driven hydrodynamics and beach response during Dorian. Funded by USACE, NSF, USCRP, and ASD(R&E).