U.S. Geological Survey simulations of hydrodynamics and morphodynamics at Matanzas, FL during Hurricane Matthew (2016) and at Fire Island, NY during Hurricane Sandy (2012)

The Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST Warner and others, 2019; Warner and others, 2010) model was used to simulate ocean circulation, waves, and sediment transport to study barrier island breaches that occurred during Hurricane Matthew (2016) near Matazas FL, and Hurricane Sandy (2012) at Fire Island, NY. Hurricane Sandy was a Saffir-Simpson Category 2 hurricane that transited the Western Atlantic Ocean relatively far offshore of the US East Coast for five days until turning west to make landfall in New Jersey on 29 October 2012, causing extreme coastal erosion and flooding with destruction to residences and infrastructure along the East coast, particularly in the New York Bight. Maximum winds were ~50 m/s, minimum sea level pressure recorded was 940 mbar, maximum observed wave heights were ~10 m and storm surge was 3.5 m in NY City. During Sandy, barrier island breaching occurred at the site of a historical breach on an uninhabited section of Fire Island, NY. Research efforts have characterized the erosion, breaching, and recovery of Fire Island and post-storm LiDAR surveys provided topographic data for model initialization and comparison. Hurricane Matthew was a Saffir-Simpson Category 5 hurricane that impacted the Caribbean Islands and US East Coast in early October 2016. The hurricane paralleled the U.S. South Atlantic coastline within 50 km for two days until landfall in South Carolina on 8 October 2016. Extensive flooding and coastal erosion due to extreme storm surge, waves, and rainfall were experienced. Maximum wind speeds were ~75 m/s, maximum observed wave heights were ~8 m , and maximum storm surge was reported to be ~3 m in parts of Florida. Breaching of a small barrier separating the ocean from the Intracoastal Waterway south of Matanzas, FL occurred on 7 October 2016. The barrier is 1.7 km long and less than 0.15 km wide, characterized by a sandy beach with houses and a paved road running along parts of the dune crest. The breach location is 2 km south of Matanzas Inlet. Pre-storm and post-storm topo-bathymetric LiDAR were available to capture hurricane-driven morphological changes. The model employed a recently implemented infragravity wave model to represent the important effects of infragravity wave motions on nearshore water levels and sediment transport. The model simulated breaching. The breach simulated at Fire Island was 250 m west of the observed breach, whereas the breach simulated at Matanzas was within 100 m of the observed breach. Implementation of the vegetation module of COAWST to allow three-dimensional drag over dune vegetation at Fire Island improved model skill by decreasing flows across the back-barrier. Analysis of breach processes at Matanzas indicated that both far-field and local hydrodynamics influenced breach creation and evolution, including remotely generated waves and surge, but also surge propagation through back-barrier waterways. This work underscores the importance of resolving the complexity of nearshore and back-barrier systems when predicting barrier island change during extreme events. Further details are provided in Hegermiller et al., 2022. This is a summary page for the collection of 4 sub pages. -The first sub page is for the simualtion of Hurricane Matthew at Matanzas, FL. -The second sub page is for the simulation of Hurricane Sandy at Fire Island, NY using a constant bottom roughness over the barrier island. -The third sub page is for the simulation of Hurricane Sandy at Fire Island, NY using a variable bottom roughness over the barrier island. -The fourth sub page is for the simulation of Hurricane Sandy at Fire Island, NY using a variable bottom roughness and vegetation drag over the barrier island. Reference cited: Hegermiller, C.A., Warner, J.C., Olabarrieta, M., Sherwood, C.R., and Kalra, T.S., 2002, Barrier island breach dynamics during Hurricanes Sandy and Matthew: Journal of Geophysical Research - Earth Surface, https://doi.org/10.1029/2021JF006307. Warner, J.C., Armstrong, Brandy, He, Ruoying, and Zambon, J.B., 2010, Development of a coupled ocean-atmosphere-wave-sediment transport (COAWST) modeling system: Ocean Modelling, v. 35, issue 3, p. 230-244. Warner, J.C., Ganju, N.K., Sherwood, C.R., Tarandeep, K., Aretxabaleta, A., He, R., Zambon, J., and Kumar, N., 2019, Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System: U.S. Geological Survey Software Release, 23 April 2019, https://doi.org/10.5066/P9NQUAOW. (URL for the specific version of the code used for these model results: https://code.usgs.gov/coawstmodel/COAWST/-/tags/COAWST_v3.7)