Wave and Longshore Current Modeling on the North Carolina Continental Shelf

The object of this work was to use a wave model to determine the importance of wave-driven longshore sediment transport to erosion and accretion of North Carolina's Outer Banks between Oregon Inlet and Cape Hatteras. A wave history was created from 10 years of hourly measurements at NOAA buoy 44014 (36.58^{o }N, 74.84^o W, 47.5 m water depth). Twenty-three reoccurring conditions were identified representing storms originating over North America, storms originating in the tropics, and low-energy periods. These conditions were used as input to the Simulating Waves Nearshore (SWAN) model, developed at Delft University of Technology, the Netherlands. Bathymetry collected during the SHOaling waves Experiment (SHOWEX) combined with National Ocean Survey (NOS) bathymetry defined the grid. Output from the SWAN model was used as input to a longshore current equation driven by both oblique wave approach and variation in wave height. A time averaged longshore distribution of velocity was produced from the 23 representative events. This distribution was compared with average yearly erosion and accretion rates measured by the North Carolina Department of Environmental Heath and Natural Resources, Division of Coastal Management. Areas of greatest long-term erosion corresponded to areas with increasing gradients of longshore velocity regardless of specific wave input. Output from SWAN was also input to the Coastal Engineers Research Center (CERC) equation for longshore sediment transport. This equation includes only transport due to the oblique approach of waves. The time-averaged distribution of immersed weight transport was compared with the average annual shoreline change, but the patterns of coastal change were not well explained, perhaps because the formulation did not include forcing by longshore gradients in wave height.