A simple model for the spatially-variable coastal response to hurricanes Hilary F. Stockdon a, ⁎ , Asbury H. Sallenger Jr. a , Rob A. Holman b , Peter A. Howd a a U. S. Geological Survey, Center for Coastal and Watershed Studies, 600 4th Street S., St. Petersburg, Florida, 33713, United States b College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon, United States Received 18 May 2006; received in revised form 16 November 2006; accepted 28 November 2006 Abstract The vulnerability of a beach to extreme coastal change during a hurricane can be estimated by comparing the relative elevations of storm-induced water levels to those of the dune or berm. A simple model that defines the coastal response based on these elevations was used to hindcast the potential impact regime along a 50-km stretch of the North Carolina coast to the landfalls of Hurricane Bonnie on August 27, 1998, and Hurricane Floyd on September 16, 1999. Maximum total water levels at the shoreline were calculated as the sum of modeled storm surge, astronomical tide, and wave runup, estimated from offshore wave conditions and the local beach slope using an empirical parameterization. Storm surge and wave runup each accounted for ∼ 48% of the signal (the remaining 4% is attributed to astronomical tides), indicating that wave-driven process are a significant contributor to hurricane-induced water levels. Expected water levels and lidar-derived measures of pre-storm dune and berm elevation were used to predict the spatially-varying storm-impact regime: swash, collision, or overwash. Predictions were compared to the observed response quantified using a lidar topography survey collected following hurricane landfall. The storm-averaged mean accuracy of the model in predicting the observed impact regime was 55.4%, a significant improvement over the 33.3% accuracy associated with random chance. Model sensitivity varied between regimes and was highest within the overwash regime where the accuracies were 84.2% and 89.7% for Hurricanes Bonnie and Floyd, respectively. The model not only allows for prediction of the general coastal response to storms, but also provides a framework for examining the longshore-variable magnitudes of observed coastal change. For Hurricane Bonnie, shoreline and beach volume changes within locations that experienced overwash or dune erosion were two times greater than locations where wave runup was confined to the foreshore (swash regime). During Hurricane Floyd, this pattern became more pronounced as magnitudes of change were four times greater within the overwash regime than in the swash regime. Comparisons of pre-storm topography to a calm weather survey collected one year after Hurricane Floyd's landfall show long-term beach volume loss at overwash locations. Here, the volume of sand eroded from the beach was balanced by the volume of overwash deposits, indicating that the majority of the sand removed from the beach was transported landward across the island rather than being transported offshore. In overwash locations, sand was removed from the nearshore system and unavailable for later beach recovery, resulting in a more permanent response than observed within the other regimes. These results support the predictive capabilities of the storm scaling model and illustrate that the impact regimes provide a framework for explaining the longshore-variable coastal response to hurricanes. © 2007 Elsevier B.V. All rights reserved. Keywords: coastal change; shoreline change; hurricanes; runup; storm surge; lidar; dune toe; dune crest; Hurricane Bonnie; Hurricane Floyd; Onslow Bay; Topsail Island; North Carolina Marine Geology 238 (2007) 1 – 20 www.elsevier.com/locate/margeo ⁎ Corresponding author. Tel.: +1 727 803 8747; fax: +1 727 803 2032. E-mail address: hstockdon@usgs.gov (H.F. Stockdon). 0025-3227/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2006.11.004