OBSERVATIONS OF STORM-INDUCED SCARPING AND SLUMPING DYNAMICS IN THE OUTER BANKS, NC

Hurricanes and other major storm events can produce storm surges and energetic waves which may drive vertical scarping and retreat of the dune face. These scarps initially exceed the angle of repose for sand and are therefore are not stable features. Despite exceedance of the angle of repose criteria, scarped faces can persist for periods of days to years after the initial triggering storm event due to the combined effects of moisture, compaction, grain size, roots, and mycorrhizal fungi. However, existing numerical models which aim to predict the temporal evolution of coastal beach profiles have simplistic representations of scarp dynamics; these tools either assume that scarps remain vertical indefinitely (e.g., Palmsten and Holman, 2012) or that they instantaneously avalanche to the angle of repose (e.g., XBeach). Neither of these approaches represents realistic scarping dynamics in vegetated coastal dune systems – contributing to a lack of reliable morphologic prediction of beach-dune systems on engineering time scales (e.g., days to decades). Unfortunately, there remains limited field data to improve parameterization of scarp decay processes and for de-coupling the relative roles of the environmental, geological, and ecological processes on maintaining scarps.

To elucidate the spatio-temporal complexity of scarp decay on dune faces, here we utilize repeat, high-resolution remote sensing measurements from the Coastal Lidar and Radar Imaging System (CLARIS) collected in Duck, NC, USA. Nearly continuous scarps were developed during Hurricanes Michael (2018) and Dorian (2019) along a stretch of recently built dunes along a beach nourishment project in Duck. Over the time span from 2018 to present, 14 CLARIS lidar scans with point densities of ~100 pts/m² and covering a 1 km alongshore span (a subset of the available data) are used to understand the collisional events which initiated scarp development and to track the temporal evolution of the vertical scarp face. Here we utilize these new high-resolution datasets to assess the time scale and mechanisms of dune scarp decay and to explore limitations of current dune scarp parameterizations used within numerical modeling tools.