Observations of Tides, Waves, and Erosion on a Low-lying Barrier Island During Hurricane Nate

Measurements of storm tides and waves during barrier island overwashing events are rare. Such measurements have the potential to dramatically improve our understanding of wave propagation and decay, surge-induced flood and ebb flows, and the morphological response of low-lying barrier islands to storm impacts. Prior to Hurricane Nate’s landfall on 7 October 2017, we established seven observational transects on the West End of Dauphin Island, Alabama, each spanning the entire island width from the Gulf of Mexico to Mississippi Sound. We measured pre- and post-storm elevations, using an RTK GPS, along each transect. Fifteen pressure gages measured storm water levels and waves throughout the storm event within a smaller subarea of the seven-transect study area. Distributed along two transects, each having unique elevation and vegetation characteristics, nine high frequency wave gages and four water level gages were recovered with complete time-series. We were unable to recover one wave gage and one water level gage, and one wave gage failed to record data. All observational transects experienced net erosion from the subaerial portions of the profiles, and all exhibited some degree of inundation and overwashing (see included figure). Having surveyed all gages into a common vertical datum, comparisons of water levels along each transect provide an opportunity to infer patterns of flood and return flows over the island. Preliminary analysis of one-dimensional (wave frequency) spectra show a concentration of energy in the infragravity band and a notable change in behavior at the onset of ebb-directed return flow. This poster presentation will focus on the time-series measurements of storm water levels and waves across the island during the overwashing event.