THE INFLUENCE OF STORM FREQUENCY ON BARRIER ISLAND BISTABILITY: ASSESSING ALONGSHORE DISTRIBUTIONS OF FOREDUNE HEIGHT ALONG THE U.S. ATLANTIC COAST

The impact of storms on barrier islands is largely a function of the height of the seaward-most dune, or foredune. Recent work (Durán and Moore, 2015) suggests that dunes and barrier islands can be bistable, tending to exist in one of two alternate stable states for a given set of conditions—either as low, frequently overwashed features or high features, which are resistant to storms. In the bistable regime, feedbacks cause foredunes that are neither high nor low to quickly evolve toward one of the two end member stable states. A combination of internal and external factors (i.e., relative sea-level rise rate, vegetation growth rate etc.), appear to determine whether dunes are in the high or low state. The bimodal distribution of dune height for the Virginia Barrier Islands, identified by Durán and Moore (2015), provides evidence for island bistability.

Here, we test a hypothesis that dune height distributions will be bimodal in areas having a higher storm frequency (i.e., Core Banks, North Carolina, Virginia Barrier Islands, Virginia) compared to areas having a lower storm frequency (i.e., Cumberland Island, Georgia; Plum Island, Massachusetts). In these settings we expect height distributions to be strongly influenced by storm frequency, as well as by other factors such as relative sea-level rise rate and the distribution and intensity of dune-forming winds. To test this hypothesis we measured foredune height from LiDAR data for areas noted above from cross-shore cross sections spaced every 2 m alongshore. Initial results suggest that islands in areas where storm frequency is higher (i.e., Core Banks, NC and Virginia Barrier Islands, VA) the distribution of island height is bimodal whereas in areas where storm frequency is lower (i.e., Cumberland Island, GA; Plum Island, MA) the distribution of island height tends to follow a normal distribution, though storm frequency alone is not a predictor of relative differences in the distribution of dune height.