BARRIER ISLAND STABILITY AND CHARACTERISTIC SEGMENTATION LENGTH SCALES EXPLORED THROUGH THE COMPETITION BETWEEN OVERWASH AND ALONGSHORE SEDIMENT TRANSPORT

Segmented barriers found in regions with small tidal ranges typically have curved shorelines and show little indication of tidal flow between neighboring barrier segments. Here, we quantify the controls on and scales of barrier segmentation in the relative absence of tides. On a homogeneous barrier, the onset of overwash can transition a stable barrier into a rapidly overwashing migratory stage. However, the barrier will bend if runaway overwash is localized (due to alongshore heterogeneity such as variable barrier widths or heights), causing deposition by alongshore sediment transport into the overwashing region. The competition between deposition by alongshore sediment transport into the overwashing region and the ability for runaway overwash to remove the sediment may dictate the length scales at which narrow barriers in low tidal ranges segment or heal after a disturbance. Here, we develop a theoretical framework to estimate the alongshore length scales at which overwashing regions or segmentation due to runaway overwash may occur by applying a Peclet number analysis which compares overwash (advective) and alongshore sediment transport (diffusive) processes along barrier island chains. The predicted length scale of segmentation is tested using a numerical model of coupled alongshore and cross-shore barrier evolution. Future work will compare both theoretical and modeled barrier predictions to segmented barriers found in regions with low tidal ranges, such as the Gulf of Mexico, Alaskan, and Canadian coasts.