Barrier islands are dynamic and ephemeral, facing uncertain changes from climate change and anthropogenic redistribution of sediment. Here, we couple a cross-shore, morphodynamic barrier evolution model (LTA model) with an alongshore shoreline evolution model to better understand the internal dynamics of barrier evolution. Under constant sea level rise and waves, we numerically evolve a barrier that is initially narrow in the middle. Rapid overwash over the narrow middle portion of the barrier sets up gradients in alongshore sediment transport, which attempt to straighten the bending shoreline, translating the overwashing region laterally. Comparison of cross shore (overwash) and alongshore transport provides a novel tool to evaluate barrier stability, the Washover Ratio. Using this ratio, we find that decreases in overwash flux within this narrow middle section, possibly representing the effects of development, lead to diminished barrier response to sea-level rise across the entire barrier, and therefore a more vulnerable barrier overall.
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