Overwash deposition increases backbarrier marsh resiliency to sea level rise: Insights from a coupled barrier island-marsh model

I develop and apply a coupled barrier island-marsh model (GEOMBEST+) to assess the impact of 1) overwash deposition on backbarrier marsh morphology and 2) marsh morphology on rates of island migration. Simulations indicate that overwash deposition provides backbarrier marshes with an important source of sediment that maintains existing narrow marshes in a transient state (approximately 500m wide) within a range of conditions under which they would otherwise disappear. This existence of an alternate state in marsh width is supported by observations of backbarrier marshes along the eastern shore of Virginia, a significant proportion of which are approximately 500m wide. Additional simulations demonstrate that marshes reduce accommodation space in the backbarrier bay, which, in turn, decreases island migration rate. As sea level rises, and the potential for intense hurricanes resulting in overwash increases, it is likely that these couplings will become increasingly important in the future.