Coupled Interaction of Shrubs, Dunes, and Barrier Overwash

Overwash is an essential mechanism for the subaerial maintenance of low-lying barrier islands and an important source of sediment for fringing back-barrier marshes, yet how overwash processes operate within the interior of a barrier island - the area between the frontal dune and the back-barrier marsh or lagoon - remains a critical gap in our understanding of barrier systems. Vegetation cover type may play the largest role in impacting interior overwash processes by impeding overwash flow, which could limit the ability of an island and marsh to aggrade and transgress in order to survive RSLR. This work highlights feedbacks between shrubs and overwash that can potentially impact long-term barrier island evolution and survival. Analysis of lidar-derived elevation data collected from the barrier islands of the Virginia Coast Reserve (VCR), USA, indicates that the presence of shrubs is associated with high fronting dunes, and suggests that a threshold dune height is required for shrub growth. Using this analysis along with parameters derived from other ecological and geophysical VCR datasets, we develop a model of dune growth/destruction and shrub propagation to address how storm-dune interactions impact shrub colonization. In addition, we introduce ongoing field work designed to measure the impacts of shrubs on overwash flow and deposition during storm overwash events.