Barrier vulnerability following outwash: A balance of overwash and dune gap recovery

Alexis Gabrielle Van Blunk, Katherine Anarde, Brad Murray, Laura J Moore , Chris Sherwood 

Existing barrier evolution models only simulate storm impacts from landward-driven flows (overwash), neglecting the impacts of seaward-directed flows (outwash). Here, we modify an existing model to incorporate outwash processes. We find that outwash enhances barrier vulnerability (the tendency to drown) over decadal timescales by scarring the island interior, creating lower, narrower landforms. If outwashed sand stays nearshore, a wider beach and steeper shoreface facilitate dune recovery and closure of gaps, which are otherwise maintained by overwash. Importantly, faster (natural) dune growth means the barrier is less vulnerable to future outwash events, but potentially more vulnerable to back-barrier drowning from sea-level rise because dunes also limit building of interior elevation by overwash. Any changes in storm climatology could alter the balance between dune recovery and overwash making the future vulnerability of modern outwashed barriers difficult to assess.