FUTURE OF BARRIER ISLANDS: A FUNCTION OF BACKBARRIER SUSTAINABILY

The IPCC (2013) forecasted regime of accelerating sea-level rise indicates that many, if not all, platform marshes and tidal flats will deteriorate/drowned as backbarrier basins are transformed to intertidal and subtidal areas. As this process proceeds, the extent of open water and the overall depth of the backbarrier will increase, causing greater tidal exchange. The resulting increase in tidal prism will enlarge the size of tidal inlets and will sequester an increasingly larger volume of sand in ebb-tidal delta shoals. At the same time, hypsometric changes in the backbarrier will intensify the flood-dominance of existing inlet channels and will transform ebb-dominated channels to flood-dominated channels. This will result sand movement into the backbarrier building and enlarging flood-tidal deltas filling the newly created accommodation space. We hypothesize that the sand contributing to the growth of the ebb and flood tidal delta shoals will be gained at the expense of barrier-island reservoirs. This will result in diminished sand supplies along the coast eventually leading to a fragmentation of barrier island chains and formation of a transgressive coastal system. This model best applies to mixed-energy barrier coasts, which are characterized by short stubby barrier islands, numerous tidal inlets, well-developed ebb-tidal deltas, and backbarriers consisting of supratidal salt marshes, tidal flats, and/or mangroves incised by tidal creeks. The relevancy of this model and the rates at which these interconnected processes will take place are explored by looking at case studies throughout the world.