A cross-shore model of barrier island migration over a compressible substrate

Barrier islands that overlie a compressible substrate, such as islands in deltaic environments or those that overlay mud or peat deposits, load and consolidate the underlying subsurface. Through time, the elevation and aerial extent of these islands are reduced, making them more susceptible to future inundation and overwash. Sand washed over the island and onto back-barrier marsh or into the bay or estuary begins the consolidation process on a previously non-loaded substrate, with time-dependent consolidation as a function of the magnitude of the load, duration of load, and characteristics of the substrate. The result is an increase in the overwash, migration, breaching, and segmentation of these islands. esearch developed a two-dimensional (cross-shore) numerical model for evolution of a sandy barrier island that spans durations of years to decades as a function of erosion, runup, overwash, migration, and time-dependent consolidation of the underlying substrate as a function of loading by the island. The model was tested with field data and then applied to evaluate the effects of a compressible substrate on long-term barrier island evolution. Results illustrate that barrier islands overlying a compressible substrate are more likely to have reduced dune elevation due to consolidation, incur overall volumetric adjustment of the profile to fill in compressed regions outside the immediate footprint of the island, and experience increased overwash and migration when the dune reaches a critical elevation with respect to the prevalent storm conditions.