BARRIER ISLAND GEOMORPHOLOGICAL EVOLUTION: INTERACTION AMONG SEDIMENT BUDGET AND EXTREME EVENTS

Eustatic sea-level rise has been occurring since the LGM. Barrier islands have been responding to this threat by moving “landward and upward through space and time”. Two response mechanisms include washover and the creation of inlets. Sediment transported inland as washover fans result in barrier aggradation, which increases its resilience to future sea-level rise. Breaches in narrow sections of a barrier island allow for new inlets to form, distributing sediment inland in the form of a flood-tidal delta. Sediment budget is a key aspect of barrier island morphological evolution.

The conceptual approach to describing, depicting, and mapping the geomorphological characteristics of coastal systems is based on the components of morphometrics, causative processes, and temporal sequence of development of the surface. This tripartite organization is the essence of modern geomorphological maps that combine the surface expression of the sedimentary formations with the processes. The legend categories incorporate the spatial and temporal evolution of a natural coastal system influenced by a variety of anthropogenic modifications. A geographic information system (GIS) was developed for the construction of a geomorphological map to be displayed at a 1:12000 scale. The GIS includes orthophotographs, LiDAR datasets, and recent cultural history.

The spatial assemblage of mapped geomorphological features reflects sediment transportation and stabilization through space (beach, dune, backdune) and time (active, abandoned, ancestral). A positive sediment budget facilitates foredune growth that may create a new active dune ridge, abandoning the preexisting one; whereas a negative budget increases vulnerability to foredune dissection by washover due to storm events. Sediment budget fluctuations drive expansion and contraction of the surface features. The continual alteration of surface features by ambient environmental conditions and significant storm events, such as Hurricane Sandy, both underscores the importance of the geomorphological map and provides a challenge in the maintenance of a contemporary dataset.