ANALYZING HISTORICAL CHANGES TO TIDAL INLET AND TIDAL DELTA GEOMETRIES ALONG THE VIRGINIA BARRIER ISLANDS: A TEST OF THE RUNAWAY BARRIER ISLAND TRANSGRESSION MODEL

This research sought to examine temporal changes in the geometric/areal configurations of thirteen tidal inlets and associated tidal deltas within the Virginia barrier island chain from Little Inlet in the south to Chincoteague Inlet in the north. Historical inlet examination allows for a test of the Runaway Barrier Island Transgression model. In short, the model stipulates that ebb-tidal deltas would sequester sand during a regime of accelerated sea-level rise and therefore, grow in extent and volume at the expense of the barrier islands. Previous research has yielded inconclusive evidence to support this hypothesis. Our research, in part, involved digitizing the bathymetric contours or contouring soundings available on historical maps and coastal charts spanning the late 1800s to the modern day. This work allowed us to examine and quantify the temporal and spatial changes to the main ebb channel orientations and areal extent (surface area) of the tidal deltas along this reach. Preliminary results show a seaward extension (growth) of the ebb-tidal deltas in the central part of the barrier island system during the past 60 years (in the “rotational instability” reach), but a landward migration (shrinking) to the south (non-parallel beach retreat reach). Additionally, while previous research also suggested that antecedent geology “locked in” the main ebb channel positions, our research indicates that spatial variation existed in the channel positions through time. In the future, we plan to analyze older maps and relate main ebb-tidal channel configuration changes to island shape changes.