Subsurface Geologic Controls on the Dune Morphology in Barrier Islands

Abstract:

Coastal communities are extremely vulnerable to natural forces such as flooding and hurricanes. Barrier island systems provide a first line of defense for these communities by absorbing much of the force of storms and reducing wave energy. The dune morphology of barrier islands controls storm impacts, determines which areas across the island are most likely to experience overwash and/or blowouts, and affects island recovery from tropical storms, hurricanes, and flooding. However, the dune morphology depends on the antecedent geological and stratigraphic features (AGSF) such as paleochannels. The location, thickness, and spatial extent of, and depth to, these AGSF control patterns of sediment erosion, transport, and deposition along the barrier island. In this study we have collected 24 km-long conductivity profile, using EM-31 system, along Padre Island National Seashore shoreline, to investigate (1) how do the AGSF vary spatially, along-shore, cross-shore, and with depth, within Padre island, and (2) how do variability in the AGSF control dune morphology in Padre Island. A high-resolution (spatial resolution: 1 m) digital elevation model (DEM) was correlated with the measured EM-31 conductivity values. Our preliminary results indicate that higher conductivity readings (300 – 450.75 mS/m) were (1) associated with smaller beach width (2.3 - 2.9 km), (2) correlated with the center of a paleochannel (paleochannel width: ~15 km), (3) correlated with lower dune elevations (1 – 4 km). This research enhances the prediction of barrier island responses to natural forces and will eventually facilitate extreme-event mitigation and remediation; this, in turn, will improve the resiliency of coastal communities.