Application of GPR, EMI, and Lidar to Assess the Role of Antecedent Geology in Barrier Island Evolution

Abstract:

Barrier island longevity is threatened by the observed and modeled accelerating rates of sea-level rise. It has been suggested that subsurface geologic structure is also an important factor controlling barrier island morphology and long-term island evolution, yet the precise role of antecedent geology on the response and recovery of barrier islands to hurricanes and sea-level rise remains unclear. Thus, this study aims to provide more detailed insight into the role of the antecedent geology on barrier island evolution at two sites along the Texas, USA coast: Follets Island and a portion of North Padre Island. Alongshore and across-island ground-penetrating radar (GPR) and electromagnetic inductance (EMI) surveys are used in this study to infer subsurface geologic structure. The accuracy of the interpreted geophysical survey data was assessed using selective vibracoring. Information about island morphology is derived from airborne and terrestrial LiDAR-derived digital elevation models (DEMs). Preliminary results suggest that dune height is generally lower and washover frequency higher in areas where the antecedent geologic surface is deeper. Another important factor influencing dune breaching and washover locations is offshore bathymetry. The barrier island is generally narrower in areas where an offshore swale is present. The antecedent geologic structure is an important factor influencing barrier island morphology. Integrating EMI, GPR, and seismic subsurface geologic structure information and surficial morphology information helps improve our understanding of factors affecting barrier island evolution and the role that antecedent geology plays in island morphology.