Subsurface controls on the responses of barrier islands to natural interventions

Abstract

More than one third of the world's population lives in coastal areas. Coastal communities, however, are extremely vulnerable to natural forces such as flooding, hurricanes, tsunamis, and sea level rise. Barrier systems provide a first line of defense for coastal communities by absorbing much of the force of hurricanes and storms and reducing wave energy. The alongshore variation in dune morphology of a barrier island generally 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 to a large extent on the antecedent geological and stratigraphic features. In this study, we used the Ground Penetrating Radar (GPR) and Electrical Resistivity tomography (ERT) techniques to map subsurface geology and stratigraphy and investigate how these subsurface features control the dune morphology in barrier islands. The Padre Island in the Texas gulf coast region was selected as a case study. Long (length: 6 km) GPR profiles are collected, parallel and perpendicular to the shoreline of Padre Island, using 200 MHz and 350 MHz antennae. In addition, one ERT profile is collected perpendicular to the shoreline along the same GPR transect. Preliminary results indicate that GPR profiles were able to image the concave upward scour-and-fill features related to tidal and washover channels. The thickness of the scour-and-fill features reaches up to 8 m in some locations. ERT profile successfully shows the freshwater/saltwater interface at depth of 7 m near the Laguna Madre side of the island. Results from this study will integrate geophysical, geological, and hydrogeological information to develop an enhanced coastal system models that explain the relationships between subsurface geology and morphological features of barrier islands and demonstrate how barrier islands respond to natural interventions.