Application of Ground Penetrating Radar to Study the Internal Architecture of Coastal Dunes, North Padre Island, Texas

The Texas Coast is eroding at a fast rate, and maintenance is necessary to protect the public beaches so that they are accessible under the Open Beaches Act. Therefore, sand dunes are constructed in these areas by building fences, planting vegetation, or importing sand. This study examines the internal structure and grain size variations of a maintained dune and a natural dune on Padre Island, Texas. The maintained dune is located on Padre Balli Park and is revegetated twice a year on the seaward side, and the natural dune is within the Padre Island National Seashore limits. Data were collected using a ground penetrating radar with 200- and 400-MHz antennae, and sediment samples were collected and measured with a laser diffractometer to analyze the grain size of the dunes. Ground penetrating radar was used to collect two shore-perpendicular and three shore-parallel surveys on the natural dune, and two perpendicular and two parallel to shore surveys on the maintained dune using a 200- and 400-MHz antennae. The 200-MHz antenna datasets have a vertical resolution of 15 cm on the natural dune and 16.6 cm on the maintained dune. The 400-MHz antenna datasets have a vertical resolution of 10.7 cm on both the natural and maintained dunes. Sediment samples were collected every 10 cm at three locations on each dune with depths up to two meters. The results show that the natural dune contains continuous reflectors, a dune core, rearslope accretion, foreslope accretion, and a water table within. The natural dune contains well-developed internal structures and is homogenous. The data for the maintained dune contains discontinuous reflectors in the pre- processed data, a water table, dune core, foreslope accretion, and biotopographic accumulation. The discontinuous reflectors suggest that the dunes contain more debris, and form similar internal structures to a natural dune. The natural and maintained dunes contain about 78% fine-grained sand, they are well sorted, and are platykurtic. This suggests that the maintained dune can form subsurface structures comparable to a natural dune, therefore providing similar protection from erosional events.