Geophysical Survey for Dune Stability Assessment Assateague State Park, Maryland

Abstract

Assateague State Park spans two miles of shoreline on Assateague barrier island on Maryland’s Eastern Shore. The park is managed by the Maryland Department of Natural Resources and is located between the north and south ends of Assateague Island National Seashore, which is managed by the National Park Service. The park is bordered by the Atlantic Ocean on the east and the Sinepuxent Bay on the west, and is home to diverse wildlife, including numerous rare, threatened, and endangered species. The park is a popular tourist destination; in 2023, 2.3 million people visited Assateague Island National Seashore, producing a revenue of around $2 million for the State. As the park contributes vitally to Maryland’s economy and ecological diversity, maintaining its health and infrastructure is a serious concern. The approximately three-kilometer-long dune parallel to the eastern seashore characterizes the park’s landscape. This dune acts as a defensive barrier against flooding and immense wave energy, absorbing the primary impact of severe storms and protecting more inland areas. However, it faces erosional challenges due to natural processes, exacerbated by climate change. Severe weather events such as hurricanes and winter storms induce substantial outwash, damaging the dune and threatening the integrity of the surrounding infrastructure. For example, significant sand loss from erosion is redeposited elsewhere, encroaching on campsites and permanent buildings. Even though the dune is actively managed by the State Park, the natural cycle of barrier islands is rapid and unpreventable. The State aims to adapt to the changing Assateague environment through infrastructure improvements and dune management strategies. Past efforts have included relocating roads to create a buffer zone, moving them 50 to 100 feet back from the dune to provide more space for its migration westward. In addition, sand grass has been planted and fences installed, with different levels of success in stabilizing the dune. Given the challenges posed by erosion and climate change, a more comprehensive understanding of the dune is needed. To better understand seasonal changes to the dune and plan for mitigation strategies, a geophysical study of the dune’s current state is needed. This study aims to answer the following questions: How does the subsurface structure of the dune affect its stability or vulnerability? How have the implemented management strategies (installation of fences along the dune axis) affected the structure of the dune? To address those questions, the objectives of this project are to characterize the dune’s subsurface structure and geological variability by carrying out Ground Penetrating Radar (GPR) and Magnetometry scans parallel and perpendicular to the dune axis. Knowledge of the subsurface composition and variability can help assess the health of the dune, i.e. its ability to resist the effects of erosion from wind, rain, and wave damage. In addition, the scans may provide useful information about the water table and the sand depth, which affect vegetation growth. Plants such as American beach grass are effective at reducing erosion, but some areas of the beach may not be able to sustain plant life due to subsurface conditions. Finally, geophysical imaging may reveal information about the history of erosion and dune migration, which may be helpful for understanding the dune’s long-term behavior and how the management strategies have influenced the current state of the dune.