Mapping the Fresh-Saltwater Transition Zone Across the Beach Environment Using Ground-Penetrating Radar (GPR)

As sea level rises, saltwater migration can threaten coastal ecosystems and beach-dune environments, which negatively impacts coastal flora. This study uses ground penetrating radar (GPR) to evaluate the spatiotemporal variability of saltwater migration in the near shore at high lateral resolution (i.e. cm) by using daily micro tidal cycles as analogs to infer saltwater migration. Time-lapse GPR profiles were collected at low and high tide capturing phase lags of the tidal flux through different substrates. GPR measurements were collected at two sites in Miami with contrasting lithologies: a) Crandon Park, composed of unconsolidated sand; and b) the Barnacle Historic State Park, composed of the Miami Limestone Formation. Laboratory-scale GPR measurements were collected over samples mimicking field conditions. The results may be helpful to identify regions vulnerable to saltwater migration in the near shore based on lithological variability, and to mitigate negative impacts for flora in beach-dune habitats during sea level rise.