Physical monitoring of an erosional hotspot on a nourished beach: a case study of Ortley Beach, New Jersey

Beaches worldwide play an essential role in shore protection under storm conditions. How to identify the threshold beach width for effective shore protection remains largely unresolved due to a scarcity of measured beach profiles with sufficient temporal and spatial resolutions. In this study, weekly to monthly surveys spaced 100 m along the shoreline have been conducted at Ortley Beach, New Jersey since Fall 2023. The survey covered beach changes induced by Hurricane Lee and Tropical Storm Ophelia in Fall 2023. About half of the lost beach volume recovered within 1–2 weeks after the passage of these storms. With the onset of winter, cold fronts caused significant longshore variations in beach/dune erosion. At the erosional hotspots, severe dune line retreat occurred where the dry beach was narrower. Results indicate a critical threshold of dry beach width of about 35 m, below which dune-line retreat becomes more likely, increasing risks to landward infrastructure. As the weather shifted to summer of 2024, the beach gradually recovered, but net shoreline erosion and beach volume loss persisted, which created a more vulnerable condition for the following winter until the renourishment in Spring 2025. A simple empirical equation for threshold beach width was developed by integrating grain size and offshore wave height, supplemented by long-term beach-profile measurements from North Sand Key along the west-central Florida coast. Accurate estimation of this threshold provides a useful indicator for emergency beach management during storm conditions.