Assessing the Spatiotemporal Variability in Geotechnical Sediment Properties of Beach Cusps on a Sandy Beach

Abstract This study examined the spatiotemporal variability in geotechnical properties of beach cusp sediments on a sandy beach and tested if such variability can be used for cusp monitoring from satellite imagery. Specifically, sediment properties (including moisture content ( w ), relative density ( D r ), sediment strength (QSBC) and friction angle ( ϕ )) were compared from cusp horns and bays with those from areas lacking visible cusp features. Results indicate marked differences between cusp horns and bays where bays consistently exhibited higher w (9%–23%), D r (38%–83%), ϕ (36°–43°), and QSBC (44–82 kPa) than horns ( w = 4%–6%; D r = 7%–23%; ϕ = 32°–33°; QSBC = 14–22 kPa), while both showed similar median grain sizes ( d 50 = 0.34 mm). The properties measured at cusp horns were comparable to those obtained along longshore and cross‐shore transects with no cusps. This work represents a first quantitative assessment of the geotechnical properties of beach cusps and provides insights that could enhance models of beach evolution and sediment transport. Furthermore, the variability in w enabled the coupling of a K‐means clustering algorithm with image morphological operators to identify beach cusps and estimate cusp spacing from high‐resolution multispectral satellite imagery. The remotely derived cusp spacing showed strong agreement with measurements obtained from a digital elevation model of the beach. This approach offers a simple and effective method for remotely monitoring beach cusp morphodynamics and associated variability in sediment properties, contributing to improved coastal management and modeling efforts.