Grain size distribution characteristics of sediments in recreational beaches: a case study of three major beaches in Zhanjiang City of western Guangdong

Recreational beaches are widely distributed in coastal cities. Investigating the coupling mechanisms between anthropogenic interventions and natural coastal processes on sediment grain-size distribution is critical for maintaining and enhancing recreational beach functionality and value. This study examines three major recreational beaches within Zhanjiang Bay, conducting comparative analyses of surface sediment characteristics including representative grain-size metrics, granulometric composition, and statistical parameters. Key findings include: (a) significant variations in mode size (0.87–1.89 φ) and D₁₀ values (-0.80 to -0.09 φ) among the three beaches, contrasted with limited differences in D₅₀ and D₉₀ metrics; (2) dominance of medium sand (26.16–39.14%) and coarse sand (26.75–31.43%) fractions, supplemented by fine and very coarse sand components, with central transects exhibiting higher medium-coarse sand concentrations than southern/northern sections; (3) sorting coefficient gradients (0.90–1.21) ranking central > northern > southern beaches, while mean grain size (0.83–1.21 φ), skewness (-0.12 to -0.02), and kurtosis (0.87–1.18) show no distinct spatial patterns. Sediment grain-size distribution patterns are governed by four primary mechanisms: artificial nourishment inputs, anthropogenic sediment modification (harvesting/excavation), natural sediment supply processes, and hydrodynamic forcing. This research establishes a typical framework for characterizing recreational beach sediments, advancing understanding of multi-factor controlled grain-size distribution patterns and sediment transport dynamics.