Grain size distribution and characterization of sedimentary processes of Cox's Bazar Beach, Bangladesh: Implications for understanding coastal morphodynamics

This study aims to investigate the factors influencing modern beach development along the southeastern Bengal Basin coast by analyzing the grain size and heavy mineral (HM) distribution in sediment. This study provides insight into the granulometric characteristics, depositional environments, and sedimentation processes that shape the coast. Eighty surficial beach samples were collected from Kakra in the north, Inani, and Teknaf in the south, along Cox's Bazar Beach to characterize the sediment. The fine-to medium-grained (1.76–2.54 φ), well-to moderately well-sorted (0.34–1.23 φ), nearly symmetrical ((−0.10)–0.03), and mesokurtic (0.93–1.28) sands indicate the uniformity of the grain sizes. The bivariant plot of the grain size parameters, linear and multivariate discriminant functions, and course (one percentile value) to medium (C−M) diagram reveal that the sediment was deposited in an aeolian, shallow agitated, turbidity-influenced beach environment. The sand has higher concentrations of HMs in the swash zone (4.9 %–19.1 %), followed by the surf zone (3.5 %–12.3 %), backshore area (2.2 %–12 %), and dunes (2.5 %–6.2 %). The spatial distribution of the grain parameters indicates that moderately well-sorted medium-grained sand was deposited in the swash zone, whereas well-sorted to very well-sorted fine-grained sand was found toward the land. Waves with strongly asymmetric currents carry sediment from offshore areas in a turbulent manner, resulting in coarser sand and a greater proportion of HM deposits in the swash zone and finer particles back to the ocean. In contrast, the wind carries sediment landward, forming dunes. The oblique approach of waves along the coast results in the formation of longshore currents, which influence sediment movement and lead to decreasing grain sizes from south to north. Overall, this study enhances the understanding of the factors influencing modern beach development along the Bengal Basin coast, providing valuable insight into coastal sedimentation and its management.