Grain size sorting because of wave propagation over sloping sand bed

Abstract This study explores the effect of waves on sediment beds of known grain‐size distribution under controlled experiments for simulating coastal environments. The experimental setup replicates flat and upward sloping bed conditions, comprising a bimodal grain‐size distribution, and evaluates the changes in distribution under the surface waves of different frequencies. The results demonstrate a significant modulation from an initial bimodal to a unimodal grain‐size distribution in the sloping bed. In contrast, the original size distribution is retained in the flat bed. Statistical analyses revealed a shift towards finer grains in the upward sloping area, driven by wave‐induced sorting mechanisms. It is interesting to note that the observed grain‐size distribution in the transitional region from the plane bed to the upward sloping bed follows a Gaussian distribution, as both the coefficients of skewness and kurtosis show zero, irrespective of the wave frequencies. These outcomes align with previous research, contributing to a deeper understanding of sediment transport and grain‐size distribution in coastal zones. In addition, prototype field photographs of bedforms because of low tidal waves show immense similarities with the ripple morphology along the upward slope generated in the laboratory flume. Moreover, the concentration of heavier coarse fractions of grains occasionally dropped at the trough regions of the fine‐grained ripples of lunate shapes. The study's insights are valuable for improving coastal management strategies, particularly in areas vulnerable to sediment redistribution and erosion.