Assessing the impacts of typhoon events and high-level pond aquaculture discharges on sediment grain size and shape recovery patterns along western Guangdong beaches

Abstract Storm surges and the discharge of high-level pond aquaculture effluent (HPAE) are critical factors influencing the erosion and deposition dynamics of sandy coasts in South China. Understanding the mechanisms by which these factors affect sediment grain size and shape distribution patterns is significant for ecological disaster mitigation and restoration of sandy coastlines. This study examines sediment samples collected from beaches in Western Guangdong, impacted by HPAE, two days and six days after the landfall of Typhoon “Chaba” (No. 2203). We analyze grain size parameters (mean size, sorting coefficient, skewness, and kurtosis) and shape parameters (sphericity, aspect ratio, convexity, circularity, symmetry), focusing on their characteristic values and spatial distribution patterns, as well as the underlying reasons for their similarities and differences. The results indicate that: (1) From two to six days post-typhoon, sediments on the affected beaches near the shore become coarser and less well-sorted, while sediments in the middle region become finer and better sorted. On the unaffected beaches, sediments near the shore become coarser, and those further offshore become finer, with no consistent pattern in sorting coefficient; (2) Landward sediments of the affected beaches exhibit a shift towards a more flattened shape, whereas sediments on the unaffected beaches trend towards a more rounded shape; (3) The correlation between the mean size, kurtosis, and grain shape parameters of the affected beaches weakens, while the correlation between the sorting coefficient and skewness strengthens. In contrast, the unaffected beaches exhibits the opposite trends. This study provides a case for understanding the impact mechanisms of sediment grain size and shape distribution under the combined influence of storms and HPAE. The findings contribute to a deeper understanding of sediment dynamics and the role of marine aquaculture in shaping sandy coastal geomorphology.