Dramatic typhoon-induced variability in the grain size characteristics of sediments at a meso-macrotidal beach

Knowledge of sediment grain size characteristics is important for a better understanding of the morphodynamic behavior of beaches worldwide. In this paper, dramatic changes in the grain size of sediments at Yintan Beach, South China in response to Typhoon Rammasun (tropical storm no. 1409) were analyzed on the basis of the collected sediments, beach elevation, and hydrological data from June 1 to July 31. Variations in beach geomorphology were interpreted using the digital elevation taken by LiDAR technology, while changes in sediment grain size were detected by sediment parameters and associated sediment components. The results show that the sediments of Yintan Beach were nearly pure sand before Rammasun and became coarser and slightly better sorted with a higher negative skew after Rammasun. The sediment grain size pattern shifted from a high content (39%) of very fine sand in the lower intertidal zone pre-Rammasun to a high content (76%) of fine sand in the swash zone post-Rammasun. During Rammasun, wave action was responsible for the main transition of grain size pattern in the lower intertidal and mid-tidal zones, and tidal level and beach morphology could affect the grain size distribution of the sandbar and trough in the swash zone. In addition, the increase in the coarse-grained fraction in the upper beach and berm was primarily due to wind action.