Erosion and accretion of a meso-macro-tidal beach profile—A case from the Yintan Beach of Beihai

Changes in the erosional and depositional regime on a meso-macro tidal coast, under the actions of wave and tide, are significant for understanding coastal evolution, and making coastal engineering design and tourism resource development plan. In this study, the variation in beach profiles and associated driven factors are investigated, based on the hydrological data and measured monthly profile elevations, from July 2014 to February 2018 on the Yintan beach of Beibu Gulf. The results can be summarized as follows: (1) The inshore area of the Yintan Beach remained in a state of net erosion, while the low-tide zone and its shallow surf zone were in weak siltation, and the swash zone in continuous and constant net siltation. (2) In a year there are 263 days, during which wave can make the sediment frequently disturbed in the shallow area less than 3.41 m, which can induce rapid changes in inshore zone, and the eddy water depths induced by the wave 0.3 m to 0.5 m in height control the depositional processes in the swash, surf and low-tide zones. (3) Fluctuation of tide level may cause the spatial differences in sediment movement on seabed and results in the distribution pattern of "strong siltation - weak siltation - weak erosion" from land to sea. (4) The typhoon may greatly cause storm surge elevation, increase the wave disturbance range, and bring about strong erosion of the whole beach.