Seasonal evolution of the typical sandy coast of southeastern Shandong Peninsula and controlling factors—Take the 10 000-meter beach in Haiyang as an example

Beach profile morphological survey and surface sediment grain size analysis along the Haiyang coast were carried out by the authors for the four seasons from the autumn of 2018 to the summer of 2019, and the seasonal variation of beach topography and surface sediment grain size as well as the factors controlling the seasonal evolution of sandy coast in the surveyed area were studied. The results show that the beach profile to the west of Lianlidao-Dongcun estuary is characterized by patterns of "upper erosion and lower siltation" under strong dynamic and "lower scoured and upper molded" under weak dynamic conditions, respectively, and the erosion of beach berm caused by the summer typhoon is much stronger than that caused by the winter monsoon. A large number of sand bars of small scale were formed on the beach surface, and extended offshore farther than those formed under the winter monsoon. The beach profile at the Lianlidao-Dongcun estuary is silted in general, and the siltation under strong dynamic is larger than that under weak dynamic condition. The seasonal variation of the beach profile to the east of the Lianlidao-Dongcun estuary is smaller than that to the west, and the shape of the beach berm top shows obvious a concave feature in the summer. The variation of grain size of surface sediments also shows the difference between the east and the west. From autumn to winter, the grain size of surface sediments on the west side becomes coarser and the sorting becomes worse. On the east side, however, the sediments become finer with almost unchanged sorting. From winter to spring, the grain size of beach surface sediments becomes finer in grain size and better in sorting. and the variation trend in summer is similar to that in winter, although the variation range is different. Coastal engineering construction such as artificial islands and ports are the main factors leading to the difference of beach profile shape and grain size of surface sediments from east to west, and waves and typhoon events are the main dynamic factors that control the seasonal evolution of sandy beaches. Tidal action, tourism development and other human activities will also have a certain impact onto beach evolution.