The study of the difference of beach response under sediment supply in southeast of Xiamen Island

The morphological evolution of a beach in the southeastern part of Xiamen Island, Fujian, China was analyzed as an example to show the responses of the beach to different sediment supplies. Based on the topographic data from 10 beach profiles monitored for six consecutive years, the method of Empirical Orthogonal Function (EOF) analysis was applied to help identify the morphological evolution and the associated driving factors. More than 90% of the total variance of the first three empirical orthogonal functions was used to reflect the basic evolution of the beach. The first mode represents the remarkable erosion or deposition trend of beach profiles on a long time scale, indicating that sediment source plays a dominate role in long-term beach evolution. Beach profiles in the northern part of the study area show continuous seaward accretion, while those in the southern part show retreat. The second mode represents the seasonal transition in beach berm between summer and winter, which is associated with the seasonal variation in wave climate. The third mode represents the morphological changes of intertidal zone, which indicates the impacts of human activities, especially artificial structures along the coast. This study highlights the dominant role of sediment source in medium- to long-term morphological evolution of beaches. Beaches with sufficient sediment supply show a larger range of morphological adjustment and stronger adaptability than those with limited sediment supply.