SEDIMENTATION AND RECENT MORPHOLOGICAL CHANGES AT DONGSHA BEACH, ZHUJIAJIAN ISLAND, ZHEJIANG PROVINCE

Sandy beaches are precious resources in Zhejiang coastal region. For the purpose to understand the regional sandy beach morphological changes, we selected the Dongsha Beach of Zhujiajian Island as an example. During the period of 2010-2012, we repeated 4 times of topographic survey at the Dongsha Beach. At the same time, sediment samples were collected. Compared with previous beach profiles and the composition of the beach sediments, we discussed the sediment characteristics and the recent morphological changes of the Beach. Sedimentary differentiation is obvious at the Dongsha Beach. From the coastal area to the open sea, we can see the changes of sediments from gravel, medium sand, fine sand, silt, up to clay silt. The beach morphological section shows seasonal changes, with accretion in winter and erosion in summer. The sandy bar and coexisted trough in winter may become a smooth slope in summer. Hydrodynamics, the source of sediments and human activities are the main factors affecting the beach development. Spilling waves and meso-tides often led to a non-barred dissipative beach. Abundant suspending sediment from the Yangtze River resulted in a limited sandy deposition zone and the mudline is close to the shore. Human activities, such as beach sand mining and land reclamation, will change or even block the sand source of the beach resulting in beach erosion.