Long-Term Morphological Evolution of a Tidal Island as Affected by Natural Factors and Human Activities, the Yangtze Estuary

Bathymetric data based on sounding surveys and intertidal elevations measured using Real-Time Kinematic Global Positioning System methodology were analyzed using Geographical Information System techniques to examine the morphological evolution of the tidal island Jiu Duan Sha (JDS) in the Yangtze estuary. It was found that, from 1958 to 2005, the area and sediment volume of JDS increased by 96% and 156% above the 5 m isobath and by 331% and 504% above the Lowest Astronomic Tide (LAT). Specifically, the maximum elevation of the island increased from 0.3 to 4.9 m above the LAT, and the salt marsh increased from 0% to 40% of the intertidal area. The dominant factor controlling the growth of this wetland was found to have varied with time. The growth was mainly due to the deposition of riverine sediment before the 1970s but was primarily the result of the merging of a shoal into JDS between 1971 and 1994 and, later, the local engineering projects between 1994 and 2005. It was concluded that human activities are playing an increasingly important role in the morphological evolution of tidal wetlands in the Yangtze estuary.