GEOMORPHIC EVOLUTION OF EASTERN CHONGMING ISLAND DURING THE LAST 40 YEARS AND ITS FUTURE TREND,BASED ON THE SEA CHARTS COMPARISON

According to the 10 sea charts from 1958 to 2001, covering the Yangtze river estuary and its southern Channel,and the areas from the Lusi Port to Huaniao Hill and from the Hengsha Island to the Liuhe River Estuary as well as the northern part of the Changjiang River Estuary, based on the data of observation from 2002 to 2003,the authors analyzed the erosion-accretion processes around the Eastern Chongming lsland over the past 40 years through the study of cross-sections, changes in island axis and areal variations, with the help of GIS. The results show that (1) in the past 40 years the Chongming Eastern Tidal Flat was under accretion and expanded by a rate of 150 m/a. The expansion in the north-east was faster than other parts. The erosion and deposition patterns are very different in different years. The evolution of the Eastern Chongming Island can be divided in two stages, a quick expansion from 1950's to 1980's, and a slow expansion from 1980's onward. During the later stage, erosion prevailed in some parts of the study area. (2) The axis of the Eastern Chongming Island migrated from the southeast to the north-east during the period by a rate 0.56°/a. (3) According to the results of the study, if the evolutionary trend remains unchanged, the Eastern Chongming Island may join with the Guyuan Island after 118 years and with the north Jiangsu Banks after 206 years. However, the process may slow down because of the change in sadiment budget caused by the consteruction of the Three Gorges Reservoir and other human impacts. (4) Human's activities,such as land reclamation,engineering construction,and the decrease in sediment supply of the Yangtze River have important effects on the evolution of the eastern Chongming tidal flat.