Processes And Influence Factors Of Typical Coastal Erosion In The Yangtze River Estuary

The estuary region locates at the interaction of the rivers and oceans, is the interactional area of 4 spheres and various interfaces. The coastal beach which the most hypersensitive zone of land-ocean interactions also is the important land resource of the big cities in delta area. Beach erosion is a kind of natural calamities in estuary. With the input of silt to the river mouth area continually declining, the speed of coastal beaches siltation in the Yangtze River estuarine has been slowing down. Not only erosion state of the coastal has enhanced erosion, some siltation state of the coast has been transformed into erosion. The dynamical factors of estuary region are complex, beach erosion is more complex, study beach erosion is important. In this paper, we choose the Yangtze River estuary's three typical beaches to study the process and mechanism of coastal erosion. Use the hydrologic and sediment tests and historical charts information, we can analysis basic rule and master factors from beach erosion and siltation, water dynamical factors, and then we can forecast the current of beach erosion.The result shows that:1. The coastal erosion in Yangtz River estuary from 2000: the south part of south channel from Xuliujin to Jiuduansha, the upside part of the south of Chongming Island and the Jinshan section was mostly in steady state. Jiuduansha, Chongming Dongtan, Hengsha Dongtan, Nanhui Dongtan was mostly in siltation state. Nanhui Nantan, the the south of Chongming Island from middle part to Tuanjiesha, Zhongyangsha, the south of Changxing Island, the west and northwest of Hengsha Island and the Fengxian section was in erosion state.2. The south of Chongming Island from Nanmengang to Tuanjiesha each section has different dynamical conditions, the reason of erosion is different. When dynamical condition changed, the erosion and siltation status also changed, coastal evolvement decided the erosion and siltation status. From Nanmengang to Xijiagang there are 2 flood channels, these 2 flood channels' evolve immediately affect the erosion and siltation. In the different phases when flood channel develop, the erosion status are different. But different section of a flood channel maybe in different phases, so different section of a flood channel maybe in different erosion status. Tuanjiesha section was mostly affected by storm, was the mostly eroded section.3. The south of Changxing Island: Shitousha to Panshigang is in erosion state, Panshigang to Majiagang is in siltation state, Majiagang to Xinkaigang is in siltation state, Xinkaigang to Yuanshazha is in erosion state.4. In the past 30 years 3 different sections in the north of Hangzhou Bay have different states, the Nanhui section was mostly in siltation state before 1997 and in erosion state after 1997, the Jinshan section was mostly in steady state, and the Fengxian section was in erosion state, but the erosion zone has moved from the east to the west and the erosion zone has moved to north, the erosion zone has moved from the tidal flat below -5m to the tidal flat above 5m.