Analysis Of Recent Evolution Of Yangtze Estuary Based On GIS

The Yangtze estuary is a typical estuary where fluvial factors play dominant roles. Sediment from upstream is the basis of healthy development in estuary area. With the construction of the Three Gorges project, hydrological situation in lower reaches has changed in a certain degree, including the changes of the sediment condition in estuary, which leads to the influence of beach erosion and deposition. People are commonly attracted by this issue which becomes a hot spot within the academic and engineering realm. In this paper, the erosion and deposition condition before and after the Three Gorges Project is studied in order to make clear what the influence to Yangtze Rive estuary.With the methods of sediment transport mechanics, engineering hydrology, coastal dynamics, GIS and DEM are leading into this paper to analyze the evolutional processes of the estuary which may be influenced by the Three Gorges Project. Furthermore, several pieces of charts of Yangtze Estuary from 1981 to 2004 are digitized with the help of Maplnfo, one kind of GIS software, and the digital elevation model of the Yangtze Estuary is established which includes north and south branch of the Yangtze River as well as Nanhuizui area by the means of surfer8.0. By comparing different series of topography data, scouring and sedimentation are calculated in a more accurate way. By analyzing the shift of the isobath and shore line, the evolution of typical cross section, a preliminary study of the response to the changes of upstream runoff and sediment are carried out, due to the effect of the construction of the Three Gorges Project.According to the study, three Gorges project plays little effect on the north branch of the River, but may slowdown the down-draught from north branch to South Branch. Moreover, North Branch is presented in a depositing tendency and will keep on depositing by the enclosing sludge project. Meanwhile, South Branch is the main channel into the sea, which has a more sensitive response to the Three Gorges project. With the storage of the water in Three Gorges Project, the South Branch presents an overall erosion, which is benefit to maintain the stability of channel depth and riverbed. However, the decreasing of the sediment will slow down the deposition of the sediment in Yangtze estuary, which will cause an adverse effect to the development and utilization of the estuarine resources. Nanhui beach, on the whole, is silting up, and meantime erosion and deposition on east and south Nanhui tidal flat change alternately. Under the influenced of the Three Gorges Project, the deposition in Nanhui is slowing down. On the whole, the erosion and deposition in estuary district are greatly influenced by the Three Gorges Project and more researches are needed in the future.