Research On Coast Evolution Of The Abandoned Yellow River In Northern Jiangsu Based On GIS And RS

The coastal zone, located at the area of land and sea interactions with rich resources endowment and favorable natural conditions, is an important habitat for human survival and development, it is also the forward base of social economic development and modernization, as well as the civilization. Coastline and coastal morphological erosion or deposition will directly impact the coastal resources amount and ecological environment, as a result, it will significantly impact on the human living conditions, economic construction etc. Thus, the problems have attracted worldwide attention. Therefore, to strengthen the study on coastal evolution has an important practical significance for understanding the coastal eco-environmental changes, serving the economic and social development as well as global changes in coastal areas.Based on the regional topographic maps, charts, multi-temporal satellite remote sensing images and annual measurement data,a geodatabase of coastlines and subaqueous reliefs was established by geographic information system(GIS), RS, digital elevation model(DEM). Quantitative information of shoreline and the underwater terrain changes was calculated by using the superposition of different periods of shoreline and underwater terrain data.The results are shown as follows:1. Since the Spring and Autumn Period, the coastline of the abandoned Yellow RiverDelta has experienced a process of promoting the transfomation of rapid progradation to retreat and gradually stabilized. The shoreline kept straight and had little length change from the Spring and Autumn Period to the Northern Song Dynasty (1111A.D.) as a whole:roughly to1890A.D.for the sector in the remaining years, the overall growth momentum was maintained(1760A.D. with sandbar shoreline) from1330A.D. to1890A.D., however, due to the north migration of the Yellow River, the length of coastline gradually reduced from1890A.D. to1958.2. Since the1970s, the abandoned Yellow River Delta coastline has experienced more complex spatial and temporal variation.The main eroded area is located within the range from Zhongshan River mouth to Biandan River mouth, while the erosion intensity has gradually weakened. Coastal protection projects were implemented separately inl967-1981,1986-1996and1998-2008at the Abandoned Yellow River mouth. Revetment projects at the tip of the mouth played a role of protective barrier for the near coastline, as a result, the rate of erosion in this section had significantly slowed down since1995. Retrogradation rate varied in different parts in the whole eroded area, which is showed that the north of the Abandoned Yellow River mouth is lower than the southern. Possibly beening affected by the planting of alterniflora in the north part of Sheyang River mouth in1986, the south area of Biandan River mouth showed a trend of erosion and siltation alternatively.3. The entire region of the abandoned Yellow River subaqueous delta was scouring dominated from1930-47to1979. while the coastal areas, north of the the abandoned Yellow River tip as well as roughly-18m deep off the coast demonstiated evident siltation. The net erosion and deposition of the entire region was-44.2×108m3, averaging-1.105×108m3per year, and the average annual scouring and silting thickness was about-1.06cm/a.4. Except the north shore of the abandoned Yellow River mouth and along the north shore and the part off the coast of southeast were in weak deposition in Binhai Port from1989to1994, the vast majority was scouring. Till2007, the offshore waters in the abandoned Yellow River Tip has carved out a scouring groove with1km wide, deeper than-15m, of which the direction generally parallels to the isobath.5. The evolution of scouring and silting of the underwater terrain, combined with analysis of the depth sections shows that all the offshore slopes of the abandoned Yellow River subaqueous delta present up-convex erosion shape except the north Zhongshan estuary section.The lower limits of erosion are roughly at-12m～-15m depth, which may indicate that the lower limit of wave action is at about-15m water depth. Combined with the analysis of the erosion and deposition rate in each depth site, the place with the greatest erosion intensity is in about-3 meters to-12meters between. Setting the abandoned Yellow River mouth as borderline, the underwater plains of northern sections are mostly erosion based, while the southern section are depositing.There is no measured deptn data late in1979covering for the whole region, and repeated measurement data is limited to local, theverfore, it is still difficult to sum up the recent overall deposition and erosion evolution dynamics of underwater terrain for the whole region.