| As the second largest island of China, Hainan Island has anadvantageous geographical location. Surrounded by the sea, it faces LeizhouPeninsula crossing Qiongzhou Strait. Rich in mangrove resources, there arealso numerous lagoons and cape bays along the coastline. Since HainanProvince was established in April1988, the Island had become the largestspecial economic zone in the whole country. However, under the hugepressure brought by the rapid development of economy, the coastline changeddramatically for both natural factors and human intervention. In this paper,based on Landsat TM/ETM+/OLI images and topographic maps of HainanIsland, the coastlines of6periods(1973,1980,1990,2001,2010,2013) wereextracted with GIS and RS technology, the position, length, distribution ofwhich were analyzed, as well as the reasons of coastal erosion and siltation.Besides,4typical coast sections of Hainan Island were selected for furthercoastline dynamics analysis details. The main work and achievements are asfollows:Firstly, the coastlines were divided into6types, that were rocky, muddy,sandy, biological and artificial types. Red, green and near infrared bandswere combined to synthetize false color images. With the color, texture,spectral reflection characteristics and adjacency relationship among features,the coastline interpretation keys were established, then the coastlines of6periods were extracted according to the keys and shoreline extractionprinciples we proposed.Secondly, based on the type, length, distribution characteristics of thecoastlines and the changes of coastal area, Hainan Island coastline dynamicswere analyzed, the results showed that: the coastline of Hainan Islandpresented a general trend of rising-stable-reducing-stable during the last40years, with a net reduction of38.15km in length. And the most significant change type located in the sandy coastline, which reduced227.68km, that was5.69km per year. Almost a quarter of the coastline changed,90%of whichwas the transformation from natural to artificial, and the rest transformedamong the different natural types. The area of Hainan Island increased121.96km2, and reduced48.13km2, with a net increase of73.73km2, whichmeans a land growth of1.84km2per year.Thirdly, based on the analysis of the distribution and the status of thecoastline, the reasons for these changes were analyzed from both natural andanthropogenic aspects combining with relevant information. The resultsshowed that Hainan Island coastline was affected by both natural andanthropogenic factors. Especially since the reform and opening up policies,anthropogenic factors have gradually become dominating. For detail, naturalfactors include the amount of runoff and sediment in estuaries, river migration,inland topography evolution, sea level rise and the impact of wind, wave andflow, while anthropogenic factors are the construction of ponds, salt ponds,embankments and ports, land reclamation, beach sand mining, waterconservancy projects and so on.Fourthly,4typical coast sections of Hainan Island, which are Sanya Bay,three estuaries, Qinglan Bay and Dongzhai Harbor, were selected for furtheranalysis. The results turned out that: suffered from natural and anthropogenicfactors, both the sandy and rocky coastline of Sanya Bay dramatically shrunk,and the former eroded about15-30m backwards, while the artificial increased14.34km and the landscape pattern of this zone changed greatly. Estuary areasof Nandu River, Changhua River and Wanquan River kept eroding andstraight, and along with the succession of morphology of sandbanks, there is aconstant transformation from natural to artificial coastline. The lagooncoastline of Qinglan Bay had an overall growth of1.39km. Especially for theeastern part, it eroded in the maximum length of54m, while Bangtang coralreef sandy coastline undergone a strong erosion with the maximum length ofabout180m. Beside these two areas, the rest advanced to the sea, and coastaltidal channel became narrower along with the changed coastline of both sides. No obvious erosions have been found in the mangrove coastline of DongzhaiHarbor, and the overall length of coastline slightly shrunk, with a decrease inmangrove area of5.3068km2. |
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