江苏海岸侵蚀过程及其趋势

江苏省侵蚀海岸的总长度为 30 1 7km ,分为 4段 :废黄河三角洲海岸、港海岸、吕四海岸以及海州湾的沙质海岸。各段海岸侵蚀原因不同。废黄河三角洲海岸是因黄河改道失去泥沙来源 ;吕四与港海岸则因辐射沙洲调整过程中滨岸水道的向岸移动造成的 ;而北部沙岸则是因人类活动 (上游建设水库及开挖海滩沙 )的干扰。江苏海岸是一个沉积物准封闭系统 ,全球性海平面上升将加剧这一侵蚀过程 ,预计未来侵蚀海岸的长度将增加 ,辐射沙洲区的外围沙洲将因侵蚀而向中心区退缩。一些目前是隐型侵蚀的岸段将向显性侵蚀的阶段发展。由于连云港到长江口北支的岸段是软性海岸 ,缺乏硬质节点 ,在没有建造大型人工设施的前提下 ,估计江苏海岸动态及制定开发规划时必须考虑平直化的大趋势。

The mechanism and trend of coastal erosion of Jiangsu Province in China

The coast of Jiangsu is famous for its dynamic singularity of both serious eroded coast reach and rapid progradingone. The erosional coast of Jiangsu is 301.7km long or 31.6% of the province total shoreline. Of them muddy coast is 271.6km and sandy coast, 30.1km, which is the only segment of sandy coast in Jiangsu. This singularity is relevant to the following three features. The first one is the effect by great changes of the two big river mouths. The lower reaches of the Huanghe River began to enter the Yellow Sea by north of Jiangsu in 1128 after capturing the Huaihe River and was back to the Bohai Sea by Shandong Province in 1855. This evolution of the Huanghe River, which famous for carrying plenty of sediments, caused great hydrodynamic change, especially the sedimentation conditions of the Jiangsu coast. The second one is the long muddy coast.During the 700 years that the Huanghe River entered the Yellow Sea by Jiangsu, the coast was transformed from sandy coast to muddy, and 92% of the shoreline of Jiangsu is muddy coast now. The third one is the diversity of the openness of the several coast reaches. With the substantial change of the large-scale submarine sand ridge fields on the inner continental shelf, the screening state of the coast reaches changes accordingly. There are four segments of the erosional coast reaches in Jiangsu. The first one is the abandoned Huanghe River Delta coast. The delta shoreline and the subaquatic delta have been heavily eroded because of the losing of sediments supply. Meantime, the coast reach of the abandoned river mouth retreated rapidly and has not been controled until the 1970s when the seawall and the bank protection were built. But this promotes the vertical erosion on the intertidal flat.The average rate of vertical erosion from 1980 to 1992 is 13.5 cm/a. The isobath of 15 m is only 4.65 km away from the bank, and the isobath of 10 m moved 0.37 km every year toward the bank from 1937 to 1994. The second isLusi coast, the southern part of the coast of Jiangsu. The erosion of this segment is mainly because of large-scale tidal channel movement toward the bank and development of winding. The shoreline retreated more than 1 km from 1916 to 1969. The super tidal flat in front of the seawall was wholly eroded, and the rate of vertical erosion on the intertidal flat is 3.6 cm/a. The third segment is the Jianggang coast. Some tidal creeks on the tidal flat moving toward the bank caused heavy erosion, and some erosional mud cliffs are as high as 5 m. The cliffs can retreat 20-30 m within one spring tide cycle. The fourth is the sandy coast in the northern part of Jiangsu coast. Some dams were built on some rivers flowing into the sea and break off the sediment source supplying the coast. Meanwhile, digging of coastal sands helped the erosion.