苏北、长江口海岸的演变及其动态

连云港至杭州湾北岸,海岸线长达千余公里;其海岸为一低地堆积平原岸,由于古黄河及长江的固体径流等的影响,曾经历了一个复杂的演变过程。海岸与河口面临开阔的浅海海域,经受着潮流强风浪与径流的作用,其岸滩与河口沙岛的动态具有独特之处。 对于苏北及长江口海岸的一些基本问题,不少学者先后从不同角度进行过研究,本文仅就海岸演变及其动态论述如下。

COASTAL EVOLUTION AND DYNAMICS OF NORTHERN JIANGSU AND CHANGJIANG RIVER ESTUARY

The three coastal lines north of Hai''an, Jiangsu Province, about 6000, 2000 and 900 years ago respectively were very close. They were smooth, straight and stable for a considerable period of time. The coast south of Hai''an advanced rapidly owing to the development of the northern bank and the southward shift of Changjiang River (Yangtze River) mouth. The Huanghe River (Yellow River) changed its course and entered into the sea in the central region of Jiangsu Province at the begining of 1lth century. Abundant materials were brought into the sea, sedimental accumulation increased rapidly and a delta was thus formed toward the sea. Terrigenous materials were, however, cut off in the middle part of nineteenth century when the Huanghe River shifted again its course to the north. Abrasive process of the aleurite aceumulation began, resulting the convex coast being regressed and the concave one being adnanced. The charaeteristics of this dynamic coast was exhibited in sections of its growth and collapse as shown by coastal abrasion-tidal shoal erosion, coastal accumulation-tidal shoal accumulation, coastal abrasion-tidal shoal accumulation. The mouth of Changjiang River (Yangtze River) was of a bugle shape some 6000 years ago. Through the incorporation of sandy islands and bars into the north bank and the expansion of shoals near by the south bank, the channel narrowed and the estuary shifted to the south to form the present geography of the river mouth. The south bank of Changjiang River (Yangtze River) remained stable before the 8th century and between the 16th and 19th centuries. There are scores of shoals, sandy bars and islands in the river mouth at present. The dynamics of their formation and development are the result of the interaction of runoff and tidal current. There exist a regression of the south edge and an accumulation of the north edge of the sand island. There is a general tendency for the Chongming Island to incorporate into the north bank to form a new Qidong Spit and the Changxing Island into other sand islands to form a new Chongming Island. The south bank will regress under the combined action of runoff and wind waves. The south navigation channel will be considerably affected by the siltation of the shoal of Nanhui Spit shoal.