长江口九段沙的形成演变及其与南北槽发育的关系

THE FORMATION AND EVOLUTION OF THE JIUDUANSHA TIDAL ISLAND AS WELL AS THEIR RELATION TO THE DEVELOPMENT OF THE NORTH AND SOUTH PASSAGES IN THE YANGTZE RIVER ESTUARY

根据１８４２～１９９５年的地形图和１９９６、１９９７年的野外观测，探讨了九段沙和南北槽的形成历史及形成后的演变过程。研究表明：九段沙是原铜沙浅滩南沿经涨、落潮槽对切贯通后形成的，北槽和北港一样最初原形是涨潮槽；南槽的前身是南港下段。九段沙形成以来具有趋势性和非趋势性两种冲淤变化。前者表现为扩大、淤高和位置向下游移动，后者反映在南北两侧的频繁冲淤。九段沙和南北槽在冲淤上存在相互制约关系。目前，南北槽河势已进入相对稳定时期。

Based on the topographic maps dated from 1842 to 1995 and the field surveys in 1996 and 1997, the paper mainly deals with the history of formation and evolution of the Jiuduansha tidal island and the North and South Passages. The results show: Jiuduansha originated from the partition of the south part of the Tongsha Shoal cut upstream by a flood channel and downstream by a ebb channel. The embryo of the North Passage was a flood channel, and that of the South Passage was the lower reaches of the old South Channel. There have been two basic types of change in erosion and accumulation since the birth of the Jiuduansha:continuous change and periodic change. The former includes broadness of the island area, accretion in tidal marsh and flat and downstream migration of the island. The latter includes cyclic erosion and accumulation on the two sides of the island and the North and South Passages. The island and the two bifurcated river passages interacted on each other in erosiveaccumulative changes. At the pressent, the course of the North Passage and the South Passage is relatively stable.