中文摘要：

1998年以前,九段沙是一个人类活动干预很小的天然河口江心沙洲。北槽深水航道治理工程建设,使九段沙头部和北边界基本固定,南北槽分流分沙比改变,水沙交换减少。同时,随着流域来沙和河口河道底沙来源减少,近期九段沙冲淤演变发生新的变化。如今的九段沙0m水深线包络体在不断地淤高扩宽。上沙沙头迅速淤涨,并越过南导堤向北偏伸入北槽,沙尾则快速向南槽延伸,并与南导堤和中沙之间形成新的涨潮沟通道;九段沙南北侧由于冲淤不均其水边线形态出现明显不规则变化,下沙尾部东南端冲蚀,东北端淤涨,沙洲长轴线逆时针转动,但洲体整体位置摆动极小。作为国家级自然保护区,其上沙沙尾的快速延伸和沙洲南侧局部冲淤不平衡须引起重视,确保九段沙沙洲整体稳定。

英文摘要：

The Jiuduansha Shoal in the Yangtze Estuary is a natural estuarine shoal with insignificant human interventions before 1998.With the construction of the Deep-water Navigation Channel Project in the North Passage,the head and the northern boundary of the Jiuduansha Shoal were fixed,the distribution of the flow and sediment between the North Passage and the South Passage has been changed,and the exchange of flow and sediment between them has been decreased,simultaneously.Along with the decrease of sediment load from the Yangtze drainage area and of bed-load from the upper channels,the Jiuduansha Shoal has experienced a new change in the characteristics of morphological evolution.At present,the part of the Jiuduansha Shoal above 0-m isobath is accumulating wider and higher gradually.The head of the upper shoal extends rapidly by accumulation and climbs over the training wall,reaching into the North Passage,while its tail extends to the South Passage,and a new flood channel occurs between it and the southern training wall as well as the middle shoal.With respect to the lower shoal,there are erosion in the southeastern end,siltation in the northeastern end,counterclockwise rotation of the longitudinal axis and general increase in elevation,but the displacement of the whole Jiuduansha Shoal is invisible.The morphological evolution of the Jiuduansha Shoal has experienced a significant change,especially the rapid extension of the tail of the upper shoal and the unbalanced local erosion and accumulation at southern side of the shoal.More attention should be paid to keep its stabilization as a national natural reserve.