长江口北支入海河段的衰退机制

THE ATROPHY OF THE ESTUARINE NORTH BRANCH OF THE YANGTZE RIVER(CHANGJIANG RIVER)

通过不同时期海图、水下地形图对比,论述了长江北支入海河段具有沙脊发育、河槽淤浅、南涨北塌、深泓北靠并逐渐向北平移的演变特征和衰退态势。据 2003 年 11 月同步潮位、潮流、悬沙和地形资料,经单宽潮量、输沙量和断面进出潮量计算发现:黄瓜沙北水道水沙大进大出以过往为主,南水道是水沙倒灌的主通道,潮速南小北大是河道南涨北塌并向北平移的动力机制,南水道涨落潮流均携沙输向江心是江心沙脊发育、黄瓜沙淤高的物质基础,进潮量大是导致泥沙倒灌、入海河段衰退的主要原因。

The authors discuss evolution features and atrophied tendency of the estuarine north branch of the Yangtze River by comparing topographic maps of different periods. At present, the north branch has the following features: growth of the tidal ridges, river channel becoming shallower, accumulation on the south side of the channel and erosion on the north side, and the channel line moving northward. Based on data obtained from in situ observation in November 2003, tidal influx, silt discharge and single tidal amount were calculated. The results showed that the channel south of Huanggua Sand was the main water channel for sand transportation and saltwater intrusion. Tidal speed in the south channel higher than that in the channel north of the Sand is the dynamic mechanism leading its left bank to being scoured and its right bank to being deposited. Silt carried by both flood and ebb currents to the river center is the main cause of the growth of the central sand ridges, and the large tidal influx carries back a large amount of silt, which leads to the atrophy of the estuarine river section.