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

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.