Channel Morphology Processes And Stability Assessment Of The North Channel Of Yangtze Estuary

The Yangtze eestuary lies at the end of the the Yangtze River, which is mutual transition zone from the river to the sea. Affected by the combined runoff, tide, tidal current, wave and other complex hydrological factors, the channel morphology is quite complicated. It is also one of the most active system for the interaction between biosphere and estuarine environment, because it is adjacent to the Changjiang River Delta economic circle. Significant effect of human activities as the construction of some large scale hydraulic engineering on the estuarine hydrodynamic, sediment dynamics and morphodynamics is increasingly rectified for the recent years.As the second bifurcation of the Yangtze estuary, the North Channel is one of the important channel of water and sediment transport in the Changjiang estuary. For the recent years, the channel morphology is affected by variations in water and sediment discharge by the dam constructions in the Changjiang River catchment and a number of local large estuarine engineering construct in the channel. Inevitably it is quite emergent to know the natural behavior of channel morphology in the North Channel versus response to these anthropogenic measures in the Changjiang estuary. Moreover, the North Channel is planned as an auxiliary deep waterway in the estuary approved by the Ministry of Transportation in August 2010. Therefore, the regime of the North Channel channel evolution and future trends and the estuarine channel stability analysis will provide a scientific basis for the goal planning and development of deep waterway.Historical data of nautical charts from 1977 to 2013, tidal current and suspended sediment concentration during flood and dry season from 2011 to 2012 are collected. Field measurements of tidal current, suspended sediment concentration and bed configuration are detected by using the ADCP and multibeam sonar echo-sounding system Seabat 7125. A cusp catastrophe model for North Channel regime stability and quantitative research to discriminate is used. The first main control variable is selected as the ratio of width to depth as the lateral stability index. The second main control variable is selected as the variation in the bed elevation as longitudinal stability index. Main conclusions is as following:(1) The entrance channel around the diversion of North Channel and South Channel tends be stable after the allied Xinliuhesha protective seawall engineering with submerged breakwater engineering in the Nanshatou waterway and land reclamation around the Zhongyangsha shoal.(2) Intensifying erosion deepwards and northwards at the upper and medium segment of the North Channel occurs attributed to the channel narrowing after the Qingcaosha fresh water reservoir construction. Hereafter, main deep channel with-10 m contour migrate southwards to eastern shoal of Hengsha, the Hengsha channel and north bifurcation of the North Channel tend to extension. Strong deposition and enlarged area of deposition area appear in the lower channel where is located at the estuarine turbidity maxima in the North Channel of the Changjiang estuary and the deep channel migrate northwards.(3) The estuarine channel regime between Baozhen and Tuanjiesha of North Channel from 1977 to 1992 is instable, After then it tends to be stable. The channel regime within the estuarien turbidity maxima become to stable from 1977 to 2010 while it is instable from 2010 to 2013 after the land reclamation along the norther coastline of eastern Hengsha shoal.