Research on navigation-obstruction with complex boundary and its counter measures in middle reaches of the Yangtze River

摘要

Channel characteristics in the middle and lower reaches of Yangtze river were complicated and changing, which showed up as mainstream swing frequently, staggered beach moving down significantly, delta and channel changed violently etc. In this paper, navigation-obstruction in the Jiepai Reach in the middle reach of the Yangtze River and its countermeasures were discussea based on the analysis of the historical riverbed evolution of the Jiepai reach. The Jiepai Reach is characterized by a frequent sway of mainstream, significant moving down of the intersectional point bar,and drastic changes between main channel and floodplain. Navigation-obstruction in the Jiepai Reach can be described as follows: the dredged channel location is very unstable, leading to the navigation obstruction of refloating in the frequent transition between the left and the right branch. Besides, the frequent sway of mainstream causes different levels of damages to the existing regulating structures. These problems can mainly be attributed to the unstable and less controlled distribution of the Jiepai reach between main channel and floodplain. The general idea of regulating the Jiepai reach is: based on the existing projects, according to the facilitating pattern of main channel and floodplain during the river evolution; appropriate engineering measures can be taken to gradually form eflicient patterns between main channel and floodplain phase by phase,which will improve the navigation conditions. In the early stage, bar protection engineering should be implemented in the transition section the low shallow beach, wnich controls an appropriate location of the transition section, and promotes the formation of a stable transition channel. In the later stage, according to the adjustment of the channel, dam and bar protection structures can be applied in the control' engineering of the upper point bar and beaches above Luoshan. Model test results showed that the implementation of the project could produce sound regulation effects, and efficiently improve the navigation conditions.