Regulation Theory And Technology For The Channel Beach Pattern Of Branch Channel In The Middle And Lower Yangtze River

This paper focuses on the problems of the severe adjustment of the beach trough pattern,the frequent occurrence of alternating navigable braided channels,and the difficulty of long-term stability of the channel conditions in the braided reach of the middle and lower reaches of the Yangtze River under the condition of new water and sediment.By analyzing the characteristics of water and sediment in the middle and lower reaches of the Yangtze River after the impoundment of the Three Gorges Reservoir,the variation characteristics of the river bed in the braided reach and the response law to the channel conditions are analyzed;considering the utilization requirement of multi-channel water depth navigation scale in the braided reach,the selection method of navigable braided channels and determination method of regulation parameters are put forward;the engineering area,type and layout of regulating the beach trough pattern are studied;a method for determining the bottom protection range of spur dikes is put forward based on improving the scour efficiency of the navigation channel.This paper mainly carried out the following research work:(1)By analyzing the measured data of water and sediment at major hydrological stations in the middle and lower reaches of the Yangtze River,the characteristics of water and sediment movement in the middle and lower reaches of the Yangtze River after the impoundment of the Three Gorges Reservoir are summarized,and the characteristics of the overall changes in the riverbed and the general changes in the channel conditions in the middle and lower reaches of the Yangtze River under the condition of new water and sediment are concluded.The characteristics of the river bed change and the response law of the channel conditions to the change of the new water and sediment are emphatically analyzed.(2)By refining and summarizing the experience of branching selection for constructed projects in the braided reach of the middle and lower reaches of the Yangtze River and considering the demand and possibility of navigable braided channels in the braided reach,the principles and evaluation factors for the selection of navigable braided channels are proposed.(3)In view of the utilization requirement of multi-channel water depth in the braided reach,based on the concept of “the same regulation effect of the same shoal reach under the combination of different regulation parameters”,with nodal point of sediment transport volume in the regulation of the shoal reach,the determining method combined with the regulation water level and regulation line width is put forward,and the relation between the regulation parameters and the multi-target navigation scale is established.(4)Based on the background of the intensified relationship between upstream and downstream river regimes due to the impoundment of the Three Gorges Reservoir and upstream reservoir group,an evaluation index for the calculation of the linkage evolution process in the upstream and downstream reaches is proposed,and based on the quantified linkage evaluation index,a new method for the selection of the engineering area in the channel regulation project is proposed.(5)By using the theory of river dynamics and combined with the generalized flume test,the improvement degree of the guardian engineering for the channel condition is studied,and the mathematical expression formula of maximum navigation depth that can be achieved after the implementation of the guardian engineering is established,which can be compared with the target navigation depth.If it is larger than the target navigation depth,the guardian engineering can be considered;if it is less than the target navigation depth,it means that the strength of the guardian engineering is not enough for the improvement of the channel condition,and it is necessary to use adjustment engineering with higher strength.(6)By using the flow zone method and combined with the generalized model test,a method for determining the main scale of an adjustment engineering that is suitable for the braided reach is proposed.This method overcomes the determination of the main scale of buildings dependent on the regulation parameters in the design of the previous channel regulation buildings,so it is only suitable for the deficiencies of the normal transitional shoals and the inadaptability of the braided reach.(7)The two-dimensional flow mathematical model calculation and the local scour test of the typical river section of the physical model are carried out.The effect of the bottom protection on the efficiency of the spur dikes is analyzed.On this basis,the method of determining the bottom protection range based on the improvement of the scour efficiency of the navigation channel is further proposed.