Research Of Connection Between River Channel In Condition Of Hydraulic Scour And Navigation Channel With Elevated Channel Grade

The successive impoundment of the Three Gorges Reservoir and other cascade reservoirs makes the middle reach of the Yangtze River have a top-down scouring,which creates favorable conditions for the promotion of channel level in the middle reach of the Yangtze River.Taking Jinkou to Wuqiao reach for example,With the basic theory analysis,summary of engineering experiences,the measured data analysis and mathematical model prediction method,this paper studies river channel's and navigation channel's evolution characteristics and mechanism comprehensively.And according to the channel condition change tendency,this paper does the connection research between river channel in condition of hydraulic scour and navigation channel with elevated channel grade systematically.The research can be summarized as follows:(1)Research on water-sediment relationship in the middle reach of the Yangtze River before and after the impoundment of the Three Gorges Reservoir.After the impoundment of the Three Gorges Reservoir,in the middle reach of the Yangtze River,the coming water has not changed much over the years,but the amplitude decreases during the year for the performance of decreased flow rate in flood season and increased flow rate in dead season.Moreover,the sediment discharge reduces obviously.As a result,the annual minimum low water flow of Hankou water station increases from the historical minimum of 4830m~3/s to the annual minimum of 8080~10300m~3/s,and the annual minimum low water level increases by 1.5-2.2m.At the same time,the water level-flow rate relationship of Hankou water station from 2013 to 2016 shows that when the water flow is below 30,000 m~3/s,the water level of Wuhan reach has decreased significantly compared with that before impoundment,indicating that the severe scour has extended to Wuhan reach,and the scour mainly occurs in the river channel with the low and middle water level.(2)The evolution characteristics and mechanism of the river channel and navigation channel in Jinkou to Wuqiao reach.Before the impoundment of the Three Gorges Reservoir,Jinkou to Wuqiao reach has an overall balance of scour and deposition,and presents periodic changes within and between years.After the impoundment of the Three Gorges Reservoir,Jinkou to Wuqiao reach also presents periodic changes within and between years,but the riverbed is scoured and cut down.As a result,the channel condition appears new change,and the navigation-obstruction of Hanyang Shoal blocking navigation span of Wuhan Yangtze Grand Bridge still exists.The evolution mechanism of Jinkou to Wuqiao reach is that the scour and deposition of marshland and flume is influenced by two factors,one is the periodic adjustment of dynamic conditions for water and sediment transport,the other is the random fluctuation of coming water and sediment.(3)Simulation and prediction of scour and deposition using the two-dimensional hydrodynamic and sediment numerical model in Jinkou to Wuqiao reach.The simulation and prediction mainly includes two aspects.One is the simulation and prediction in three typical years of high water period,median water period and low water period.Another is the simulation and prediction using the water-sediment data of 2008-2012 twice from Luoshan water station,but data is to be less sediment according to the tendency of runoff and sediment variety in the future.The prediction result shows that the scour of Jinkou to Wuqiao reach will be severe in the future.The riverbed will loss 24.104 million cubic meters sediment in 10 years and the average depth of flushing will be 2.8 meters.As a result,the channel condition will be optimized and beneficial to upgrade channel level.At the same time,some areas are at risk of navigation obstruction,such as the channel becoming wider and shallower,navigation channel shifting,etc.The navigation-obstruction of Hanyang Shoal blocking navigation span of Wuhan Yangtze Grand Bridge still exists.(4)Research of connection between river channel in condition of hydraulic scour and navigation channel with elevated channel grade.Firstly,this paper analyzes different section morphology from Wuhan reach and compared with navigation channel size.Then expound that the efficient approach of upgrading navigation channel is to shape ideal trapezoidal channel form.Secondly,upgrading navigation channel must accord to the non-equilibrium new water-sediment condition and follow the change rule of channel under hydraulic scour.The channel regulation project must be implemented to take advantage of the situation.The author puts forward the method of iterative adjustment to improve the grade of navigation channel to get twice the result with haft the effort.In the end,taking Jinkou to Wuqiao for example,the channel regulation thought is that for parts with better channel condition,solidifying the existing beach groove pattern;for parts with non-main channel development,reducing the main channel's conveyance capability,curbing the development of non-main channel;for the sedimentation area of main channel,increasing its flow capacity and water scouring power;for the non-navigation channel with the navigable condition,doing the in-depth analysis of channel for navigation,the channel will be allowed if more good than harm.According to the prediction result of scour and deposition,on the basis of existing channel regulation experience,this paper proposes the connection schemes of river channel and navigation channel.The connecting schemes of river channel in the condition of hydraulic scour and navigation channel with elevated channel grade can be mainly divided into two categories,protective types and constructive types.The protective types mainly include protecting existing base slopes and marginal banks or optimizing branching channel.The constructive types mainly include jamming tributary to strengthen main stream or choosing new channel.