Study On Regulation Parameters Of Branched Reaches In The Upper Reaches Of The Yangtze River Under New Water And Sediment Conditions

There are many braided reaches in the upper stream of the Yangzi River.The characteristics of rivers and different obstacles in different ramps are different.Some of the ramps have been rectified several times,and it is difficult to rectify.In recent years,the water and sediment conditions of the upper reaches of the Yangzi River have undergone significant changes,mainly reflected in the inconsistency of the inflow and the significant decrease in the amount of incoming sand;In addition to the current requirements for upgrading the navigation channel,the applicability and improvement methods of the method for determining the regulation parameters of the Class III channel under the original water and sediment conditions are for further study.The research on regulation parameters of mountain rivers is mostly focused on the two parameters of regulation water level and regulation line width,while the research on rectification line parameters is rare;In addition,infrastructure dredging is also an important measure for the regulation of the upper reaches of the Yangzi Rive.Therefore,this paper adopts the combination of prototype data analysis,generalized water tank test,model test and theoretical analysis to adjust the water level and the width of the rectification line of braided reaches and the cross-sectional dimension of the infrastructure trenching under the new water and sediment conditions.The method for determining the parameters such as rectification line type has been studied comprehensively.The main conclusions are as follows:(1)There are few studies on the classification and evolution of the river patterns in the mountain section.From the perspective of river channel and obstacle navigation characteristics,this paper divides the single-type river bay ramp into a curved top-flat section or a dark-spotted branch;The transition section of the compound river bend is divided into three types: concave bank type tiller,convex bank type first class tiller and convex bank type second class tiller.At the same time,river relations of different subtypes are established.Through the generalized model test,the formation and evolution process of the transition section of the natural bend relaxation is simulated,which indicates that the relative scale and water and sediment conditions of the beach are the main influencing factors for the formation of different types of ramps.(2)After the upstream construction,the flow during the dry period increased,and the flow during the flood season decreased slightly,but the duration of the rise and fall was equivalent.The non-constantity inflowcan be reflected by the ratio of the shear increase of the bed surface caused by the non-constant flow to the shearing force of the constant flow bed surface.The maximum value of ? in the dry season of Zhutuo station is 0.5%.The product of river power and frequency of occurrence under non-constant flow is used as an indicator of bed making,which can reflect the effect of bed formation under non-constant.Under new water and sediment conditions,the branching channel is generally stable,and the extent of erosion and siltation in the long section of the dam is reduced during the year,but due to the adverse effects of sand mining on the evolution of the channel.(3)The main navigation problems in the upper reaches of the Yangtze River are shallow,insufficient bending radius,oblique flow pattern and so on.Based on the analysis of the navigation obstruction characteristics and causes of different types of river branches,the selection method of navigation regulation branches is proposed according to the actual needs of channel upgrading.In the case that it is difficult to completely improve the bending radius of the lower section of the curved tunnel,it is conceivable to open a straight slot to navigate and form a smooth channel connecting the upper and lower deep grooves.Aiming at the navigation and rectification ramps of different types of ramp rivers,it is proposed to rectify dry water,stabilize or adjust the tiller pattern,and adopt the rectification idea of “mainly dredging and supplementing dams”.(4)The calculation of the regulation parameters should consider the influence of bed surface roughening and non-constant flow.Through the analysis of the theory and typical engineering regulation practice data,the proposed method for determining the cross-section parameters such as the same method for regulation of sediment flow,the method for correcting the sediment transport capacity during the retreating process,and the relationship between the rivers and rivers in the excellent river section.The same method of sediment transport before and after regulation of the flow rate uses the modified formula of Einstein's load-bearing sediment transport rate,and proposes that the water transport intensity required for the same sediment transport capacity is the same;The water flow intensity function including the concealment coefficient is used to establish a formula suitable for the change of the bed surface composition under the new water and sediment conditions.The principle of the method for correcting the sediment transport capacity balance in the water withdrawal process is unchanged.First,the calculated starting water level is corrected.The straight groove is at the position of the water flow force axis under the first bed flow rate,and the start calculated water level should take the average annual flow rate,but the curved squat can take a low value;Second,the sediment transport rate formula adopted reflects the impact of unsteady flow.(5)The three-dimensional flow characteristics test of the trench shows that the narrower the groove,the larger the average flow velocity of the vertical line in the deep trench;However,when the near-bottom flow rate reaches a maximum when the groove width-to-depth ratio is reduced to 17.8,the width-depth ratio decreases and the near-bottom flow rate decreases again;The relative turbulence intensity and the frictional flow rate distribution are opposite.The starting flow rate condition with a high probability of starting is obtained,and the aspect ratio when obtaining the optimal hydraulic condition in the trench is about 17.8.(6)Through theoretical calculation and analysis,it reveals the distribution law of the near-bottom water flow intensity at the shallow exit of the curved channel with different relative bending radius R/B2,and obtains maximum value velocity in the shallow region when R/B2 =2.5.which is consistent with the river relationship between the relative bending radius and the shallow water depth,and the model test results of the typical beach segment;It provides a basis for the selection of the regulation line parameters of this type of shoal.(7)The general layout methods be summarized of regulation lines and control projects for different types of braided channel.To the convex-type first-class braided channel,the obstruction features lincluding channel depth and curvature radius of approach channel are insufficient,with cross current flow pattern.Through the arrangement of the regulation line on the concave bank and longitudinal damdam at the head of islet,it can narrow and return the water flow and enhance the sediment transport intensity.To the convex-type second-class braided channel,when the existence of the low-water beach in the river section is favorable to navigationl,the longitudinal dike and the spur dike can be built on the low-lying heart beach to fixed and increased the beach bed.Adjusting the river regime from “invisible” branching of the water level transforms into the “obvious” direction of the branch.If the navigation conditions of the two branches of the dry water heart beach are difficult to meet the requirements of the navigational scale,the regulation idea of “enhancing the primary tillering and weakening the secondary tillering” may be adopted.