| The flow distribution of each branch of natural bifurcated river often can not meet the needs of human life and production.Diversion weir for blocking water is an effective method to adjust the ratio of shunt,such projects are often vulnerable to flood damage because of the complex flow condition.This paper takes that Aihe River in Dandong is suffered by flood damage frequently as the starting point,flow characteristics of the braided channel is studied.The contents and achievements of this paper are as follows.1.Summed up the predecessors on the evolution of the braided river channel,the characteristics of branch river water flow research results,It is found that the research results have some theoretical value,but the influence of the natural river bed topography on the flow characteristics of the braided river is neglected.Therefore,it is determined that this study simulates the natural river topography to make the fixed bed model.By summing up the experience of the construction of the diversion project in the past,the main form of the model diversion building is the combination of weir and sluice.2.In this study,taken natural river as the prototype,using physical fixed bed model test method,Successively analyzed natural river flow state and flood damage of the original division weir in Aihe Dandong,get the following conclusionsdesign.(1)The water flow in natural channel are mostly concentrated in the main river,and the smaller river flow is,the greater the effect of channel flow by main channel is.The appearance of the recirculation zone in the river promotes the development of point bar,the flow line is significantly concentrated near the bifurcation point of the river.(2)The main reason of that original diversion weir is suffered frequently by flood damage is that diversion weir is side weir,and the water flowing into the branch flows from the right bank to the left side,and the effect of oblique flow makes the energy dissipator fail and the downstream flow velocity is larger,and the vertical vortex is formed near the left side wall of the stilling pool,which causes damage to structures in stilling pool and the left side wall and serious erosion to downstream river.Therefore,in the layout of the diversion of the building,to eliminate or weaken the oblique flow conditions,must be considered the design points.3.Through the analysis of the mechanism of water flow in the natural river channel,get the scheme of weir gate at the entrance of diversion gate(programme 1)and a new weir gate scheme at the lower reaches of the tributary(t programme 2).The main conclusions are as follows:(1)The adjustment of the position of weir sluice gate structure has significant influence on the main line of the branch.When the weir sluice is located downstream of the branch,where has a phenomenon of velocity concentration near the shore of the bifurcation point.And with the increase of flow rate,the main line moves back to the center of the river.(2)Under the main flow with a fifty year return,the diversion ratio is 37%,when the weir is arranged at the downstream of the branch.And when the weir gate is arranged at the position of the original entrance door,the branching ratio is 47%.It can be seen that when the weir gate is arranged at the downstream of the branch,the ability to adjust the diversion ratio is stronger.(3)Under the design flow condition,the water level at the bifurcation point of the project is 17.37m and 16.53m respectively,when the gate is located at the position of the branch gate,the main branch branch flow divergence makes the barrier of the dam more obvious.The effect of the oblique flow of the original weir gate scheme is weakened,but the energy dissipation after weir is still not enough,and the flow velocity after sea mantle is 4m/s.While in the downstream weir sluice gate scheme,the flow direction is perpendicular to the axis of weir,and energy dissipation effect is good.(4)Through calculation,the integrated flow coefficient of original weir sluice scheme is 0.40?0.47,and the flow capacity is strong.At the same time,the integrated flow coefficient of the downstream weir sluice gate scheme is only 0.32?0.43.This shows again that the new downstream weir sluice gate scheme is more favorable to control the flow of the branch.Through the test,it is more suitable to build the weir in the downstream branch of the 500m,And the corresponding measures are found in the adverse hydraulic phenomena found in the experiment.The experimental results have reference significance for the design and research of river diversion buildings in plain and shallow braided river channels in plain areas. |
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