| Due to the excessive consumption of river ecosystem by human activities,the annual runoff of rivers continues to decline.Some rivers have become "seasonal rivers" or "partly rivers",some are even without water all year round.The construction of hydraulic dams in the middle and small rivers is an important measure to realize ecological restoration and improve the situation.However,the construction of hydraulic dams will also have a great impact on the hydraulic characteristics of the river,and then affect of erosion and deposition and of the river.Therefore,it is necessary to study the influence of hydraulic dams on the hydraulic characteristics and deposition and erosion.In this paper,three hydraulic dams are set in the flume with variable curvature for physical model test.Based on the test results,the influence of hydraulic dams on hydraulic characteristics such as velocity,water level and turbulent kinetic energy in the flume under four working conditions is analyzed.Secondly,based on Delft 3D software,a hydrodynamic model and a scouring and erosion and deposition model for the influence of hydraulic dams on a river with variable curvature are established.Numerical simulation is carried out for four working conditions of the test,and the reliability of the hydrodynamic model is verifiedby comparison with the test results.Finally,the model is used to simulate the impact of the periodic fixed bed formed by the collapse of hydraulic DAMS on the scouring and silting of the section with variable curvature during flood discharge,which can provide reference for the design and operation of hydraulic dams.The main conclusions are as follows:(1)When there is no hydraulic dam in the flume with variable curvature,the maximum velocity is not near the liquid level,the maximum velocity in the straight section is in the depth 2/5 from the bottom of the tank,and the maximum velocity in the transition and bending sections is in the depth 4/5 from the bottom of the tank.When hydraulic dams are added to the water tank,the vertical velocity of the upstream of each hydraulic dam changes very little along the direction of water depth,and the velocity distribution is uniform,while the downstream velocity of each dam varies greatly along the water depth and the size,and the location of the maximum velocity is different,and the maximum velocity of the downstream of the three hydraulic dams is negative,that is,reflux occurs.Under various working conditions,the turbulent kinetic energy decreases along the direction of water depth.The more hydraulic dams are erected in the tank,the greater the difference in water level between upstream and downstream of the last hydraulic dam.(2)Delft3D under various operating conditions on the water level in the simulation accuracy is higher,for the velocity of flow,without hydraulic dam when the working condition of the simulation value and experiment valuedegree is high,the working condition of the other three due to the existence of hydraulic dam,and the model only considering the energy loss caused by the hydraulic dam,does not take into account its due to structure change of the flow of water,so the model of average flow velocity simulation effect is better for point velocity simulation accuracy is poor.(3)When there is no hydraulic dam,the longitudinal velocity of convex bank in the section with variable curvature is much larger than that of concave bank.The riverbed is scoured in the upstream of convex bank bending top,and there is a local low velocity area in the downstream of convex bank bending top.The upper and lower reaches of the curved roof of concave bank are opposite to that of convex bank.After the hydraulic dam is added to the water tank and collapsed,the surface of the hydraulic dam together with the foundation of the hydraulic dam and the anti-scour measures form a periodic fixed bed.Compared with the situation without dam,the hydraulic dam and its upstream deposition,downstream scour,scour on the bending section has no obvious impact.However,increasing the base elevation of the hydraulic dam can reduce the downstream scour length and the scour depth and deposit thickness of the bending section. |
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