| China is rich in shoreline resources,which have both economic and ecological attributes,and play an important role in economic development and river ecological environment,so the protection of shoreline resources is particularly important.Spur dike,as a common hydraulic structure for shoreline protection and river regulation,has been widely used in large and small river basins in China,and has achieved good results in a certain historical period.However,in the new environment,some spur dike functions are limited,and frequent accidents and damages of spur dike can not give full play to its estimated effect,To a certain extent,it will also restrict the efficient use of shoreline and have a negative impact on the river ecological environment.Therefore,it is necessary to carry out ecological transformation on some existing spur dikes.In this paper,the local flow characteristics of river spur dike and its ecological transformation are studied by means of measured data analysis and numerical simulation(1)This paper analyzes the current situation of spur dikes in typical reaches of main rivers(Yangtze River and Yellow River)in China.It is found that the current water and sediment conditions and the construction of spur dikes have undergone great changes.In addition,some built spur dikes are in frequent danger and the dam body damage is not optimistic.The equivalent effect of protecting the shoreline and stabilizing the river regime can not be fully exerted,and the role gradually weakens,It is the general trend to carry out ecological transformation for some spur dikes.(2)The two-dimensional hydrodynamic mathematical model is used to simulate the flow characteristics of two different permeable groins,which provides ideas for the renovation of groins in the middle and lower reaches of the Yangtze River.The results show that the effect of slow flow and sedimentation of hydraulic plug-in permeable groins is better than that of pile permeable groins with the same permeability,and the effect of slow flow and sedimentation of hydraulic plug-in permeable groins with 20%permeability is the best;The slow flow effect of non submerged permeable groins is better than that of submerged permeable groins;When the number of permeable holes is 2,the slow flow effect of spur dike is the best,and the velocity uniformity is also good;With the increase of spur dike length,the influence scope and effect of spur dike on river velocity and water level are increasing.The selection of spur dike length should be combined with the actual situation of the project.(3)Taking LiuXu bend in the middle and lower reaches of the Yangtze River as an example,the flow velocity,water level and backflow of the current spur dike,the demolition spur dike and the ecological transformation spur dike under different flow levels are analyzed by using mathematical model.The results show that the demolition spur dike and the ecological transformation spur dike have little influence on the water level,and the water level in most waters changes within 1cm;The results show that the flow pattern of the spur dike is more straight after the removal of the spur dike and the ecological transformation of the spur dike;After the two schemes,the flow velocity at the groin head and berth 5 increases,but generally speaking,the influence degree and scope of the ecological transformation scheme on the flow velocity are less than that of the direct demolition scheme;Both the removal of spur dikes and the ecological transformation of spur dikes can improve the backflow phenomenon between spur dikes,but the flow velocity in the backflow area is still large after the removal of spur dikes,which is not conducive to wharf operation.After the ecological transformation of spur dikes,the backflow flow flow is significantly reduced,and the flow velocity is weakened,which is conducive to the stability of the riverbed in the backflow area and wharf operation,and is more conducive to fish habitat and more eco-friendly. |
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