Numerical Simulation Of Flow And Mass Transport In The Downstream Of The Xiangjiang River

The construction of cascade reservoirs in natural rivers,can effectively solve the economic development demand for electricity,shipping,industrial and agricultural water and domestic water,but on the other hand,due to the manual intervention and scheduling,greatly changed the hydrological situation of the river,and may have an important impact on the material transport and water quality.Carry out study on the effect of the hub construction on the material transport is conducive to in-depth understand and awareness of the adverse effects of the development of the water conservancy project on the water environment,and to provide decision support for the reasonable scheduling and protection of the environment.River sand is one of the main raw material of the infrastructure construction.In the past 20 years,artificial sand excavation provide the guarantee of raw materials for the smooth construction of building engineering.But the lack of planning disorderly sand mining changed the bed form and lead to the river bed cutting,it will bring important influence on the water flow pattern and water level.The study on the influence of riverbed cutting on the flow pattern and material transport of river channel is helpful to regulate the artificial sand mining activities and provide technical support for the management department.In this paper,the construction and operation of Changsha comprehensive hub in the lower reaches of Xiangjiang is taken as an example,conduct research on the influence of the construction of the water conservancy project on the water movement and material transport on its' upstream of the river and tributaries.By establishing the three-dimensional hydrodynamic and mass transport model,by set the appropriate simulation scenarios,calculated the water movement and the material conveying process under typical flow conditions of the Xiangjiang urban section of Changsha before and after the construction of Changsha comprehensive hub,the influence of Changsha integrated hub on flow and material transport of the tributaries of the Liuyang river,and analyzed the influence extent and scope of hub on the upper reaches of the river and tributaries.Research shows that as the same flow conditions because of the water level and water depth increase when the hub is running the flow velocity changes,makes the material convection diffusion speed significantly reduced,the retention time of material in the study area increased significantly.The flux is small,the effect is more significant.Be aimed at the influence of Riverbed Cutting on water movement and material transport in the lower reaches of Xiangjiang,this paper based on the underwater topography respectively in 1983 and 2008,established a three-dimensional hydrodynamic model and mass transfer mathematical model of Xiangjiang downstream Xiangtan to estuary,using the same inflow conditions and downstream water level,through the set the appropriate scenario calculation and comparison,analysis the effect of riverbed cutting on flow and mass transportation of the downstream of Xiangjiang.The results show that the influence of riverbed cutting on flow state of the lower reaches of Xiangjiang is significant.Under the same flow condition the water level is significantly reduced,the flow rate is significantly slowed down,and the material stagnation time is significantly prolonged.