| Rivers in mountainous areas have a large water level difference and are rich in hydropower,but there are some factors that are not conducive to navigation,such as large specific gradient,fast flow speed and many beach risks.In order to meet the needs of power generation and shipping,cascade development of water control projects is often used to achieve the goals of power generation and shipping.After the project is completed and impounded,it will intercept a large amount of sediment in the upstream river,which may cause significant changes in the water and sediment conditions in the downstream river,and the natural waterway and the original waterway regulation project will face new water and sediment conditions.Therefore,it is of great significance to study the applicability and optimization measures of waterway regulation project under the new water and sediment conditions in view of the possible navigation obstruction caused by the sudden change of incoming water and sediment caused by cascade development of rivers in mountainous areas.A large number of practical engineering results show that the original balance of water and sediment in the downstream of the hub will be broken under the new water and sediment conditions,which will weaken the effect of previous waterway regulation projects and produce new navigation obstacles.Nujiang River is a natural mountain river with great shipping development value in Yunnan Province.Recently,the waterway regulation project has been studied in the middle and lower reaches of Menggu Ferry to Hongqi Bridge,which is about 114.5km long.In addition,the Nujiang River is planned to have cascade development in the long term.Therefore,this thesis takes Mangdan Beach,a complex beach in the middle and lower reaches of the Nujiang River,as the research object.Through two-dimensional numerical simulation of water and sediment,the channel regulation is studied according to its beach risk characteristics and navigation obstruction characteristics.Considering the long-term effect of the regulation project and the reduction of incoming sediment caused by the long-term cascade development,the river bed evolution law and the applicability of the channel regulation project are studied.By collecting and studying hydrological and sediment data and prototype observation data,this thesis analyzes the current hydraulic factors such as water level,velocity,flow direction and sediment concentration in Mangdan Beach,section,studies its flow characteristics by using a two-dimensional hydrodynamic numerical model,and puts forward a waterway regulation scheme that meets the shipping requirements of Mangdan Beach,by taking the flow conditions and ship beach parameters as evaluation indexes.The sediment in the upper reaches of Mangdan Beach,is bound to decrease significantly after the completion of the hub.Two-dimensional water and sediment numerical simulation is used to simulate the changes of sediment erosion and siltation before and after the Mangdan Beach,project.By comparing the changes of sediment erosion and siltation in the first,third,fifth and tenth years with the navigation index,it is studied whether the navigation in the upper reaches will be blocked by ships within 10 years after the completion of the upstream hub,and some optimization suggestions are put forward to ensure the long-term and effectiveness of the regulation scheme. |
