The Impact Of The River-lake Relationship Changes On The Hydrological And Hydrodynamic Conditions Of Poyang Lake

Firstly,based on the empirical formula and the statistic method,this paper studies the relationship between the Yangtze River and Poyang Lake,establishes the water level-discharge relationship of Hukou station,which is the intersection of the Yangtze River and Poyang Lake.And then,the author discusses the water storage capacity of the lake and its critical state.Also,from the perspective of the energy,the author reinterprets the principle of the river-lake relationship and constructs a new index for expressing the relationship.Secondly,on the basis of the foregoing research,a two-dimensional mathematical model of Poyang Lake was established by MIKE 21 software.The temporal and spatial changes of hydrological and hydrodynamic conditions of Poyang Lake are quantified by analyzing simulations of different scenarios.The main conclusions are as follows:i.Flows from the mainstream of the Yangtze and the lake basin are the main driving factors for the change of the river-lake relationship,and they affect Qo(the outflow of Hukou station)and the amount of water in the lake,by changing Zhx(the water level difference between Hukou station and Xingzi station)and Zh(the water level of Hukou station).When Qi(the inflow from the lake basin increases),Zhx increases and Qo increases too.When Qy(the flow from the mainstream of the Yangtze River)increases,Zh increases,while Zhx and Qo decrease.When Qi increases by 500 m3/s,Zx(the water level of Xingzi station)increases by 0.04-0.18m,and the lake volume increases by 1.1-9.3 billion m3.When Qy increases by 500 m3/s,Zx increases by 0.06?0.28m,and the lake volume increases by 2.2?8.4 billion m3.ii.The process of the water storage of Poyang Lake is always approaching the zero storage.And the water storage is not only related to the inflow from the lake basin,but also closely related to the blocking effect of the Yangtze River.The critical water level is a characteristic index of the change of water storage capacity of the lake,which is determined by the flow from the river basin and the lake basin and the section shape of Hukou station.After the operation of the Three Gorges Dam,the critical level and the water storage capacity are affected obviously because of the change of the annual flow process.Compared with before the impoundment of the Three Gorges Dam,the amount of water in the lake increases by approximately 47.7%in May,but decreases by approximately 49.4%in September.iii.Based on the theory of energy,the relationship between the Yangtze River and Poyang Lake is reinterpreted,and the change of the water level and discharge at Hukou station could be considered as the result of the balance between the energy of the flow from the river basin and the lake basin.Besides,a new index for expressing this relationship is established.The result shows,the river effect is strong in 1980s,while the lake effect is strong in 1970s.Because of the operation of the Three Gorges Dam,the river effect is slightly enhanced in dry season,but weakens obviously at the end of flood period.iv.Changes in the relationship between the Yangtze River and Poyang Lake will trigger the response of the hydrodynamic conditions in the lake,which shows obvious spatiotemporal diversity.The effect of river-lake relationship changes on the conditions in the lake will not be instantaneously spread to the entire area.There are time-space transfer processes and the area influenced is limited.And they are affected by the degree of the river-lake relationship changes and the state of the water level in the early period of the lake.v.Because of the operation of the Three Gorges Dam,the flow of the mainstream of the Yangtze River is adjusted in the year,which increases in dry season and before the flood period,but decreases at the end of the flood period.Along with the river bed degradation in the middle and lower reaches of the Yangtze River,the dry season appears ahead of time and is prolonged,also the exposed area of beaches expands.However,due to the influence of the climate changes and human activities,the flow from the lake basin will increase,which will effectively relieve these adverse effects.