Research On The Distribution Law Of The East-West River At The Lower Reaches Of The Ganjiang River

As a common form in natural rivers,the flow movement law of branch channel is more complex than that of single river channel.Ganjiang River is the largest river in Jiangxi Province,and it is a typical branch river.The change of its diversion and sediment distribution law directly affects the shipping,flood control,water intake project and the prosperity and development of economy and society in this area.In this paper,taking the tail reach of Ganjiang River as the research object,the hydrodynamic field of the tail reach of Ganjiang River is simulated and calculated based on Mike21 numerical simulation software,and the flow movement characteristics of the tail reach of Ganjiang River and the shunt law of Dongxi River at the end of Ganjiang River are analyzed.The main research contents are as follows:1.Based on the measured data of each hydrological station and the topographic data of the tailwater section,the two-dimensional mathematical model of the water level of the tail section of the Ganjiang River is established,and the measured water level data of each water station is selected to verify the mathematical model.2.Combined with the change of the topography in the recent years,this paper simulated the water power field from 1991 to 2000,from 2001 to 2012,and from 2001 to 2012.The results show that in the period of the Poyang Lake not generating the back-back jacking effect on the tail of the Ganjiang River,The flow rate of the East River is decisive for the flow of the east and west of the Ganjiang River,and the distribution ratio of the East River increases with the increase of the flow of the outer continent,and the distribution ratio of the Xihe River decreases with the increase of the flow of the outer continent.In 1991~2000,when the flow of the outer continent is equal to 4300m3/s,the east-west flow is about 50%;in 2000~2012,when the flow of the outer continent is equal to 4600 m3/s,the east-west flow is divided by about 50%.This indicates that the distribution ratio of the Xihe River in the mid-dry-water condition has increased after 2000,which is mainly related to the man-made sand-mining activities in the Xihe River of the Ganjiang River in recent years.In this paper,a multiple regression model of the distribution ratio of the east and west river is established by the multi-element stepwise regression analysis in the time of the return of the back of the Ganjiang tail water to the Poyang Lake.The results of the model show that the main factors that influence the distributary ratio of the east-west river in the back-up period include the speed ratio of the Xihe-Donghe River,the water level difference between Nanchang and Wucheng and the water level difference between Nanchang and Kangshan.3.By sorting the annual runoff of the control station of Ganjiang River from 1957 to 2012,The results show that the outer continent flow plays a decisive role in the east-west river diversion during the period of time when Poyang Lake does not have the effect of backwater jacking on the tail reach of Ganjiang River.The diversion ratio of the East River increases with the increase of the flow rate of the outer continent,while the diversion ratio of the West River decreases with the increase of the flow rate of the outer continent.In the year of abundant water,when the discharge of the outer continent is 3900 m / s,the ratio of the east and west rivers is about 50%;in the year of flat water,when the discharge of the outer continent is 3600m3/s,the ratio of the two rivers is about 50%;in the dry year,when the discharge of the outer continent is 4700 m3/s,the ratio of the east and west rivers is about 50%.Compared with the peaceful water year in the year of abundant water,the flow of the outer continent corresponding to the equilibrium of the east-west river in the dry year increases by about 900 m3/s,which indicates that under the condition of the same flow on the outer continent,the volume of the Xihe River is the largest in the dry year,the second in the year of abundant water and the smallest in the year of flat water.During the time when Poyang Lake has the effect of backwater support on the end of Ganjiang River,the multivariate regression model of the diversion ratio of the Donghe-Xihe River is established by means of multivariate stepwise regression analysis.The results of the model show that the main factors affecting the distribution ratio of the east-west river in the period of backwater top support include the velocity ratio of the west river to the east river,the water level difference between Nanchang and Wucheng and the water level difference between Nanchang and Kangshan.