Research On The Impact Of Cascade Reservoir Group Dispatching On Runoff Process

The Yalong River Basin is rich in water energy resources.Based on the principles of rational utilization and orderly development,a number of water conservancy and hydropower projects have been constructed in a cascade development plan,which has produced significant flood control and profit benefits.With the increase of reservoirs in Yalong River,the disturbance to natural runoff has become more severe,which has significantly changed the process of runoff.Under the background of the cascade reservoirs operation influencing the hydrological cycle,this paper carries out the influence of the reservoir group dispatching on the runoff process in Yalong River,based on the evolution law of the water cycle elements in the Yalong River basin and the influence of the cascade reservoir operation mode on the runoff process.The main research work and results of the thesis are as follows:(1)Through the tendency rate method,M-K test method,Sliding-t test and Kriging interpolation method,the variation law of hydrological factors such as temperature,precipitation,evaporation and runoff in the basin has been analyzed in recent decades.It is found that the annual average temperature of the Yalong River Basin in 1961-2010shows a significant rising trend,and the rising trend of annual average precipitation and evaporation is not significant.The runoff from 1958 to 2017 shows a decreasing trend,which may be caused by the evaporation increment rate being greater than the precipitation increment rate and the operation of the cascade reservoirs.The temperature mutated in 2001,and the mutation points of precipitation and runoff were in 2005.The average annual temperature,precipitation and evaporation have gradually increased from northwest to southeast of the basin.(2)By constructing the SWAT model of the Yalong River Basin,the runoff processes of the operation of Jinping I,Jinping II and Guandi dams and without dams were compared and analyzed.It is found that after the operation of the three reservoirs,the water volume in the flood season of the Yalong River Basin in 2015-2016 is reduced by 44.4%,and the water volume in the non-flood season is increased by 70%.(3)Through numerical simulation experiments,this paper quantitatively analyzed the effect of cascade reservoir group operation on runoff process under the five reservoir combination scenarios,and attempts to reach a certain universal conclusion.It is found that the cascade reservoir group dispatching tends to homogenize the runoff process,mainly because the reservoir group impounds the water volume to reduce the runoff during the flood season and supply the river water during the non-flood period.In the Yalong River basin,when the daily regulation reservoir is located upstream of the annual regulation reservoir,it has a better regulation effect on the runoff during the flood season.When the annual regulation reservoir is located upstream of the daily regulation reservoir,it has a better regulation effect on the runoff during non-flood season.The reservoir regulation capacity and reservoir capacity have a certain statistical law:for every 100 million m~3 of flood control capacity,the maximum 3-day runoff decreasing 18-57 million m~3,and the annual maximum 1-day flow decreasing 45.5-159.6 m~3/s,which is postponed for 1.3-5 days,and the minimum 30-day average flow decreasing 5.1-34.2 m~3/s.In the water-rich watershed,it is suggested that the reservoir capacity can be appropriately increased to improve its regulation performance.When the joint operation of the two reservoirs is proposed in the water-rich watershed,it is recommended to build the small reservoir upstream of the large reservoir.(4)Through the method of precipitation reconstruction,the influence of cascade reservoir group dispatching on runoff during flood season is analyzed under different precipitation characteristics.It is found that the runoff formed by the precipitation of precipitation center in upstream and large amount of precipitation,the reservoir regulation effect is better.However,under the large amount of precipitation,the postponement of the annual maximum daily flow of the reservoir is limited.