| The Hanjiang-to-Weihe River inter-basin water transfer project is located across the Yellow River and the Yangtze River.The purpose of its construction is to introduce high-quality Hanjiang River water into the Guanzhong area,create basic conditions for ecological construction and environmental protection in the Guanzhong area,and provide water resources for the economic development of the Guanzhong area and the specific implementation of the national strategy in Shaanxi.However,there are situations such as consistent drought conditions in the water-receiving areas of the Hanjiang-to-Weihe River project and the synchronization of high and low inflows.Therefore,in the case of fully meeting the water use of the Middle Route Project of the South-to-North Water Transfer Project and the middle and lower reaches of the Hanjiang River Basin,how to avoid the occurrence of extreme water shortage events and reasonably allocate water to the Guanzhong area is particularly important.The purpose of this paper is to give full play to the limiting role of the reservoir ’s graded and phased drought limit water level,through the redistribution of reservoir water volume,reduce the depth of damage caused by drought and water shortage,and improve the reliability of water supply.The main research contents include the construction and drought evaluation of the Comprehensive Drought Index(CDI)in the water receiving area of the Hanjiang-to-Weihe River Water Diversion Project,the joint simulation operation model of the two reservoirs,the study of the reservoir classification and staging drought limit water level model based on the reverse recursive method and the reservoir classification and staging drought limit water level model based on the optimization idea.The research results not only provide technical reference for the construction of water diversion model of Hanjiang-to-Weihe River Water Diversion Project,but also increase the reliability of water supply in continuous drought years.The specific research conclusions are as follows:(1)Based on the Copula function combined with precipitation and runoff data,the comprehensive drought index(CDI)of the project regulation and water receiving areas was constructed.Through drought evaluation,the results showed that the comprehensive drought index of the project regulation and water receiving areas showed a downward trend with time,indicating that the drought had a non-significant increase trend.At the same time,the drought in the water transfer and receiving areas mostly occurred from November to June,and there was no drought from July to October.From 1994 to 2001,the drought in the water transfer and receiving areas of the project occurred simultaneously,and the drought degree was serious.(2)Based on the long sequence annual runoff process of Huangjinxia and Sanhekou reservoirs,the least square approximation method is used to obtain that the wet year of the Hanjiang-to-Weihe River Water Diversion Project is 1958,the normal year is 2009,and the dry year is 1997.According to the water transfer rules of the project,a simulation scheduling model(model 1)is established.Through the analysis of water transfer under different scenarios,it is found that the Hanjiang-to-Weihe River Water Diversion Project can meet the multi-year average water transfer target of 1 billion m3 with or without the restriction of the Yangtze River Commission.At the same time,under the multi-year average water transfer target of 1.5 billion m3 without the restriction of the Yangtze River Commission,the annual water supply guarantee rate reaches 92.8%,and the water transfer process is better.In the case of multi-year average water transfer of 1.5 billion m3 under the restriction of the Yangtze River Commission,the frequency of water shortage is higher,and the water shortage is the most serious in 1997.The depth of water shortage damage is large,the water shortage rate is as high as 54.42%,and the depth of water shortage damage is large.The multi-year average monthly precipitation,multiyear average monthly reservoir inflow and multi-year average monthly potential evapotranspiration are selected,and the Fisher optimal segmentation method is used to divide the drought period of Sanhekou Reservoir.The staging result is:T1=[July-September];T2=[October];T3=[November-March];T4=[April-June].(3)Based on the above drought stages,the inverse recursive method was used to determine the drought limit water level of the Sanhekou Reservoir,including the drought warning water level:602.86 m from July to September,608.70 m in October,608.51 m from November to March,and 575.70 m from April to June;the drought water level is 602.00 m from July to September,607.96 m in October,606.79 m from November to March,and 573.64 m from April to June.According to the conditions of water inflow in the water transfer area,the limited water volume of the Long Committee and the water demand in the water-receiving area,the SUI(Start Up Index)is constructed.By comparison,it is found that the SUI index corresponds to the drought identified in the drought assessment and the water shortage in the model 1,which verifies the rationality of the SUI index as the starting condition of the drought limit water level.The scheduling model(Model 2)was established and solved by coupling the staged drought limit water level.It was found that in the long series of scheduling results,compared with Model 1,the average water shortage rate of Model 2 increased by 3.51%,but in 1957,1972,1978,1998 and 2007,the water shortage rate of Model 2 scheduling results decreased to varying degrees.In the typical year scheduling results,the water supply,power generation,power consumption and net income of Model 1 and Model 2 are exactly the same in the wet year and the normal year.In the dry year,the water supply of Model 2 increases,the water shortage index decreases by 6.09%,and the net power generation and income decrease by 454 million kW·h and 222.8 million yuan respectively.In the scheduling results of continuous drought years,the average water shortage rate of Model 2 increased by 9.48%compared with Model 1,while the standard deviation of water shortage sequence decreased by 3.66%.In summary,it shows that the use of graded and phased drought limit water level can reduce the occurrence of serious water shortage events,reduce the depth of water shortage damage,and the water supply process tends to be uniform.(4)Based on the optimization idea,the objective function is to minimize the water shortage index and maximize the production benefit,and the optimal operation model(model 3)is established and solved by coupling the reservoir classification and stage drought limit water level.It is found that in the long series of operation results,the average water shortage of model 3 is 114.4 million m3,and the average water shortage rate is 7.63%.Compared with model 1 and model 2,the average water shortage rate of model 3 is increased by 0.645%and decreased by 2.76%respectively.In the typical year scheduling results,in terms of water supply:the three models of the wet year and the normal year,the performance is better,can fully meet the water transfer,and the dry year still can not meet the water supply,but with the use of the classification and staging of the drought limit water level and the optimization of the model,the depth of water shortage is decreasing;net income:the three models are the worst in the normal year,and also lower than the dry year.In the scheduling results of continuous drought years,the standard deviations of water shortage sequences of the three models are 2.46,2.37 and 1.90,respectively.Compared with models 1 and 2,the standard deviations of model 3 are reduced by 22.76%and 19.83%,indicating that the water supply process of model 3 tends to be more uniform.In summary,the optimized grading and staging drought limited water level is more reasonable to limit the water supply demand,increase the reserved water volume,reduce the depth of water supply damage in dry years,and the water supply process is developing towards’wide and shallow’. |
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