| In large-scale irrigation areas in arid and semi-arid areas in Northwest my country,surface water sources cannot meet the needs of agricultural development,production and life.Groundwater has become the main water source to meet the needs of production activities in the irrigation areas,resulting in significant reduction of groundwater and long-term failure to restore and replenish.When droughts continue to occur,the amount of natural replenishment from precipitation is reduced,and the contradiction between water supply and demand becomes more prominent,making agricultural water use often unsatisfied,which has a huge impact on agricultural production,often resulting in reduced or even no harvest of grain,which seriously affects the local economy.Social development.For this reason,reasonable allocation of the limited water resources in the region is one of the effective ways to solve the above problems and maximize the benefits of water resources.The Jinghuiqu Irrigation District in Shaanxi Province is a typical canal and well combined irrigation area.In the early stage of meteorological drought,water diversion from the Jing River can be used to deal with drought,and the continuous occurrence of drought can use groundwater as an emergency drought-resistant water source to alleviate the adverse effects of drought.Therefore,in this study,the Jinghuiqu irrigation area and the upper reaches of Zhangjiashan of the Jing River were selected as the study area,and the surface water SWAT and groundwater model MODFLOW were constructed.Finally,a multi-objective coupling simulation optimization model was constructed based on FloPy-Pymoo,and the limited surface water Reasonable allocation of groundwater that can be used for drought and emergency response can not only effectively alleviate the contradiction between water supply and demand during drought periods,reduce the adverse economic and social impact of drought,but also provide technical support for the sustainable,efficient and safe use of water resources in irrigation areas.The research has reached the following conclusions:(1)The intra-annual and inter-annual changes of rainfall,temperature,and evaporation in Jinghuiqu Irrigation District pointed out that the precipitation in the irrigation area is showing a downward trend,while the temperature and evaporation show an upward trend.60%of precipitation and 53%of evaporation are concentrated in the flood season 6-9 Months,and the temperature is above 19℃.The inter-annual variation of Jinghe River surface water and groundwater in the irrigation area pointed out that the annual runoff of the upper Jinghe River Basin,the amount of water diversion from agricultural irrigation at the head of the canal,and the amount of groundwater that can be extracted show a downward trend.There will be continued shortages,causing the groundwater level in some areas to continue to drop.The SPI index is used to reflect the drought situation,indicating that the irrigation area is under the threat of drought for a long time,and the impact is increasing year by year.(2)In the Jing River Basin,a distributed runoff and sediment yield model was constructed using SWAT,sensitivity analysis of various parameters,and coefficient of determination(R~2),Nash coefficient(NSE)and coefficient of deviation(PBIAS)were selected to evaluate the accuracy of the model.The results show that the monthly runoff simulation rate is regularly R~2=0.89,NSE=0.89,PBIAS=1.3,the validation period is R~2=0.88,NSE=0.85,PBIAS=2.5,and the daily runoff simulation rate is regularly R~2=0.63,NSE=0.63,PBIAS=3.3,R~2=0.61,NSE=0.58,and PBIAS=12.8 in the validation period.This runoff model is suitable for the Jing River Basin and can describe the runoff generation process in the study area.In addition,the sediment is simulated.The monthly sediment simulation rate is R~2=0.80,NSE=0.77,PBIAS=-33.7,and R~2=0.87,NSE=0.86,PBIAS=-26.9 in the validation period.This sediment model is suitable for Jing river basin can describe the sediment production process in the study area.(3)In the Jinghuiqu irrigation area,GMS’s MODFLOW was used to construct a groundwater flow model,and the applicability of the model was tested.The results show that the built model has a good simulation accuracy,a good fit for the dynamic changes of the groundwater level,and can describe the changes of the groundwater level in the irrigation area.Finally,import the MODFLOW model of Jinghuiqu irrigation area into the Python version of the MODFLOW model Fol Py,and modify the subroutine WEL module through FloPy programming to make the subsequent water resources configuration more in line with the actual situation of the irrigation area.(4)With the goal of maximizing crop yields,minimizing average groundwater depth,and maximizing economic benefits,based on the genetic algorithm NSGA-Ⅲ,the FloPy-Pymoo water resources simulation optimization coupling model for irrigation districts is constructed to realize the dynamic exchange of data between the optimization algorithm and the simulation model.The constructed multi-objective coupling simulation optimization model is suitable for solving the multi-objective and multi-constrained water resources optimization allocation problem.It can provide solutions according to the needs of different decision makers,that is,when the maximum crop yield is met during the drought period,the winter wheat irrigation water is given priority,The water consumption ratio of canal wells is 0.9;when the average cumulative drawdown of groundwater is met,the irrigation water of fruit trees is given priority,and the water consumption ratio of canal wells is 1.26;when the economic benefit is the greatest,the irrigation water of summer corn and fruit trees is given priority,and the water consumption of canal wells The ratio is 1.07.(5)According to the set of two changing environmental scenario data(A2 and B2),run the validated SWAT model to calculate the surface water volume of the Jing River.After FloPy calls the SWAT calculation value,it couples with Pymoo to calculate the water resource allocation in each region in the drought year of 2020s.Changes in conditions and groundwater levels.The results show that the groundwater level under the two scenarios in 2020s has a downward trend.The average decline in the A2 scenario is greater than that in the B2 scenario,and the decline in the groundwater level gradually decreases from northwest to southeast.Under the A2 scenario,the minimum groundwater level drop of each observation well is3.98m,2.69m,4.03m,0.65m,all of which are option two;the largest drop of groundwater level is 8.37m(the first option of observation well 1),11.36m(Option 1 of Observation Well2),4.47m(Scheme 3 of Observation Well 3),5.06m(Scheme 3 of Observation Well 4);the minimum groundwater level drop of each observation well in the B2 scenario is 6.48m,1.87m,4.12m and 0.74m,all of which are in Option Two;the largest drop of groundwater level is7.95m(Scheme 1 of Observation Well No.1),8.85m(Scheme Three of Observation Well No.2),4.53m(Scheme 3 of Observation Well No.3).Plan 3),4.84m(Plan 3 of Observation Well No.4).After reasonable allocation of the limited water resources in the two scenarios,the output of the three scenarios in A2 decreased by 0.73%,9.28%,and 0.49%per mu,respectively,compared with 2013,and the three scenarios in B2 decreased per mu respectively.1.26%,0.88%,1.21%;compared with 2013,the economic benefits of the three programs in A2 decreased by 2.34%,9.83%,and 0.25%per mu,respectively,and the three programs in B2 decreased by 1.17%and 1.13 per mu,respectively%,1.02%. |
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