| The Naoli River Basin in the Sanjiang Plain is one of China's largest grain production bases and largest inland freshwater wetland region,which plays an important role in ensuring security of grain production and the wetland ecology.The hydrological processes of the basin have been changed significantly as a result of climate change and intensive human activities,which eventually lead to a series of ecological and environmental problems,such as streamflow decrease,groundwater level decline,shrinking of wetlands area,and so on.In addition,influence of climate change and agricultural irrigation water utilization in future,water shortage become more and more serious in the Naoli River Basin.Fortunately,Heilongjiang Province Government is planning to carry on the Songhuajiang River to Naoli River water transfer(SR-NRWT)project to solve the problem of water shortage.In view of the above problems,it is difficult to ensure the water security in the basin by considering only one of groundwater or surface water.Therefore,the study of optimal allocation of water resources based on conjunctive use of groundwater and surface water is greatly important to the sustainable utilization of water resources to coordinate with the relationship between agricultural development and wetland protection and to achieve the goals of grain security and ecological security of wetland,which is also of great significance to the development of modern agriculture and the construction of water ecological civilization in the Naoli River Basin.A coupled model combined groundwater and surface water was constructed based on hydrogeological conditions,the characteristics of hydrological cycle and the interaction between groundwater and surface water in Naoli River Basin.Then,the water resources were simulated from 2021 to 2050 by means of the coupled model and two climate scenarios of BNU-ESM database,RCP4.5 and RCP8.5.An optimal allocation model of water resources based on conjunctive use of groundwater and surface water,which was simulated by the particle swarm algorithm.The water resources was allocated based on conjunctive use of groundwater and surface water in2015,2021-2035 and 2036-2050.The results are as follow:(1)The evolution characteristics of precipitation,streamflow and groundwater levelThe observed data of precipitation,streamflow and groundwater level were analyzed based on mathematical statistics,Mann-Kendall method,singular value decomposition(SVD)and cross wavelet analysis.The results showed that the precipitation experienced insignificantly change,the streamflow all changed abruptly in the 1960s.After the abrupt change,the interannual variation of streamflow at each station increased significantly.Moreover,the decrease in streamflow during the flood season was the largest.Except for the reduction of 55.5%at the Hongqiling station,the streamflow at all other stations decreased by more than 65%.Besides,due to the influence of human activities,the dynamic characteristic of groundwater level in this basin gradually changed from the infiltration-evaporation type to coexistence of the infiltration-evaporation type and the extraction type.The groundwater level in the local monitoring wells showed a rapid decline trend of-0.59m/a.In addition,the response pattern of groundwater level to precipitation can be classified four into four types.(2)Construction of model coupled groundwater and surface waterThe interaction between groundwater and river in the Naoli River Basin is mainly divided into three types based on the relationship between groundwater level and river stage,ie,groundwater recharges river water in the upstream,river water recharges groundwater in the downstream and mutual recharge between groundwater and river water.A coupled simulation model combined groundwater with surface water was constructed based on the characteristics of hydrological factors change,the interaction between groundwater and surface water,and the model was solved by the SWAT-Modflow software.The coupled model has a better results based on the comparison of simulated and observed values of streamflow and groundwater level during calibration and validation periods.(3)Estimation of streamflow and groundwater recharge based on different climate scenarios in the Naoli River BasinThe water resources were assessed based on the coupled model and data of future climate change scenarios.Under the RCP4.5 scenario,the annual average streamflow in the Naoli River Basin are 20.78×10~8m~3 and 22.00×10~8m~3 during 2021-2035 and 2036-2050,respectively.The annual average groundwater recharge are 18.38×10~8m~3 and19.42×10~8m~3,respectively.Under the RCP8.5 scenario,the annual average streamflow are 15.35×10~8m~3 and 22.95×10~8m~3,respectively.The annual average groundwater recharge are 13.97×10~8m~3 and 20.05×10~8m~3,respectively.(4)The results of optimal allocationAccording to the sequence of water supply for ensuring the water demand of life,domestic,industry,ecology and agriculture,the water resouces was optimally allocated based on conjunctive use of groundwater and surface water.1)The results of optimal allocation in 2015After optimized allocation,there is no water shortage in the life and industry,and the water shortage of agricultural irrigation is 15.98×10~8m~3.Compared with before the optimal allocation,the extraction of surface water was reduced by 0.38×10~8m~3.The water shortage in the Qixinghe reserve was 0.34×10~8m~3 before the optimal allocation,and then there is no shortage of water in the reserve after optimal allocation.In addition,there is no water shortage before and after optimal allocation of water resources in Naolihe Reserve.2)The results of optimal allocation of water resources in 2021-2050(1)Scenario 1:The current water supply capacity of hydraulic engineering,0.53of surface water irrigation coefficient and 0.9 of groundwater irrigation coefficient will all remain unchanged from 2021 to 2050.Four schemes are set up based on the supply and remand of water resources in RCP4.5 and RCP8.5 climate scenarios and the water supply planning for Longtouqiao reservoir.According to the results of optimal allocation of four schemes,there is no water shortage in the life and industry.The average annual water shortages of agricultural irrigation are 16.46×10~8m~3,24.95×10~8m~3,18.85×10~8m~3,and 24.64×10~8m~3,respectively.The annual average water shortages in the wetland reserve are 0.89×10~8m~3,0.61×10~8m~3,1.76×10~8m~3 and0.65×10~8m~3.(2)Scenario 2:The surface water irrigation coefficient will increase to 0.6 and the0.9 of groundwater irrigation coefficient will all remain unchanged during 2021-2050.The current water supply capacity of hydraulic engineering also remain unchanged in2021-2035.The objection of water supply for the Longtouqiao Reservoir is adjusted and the SR-NRWT project is applied in 2036-2050.Four schemes are also set up based on above factors.According to the results of optimal allocation of four schemes,there is no water shortage in the life and industry.The average annual water shortages of agricultural irrigation are 16.26×10~8m~3,5.09×10~8m~3,18.55×10~8m~3 and 5.03×10~8m~3,respectively.The annual average water shortages in the wetland reserve are 0.88×10~8m~3,0 m~3,1.73×10~8m~3 and 0 m~3.In addition,the average annual and absolute water transfer is 19.62×10~8m~3 and 19.35×10~8m~3,and the largest water transfer is 23.99×10~8m~3 for irrigation,by the SR-NRWT project at scheme 2 and scheme 4.Simultaneously,the average annual water transfer is 0.66×10~8 m~3 and 0.64×10~8 m~3,and the largest water transfer is 6.20×10~8 and 5.67×10~8m~3 by the SR-NRWT project for wetland reserves at scheme 2 and scheme 4,respectively.In summary,the results will provide scientific and technological support for the sustainable utilization of water resources in the Naoli River Basin,and may also be used as a guide for the water resources dispatch of SR-NRWT project,and then support the sustainable development of agriculture,wetlands and social economy in the Naoli River Basin. |
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