Conjunctive Regulation Of Surface Water And Groundwater With HYDRUS-MODFLOW In Arid Oasis Irrigated Land

In the inland arid oasis irrigation area of northwest China,surface irrigation water resources and groundwater resources are both important parts of water resources.Rational allocation of surface water resources and groundwater resources in the irrigation area can prevent soil salinization and promote water-saving irrigation.At the same time,it can alleviate the contradiction between water supply and demand and realize the efficient and sustainable use of water resources in irrigation areas.Therefore,the Xia-wuqu Village in Yanqi Basin,a typical arid oasis farmland,was selected as our study area.Based on the field experiments and groundwater dynamic monitoring data,the HYDRUS-1D model and the PMWIN model are used to analyze the surface irrigation scheme,groundwater resource evaluation,the definition of rational groundwater controllable key water levels in different periods of the whole year,and surface water-groundwater control scheme.The main results are as follows:(1)Considering the changes of groundwater level and irrigation frequency,and taking moisture fluctuation and soil water infiltration as evaluation index.,the optimal irrigation scheme in Xia-wuqu Village is recommended as drip irrigation for 7 times.Each time irrigates 132.85 m~3/hm~2,and the total irrigating amount is 930 m~3/hm~2,with the average groundwater level is 1051.07 m.(2)In oasis irrigation area,the main groundwater recharge is vertical recharge,the main groundwater discharge is transpiration and evaporation.The farmland infiltration recharge and canal system leakage recharge are both concentrated in April to November,and the evaporation in arid oasis irrigation area is mainly concentrated in May to August,while the drainage is mainly concentrated in January and October to December.(3)The groundwater depth for preventing secondary salinization of farmland in the northwest irrigated area shall be controlled above 1.2 m,the groundwater depth for preventing soil desertification shall be controlled within 5 m,and the limit groundwater depth of phreatic evaporation shall be controlled within 4 m.The reasonable groundwater depth of farmland in different periods is also different:the suitable groundwater depth in the spring salinization period is 1.8-3.0 m,the suitable groundwater depth in crop growth period is 0.9-2.5 m,and the suitable groundwater depth in winter salt washing period is generally 1.3-2.5 m.(4)Based on the principles of promoting water-saving irrigation area,changing groundwater level to meet reasonable groundwater controllable key water levels,and supplying and demanding water balance,the surface recharge-groundwater exploitation control scheme was designed.Besides,the groundwater controllable key water levels and the amount of groundwater resources are taken as constraints.With these constraints,the optimal surface recharge-groundwater exploitation control scheme is determined,then combined with the optimal irrigation scheme,the optimal utilization scheme between surface irrigation and groundwater exploitation based on HYDRUS-MODFLOW in the study area is finally recommended as follows:drip irrigation is used during tomato mature periods for 7 times,each time irrigates 132.85m~3/hm~2,the average groundwater level is 1051.07 m,and the annual surface water diversion is 5.9 million m~3,the annual groundwater exploitation is 675000 m~3,which means exploited well of W4,W7 and W9 exploit 69000 m~3,the rest exploited well remaining exploit 78000 m~3.