Effect Of Saline-Alkali Land Improvement Project On The Dynamic Time-Space Evolution Of Groundwater And Numerical Simulation In Hetao Irrigation Area

As the main environmental factor of soil salinization and soil secondary salinization in Hetao Irrigation Area,groundwater has an important influence on the formation of saline-alkali land in Hetao Irrigation Area.In 2018,Wuyuan County,Bayannaoer City,launched a 50,000-mu demonstration project of "changing salt and increasing grass(feeding)to promote animal husbandry".Soil salinity improvement is carried out in the area,and with the implementation of soil salinity improvement,the groundwater environment is inevitably affected.Aiming at the impact of soil salinity improvement on groundwater environment,this thesis takes the whole area of the 50,000 mu demonstration project as the research object,and studies the temporal and spatial evolution law and influencing factors of groundwater environment under the background of soil salin ity improvement and the influence of irrigation on the characteristics of groundwater ions.On this basis,a reliable groundwater numerical model and groundwater prediction model of the study area are established by using the Visual Modflow model,and the future groundwater table and the impact of different irrigation levels on the groundwater table in the study area are predicted.The main research conclusions are as follows:(1)Groundwater burial depth in the study area decreased with the progress of soil improvement,and the annual average buried depth of groundwater after the improvement was stable at about 1.63 m,Compared with that before soil improvement,it is reduced by about 0.4 m.After soil improvement,the effect of irrigation and leaching of soil salinity and drainage effect of open ditches were strengthened,and groundwater salinity increased significantly.Among them,groundwater salinity increased by 0.59 g/L in the early stage of improvement;groundwater salinity increased by 0.8 g/L;in the later stage of improvement,groundwater salinity increased by 1.2 g/L.(2)After spring irrigation,the TDS of groundwater increases as a whole,with an average increase rate of 15.6%.The main factors affecting groundwater components are not only rock weathering and evaporative crystallization,but also cation exchange.(3)The groundwater in the study area is in negative equilibrium as a whole.The main factors affecting the groundwater recharge in the study area are the channel and irrigation infiltration,which accounted for 66.99% and 55.67% in the identification period and verification period respectively,affecting the groundwater in the study area.The factor of excretion is the combined effect of open ditch drainage and evaporation.The p roportion of open ditch drainage in the identification period and verification period is 26.95% and26.31%,respectively,and the proportion of evaporation in the identification period and verification period is 31.99% and 26.31%,respectively.47.09%.(4)According to the prediction model,the change of groundwater table in the study area in the next 10 years is predicted: without changing the irrigation program and planting structure,the groundwater table will be basically stabilized at the level after saline-alkali improvement.(5)When the irrigation amount in the study area is 90% and 80%,the groundwater can reach a new dynamic balance in the future.Combining the influence of different irrigation amounts on the groundwater table depth and factors such as reducing the irrigation water amount of the Yellow River,when the irrigation water amount is 80%,it can not only reduce the Consumption of Yellow River water,and can control the buried depth of groundwater after irrigation,to achieve the purpose of increasing crop water use efficiency and reducing salinity stress.