Temporal And Spatial Characteristics And Driving Mechanism Of Groundwater Level In Typical Middle And Lower Reaches Of The Yellow River Irrigation District

Groundwater is an important component of water resources,which is playing a crucial role mainly in protecting domestic water for urban and rural residents,maintaining socio-economic development and ecological balance.As the natural intervention made by human activities is increasing significantly,groundwater circulation systems are becoming more and more complicated,dynamic change of groundwater level starts to possess new characteristics,how to understand the law of groundwater circulation under the varying conditions is one of the hot and difficult problems in hydrogeology study.People's Victory Canal Irrigation District is located in the middle and lower reaches of the Yellow River,drawing water conditions is relatively good.Irrigation district has more than 60 years development history,developing gradually from the initial gravity irrigation agriculture to the urban and rural industry,domestic water and other multi-functional water areas.With the socio-economic development,the water consumption of all regions and departments increases,and the contradiction between supply and demand of Yellow River water resources is becoming intensely.Since drawing Yellow River water into irrigation district is limited,well water for irrigation has become an important source of irrigation water,which leads to the variation of groundwater systems in irrigation district.It is beneficial for revealing regional differences in groundwater level and also favorable for providing reference for the rational use of groundwater resources,protecting the ecological environment about irrigation district,and achieving sustainable utilization of water resources by studying temporal and spatial characteristics and driving mechanism of groundwater level evolution.The main research contents and results in this paper are as follows:(1)Based on People's Victory Canal Irrigation District from 1993 to 2013 measured water level data,we analyzed spatial and temporal variation of groundwater level.The result showed: The study area groundwater level shows annual decline trend,the decline ranges of groundwater only vary in different locations;the distribution features of the irrigation area ground water level is high in the west and is low in the east,groundwater level rise area shows a decreasing trend within the scope of the study area,groundwater level falling area shows an increasing trend,and the cumulative decline of the groundwater level is increasing.(2)Based on the accumulative anomaly,Mann-Kendall trend analysis method and so on,we analyzed the trends of various factors,using correlation analysis to get the relationship between groundwater level and the influencing factors,also analyzed the dominant factors which affect the evolution of the groundwater level by using principal component analysis and gray correlation degree method.The result showed: Groundwater level decrease with decreasing rainfall,groundwater level decrease with the decrease of the amount of irrigation canal,groundwater level decrease with the increase of well irrigation water,domestic and industrial water consumption;human activity(well irrigation water,domestic and industrial water consumption)plays a main role in the process of groundwater dynamic variations,which means that groundwater exploitation is the main driving factor for variations of groundwater level in irrigation district.(3)We use Visual Modflow4.2 software to build a dimensional unsteady flow model of groundwater in irrigation district.Based on the simulation results,which are from Nor ESM1-M model in RCP4.5 scenario,as input items of climate variation,existing experimental data to predict the amount of groundwater exploitation from 2014 to 2030,on this basis,assuming that the same amount of exploitation,exploitation increased by 20%,exploitation decreased by 20% as three scenarios,we predicted variation of the flow field in 2020 and 2030 in People's Victory Canal Irrigation District,and made a reasonable program of regulation.The results showed: Predicting exploitation trend increased significantly from 2020 to 2030,groundwater level is downward trend in irrigation district,local groundwater over exploited,funnel area range extend to the north,and appeared a new funnel center;if exploitation increased by 20%,groundwater level declined overall,funnel area significantly expanded,landing amplitude increases,level contour becomes dense;if exploitation decreased by 20%,ground water level rose overall funnel area significantly reduced,landing amplitude decreases level contour becomes sparse;irrigation district is divided into appropriate exploitation area,restricted exploitation area and groundwater recovery area,the exploitation of appropriate exploitation area could be increased by 20448m~3/d,the well-irrigation area could be increased by 5.1 ten thousand mu,the exploitation of restricted exploitation area should be controlled under 161936m~3/d,irrigation area should be controlled under 40.1 ten thousand mu,in groundwater recovery area,new wells are prohibited,old wells production is controlled strictly,and it can make underground water level gradually pick up.