| Groundwater system of the irrigated district belongs to the half-natural system,as well as the water cycle is more complex due to the influence of human activities.Along with rapidly development of industrial and agricultural,water supply and demand contradictory is day by day prominent.The characteristic of underground water supply,runoff and drainage is not understand enough,and groundwater is unreasonable developed and utilize in the irrigated district.Due to these factors,the conditions of groundwater exploitation are deteriorating and the secondary disasters,such as ground subsidence,brackish water and saltwater intrusion,are produced.Therefore,the study of groundwater influence factors and the evolvement regularity of groundwater system,and ascertain the characteristics of groundwater recharge in irrigated district,they provide theoretical basis for the scientific and rational utilization and deployment of groundwater resources and surface water resources,stable and healthy development of irrigation areas and groundwater environment protection.In this paper,the Weishan irrigated district as the research object,which is the largest Yellow river irrigated area downstream,the fifth large irrigated district nationwide.According to the hydrological and groundwater data of the Weishan irrigated district,the dynamic variation characteristics and influencing factors of shallow groundwater are analyzed by the extremum method and the grey relational method.The influence factors of shallow groundwater recharge in irrigated district is studied by using the artificial isotope tracer technique.Combining Arc GIS and Visual MODFLOW software to simulate the groundwater coupling in the study area,the temporal and spatial distribution characteristics of groundwater recharge are revealed in the Weishan irrigated district.The main results of the thesis are as follows:(1)The interannual variation of shallow groundwater level in the Weishan irrigated district has periodic fluctuation,and the trend of stability,descent,uplift and stability is presented,and the variation amplitude is larger during the year.In space,the groundwater level is consistent with the change of ground elevation,which decreases from south to northeast in the Weishan irrigated district.The water level in the south and middle of the irrigated district is relatively high and stable,the water level is lower and stable in the northeast and the groundwater depth and the variation rang are large in the western and northern regions.By the Grey relational analysis,the influence of natural factors on groundwater is larger than the human factors,and the human factors on groundwater varies from region to region in the Weishan irrigated district.The upstream and middle reaches of the irrigated district are mainly influenced by surface water irrigation,and the downstream groundwater exploitation is greatly affected.Rainfall and surface water irrigation are the main factors of groundwater recharge in the Weishan irrigated district.(2)Based on the groundwater influence factors and the artificial tracer test,it is known that the average value of groundwater recharge intensity is 167.7mm/a by precipitation and surface water irrigation,which is 193.1mm/a in the irrigated district,and the supply strength of no irrigated district is 104.4mm/a.Under the same planting type,the groundwater recharge intensity is 198.6mm/a and 110.7mm/a under the condition with or without irrigation in winter wheat and summer maize,and the average value of the groundwater recharge strength is 138.3mm/a and 85.5mm/a under the same condition in cotton.The scope of the integrated infiltration recharge coefficient of the Weishan irrigated district is: 13.70%~25.33%,the mean value is 19.36%.(3)According to the hydrological geology and groundwater level and other data of the the Weishan irrigated district,the numerical model of shallow groundwater is constructed by Visual MODFLOW software,and the water balance simulation is carried out by the model.The simulation results show that the groundwater recharge quantity is 103508.2×104m3,the groundwater excretion is 106743.8×104m3,and the difference is-3235.6×104m3 It can be seen that the groundwater is the negative equilibrium state in the simulated period.The simulation results are in accord with the current situation of shallow groundwater resources development in the Weishan irrigated district.(4)By analyzing the simulated results of groundwater volume from 2000 to 2014 and different hydrological years of the Weishan irrigated district,the amount of groundwater recharge with atmospheric precipitation and surface water irrigation has decreased trend in tim e.The annual average groundwater recharge is 79104.5×104m3,and the rate of descent is-402.68×104m3.The average annual amount of shallow groundwater recharge of rivers and lateral of aquifer is 1638.8×104m3 and 107.5×104m3,respectively.The distribution of groundwater recharge is uneven during the year.In flood season(from June to September)and irrigation period(from March to May and from September to October),accounted for 87.5% of the annual replenishment,in dry season and non-irrigation periods such as(January,February,November,and December),accounted for 16.7% of the annual supply volume.In space,the groundwater recharge average of atmospheric precipitation and irrigation is 166.5mm/a in the Weishan irrigated district.The groundwater recharge rate of precipitation and irrigation water in the upstream,midstream,and downstream is larger,less and minimal,respectively,and the average is 185.6mm/a,166.2mm/a and 147.1mm/a,respectively.According to the characteristics of groundwater recharge,the paper puts forward some suggestions on the current situation and problems of water resources utilization to ensure the coordinated development of social economy and groundwater in the Weishan irrigated district. |
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