Study On The Evolution Of Groundwater In Jiuquan East Basin

In the past 60 years,the amount of groundwater resources has changed in time and space,and the amount of groundwater resources in plain areas has been declining.In northwest inland arid region,rainfall is scarce and surface water resources are scarce.In recent years,the development of human economic activities has set higher requirements on water resources and quality.Therefore,groundwater plays a particularly important role and even becomes the only water source in some regions,and plays an irreplaceable role.Jiuquan East basin is located in the northwest of Gansu province,central Hexi Corridor.groundwater has become an important water source mode in Jiuquan East Basin because of the wide spatial distribution and convenience.Therefore,the analysis of groundwater evolution in this area is very importance to people's life and economic development.This paper analyzes the groundwater system characteristics of Jiuquan East Basin based on the system theory and previous research results.Combined with the collected groundwater level and hydrochemical dynamic monitoring data,rainfall,runoff and other data,through the analysis of groundwater dynamics and groundwater chemistry,the following results are obtained:(1)Find out the type and direction of groundwater.The groundwater in the study area is divided into diving and confined water,with Jiuquan County-Xiaheqing Farm as the boundary.The diving water aquifer is mainly sand and gravel,the confined water aquifer is mainly sand and gravel,and the local section is mainly sand.The groundwater level is generally high in the south west and low in the north east.Part of the groundwater flows from Jiuquan City to Yuanyangchi Reservoir,and part flows from the south west to the north east and flows into Heihe River.The depth of groundwater table and the hydraulic gradient decrease along the direction of groundwater flow.(2)The groundwater level in the study area is mainly affected by rainfall,river runoff,artificial exploitation,irrigation and evaporation.By analyzing the influencing factors and characteristics of water level changes,the water level dynamics can be divided into river hydrologic type,runoff type,runoff-exploitation type,infiltration-exploitation type and evaporation type.(3)Revealed the dynamic change rule of groundwater level.By comparing and analyzing the groundwater level at the beginning and the end of 2018,it is concluded that most of the groundwater level in 2018 is in a weak rising.Based on the time series analysis of groundwater level of 37-1 monitoring well from 1988 to 2009,it is found that the water level is generally in a downward trend,and the change of water level has gone through three stages,which may be related to the periodic changes of rainfall and artificial exploitation in the area.The grey GM(1,1)model extended to interval number series can better predict the fluctuation range of groundwater level in the study area.(4)The chemical formation mechanism of groundwater was analyzed and the groundwater quality was evaluated.By analyzing the groundwater chemistry in Jiuquan East Basin,it is concluded that the regional groundwater is weakly alkaline and mostly belongs to fresh water.Along the recharge and discharge path of groundwater,groundwater chemistry has obvious zoning characteristics.The chemical composition of groundwater in Jiuquan East Basin is mainly affected by weathering leaching cation adsorption and evaporation concentration.The possible reasons for the excessive water quality in the area are industrial production,the discharge of pollutants from residential activities and the use of large amounts of ammonia fertilizer in regional agricultural activities.(5)It can be calculated that the groundwater reserves in the study area increased in 2018.