Study On Groundwater Circulation And Evolution Law In Weihe River Delta Area

Groundwater circulation velocity plays an important role in controlling water-rock interaction.Therefore,the hydrochemical and isotopic characteristics of groundwater contain the information of groundwater circulation process.The groundwater flows through the alluvial plain and coastal plain in Luanhe Delta plain,which forms a groundwater flow system with Bohai Sea as discharge terminal,and the horizontal runoff distance is 50⁷0km.The purpose of this paper is to find out the characteristics of groundwater evolution in the study area,with emphasis on the circulation law of regional deep confined water and the main mechanism of groundwater chemical evolution.Based on comprehensive use of hydrochemistry,isotopes(¹⁸O,D,¹⁴C)and groundwater numerical simulation,the circulation and evolution of groundwater in Luanhe Delta are revealed,and the following understandings are obtained:?1?The chemical types of groundwater in the study area are obviously zonal from upstream to downstream.The shallow groundwater in the upstream of alluvial plain receives the recharge of atmospheric precipitation and surface river water and replenishes deep confined groundwater.The deep groundwater in the upstream of alluvial plain mainly has the effect of leaching.In the downstream of coastal plain,the deep groundwater mainly occurs desulfuric acid and cation exchange and a large number of salt rocks have dissolve,while shallow groundwater is controlled by evaporation and concentration and mixing of seawater and regional salt water,and there is no hydraulic relationship between them.?2?Based on the characteristics of hydrogen and oxygen isotope and its temperature effect analysis,different water bodies in the study area are from atmospheric precipitation.The diving is the recharge of modern atmospheric precipitation.The pressurized groundwater receives the infiltration and infiltration in the upstream,and then supplies the downstream groundwater through the lateral runoff.The confined groundwater in the downstream coastal plain is infiltrated by the glacial period during the period of 40¹1 ka,which is relatively isolated from the shallow groundwater and only accepts the lateral recharge of the groundwater under pressure.Combined with the age analysis of ¹⁴C groundwater test,it is considered that the groundwater flow pattern of the III aquifer group conforms to the plug flow model,and the deep groundwater in the region has stable runoff recharge conditions from upstream to downstream.Shallow groundwater in the downstream area is significantly affected by evaporation and concentration.?3?Based on the simulation results of longitudinal 3 profile,it is shown that under the control of the groundwater flow field,the shallow groundwater infiltration recharges the deep groundwater in the upstream area,and the flow mainly moves along the horizontal and downward.In the coastal plain area,the water flow is divided,and some of the deep groundwater flows near horizontal along the aquifer,showing a plug flow model;while the partial water leaks upward in the downstream area and is discharged by evaporation or excreted into the sea through shallow groundwater.According to the groundwater age simulation results,the maximum simulated age of groundwater in the Weihe River Delta plain is about 55,000 a.Generally speaking,along the direction of groundwater runoff,the groundwater age gradually increases,the groundwater runoff velocity decreases gradually,and the groundwater renewing capacity is weakened.