Study On Seawater Intrusion On The South Bank Of Laizhou Bay Based On Hydrochemical And Geophysical Methods

The south of Laizhou Bay is one of the typical study areas of saltwater intrusion.The earliest research can be traced back to the 1980s.The research content involves mathematical models,field survey sampling,and laboratory test research.This article mainly conducts a comprehensive study on saltwater intrusion on the south of Laizhou Bay through two monitoring methods:hydrochemistry and high-density resistivity.Based on the 41 water samples collected in the research area in November 2018,this paper selects a series of physical and chemical indicators and reveals the evolution process of groundwater in the south of Laizhou Bay from a multidimensional perspective through end-element mixing and Gibbs diagrams.The results show that the groundwater on the south of Laizhou Bay originates from modern atmospheric precipitation,and the river is the source of groundwater recharge in this area.Under the influence of seawater/saltwater intrusion and water-rock interaction,the salt composition,content and ratio of groundwater in the study area showed a non-conservative increase along the mixed line of saltwater and freshwater toward the saltwater end.The evolution path of groundwater in Laizhou Bay is Ca·Mg-HCO₃?Na?Ca/Mg?-HCO₃ and Na?Ca/Mg?-Cl?Na-Cl.The indoor sand box was used to simulate the process of salt water intrusion under different hydraulic gradients.The results show that?1?the aquifer medium of Laizhou Bay is mainly clayey silt and silty clay with low permeability.As the permeability decreases,the hydraulic gradient threshold caused by seawater intrusion gradually increases.The rate of saltwater invasion increases with the increase of hydraulic gradient.And at different locations of the aqueous medium,the speed of water-salt migration is very different.?2?During the process of saltwater intrusion,the width of the transition zone is related to the speed of groundwater migration and the permeability of the aquifer layer.The faster the groundwater migration rate,the smaller the width;The lower the permeability of the aquifer medium,the greater the width.The high-density resistivity method as the monitoring method was used to study the law of water-salt transport in the soil layer under the field conditions,two conditions were set up to irrigate the test site with fresh water and brackish water.In a heterogeneous medium,water and salt must first follow the dominant channel with greater permeability during the migration process.The migration characteristics of fresh water are slightly different from that of salt water.Under the combined action of water and salt,it will have a stronger infection effect on the medium layer with low permeability.This article systematically studies the saltwater intrusion on the south of Laizhou Bay through groundwater chemical analysis,laboratory simulation and field high-density resistivity monitoring test.The research reveals the sources of water and salt in groundwater on the south of Laizhou Bay,the mixed evolution of fresh groundwater and saline groundwater,and the characteristics of water and salt transport in aquifer.The research results of this paper also provide reference materials for further revealing the saltwater intrusion mechanism of Laizhou Bay,which is helpful to build a judgment system that distinguishes saltwater intrusion from modern seawater intrusion.It provides a certain reference for the planning and management of water resources,monitoring and early warning of seawater intrusion and prevention and treatment.