Effects Of Precipitation And Tide On Seawater Intrusion In The Laizhou Bay

As a geological hazard, seawater intrusion has greatly hampered thesoci-economic development in the coastal zone. What’s more, seawater intrusion incoastal zone substantially contaminates the freshwater resources, posing high risk tothe ecological environment. Laizhou Bay, an extreme case of seawater intrusion inChina, has attracted much attention for30years. This study analyzed the evolutionand characteristics of the seawater intrusion in the Laizhou Bay on the basis of fielddata. Then the effects of rainfall and tide on seawater intrusion were further analyzed.Firstly, the evolution of seawater intrusion in the Laizhou Bay over the past30years was analyzed based on a combination of field data and previous findings. Theevolution of seawater intrusion in this area can be divided into5stages: initial stage,progress stage, deterioration stage, attenuation stage, divided stage. The area ofsaltwater intrusion in the coastal area of the Laizhou Bay had amounted to4300km2by2010.Secondly, the tempo-spatial distribution and variation trend of saltwater intrusionwere discussed based on the records of electric conductivity and the burial depth ofthe groundwater in automatic monitoring wells. The results revealed that:1) theelectric conductivity and the burial depth of the groundwater fluctuated frequentlyduring April to September;2) spatially, the seawater intrusion exhibits belt-shapedistribution. And from north to south, the study area can be divided into seawaterintrusion zone, brackish-fresh transitional zone and freshwater zone. The maximumintrusion distance was as long as30km;3) The variation amplitude of groundwaterelectric conductivity in seawater intrusion zone> brackish-fresh transitional zone and>freshwater zone. But the burial depth of groundwater shows an opposite pattern.Thirdly, the impact of rainfall on seawater intrusion was analyzed based on thelong-term yearly-averaged rainfall observations. In the oncoming decade, arid climatewill continue to dominate this area, which implies that the saltwater intrusion will deteriorate. And daily rainfall data in Changyi in2012, suggests that the groundwaterrecharge can last2-3days after a heavy rainfall.Finally, the relationship between tide and burial depth of groundwater wasexplored. The tide effect can extend inland for about25km. And the variations ingroundwater burial depth lag the tide changes, with the time delays of7h,9h,9.5h,9.5h,10.5h for the five monitoring wells, respectively. The time delays for the5monitoring wells correlate well with their distances to the sea.