Research On Evolution Characteristics Of Salt-Water Intrusion In South Of Laizhou Bay

Salt-water intrusion is a kind of delayed geological hazards which is frequentlyhappened in coastal area under the dual role of both natural and artificial, and it hasserious negative impact on local industry and agriculture and the health of residents.With climate change of ice age and inter-glaciation and sea-level repeated movementssince the late Pleistocene, seawater intrusion of Cangzhou, Xian Couty and Huanghuaand regressive events between them took place in Bohai Sea. Plain area of fluvial andmarine deposits in south of Laizhou Bay will accordingly deposited formationbetween land and Sea. In this thesis, the evolution characteristics of the phenomenonof salt-water intrusion are discussed, including the historical evolution anddevelopment characteristics.Underground brine formed in south coast of the Laizhou bay distributes widelywith large volume since Late Pleistocene. Its origin is complicated. According to theanalysis, it is the fluvial delta sedimentary system that creates a good replenishment,migration, filtration, capping condition for the generation of underground brine. In theearly stage of brine evolution, the lagoon water consisted of continuously injectednormal seawater, which ran across the bar under the process of storm surge, and freshgroundwater lying below the river sediment. High salinity brine generated in lagoon,running into the tidal flat and the delta front belt under the effect ofbackflow-infiltration. Lagoon water would remain stable with relatively highconcentrations for a long time. In the regression period, a large amount of long-termevaporation and seasonal muti-source river sediment transport modes formedbrine-producing-reservoir. The terrestrial deposit covered early brine, which becameunderground brine formations, and in this way, several large scale sea-land changeshad formed alternative distribution characteristics. Taking the sand bar-lagoon as thebrine generated reactor, dissolved components were fractionated under the effect ofpump evaporation, and took ion exchange in sediments, which led to mineral alteration. As a result, underground brine was generated in the tidal flat and deltafronts under the effect of backflow-infiltration. Based on the comprehensive analysisof the underground brine distribution, buried depth of roof and floor, aquifer thickness,brine concentration and hydro-chemistry types of underground brine, this paperredefined the relationship between underground brine deposits on the southern coastof Laizhou Bay and the three transgression since Late Pleistocene，with comparativestudying of depositing background and underground brine distribution. This paperanalyzed distribution characteristics and exploitation status of underground brine,laying the foundation of sedimentology for further study of the origin of undergroundbrine formation and providing the scientific basis for more reasonable and effectiveutilization of coastal underground brine resources. Meanwhile, the formation of brinealso provides the foundation for the provenance salt-water intrusion.Through the development salt-water intrusion analysis in south of Laizhou Bay,the main affecting factors are groundwater exploitation and characteristics of rivers inthe study area. Groundwater in formation of Late Pleistocene almost shows norelationship with recharge from precipitation and rivers, but with large correlation togroundwater exploitation. Salt-water intrusion of this formation is related to its brineand salt-water distribution characteristics. Groundwater in formation of Holocene isassociated with precipitation and exploitation in flood season, and is relevant togroundwater exploitation in normal or dry season, and the supply source issurrounding groundwater. The salt-water intrusion phenomena are related to types ofsurrounding groundwater. In addition, saltwater-freshwater interface in the monitoringtime can be divided into three stages. It moves northward1136.43m on the whole andwith an average moving speed of1.2km/a. The range of salt-water intrusion presents adecreasing trend. The analysis of real-time monitoring data indicates that thefluctuation of groundwater level is similar to tidal fluctuation. The fluctuation isapproximate to an irregular sinusoidal curve. he fluctuation of groundwaterconductivity is also approximate to an irregular sinusoidal curve. The reason is thatthe dynamic change of late Pleistocene groundwater head and conductivity based on tidal pressure’s changing.With building groundwater model，the brine is influcedbased on groundwater brine exploitation. The mineralization of groundwater isreducing, with exploitation increasing.