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汉江上游郧西段归仙河口剖面全新世古洪水事件研究.docx

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汉江上游郧西段归仙河口剖面全新世古洪水事件研究 Introduction Thestudyofancientfloodeventsisessentialtounderstandthenaturalhazardsandrisksassociatedwithfloods.Inthispaper,wefocusonthestudyoftheancientfloodeventsintheGuixianRivermouth,locatedintheYunxisectionoftheHanRiver,upstream. GeologicalSetting TheYunxisectionoftheHanRiverislocatedinthewesternpartofHubeiprovinceinChina.TheriverflowsthroughthemountainousterrainoftheQinling-DabaMountains,whichformthenorthernandsouthernboundariesoftheSichuanBasin.TheHanRiveristhelargesttributaryoftheYangtzeRiverandhasalengthof1532km,withadrainageareaof166,000km2.TheYunxisectionoftheHanRiverhasalengthof130km,withadrainagebasinof4,812km2,andanelevationrangebetween150-1875mabovesealevel. TheGeomorphologyoftheYunxiSectionoftheHanRiver TheYunxisectionoftheHanRiverhasacomplexgeomorphologythatischaracterizedbyhighmountains,deepvalleys,andsteepslopes.Themaingeomorphologicalformsincluderiverterraces,valleybottoms,alluvialfans,andhillslopes.Theriverterracesaremainlydistributedinthemiddleandlowerreaches,withanelevationrangebetween300-500mabovesealevel.Thevalleybottomsarebetween150-200mabovesealevel,andthealluvialfansarefoundatthemouthoftributaries.Thehillslopesaresteepandcoveredbythickvegetation,whichmakesthemhighlysusceptibletosoilerosionandlandslides. TheGuixianRiverMouth TheGuixianRiverisatributaryoftheHanRiver,locatedintheYunxisection.ThemouthoftheGuixianRiveriswheretheriveremptiesintotheHanRiver,anditischaracterizedbyawidefloodplain,withaslopeofabout0.5%.Thefloodplainhasawidthofabout200-600mandhasbeenextensivelymodifiedbyhumanactivities,includingfloodcontrolworks,agriculturalactivities,andurbanization.TheGuixianRiverisfedbyseveralsmalltributaries,anditispronetofloodingduringtherainyseason. TheStudyofAncientFloodEvents ThestudyofancientfloodeventsintheGuixianRivermouthisbasedonthesedimentologicalandstratigraphicanalysisofthesedimentsdepositedduringthefloods.ThesedimentswerecollectedfromacoredrilledatthemouthoftheGuixianRiver,andtheywereanalyzedusingvariousmethods