Dutch-Polder-System-荷兰围垦地系统

TheremarkablehistoryofpoldersystemsinTheNetherlands12SummaryThetraditionalpoldersinTheNetherlandshavebeenformedfromthe12thcenturyonwards,whenpeoplestartedcreatingarablelandbydrainingdeltaswampsintonearbyrivers.Intheprocess,thedrainedpeatstartedoxidizing,thussoillevelslowered,uptoriverwaterlevelsandlower.Throughoutthecenturiesfarmershavebeenadaptingtheiragriculturalsystemtoloweringsoillevelsandoccasionalfloodsandinventednewwaystoorganisethemselvesandkeepseaandriverwaterout–resultinginthebuildingofhundredsofdrainagewindmillsandlaterpumpingstationstopumpwaterfrompoldersintotheriversandthesea.Thisdevelopmentresultedinthecreationofpresent-daypolderlandscapesthatarecharacterisedbygrasslandsonpeatysoilwithdrainagechannels,economicallysustainedbydairyfarming,whichharbourarichfloraandfauna.Thesesystemsfunctioninacontextof(amongothers)risingseaandriverlevels,continuedloweringlandlevels,increasinglymulti-functionaluseofland(urbanisation,recreationandtourism,natureconservation,cultureconservation),interferenceofagriculturalpolicies,andotherinterests.Aplethoraofgovernment,non-governmentandprivatepartieswithintensenegotiationpracticemakeupthepoldergovernancearena.Theoldestofsuchorganisationsarethe“waterboards”withthemandatetoprovidesafetyfromwaterthreatsforallcitizens.ThephysicalandinstitutionalpoldercultureisindeedacrucialaspectoftheDutchnationalidentity.1IntroductionDeltageologyTheNetherlandsisastateinthedeltasofthreeEuropeanrivers.ThebiggestriveristheRhine,whichflowsfromthenorthernAlpsthroughwesternGermanyrightthroughTheNetherlands(Figure1).TheMeuseflowsfromFrancethroughBelgiumthroughthesouthofthecountry,andthelargelyBelgianScheldeshapedanareainthesouth-westofthecountry.Geologically,thisareaisshapedbysandbanksputupbytheinterferenceofwaterstreamsfromtheserivers,andthenorth-eastboundcurrentoftheNorthSea.Afterthelasticeage,twelvethousandyearsago,bothattheriversidesandatthenorthseacoast,therewerelong-shapedstretchesofsandybanks.Suchbanksallowedforhumansettlementintheyears600-1200thatformthehistoricalcentresofpresent-daytowns.OnlyafterWorldWar-II,present-dayoutskirtswerebuilt,oftenintheareaswithpeat(orheavyclay)soils.1ThispaperwaspreparedonrequestofDrParvizKoohafkan,Director,LandandWaterDivisionandCoordinatoroftheGloballyImportantAgriculturalHeritageSystems(GIAHS)Initiative,FAO,Rome.ItsobjectiveistodocumentapotentialGIAHSsystemthatfeaturedcopingstrategiesforrisingseawaterlevelsinthecontextofclimatechange.ThepaperwasalsopresentedduringtheInternationalConsultationon“AgriculturalHeritageSystemsofthe21stCentury”thatwashostedbytheMSSwaminathanResearchFoundationon18February2010inChennai,India.2PaperwrittenbyFrankvanSchoubroeck,Ph.D.,consultant,policy-practicelinkagesinsmall-scalefarming,[e-mail];andHarmKool,MSc.,WaterschapRivierenland,Tiel,TheNetherlandsFigure1.TheRhinecatchmentareawiththedeltainthenorth-west.Figure2.Anareawithtraditionalpolders(red,dottedcircle)andareawithmodernpolders(yellowcircle).ModernpoldersThestateofTheNetherlandshasalonghistoryofcreating“polders”-sub-sealevel(orsub-riverlevel)land,thatisprotected–orevenreclaimed-fromthesea.Inthemid-20thcenturythestatecommissionedtherealisationofpoldersinthethen“SouthernSea”(Zuiderzee)thatwiththeconstructionofdykesnowisalake(calledIJsselmeer).ThethenZuiderzeewasandisinthecentreofthecountry(yellowcircle,Figure2)andtheGovernmentindeedreclaimedlandfromthe(shallow)sea.ItwastheDutchStatewhocarriedoutthislandreclamationandcreatedamodernagriculturallandscape,withoccasionalmoderntownsthatwerebuiltafterthe1960s.TraditionalpoldersBesidestheselarge-scalemodernpolders,therearepoldersthathavebeencreatedinthecourseofhistoryandthatmaybeonetoafewhundredyearsold.Theso-called“GreenHeartofHolland”(red,dottedcircle)issituatedbetweenthecitiesofRotterdam,TheHague,AmsterdamandUtrechtconsistsofdifferentpolders.Thesepoldersarenotexactlylandreclamations,theyareratherconservedareas–astheyhavenotbeenreclaimedfromtheseabutratherprotectedfromthesea.Figure3.Inthe1990sriverlevelsreacheddangerousheights,sparkingoffanewpolicywithregardstorivermanagement.RiverthreatsBothwaterfromtherivercatchmentareasandwaterfromtheseathreatenlargepartsofTheNetherlands.Overthelastcentury,rivercatchmentareasbothinGermanyandinTheNetherlandsimproveddrainagesystemsbothincitiesandinruralareas.Therefore,duringwetperiodsinthecatchmentarea,riversgetamoreirregularwaterregime,challengingthedykesalongtheriver.Afteracoupleofnear-floodsindenselypopulatedareasintheearly1990s(Figure3),TheNetherlandsdecidedtodeepentheriverandwidentheareasfitforflooding.Thisprojectiscalled“RoomfortheRiver”andallowsformoretraditionalnatureandagricultureinawidebandalongtheriversinthemiddleofthecountry.Figure4.Riverandsealevelsarestronglyrelateduptoahundredkilometersfromthecoast.Accompanyingpolderlandscapeshavebeenformedaspartoftheriverlandscape.SeathreatsTheseaposesamorestructuralthreat.Astheriversonlygodownbyafewmetersoveranareaof100km,thetidesarebeingfeltuptoalmostahundredkminsidethecountry.Withglobalwarming,bothpolaricemeltsandseawate