伦敦的泰晤士河 　　ThamesRiver 　　Itrisesinfourheadstreams(theThamesorIsis,Churn,Coln,andLeach)intheCotswoldHills,EGloucestershire,andflowsgenerallyeastwardacrossSEnglandandthroughLondontotheNorthSeaatTheNore.Initsuppercourse—aroundandaboveOxford—itisoftencalledIsis.TheThamesdrainsc.5,250sqmi(13,600sqkm);itstributariesincludetheWindrush,Cherwell,Thame,Kennet,Wey,Mole,Lea,Roding,andMedway.Itisjoinedbycanals(includingtheOxford,ThamesandSevern,andGrandJunction)thatcoverawidearea.TheriverisnavigablebybargestoLechlade,belowwhichthereareanumberoflocks.TheThamesistidaltoTeddington;thereisa23-ft(7-m)differencebetweenlowandhightideatLondonBridge.ThepartofthestreamnearLondonBridgeisknownasthePool.ThemainpartoftheportofLondonstretchesfromLondonBridgetoBlackwall.TheThamesConservancyBoardwasestablishedin1857;thedocksandthetidalpartoftheriverbelowTeddingtonhavebeenadministeredbythePortofLondonAuthoritysince1908.Partoftheriverisofgreatbeauty,ismuchusedforboating,andisstillpopularforfishing.TheuppervalleyoftheThamesisabroad,flatbasinofalluvialclaysoil,throughwhichtheriverwindsandturnsconstantlyinalldirections.AtGoringGapthevalleynarrows,separatingtheChilternHillsfromtheBerkshireDowns.ThelowervalleyformsasecondbroadbasinthroughwhichtheThamesalsomeanders.Thelandaroundtheriverwasformerlymarshy,andtheancientroadswerefarfromtheriverbanks.IntheMiddleAgesthevalleywasveryprosperous,withmanyreligioushousesandseverallargetowns,includingReadingandWindsor.BetweenOxfordandLondon,thevalleyispredominantlyagricultural,withscatteredvillages;Readingistheonlyindustrialtownthere.TheGreaterLondonconurbationalongtheriver'slowercourseisoneofthemostimportantindustrialregionsofGreatBritain.AmongthemanyinterestingarchaeologicaldiscoveriesmadeinthevalleyarefossilsofseashellsandahumanskullfromthePaleolithicperiod.InLondontheriveriscrossedby27bridges,includingthenewLondonBridge,WestminsterBridge,WaterlooBridge,andTowerBridge.TherearetwomaintunnelsundertheriverinLondon,andonebetweenDartfordandPurfleet,aswellasseveralfootpathsand5railroadtunnels.In1963governmentaleffortsbegantocombatpollutionofthewatersthroughaseriesofrulesandregulations.Atpartsalongtheriverdownstreamfloodbarrierswereconstructed,whichbecameoperationalin1982,topreventLondonfromdamagebyNorthSeagales.