水利水电工程专业英语教材

高等学校水利类统编教材《水利专业外语》迟道才周振民主编上传人单位：华北水利水电学院水利系Waterisbestknownandmostabundantofallchemicalcompoundsoccurringinrelativelypureformontheearth’ssurface.Oxygen,themostabundantchemicalelement,ispresentincombinationwithhydrogentotheextentof89percentinwater.Watercoversaboutthreefourthsoftheearth'ssurfaceandpermeatescracksofmuchsolidland.ThePolarRegions(原文polarregions)areoverlaidwithvastquantitiesofice,andtheatmosphereoftheearthcarrieswatervaporinquantitiesfrom0.1percentto2percentbyweight.Ithasbeenestimatedthattheamountofwaterintheatmosphereaboveasquaremileoflandonamildsummerdayisoftheorderof50,000tons.在地球外表以相对纯的形式存在的一切化合物中，水是人们最熟悉的、最丰富的一种化合物。在水中，氧这种最丰富的化学元素与氢结合，其含量多达89%。水覆盖了地球外表的大约3/4的面积，并充满了陆地上的许多裂缝。地球的两极被大量的冰所覆盖，同时大气也挟带有占其重量0.1%～2%的水蒸气。据估计，在温暖的夏日，每平方英里陆地上空大气中的水量约为5万吨。Alllifeonearthdependsuponwater,theprincipalingredientoflivingcells.Theuseofwaterbyman,plants,andanimalsisuniversal.Withoutittherecanbenolife.Everylivingthingrequireswater.Mancangonearlytwomonthswithoutfood,butcanliveonlythreeorfourdayswithoutwater.地球上所有的生命都有赖于水而存在，水是活细胞的根本组分〔要素〕。人类、植物和动物都得用水。没有水就没有生命。每一种生物都需要水。人可以接近两个月不吃食物而仍能活着，但不喝水那么只能活三四天。Inourhomes,whetherinthecityorinthecountry,waterisessentialforcleanlinessandhealth.TheaverageAmericanfamilyusesfrom65,000to75,000gallonsofwaterperyearforvarioushouseholdpurposes.在我们的家庭中，无论是在城市还是农村，水对于卫生和健康来说都是必不可少的。美国家庭的年平均用水量达6.5～7.5万加仑。Watercanbeconsideredastheprincipalrawmaterialandthelowestcostrawmaterialfromwhichmostofourfarmproducesismade.Itisessentialforthegrowthofcropsandanimalsandisaveryimportantfactorintheproductionofmilkandeggs.Animalsandpoultry,ifconstantlysuppliedwithrunningwater,willproducemoremeat,moremilk,andmoreeggsperpoundoffoodandperhouroflabor.水可以被认为是最根本的和最廉价的原料。我们的农产品，大局部都是由它构成的。水是农作物和动物生长的要素，也是奶类和蛋类生产的一个很重要的因素。动物和家禽，如果用流动的水来喂养，那么每磅饲料和每个劳动小时会生产出更多的肉、奶和蛋。Forexample,applesare87%water.Thetreesonwhichtheygrowmusthavewateredmanytimestheweightofthefruit.Potatoesare75%water.Togrowanacreofpotatoestonsofwaterisrequired.Fishare80%water.Theynotonlyconsumewaterbutalsomusthavelargevolumesofwaterinwhichtolive.Milkis88%water.Toproduceonequartofmilkacowrequiresfrom3.5to5.5quartsofwater.Beefis77%water.Toproduceapoundofbeefananimalmustdrinkmanytimesthatmuchwater.Ifthereisashortageofwater,therewillbeadeclineinfarmproduction,justasashortageofsteelwillcauseadecreaseintheproductionofautomobiles.例如，苹果含87%的水分，苹果树就必须吸收比苹果多许多倍的水分；土豆含75%的水分，那么种植每英亩土豆就需要假设干吨水；牛奶含水量为88%，为了生产每夸脱牛奶，母牛需要3.5～5.5夸脱的水；牛肉含77%的水，为生产1磅牛肉牛必须饮用许多磅水。如果缺水，就会使农产品减产，就像缺乏钢会引起汽车产量下降一样。Inadditiontothedirectuseofwaterinourhomesandonthefarm,therearemanyindirectwaysinwhichwateraffectsourlives.Inmanufacturing,generationofelectricpower,transportation,recreation,andinmanyotherways,waterplaysaveryimportantrole.水除了直接为我们的家庭和农场利用外，它还以许多间接的方式对我们的生活产生影响。在制造、发电、运输、娱乐以及其他许多行业，水都起着很重要的作用。Ouruseofwaterisincreasingrapidlywithourgrowingpopulation.Alreadythereareacuteshortagesofbothsurfaceandundergroundwatersinmanylocations.Carelesspollutionandcontaminationofourstreams,lakes,andundergroundsourceshasgreatlyimpairedthequalityofthewaterwhichwedohaveavailable.Itisthereforeofutmostimportanceforourfuturethatgoodconservationandsanitarymeasuresbepracticedbyeveryone.我们对水的利用随人口的增长而迅速增加。在许多地方，无论地面水或地下水都已经严重短缺了。由于任意污染河流、湖泊和地下水源，已经大大地损害了人们能够利用的水的水质。因此，人人有责对水采取保护措施和卫生措施，这对于我们人类的未来是极端重要的。Innature,waterisconstantlychangingfromonestatetoanother.Theheatofthesunevaporateswaterfromlandandwatersurfaces,thiswatervapor(agas),beinglighterthanair,risesuntilitreachesthecoldupperairwhereitcondensesintoclouds.Cloudsdriftaroundaccordingtothedirectionofthewinduntiltheystrikeacolderatmosphere.Atthispointthewaterfurthercondensesandfallstotheearthasrain,sleet,orsnow,thuscompletingthehydrologiccycle.在自然界中，水总是不断地从一种状态改变成另一种状态。太阳热使陆地和水面上的水蒸气。这些水蒸气〔一种气体〕由于比空气轻，会上升直至到达高空冷气层，并在那里凝结成云。云层随风飘荡，直至遇到更冷的大气层为止。此时水便进一步冷凝，并以雨、雹或雪的形式落到地面。这样便完成了水的循环。Thecompletehydrologiccycle,however,ismuchmorecomplex.Theatmospheregainswatervaporbyevaporationnotonlyfromtheoceansbutalsofromlakes,rivers,andotherwaterbodies,andfrommoistgroundsurfaces.Watervaporisalsogainedbysublimationfromsnowfieldsandbytranspirationfromvegetationandtrees.然而，完整的水循环要复杂得多。由于蒸发作用，大气不仅从海洋而且从湖泊、河流和其他水体，以及从潮湿的地外表获得水蒸气。也可从雪地中雪的升华和从植物与树木的蒸腾获得水蒸气。Waterprecipitationmayfollowvariousroutes.Muchoftheprecipitationfromtheatmospherefallsdirectlyontheoceans.Ofthewaterthatdoesfalloverlandareas,someiscaughtbyvegetationorevaporatesbeforereachingtheground,someislockedupinsnowfieldsorice-fieldsforperiodsrangingfromaseasontomanythousandsofyears,andsomeisretardedbystorageinreservoirs,intheground,inchemicalcompounds,andinvegetationandanimallife.降水可以有各种不同的途径。大局部降水都直接落到海洋。落在陆地区域内的水，有些被植物所摄取，或降至地面之前就蒸发了；有些被封冻在雪原或冰川中达一个季度乃至成千上万年；有些那么因储存在水库、土壤、化合物以及动植物体内而滞留下来。Thewaterthatfallsonlandareasmayreturnimmediatelytotheseaasrunoffinstreamsandriversorwhensnowmeltsinwarmerseasons.Whenthewaterdoesnotrunoffimmediatelyitpercolatesintothesoil.Someofthisgroundwateristakenupbytherootsofvegetationandsomeofitflowsthroughthesubsoilintorivers,lakes,andoceans.降到陆地区域的水可能作为溪流与江河的径流，或在温暖季节融化的雪水直接回到海洋。当降水不立即流走时，它会渗入土壤。这些地下水中有一些被植物的根吸收，有一些那么通过下层土壤流入河流、湖泊和海洋。Becausewaterisabsolutelynecessaryforsustaininglifeandisofgreatimportanceinindustrymenhavetriedinmanywaystocontrolthehydrologiccycletotheirownadvantage.Anobviousexampleisthestorageofwaterbehinddamsinreservoirs,inclimateswherethereareexcessesanddeficitsofprecipitation(withrespecttowaterneeds)atdifferenttimesintheyear.Anothermethodistheattempttoincreaseordecreasenaturalprecipitationbyinjectingparticlesofdryiceorsilveriodideintoclouds.Thiskindofweathermodificationhashadlimitedsuccessthusfar,butmanymeteorologistsbelievethatasignificantcontrolofprecipitationcanbeachievedinthefuture.因为水对于维持生命来说绝对必要，在工业上也很重要，所以人们为了自身的利益试图以各种方式来控制水的循环。一个明显的例子就是在一年中不同的时间根据当地降水的多寡〔按对水的需要来说〕将水储存在水库中。另一种方法是试图将干冰或碘化银微粒射入云层来增多或减少天然降雨量。虽然这种改造气候〔人工影响天气〕的方法迄今只取得了有限的成功，但许多气象学家都认为，有效地控制降水在将来是可以做到的。Otherattemptstoinfluencethehydrologiccycleincludethecontourplowingofslopingfarmlandstoslowdownrunoffandpermitmorewatertopercolateintotheground,theconstructionofdikestopreventfloodsandsoon.Thereuseofwaterbeforeitreturnstotheseaisanothercommonpractice.Variouswatersupplysystemsthatobtaintheirwaterfromriversmayrecycleitseveraltimes(withpurification)beforeitfinallyreachestheriversmouth.其他一些影响水循环的努力包括沿等高线耕作梯田，以使径流减速，让更多的水渗入地下；建筑堤坝以防洪水等。在水回归大海之前将它重复使用，也是一种常用的方法。自河道取水的各种供水系统可将水在最终到达河口之前，经过净化，可重复使用屡次。Menalsoattempttopredicttheeffectsofeventsinthecourseofthehydrologiccycle.Thus,themeteorologistforecaststheamountandintensityofprecipitationinawatershed,andthehydrologistforecaststhevolumeofrunoff.人们还试图预测水循环过程中一些事件的结果。例如，气象学家预报一个流域的降雨量和降雨强度；水文学家预报径流量等。1historyThefirsthydraulicprojecthasbeenlostinthemistsofprehistory.Perhapssomeprehistoricmanfoundthatpileofrocksacrossastreamwouldraisethewaterlevelsufficientlytooverflowthelandthatwasthesourceofhiswildfoodplantsandwaterthemduringadrought.Whatevertheearlyhistoryofhydraulics,abundantevidenceexiststoshowthatthebuildersunderstoodlittlehydrology.EarlyGreekandRomanwritingsindicatedthatthesepeoplecouldaccepttheoceansastheultimatesourceofallwaterbutcouldnotvisualizeprecipitationequalingorexceedingstream-flow.Typicaloftheideasofthetimewasaviewthatseawatermovedundergroundtothebaseofthemountains.Thereanaturalstilldesaltedwater,andthevaporrosethroughconduitstothemountaintops,whereitcondensedandescapedatthesourcespringsofthestreams.MarcusVitruviusPollio(ca.100B.C.)seemstohavebeenoneofthefirsttorecognizetheroleofprecipitationasweacceptittoday.最早的水利工程在有史以前就已经销声匿迹了。也许史前的人曾发现横贯河流的一堆石头就能提高水位，足以淹没作为生长野生食用植物源泉的土地，而这样在干旱季节就能给植物浇水。不管水力学的早期如何，充分的的迹象说明，建造者们还不懂多少水文学知识。早期的希腊和罗马文献说明这些人成认海洋是一切水的主要源泉，但是不能想象降雨量会等于或超过河道径流量。当时典型的想法是海水从地下流到山脉底部，那儿有一个天然蒸馏器除去水中的盐分，水汽通过管道上升到山顶，在那里凝结，并从河流的源头流走。M.V.波利欧〔大约公元前100年〕看来就是像我们今天这样认识降水作用最早的人。LeonardodaVinci(1452-1519)wasthenexttosuggestamodernviewofthehydrologiccycle,butitremainedforPierrePerrault(1608-1680)tocomparemeasuredrainfallwiththeestimatedflowoftheSeineRivertoshowthatthestream-flowwasaboutone-sixthoftheprecipitation.TheEnglishastronomerHalley(1656-1742)measuredevaporationfromasmallpanandestimatedevaporationfromtheMediterraneanSeafromthesedata.Aslateas1921,however,somepeoplestillquestionedtheconceptofthehydrologiccycle.达芬奇〔1452-1519〕是提出水文循环现代观点的第二个人，但一直到P.贝罗特〔1608-1680〕才把观测的雨量与估算的塞纳河的径流量进行比拟，说明河川径流量约为降雨量的1/6.英国天文家哈罗〔哈雷〕从一个小盘子中测得的蒸发量，并且用这一资料估算地中海的蒸发量。然而直到1921年，有一些人仍然对水文循环的概念表示疑心。PrecipitationwasmeasuredinIndiaasearlyasthefourthcenturyB.C.,butsatisfactorymethodsformeasuringstream-flowwereamuchlaterdevelopment.Frontinus,watercommissionerofRomeinA.D.97,basedestimatesofflowoncross-sectionalareaalonewithoutregardtovelocity.IntheUnitedStates,organizedmeasurementofprecipitationstartedundertheSurgeonGeneraloftheArmyin1819,wastransferredtotheSignalCorpsin1870,andfinally,in1891,toanewlyorganizedU.S.WeatherBureau,renamedtheNationalWeatherServicein1970.Scatteredstream-flowmeasurementsweremadeontheMississippiRiverasearlyas1848,butasystematicprogramwasnotstarteduntil1888,whentheU.S.GeologicalSurveyundertookthiswork.Itisnotsurprising,therefore,thatlittlequantitativeworkinhydrologywasdonebeforetheearlyyearsofthetwentiethcentury,whenmensuchasHortan,Mead,andShermanbegantoexplorethefield.Thegreatexpansionofactivityinfloodcontrol,irrigation,soilconservation,andrelatedfieldswhichbeganabout1930gavethefirstrealimpetustoorganizedresearchinhydrology,asneedformoreprecisedesigndatabecameevident.Mostoftoday’sconceptsofhydrologydatefrom1930.印度早在公元前4世纪就测量降水量了，但是令人满意的测量河道流量的方法很迟才得到开展。公元97年，罗马水利专员福朗堤努斯只按横断面面积估算流量，而不考虑流速。在美国，有组织地测量降水量是1819年在陆军军医总监领导下开始的，1870年移交给通信兵团，最后，在1891你那移交给新改组的美国气象局，该局于1970年改名为国家气象局。早在1848年密西西比河上就进行分散的河道流量测量了，但是，直到1888年美国地质调查局承当这项工作时，才开始实施系统的观测方案。霍德、米德和谢尔曼等人在20世纪早期刚开始对这一领域进行探索，因此，在这时期之前，在水文方面没有进行什么定量工作是缺乏为奇的。大约从1930年起，由于在防洪、灌溉、土地改进和有关领域中开展了大量活动，第一次为有组织地研究水文学提供了真正的动力，因为需要更精确的设计资料，这已是十清楚显的事了。大多数现代水文学的概念从1930年就开始有了。2hydrologyinengineering水文学在工程中的应用Hydrologyisusedinengineeringmainlyinconnectionwiththedesignandoperationofhydraulicstructures.Whatfloodflowscanbeexpectedataspillwayorhighwayculvertorinacitydrainagesystem?Whatreservoircapacityisrequiredtoassureadequatewaterforirrigationormunicipalwatersupplyduringdroughts?Whateffectswillreservoirs,levees,andothercontrolworksexertonfloodflowsinastream?Thesearetypicalofquestionsthehydrologistisexpectedtoanswer.在工程上，水文学主要用于水工建筑物的设计和运行，溢洪道、公路涵洞、或者城市排水系统会期望有什么样的洪水流量？需要多大的水库库容才能保证干旱季节里有足够的灌溉水量或城市供水呢？水库、堤坝或其他控制工程对河流洪水流量有什么影响？这些典型的问题等待水文学家去解答。Largeorganizationsuchasfederalandstatewateragenciescanmaintainstaffsofhydrologicspecialiststoanalyzetheirproblems,butsmallerofficesoftenhaveinsufficienthydrologicworkforfull-timespecialists.Hence,manycivilengineersarecalleduponforoccasionalhydrologicstudies.Itisprobablethatthesecivilengineersdealwithalargernumberofprojectsandgreaterannualdollarvolumethanthespecialistsdo.Inanyevent,itseemsthatknowledgeofthefundamentalsofhydrologyisanessentialpartofthecivilengineer’straining.像联邦和州辖水利机构这样的大型组织，拥有一批水文专家来分析他们的问题，但较小的单位往往没有足够的水文工作给专职水文专家做。因此，许多土木工程师们应邀进行临时的水文研究。这些土木工程师处理的工程和年费用可能比水文专家还多。无论如何，水文学的根底知识看来是培训土木工程师所必不可少的一局部。3subjectmatterofhydrology水文学研究的主要内容Hydrologydealswithmanytopics.Thesubjectmatteraspresentedinthisbookcanbebroadlyclassifiedintotwophases:datacollectionandmethodsofanalysis.Chapter2to6dealswiththebasicdataofhydrology.Adequatebasicdataareessentialtoanyscience,andhydrologyisnoexception.Infact,thecomplexfeaturesofthenaturalprocessesinvolvedinhydrologicphenomenamakeitdifficulttotreatmanyhydrologicprocessesbyrigorousdeductivereasoning.Onecannotalwaysstartwithabasicphysicallawandfromthisdeterminethehydrologicresulttobeexpected.Rather,itisnecessarytostartwithamassofobservedfacts,analyzethesefacts,andfromthisanalysistoestablishthesystematicpatternthatgovernstheseevents.Thus,withoutadequatehistoricaldatafortheparticularproblemarea,thehydrologistisinadifficultposition.Mostcountrieshaveoneormoregovernmentagencieswithresponsibilityfordatacollection.Itisimportantthatthestudentlearnhowthesedataarecollectedandpublished,thelimitationsontheiraccuracy,andthepropermethodsofinterpretationandadjustment.水文学研究很多问题。本书所介绍的主要内容可大致分成两个方面：收集资料和分析方法。2～6章研究水文学的根本资料。充足的根本资料是任何一个一门科学所不可少的，水文学也不例外。事实上，水文现象中也包含着许多自然过程的复杂特征，用严密的推理来处理许多水文现象是困难的。人们并不总是能够从根本的自然法那么出发，并由此来推求预期的水文结果。相反，从大量观察的事实出发，分析这些事实，并根据分析建立控制这些事件的系统模型确实十分必要的。因此，对于没有足够历史资料的特殊疑难地区，水文学家就将陷入困境。大多数国家有一个或更多的政府机构负责收集资料，重要的是要让学生学会这些资料是如何收集和刊出的，了解这些资料的精确度的局限性，学会整理分析和校正这些资料的专门的方法。Typicalhydrologicproblemsinvolveestimatesofextremesnotobservedinasmalldatasample,hydrologiccharacteristicatlocationswherenodatahavebeencollected(suchlocationsaremuchmorenumerousthansiteswithdata),orestimatesoftheeffectsofman’sactionsonthehydrologiccharacteristicsofanarea.Generally,eachhydrologicproblemisuniqueinthatitdealswithadistinctsetofphysicalconditionswithinaspecificriverbasin.Hence,quantitativeconclusionsofoneanalysisareoftennotdirectlytransferabletoanotherproblem.However,thegeneralsolutionformostproblemscanbedevelopedfromapplicationofafewrelativelybasicconcepts.典型的水文问题包括估算小的数据样本中无法观测到的极值及估算无资料地区〔这种地区比有资料的地区多得多〕的水文特征值，或者估算人类活动对该地区水文特征值的影响。一般来说，每一个水文问题都是不同的，因为它涉及到特定流域内特有的自然条件。因此，某种分析所得的定量结论常常不能直接移用到另一个问题上。然而，应用一些比拟根本的概念可以得出大多数问题都适用的一般解决方法。Ofalltheearth’swater97%isfoundintheoceans,2%inglaciersandonly1%onland.Ofthis1%almostall(97%)isfoundbeneaththesurfaceandcalledsub-surfaceorundergroundwater.Mostofthiswatereventuallyfindsitswaybacktotheseaeitherbyundergroundmovementorbyrisingintosurfacestreamsandlakes.地球上的总水量中，97%在海洋，2%在冰川，只有1%在陆地上。陆地上的水几乎全部〔97%〕埋藏在地面一下，称为地下水。大局部地下水或通过地下流动，回到海洋；或先进入河流或湖泊，最终又回到海洋。Thesevastundergroundwaterdepositsprovidemuchneededmoisturefordryareasandirrigateddistricts.Undergroundwateractsinsimilarwaystosurfacewater,alsoperforminggeomorphicworkasanagentofgradation.这些广阔的地下含水层为干旱地区和灌溉区域提供了迫切需要的水分。地下水的作用和地表水的作用类似，也以均夷作用塑造着地貌。Eventhoughmanhasbeenawareofsub-surfacewatersinceearliesttimes,itsnature,occurrence,movementandgeomorphicsignificancehaveremainedobscure.Recently,however,someanswershavebeenfoundtotheperplexingquestionsaboutundergroundwater’srelationshiptothehydrologicalcycle.尽管人类自古以来就知道地下水，但对它的特性、发生、运动和地貌意义还不清楚。然而，近来关于地下水和水文循环关系的这些错综复杂的问题已找到了一些答案。1sourceofundergroundwater地下水资源SincethedaysofVitruviusatthetimeofChrist,manytheorieshavebeenpresentedtoexplainthelargevolumeofwaterunderneaththeearth’ssurface.Onetheorywasthatonlytheseacouldprovidesuchlargequantities,thewatermovingundergroundfromcoastalareas.Vitruviuswasthefirsttorecognizethatprecipitationprovidedthemainsourceofsub-surfacewater,althoughhisexplanationsofthemechanicsinvolvedwerenotveryscientific.自从公元维特鲁维亚时代以来，为了解释在地面以下存在大量的地下水，已经提出了许多理论。一种理论认为：只有海洋能提供大量的地下水，地下运动的水来自海岸带。维特鲁维亚是第一个认识到降水是地下水的主要来源，尽管他所涉及的力学方面的解释很不科学。Histheory,nowfirmlyestablished,istermedtheinfiltrationtheory,andstatesthatundergroundwateristheresultofwaterseepingdownwardsfromthesurface,eitherdirectlyfromprecipitationorindirectlyfromstreamsandlakes.Thisformofwateristermedmeteoric.Averysmallproportionofthetotalvolumeofsub-surfacewaterisderivedfromothersources.Connatewateristhatwhichistrappedinsedimentarybedsduringtheirtimeofformation.Juvenilewateriswateraddedtothecrustbydiastrophiccausesataconsiderabledepth,anexamplebeingvolcanicwater.现在，他的理论已经确立，称作渗透理论：认为地下水是从地表渗入到地下的结果，或者直接来自降雨，或者间接来自河流或湖泊。这种水称作天然水。地下水总量中的很小一局部来自其他水源。原生水是在沉积岩形成时滞留在其中的水。岩浆水是由于在相当深处的地壳运动对地壳所添加的水，火山水就是一个例子。2distributionofsub-surfacewater地下水的分布Duringprecipitationwaterinfiltratesintotheground,undertheinfluenceofgravity,thiswatertravelsdownwardsthroughtheminuteporespacesbetweenthesoilparticlesuntilitreachesalayerofimperviousbedrock,throughwhichitcannotpenetrate.Theexcessmoisturedrainingdownwardsthenfillsupalltheporespacesbetweenthesoilparticles,displacingthesoilair.Duringtimesofexcessiverainfallsuchsaturatedsoilmaybefoundthroughoutthesoilprofile,whileduringperiodofdroughtitmaybenon-existent.Normallytheupperlimitofsaturatedsoil,termedthewatertable,isameterorsobelowthesurface,theheightdependingonsoilcharacteristicsandrainfallsupply.在降雨期间，水渗入地下。在重力的影响下，这种水通过土壤颗粒间的孔隙向下流动直至水流到达不透水岩层为止。向下移动的过量水，充满了土壤颗粒之间的孔隙，挤出了土壤中的空气。在雨水过多时，整个土壤剖面到达饱和状态，而在干旱时期就不存在饱和土壤。通常，饱和土壤的上部界限称为地下水位，约为地面以下1米左右，其高度取决于土壤特性和降雨量。Accordingtothedegreeofwater-occupiedporespace,sub-surfacemoistureisdividedintotwozones:thezoneofaerationandzoneofsaturation,asillustratedinFig4.1.根据水充满孔隙的程度，地下水分为两层：包气带和饱水带，如图4.1所示2.1zoneofaeration包气带Thisareaextendsfromthesurfacedowntotheupperlevelofsaturation-thewatertable.Withrespecttotheoccurrenceandthecirculationofthewatercontainedinit,thiszonecanbefurtherdividedintothreebelts:thesoilwaterbelt,theintermediatebeltandthecapillaryfringe(Fig.4.1)这一区域从地面向下延伸到水面－地下水位。根据该层中所包含的形成和运行情况，可进一步划分为三个带：土壤水分带、中间带和毛细饱和带〔图4.1〕Fig4.1zoneofaerationandsaturation(1)Soilwaterbelt土壤水分带Assumingthatthesoilisdry,initialrainfallallowswatertoinfiltrate,theamountofinfiltrationdependingonthesoilstructure.Soilscomposedmainlyoflargeparticles,withlargeporespacesbetweeneachparticle,normallyexperienceamorerapidrateofinfiltrationthandosoilscomposedofminuteparticles.Nomatterwhatthesoiliscomposedofsomewaterisheldonthesoilparticlesasasurfacefilmbymolecularattraction,resistinggravitationalmovementdownwards.Thewaterheldinthismannerisreferredtoashygroscopicwater.Eventhoughitisnotaffectedbygravity,itcanbeevaporated,thoughnotnormallytakenupbyplants.假设土壤是枯燥的，初期降雨量就向土壤中入渗，入渗量取决于土壤结构。主要由大颗粒构成的土壤，在每个颗粒之间有很大的孔隙，在正常情况下入渗速度要比在小颗粒组成的土壤中快得多。不管土壤由什么构成，土壤颗粒外表由于水分子引力吸附着一些水，就形成一层水膜，阻止重力水向下运动。以这种方式保持的水称为吸湿水。即使它不受重力的作用，它也能蒸发，但是通常不能被植物吸收。(2)Intermediatebelt中间带Thisbeltoccursduringdryperiodswhenthewatertableisatconsiderabledepthbelowthesurface.Itissimilartothesoilwaterbeltinthatthewaterisheldonthesoilparticlesbymolecularattraction,butdiffersinthatthefilmsofmoisturearenotavailablefortranspirationorforevaporationbacktotheatmosphere.Inhumidareas,withafairlyreliablerainfall,thisbeltmaybenon-existentorveryshallow.Throughit,gravitationalorvadosewaterdripsdownwardstothezoneofsaturation.中间带发生在干旱季节，地下水位在地面以下相当深的地方。中间带与土壤水分带相似，也是通过分子引力把水分保持在土壤颗粒上。但差异在于：中间带的水膜不能通过蒸腾或蒸发回到大气层。在湿润地区，降雨相当可观，中间带可能不存在或者非常浅。重力水即渗漏水通过中间带向下渗漏到饱水带。(3)Capillarybelt毛细饱和带Immediatelyabovethewatertableisaveryshallowzoneofwaterwhichhasbeendrawnupwardsfromtheground-waterreservoirbelowbycapillaryforce.Thedepthofthiszonedependsentirelyonsoiltexture,soilswithminuteporespacesbeingabletoattractmorewaterfrombelowthansoilswithlargeporespaces.Inthelattertypesofsoilthemolecularforcesarenotabletospanthegapsbetweensoilparticles.Thus,sandysoilsseldomexhibitanextensivecapillaryfringe,mergingfromsoilwaterthroughtothezoneofsaturation.这一带位于地下水位以上，是个很浅的含水带，这些水是由毛细管从地下水库吸引上来的。这一层的深度完全取决于土壤的结构，含有微小孔隙的土壤比含有大空隙的土壤能从下面吸取更多的水。在后一种类型的土壤中，分子引力不能跨越土壤颗粒间的孔隙。因此，砂质土很少出现大面积的毛细饱和带，而土壤水分带和饱水直接相通。2.2zoneofsaturation饱和带Thezoneofsaturationistheareaofsoilandrockwhoseporespacesarecompletelyfilledwithwater,andwhichisentirelydevoidofsoilair.Thiszoneistechnicallytermedgroundwatereventhoughthetermbroadlyincludeswaterinthezoneofaeration.Theupperlimitofthezoneofsaturationisthewatertableorphreaticsurface.Itisdifficulttoknowhowdeeptheground-waterzoneextends.Althoughmostgroundwaterisfoundintheupper3kmofthecrust,porespacescapableofwaterretentionextendtoadepthof16km.thisappearstobetheupperlimitofthezoneofrockflowagewherepressuresaresogreatthattheycloseanyinterstitialspaces.饱水带是孔隙完全被水充满、没有一点空气的土石层。这一层的技术术语叫做地下水，尽管这一术语广义上也包含包气带的水。饱水带的上部边界是地下水位或地下水面。要了解地下水层的深度是困难的，虽然大多数地下水是在地壳表层3千米以内发现的，但是能够保存水的微小孔隙可以延伸到16千米的深度。这似乎就是贮水岩层的上限。那里的压力大到足以充满任何孔隙。Theupperlevelofthesaturatedzonecanbecompletelyplottedbydiggingwellsatvariousplaces.Studiessuggesttwoquiteinterestingpoints(Fig.4.2).在不同的地方挖探测井就能完全标绘出饱和层的上界面。通过研究提出了两个十分有趣的论点〔图4.2〕1)Thewatertablelevelishighestunderthehighestpartsofthesurface,andlowestunderthelowestpartsofthesurface.Hillsandmountainshaveahigherlevelphreaticsurfacethanvalleysandlakes.Thereasonforthisisthatwatercontinuallypercolatingthroughthezoneofaerationliftsthewatertable,whileseepagefromtheground-waterzoneintocreeksandlakeslowersthelevel.1〕在地面最高的地方，地下水位也最高；而在地面最低的地方，地下水位就最低。丘陵和山脉的地下水位比峡谷和湖泊的地下水位高。这是因为水通过包气带不断地渗透提高了地下水位；地下水层的渗流进入河沟和湖泊，从而降低了地下水位。2)Thedepthofthewatertablebelowthelandsurfaceisgreatestinuplandareaswherethewatermovesquitefreelydownhillundergravity.Closetostreams,lakesandswampsthewatertableiscloseto,ifnotatthesurface,aswaterfromthehigherareasbuildsitup.2〕在山区高地，地下水位的埋藏深度最大，在重力作用下，那里的地下水非常顺畅地向下流动。靠近河流、湖泊和沼泽地区时，地下水位即使未到达地表，也接近地表，因为水从较高的地方聚集而来使地下水位升高。Whatcausesflooding?Thebasiccauseisexcessiverunofffromcatchmentsintoriversystemsincapableofcarryingthisextravolume.Canscienceandtechnologypreventfloodingor,atleast,reduceitsseverity?Unfortunately,thisisacomplexproblemtowhichasyetthereisnoverysatisfactorysolution.洪水是怎样形成的？根本的原因是流域内过多的径流汇入河系，超过了河系的承载能力。科学技术能防止洪水发生吗？或者至少能降低洪水的危害吗？遗憾的是，这是一个迄今为止还没有满意答复的复杂问题。Letusconsiderfirstthereductionofrunofffromcatchmentareas.Someregionshavesoilswhichhavelowabsorbingcapacity.Inaheavyrainstormsuchsoilisquicklysaturatedandalladditionalrainfallthenrunsoffintotheriver.Aseasonalvariableisthemoisturestatusofthesoilatthecommencementofarainstorm.Ifthesoilisalreadymoist,arelativelyminorstormcouldstillcauseheavyrunoffbecausethesoilisincapableofretainingadditionalmoisture.Thesefactorsarenoteasilyinfluencedbyman.However,man’sutilizationofthecatchmentareacanhaveanimportantinfluenceonflooding.Largescalecleaningoftreesandscrubgreatlyreducesthecapacityofthesoiltoretainwater.Italsotendstocausesoilerosionwhichaggravatesfloodingbychockingriversandstreamswithdepositedsilt.Correctmanagementofcatchmentareasisthereforeoneimportantapproachtotheproblemoffloodcontrol.让我们首先考虑一下如何减少流域的径流。有些地区的土壤吸水能力很低。下暴雨时，这种土壤很快就饱和了，多余的雨水全部流入河道。季节性的变量就是暴雨开始时土壤的水分状态。如果土壤已经湿润，较小的暴雨也会引起大量的径流，因为这种土壤已不能保持更多的水分。这些因素不易受人类的影响。然而，人类对流域土地的利用情况会对洪水产生重要影响。大规模地砍伐树木会降低土壤保持水分的能力。砍伐树木也会加剧土壤侵蚀，导致河道淤塞，从而加剧了洪水。所以对流域正确的开发利用是控制洪水的一项重要方法。Moredirectapproachwhichisusedinanemergencyistheconstructionoflevees.whenrisingfloodwatersthreatenatownshipthecitizensformwork-partiestobuildbarricadesofsandbagsalongtheriverbank,hopingthatthosebarricadeswillholdbackthefloodwatersuntiltheemergencypasses.Itmaybewanderedwhyleveesarenotusuallybuiltaspermanentstructurestowhichthetownisprotectedatalltimes.Thereasonisthatleveesareanunsatisfactorysolutiontotheproblem.Ifaleveescollapses,thefloodwatersescapeasasuddendelugewithincreasedcapacityfordestruction.Leveesastheydivertthefloodwaterfromoneareafrequentlycreateoraggravateproblemsinanother.Theycanbeacauseofenmitybetweencommunitiesforthisreason.筑堤是在紧急情况下可采用的更加直接的方法。当上涨的洪水威胁城镇时，居民通常组成修堤队，沿河岸用沙袋筑堤，想用岸堤挡住洪水，直到紧急状态消失。人们或许想知道为什么通常不把河堤建成永久性设施，让城镇永保安宁。原因在于筑堤不是解决问题的圆满方法。如果堤岸崩溃，洪水涌出，就成为破坏能力剧增的突发性水灾。大堤会使一个区域来洪水转向，常常在另一地区引起问题或使问题变得更为严重。因此大堤也会成为居民点之间不和的原因。Antherapproachistheconstructionofdamssothatfloodwaterscanberetainedinareservoiruntilthecrisisisover,slowreleaseofthewaterduringthesucceedingweeksormonthswouldthenbepossible.Combinedpurposeirrigationandfloodcontroldamswouldseemtobealogicalsolution.Unfortunately,areservoirwhichistobeusedforirrigationneedstobekeptnearlyfullinwinter,whileonewhichistobeusedforfloodcontrolneedstobekeptempty,sothatitisavailableasawaterstorewhenneeded.Thisconflictofoperatingrequirementsmeansthatcombinedpurposedamsarerarelyfeasible.Separatedamswouldberequiredforfloodcontrolandtheirveryhighcostmakesthisanimpracticalsolution.Thenextapproachtotheproblemisthatofimprovingthecapacityoftherivertocarrylargervolumesofwaterwithoutoverflowingitsbanks.Anumberofmeasuresareavailable,somesimple,somecomplex.Theyallhavewidespreadeffectsontheriversoanyofthesemeasuresshouldbeusedaspartofacomprehensiveplan.Workofthiskindisknownas“riverimprovement”or“rivermanagement”.另一种方法是筑坝，让洪水存蓄在书库里，而在随后的几周或几个月内把洪水慢慢地放掉以度过危机。灌溉和防洪两用的坝似乎是合理的解决方法。遗憾的是，用于灌溉的水库冬季要蓄水，而用于防洪的水库却要放空，以便需要时，可以蓄水。运行要求的矛盾意味着两用坝很少能办得到。防洪需要单独筑坝，造价很高，这又使它成为不切实际的解决方法。能解决这一问题的另一个方法是改善河道的过水能力，使河道能宣泄更多的水量而两岸并不漫溢。有许多措施都是可行的。有的简单，有的复杂。所有这些方法对河流都普遍有效。所以任何一种措施都应作为全盘方案的一局部。这种工作称作“河道整治”或“河道管理”Onesimple,