环境工程专业英语unit1

Unit1Thehydrologiccycle水循环

Professional-relatedEngineering1.ThehydrologiccycleTheworld’ssupplyoffreshwaterisquitesmallcomparedtotheenormousvolumesofsaltwaterintheoceans.世界的淡水供给比起海洋中浩瀚的咸水来是十分少的。Fortunatelythefreshwatersupplyisrenewedbythehydrologiccycle,whichisanimmensesolardistillationsystem.所幸的是，借助于水循环使淡水得以更新，而水循环是一个无限大的太阳蒸馏系统。Professional-relatedEngineeringProfessional-relatedEngineeringWaterevaporatedfromtheoceansistransportedoverthecontinentsbymovingairmasses.Whenthismoisture-bearingairiscooledtoitsdewpointtemperature,thevaporcondensesintowaterdropletsformingfogorcloud.从海洋蒸发的水借助于空气团的移动被传输到陆地上空。当这些潮湿的气团冷却到它的露点温度以下时，蒸汽冷凝成水滴形成雾和云。Professional-relatedEngineeringThecoolingoccurswhenthemoistairisliftedtohigherelevations.Sinceairpressuredecreaseswithelevation,theairexpandsasitisliftedandcooledinaccordancewiththeIdealGasLaw:在湿气团被抬升到更高高度时，温度不断下降。因为大气压随高度增加而下降，空气在被抬升的过程中发生膨胀，按照理想气体定律，气团温度将下降。Professional-relatedEngineeringLiftingoccursinthreeways.Orographicliftingoccurswhentheairisforcedupovertheunderlyingterrane.Frontalliftingoccurswhentheairmassispushedupbyacoolerairmass.Theboundarybetweenthetwoairmassesiscalledafrontalsurface.抬升在三种情况下发生。当气团被迫从岩层上空越过时，发生山体抬升作用。当气团受到另外一个冷气团的冲击时，发生前部抬升作用。两个气团之间的分界面叫做前端表面。Professional-relatedEngineeringFinally,themoistairmaybeheatedfrombelowasitpassesoverawarmersurface,causingconvectivelifting,whichmayresultinaconvectivethunderstorm.最后，当湿气团从一个热气团上方经过时，下部被加热，引起对流抬升，有可能导致对流暴雨的形成。Professional-relatedEngineeringOftentwoormoreofthosemechanismsmaytakeplacetogether.经常地，是两种或更多种机理一起发生作用。Abouttwo-thirdsoftheprecipitationthatreachesthelandsurfaceisreturnedtotheatmospherebyevaporationfromwatersurface,soil,andvegetationandthroughplanttranspiration.大约地面降水的三分之二借助于水面、土壤、植被的蒸发作用和植物的蒸腾作用返回到大气中。

Professional-relatedEngineeringTheremainingthirdoftheprecipitationreturnsultimatelytotheoceanthroughsurfaceorundergroundchannels.剩余的三分之一降水通过地表和地下的渠道最终回到海洋。

Professional-relatedEngineeringThelargepercentageofprecipitationthatisevaporatedhasoftenledtothebeliefthatincreasingthisevaporationbyconstructionofreservoirsorplantingoftreeswillincreasethemoistureavailableintheatmosphereforprecipitation.大部分的降水被蒸发，使得人们相信通过修建水库和植树能够提高水的蒸发量，而这进一步能够增加大气湿度以利于形成降水。Professional-relatedEngineeringActuallyonlyasmallportionofthemoisture(usuallymuchlessthan10percent)thatpassesoveranygivenpointontheearth’ssurfaceisprecipitated.Hence,moistureevaporatedfromthelandsurfaceisaminorpartofthetotalatmosphericmoisture.事实上，在经过地球表面任何一个特定区域上空的湿气，只有很小部分（经常不足10%）形成了降水。因此，从陆地表面蒸发的湿气只是大气总湿度中很小的一部分。Professional-relatedEngineeringThehydrologiccycleisdepicteddiagrammaticallyinfig.1-1.图1-1描述了水循环。

Professional-relatedEngineeringNosimplefigurecandojusticetothecomplexitiesofthecycleasitoccursinnature.没有一个简单的示意图可以适当地描述自然界中实际发生的这种循环的复杂性。Thescienceofhydrologyisdevotedtoastudyoftherateofexchangeofwaterbetweenphasesofthecycleandinparticulartothevariationsinthisratewithtimeandplace.水力学正是致力于研究该循环的各阶段之间水的交换速率，特别是这种速率随时间和地点的变化。

Professional-relatedEngineeringThisinformationprovidesthedatanecessaryforthehydraulicdesignorphysicalworkstocontrolandutilizenaturalwater.这些研究给我们为了控制和利用天然水而进行的水力设计或实际工程提供所需要的数据。2.Typesofprecipitation

降水的形式Precipitationincludesallwaterthatfallsfromtheatmospheretotheearth’ssurface.降水包括所有从大气降落到地球表面的水。Professional-relatedEngineeringProfessional-relatedEngineeringprecipitationoccursinavarietyofformsthatareofinteresttothethemeteorologist,butthehydrologistisinterestedindistinguishingonlybetweenliquidprecipitation(rainfall)andfrozenprecipitation(snow,hail,sleet,andfreezingrain).降雨以各种各样的形式发生，气象学者对降雨的形式比较干兴趣，但水文学家只想区分它是液态降水（降雨）或固态降水（雪、雹、雨夹雪和冻雨）。Professional-relatedEngineeringRainfallrunsofftothestreamssoonafteritreachesthegroundandisthecauseofmostfloods.降雨在它到达地面不久后形成径流汇集到河流中，是引发大多数洪水的原因。Frozenprecipitationmayremainwhereitfallsforalongtimebeforeitmelts.固态降水在它融化之前，可以在降落地点保持很长时间。Professional-relatedEngineeringMeltingsnowisrar