环境工程概论 第三章

HydrologyAssociateprofessor:XieliResearchinterest:anaerobictechnologyforbiogasproduction;industrialwastewaterandmunicipalwastewatertreatmentEmail:[e-mail]racrossandthroughnearsurfaceenvironmentsTermsEvaporation:theconversionofliquidwaterfromlakes,streams,andotherbodiesofwatertowatervaporEvaporatingplayalakewithsaltsaroundmargin,easternWashingtonTermsTranspiration:theprocessbywhichwaterisemittedfromplantsthroughstomataEvapotranspiration:todescribethecombinedlossesofwaterduetotranspirationandevaporationFig.4.1Evaporation&TranspirationPrecipitationTheprimarymechanismbywhichwaterisreleasedfromtheatmosphereFormedbywatervaporintheatmosphereInfiltration(percolation):watermovesverticallythroughthesoilstoformgroundwaterSurfacerunoff:waterfallstotheearth’ssurface,thedropletseitherrunoverthegroundintostreamsandriversRainfall(precipitation)Whydoweneedtoconsiderrainfall?Agriculture–whattoplantincertainareas,whereandwhentoplant,whentoharvestHorticulture-howandwhentoirrigateEngineers-todesignstructuresforrunoffcontroli.e.storm-waterdrains,bridgesetc.Depth,VolumeandIntensityRainfallamounts:expressedintermsofthedepthofwateraccumulatedintheraingageduringastorm,millimetersorinchesVolume=depth*areaRainfallintensity:therateatwhichtherainfallsExample1Duringa20minrainstorm,adepthof25mmofrainfallwasrecordedforanareaof2.5ha.Computethetotalvolumeofwaterfellonthatarea,andtherainfallintensityTermsRecurrenceInterval：theaveragenumberofyearsbetweenstormsofspecificintensityanddurationscanbedetermined,byexaminingmanyyearsofrainfallrecordsandapplyingstatisticalanalysesN-yearstorm:NistherecurrenceintervalinyearsQuiz5-yearstormAsimilarstormwilloccuronceexactlyevery5yearsOveralongperiodoftime,theaveragetimespanbetweenstormsofthatparticularintensityanddurationis5yearsProbabilityofoccurrenceP=1/NDiscussionquestionsWhenafloodhasarecurrenceinterval(returnperiod)of5years,itmeansthatthechanceofanotherfloodofthesameorlessseverityoccurringnextyearis5%.Isthissentencetrueorfalse?Intensity-Duration-FrequencyRelationshipTypicalIDFcurves,Fig.3.6Example3.4forapplicationSurfacewaterhydrologyWatershed:thetotallandareathatcontributesrunofftoastreamorriver,namedalsoasdrainagebasin,orcatchmentareaDrainagedividelineorridgeline:theboundaryofthewatershedSubbasin:thesmallerareaofthewatershedWatersheddivideOutflowpointOverlandflow,TennesseeValley,CaliforniaFigureMississippiRiverWatershedTermsStreamflow:theamountorvolumeofwaterthatflowsinastreamiscalledtheflowrateordischargeofthestream(m3/s)Droughtflow:thelowestaveragedischargeoveraperiodof1weekwitharecurrenceintervalof10years,theminimumaverage7-consecutive-day10yearflow(MA7CD10Flow)CheckExample3.8GroundwaterbeginsasINFILTRATIONPrecipitationfallsandinfiltratesintothesubsurfacesoilandrock•Canremaininshallowsoillayer•Mightseepintoastreambank•Mayinfiltratedeeper,recharginganaquifer•Maytravellongdistances•MaystayinstorageasgroundwaterOriginationofGroundwaterGroundwater&theVadoseZoneaquifersAlayerofsoilorrockinwhichgroundwatercanmoverelativelyfreelyConfinedorartesianaquifer:sandwichedbetweentwoimpermeablelayersthatblocktheflowofwaterGroundwatervelocitySlow,1m/yrDarcy’slawNatural&ArtificialRechargeRapid-infiltrationpitsSpreadwateroverthelandinpits,furrows,ditchesorbuildsmalldamsincreeksandstreamstodeflectrunoffGroundwaterinjectionConstructrechargewellsandinjectwaterdirectlyintoaquifersInfiltrationreplenishedaquifersSlowprocess--groundwatermovesslowlythroughtheunsaturatedzoneRechargeRatedeterminedbyprecipitation&depthAnaquiferinNewMexico,ifemptied,wouldtakecenturiestorefillwhereasashallowaquiferinsouthGeorgiamaybereplenishedalmostimmediatelyGroundwaterFlowDrivenbyhydraulicgradientsQ=KIAKishydraulicconductivityAiscrosssectionalareaIishydraulicgradient