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CulvertDesign1Introduction：Culvertshavebeenutilizedforthousandsofyearsasameanstotransmitwaterunderwalkwaysorroads.Often,aculvertissimplyinstalledwithoutmuchthoughttohowmuchwateritneedstoconveyunderextremeconditions.Ifaculvertcannotconveyalloftheincomingwater,thenthewaterwillflowoveroraroundthepipe,orsimplybackupbehindtheculvertcreatingapondorreservoir.Ifanyoftheseconditionsareunacceptable,thentheproperculvertdiameterandnumberofculvertsmustbeselectedpriortoinstallationinordertoconveyalloftheanticipatedwaterthroughthepipe(s).Thiscalculationhelpsthedesignersizeculvertsaswellaspresentaheadwaterdepthvs.dischargeratingcurve.TheLMNOEngineeringcalculationisprimarilybasedonthemethodologypresentedinHydraulicDesignofHighwayCulvertsbyNormann(1985)andpublishedbytheU.S.DepartmentofTransportation'sFederalHighwayAdministration.ItisalsoknownasHDS-5(HydraulicDesignSeriesNo.5).HDS-5focusesonculvertdesign.Culvertdesignisusuallybasedonthemaximumacceptabledischarge-thustheHDS-5methodologyisgearedtowardculvertsflowingfullwithwaterpossiblyflowingovertheroadabovetheculvert.InadditiontoprogrammingtheHDS-5methodology,LMNOEngineeringwishedtocomputeheadwaterdepthsforlesserflows.Therefore,inadditiontotheHDS-5methodology,wehaveaddedtheManningequationforculvertsflowingpartiallyfull.TheHDS-5methodologyalsoassumesthattheuserknowsthetailwaterdepth(Yt)beforeusingthemethodology.ThoughYtcanbefoundbyfieldmeasurements,itisoftencomputedintheofficeusingManning'sequationbasedonbottomwidth,sideslopes,channelroughness,andchannelslope.Therefore,LMNOEngineeringaddedtheadditionalfeatureofabuilt-insubroutineforcomputingYtfortrapezoidalchannels.Notethatforthegraphingportionofourcalculation,Ytisre-computedfor1摘自：科技报告缩微资料库《涵洞和水工结构》作者：wellen·凯恩·dl;费尔班克斯·斯特--阿拉斯加大学theentirerangeofflows(Qt)shownonthegraph(unlesstheuserspecificallyinputsYt).DesignCulvertAndDesignRequirementsforCulvertJointsTheCulvertcommandletsyoumodelthebehaviourofaculvertundervariousconditionsofflow.Aculvertisashort,closed(covered)conduitthatconveysstormwaterrunoffunderanembankment,usuallyaroadway.Theprimarypurposeofaculvertistoconveysurfacewater,butproperlydesigneditmayalsobeusedtorestrictflowandreducedownstreampeakflows.Inadditiontothehydraulicfunction,aculvertmustalsosupporttheembankmentand/orroadway,andprotecttrafficandadjacentpropertyownersfromfloodhazardstotheextentpracticable.Mostculvertdesignisempiricalandreliesonnomographsandstandardprocedures.Thepurposeofthissectionistoprovideanoverviewofculvertdesignstandardsandprocedures.Becauseofthemanyvariablesinvolved,theprocessislargelyoneoftrialanderrorandMIDUSSdoesnotsuggestinitialfeasiblevaluesforthedesign.Culvertdesigncanbecarriedoutforeithersteady,(i.e.timeinvariant)floworforaninflowhydrograph.Wheninflowisintheformofahydrographthehydraulicdesigncanbefollowedbyaroutingprocessthatshowstheattenuationoftheinflowhydrographcausedbypondingthatoccursupstreamoftheembankment.Insuchcasesthepeakoutflowfromthebarrelwillbelessthanthepeakinflowandyoucanrefinethebarreldesignforthereducedflowifdesired.Thedesignofaculvertshouldtakeintoaccountmanydifferentengineeringandtechnicalaspectsattheculvertsiteandadjacentareas.Thelistbelowpresentsthekeyconsiderationsforthedesignofculverts.25-yeardesignstormevent.Theallowableheadwateristhedepthofwaterthatcanbepondedattheupstreamendofthecul...