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Statistical Analysis of Straits of Mackinac Line 5: Worst Case Spill Scenarios
UNIVERSITY OF MICHIGAN, ANN ARBOR
DAVID J. SCHWAB, PH.DMARCH 2016
University of Michigan Water Center • www.graham.umich.edu/water 1
StatisticalAnalysisofStraitsofMackinacLine5WorstCaseSpillScenarios
DavidJ.Schwab,Ph.D.
IntroductionTheStraitsofMackinacistheroughly10kmlongsectionofwaterwaythatjoinsLakesMichiganandHuronintoasinglehydraulicsystem.Itisspannedatitsnarrowestpoint(6km)bytheMackinacBridge,whichconnectsMichigan’supperandlowerpeninsulas.JustwestoftheMackinacBridge,itisalsospannedbyasubmergedsectionoftheEnbridgeInc.Line5oilpipeline.Line5typicallycarriesupto20milliongallonsoflightcrudeoil,lightsyntheticcrudeoil,andnaturalgasliquidsacrosstheStraitseachday(AlexanderandWallace,2013).CurrentsintheStraitscanbeasstrongascurrentsintheDetroitRiver(upto1m/s)andtendtoreversedirectionbetweeneastwardflowingandwestwardflowingeveryfewdays(SaylorandSloss,1976).PeakvolumetrictransportthroughtheStraitscanreach80,000m3/s(morethan10timestheflowoftheNiagaraRiver).FlowthroughtheStraitscanplayanimportantroleinwaterquality,contaminanttransport,navigation,andecologicalprocesses.Tobetterunderstandandbettercommunicatetheseuniqueflowconditions,in2014theUMWaterCenterusedarecentlypublishedhydrodynamicmodel(AndersonandSchwab,2014)oftheconnectedMichigan-Huronsystemtoproducecomputersimulationsandanimationsofhypotheticaltracer(dye)releasesintheStraits(Schwab,2014).Thesesimulationswerecarriedoutfortworeleaseperiods,oneinsummerandoneinfall.ThesimulationsshowedgraphicallyforthesetwoexamplecaseshowfarandhowfastanoilspillcouldspreadfromtheStraits.ThepurposeofthisreportistoexpandontheresultsoftheSchwab,2014studybyusingsimilarcomputersimulationtechnologytorunalargenumberofoilspillsimulationcases(840)coveringawidevarietyofweatherconditionsusingrealisticestimatesofworst-casedischargespillparameters,includingamountofoilreleased,oilcharacteristicsoflightcrudeoil(suchasspecificgravityandevaporationrate),andrealisticoilspilldispersionproperties.ThespillsimulationcasesusecurrentsfromhydrodynamicsimulationsofflowintheStraitsfor2014,basedonthesamehydrodynamiccomputermodelusedinAndersonandSchwab,2014.Theresultsofthecasesarethenanalyzedtodevelopstatisticaldistributionmapsbasedonallcasesforseveralparameters,whicharerelevantforquantitativeriskassessment.Theseincludetimeseriesoftheopenwaterareacoveredbythespill,timeseriesofthelengthofimpactedshoreline,timeseriesofthebeachedvolumeandopenwatervolume,probabilitymapsofoffshoreimpactarea,probabilitymapsofimpactedshorelinearea,andamapoftheshortesttimeitwouldtaketoreachaspecificareainanyofthe840cases.Inallcases,itisassumedthatnooiliscontainedorrecovered
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bycleanupefforts.Thisassumptionisconsistentwiththe“worstcase”scenario.Thestatisticalapproachusedhereissimilartotheapproachusedinarecentreportonthepotentialimpactofadeep-seaoilspillonthecoastsofNewZealand(LebretonandFranz,2013).HydrodynamicModelThecurrentsusedtocalculatetrajectoriesinthisstudyarebasedonthehydrodynamicmodeldescribedinAndersonandSchwab(2013).Thatmodelisathree-dimensional,unstructuredmeshhydrodynamicmodelthatextendsoverLakesMichiganandHuron,includingtheStraitsofMackinac.ThemodelisbasedontheFiniteVolumeCoastalOceanModel(FVCOM;Chenetal.,2006),afree-surface,hydrostatic,primitive-equationhydrodynamicmodelthatsolvesthecontinuity,momentum,andenergyequationsinthree-dimensionsonanunstructured,sigma-coordinate(terrain-following)mesh.TheFVCOMhasbeenvalidatedandimplementedsuccessfullyinseveralcoastaloceanapplications,aswellasintheGreatLakesandconnectingchannels(seeAndersonandSchwab,2013fornumerousreferences).Forthecombined-lakemodel,threearc-secondbathymetricandcoastlinedatafortheGreatLakeswereobtainedfromtheNOAANationalGeophysicalDataCenter(NGDC)andinterpolatedtotheunstructuredmesh.Thehorizontalgridresolutionofthemeshrangesfrom100mintheMackinacStraitsto2.5kminthecenterofthelakes.20uniformlydistributedsigmalayersprovideverticalresolution.TheAndersonandSchwabmodelwasrunusingmeteorologicalconditionsfromApril-December,2014.TherequiredsurfacemeteorologicalfieldswereextractedfromtheNOAANCEPCFSR(NationalOceanicandAtmosphericAdministration,NationalCentersforEnvironmentalPrediction,ClimateForecastSystemReanalysishttp://cfs.ncep.noaa.gov/cfsr/)hourlygriddedfieldsfor2014.ResultsofthemodelrunshowedexcellentagreementwithactualcurrentsmeasuredintheStraitsduringthisperiod(AndersonandSchwab,2016).OilSpillSimulationModelInthisstudy,anoilspillisrepresentedbyacloudofindividualtracerparticles,movingwiththecurrentsfromthehydrodynamicmodel.ThecomputercodeusedtosimulatetheparticlemotionisbasedontheLagrangianparticletrackingcodesuppliedwiththeFVCOMhydrodynamicmodel.Inthisversionoftheparticletrackingcode,wehaveoptimizedthecomputationalschemebyimprovingthealgorithmforidentifyingthemeshelementcontainingaparticularparticlelocation.Ingeneral,theparticletrackingapproachusedhereisverysimilartothewidelyusedGNOME(GeneralizedNOAAOilModelingEnvironment,http://response.restoration.noaa.gov/gnome),buthasbeenoptimizedforcarryingoutalargenumberofsimulationsbasedonasinglehydrodynamicmodelrun.Arandomwalkprocessisusedtosimulatesubgrid-scaleturbulentvariabilityinthevelocityfield.Weusedahorizontaldiffusioncoefficientof10m2/secasrecommendedforthedefaultGNOMEsetting.
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Foreachspillsimulation,theoilisrepresentedby10,000discreteparticlesreleasedonthesurfaceofthewateratapointjustsouthofhalfwaybetweenthenorthandsouthpipelineterminalsintheStraits(45.81111°N,84.76944°W).Theparticlesarereleasedatthesurfacesincethespecificgravityofthepetroleumproductscurrentlycarriedinthepipelinewouldcausetheproducttoquicklyrisetothesurfaceintheeventofapipelinebreach.WeexpectthatareleasepointnearthecenteroftheStraitsisthe“worstcase”condition,particularlyintermsofmaximizingtheareaofpotentialimpact.Threedifferentspillvolumesareconsidered:1)5,000bbl,2)10,000bbl,and3)25,000bbl.The5,000bblamountisclosetothe4,500bblvolumeusedinthemulti-agencyspillsimulationexerciseintheStraitsin2015.The10,000bblvolumeisslightlymorethanthe8,583bbl“worst-casedischargeattheStraits,”estimatedbyEnbridgeintheirresponsetotheApril,2014informationrequestfromtheStateofMichiganAttorneyGeneral.It’simportanttonotethattheestimatedamountofoilreleasedintheKalamazooRiverspillfromEnbridgeLine6Bin2010is25,000bbl.Forthethreespillvolumes—5K,10Kand25K—eachdiscreteparticleofoilinthecloudof10,000particlesinitiallyrepresents0.5,1.0,or2.5bblofoilrespectively.Thetracerparticlesinthesesimulationsarereleasedsimultaneously,buttheresultswouldnotchangesubstantiallyforreleasedurationslessthananhourortwo.Forlongerreleasedurations,thelowerreleaseratewouldlikelycauseevenmoredispersionofthespillthanthesimultaneousreleasecase.Evaporationisanimportantprocessformostoilspills.Therateofevaporationdependsprimarilyonthecompositionoftheoilproduct,andsecondarilyonenvironmentalconditions,suchastemperatureandwaves.Forthisstudy,weassumealogarithmicfunctionfortheevaporationratewithcoefficientsappropriatefor“AlbertaMixedSweetBlend”crudeoil(Fingas,2013and2015):
%Evaporation=(3.41+0.054T)ln(t)HereTistemperatureindegreesCandln(t)isthenaturallogarithmofthetimeinminutes.Weuseatemperatureof20degreesCforallsimulations.Thisresultsin32%evaporation1dayafterreleaseand40%evaporationafter10days.AlthoughwatertemperatureintheStraitsislowerthan20°Cintheearlyspringandlatefall,whichwouldslightlydecreasetheevaporationrate,itcanalsobehigherthan20°Cinthesummer,whichwouldslightlyincreasetheevaporationrate.Whencurrentsandrandom-walkdiffusioncarryaparticleintotheshoreline,theparticleisconsidered“beached”andnotallowedtomoveagain.Theamountofoiltheparticlerepresentsisitsinitialvaluereducedbyevaporation,accordingtotheequationabove.
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Spillsimulationcaseswerecarriedoutfor840overlapping60-dayperiodswithstartingdatesfromMarch31,2014andtoOctober27,2014.ThecasesendinOctobertoavoidextendingintotheStraitsicecoverseason.Littleisknownaboutthebehaviorofanoilspillunderice,sothewinterperiodwasexcludedfromthesimulations.Eachnewcasestarted6hoursafterthepreviouscase.The60daydurationofthecaseswassufficienttoestablishthemaximumextentofimpactedshorelineinallbutafewcases,andinthesecasesthelowamountandlowconcentrationofoilremaininginopenwaterafter60dayswasunlikelytocausefurthersignificantshorelineimpact.Particletrajectorieswererecordedforeachcaseandthenanalyzedstatisticallytodeveloptheprobabilitygraphsandchartsdescribedinthenextsections.SampleCasesAnimationsofparticletrajectoriesfor6ofthecaseswerecreatedtoillustratethewidevarietyofconditionsencounteredduringspring,summerandfallintheStraits.Intheanimations,theoiltracerparticlesareshownasblackdots.Amagentadotrepresentsabeachedparticle.Thelegendintheanimationindicatestheamountoftimethathaselapsedsincethebeginningofthecase,thepercentofparticlesthathavebeached,andanestimateofthelengthofshoreline,exceedingathresholdimpactlevelof12particlesperkm2.Usingadensityforlightcrudeoilof850kg/m3,forthethreereleasevolumesof5,000,10,000,and20,000bblthisimpactlevelcorrespondstoanoildensityof0.5,1.0,or2.5gm/m2respectively.Thesevaluescanbecomparedtothethresholdvaluefor“socio-economicimpactonland”of1gm/m2citedbyNOAA(2013),as“…thatamountofoilwouldconservativelytriggertheneedforshorelinecleanuponamenitybeaches.”Fingas(2015)alsosuggests1gm/m2asthethresholdforimpactstoshorelineresources.Viewthecaseanimationsonline,see:http://graham.umich.edu/news/mackinac-straits-oil-linesThestarttimesandabriefdescriptionofthe6selectedcasesfollow.• Case1:4/3/1400Z:Inthiscase,thereleasedoilformsapatchmovingwestward,away
fromtheStraitsintoLakeMichiganforalmost2dayswithoutanysignificantbeaching.After2days,waterflowintheStraitsreversesdirectionandtheoilpatchstartstomovebacktowardtheStraits.After3days,someoilhasbeguntoimpingeontheshoresfromMackinawCitywestward.Partofthepatchseparatesandcontinuestomoveeastward,eventuallyimpactingthesouthwesternshoresofBoisBlancIsland.Meanwhile,thebulkofthespillmovesbackandforththroughtheStraits,impactingtheLakeMichiganshoresofboththeUpperandLowerpeninsulaswestoftheStraits,aswellastheLowerpeninsulashoreofLakeHuroneastoftheStraits.After10days,40%oftheinitialspillisstillinthewater.ItgraduallymovesintoLakeMichiganandslowlydepositsalongthenorthernshoreasfarwestasManistiqueoverthenext30days.Inthiscase,ittookalmost25daysbefore90%oftheoilwasbeachedanditultimatelyimpactedover100kmofshoreline.
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• Case2:4/14/1400Z:Thiscaseillustrateshowquicklyaspillcouldimpactalarge
amountofshoreline.TheinitialoilpatchinthiscasemovesquicklysoutheastwardintoLakeHuronfor6hours,butthenreversesdirectionandmovesbackintothesouthernpartoftheStraitswhiledepositingoilalongthesouthernshorelinebotheastandwestofMackinawCity.After1day,morethan60%oftheoilhasbeachedandimpacted15kmofshoreline.Inthenext12hours,30%morehasbeachedand22kmofshorelinearesignificantlyaffected.
• Case3:4/16/1406Z:Thiscasestartsonly2daysaftercase2,buthasavastlydifferent
outcome.OilinitiallymovesnortheastwardtowardSt.HelenaIslandinLakeMichigan,andis90%beachedonday40when90kmofshorelineareimpacted.
• Case4:4/27/1412Z:Thisisoneofthemostextremecasesintermsofamountof
impactedshoreline.ThiscasestartssimilarlytoCase3,butafter5daystheoilpatchhasspreadtobothLakesMichiganandHuron.Bythetime90%oftheoilhasbeachedafteralmost30days,theoilhasimpacted168kmofshorelineinbothlakes.
• Case5:7/1/1406Z:Inthiscase,oilmovesalmostexclusivelyeastward,withmorethan
30%oftheoilbeachedonMackinacIsland,BoisBlancIsland,andalmosttheentireLakeHuronshorelinefromMackinawCitytoCheboyganafter3days.TheoiltravelsasfarsouthasPresqueIsleontheLakeHuronshorelinein15days,andasmallpercentageoftheparticlesreachnorthernSaginawBayonday30.ThiscasealsoillustratesthesomeofextremedistancesinLakeHuronthatcouldbereachedin30days.
• Case6:8/4/1406Z:MostoftheoilinthiscasemovesintoLakeMichigan,buta
substantialamountimpactstheshoresofMackinacIslandandSt.MartinBay.ThebulkofthespillinLakeMichiganhasimpactedtheentirenorthshoreofWildernessStateParkbyDay3.OilisbeachedonBeaverIslandonDay10,andhasreachedasfarsouthasLittleTraverseBaybyday14.Byday30,atotalof116kmofshorelinehavebeenimpacted.
StatisticalAnalysisofResults1.TimeseriesMapsoftracerparticlelocationsfromeachofthe840caseswereanalyzedateachhourafterspillinitiationtocalculate1)theopenwaterareacoveredbythespill,2)thefractionoftheinitialvolumeofoilstillinthewater,and3)thefractionoftheinitialvolumeofoilonthebeach.Atanygiventime,thevolumerepresentedby2)plus3)equalstheinitialvolumelessevaporation.
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Figures1-3showthehour-by-hourstatisticaldistributionofthesethreeparametersintermsofthemedianvalue(darkline),the25thand75thpercentiles(lightlinesborderingtheshadedarea)andthe0and100thpercentiles(bottomandtoplightlines).AsshowninFigure1,themedianvalueofopenwaterareacoveredbythespillincreasesto300km2afterabout7days,andthengraduallydecreasesasmoreoilisbeached.Themaximumopenwaterareaaffectedbyasinglespillcanreach1600km2at35days.Fiftypercentofthecaseshavemaximumopenwaterareasbetween200and400km2withthepeakoccurring5-7daysaftertheinitialrelease.AsshowninFigure2,themedianfractionofoilvolumestillonthewaterrapidlydecreasestolessthan10percentafter5days.Thelargestamountofoilremainingonthewaterafter35daysisabout10percentoftheinitialvolume.Figure3showsthatinhalfofthecases,morethan65percentoftheinitialvolumeofoilisbeachedafter7days.Inatleastonecase,70percentoftheinitialreleasevolumeisbeachedinlessthan24hours.2.OffshoreImpactThenextseriesofmapsdepictthedistributionprobabilityofoilataparticulartimeintervalafterthestartofthecase.TheareaaroundtheStraitsisdividedinto1kmx1kmsquarecellsandthepercentofcasesthathadatleastonetracerparticleinacelliscalculated.MapsareprovidedinFigures4-11forintervalsof6hours,12hours,1day,2days,4days,10days,30days,and60days.Themapsshowsthatinthefirstsixhoursaftertherelease,oilisalmostequallylikelytobefoundeastorwestoftheStraits,andcouldtravelasfaras15kmineitherdirection(Figure4).After12hours,thereisa10%chancethattheshoresofMackinacandBoisBlancIslandscouldbeaffected(Figure5).At1day(Figure6),itbecomesclearthatthereisahigherlikelihoodforoiltobefoundinLakeHuronthaninLakeMichigan,althoughitmayhavetraveledfurtherintoLakeMichigan(upto25km)thanintoLakeHuron(20km).After2days(Figure7),themostlikelylocationofoilisabout10kmeastoftheStraitswithabouthalfofthespillcasesindicatingthepresenceofoilthere.TheentireshorelinesofMackinac,BoisBlanc,andSt.HelenaIslandshavebeenimpactedinatleastoneofthecases.At4days(Figure8),themostlikelylocationtofindoilhasmovedto15kmeastoftheStraitsandover20%ofthecasesshowimpactsonMackinacIslandandBoisBlancIsland.Figures9-11showthatafter4dayssomeoilcontinuestospreadfarintoLakeHuronandtoalesserextentintoLakeMichigan,butbythistimemostoftheoilhasbeachedorevaporatedasshowninFigure2.Ananimationwascreatedofthearealprobabilitymapsathourlyintervalsforthefirst5daysafterrelease.Theanimation(availableonline,see:http://graham.umich.edu/news/mackinac-straits-oil-lines)showsthatthemostprobablelocationforoiltobefoundiscenteredintheStraitsforthefirst12hoursaftertheinitialrelease,butgraduallymovestowardthesouthshoreofLakeHuron,southandeastofMackinacIsland,duringthenext24hours.Overthenext3days,theareawhereoilispresentinatleast20%ofthespillcasesextendstothenorthofMackinacIsland,reaches15-20kmwestintoLakeMichigan,andhasmovedasfarsouthasCheboyganinLakeHuron.
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Figure12andTable1showsthepercentofcasesinwhichoilreachedaparticularareaatanytimeduringthe60-daydurationofthecaseandFigure13depictstheshortesttime(upto10days)thatitwouldtakeoiltoreachanareainanyofthe840spillcases.AsshowninTable1,over15%ofLakeMichigan’sopenwater(9,141km2)andalmost60%ofLakeHuron’sopenwater(35,264km2)couldbeaffectedbyvisibleoilfromaspillintheStraits.Atleast60%ofthecasesaffectedanareaof207km2inLakeMichiganand1,953km2inLakeHuron.Table1.Offshoreareaaffectedbyanycase.Firstcolumnisthepercentagerangeofcases,whichaffectedthisarea.SeeFigure12forgraphicalrepresentation.Percentofcases
Totalarea(km2) L.Michiganarea(km2) L.Huronarea(km2)
>0% 44,405 9,141 35,264>20% 12,931 1,688 11,243>40% 5,684 518 5,166>60% 2,160 207 1,953>80% 635 64 571
3.ShorelineImpactFigures14-16showthepercentofcasesthatwouldresultintheamountofbeachedoilexceeding“socio-economicimpact”thresholdof1gm/m2alongeach1kmsectionofshoreline.Thethreefiguresarebasedoninitialreleasevolumesof25,000,10,000,and5,000bblrespectively.Thetotallengthofshorelinethatcouldbeimpactedinanyofthe840casesis1162,835,and709kmforthethreereleasevolumesrespectively.Tables2and3showtheminimumarrivaltime(fromFigure13)andpercentofcasesexceedingthe“socio-economicimpact”thresholdfortheshoreline(fromFigures14-16)atanumberofselectedlocationsalongtheshorelinesnorthandsouthoftheStraitsforthethreeinitialreleasevolumes.
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Table2.Minimumarrivaltime(ColumnA)andpercentofcasesexceedingthe“socio-economicimpact”thresholdforshoreline(ColumnsB,C,andDcorrespondingtoinitialreleasevolumesof25,000,10,000,and5,000bblrespectively)forselectedlocationsalongtheshorenorthoftheStraits.
NorthShore A B C DGardenPeninsula 29days 1 <1 <1Manistique 27days 2 1 <1SeulChoixPoint 14.5days 5 3 1Naubinway 6days 10 5 3Brevort 40hrs 25 20 16PointAuxChenes 18hrs 40 32 30St.HelenaIsland 6hrs 58 52 50GrosCap 6hrs 60 56 54PointLaBarbre 5hrs 80 65 60BridgeViewPark 5hrs 74 57 56GrahamPoint 10hrs 75 70 67St.IgnaceFerryDocks 15hrs 50 38 35CastleRockCampground 20hrs 40 25 10MackinacIslandSouthShore 9hrs 90 85 80MackinacIslandNorthShore 12hrs 60 48 45RoundIsland 8hrs 92 88 85BoisBlancIslandSouthShore 10hrs 90 85 82BoisBlancIslandNorthShore 12hrs 70 65 60HorseshoeBay 24hrs 20 12 10SaintMartinBay 30hrs 10 6 5MarquetteIsland 51hrs 20 10 7DeTourStatePark 8days 2 1 <1DrummondIsland 9days 2 <1 <1CockburnIsland 12.5days 1 <1 <1ManitoulinIslandSWShore 14.5days 1 <1 <1
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Table3.Minimumarrivaltime(ColumnA)andpercentofcasesexceedingthe“socio-economicimpact”thresholdforshoreline(ColumnsB,C,andDcorrespondingtoinitialreleasevolumesof25,000,10,000,and5,000bblrespectively)forselectedlocationsalongtheshoresouthoftheStraits.
SouthShore A B C DCharlevoix 11days 1 1 <1Petoskey/HarborSprings 10days 1 1 <1BeaverIsland 9days 2 1 1CrossVillage 4.5days 10 5 2SturgeonBay 4days 8 5 2WaugashanceIsland 30hrs 20 16 14WildernessStateParkNorthShore 10hrs 35 30 29TheHeadlands 2.5hrs 75 70 66OldMackinacPoint 2.5hrs 92 85 82MackinawCityFerryDocks 3.5hrs 85 80 74CadottesPoint 6hrs 90 80 75PointNipigon 15hrs 85 78 72Cheboygan 30hrs 65 50 40HammondBay 3days 30 20 10RogersCity 6days 25 20 13PresqueIsle 7days 20 10 5ThunderBay 10days 5 2 1Harrisville 21days 1 <1 <1OscodaTwp. 27days 1 <1 <1AuSablePoint 29days 1 <1 <1Theshortestarrivaltimesare2.5hoursonthesouthshoreoftheStraitsnearMackinawCity,and5hoursonthenorthshore.ThesetimeswouldbereducediftheoilreleasewereclosertothenorthorsouthshorethanthereleasepointusedinthesimulationsnearthemidpointoftheStraits.MackinacIslandcouldbeimpactedinaslittleas9hours,RoundIslandin8hours,andBoisBlancIslandin10hours.LocationsthatcouldbeaffectedinlessthanadayextendfromPointAuxChenestoHorseshoeBaynorthoftheStraitsandfromthenorthshoreofWildernessStateParktoapointnorthwestofCheboyganonthesouthsideoftheStraits.SignificantshorelineimpactcouldstilloccurasfarawayastheGardenPeninsulaandCharlevoixinLakeMichigan,andthewesternendofManitoulinIslandandAuSablePointinLakeHuron.Atleast20percentofthecasesusinga25,000bblinitialdischargeshowedsignificantshorelineimpactatpointsfromBrevortinLakeMichigantoHorseshoeBayinLakeHuronalongthenorthsideoftheStraits,andfromWaugashanceIslandinLakeMichigantoPresqueIsleinLakeHuronalongthesouthsideoftheStraits.Figures17-19showthestatisticaldistributionoftheamountofimpactedshorelineasafunctionoftimeaftertheinitialreleaseforthethreeinitialvolumesof25,000,10,000,and
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5,000bbl.Themedianvalueisshownasadarkline;lightlinesborderingtheshadedareabelowandabovethemedianrepresentthe25thand75thpercentiles;andthebottomandtoplightlinesarethe0and100thpercentiles.Table4isasummaryofthelengthofimpactedshorelineforthethreedifferentinitialreleasevolumesintermsof1)thelengthofshorelinethatcouldbeimpactedbyanyspill,2)themaximumlengthofimpactedshorelineinasinglecase,and3)themedianlengthofimpactedshorelinefromallcases.Table4.Length(km)ofimpactedshorelineforthreeinitialreleasevolumesInitialrelease
volumeAllCases SingleCase MedianCase
25,000bbl 1162 245 12010,000bbl 835 170 855,000bbl 709 115 60
ConclusionsandsuggestionsforfutureworkThemainconclusionofthisreportisthataquantitativeanalysisof840oilspillcasesintheStraitsofMackinacusinga“worst-casedischarge”fromLine5showsthatmorethan1,000kmofLakeHuron-MichiganshorelineandspecificislandsarepotentiallyvulnerabletoanoilreleaseintheStraits.Thisconclusionstronglysupportstheassertionthatundertherightweatherconditions,aspillintheStraitscouldaffectasignificantamountofshorelineandopenwaterareaineitherLakeMichiganorLakeHuroninaveryshorttime.Inthecaseofa10,000bblrelease,themedianlengthofimpactedshorelinefromall840casesis85km.Threequartersofallcasesimpactedmorethan65kmofshoreline.ThemediansizeofanoilpatchfromareleaseintheStraitswas300km2after7days.Threequartersofthe840casesresultedinmaximumopenwateroilpatchsizesgreaterthan200km2afteraslittleas5days.Themaximumopenwaterareasubjecttooilinginanyofthecaseswasover1600km2.LimitationsoftheReportandResultsTheaffectoficecoverintheStraitswasnotconsidered.IcetypicallyaffectstheStraitseachwinterfromlateDecembertoApril.CommercialvesseltrafficcontinuesduringatleastpartofthisperiodwithassistancefromU.S.CoastGuardicebreakingoperations.ThepossibilityofanoilspillfromLine5alsocontinuesthroughwinter,butlittleisknownabouthowicecoverwouldaffectanoilspillintheStraits.Thisisanareathatrequiresfurtherinvestigation.OnedifferencebetweenthespillsimulationscarriedoutinthisstudyandthemethodologyusedinGNOMEisthattheGNOMEsoftwareincludesaprovisionfora“minimumregret”
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solutionbasedonuncertaintyintheassumedwatercurrents.Wedidnotincludethisfactorinourcalculations.Ifitwereincluded,the“minimumregret”solutionswouldtendtoencompasswideropenlakeareasandincreasetheamountofimpactedshoreline,sotheresultspresentedinthisreportcanbeconsideredsomewhatconservative.Thedirectaffectofwindonthespilltrajectorywasnotconsidered.Includingthisaffectwouldlikelyincreasetheaffectedopenlakeareaandamountofimpactedshoreline.Sotheresultswepresentareconservativeinthisrespect.Finally,wehavenotconsideredprocessesbywhichoilwouldsinkorbeotherwiseincorporatedintothewatercolumnbelowthesurface.ForthetypeofpetroleumproductsbeingcarriedbyLine5,thiseffectwouldprobablybesmall,butinanycase,ourfindingswouldstillapplytooilremainingonornearthesurface.Theresultsfromthisreportareanticipatedtoprovideguidelinesforthedevelopmentofafullriskanalysisinthefuture.RecommendationsforFurtherStudyThespillscenariosimulationsinthisstudyareonlythefirststepinacompleteriskanalysisofa“worstcasedischarge”ascalledforintheStateofMichiganPetroleumPipelineTaskForceReport(2015).Otherconsiderationsinamorecompleteriskanalysiswouldinclude1)analysisofenvironmentalimpacts,2)cleanupcosts,3)restorationandremediationmeasures,4)anaturalresourcedamageassessment,and5)Economicdamagetopublicandprivatesectorinterests.Inaddition,informationabouthowicecoverwouldaffectanoilspillintheStraitsrequiresfurtherinvestigation.AcknowledgementSupportedbytheNationalWildlifeFederation,GreatLakesRegionalCenter
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Schwab,D.J.,2014.StraitsofMackinacContaminantReleaseScenarios:FlowVisualizationandTracerSimulations.U-MWaterCenterResearchReport,7pp.(http://graham.umich.edu/water/news/mackinac-straits-contaminant-scenarios)
University of Michigan Water Center • www.graham.umich.edu/water 13
FiguresFigure1.Timeseriesofstatisticaldistributionofaffectedopenwaterareaineachofthe840spillcases.Thedarklineisthemedianvalue,thelightlinesborderingtheshadedareaarethe25thand75thpercentiles,andthelowerandupperlinesarethe0thand100thpercentiles.Figure2.Timeseriesofstatisticaldistributionoffractionofinitialoilreleasevolumeremainingonwaterineachofthe840spillcases.Thedarklineisthemedianvalue,thelightlinesborderingtheshadedareaarethe25thand75thpercentiles,andthelowerandupperlinesarethe0thand100thpercentiles.Figure3.Timeseriesofstatisticaldistributionfractionofinitialreleasevolumethathasbeachedineachofthe840spillcases.Thedarklineisthemedianvalue,thelightlinesborderingtheshadedareaarethe25thand75thpercentiles,andthelowerandupperlinesarethe0thand100thpercentiles.
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University of Michigan Water Center • www.graham.umich.edu/water 14
Figure4.Probabilityofpresenceofoil(percentofcases)at6hoursafterinitialrelease.
Figure5.Probabilityofpresenceofoil(percentofcases)at12hoursafterinitialrelease.
Probability at 6 hours
> 0%
20 %
40 %
60 %
0 50
Scale (km)
Probability at 12 hours
> 0%
20 %
40 %
60 %
0 50
Scale (km)
University of Michigan Water Center • www.graham.umich.edu/water 15
Figure6.Probabilityofpresenceofoil(percentofcases)at1dayafterinitialrelease.
Figure7.Probabilityofpresenceofoil(percentofcases)at2daysafterinitialrelease.
Probability at 1 day
> 0%
20 %
40 %
60 %
0 50
Scale (km)
Probability at 2 days
> 0%
20 %
40 %
60 %
0 50
Scale (km)
University of Michigan Water Center • www.graham.umich.edu/water 16
Figure8.Probabilityofpresenceofoil(percentofcases)at4daysafterinitialrelease.
Figure9.Probabilityofpresenceofoil(percentofcases)at10daysafterinitialrelease.
Probability at 4 days
> 0%
20 %
40 %
60 %
0 50
Scale (km)
Probability at 10 days
> 0%
20 %
40 %
60 %
0 50
Scale (km)
University of Michigan Water Center • www.graham.umich.edu/water 17
Figure10.Probabilityofpresenceofoil(percentofcases)at30daysafterinitialrelease.
Figure11.Probabilityofpresenceofoil(percentofcases)at60daysafterinitialrelease.
Probability at 30 days
> 0%
20 %
40 %
60 %
0 50
Scale (km)
Probability at 60 days
> 0%
20 %
40 %
60 %
0 50
Scale (km)
University of Michigan Water Center • www.graham.umich.edu/water 18
Figure12.Percentofcasesinwhichoilispresentatanytimeafterinitialrelease.
Figure13.Minimumtraveltime(upto10days)toalocationfromanycase.
Percent of Cases
> 0%20 %40 %60 %80 %100 %
0 50
Scale (km)
Travel time
1 day2 days5 days10 days
0 50
Scale (km)
University of Michigan Water Center • www.graham.umich.edu/water 19
Figure14.Probability(percentofcases)thatbeachedoilconcentrationexceeds1gm/m2after60daysfromanyspillcase,basedonaninitialreleasevolumeof25,000bbl.
Figure15.Probability(percentofcases)thatbeachedoilconcentrationexceeds1gm/m2after60daysfromanyspillcase,basedonaninitialreleasevolumeof10,000bbl.
25,000 bblTotal length 1162 km
> 0%20 %40 %60 %80 %100 %
0 50
Scale (km)
10,000 bblTotal length 835 km
> 0%20 %40 %60 %80 %100 %
0 50
Scale (km)
University of Michigan Water Center • www.graham.umich.edu/water 20
Figure16.Probability(percentofcases)thatbeachedoilconcentrationexceeds1gm/m2after60daysfromanyspillcase,basedonaninitialreleasevolumeof5,000bbl.
Figure17.Timeseriesofstatisticaldistributionoflengthofimpactedshorelinebasedonaninitialreleasevolumeof25,000bbl.Thedarklineisthemedianvalue,thelightlinesborderingtheshadedareaarethe25thand75thpercentiles,andthelowerandupperlinesarethe0thand100thpercentiles.
5,000 bblTotal length 709 km
> 0%20 %40 %60 %80 %100 %
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University of Michigan Water Center • www.graham.umich.edu/water 21
Figure18.Timeseriesofstatisticaldistributionoflengthofimpactedshorelinebasedonaninitialreleasevolumeof10,000bbl.Thedarklineisthemedianvalue,thelightlinesborderingtheshadedareaarethe25thand75thpercentiles,andthelowerandupperlinesarethe0thand100thpercentiles.Figure19.Timeseriesofstatisticaldistributionoflengthofimpactedshorelinebasedonaninitialreleasevolumeof5,000bbl.Thedarklineisthemedianvalue,thelightlinesborderingtheshadedareaarethe25thand75thpercentiles,andthelowerandupperlinesarethe0thand100thpercentiles.
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The Water Center engages researchers, practitioners, policymakers, and nonprofit groups to support, integrate, and improve current and future freshwater restoration and protection efforts. The Water Center conducts collaborative science, supporting Great Lakes restoration and coordinates the National Estuarine Research Reserve System (NERRS) Science Collaborative. The Water Center is part of the U-M Graham Sustainability Institute, which fosters sustainability through translational knowledge, transformative learning, and institutional leadership.
UNIVERSITY OF MICHIGAN BOARD OF REGENTSMichael J. Behm, Grand Blanc; Mark J. Berstein, Ann Arbor; Laurence B. Deitch, Bloomfield Hills; Shauna Ryder Diggs, Grosse Pointe; Denis Ilitch, Bingham Farms; Andrea Fischer Newman, Ann Arbor; Andrew C. Richner, Grosse Pointe Park; Katherine E. White, Ann Arbor; Mark S. Schlissel, ex officio
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