2020_All roads lead to retreat: adapting to sea level rise using a trigger-based pathway by audrc

Australian Planner

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Bill Grace & Colleen Thompson

To cite this article: Bill Grace & Colleen Thompson (2020): All roads lead to retreat: adapting to sea level rise using a trigger-based pathway, Australian Planner, DOI: 10.1080/07293682.2020.1775665

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Published online: 20 Jun 2020.

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AUSTRALIANPLANNER

https://doi.org/10.1080/07293682.2020.1775665

Allroadsleadtoretreat:adaptingtosealevelriseusingatrigger-based pathway

BillGracea andColleenThompsonb*

aAustralianUrbanDesignresearchCentre,Perth,Australia; bGHDPerth,Planning,Perth,Australia

ABSTRACT

Ascoastalcommunitiesallovertheworlddealwiththeconsequencesofrisingsea-leveland moreintensestormevents,plannersandmanagerscontinuetograpplewiththeoptimal policyapproachtomanagingincreasingriskstocoastalecosystems,peopleandproperty.In thisarticle,wedescribea flexiblepathwayapproachtoadaptationderivedinsouthwest Australiaforlocalgovernment.Whiletheissueisusuallyaddressedusingaconventional optionanalysisofthe ‘retreat-accommodate-protect’ alternativeswithinagiventimeframe (oftenuntil2100),wearguethatthisapproachismisleadinginthatitobfuscatesthelong termrealitiesofclimatechange.Sea-levelwillberisingforhundredsifnotthousandsof years,meaningthatretreatisultimatelyinevitableforanycoastlinescurrentlydeterminedto bevulnerable – theonlyuncertaintyiswhenthiswillbenecessary.Accordinglythefocus shouldbeoncontinualmonitoring,updatedhazardmapping,andtheidentificationof sequentialtriggersthatregulatelanduses.Weproposethissimplified flexiblepathwayasa rationalapproachtodealingwiththetemporaluncertaintyoffutureclimatechangethat shouldbewidelyadopted.

Introduction

Theyear2017waseitherthesecondorthirdwarmest year(NationalOceanicandAtmosphericAdministration 2018)onrecord,andthe fivewarmestyears onrecordallhavetakenplacesince2010.Climate changeishereanditsimplicationsarebeingfelt throughextremeweatherevents,bushfires,melting glaciersandcoralbleaching.Evenastheworld’ s nationsseektomitigatethefutureeffectsbyreigning incarbonemissions,adaptingtoclimatechange becomesmorecriticaleveryyear.

Sealevelriseduringperiodsofglobalwarmingoccur (mainly)throughacombinationofthermalexpansion andlossoficestoredonland(e.g.,glaciersandicesheets). AlthoughthisprocesshasbeenongoingsincetheLast GlacialMaximumsometwentythousandyearsago (Clarketal. 2009),theratehasrisensigniﬁcantlyover therecentpast.Duringthetwentiethcentury,global meansealevelsrosebyaround190mm,aratelarger thanthepriortwothousandyears(Churchetal. 2013). Ratesofchangevaryconsiderablyaroundtheworld.In thesouthwestofAustralia,sea-levelhasrisensome 150mmbetween1900and2010(Bicknell 2010).

ProjectionsinthelatestAssessmentReport(AR5)of theIntergovernmentalPanelonClimateChange (IPCC)areforglobalmeansealevel(GMSL)to ‘likely’ riseabove1986–2005levelsbetween0.28and0.98m bytheendofthecentury,dependingonfuture

CONTACT BillGrace bill.grace@uwa.edu.au

*Presentaddress:SeniorProjectOﬃcer,CityofJoondalup.

ARTICLEHISTORY

Received7July2018

Accepted6May2020

KEYWORDS

Sealevelrise;adaptation; strategicplanning;climate change;pathway;triggers

greenhousegas(GHG)emissions(Pachaurietal. 2014).Theterm ‘likely’ reflectstheconfidenceofthe authors.Someresearchershavequestionedwhether theIPCCestimatesare fit-for-purposetouseincoastal decision-making.Hinkeletal.(2015,188)notethat ‘thereisa0–33%probabilityofGMSLriselyingoutside thisrange,whichisnottolerablefromarisk-averse perspective’.Hansenetal.(2015)haverecentlyre-activatedtheprojectiondebatewithaconclusionthatsealevelrisecouldbeseveralmetresbytheendofthiscenturydue(mainly)topreviouslyunderestimatedlevels oficemeltfromAntarcticaandGreenland.Differences betweensealevelrisemodelspresentcomplexityfor coastalplanners,astheappropriatetimingforland useresponsesisuncertain.

Ofcourse,theslowlyrisingsealevelitselfisnotthe onlyissueofrelevanceforcoastalplanners.Firstly,a riseinsea-levelincreasescoastalerosionsigniﬁcantly invulnerablesandysiteswithabundantsandsupply andminimallongshoretransport,notablycharacterisedbyBruun(1962).Theso-called ‘BruunRule’ suggestsaonemetreriseinsealevelwillleadtoa 100mretreatofthecoastline.WhiletheBruunRule hasbeenshowntobetoosimplistictoapplygenerally (Ranasinghe,Callaghan,andStive 2012)andsome believeitshouldbeabandonedaltogether(Cooper 2004),ithasdrawnattentiontothepotentialimpact of sea-levelriseoncoastlinestability.

Secondly,stormsurgestemporarilyincreasesealevelduringsevereweatherevents,causedmainlyby windspushingwateronshore.Stormsareprojected toincreaseinseverity(ifnotfrequency)inmany regionsduetoclimatechange(Pachaurietal. 2014) thusincreasingtheimpactof ﬂoodinganderosion duetostormsurges.Theabilityofshorelinestorecover fromtransienterosioneventsreducesassea-levelrises.

Thirdly,itisalsopredictedbytheIPCCthat ‘..extremeprecipitationeventswillbecomemore intenseandfrequentinmanyregions.’ Clearly,the probabilityoftheseeventscoincidingwithstorm surgeeventsissigniﬁcant,thusexacerbatingincidences ofcoastal ﬂooding.

TheprojectionsoftheIPCCfocusontheperiodto theendofthecentury,andsoaccordinglydomost authoritieswithresponsibilitiesforadaptationtosea levelrise.Asnotedabove,therearemanyuncertainties aboutboththemagnitudeandrateofsealevelriseby 2100.Theseuncertaintieshavegivenrisetomanytheoriesaboutwhatisanoptimalmanagementapproach (Haasnootetal. 2013).Inthisarticlewehighlightthe roleoflanduseplanninginaddressingsealevelrise, citingasacasestudyastrategydevelopedfora coalitionofcoastalcouncilsinPerth,Western Australia.

Howdoesaplanningauthoritydecidewhereand whetheranareashouldbeprotectedornot?How andwhenis ‘Retreat’ invoked?Thesehavebeenquestionsforalongtime(Walshetal. 2004)andremain thekeyquestionsforcoastalplannersandmanagers asidentiﬁedbyRobbetal.ininterviewswithlocal WesternAustralianplanners(Robbetal. 2017).We drawonthelearningsfromourcasestudytocontribute answerstothosequestions.

Thecasestudy

ConsultantsGHDwerecommissionedtopreparea coastaladaptationplan(GHD 2016)fortheCockburn CoastalAlliance(CSCA),apartnershipbetweenthe

CitiesofCockburn,Fremantle,KwinanaandRockinghaminPerth’ssouthernsuburbs.Theauthorswere membersoftheconsultingteamcommissionedby CSCA,fromwhichtheapproachesproposedhere havebeenderived.Theoutputsoftheworkwere coastaladaptationplansforeachofthelocalgovernmentareas,andanoverarchingprojectreportthatprovidestheanalysisunderpinningtheplans.Asimilar projectundertakenbyGHDandtheauthorsforthe CityofFremantleandtheTownofMosmanParkfor thePort,LeightonandMosmanBeachesandadjacent landhasalsoinformedtheviewspresentedhere.

Inapreviousstageoftheproject,otherconsultants (CoastalZoneManagementetal. 2013)preparedan erosionandinundationhazardassessmentofthecoastlinecomprisingCockburnSound,OwenAnchorage andtheeastcoastofGardenIsland.

ThekeyoutputsfromtheCoastalZoneManagementetal.(2013)studywereerosionandinundation hazardmapsthatillustratethelikelyextentofcoastal inundationanderosionatdifferenttimeframes(presentday,2070and2110)basedonsealevelrisescenariosforthesetimeframes(0m,+0.5mand+0.9m respectivelyinlinewithAR5).Additionally,asea levelriseof1.5mat2110wasalsoselectedtodeterminesensitivitytohigherestimatesofsealevelrise. Thestudyconcludedthattherewouldbeanaverage recessionofthecoastlineof25mby2070and45–75mby2110,althoughtherewouldbesignificantvariationacrossthestudyareaduetosandtransfer betweencoastalsegments.Sedimenttransferisan importantconsiderationinmodellingrecession (Thometal. 2018),althoughinthelongtermthe studyauthorsnote: ‘Changestotheareasexperiencing recessionarelikelytooccurthroughseveraldifferent mechanisms,includingsealevelrisecontributingto decreaseorcessationofonshoresedimentsupply’

Theobjectivesoftheadaptationplanphaseofthe projectwereto:

. developaneﬀectivecoastaladaptationplan(or plans)tobeimplementedbytherelevantlocalgovernmentsandstakeholders;

. engagewithkeycommunitygroupsandstakeholderstogaintheiropinionsandvalues(economic, environmental,socialandcultural)regarding coastalassets(naturalandbuilt)atriskinthecoastal zoneandpotentialadaptationoptions;and

. buildcapacityinthecommunity,localgovernments, naturalresourcemanagementgroups,Coastcare groups,industryandotherstakeholdersbyfacilitatingtheunderstandingofclimatescience,coastal processes,hazardsandrisksthroughthedevelopmentanddisseminationoftheadaptationplan(s).

Thestudywasguidedby ‘TheCoastalHazardRisk ManagementandAdaptationPlanningGuidelines’ Figure1. Riskmanagementandadaptationhierarchy.

(DepartmentofPlanningandWesternAustralian PlanningCommission 2014),adocumentoftheWesternAustralianPlanningCommission(WAPC).1 That documentsetsoutcoastaladaptationoptionswhichare consideredasahierarchy(see Figure1) – thefurther downthehierarchy,theless ﬂexibilitythereistoconsideralternativeadaptationmeasures.

Thestudyprogressedthroughanumberofsteps, includingidentifyinglocalisedadaptationoptionsfor eachcoastalmanagementunitanddevelopmentof coastaladaptationplansforeachcoastalmanagement unitwithineachlocalgovernmentarea.

Inparallelwiththesetasksthestudyteamprepared andimplementedastakeholderandcommunity engagementstrategy,andliaisedwithlocalgovernment oﬃcers,externalstakeholderrepresentativesandthe communitytotestvaluesandoptions.

Establishingtherisk

Assessinghazardsarisingfromcoastalprocesses usuallyinvolvesapplyingtheconventionalriskanalysis technique:evaluatethelikelihoodoftheoccurrence; thenevaluatetheconsequenceoftheoccurrence.In thiscase,theoccurrenceistheerosionand/orinundationofcoastalland.Thelikelihoodwasevaluatedin Stage1oftheprojectatdifferentpointsintime:now, 2070and2110.Asthecoastalprocessesaredominated bysealevelrise,theamountoflandaffectedincreases ateachofthesedates.Locationscurrentlyidentifiedas atriskofsporadicinundationoracuteerosionwillin futurehaveanincreasedrisk.

Whilethereisunderstandablyconsiderableinterest inthesealevelat2100,thisfocusmasksthelongterm scientiﬁcallyacceptedrealitythatsea-levelwillberising forhundreds,ifnotthousandsofyearsirrespectiveof futureGHGemissions.IntheirarticleinNatureClimateChange,Clarketal.(2016,360)provideamuch longertemporalperspectiveonclimatechange,contextualisingchangesoveraperiodfrom20,000years beforethepresent(thetimeoftheLastGlacialMaximum),to10,000yearsbeyondthepresent.Whether fossilfuelscontinuetobeuseduntilreservesare exhausted,orabandonedtocombatclimatechange, theemissionsreleasedwillbeshorttermbliponthe graphoverthattimeframe.Howevertheirinﬂuence onatmosphericcarbondioxide(CO2)levelswilllast forthousandsofyears,meaningtemperatures,and hencesealevels,willremainhighoverthatperiod.

… thescientiﬁcemphasisontheexpectedclimate changesby2100hascreatedamisleadingimpression inthepublicarena theimpressionthathumancausedclimatechangeisatwenty-ﬁrst-centuryproblem,andthatpost-2100changesareofsecondary importance,ormaybereversedwithemissions reductionsatthattime.(Clarketal.)

Therealityisthattheeﬀectsofclimatechangein respectofbothtemperaturesandsealevelriseare withusnowandhave ‘multi-millennial’ implications. Sealevelriseisaresultofseveralcoincidentprocesses, eachwiththeirownresponsetimetochangesinduced bywarming.Clarketal.’scalculationsincorporatethe impactonsealevelriseofarangeofemissionscenarios oneachprocess:

. Thermalexpansionoftheoceans:1.1–3.4mrise whichislikelytopeakinaround2300yearsand thenfall;

. Glacierloss:0.25–0.34mrise,likelytooccurwithin afewcenturies;

. MeltingoftheGreenlandicesheet:4–7mriseover 2,500–10,000years;

. MeltingoftheAntarcticicesheet:24–45mriseover 10,000years.

Inaggregate,theauthorsprojectGMSLtorise somewherebetween25and52moverthenext 10,000years,dependingonfutureemissions.Their modellingsuggeststhatemissionstodatehavealready ‘committedEarthtoaGMSLriseof ∼1.7m(rangeof 1.2to2.2m)’.These ﬁguresputthe2100estimatesin AR5intheirproperperspective.

Itisthereforeclearthatthe ‘likelihood’ ofthose partsoftheCockburncoastidentifiedasvulnerable intheperiodto2100becomingerodedand/orinundated,willeventuallybe ‘certain’.Theonlyuncertainty relatestowhenthiswilloccur.Itisalsoclearthatthe areaidentifiedasvulnerablewillsteadilygrowover time.Accordingly,thepracticeofestablishinglikelihoodscales(e.g., ‘almostcertain’ to ‘ rare ’)forerosion/inundationbasedoncurrentmodellingis unhelpfulinconveyingthereallongtermriskand forplanningforthefuture.Dealingwiththetemporal uncertaintyrequiresa flexibleadaptationpathway.

Theneedtoarticulateapathway

Duringcommunityengagement,theprojectteam identiﬁedthattheriskmanagementandadaptation hierarchywasnotinitselfasuﬃcientpolicytoolto clearlycommunicatetheneedforongoing,iterative adaptationplanning.

Oneofthecoreaimsofthestakeholderengagement componentoftheprojectwastoconsiderandtestthe valuesofthecommunityinrelationtothecoast,and theimplicationsoftheimpactsofsealevelrise.These valueswereintendedtobeusedaspartofthemethodologyfortestingthevariouscoastalmanagement options.Asfoundbyothers(Alexander,Ryan,and Measham 2012;CoviandKain 2016),diﬀerentcommunitymembersrespondedaccordingtotheirdiﬀerentinterests.Thiswasexpressedthroughthosewho potentiallyhadat-riskpropertybeinginclinedto

expecthardinfrastructureprotection(groynes,seawalls,etc.),andthosewithnodirectpropertyimpact, e.g.,beachgoers,beinginclinedtoexpecttheretention oftheirbeachandadjacentparkingareasand parklands.

Theengagementprocessillustratedthatthecommunityisnotsuﬃcientlyawareof,orinformed about,thepotentialimpactsofsealevelriseanderosiontoarticulatetheirvaluesinawaythatwasconstructiveforassessingthevariousoptionsforcoastal management.Thiswasfurtheremphasisedbythegenerallylowlevelofinterestinbeingengaged.

Furthermore,therewaslimitedcapacitytoimagine andengagebeyondtheimmediateplanninghorizon, beyondthetemporalscaleofpersonalimpact.This inabilitywasatoddswiththeexpectationthatcoastal adaptationplanswouldmakerecommendationsfor mitigatingrisksinthelong-term.

Thedynamicnatureofcommunityneedsandvalues requiresa flexibleapproachwhenconsideringadaptationoptions.Theeffectsofclimatechangeonthe coasthaveonlyrecentlybeenidentifiedasapotential concernforsomeinthecommunity,asapparent fromtheminimalinterestshownduringtheconsultationprocess.Thelevelofinterestandvaluesofthe communitywillchangeovertimeasmoreinformation becomesavailable,andtheimpactsofclimatechange becomemoreapparent.

Theselearningsandconsiderationsfromthecommunityengagementprocessdemonstratedtheneed toarticulatea ﬂexiblepathwayratherthanapplythe riskmanagementandadaptationhierarchyatthistime.

A ﬂexibleadaptationpathway

Anadaptationpathwayisadecision-makingstrategy thatismadeupofasequenceofmanageablesteps ordecision-pointsovertime.(CoastAdapt 2018)

Asa ﬁrststep,theauthorsdevelopedprinciples,based onexistingWesternAustraliancoastalplanningpolicy, toarticulatethebenchmarkforlongtermadaptation planningdecisions,andhelptomanagetheinﬂuence ofshorttermpoliticsanddevelopmentpressure.

Principle1Adaptationplanninginthecurrentplanninghorizondoesnot impedetheabilityoffuturegenerationstorespondto increasingriskbeyondcurrentplanninghorizons.

Principle2Adaptationrequiresadecision-makingframeworkthat enablestherightdecisiontobemadeattherighttime,in linewiththevaluesandcircumstancesofthetime.

Principle3Adaptationplanningreﬂectsthepublic’sinterestinthesocial, environmentalandeconomicvalueofthecoast.

Principle4Alternativeadaptationmeasuresshouldconsiderthefull rangeoflandusesandvalues.

Principle5Thefulllifecyclebeneﬁts,costsandimpactsofcoastal protectionworksshouldbeevaluatedwhileconsidering adaptationoptions.

Theadaptationprincipleswereusedtoarticulatea pathwaythatwouldapplytheadaptationhierarchyto avulnerablecoastalareaovertime.

TheStateCoastalPlanningPolicy(SPP2.6)(Western AustralianPlanningCommission 2013)includesan assessmentmethodologythatestablishesacoastalsetbackfornewdevelopment(fora100yeartimeframe) toallowforcoastalprocesses,involvingcomponentsof:

. Erosion

○ currentriskofstormerosion(S1);plus ○ historicshorelinemovementtrends(S2);plus ○ futuresealevelrise(S3).

. Stormsurgeinundation(S4)

Thestormeventsfordeterminingthecurrenterosionandinundationriskaredeﬁnedinthepolicy. Theallowanceforerosion/accretionisbasedona1% AnnualExceedanceProbability(AEP)eventwhichis (approximately)equivalenttoa100yearAnnual RecurrenceInterval(ARI).Thestormeventtocalculatethestormsurgeinundationallowancehasa0.2% AEP,(approximately)equivalenttoa500yearARI. Theworstcaseoferosionorinundationsetstheminimumacceptabledistance(setback)fromtheshoreline fornewdevelopment,consideringaperiodof100 years.Ifthissetbacklineistranslatedtoamapthis wouldrepresentacontour(Y100).Similarcontours canbedevelopedusingthesameanalysisforanytimeframe.Forexample,theY50contourrepresentsthesetbackthatrepresentsacceptablerisk(e.g.,1%AEP erosionevent)foraperiodof50years.

Reﬂectingthisapproachweproposethefollowing pathwayandhierarchytosettriggerpointsatwhich decisionsaretobetaken(see Figure2 and Table1).

SettingTrigger3atY15meansthatthereisa15yearperiodduringwhichadecisionismadeand implementedtoeitherprotectthecoastlineorretreat beforetheriskoferosionand/orinundationbecomes unacceptableforassetswithinthatcontour.Abeneﬁt ofthetrigger-basedpathwayfordecision-makingis that – irrespectiveoftheuncertaintysurrounding sea-levelriseestimatesusedinpolicydevelopment –decisionsarenotmadepre-emptively,i.e.,beforethe risklevelisrealisedandunderstoodinreality.

Table2 illustratesthekeydecisionsthat ﬂowateach triggerpoint.Theavailablemeasuresarebasedonthe leveloftolerabilityaccepted.

Reframingtheprotectvsretreatquestion

Coastalworksaimtoprotectphysicalassetsatthreat fromerosionandinundation.However,suchworks arenotbenign-seawallsresultinlossofbeachby restrictinglandwardmigrationanddeﬂecterosionto adjacentunprotectedbeach(Kraus 1988).Theintertidalpartofthebeachisalsohabitattomacroinvertebratesandtheirshorebirdpredators,andthe narrowingandeventuallossofbeachadverselyimpact thisecosystem(Duganetal. 2008).

Triggerbased,long-termadaptationpathway.

Engineeredstructuresaredesignedtowithstanda speciﬁedstormevent,andhaveadesignlifeafter whichtheynolongeroﬀerviableprotection.Itis importantforstakeholderstounderstandthetemporarynatureofprotectionmeasures.Inthelongterm, thesizeandextentofengineeringstructuresrequired towithstandsealevelriseandmoreintensestorm eventswillnecessarilybecomelarger,increasingtheir costandimpact.Thelogicalconclusionisthatthe feasibilityandcostofcontinuingprotectionwill becomeuntenable,andeventualretreatfromthevulnerablelandisthereforeinevitable.

Thismeansthatthelosses(landvalue)andcosts (disruptiontooperations)associatedwithRetreatare commontoallpossiblemeasurestakenintheforeseeablefuture.Thevariousadaptationmeasures(AccommodateorProtectorcombinationthereof)willhavea finiteeffectivelifeandthereforeonlyservetodelay theselossesandcosts,albeitconsiderablyinsome cases.Tobe financiallypreferable,thecapitaland ongoingcostsofthesemeasuresmustbelessthanthe

Table1. Calculationoftriggerpoints.

Trigger RiskLevel Locationofmostseaward asset/valueatrisk:

Trigger 1 Tolerable BetweentheY100andY50 contour

Trigger 2 Increasinglikelihoodof intolerablerisk BetweentheY50andY15 contour

Trigger 3 Intolerable.Interimprotection maybefeasible SeawardoftheY15contour

Trigger 4 Intolerable.Protectionisnot feasible

SeawardoftheY15contour

benefitobtainedbydelayingtheinevitablelossesand costsofeventualretreat.Thistestisrelativelystraightforwardusingdiscountedcash flowtechniques. ApplyingthislogicintheCockburncaseledtoan optionanalysisprocess(includingbutnotlimitedto financialcosts)thatcomparedthefollowingalternatives:

. Retreatwhenriskbecomeunacceptable;and

. ProvideInterimProtectionincorporatingarangeof shorttolongtermprotectionmeasuresthatdelay (buteventuallyleadto)Retreat.

Interimprotectionmeasurescompriseeither:

. CoastalProtection – protectingsiteslandwardofthe coastlineitselffromrecession/inundationthrough either ‘hard’ (engineering)measuresor ‘soft’ (regenerative)measures;or

. AssetProtection – protectingtheassetitselffrom measurestakenatthelotscale.

Coastalprotectionoptionsweredeveloped,reﬂectingthenatureofthedefencesprovided(see Table3).

Optionevaluation

Inorderforcoastalprotectionworkstobeanappropriateresponse,thereneedstobesufficientbenefittojustifythelifecyclecostandotherconsequencesofthe works.Asnotedabove,the financialequationisthe comparisonbetween:

Figure2.

Table2. Triggeranddecisionpoints.

Trigger Decision Implication/action

Trigger1:Assetsorvaluesincoastalzonereach highrisklevel

Trigger2:Assetsorvaluesincoastalzonewill reachextremerisklevelduringtheplanning period

Trigger3:Assetsorvaluesincoastalzonereach extremerisklevel

Trigger4:Assetsorvaluesincoastalzone continuetobeatextremerisklevel

Riskistolerable . Avoid throughstrategicplanningmeasures . Ongoingmonitoring

Increasinglikelihoodof intolerablerisk . Accommodate throughassetorareaspeciﬁcmeasures

Intolerablerisk – interim protectionmaybefeasible

Intolerablerisk – protectionis notfeasible

. thecapitalandongoingcosts(includingdecommissioning)ofthesemeasures,and . thebeneﬁtsobtainedbydelayingthelossesandcosts ofeventualretreat.

Ofcourse,therearenon-ﬁnancialcostsandbeneﬁts, andmulti-criteriaanalysis(MCA)incorporatinga rangeofcriteria(Table4)wasusedtoranktheRetreat, andoneormoreInterimcoastalprotectionoptions. Weightingsweredevelopedforthecriteriathrough engagementwiththeprojectstakeholders.

Thestudyareacomprisessome18separatecoastal managementunits.Thepurposeoftheoptionevaluationprocesswastocomparethecostsandbeneﬁts ofRetreattooneormoreInterimprotectionmeasures foreachmanagementunit:

. atthedecisiontriggerpointwhichisdeterminedby thelevelofrisktocoastalassets;and

. overthelifeofthatprotectionmeasure.

Itisintendedthatthisprocessisappliedatthepoint intimewhen Trigger3 occurs.Formostcoastalmanagementunitsconsideredinthisproject(i.e.,14of the18),thiswasapointinthefutureandsotheassessmentwasa ‘ﬁrstpass’ onlyfortheseunits.Itisintended thattheoptionevaluationiscontinuallyupdatedas newinformationonsealevelrisebecomesavailable. Theexerciseresultedin:

. Retreat beingthepreferredoptionin5ofthe18 coastalmanagementunits;

. Ongoingmonitoring

. Evaluatewhether InterimProtection isjustiﬁableonsocial, environmental,andeconomicgrounds.

. Whereinterimprotectionisjustiﬁable,determinethenatureofthe worksbasedonsocial,environmentalandeconomicgrounds.

. Whereinterimprotectionisnotjustiﬁable, Retreat

Activelyplanfor Retreat inacoordinatedmanner.

. Hard-active measuresbeingpreferredin4ofthe units;

. Soft-passive and hard-passive measuresbeingpreferredin7oftheunits;and

. Nomeasureswererequiredin2oftheunits(which havearockycoastlineunlikelytobeaﬀectedinthe evaluationtimeframe).

Whereinterimcoastalprotectionmeasureswere foundnottobejustiﬁed,thosepartsofthecoastwill beassumedtobecomeaﬀectedovertimebyerosion andinundation,requiringtheeventualretreatfrom thatlocationandintheinterim,considerationofprotectionofindividualassetsbytheassetowners,includinginfrastructureproviders.

Theidentiﬁedpreferenceforprotectionmeasuresin otherlocationsarisesessentiallybecausetheseoptionsprovideprotectiontothelandwardassetsaswellasbeach retentionforthelifeofthemeasures.However,theresults needtobeconsideredfurtherinthelightofcumulative environmentalimpact,includingmaterialsavailability.

Planningresponse

Theplanningsystemwillneedtobemodiﬁedtoincorporateandregulatetherecommendedapproach.The localplanningstrategywillbeakeyconsultationand communicationtoolthatwillengagethecommunity indecision-making,andcommunicatetriggersand timeframesforadditionalcontrolsofcoastallanduse tomanagecoastalrisks.Thisinvolvesanumberof keyplanningactions.

Table3. Coastalprotectionmeasures.

Approach Description Examples

Soft – PassiveForeshoreprotectionworksthatofferbenefitstoerosionandinundationbutdonotinvolve constructionofstructuresanddonotdirectlyaffectcoastalprocesses.

Hard – PassiveForeshoreprotectionworksthatinvolvetheconstructionofstructureswhichalterthecoastalprocesses thatactontheland/beachwiththeintentiontomaintainorimprovebeachamenitythrough retentionofsand.

Hard – ActiveWorksthatinvolvetheconstructionofstructureswhichoﬀerasourceofprotectiontolandsideassetsin proximitytotheforeshore.Theconstructionofhardactiveengineeringoptionscanaltertheway coastalprocessesactontheland/beachinterface.Thesechangestotheshapeoftheland(e.g., erosionofabeachinfrontofaseawall)canhaveimplicationsforlanduse(e.g.,lossofbeach amenity).

Sandnourishmentanddune stabilisation

Groynesandoﬀshore breakwaters

SeawallsandLevees

Table4. Optiondecisioncriteria.

DecisionCriteria

Lossoflandvalue

Interimprotectioncosts

Industrialpropertyimpact

Residential&commercialproperty impact

Metric

Duringthelifeoftheinterimprotectionmeasure: Retreatmeans … Interimprotectionmeans …

Discountedcost($) ImmediatelossoflandvalueDelayedlossoflandvalue

Discountedcost($) Nil

Numberofpotentiallots

aﬀected

Numberofpotentiallots

aﬀected

Capitalandoperatingcosts

Relocation&disruptionNil

Residualrisktoproperty Scaleof1–5 Nil

Parksandreservesimpact Area(ha)

Riskfromfailureand/orextremeevents

Arealosttoencroaching foreshore Nil

Beachrecreation/amenityimpactLinealmofbeach Nil

Heritageimpact

No.ofheritageproperties

aﬀected

Beachloss(forhard-passiveengineering approaches)

Loss/degradationofheritage assets Nil

Habitatloss Area(ha) Nil

Planningaction – incorporateaspecialcontrol areaforvulnerablecoastalarea

Akeyplanningmechanismisthedemarcationofa SpecialControlArea(SCA)appliedtothevulnerable coastalareaat Trigger1,whichprovidesadditionalplanningcontrolsforaspeciﬁcarea.Thelocalplanning schemeshouldincorporatetheSCAtoadviselandownersandplannersthattheareaisinavulnerablecoastal areaforthelong-term(100-year)planninghorizon.

TheSCAwouldencompasslandthatwouldbeboth impactedandinﬂuencedbyfuturelandusechangein responsetocoastalprocesses,comprisinglandseaward ofthephysicalprocessesallowancefora100-yearplanninghorizoncalculatedinaccordancewithSPP2.6 (theY100contour)usingcoastalvulnerabilitymapping undertakenandupdatedatregularintervals,(say)5 years.ThereshouldbeapresumptionthattheSCA willexpandlandwardsovertimeasthesea-levelrises. Developmentcontrolswouldbeinvokedforthe SCA,including:

. Notiﬁcationsontitleforexistingproperties, reviewedandupdatedovertime;

. Presumptionagainstmajornewdevelopment/redevelopmentwithintheSCA;and

. Conditionsunderwhichexceptionsareallowable, includingfortemporaryand/orshortliveddevelopmentandforfacilitiesrequiringdirectcoastalaccess (e.g.,industrialfacilities,surfclubs).

ForlandwithintheSCAsubjectto Trigger2 (i.e.,within theY50contour),thelocalgovernmentwouldadviseownersandoccupiersthattheirassetsareatriskoferosion/ inundationassociatedwithsealevelrisewithin50years.

At Trigger3 (affectinglandwithintheS15contourof theSCA),riskisassessedasintolerable,requiringa studytodeterminethecost–benefitofProtectionvs Retreatinlinewiththeapproachoutlinedabove.Landownersshouldberestrictedfromundertakingcoastal protectionmeasuresthatseektoprotectprivateassets. Protectionmeasureshaveconsequenteffectsonadjacent coastlineandad-hocinstallationswouldunderminethe

Shorelineloss

whole-of-coastplanpromotedhere.Anycoastalprotectionmeasuresthatdoprogressshouldbecommissioned bythestategovernmentandincorporatedwithin,andas partof,coastalforeshorereserves.

At Trigger4,i.e.,whenprotectionisdeemedunviable,Retreatisinvoked.

Planningaction – expandthecoastalforeshore reservetosupportlong-termretreatfrom coastalland

Theprimaryplanningresponsetoenableretreatfrom thevulnerablecoastalareaisthroughexpansionofthe coastalforeshorereserve,requiringthere-zoningof landforthispurpose.Foreshorereservesshouldbe suﬃcientinwidthtomaintainthesocialandenvironmentalfunctionsofthereserveoncephysicalprocesses havebeenallowedfor(notingthatmanyexisting reservesaredeﬁcient).

Insituationswhereacoastalforeshorereservealready exists,thereservationwouldbeexpandedlandwardsin logicallandparcels,takingintoaccounttheadjacent landuse.Insituationswherethereisnoexistingforeshorereserve,thereservationwouldbecreatedonprivatelandandtheadjacentroadreserve.Accordingly, overtimethepolicywouldresultinacontinuouscoastal foreshorereserve,providingthedualbeneﬁtsofbuﬀeringcoastalprocessesandmaintainingthesocialandculturalvaluesoftheforeshore,includingbeachaccess.

Overtime,toimplementRetreat,reservedland wouldbeacquiredusingpublicfunds,justasitisfor infrastructureprojectssuchasmajorhighways.

Planningaction – developforeshore managementplansthatincludecomprehensive policyguidancefortemporarydevelopmentand landusewithinthecoastalforeshorereserve

Undertheapproachesoutlinedhere,foreshoremanagementplansbecomeanimportantelementofthe adaptationstrategy.Coastalprotectionshouldbethe highestpriority,requiringtheidentiﬁcation,

prioritisation,andfundingofnaturalcoastalanddune managementtechniquestoenhancetheabilityofthe naturalsystemtobuﬀercoastalprocesses.

Theplanshouldidentifyappropriate,impermanent communityfacilities,whileincorporatingtrigger pointsfortherelocationordecommissioningofexistingassets.Anynewtemporarydevelopmentthatis approved,shouldaddressdesignlifeandarchitectural andconstructionrequirementsthatcommunicatethe impermanentnatureoffacilitiestothecommunity.

Conclusions

Thescienceisin.Theworldwillbeadaptingtosealevelriseforseveralcenturiesatminimumandcoastal managers,national,stateandlocalgovernmentsare, orshouldbe,awareofthesituation.Althoughsubject tomuchresearchandanalysis – theliteratureisextensive(Tompkinsetal. 2010;Bowering 2014;Hurlimann etal. 2014;Kellett,Balston,andWestern 2014,Abel etal. 2011;Taylor,Harman,andInman 2013;Bray, Hooke,andCarter 1997;Hill 2016;Robbetal. 2017),thereisnotyetanyrealconsensusonhowto progresstowardsaconsistentandrationallandplanningprocessthatcan,andwillbebroadlyapplied everywhere.

Insituationswhereplannedretreathasbeen attempted,outragefromaffectedlandholdershas oftenreversedthepolicyinfavourofcoastalprotection works,mostnotablyinByronBay2 (Kellett,Balston, andWestern 2014).InCalifornia,morethan10per centofthecoastlineisnow ‘armoured’ (Meliusand Caldwell 2015).Theprocesssuggestedinthisarticle doesnotprecludeprotection,andindeedthiswasthe nominallypreferredoptioninsomeareasinourcase study.However, whether toprotectornotprotectisa falsecomparisongiveninevitablesealevelrise.The correctcomparisonisbetweenretreatnow,orprotect temporarilybeforeretreatinginthefuture.Framing theissueinthiswayshouldreducethetensions betweenprivateandpublicintereststhathaveoften preventedrationalpolicydevelopmentinthepast. Manycoastaladaptationplanningprojectsand researcherspromotetheuseofa flexiblepathway approach(Haasnootetal. 2013;Brownetal. 2014; Wiseetal. 2014;CoastAdapt 2018;Abeletal. 2011). Akeyinnovationinthepathwayoutlinedhereisthat longterm flexibilityinadaptationisenabledthrough anongoingstrategicplanningprocessthatmaintains andpreparesforfutureavoidandretreatdecisions. Inessence,thestrategicplanningpathwayplansfor ultimateretreatwhilecontemplatingthatits implementationmaybedelayedthroughinterimprotection.Developingaconsistent,yet flexiblepolicyframeworkiscriticallyimportanttobuildcommunity trust,insulatepolicymakersfromthecontroversies thatinevitably flowfrompolicyparalysis,and

ensureeﬃcientpublicandprivateinvestmentin coastalassets.

Notes

1.ThisdocumentwasrevisedinJuly2019afterthedraft ofthisarticlewasprepared,andcontainssomeofthe recommendationssetouthereandintheGHD reports(WesternAustralianPlanningCommission 2019).

2.ThecaseforretreatatByronBayiscontested,with somearguingthatitis ‘unworkableinpractice’ (Buckley 2013).

Acknowledgements

Theauthorswouldliketoacknowledgethecontributionsto thisworkbyGHDstaﬀ andthankthelocalgovernmentsthat commissionedtheCockburnCoaststudy.

Disclosurestatement

Nopotentialconﬂictofinterestwasreportedbytheauthor(s).

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