• Nenhum resultado encontrado

The impact of Sea level rise in the guadiana estuary

N/A
N/A
Protected

Academic year: 2021

Share "The impact of Sea level rise in the guadiana estuary"

Copied!
10
0
0

Texto

(1)

ContentslistsavailableatScienceDirect

Journal

of

Computational

Science

j o u r n al ho me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / j o c s

The

impact

of

Sea

level

rise

in

the

guadiana

estuary

Lara

Mills

a,∗

,

João

Janeiro

a

,

Antonio

Augusto

Sepp

Neves

a

,

Flávio

Martins

a,b aCentrodeInvestigac¸ãoMarinhaeAmbiental(CIMA),UniversityofAlgarve,Faro,Portugal

bInstitutoSuperiordeEngenharia(ISE),UniversityofAlgarve,Faro,Portugal

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received8January2020

Receivedinrevisedform8May2020 Accepted8June2020

Availableonline12March2020 Keywords:

Guadianaestuary Sealevelrise MOHID Salinityintrusion

a

b

s

t

r

a

c

t

Understandingtheimpactofsealevelriseoncoastalareasiscrucialasalargepercentageofthepopulation liveonthecoast.Thisstudyusescomputationaltoolstoexaminehowtwomajorconsequencesofsea levelrise:saltintrusionandanincreaseinwatervolumeaffectthehydrodynamicsandfloodingareasof amajorestuaryintheIberianPeninsula.A2DnumericalmodelcreatedwiththesoftwareMOHIDwas usedtosimulatetheGuadianaEstuaryindifferentscenariosofsealevelrisecombinedwithdifferent freshwaterflowratesconsideringvaryingtidalamplitudes.Anincreaseinsalinitywasfoundinresponse toanincreaseinmeansealevelinbothhighandlowfreshwaterflowratesatallareasaroundtheestuary. Anincreaseinfloodingareasaroundtheestuarywasalsopositivelycorrelatedwithanincreaseinmean sealevel.

©2020TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).

1. Introduction

Ariseinmeansealevelisaglobalconcernas10%oftheworld’s

populationlivewithin10melevationofthecurrentsealevel[3].

BasedonprojectionsbytheIntergovernmentalPanelonClimate

Change(IPCC),therateofsealevelriseisaccelerating.An

accel-erationinglobalsealevelrisehasbeenreportedthroughoutthe

20thcenturybasedonsatellitealtimeterdata[6].Globalmeansea

levelrisecouldbeashighas1mbytheyear2100ifgreenhouse

gasemissionscontinuetobeveryhigh[5].Asthenumberof

peo-pleaccommodatingcoastalareasincreases,anaccelerationinthe

rateofsealevelrisewillseverelyimpactsocietyandtheeconomy.

Impactsofsealevelriseoncoastalareasincludesubmergenceof

land,increasedflooding,increasederosion,changesinecosystems

andanincreaseinsalinity[16].Notyetfullyexploredinthe

litera-tureishowthedynamicsofsalinityinestuarieswillevolvedueto

sealevelrise.Itisthustheaimofthisworktoquantifya

relation-shipbetweensealevelriseandsalinitycontentinestuaries,asan

increaseinestuarinesalinityhasthepotentialtodamageestuarine

environments.

Fromaphysical standpoint,anestuaryis definedasa

semi-enclosedbodyofwaterwhererivermeetssea,extendingintothe

riverasfarastheupperlimitofthetides.Estuariesare

produc-tiveenvironments,hostinghighlydiverseandcomplexecosystems

∗ Correspondingauthor.

E-mailaddresses:a60162@ualg.pt(L.Mills),jmjaneiro@ualg.pt(J.Janeiro), aaneves@ualg.pt(A.A.S.Neves),fmartins@ualg.pt(F.Martins).

[20].Fisheries,aquaculture,ecotourism,andportfacilitiesrelyon

estuariestocontributerevenuestonational, regional,and local

economies.

Thesetransitionalareaswherefreshwaterderivedfromland

mixeswithsaltwaterfromtheseaaresensitivetochangesin

cli-mate suchas sealevel rise.Estuariesadapt tosealevelriseby

deepeningtheirchannels.Thisincreasestheaccommodationspace

ofsediments,furtherenhancingebbandfloodasymmetry[20].

Awatercolumnisconsideredstratifiedwhenlessdensewater

liesoverdenserwater.Thus,thestratificationofanestuaryis

deter-minedbythebalance betweenbuoyancyand mixingof denser

saltwaterfromtheseaandlessdensefreshwaterfromland.An

increaseinsealevelallowsmoresaltwatertoentertheestuary

[19].Thus,amajorconsequenceofsealevelriseinestuariesisthe

intrusionofsaltfromseawaterintofreshgroundwater,whichcan

furtherimpactstratification[15].

Theintrusionofsaltwillhaveaprofoundeffectonthephysical

propertiesofestuariesasthedynamicmixingofsaltwaterandfresh

wateristhedrivingfactorregulatingstratification[19].Changesin

oceanicsalinitycombinedwithvaryingflowratesoffreshwater

dischargeintotheestuarywillaltertheentireestuarinecirculation

[19].HongandShen[11]foundanincreaseinstratificationinthe

ChesapeakeBayasaresultofanincreaseinsalinitybasedonthe

resultsofathree-dimensionalnumericalmodel.Thischangein

hor-izontalsalinitygradientswillfurtheralterestuarinecirculationand

causeoxygendepletion[11].Alterationsinestuarinecirculation

willbedetrimentaltomarineecosystemsthatcannottoleratehigh

salinitycontent[4].Furthermore,sealevelriseincreasessalinity

upstreamandimpactstidalcurrents[11].Astudyontheimpactof

https://doi.org/10.1016/j.jocs.2020.101169

(2)

2 L.Mills,J.Janeiro,A.A.S.Nevesetal./JournalofComputationalScience44(2020)101169

anincreaseinsalinityonLouisianaestuariesbyWisemanetal.[22]

foundbothpositiveandnegativetrendsattributedtothe

variabil-ityoffreshwaterflowrates.Theseauthorsfoundthatanincrease

insalinityresultsin thedeathor declinein theproductivityof

marshes,whicheventuallyleadstolandloss[22].Furtherimpacts

ofsaltintrusionincludecontaminationofwatersuppliesforboth

consumptionandfortheindustry[10].

Theaimofthisarticleistopresenttheresultsofanumerical

modelsimulatingsaltintrusionintheGuadianaEstuary,amajor

estuaryontheIberianPeninsula. Themodelsimulatesdifferent

sealevelrisescenariosasprojected bytheIPCCalongwith

dif-ferentriverdischargeflowratesandvarioustidalamplitudes.As

changesinsealevelinevitablyalterthetopographyofestuaries

[17],thesimulationsofthepresentstudywererunovertwo

pos-siblefuturebathymetriesoftheGuadianaEstuarytodetermineif

actionmustbetakentomaintainthecoastlineortoallowflooding

ofsurroundingareasoftheestuary.

2. Methods

2.1. Studyarea

TheGuadianaEstuaryconnectstheGuadianaRivertotheGulfof

Cadiz.TheGuadianaRiveristhefourthlongestriverontheIberian

Peninsulawithalengthof810km,200ofwhichforma border

betweenPortugalandSpain[7].Beginningatitsmouthinfront

ofVilaRealdeSantoAntóniointheAlgarveregionofPortugaland

Ayamonte,Spain,theestuaryextendsabout80kmnorthtoitstidal

limitatMértola.Theestuarydrainsatotalareaof66,960km2[9]

infrontofthesehighlypopulatedregions.TheGuadianaEstuaryis

atitswidestinfrontofVilaRealdeSantoAntóniowithawidthof

800mandismostnarrownearMértolawithawidthof70m.The

averagedepthoftheestuaryis5m,butinsomecases,itcanreach

10m.

Downstream,theestuaryisintheformofasubmergeddelta

wherethereismoderatewaveenergy [9]. Theestuaryis

classi-fiedasarock-boundestuaryduetoitsnarrowandrelativelydeep

channel,locatedonapassivemarginwherethevolumeofwater

enteringtheestuaryduringthefloodtideislargerthanthe

freshwa-terdischargefromtheGuadianaRiver[9].TheGuadianaEstuaryis

characterizedbyasemi-diurnalmeso-tidalregimewithtidal

influ-ence80kmupstreamfromwhereitmeetstheGulfofCadiz[7].The

averageneaptidalrangeis1.28mandtheaveragespringtidalrange

is2.56mwithamaximumspringtidalrangeupto3.44m[9].

Tidesandfreshwaterinputcontroltheverticalmixingand

strat-ificationof theestuary, which rangesfrom very well-mixedto

partiallystratified[9].Themixingoftheestuaryvariesbyseason,

withawell-mixedwatercolumnwhenthereislowdischargefrom

theGuadianaRiverduetoalackofrainfallandapartiallystratified

watercolumnwhenthereismoredischargefromtheriver.Itis

onlyunderextremeconditionsthatthewatercolumncanbecome

stratified[9].Theebbcurrentsoftheestuaryaregenerallyfaster

thanfloodcurrents,eveninlow riverconditions,aneffectmost

likelyduetothelargehydraulicdepthoftheestuarinechannel.The

ebb-dominancebecomesmorepronouncedastheriverdischarge

increases[9].

The freshwater discharge of the Guadiana River can range

between10m3/sand4660m3/s.Theconstructionofover100dams

sincethe1950shascontrolled70%ofthedrainagebasinbytheend

of2000[9].OfrelevanceistheAlquevaDam,located60kmfrom

theheadoftheestuary.Itisthelargestreservoirinsouthernand

westernEuropestoring4150hm3ofwater[9].Itsclosurein2002

hassignificantlyreducedthemeanriverflowfromanaverageof

143m3/soverthelast26yearsto16m3/safter2002[9].

Down-streamthedam,theriverhasephemeralflowsandisdryfor40%

oftheyear[8].TheGuadianaEstuarycurrentlyfacesareduction

inriverflowduetoscarcerainfallandanincreaseinfreshwater

storage.AmapofthestudyareaisshowninFig.1.

2.2. Hydrodynamicmodelsetupandsimulatedscenarios

The MOHID water modelling system was used to simulate

the hydrodynamicsof theGuadiana Estuary and the effects of

differentsealevelrisescenariosonsalinitydistributionand

trans-port. MOHIDis a three-dimensional hydrodynamical modelling

system that integrates diversenumerical models in an

object-orientedprogrammingapproach[13].MOHIDsimulatesphysical

andbiogeochemicalprocessesinthewatercolumnandsediments

[13]. MOHID hasbeen used to simulatethe hydrodynamics of

manycoastalandestuarinesystems,mainlythemajorestuariesof

Portugal,butalsointheNetherlands,FranceandIreland[18].The

modelhasbeenpreviouslyvalidatedandcalibratedintheGuadiana

Estuarybycomparingin-situmeasurementsofsalinitywithmodel

results[12].ArecentstudybyQuesadaetal.[18]usedMOHIDin

2Dbarotropicmodetosimulatetheeffectsoffreshwaterdischarge

andtidalforcingontidalpropagationintheGuadianaEstuary.This

modelaccuratelyproducedphasevaluesoftidalelevationsand

cur-rentsasconfirmedbyaharmonicanalysis[18].Themodelwasable

todemonstratehowfreshwaterdischargehasastrongereffecton

tidalwaveamplitudeupstreamtheestuary,whereastidalforcing

controlstidalwaveamplitudedownstreamtheestuary[18].

ThemodelsolvestheNavier-Stokesequationsconsideringthe

hydrostaticandBoussinesqapproximations.uiisthevelocity

com-ponentineachdirection;fistheCoriolisparameter,␳=␳0+␳’isthe

densitydecomposedinitsreferencevalueplusanomaly,andAiis

theturbulenceviscosityineachdirection.Theequationsare

dis-cretizedusingthefinitevolumemethod.Thesolutionschemeis

semi-implicitoftheAlternatingDirectionImplicit(ADI)type.The

S21schemeofAbbottetal.[1]forshallowwaterequationswasused

andadaptedto3DaccordingtoMartinsetal.[14].Theequations

areasfollows:

u1

x1 +

u2

x2 +

u3

x3 =0

u1

t +



uju1



xj =fu2−gn 0



x1 − 1 0

ps

x1 − g 0



 z



x1 dx3 +

xj



Aj

u1

xj



u2

t +



uju2



xj =−fu1− gn 0



x2 − 1 0

ps

x2− g 0



 z



x2 dx3 +

xj



Aj

u2

xj



p

x3 = −g

Thesamediscretizationandcomputationalsolutionwereused

totransportsalinity,whichisassumedtobeapassivetracer.

Thecalculationtimetostabilizethesalinityfieldisveryhigh

whentheriverflowislowduetothehighresidencetimeofthe

estuaryinlowriverdischargeconditions.Forexample,withariver

flowof10m3/sittakestwomonthsofsimulatedtimeforthe

salin-ityfieldtostabilize.Thecomputationalmeshwaschosentoprovide

a spatialresolutionappropriate forthestudywithoutincurring

excessivecalculationtime.Thus,eachsimulationusedaCartesian

(3)

Fig.1. Mapof(a)theIberianPeninsulastudyareaand(b)acloserlookattheGuadianaEstuary.Orangedotsin(b)markwheresalinity,velocityandelevationtimeseries werecollected.Bluedotsmarkreferencepointsinthestudyarea(Forinterpretationofthereferencestocolourinthisfigurelegend,thereaderisreferredtothewebversion ofthisarticle).

of30mtoevaluatesalinitydistributionandtransportaswellas

coastalfloodingatthemouthoftheGuadianaEstuary.The

simula-tionswereruninanIntelXeonGold6138serverandthecodewas

parallelizedusingOpenMPanddistributedover8cores.Withthis

setup,twomonthsofsimulatedtimetakesmorethanfifteendays.

The model incorporates various sea level rise scenarios

combined with different river discharge scenarios typical of

the Guadiana River over two separate bathymetries. The first

bathymetrywascomputedbytriangularinterpolationofmeasured

bathymetricdataonthemeshof1400×350cellswithaspacestep

of30m.Thisbathymetryisindicativeofthepresentbathymetryof

theestuaryandcorrespondstoacaseinwhichmaximumhuman

interventionistakentokeepthecoastlineunchanged.Thesecond

bathymetryrepresentsasituationinwhichthereisnohuman

inter-vention,thusallowingmaximumfloodingofthesaltmarshesand

low-lyingareas.Process-basedmodelssuchasMOHIDcannot

eval-uatelong-termgeomorphologicaldynamicssotheresultsfroma

behavior-orientedmodelbySampathetal.[21]wereusedforthis

specificbathymetry.Thebathymetrywascomputedbasedonthe

rateofsealevelrise,accommodationspaceforsedimentdeposition

andverticalaccretionofsedimentsduetoinundation[21].Thetwo

differentbathymetriesareshowninFig.2.

Twodifferentfreshwaterdischargeswereimposedinthemodel

representing:(1)alowfreshwaterdischargeof10m3/swhenthere

islittlerainand(2)ahighfreshwaterdischargeof100m3/swhen

thereismorerain.Themodelfurtherexploresthreevaryingtidal

amplitudesoftypeM2representing:(1)typicalsystemconditions

equivalenttotheaveragetideconditions,resultinginanamplitude

of1m;(2)springtideequivalenttoanamplitudeof1.28mand

(3)neaptideequivalenttoanamplitudeof0.64m. Tosimulate

thesalinitytransportintheGuadianasystem,thesalinityofwater

fromtheGuadianaRiverwasconsiderednullandthesalinityofthe

coastalregionadjacenttotheestuarywassettoaconstantvalue

of36.Thesevaluesaretypicalforthisregion.Therearenounitsfor

salinity,inagreementwithrecommendationsbyUNESCO.

Thetwodifferentriverdischargescenarios mentionedabove

were combined with different sea level rise scenarios derived

fromsealevelrise projectionsprovided bythe5th IPCCreport

forRepresentativeConcentrationPathway(RCP)4.5andRCP8.5.

RepresentativeConcentrationPathwayreferstogreenhousegas

concentration[5].The5threportoftheIPCCprojectedseveral

pos-siblevaluesinglobalmeansealevelriseforthesetwoRCPvalues

overtheyears2046–2065,2081–2100and2100.Duetothehigh

computationalcostandthefactthatsealevelrisescenarioswould

becombinedwithtwodifferentriverdischargescenariosaswell

asthreedifferenttidalamplitudes,itwasnotpossibletosimulate

allsealevelriseforecastsfromtheIPCC.Itwasdecidedtoconsider

threecasesofsealevelrisethatcoveredallpossibilitieswithinall

scenariosfromtheIPCC.Thesealevelriseprojectionscorrespond

toasealevelriseof0.24m,0.48m,and0.79mcorrespondingto

theyearsof2040,2070and2100,respectively.Thevalueswere

imposedinthemodelbychangingthereferencelevelofthetidal

components.

Threedifferentsealevelrisescenariosalongwiththecurrent

sealevelwerecombinedwiththetworiverdischargescenarios

along twopossiblebathymetriesoftheestuary. Additionally,in

ordertoassessthefuturestateoftheGuadianaEstuarywithrespect

tospecifictidalevents,springandneaptidescenarioswerealso

simulated.Theseboundaryconditionsonthemodelproducean

evaluationofthepreviouslymentionedscenariosresultingin

pro-jections,notforecastsofthefuturestateoftheGuadianaEstuary.

Whileitisexpectedforthetidesandriverfluxestochangedueto

sealevelrise,theaimofthisstudyistoanalyzethetrendsproduced

bysealevelriseonspringandneaptides.Therefore,theresults

provideanevaluationofthesensibilityoftheGuadianaEstuaryto

changesintidalamplitudecombinedwithsealevelrise.

Each sea level rise, river discharge and tidal scenario were

imposedinthemodeltoproduceseveraltimeseriesandhorizontal

distributionmaps.Thelocationsforeachtimeseriescanbeseen

inFig.1,correspondingtotheintersectionoftheGuadiana

Estu-aryandEsteirodaLeziria(381147),inthemiddleofEsteiroda

Leziria(39196)andatthewesternmostregionofEsteiroDaLeziria

(39223).

Thetimeserieswereconstructedoveraperiodof2tidalcycles

(24.83h)andrepresentthetemporalevolutionofaveragevalues

(4)

4 L.Mills,J.Janeiro,A.A.S.Nevesetal./JournalofComputationalScience44(2020)101169

Fig.2.ComputationalbathymetryoftheGuadianaEstuaryforamaintainedcoastline(left)andanunmaintainedcoastlinethatallowsfloodingofthesaltmarshesand low-lyingareas(right).

Table1

Classesoffloodingtimeduringonetidalcycle.

Class FloodIntervalInHours

1 0–1.2 2 1.2–2.4 3 2.4–3.7 4 3.7–4.9 5 4.9–6.1 6 6.1–7.3 7 7.3–8.6 8 8.6–9.8 9 9.8–11.0 10 11.0–12.2

respectiveminimum/maximumvaluesobservedwithinthe

sim-ulatedscenarios.Average,maximum,andminimumvalueswere

obtainedbygroupingallthree tidalamplitudes combinedwith

bothfreshwaterflowratestoexaminethedifferencesbetweenthe

presentand2100.Scenariosbasedonthepresentbathymetrywere

analyzedseparatelyfromthosesimulatedontheflood-permitting

bathymetry.

Floodingareaswerecomputedfortendifferentclassesof

sub-mersiontimeduringonetidalcycleoverthebathymetryallowing

maximumflooding.Table1outlinesthedifferentfloodingclasses.

ForeachclassinTable1theareaoffloodingwascomputed,and

ahistogramwasconstructedforthevariousscenarios.Flood

distri-butionmapswerecreatedtoshowtheamountoflandsubmerged

duringatidalcycleaccordingtofloodingclass.

3. Results

Theresultsofthemodelaredisplayedasfollows:section3.1

includestheresultsofthreetimeserieslocationsonthewestern

marginoftheestuaryinthesaltmarshesofCastroMarim,section

3.2includesthehorizontaldistributionofsalinityaswellaschanges

insalinityintrusionlengthinresponsetosealevelrise,section3.3

exploressalinitydistributionatspringandneaptide,andsection

3.4examinesfloodingareasduetosealevelrise.

3.1. Timeseriesofvelocity,salinityandelevation

Figs. 3, 4 and 5 show the time series results at the

previ-ouslymentioned locationsfor boththepresent bathymetryand

bathymetrythatallowsflooding.

The time series results for the three locations downstream

EsteirodaLeziria(381147,39196and 39223),ascanbeseen

in Figs. 3–5, portrayan increase insalinity from 2019to2100

duetosealevelrise.Theincreaseinsalinityisdirectlycorrelated

withwaterelevation:salinityvaluesarehigherwhenwaterlevelis

higherandsalinityvaluesarelowerwhenwaterlevelislower.The

locationclosesttothemainchannel(381147)containsthehighest

salinityvaluesandmostvariabilityoverthe2tidalcycleperiodas

canbeseenin

Fig.3.

Locationsfurtherwest(39196and39223)containsmaller

val-uesinsalinityandlessvariabilityduringthe2tidalcycleperiod.

Theincreaseinsalinityforalllocationsismorepronouncedforthe

bathymetrythatallowsflooding,withsalinityincreasingbyabout

4witha0.79mriseinsealevel.Velocitydoesnotchange

signifi-cantlyfromthepresentto2100butFigs.3–5showaslightdecrease

invelocityduetothe0.79msealevelrise.

3.2. Horizontaldistributionofsalinitytransport

Thesalinitydistributionmapsforthepresent bathymetryin

highwaterconditionsforthevariousscenariosofsealevelrisecan

beseeninFig.6andforlowwaterconditionin

Fig.7.Onlysalinitymapsforariverdischargeof10m3/sand

100m3/salongwithaverageM2tidalamplitudeof1mareshown

astheyaremostrepresentativeoftypicalsystemconditions.

Forscenarios withalow freshwaterdischarge (10m3/s)and

athightide,thesalinityprogressesupstreaminresponsetosea

(5)

inter-Fig.3. Timeseriesresultsofsalinity,velocity,andelevationat381147forthepresentbathymetry(left)andbathymetryallowingflooding(right).

Fig.4. Timeseriesresultsofsalinity,velocity,andelevationat39196forthepresentbathymetry(left)andbathymetryallowingflooding(right).

sectionofthemainchannelandCarresqueiraandLezíriawhere

thesalinityhasa valueof20, salinityprogresses about3100m

upstreamfromthepresentsituationtotheyear2040.The

salin-ityintrusionaftertheyear2040continuestoprogressupstream,

butatamuchslowerrate.Theevolutionofsalinityatthemouthof

theestuaryislessdramaticasmentionedinthetimeseries

analy-sis,butsalinityintrusioncanevolvebytensorhundredsofmeters

Fig.8.

Thedistanceofsalinityintrusionatspringand neaptidefor

thetwo freshwaterflowrateswasalsocomputedforboth high

waterandlowwaterconditions.Table2showstheincreaseinsalt

intrusionlengthfromnowto2100forbothtypesofbathymetry.

Allcases of tide, freshwater flow, and bathymetry result in

an increase in salt intrusion length due to sea level rise. The

increase is much more significant for the bathymetry allowing

flooding compared to the increase in salinity for the present

bathymetry. The increase in salinity intrusion length is also

higherfor thelowfreshwater discharge.Thefurthestextension

of salinity intrusion is at spring tide with a freshwater flow

of 10m3/s where the salinity intrusion length increases from

26.31km to28.14km upstreamthe mainchannel fromnow to

2100.

3.3. Salinitydistributionatspringandneaptide

Salinityclassesforspringandneaptidescenarioswere

com-putedbasedontheamountofareacontainingsalinityvalueswithin

theintervalsasshowninTable3.

Theresultsdemonstrateanoverallincreaseinareacoveredby

highersalinityvalueswithrespecttosealevelriseforallcasesof

(6)

salin-6 L.Mills,J.Janeiro,A.A.S.Nevesetal./JournalofComputationalScience44(2020)101169

Fig.5.Timeseriesresultsofsalinity,velocity,andelevationat39223forthepresentbathymetry(left)andbathymetryallowingflooding(right).

(7)

Fig.7. Salinitydistributionmapsinlowwaterconditionsforadischargeflowof10m3/s(left)and100m3/s(right)forthepresentyear,2040,2070and2100.

Table2

Differencesinsalinityintrusionlengthfromthepresentto2100.

SalinityIntrusionLengthIncreasefromPresentto2100(km)

HighTide LowTide

Present Flooding Present Flooding

SpringTide10m3/s 0.99 1.83 0.52 2.10

SpringTide100m3/s 0.26 1.23 0.13 1.70

NeapTide10m3/s 1.55 1.73 0.79 2.10

NeapTide100m3/s 0.12 2.00 0.47 2.29

Table3

Changesinsalinityfromthepresentto2100forspringandneaptide. AreasbySalinityClassfrom

Presentto2100(km2)

SalinityClass Spring100m3/sHighTide Spring

100m3/s LowTide Spring 10m3/s HighTide Spring 10m3/s LowTide Neap 100m3/s HighTide Neap 100m3/s LowTide Neap 10m3/s HighTide Neap 10m3/s LowTide 0−5 −3.49E+00 −4.09E+00 −1.09E+00 −1.22E+00 1.13E+00 2.76E+00 −9.52E-01 −9.68E-01 5-10 2.36E+00 3.56E+00 −1.08E-02 −6.84E-02 −2.42E+00 −2.35E+00 −3.27E-01 −8.22E-01 10-15 9.93E-01 2.66E+00 −2.45E-01 −5.25E-01 4.47E+00 4.15E+00 4.06E-01 1.31E+00 15-20 −3.49E-02 6.36E-01 −5.00E-01 1.13E-01 2.20E+00 2.55E+00 −4.37E+00 −5.28E+00 20-25 −4.45E+00 −4.06E+00 −5.56E-02 −2.47E-01 7.20E-02 1.07E-01 3.17E+00 4.86E+00 25-30 5.14E+00 6.96E+00 −6.81E+00 −8.59E+00 1.85E+00 7.56E-02 6.79E+00 6.97E+00 30-35 5.64E+00 4.87E-01 9.16E+00 1.58E+01 8.45E-02 8.45E-02 2.58E+00 1.23E+00 35-36 2.00E-01 2.00E-01 5.91E+00 1.08E+00 0.00E+00 0.00E+00 8.27E-02 8.27E-02

ityclassbetweenthepresentand2100.Thedifferencesaremore

pronouncedathightideandforlowerfreshwaterflows.

3.4. Areasofflooding

Floodingareawascomputedasa functionof thenumber of

hoursofsubmersionoveronetidalcycleinthevariousscenariosof

sealevelriseasshowninTable4.Theanalysiswascarriedoutfor

thescenarioofthehighestfreshwaterdischarge(100m3/s).

Thetotalintertidalsubmersionareaincreasesfromavalueof

10km2forthepresentyeartoavalueof14km2inthe“2100

sce-nario.Therelationshipbetweenmeansealevelandfloodingarea

isnearlylinear.Furthermore,anincreaseinmeansealevel

(8)

8 L.Mills,J.Janeiro,A.A.S.Nevesetal./JournalofComputationalScience44(2020)101169

Fig.8.Histogramofflooddistributionareasasafunctionofthenumberofhoursofimmersionoveronetidalcycleinthevariousscenariosofsealevelrise.

Table4

Flooddistributionareasbasedonhoursofsubmersionoveronetidalcycleinthe variousscenariosofsealevelrise.

Class HoursofSubmersion Area(km2)

Present 2040 2070 2100 1 0–1.2 0.57 0.56 0.60 0.59 2 1.2–2.4 1.39 1.45 1.65 1.45 3 2.4–3.7 1.46 1.59 1.54 1.86 4 3.7–4.9 1.82 1.93 2.04 2.11 5 4.9–6.1 1.19 1.63 1.69 1.86 6 6.1–7.3 1.29 1.46 1.97 2.17 7 7.3–8.6 0.81 1.03 1.18 1.38 8 8.6–9.8 0.82 0.99 0.97 1.22 9 9.8-11 0.63 0.54 0.72 0.85 10 11–12.2 0.24 0.24 0.31 0.44 Total 10.23 11.41 12.67 13.93

upinfloodingclass,meaningahigheramountoflandwillbe

sub-mergedforalongerperiodwithrespecttosealevelrise.Theflood

distributionmaps(

Fig.9)demonstratethatareaslocatedfurtherdownstreamthe

estuaryarenotasaffectedbymeansealevelrisecomparedtoareas

locatedupstream.Theevolutionoftheinundatedareaismore

pro-nouncedinthenorthmarginoftheinletnotconfinedbyVilaReal

deSantoAntónio.ThemarshesneartheterminalsectionofRibeira

doBelichealsosufferhighinundationbecauseofsealevelrise.The

presentstudydoesnothavebathymetrydataforlocationsfurther

upstreamthispoint,sonoconclusionscanbedrawnforthe

flood-ingareasupstream.Sincetheriverhasanarrowerupstreamprofile

theareasoffloodingareexpectedtobelower.

4. Discussion

Themodelsimulationsdemonstratedthatthemixingand

trans-portofsalinityaretheresultofacomplexdynamicinwhichthe

lowerportionoftheGuadianaEstuaryisdependentonboth

fresh-waterflowfromtheGuadianaRiverandthemeansealevelofthe

adjacentcoastalwaters.TheGuadianaEstuaryalternatesbetween

purelyfreshwaterwhenthereisahighdischargefromthe

Gua-dianaRiverandwaterofvaryingsalinitiesforlowflowsfromthe

river.Inthelattersituation,thetidedominatesthesalinitywitha

semi-diurnalpattern.

For lower freshwater discharge rates, salinity increased in

responsetoanincreaseinmeansealevelwithamorepronounced

changeinsalinityinthemainchannel.Forhigherdischarges,the

increaseinwatervolumeduetosealevelriseinducedahigher

penetrationoffreshwaterfromtheoutletandthereforeresulted

inlowersalinityvalues atthemouthoftheestuary.The

veloc-itytimeseriesshowedareductioninadvectivetransportatthe

mouthoftheestuaryduetomeansealevelrise.Saltistransported

mainlybydiffusion,intheinnermostregionswherethesignalof

thetideisnotdetected.Thisresultisconsistentwithothervalues

ofvelocityobtainedforthis region.Timeseriesresultsfor

loca-tionsfurtherupstreamtheestuaryrevealedanincreaseinsalinity

ofabout4inresponsetosealevelrise.Theincreaseinsalinityin

responsetoanincreaseinmeansealevelismorepronouncedcloser

tothecoastlinethanitisupstreamthemainchannel.Theincreaseis

alsomuchmorepronouncedforthebathymetryallowingflooding,

withanearlylinearrelationshipbetweensealevelriseand

(9)

Fig.9. Flooddistributionmapsforadischargeof100m3/sfortheaverageM2tideforthevariousscenariosofsealevelrise.Colorsrepresenttheratiobetweentimebelow waterlevelandtotallengthoftidalcycle.

extensionofsalinityfurtherupstreamtheestuarywhenthe

simu-lationswererunoverthepresentbathymetry.Changesinsalinity

fortheflood-permittingbathymetryshowtheimpactthe

topog-raphyhasonthehydrodynamicsandsalttransportoftheestuary.

Theresultsfromthespecificlocationsusedinthetimeseries

anal-ysiscanbeusedbycoastalmanagerstodetermineiftheincrease

insalinityatCastroMarimwillimpacttheecosystem,society,and

theeconomy.

Theresultsoftheflooddistributionareasforalltypesoftide

demonstratedanincreaseinsubmergedlandareaduetomeansea

levelrisewithanestimatedincreaseof4km2fortheentire

inter-tidalareaofthepresentsituation.Thereismostsignificantflooding

atEsteirodaCarrasqueiraandthemarshlandsurroundingRibeira

deBeliche,asshowninFig.9.Resultsoftheareasoffloodingcan

beutilizedbycoastalmanagersandlandownerstodeterminewhat

actionshouldbetakentomanagetheinevitablefloodingduetosea

levelrise.

5. Conclusion

Thisstudyusedanumericalmodeltoanalyzeseveralimpacts

of sealevel risein theGuadiana Estuary.Sealevel rise

projec-tionsobtainedfromthe5threportoftheIPCCforRCP4.5andRCP

8.5 scenariosfor theyears 2040,2070and 2100wereimposed

in the model to simulatethree differentscenarios of sealevel

rise. The parameters of the simulations allowedan analysis of

thevelocitymodulus,salinitydistribution,and floodingareasof

theGuadianaEstuary.Severalvariables suchastide,freshwater

flow, meansealevel andchanges in topographyof theestuary

(10)

10 L.Mills,J.Janeiro,A.A.S.Nevesetal./JournalofComputationalScience44(2020)101169

levelrise.Thehighnumberofsimulationsallowedforananalysis

ofseveralpossibilitiesofthefuturestateoftheGuadiana

Estu-ary.

Themodeldemonstratedthatanincreaseinmeansealevel

gen-erallyresultsin adecreaseinthevelocitymodulusofthemain

channeloftheestuary.Thisismostlikelyduetotheincreasein

depthof themainchannelas wellas anincreasein water

vol-umeassociatedwiththeriseinmeansealevel.Increasesinsalinity

aremostsignificantforcasesofalowfreshwaterflowandfora

morelikelybathymetry thatallowsfloodingof thesurrounding

areas.

Theresultsportrayanoverallincreaseinbothsalinityand

flood-ingareaintheGuadianaEstuarywithrespecttoanincreaseinmean

sealevel.Asthesetwo consequencesaredetrimentalto

estuar-ineecosystems,societyandtheeconomy,furtherresearchmustbe

donetofurtheranalyzetheimpactsofsealevelriseinthe

Guadi-anaEstuary.Onelimitationofthisstudyisthatatwo-dimensional

modelwasusedasopposed toa three-dimensionalmodel.It is

representativeofmostcasesoftheGuadianaEstuarybecauseit

isgenerallywell-mixed,butaspreviouslymentionedtheestuary

canbecomepartiallystratifiedinhighfreshwaterflowconditions.

Athree-dimensionalmodelwouldprovideamorecomplete

anal-ysisofthe hydrodynamicsof theestuary. Additionalnumerical

modelsshouldbesimulatedtoportrayamorequantifiable

rela-tionshipbetweensalinityandsealevelriseandtofurtherexamine

howthesalinitychangeswithrespecttootherparameters,suchas

overtides.

DeclarationofCompetingInterest

Theauthorsdeclarethattheyhavenoknowncompeting

finan-cialinterestsorpersonalrelationshipsthatcouldhaveappearedto

influencetheworkreportedinthispaper.

CRediTauthorshipcontributionstatement

LaraMills: Writing - original draft,Formal Analysis,

Visual-ization.JoãoJaneiro:Methodology,Investigation,Resources,Data

curation.AntonioAugustoSeppNeves:Software,Formal

Analy-sis.Flávio Martins:Conceptualization,Methodology,Validation,

Investigation,Datacuration,Writing-review&editing,

Supervi-sion,Projectadministration,Fundingacquisition.

Acknowledgements

This work was developed under the project PIAAC-Algarve

“IntermunicipalPlanforAdaptationtoClimateChangesofAlgarve”.

References

[1]M.Abbott,A.Damsgaarde,G.Rodenhuis,System21Jupiter,Adesignsys-tem fortwo-dimensionalnearly-horizontalflows,J.Hyd.Res.1(1973)1–28. [3]A.R.Carrasco,O.Ferreira,D.Roelvink,Coastallagoonsandrisingsealevel:a

review,Earth.Rev.154(2016)356–368,http://dx.doi.org/10.1016/j.earscirev. 2015.11.007.

[4]V.P.Chua,M.Xu,Impactsofsea-levelriseonestuarinecirculation:an idealizedestuaryandSanFranciscoBay,J.Mar.Syst.139(2014)58–67,http:// dx.doi.org/10.1016/j.jmarsys.2014.05.012.

[5]J.A.Church,P.U.Clark,A.Cazenave,J.M.Gregory,S.Jevrejeva,A.Levermann, A.S.Unnikrishnan,2013:Sealevelchange.Climatechange2013:thephysical sciencebasis,in:ContributionofWorkingGroupItotheFifthAssessment ReportoftheIntergovernmentalPanelonClimateChange,2013,pp. 1137–1216,http://dx.doi.org/10.1017/CB09781107415315.026. [6]J.A.Church,N.J.White,A20thcenturyaccelerationinglobalsea-levelrise,

Geophys.Res.Lett.33(1)(2006)94–97,http://dx.doi.org/10.1029/ 2005GL024826.

[7]J.Delgado,T.Boski,J.M.Nieto,L.Pereira,D.Moura,A.Gomes,R. García-Tenorio,Sea-levelriseandanthropogenicactivitiesrecordedinthe latePleistocene/HolocenesedimentaryinfilloftheGuadianaEstuary(SW

Iberia),Quat.Sci.Rev.33(2012)121–141,http://dx.doi.org/10.1016/j. quascirev.2011.12.002.

[8]A.B.Fortunato,A.Oliveira,E.T.Alves,Circulationandsalinityintrusioninthe Guadianaestuary(Portugal/Spain),Thalassas18(2)(2002)43–65,December 2015.

[9]E.Garel,L.Pinto,A.Santos,Ó.Ferreira,Tidalandriverdischargeforcingupon waterandsedimentcirculationatarock-boundestuary(Guadianaestuary, Portugal),Estuar.Coast.ShelfSci.84(2)(2009)269–281,http://dx.doi.org/10. 1016/j.ecss.2009.07.002.

[10]T.W.Hilton,R.G.Najjar,L.Zhong,M.Li,Isthereasignalofsea-levelrisein ChesapeakeBaysalinity?J.Geophys.Res.Oceans113(9)(2008)1–12,http:// dx.doi.org/10.1029/2007JC004247.

[11]B.Hong,J.Shen,Responsesofestuarinesalinityandtransportprocessesto potentialfuturesea-levelriseintheChesapeakeBay,Estuar.Coast.ShelfSci. 104–105(2012)33–45,http://dx.doi.org/10.1016/j.ecss.2012.03.014. [12]J.Lopes,R.Neves,J.M.A.Dias,F.Martins,Calibrac¸ãoDeUmsistemaDe

modelac¸ãoparaOestuárioDo,4thSymposiumontheIberianAtlanticMargin (2003)4–6.

[13]MARETEC,MOHIDWater,RetrievedApril4,2019,from,2017http://wiki. mohid.com/index.php?title=MohidWater.

[14]F.Martins,P.Leitão,A.Silva,R.Neves,3Dmodellinginthesadoestuaryusing anewgenericverticaldiscretizationapproach,Oceanol.Acta24(S1)(2001) 51–62,http://dx.doi.org/10.1016/s0399-1784(01)00092-5.

[15]R.F.McLean,A.Tsyban,V.Burkett,J.O.Codignott,D.L.Forbes,N.Mimura,V. Ittekkot,CoastalzonesandMarineecosystems.Climatechange2001: impacts,in:AdaptationandVulnerability,pp.343–379,Cambridge,UK,2001. [16]R.J.Nicholls,N.Marinova,J.A.Lowe,S.Brown,P.Vellinga,D.DeGusmão,R.S.J. Tol,Sea-levelriseanditspossibleimpactsgivena“beyond4◦Cworld”inthe twenty-firstcentury.PhilosophicalTransactionsoftheRoyalSocietyA: mathematical,PhysicalandEngineeringSciences369(1934)(2011)161–181, http://dx.doi.org/10.1098/rsta.2010.0291.

[17]N.I.Pontee,B.A.Hamer,P.D.Turney,Sustainablefloodriskmanagementin Europeanestuaries,Proceedingsofthe1stInternationalConferenceon CoastalManagementandEngineeringinMiddleEast(ARABIANCOAST2005) (2005)(November).

[18]M.C.Quesada,J.García-Lafuente,E.Garel,J.DelgadoCabello,F.Martins,J. Moreno-Navas,Effectsoftidalandriverdischargeforcingsontidal propagationalongtheGuadianaEstuary,J.SeaRes.146(January)(2019) 1–13,http://dx.doi.org/10.1016/j.seares.2019.01.006.

[19]A.C.Ross,R.G.Najjar,M.Li,M.E.Mann,S.E.Ford,B.Katz,Sea-levelriseand otherinfluencesondecadal-scalesalinityvariabilityinacoastalplainestuary, Estuar.Coast.ShelfSci.157(2015)79–92,http://dx.doi.org/10.1016/j.ecss. 2015.01.022.

[20]D.M.R.Sampath,T.Boski,C.Loureiro,C.Sousa,Modellingofestuarine responsetosea-levelriseduringtheHolocene:applicationtotheGuadiana Estuary-SWIberia,Geomorphology232(2015)47–64,http://dx.doi.org/10. 1016/j.geomorph.2014.12.037.

[21]D.M.R.Sampath,T.Boski,P.L.Silva,F.A.Martins,Morphologicalevolutionof theGuadianaestuaryandintertidalzoneinresponsetoprojectedsea-level riseandsedimentsupplyscenarios,J.Quat.Sci.26(2)(2011)156–170,http:// dx.doi.org/10.1002/jqs.1434.

[22]W.J.Wiseman,E.M.Swenson,J.Power,TrendsinLouisianaEstuariesSalinity, Estuaries13(3)(1990)265–271.

LaraMillsjustcompletedamaster’sinsciencedegreein MarineandCoastalSystemsattheUniversityofAlgarvein Faro,Portugal.SheisoriginallyfromtheUnitedStatesbut hasbeenlivinginPortugalthepastthreeyearsto com-pletethedegree.Shereceivedherbachelor’sdegreein mathematicsattheUniversityofVermontin2013.

JoãoJaneirocompetedabachelor’sinsciencedegreein OceanographyattheUniversityofAlgarvein2004and laterreceivedhismaster’sinsciencedegreeinWaterand CostalManagementbytheGeophysicalInstituteinBergen UniversityinNorwayin2006.Heworkedasamodeler intheScottishEnvironmentalProtectionAgencyfortwo yearsandin2009hebeganaPhDinMarineSciences spe-cializinginNumericalModelling.

Imagem

Fig. 1. Map of (a) the Iberian Peninsula study area and (b) a closer look at the Guadiana Estuary
Fig. 2. Computational bathymetry of the Guadiana Estuary for a maintained coastline (left) and an unmaintained coastline that allows flooding of the saltmarshes and low-lying areas (right).
Fig. 3. Time series results of salinity, velocity, and elevation at 381 147 for the present bathymetry (left) and bathymetry allowing flooding (right).
Fig. 5. Time series results of salinity, velocity, and elevation at 392 23 for the present bathymetry (left) and bathymetry allowing flooding (right).
+4

Referências

Documentos relacionados

 A better identification of the treatment group through the cross gathering of missing data, by using different sources together with Quadros de Pessoal;  The

Theodor Adorno (Beethoven) 3 Para localizar associações entre passar dos limites e harmonias de mediante em época recente, e já situar tais associações no cenário

Os objetivos do nosso estudo visam, por um lado, i) o conhecimento dos motivos mais e menos importantes da motivação intrínseca e extrínseca dos alunos e alunas na

In low- protein supplements, the increase in carbohydrate level decreased the MP: E ratio, but in high-protein supplements the increase in carbohydrate levels increased the MP:

Sylviocarcinus pictus is the most abundant freshwater crab in the Amazon estuary as it was the dominant species both in biomass and in the number of specimens in all studies

In the course of the therapeutic process, it was possible to observe an increase in the number of figure exchanges independently, an increase in the number of vocalizations

The main participants in the correspondence were as follows: Portugal’s ambassadors to Rome, João de Almeida de Melo e Castro (1756–1814) and his successor, Alexandre de Sousa

Para a acidez em graus Dornic do leite semidesnatado (UHT) apresentado na Tabela 2, o método A destaca-se que não houve diferença significativa entre as estações do