The Role of Marsh Platform Morphology in the Geomorphic Response of Tidal Inlet Systems to Sea Level Rise

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Title:
The Role of Marsh Platform Morphology in the Geomorphic Response of Tidal Inlet Systems to Sea Level Rise
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1 online resource (140 p.)
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english
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Lovering, Jessica Loren
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University of Florida
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Gainesville, Fla.
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Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Geology, Geological Sciences
Committee Chair:
Adams, Peter N
Committee Members:
Martin, Ellen Eckels
Jaeger, John M
Hatfield, Kirk
Calantoni, Joseph

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Subjects / Keywords:
ecogeomorphology -- inlet -- level -- morphology -- sea -- tidal -- wetlands
Geological Sciences -- Dissertations, Academic -- UF
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Geology thesis, Ph.D.
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theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
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Abstract:
Morphologic evolution of tidal inlets depends on the ecogeomorphic behavior of the back-barrier basin, and exerts a strong influence on local shoreline response to sea level rise. A tidal inlet channel acts as the principal valve for water and sediment exchange in a barrier system, but changes to back-barrier basin ecology, hypsometry, and flow network configuration can alter discharge conveyed through the inlet channel. We investigate the role of wetland vegetation on tidal inlet response to sea level rise with three approaches, each investigating a set of process linkages: (1) Marsh vertical accretion control on changes to the tidal prism, inlet channel cross-sectional area, and ebb shoal volumes due to sea level rise , (2) Feedbacks between marsh vertical accretion and sediment availability changes with sea level rise, controlled by alterations to the hydrodynamics in the back-barrier basin, and (3) the impact of marsh edge erosion on the tidal prism, inlet channel cross-sectional area, and ebb shoal volume.  Tidal inlets communicate with the adjacent shoreline; Barrier islands, ebb and flood shoal complexes, and the contiguous wetlands act together as a sand sharing system.  Alterations to one morphologic component will modify the entire budget of the system, leading to changes in the erosional-depositional patterns in local longshore sediment transport.  Incorporating changes to wetland vegetation in the back-barrier basin is crucial to understanding how shorelines with barrier island systems will evolve under sea level rise worldwide. The first study investigates the role of initial marsh vertical accretion on changes to tidal prism, inlet channel cross-sectional area, and ebb shoal volume due to a rise in relative sea level.  We investigate this phenomenon by applying a numerical hydrodynamic model, paired with empirically derived morphologic relationships, to an inlet system typical of a mixed-energy, tide dominated barrier island system. We consider two end-member, marsh accretion scenarios:(A) no vertical marsh accretion, wherein marsh islands become submerged,changing both the flooded basin area and the spatial pattern of tidal wave attenuation, and (B) a marsh accretion rate equal to the rate of sea level rise, wherein marsh tidal channels deepen but maintain their courses and the associated friction reduction leads to a more efficient tidal exchange between the ocean and back-barrier basin.  Model results show a tidal prism increase for both scenarios, leading to increases in channel cross-sectional area and ebb shoal volumes.  Under both marsh accretion scenarios, the mechanism of improved tidal exchange efficiency through channel deepening,produces increases of tidal prism that are similar in magnitude.  Under conditions with no marsh accretion, an additional mechanism, namely the expansion of flooded basin area, further increases the magnitude of the tidal prism. Scenario A (no accretion) produced a tidal prism increase four times that of the increase calculated for scenario B (pace-keeping accretion), when sea level rise magnitudes were less than 50 cm; this difference increases at higher magnitudes of sea level rise.  We found an increase in the inlet cross-sectional area and ebb shoal volume for scenario A that is approximately double that of scenario B.  The increase in equilibrium inlet channel cross-sectional area, arising from scour processes, exceeds the increase due to sea level rise alone, illustrating the influence of marsh tidal flow processes.  The second study focuses on feedbacks between marsh vertical accretion rates and changes to sediment availability under various sea level rise scenarios.  Marsh vertical accretion is a function of allochthonous sediment availability and autochthonous sediment produced in situ by marsh vegetation. Variations in the initial marsh platform accretion rate relative to sea level rise rate influence the spatial distribution of marsh platform submergence and the tidal velocity asymmetry. Increased duration of marsh vegetation submergence could lead to vegetation water-logging and drowning, leading to reduced plant production and a reduction in the autochthonous sediment production of the system.  Changes to the difference in storage capacity during low and high tide, as well as, alterations to the friction through the inlet and basin channels, leads to changes in the tidal velocity asymmetry through the inlet channel.  Modifications to the tidal velocity asymmetry alter the net transport through the inlet and the balance of sediment between the ocean and basin, altering the allochthonous sediment availability to the marsh platform. We use a numerical model with the two end-member marsh accretion scenarios described above to investigate these feedbacks.  Model results indicate that,for a static marsh platform, sea level rise causes areas farther from the inlet channel to be submerged for longer periods of time than areas closer to the channel, due to a reduction in drainage efficiency during the ebb tidal exchange.  The tidal asymmetry for this system becomes more flood dominant with sea level rise because the difference in storage capacity during low and high tide is reduced, but the net transport remains in the ebb direction for all levels of sea level rise up to 100 cm.  When the platform is able to accrete vertically at the same rate as sea level rise, the system becomes more ebb dominant because channel deepening causes a reduction in the flow and some sediment is transported in the seaward direction.  Marsh platform configuration plays a crucial role in the feedbacks of the system, with drainage efficiency of the system and variations in storage capacity determining the availability of sediment to the marsh platform. In the last study, we investigate the role of wetland vegetation loss by marsh edge erosion on tidal prism, inlet channel cross-sectional area, and ebb shoal volume. Vegetation loss can change the tidal prism for a particular inlet by:(1) increasing the map-view area of open water exchanged between the back-barrier basin and the ocean during a tidal cycle and (2) reducing the spatial rate of tidal wave attenuation within the basin.  We use a simple conceptual model to explore the geomorphic response of two Florida inlets, of contrasting wetland configurations,to uniform back basin vegetation loss that might result from current projections of sea level rise. All results show that vegetation loss causes an increase in tidal prism, inlet cross-sectional area, and ebb shoal volume, but inlets with wetland configurations that strongly increase tidal wave attenuation in the back barrier basin have an amplified response to vegetation loss.  Using empirical relationships, we find that a one percent loss of back barrier basin vegetated area results in an increase of ebb shoal volume by an amount approximately equivalent to annual to biennial longshore sediment transport rates along the Florida Atlantic coast.  The conceptual model developed in this study can be used to examine morphologic response of tidal inlet systems to wetland vegetation loss at similar barrier island complexes worldwide.
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In the series University of Florida Digital Collections.
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Includes vita.
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This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Jessica Loren Lovering.
Thesis:
Thesis (Ph.D.)--University of Florida, 2013.
Local:
Adviser: Adams, Peter N.
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RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-05-31

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THEROLEOFMARSHPLATFORMMORPHOLOGYINTHEGEOMORPHICRESPONSEOFTIDALINLETSYSTEMSTOSEALEVELRISEByJESSICALORENLOVERINGADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOLOFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENTOFTHEREQUIREMENTSFORTHEDEGREEOFDOCTOROFPHILOSOPHYUNIVERSITYOFFLORIDA2013

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c2013JessicaLorenLovering 2

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Idedicatethistomylovingandsupportivehusband,JosephLovering. 3

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ACKNOWLEDGMENTS Iwouldliketothankmycommitteechair,PeteAdams,foralwaysprovidingsupportformyresearchideasandcontinuingtopushmetostriveforgreatnessinmywork.Hishighexpectationsofmyworkhelpedmetorealizemypotentialandtoworkhardtoachievemygoals.Iwouldalsoliketothankmycommitteemembers,JoeCalantoni,RobertDean,JohnJaeger,EllenMartin,andKrikHateldforalloftheirthoughtfulinputthroughoutmytimeintheGeologicalSciencesDepartment.Withoutthesupportofmycommittee,thisworkwouldnothavebeenpossible,andforthatIamforevergrateful.Iwouldalsoliketothankthegeomorphteamofstudentswhohavebecomeagreatresearchsupportsystemandmyclosefriends.IwanttothankKatherineMaloneforkeepingmyspiritshighandalwaysbeingmybiggestcheerleaderevenwhenthingsgottough.IamthankfulformyclosefriendshipwithShaunKline,myofcemateof6years.Hehasalwaysbeentheretolendanearandlistentomyresearchideasandtochallengemewithhisthoughtfulcontributionstomywork.IwouldalsoliketothankRichMacKenzieforhiscontagiousenthusiasmandpassionforthescience,aswellasbeingadependablefriendandcolleague.Iwouldliketothankmyparentswhoinstilledinmethevalueofhardworkandthejoyofeducation.MymomhasalwaysbeenoneofmygreatestsupportersandIknowIwouldnothavebeenabletoachievethisworkwithoutherloveandsupport.Lastly,Iwouldliketothankmyamazinghusband,JDLovering,whosharedinthisadventurewithmeandprovidedmewiththecouragetofollowmydreams. 4

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TABLEOFCONTENTS page ACKNOWLEDGMENTS .................................. 4 LISTOFTABLES ...................................... 8 LISTOFFIGURES ..................................... 9 LISTOFABBREVIATIONS ................................ 12 ABSTRACT ......................................... 13 CHAPTER 1GENERALINTRODUCTION ............................ 16 1.1ProblemStatement ............................... 16 1.2OutlineofPresentation ............................. 16 1.3TidalInletSystems ............................... 17 1.3.1MorphologicElements ......................... 17 1.3.1.1Floodshoal .......................... 18 1.3.1.2Ebbshoalcomplex ...................... 18 1.3.2InletClassication ........................... 20 1.3.3EquilibriumRelationships ....................... 21 1.3.3.1Inletchannel ......................... 22 1.3.3.2Ebbshoalcomplex ...................... 24 1.4SaltMarshes .................................. 26 1.4.1TypesofSaltMarshes ......................... 26 1.4.2SaltMarshResponsetoSeaLevel .................. 26 2HOWDOESVERTICALMARSHACCRETIONCONTROLHYDRODYNAMICANDMORPHOLOGICRESPONSESOFATIDALINLETTOSEALEVELRISE? ......................................... 37 2.1Introduction ................................... 38 2.2Background ................................... 39 2.3Methodology .................................. 42 2.3.1StudySite ................................ 42 2.3.2TidalFlowModelandExperimentalDesign ............. 44 2.3.3EmpiricallyDerivedHydrodynamic-MorphologicRelationships ... 45 2.3.4ModelTestingandCalibration ..................... 46 2.4Results ..................................... 49 2.4.1BasinArea ............................... 49 2.4.2TidalPrism ............................... 49 2.4.3Cross-SectionalArea .......................... 51 2.4.4EbbShoalVolume ........................... 51 2.5Discussion ................................... 52 5

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2.5.1RegionalImpacts ............................ 52 2.5.2ComparisonwithPreviousModelingStudies ............. 53 2.6Conclusions ................................... 54 3ECOGEOMORPHICFEEDBACKSBETWEENSEALEVELRISE,ESTUARYHYDRODYNAMICS,ANDVERTICALMARSHACCRETION .......... 71 3.1Introduction ................................... 72 3.2Background ................................... 72 3.3Methods ..................................... 74 3.3.1StudySite ................................ 74 3.3.2ModelSetup ............................... 75 3.4Results ..................................... 76 3.4.1SpatialDistributionofTidalRangeandMarshSubmergence .... 76 3.4.2TidalVelocityAsymmetry ....................... 78 3.5Discussion ................................... 80 3.6Conclusions ................................... 82 4THEROLESOFMARSHCONFIGURATIONANDMARSHMARGINRETREATONTIDALINLETMORPHOLOGY ......................... 98 4.1Introduction ................................... 98 4.2ModelDetails .................................. 100 4.2.1StudySites ............................... 103 4.3Results ..................................... 104 4.4Discussion ................................... 106 4.4.1TwoMainMechanismsforTidalPrismChange ........... 106 4.4.2MarshLossSpatialDistribution .................... 107 4.4.3InuenceonAdjacentShorelines ................... 107 4.4.4OtherInuenceonMarshLoss .................... 108 4.4.5ApplicationtoBarrierSystemsWorldwide .............. 109 4.5Conclusions ................................... 109 APPENDIX ADELFT3DMODELSETUP ............................. 117 A.1ModelPhysicalProcesses ........................... 117 A.2Delft3D-FLOWModelSetup .......................... 118 A.2.1LandBoundaryFileGeneration .................... 119 A.2.2GridGeneration ............................. 120 A.2.3BathymetryGeneration ......................... 121 A.2.4CreatinganMDF-File ......................... 122 A.2.5Executingmodelrun .......................... 126 A.2.6Viewingmodeloutput ......................... 126 BMODELINPUTPARAMETERS ........................... 127 6

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REFERENCES ....................................... 130 BIOGRAPHICALSKETCH ................................ 138 7

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LISTOFTABLES Table page 1-1Inletmorphologicvariables(from Hubbardetal. ( 1979 )) ............. 29 1-2Empiricalparametersforthetidalprism-inletarearelationshipsdevelopedby Jarrett ( 1976 )(formetricunits) ........................... 31 1-3Numberofinletsandcorrelationsforthetidalprism-inletarearelationshipsdevelopedby Jarrett ( 1976 )(formetricunits) ................... 33 1-4Empiricalparametersforthetidalprism-ebbshoalvolumerelationshipsdevelopedby WaltonandAdams ( 1976 )fordifferentwaveenergyregimes. .. 34 4-1Studysiteshydraulic,ecologic,andgeomorphicproperties ........... 116 4-2Inletmorphologicandhydraulicresponsetowetlandloss ............ 116 8

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LISTOFFIGURES Figure page 1-1Tidalinletelementsshownonatypicalmixed-energytidalinletsystem. .... 30 1-2Morphologyofatypicaloodshoal(reproducedfrom Hayes ( 1980 ) ...... 31 1-3Conceptualmodelsofsedimentbypassing(from FitzGeraldetal. ( 2000 )). ... 32 1-4Coastalclassication(reproducedfrom Hayes ( 1979 )). ............. 33 1-5PatternsinthenumberandspacingoftidalinletsasafunctionofwaveversustidalenergyalongtheGeorgiaBight(from FitzGerald ( 1996 )). ......... 34 1-6TidalinlettypesintheGeorgiaembayment(reproducedfrom Hubbardetal. ( 1979 )) ........................................ 35 1-7Escoferstabilitycurve(from Escofer ( 1940 1977 )). .............. 36 2-1MapoftheSeaIslandChainwithaninsetoftheSaintMarysRiverEntrancebasin. ......................................... 56 2-2ContourmapoftheSaintMarysEntrancebasinbathymetry ........... 57 2-3ThecumulativedistributionoftheelevationswithintheSt.MarysRiverbasinmodeldomain .................................... 58 2-4ThetemporaldistributionofoodedbasinareaintheSaintMarysRiverEntrancebasin .................................... 59 2-5AmapoftheNOAAFernandinaBeachCurrentsProjectbottom-mountedworkhorseADCPdeploymentlocationsandcorrespondingdeploymentdates 60 2-6WaterelevationsatNOAAtidestation8720030andtheco-locatedDelft3Dmodeledwaterlevels ............................ 61 2-7TimeseriesplotsofsurfacecurrentspeedsfromADCPdataandco-locatedmodeldatafortherst3fulldaysofdeployment. ................. 62 2-8ScatterplotsofsurfacecurrentUandVcomponentswiththe95%condenceellipseandprincipalaxesfromthesixNOAAADCPstationsandco-locatedmodeldata. ...................................... 63 2-9ModelcomparisonswithNOAAADCPdata .................... 64 2-10Modeloutputofwaterlevel,instantaneousdischarge,andcalculatedtidalprism. ......................................... 65 2-11Thechangeinthetemporaldistributionofoodedbasinareaandthechangeinthetemporallyaveragedbasinareawithsealevelrise. ............ 66 9

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2-12Thechangeintemporallyaveragedoodedbasinareaduetosealevelrise,forastaticmarshplatformandamarshplatformaccretingatthesamepaceassealevelrise. ................................... 67 2-13Theidealtidalprism,themodeledtidalprism,andtheratioofmodeledtoidealtidalprism. ...................................... 68 2-14Thechangeinmodeledtidalprism ......................... 69 2-15Changeincross-sectionalareaandebbshoalvolumeduetosealevelrise .. 70 3-1MapofSaintMarysEntrancewithmarshvegetatedareahighlighted,insetonamapoftheSeaIslandChain. ........................... 84 3-2MapofelevationsintheSaintMarysEntrance .................. 85 3-3ThedistributionofelevationsintheSaintMarysEntrancebasin ......... 86 3-4ThetemporaldistributionofoodedbasinareaintheSaintMarysEntrancebasinforpresentsealevelconditions. ....................... 87 3-5Thespatialdistributionofthechangeintidalrangefrompresentsealevelconditionsasaresultofasealevelriseonanaccretingmarshplatform. ........................................ 88 3-6Thespatialdistributionofthechangeintidalrangefrompresentsealevelconditionsasaresultofasealevelriseonastaticmarshplatform. ....... 89 3-7Thechangeintheaveragetidalrangeover10tidalcyclesduetosealevelriseforsevenchannellocations. .......................... 90 3-8Thespatialdistributionofsubmergencedurationforvarioussealevelrisemagnitudesonastaticmarshplatform. ...................... 91 3-9Timeseriesofwaterdepthatthreepointslocatedonthemarshplatformforsealevelriseof0to100cmat20cmintervalsforastaticmarshsystem. ... 92 3-10Thevelocitystageplotandthetimeseriesofthewaterlevelsandthespatiallyaveragedvelocitythroughtheinletforpresentsealevelandasealevelriseof60cmonastaticandanaccretingmarshplatform. .............. 93 3-11Thechangeintimeatwhichtidalowreversalsoccurduetosealevelrise .. 94 3-12Thespatiallyaveragedvelocityacrosstheinlet,thecubeofthespatiallyaveragedvelocity,andthecumulativeofthespatiallyaveragedvelocitycubedforsealevelriseonanaccretingmarshplatform. ................. 95 3-13Thespatiallyaveragedvelocityacrosstheinlet,thecubeofthespatiallyaveragedvelocity,andthecumulativeofthespatiallyaveragedvelocitycubedforsealevelriseonastaticmarshplatform. .................... 96 10

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3-14Theratiooftheoodtoebbsedimenttransportproxy .............. 97 4-1Conceptualmodeloftidalinletgeomorphicresponsetosealevelrise. ..... 111 4-2Diagramillustratinghowthebasinsareparameterizedintotwosectionsoneithersideoftheinletchannel. ........................... 111 4-3Mapsoftheback-barrierbasinsexaminedinthisstudy .............. 112 4-4ThechangeintidalprismduetowetlandvegetationlossforPLIandSAI. ... 113 4-5Theimpactofmarshvegetationlossontidalprism,cross-sectionalareaofinletchannel,andebbshoalvolume. ........................ 114 4-6SchematicIllustrationofwetlandvegetationlossintwobasinswithecogeomorphiccongurationssimilartoSAIandPLI ............... 115 11

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ABBREVIATIONS ADCPAcousticDopplerCurrentProlerAMAccretingMarshCIRPCoastalInletResearchProgramHWFRHighWaterFlowReversalIPCCIntergovernmentalPanelonClimateChangeLWFRLowWaterFlowReversalMHWMeanHighWaterMLWMeanLowWaterMSLMeanSeaLevelNWINationalWetlandsInventoryNGDCNationalGeophysicalDataCenterNOAANationalOceanicandAtmosphericAdministrationPLIPoncedeLeonInlet,FLSAISaintAugustineInlet,FLSMStaticMarshSMESaintMarysEntrance,FLUSGSUnitedStatesGeologicalSurvey 12

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AbstractofDissertationPresentedtotheGraduateSchooloftheUniversityofFloridainPartialFulllmentoftheRequirementsfortheDegreeofDoctorofPhilosophyTHEROLEOFMARSHPLATFORMMORPHOLOGYINTHEGEOMORPHICRESPONSEOFTIDALINLETSYSTEMSTOSEALEVELRISEByJessicaLorenLoveringMay2013Chair:PeterN.AdamsMajor:GeologyThemorphologicevolutionoftidalinletsdependsontheecogeomorphicbehavioroftheback-barrierbasin,andexertsstronginuenceonlocalshorelineresponsetosealevelrise.Inthisthesis,Iinvestigatetheroleofwetlandvegetationontidalinletresponsetosealevelrisethroughthreeapproaches,witheachapproachinvestigatingaspecicsetofprocesslinkages:(1)Verticalmarshaccretioncontrolonchangestothetidalprism,inletchannelcross-sectionalarea,andebbshoalvolumesduetosealevelrise,(2)changestothesedimentavailabilitytothemarshplatformbysealevelriseinducedalterationstotheinlethydrodynamics,and(3)theinuenceofmarshcongurationandedgeerosiononthetidalprism,inletchannelcross-sectionalarea,andebbshoalvolume.Investigatinglinksamongchangestowetlandvegetation,hydrodynamicsoftheback-barrierbasin,andinletmorphologywillbeacriticaladvanceinunderstandinghowshorelineswithbarrierislandsystemswillevolveundersealevelriseworldwide.Howdoesverticalmarshaccretioninuencethetidalprism,inletchannelcross-sectionalarea,andebbshoalvolumeduringsealevelrise?Usinganumericalhydrodynamicmodel,pairedwithempiricallyderivedmorphologicrelationships,thisstudyexploresthebehaviorofaback-barrierbasinundertwoend-memberverticalmarshaccretionscenarios:(A)noaccretion,whereinmarshislandsbecomesubmerged,changingboththeoodedbasinareaandthespatialpatternoftidalwave 13

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attenuation,and(B)amarshaccretionrateequaltotherateofsealevelrise,whereinmarshtidalchannelsdeepenbutmaintaintheircoursesandtheassociatedfrictionreductionleadstoamoreefcienttidalexchangebetweentheoceanandback-barrierbasin.Underbothmarshaccretionscenarios,asimilarincreaseintidalprismduetochanneldeepeningandimprovedexchangeefciencyisobserved.Onastaticmarshplatform,thisincreaseisampliedbytheadditionofoodedbasinareascontributingtotheexchange.ScenarioA(noaccretion)producedatidalprism,inletcross-sectionalarea,andebbshoalvolumeincreasedoublethatoftheincreasecalculatedforscenarioB(pace-keepingaccretion).Theincreaseinequilibriuminletchannelcross-sectionalarea,arisingfromscourprocesses,exceedstheincreaseduetosealevelrisealone,illustratingtheinuentialcontributionfrommarshtidalowprocesses.Howdoesverticalmarshaccretionchangethehydrodynamicresponsetosealevelriseintheback-barrierbasinandtheavailabilityofsedimenttothemarshplatform?Verticalmarshaccretionresultsfromallochthonoussedimentavailabilityandautochthonoussedimentproducedinsitubymarshvegetation.Increaseddurationofmarshvegetationsubmergencecanleadtovegetationwaterlogginganddrowning,leadingtoreducedplantproductionandautochthonoussedimentavailabilityonmarshplatforms.Changestotheinletexchangeefciencyduringatidalcyclemodiesthetemporalpatternoftidalvelocityasymmetryandthebalanceofsedimentbetweentheoceanandbasin,alteringtheallochthonoussedimentavailabilitytothemarshplatform.Usinganumericalmodelwiththetwoend-membermarshaccretionscenariosdescribedabove,resultsshowthat,forastaticmarshplatform,sealevelrisecausesareasfartherfromtheinletchanneltobesubmergedforlongerperiodsoftimethanareasclosertothechannel,duetoareductionindrainageefciencyduringebbtidalexchange.Theinletsysteminthisstudyisebbdominantundercurrentsealevelconditions,butbecomesmoreooddominantwithsealevelrise.Thisresponseisampliedwhenthemarshplatformisstatic,transitioningtoooddominancewithhighmagnitudesofsea 14

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levelrise(>70cm).Marshplatformcongurationplaysacrucialroleinthefeedbacksofthesystem,withthespatialdistributionofdrainageefciencythroughoutthebasinandchangesinexchangeefciencyoveratidalcycledeterminingtheavailabilityofsedimenttothemarshplatform.Whataretherolesofmarshcongurationandmarshmarginretreatontidalprism,inletchannelcross-sectionalarea,andebbshoalvolume?Vegetationlosscanchangethetidalprismforatidalinletsystemby:(1)increasingthemap-viewareaofopenwaterexchangedbetweenthebasinandtheoceanduringatidalcycleand(2)reducingthespatialrateoftidalwaveattenuationwithinthebasin.Inthisstudy,Iuseasimpleconceptualmodel,asopposedtothenumericalhydrodynamicmodelusedintheaforementionedwork,toexplorethegeomorphicresponseoftwoFloridainlets,ofcontrastingwetlandcongurations,touniformback-barrierbasinvegetationlossthatmightresultfromcurrentprojectionsofsealevelrise.Allresultsshowthatvegetationlosscausesanincreaseintidalprism,inletcross-sectionalarea,andebbshoalvolume,butinletswithwetlandcongurationsthatstronglyincreasetidalwaveattenuationintheback-barrierbasinhaveanampliedresponsetovegetationloss.Fromempiricalrelationships,itisfoundthataonepercentlossofback-barrierbasinvegetatedarearesultsinanincreaseofebbshoalvolumebyanamountapproximatelyequivalenttoannualtobienniallongshoresedimenttransportratesalongtheFloridaAtlanticcoast.Theconceptualmodeldevelopedinthisstudycanbeusedtoexaminemorphologicresponseoftidalinletsystemstowetlandvegetationlossatsimilarbarrierislandcomplexesworldwide. 15

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CHAPTER1GENERALINTRODUCTION 1.1ProblemStatementCoastalshorelineresponsetosealevelrisehasbeenstudiedanddebatedsincethemiddleofthe20thcentury,buttherehavebeencomparativelyfewstudiesthatfocusontheimpactofsealevelriseonthemorphologyandbehavioroftidalinletsystems( Dissanayakeetal. 2009 ; FitzGeraldetal. 2007 ; Listetal. 1997 ; VanGooretal. 2003 ).Atidalinletcanbeconsideredtobeacriticalcomponentofasandsharingsystem,inwhichthesubmergedsandbodies(ebbandoodshoalcomplexes)andadjacentbeachesareinterconnected( Dean 1988 ).Tidalinletsinterruptthewavecurrent-inducedsedimenttransportalongshore,sequesteringsedimentinebbandoodshoals,shallowfeaturesthatredistributethepatternofincomingwaveenergyuxtotheshoreline.Asaresult,shorelineretreatratesnearaninletcanbeuptotwoordersofmagnitudegreaterthanmean,long-termshorelineretreatratesalonguninterruptedportionsofsandycoasts( FitzGerald 1988 ; WaltonandAdams 1976 ).Ifsealevelriseincreasesthetidalprismthatinundatesthebackbarrierbasinviatheinlet,theequilibriumvolumeoftheinlet'sebbshoalshouldincrease,andthesedimentbudgetforthesystemwilladjust,toaccommodatethisincrease,byremovingsedimentfromadjacentbeaches( Dean 1988 ).Tidalinletresponsetosealevelriseiscomplicatedbytherelationshipsbetweeninlethydrodynamics,morphodynamics,andbackbarrierbasinwetlandecology.Thisresearchadvancesourunderstandingoftheroleplayedbymarshplatformaccretionontheresponseofinletmorphologytosealevelrise,acriticalstepinunderstandingtheevolutionofsandycoasts,ingeneral,subjecttosealevelrise. 1.2OutlineofPresentationThischapterprovidesbackgroundinformationontidalinletandback-barrierbasinmarshsystems.Theelementsofatidalinletsystemaredescribedandsomedetailsconcerningtheclassicationofinletsandequilibriumrelationships,fromthe 16

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scienticliterature,arereviewed.Saltmarshsystemsandtheirresponsetochangesinrelativesealevelarealsodiscussed.Chapter 2 presentsresearchthatusesanumericalhydrodynamicmodeltoexplorechangestothetidalprismofaninletduringsealevelriseundertwoend-member,marshaccretionscenarios.Theresultsofthemodelingexperimentareusedtomakeastatementaboutthechangesexpectedtooccurtotheinletcross-sectionalareaandebbshoalvolume.InChapter 3 ,thesamenumericalmodelisusedtoexplorethecontrolofmarshaccretionrateontheavailabilityofsedimenttothemarshplatform,throughalterationstothetidalvelocitytemporalasymmetryandthemarshplatformsubmergencedurations.Chapter 4 presentsaninvestigationofthedecadalscaleimpactsofmarshresponsetosealevelrise.Specically,howdoesthedecreaseinmarsharealextent,throughplatformedgeerosion,changethetidalprism,inletcross-sectionalarea,andebbshoalvolume?Theinvestigationisappliedtotwoinletsystemsofnotablydifferentinitialmarshcongurations. 1.3TidalInletSystems 1.3.1MorphologicElementsAtidalinletactsasaprincipalvalvefortheexchangeofwaterandsedimentsbetweentheoceanandaback-barrierbasin.Atidalinletsystemiscomposedoftheinletchannel,ebbandoodshoalcomplexes,adjacentbarrierislands,andthecontiguouswetlands.Eachcomponentofthetidalinletispartofasandsharingsystem,whichisassimilatedintotheregionalsedimentbudget.Themorphologyofaninletiscontrolledbygeologicsetting,riverinow,tidalexchange,andwaves.Aswaterlevelsintheoceanincreasewiththerisingtide,waterandsedimentistransportedthroughtheinletchannelandintothebasin,astheowexpandsintheopenbasinitslowsanddepositssedimentonoodshoals( DeanandWalton 1973 ).Asthewaterintheoceanlowerswiththefallingtide,waterandsedimentfromthebasinowsbackintotheoceananddepositssedimentonebbshoals( DeanandWalton 1973 ).Ebbshoalsinteract 17

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withlongshorecurrentsandwaves,leadingtoasedimenttransferbetweenadjacentshorelinesandebbshoals.Theoodtidalprismofthesystemisthetotalvolumeofwaterthatowsintothebasinwitharisingoceantide,andtheebbtidalprismthevolumeofwateremptiedfromthebasinduringthefallingoceantide.TidalInletsystemscanbedividedintodifferentelements,whereeachelementhasitsownfunctioninthesandsharingsystem.Figure 1-1 showstheseelementsonaninlettypicalofamixedenergysystem. 1.3.1.1FloodshoalThecharacteristicooddeltamorphology(depictedinFigure 1-2 )consistsofaoodrampandbifurcatingoodchannelsontheseawardside,andebbsshields,ebbspits,andspilloverlobesonthelandwardside.Floodcurrentsdominatetheowovertheoodrampandoodchannels;thiscanbeseenbytheexistenceofood-orientedsandwaves.Smallerbedformstransitionbetweenorientationsduringthetidalcycle( Hayes 1980 ).Theebbshieldisthetopographichigh,whichactstoprotecttheinnershoalduringebbtidalexchange.Floodshoalmorphologytendstowardanequilibriumshapeandvolumerapidlyandthendepositionslowsasitapproachesanequilibriumvolume.ThisisshowninobservationsmadeatSt.LucieInlet,FL,aftertheinletwasrstopenedthedepositionofsedimentclosetotheinletchannelwasrapidandthenslowed,atwhichpointthesedimentwasdepositedfurtherintotheinletbasin( DeanandWalton 1973 ). 1.3.1.2EbbshoalcomplexThecomponentsoftheebbshoalsystemareshowninFigure 1-1 ,andarecomposedofthemainebbchannel,channelmarginlinearbars,theterminallobe,swashplatform,swashbars,andmarginaloodchannels( FitzGeraldandFitzGerald 1977 ; GibeautandDavis 1993 ; Hayes 1979 1980 ).Themorphologicfeaturesoftheebbshoalcomplexaredeterminedbythedynamicbalancebetweenanetoffshoredirectedsedimentuxinducedbytheebbdominantcurrentsandanetonshoredirected 18

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sedimentuxinducedbyoffshorewaves( Hayes 1980 ).Thechannelmarginlinearbars,levee-likebarsthatankthemainebbchannel,andswashbars,locatedontheswashplatform,areformedbyaninteractionoftideandwavegeneratedcurrents( Hayes 1980 ).Theterminallobe,theseawardmostsedimentdeposit,hasashallowslopeonthebasinsideoftheshoal,transitioningtoasteepslopeontheoceansideoftheshoal( BuonaiutoandKraus 2003 ).Insomemixed-energycoastalsystems,thevolumeofsedimentstoredintheebbshoalcomplexcanbecomparabletothevolumeofadjacentbarrierislands( FitzGerald 1988 ). FitzGerald ( 1988 )statedfromobservationsthatthesizeofthebarcomplexisproportionaltothesizeoftheinletandthemagnitudeoflongshoretransport.Ebbshoalstransferorbypasssedimentfromtheupdriftsideofthetidalinlettothedowndriftbarriercoastaccordingtothestateofmaturityoftheshoal,themagnitudeofthetidalprism,andlocalwaveconditions( BruunandGerritsen 1959 ; FitzGerald 1988 ; Kraus 2000 ).Naturalmechanismsforthisbypassingwererstdescribedby BruunandGerritsen ( 1959 ).Themechanismforbypassingiscontrolledbytheratiooflongshoresedimenttransport(Mmeaninyd3/yr)tothemaximumdischargeoftheinletduringspringtide(Qmaxinyd3/sec),usingtheequation: r=Mmean=Qmax.(1) BruunandGerritsen ( 1959 )describedthreemechanismsfortransport:1)bywaveinducedsedimenttransportalongtheedgeoftheterminallobe,2)throughtidalcurrentinducedsedimenttransportinthechannels,and3)bythemigrationoftidalchannelsandsandbars.Thestudyshowsthat,forahighratiooflongshoretransporttotidalcurrents(r=200-300),themainmechanismforbypassingisbywaveactionalongtheterminallobe.Withsmallratios(r=10-20),sedimenttransferismainlycontrolledbytidalowbypassingandbysandbarmigration.Theyalsonotedthatatmanyinlets,bypassingoccursasacombinationoftheseprocesses. 19

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FitzGerald ( 1982 )usedeldinvestigationstodeterminethatalargeportionofsedimenttransportedatmixed-energytidalinletsystemsoccursthroughinletmigration,spitbreaching,andtheformationandlandwardmigrationofbarcomplexes. FitzGerald ( 1982 )presentedtheexistenceofdowndriftattachmentpointsforsedimentbypassing.Thelocationofthesepointsiscontrolledbythebypassingbar,whichisdependentoninletsize,ebbchannelorientation,andtherelativestrengthofwaveandtidalforces. GaudianoandKana ( 2001 )documentedtheepisodicbypassingbycyclicshoalattachmentalongthecoastofSouthCarolina.Usinghistoricalphotographsspanning58years,theyshowacycleofdiscretebarsbecomingdetachedfromebbshoalsandmigratingonshoretoadjacentshorelines. FitzGeraldetal. ( 2000 )constructedarangeofsedimentbypassingconceptualmodelsbuiltonworkdoneinpreviousstudiesby BruunandGerritsen ( 1959 ), Bruun ( 1966 ).and FitzGerald ( 1982 1988 ),andissummarizedinFigure 1-3 1.3.2InletClassication Davies ( 1964 )classiesdepositionalshorelinesaccordingtotidalrange,wheremicrotidalcoastshaveatidalrangeofupto2m,mesotidalcoastshaveatidalrangeof2to4m,andmacrotidalcoastshaveatidalrangeofover4m. Hayes ( 1975 )wasthersttorecognizetheinuenceoftidalrangeonthemorphologicfeaturesoftidalinletandbarrierislandsystems.Usingthetidalrangeclassicationof Davies ( 1964 )andassumingmoderatewaveenergy, Hayes ( 1975 )describedthemorphologicfeaturesofeachtypeofsystem.Microtidalcoastsaretypicallylongandcontinuousbarrierislandchainswithfewtidalinlets,withsmallornonexistentebbtidalshoalsandlargeoodtidalshoals.Mesotidalcoaststypicallyformdrumsticktypebarrierislands,punctuatedbyfrequenttidalinlets.Thesesystemsgenerallyhavelargeebbshoalsandoodshoalsthataresmallornonexistent.Macrotidalcoaststypicallyconsistofintertidalatsandsaltmarshesratherbarrierislandsystems. Hayes ( 1979 )renestheclassicationsystemtoincludetherelationshipbetweentidalrangeandwaveenergy.Themodied 20

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classicationisbrokenintovezones:tide-dominated(high),tide-dominated(low),mixed-energy(tide-dominated),mixed-energy(wave-dominated),andwave-dominated.Figure 1-4 illustratestheclassicationzonerangesforeachcombinationofwaveandtidalrange.NumerousstudiesdiscussthemorphologyofinletsystemsalongtheGeorgiaBightbarriersystem,extendingbetweenCapeHatteras,NCandCapeCanaveral,FL( Hayes 1994 ; Hubbardetal. 1979 ; Nummedaletal. 1977 ). Nummedaletal. ( 1977 )showsthatthewaveenergyandtidalrangesarecontrolledbythewidthofthecontinentalshelfandinnershelfslope.Astheshelfwidens,thetidalrangesareincreasedandthewaveenergyisattenuated.ThetidalrangeincreasesandthewaveenergydecreasesastheshelfwidensbetweenNorthCarolinaandGeorgiaandthereverseoccursbetweenGeorgiaandFloridawherethecontinentalshelfnarrows. Hayes ( 1994 )quantiesthistrendinordertomakesacomparisonbetweenthenumberofinletsperunitlengthofcoastline,tidalrange,andwaveenergy.Figure 1-5 from FitzGerald ( 1996 )summarizestheresultsofthesestudiesandillustratesthetrendinshelfwidth,tidalrange,waveheight,andnumberofinletsalongtheGeorgiaBight. Hubbardetal. ( 1979 )usedobservationsfromtheGeorgiaBighttoclassifyinletmorphologyasafunctionofwaveversustidedominance,astheseparameterscontrolsthezonesofequilibriumbetweenonshoreandoffshoresedimentand,therefore,thelocationofdeposition.Figure 1-6 illustratessomeofthemorphologicfeaturesseenineachofthesesystems.Theydescribetide-dominatedinletsascharacterizedbyanebbdominateddeepcentralchannelankedbyextensivechannelmarginbars.Incontrast,wavedominatedinletsaredescribedtobecontrolledbypredominatelylandwardtransport,havingsmallebbtidaldeltaswhichareoftenbreachedbynumerousshallowchannels.Transitionalinletshaveshoalswhicharecontainedintheinletthroat. Hubbardetal. ( 1979 )alsonotesthatinletsystemsintheGeorgiaBightthathavealargertidalrangehavemarshesbehindthebarriersthatareextensiveandrepresenta 21

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largeportionofthetotalmarshlandsalongtheentireAtlanticshoreline.ThemorphologicvariablesassociatedwitheachinlettypearedescribedinTable 1-1 1.3.3EquilibriumRelationshipsDespitethecomplexityoftidalinletsystems,somepredictiverelationshipshavebeendevelopedwhichrelatethevolumeandlocationoftheebbshoalcomplexandtheinletcross-sectionalareatothetidalprism.Tidalinletsystemstendtoremaininadynamicequilibrium,andvariationfromtheequilibriumstateinoneofthecomponentswillresultinsedimentexchangebetweenthecomponents( Dean 1988 ; Stiveetal. 1998 ).Largerscalepermanentchangestothesystemcancausetheentireinletsystemtoshifttowardsanewequilibriumstate. 1.3.3.1Inletchannel LeConte ( 1905 )wasthersttolookintotherelationshipbetweentidalprismandtidalinletminimumcross-sectionalarea,basedonobservationsofasmallnumberofinletsonthePaciccoastoftheU.S..Thestudyconcludesthatnaturerequires33squarefeetofmean-tidesectionforeachandeverymillioncubicfeetoftidalwaterspassinginandoutatspringtides.Thispioneeringworkwasexpandedby O'Brien ( 1931 )toincludemoreinlets.Thisstudydeterminedthattherelationshipbetweentidalprismandcross-sectionalareaisnotquitelinear,butfollowthepowerlawrelationship: A=CPq(1)whereA(m2)isthecross-sectionalarea,P(m3)isthespringtidalprism,andCandqareempiricalparametersobtainedfromobservationaldata. O'Brien ( 1969 )completedafollow-upstudywithmoretidalinlets,includingsomeontheAtlanticcoastandoneontheGulfofMexico.Theadditionofthisdatasupportedtheoriginalstudycompletedby LeConte ( 1905 )thattherelationshipwaslinear(q=1).Physicalmodelsofthesystemalsofoundthattherelationshipbetweentidalprismandcross-sectional 22

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areaatun-modiedinletscouldbeapproximatedasliner( DelmonteandJohnson 1971 ; Johnson 1972 ; Lin 1969 ; Nayak 1971 ). Jarrett ( 1976 )compileddatafrom108NorthAmericaninlets,59ontheAtlanticcoast,24ontheGulfofMexico,and25onthePaciccoast.Thestudyseparatedtheinletsintothreecategoriesaccordingtoengineeringmodication:(1)allinlets,(2)inletswithnojettiesorasinglejetty,and(3)inletswithtwojetties.Withinthecategories,inletswerefurtherseparatedaccordingtothefollowinggeographiclocations:(a)inletsonallthreecoasts,(b)inletsontheAtlanticcoast,(c)inletsontheGulfcoast,and(d)inletsonthePaciccoast.Theempiricalparameters,Candq,calculatedforeachofthetwelvecombinations,alongwiththecoefcientofdeterminationisshowninTable 1-2 andTable 1-3 .Studiesinvestigatingtheempiricalparameters,Candq,foradditionalinletdatasetinclude vandeKreeke ( 1992 )and Powelletal. ( 2006 )forNorthAmericaninlets, Shigemura ( 1980 )forJapaneseinlets, Diekmannetal. ( 1988 )forinletsintheWaddenSea, GerritsenandLouters ( 1990 )and vandeKreeke ( 1993 )forDutchinlets,and HumeandHerdendorf ( 1993 )forinletsinNewZealand.Workpresentedby Escofer ( 1940 )canbeusedtoexplainthetheoreticalderivationoftherelationshipbetweentidalprismandcross-sectionalarea.Thediagramillustratesthehydraulicrelationshipbetweentheinletcross-sectionalareaandthepeakmeanvelocitythroughtheinletchannel.Thepeakmeanvelocityisthemaximumowduringatidalcyclespatiallyaveragedthroughthecross-sectionoftheinletthroat.Thisrelationshipproducestheso-calledEscoferstabilitycurve,theshapeofwhichisdependentonthehydraulicpropertiesoftheinlet(i.e.,backbasinarea,tidalrange,inletlength,inletwidth,andfrictionthroughtheinletthroat).Itwasdeterminedthatthereisacriticalvalueofthevelocity,beyondwhichnetscouroftheinletoccurs.Fieldobservationshavefoundthatthiscriticalvelocityisapproximately1m/s,regardlessofsedimentcharacteristics( Bruunetal. 1960 ; O'Brien 1969 ).Iftheinletcross-sectionalareaislessthanequilibrium,thevelocityexceedsthecriticalvalue, 23

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generatingsufcientlyhighbedshearstresstoscouruntiltheequilibriumcross-sectionisreached.Ifthecross-sectionalareaoftheinletisgreaterthantheequilibriumvalue,thevelocitydecreases,loweringthebedshearstress,leadingtodepositioninthechanneluntilequilibriumcrosssectionalareaisattained.Figure 1-7 illustratesanexampleEscofercurveforaninlet. vandeKreeke ( 2004 )usedtheEscofercurvetoinvestigatehowthereductionofbackbasinareafortheFrisianinlet,locatedontheNorthSeaalongtheDutchcoast,wouldchangetheequilibriumcross-sectionalareaoftheinlet.Anextrapolationoftheobservationsofthecross-sectionalareachangeduringa17yearperiodfollowingbasinreductioniswithintherangeofvaluespreviouslypredictedusingtheEscofercurveforanewequilibrium( vandeKreeke 1993 ).BasedontheEscofermethods,theequilibriumcross-sectionalareawasexpectedtoreducefrom22,000m2to15,500m2 vandeKreeke ( 2004 ).Fieldmeasurementsofthethistransformationindicateanadaptationtimescaleofapproximately30years( vandeKreeke 2004 ). 1.3.3.2EbbshoalcomplexTidalexchangethroughtheinletcarriessediment,sometransportedlandwardanddepositedonoodshoal,andsometransportedseawardanddepositedonebbshoals.Asebbshoalsgrow,theybecomeshallowerandmoresusceptibletowaveforces.Thesewaveforcestendtotransportsedimentofftheshoalandbackintothenearshoresystem.Thesetwoforcesacttobalancethegrowthoftheshoal.SomestudiesfrominletsalongtheNorthAmericancoasthaveshownthatebbdeltavolumedependsonthetidalprism,inletgeometry,shorelineconguration,offshorebathymetry,waveclimate,littoraldrift,sedimentsize,andfreshwaterrunoff( FitzGerald 1988 ; HicksandHume 1996 ; Hubbardetal. 1979 ; MarinoandMehta 1987 ; WaltonandAdams 1976 ). WaltonandAdams ( 1976 )exploredthisrelationshipbycomparingebbshoalvolumesunderthethreewaveenergyregimes:(1)highlyexposed,(2)moderatelyexposed,(3)mildlyexposed.Thestudyuses44inletsalongtheAtlanticcoast,Paciccoast,andGulf 24

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ofMexicotoperformedalinearregressionttothepowerlawrelationship: V=aPb,(1)whereVisvolumeofsedimentstoredintheebbshoal(m3),PistheTidalprism(m3),andaandbareempiricalparametersdeterminedfromobservations.TheresultsofthestudyareshowninTable 1-4 foreachofthewaveregimesandforalltheinlets. FitzGerald ( 1988 )usedtheregressioncurvetocalculatethatachangeintidalprismof5%atKennebecRiverestuarywouldleadtoanincreaseintheebbshoalvolumebybetween0.57108and1.04108m3. FitzGerald ( 1988 )estimatesthatthedecitcouldcauselocalsedimenterosionofthecoast,leadingtoover100mofshorelinerecession.Theresponsetimeofthesystemtoreachthisnewequilibriumisunknown,butispredictedtotaketensofyears( FitzGerald 1988 ). MarinoandMehta ( 1987 )builduponthe WaltonandAdams ( 1976 )studybyexpandingthefactorsinuencingtheebbshoalvolumetoincludethetidalprism,inletwidthtodepthratio,thecross-sectionalarea,andspringtidalamplitude.Theyestimateebbshoalvolumesfrom18inletslocatedontheAtlanticcoastofFlorida,totaling420millioncubicmetersofsediment.ThestudyusesadimensionalanalysisapproachtodeterminewhichparametersmostaccuratelyexplainthetrendsfoundintheebbshoalvolumesofftheFloridaAtlanticcoast.Alinearregressionisappliedtotheobservationaldatatotthesamepowerlawrelationshipas WaltonandAdams ( 1976 ),ndinga=5.5910)]TJ /F7 7.97 Tf 6.58 0 Td[(4andb=1.39,withacorrelationcoefcientof0.75.Theyproposethatthisislowduetotheinuenceofotherfactorsoutsidethewaveandtidalenergy.Theydiscoveredthatifallotherfactorsweretoremainconstant,thenagreaterwidthtodepthratiooftheinletchannelwouldresultinsmallerebbshoalsandviceversa. HicksandHume ( 1996 )calculatedsandvolumesfor17ebbshoalslocatedatnaturalinletsalongtheNewZealandNorthIslandcoast.Theyfoundthatthemaincontrolonebbshoalvolumewastidalprism,theanglebetweentheoutowjetand 25

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shoreline(),andthewaveclimate.Largertidalprisms,lowerenergywaveclimates,andlargeroutowjetangles(moreshorenormal)tendtoincreasetheebbshoalvolume.Theyfoundthattheempiricalequation: V=1.3710)]TJ /F7 7.97 Tf 6.59 0 Td[(3P1.32(sin)1.38(1)accountsfor83%ofthevarianceintheebbshoalvolume.Includingtheeffectsofoutowjetanglesisofhigherimportanceonactivemargincoasts,suchasthoseinNewZealand,whererockyshorelinesmaydictatethisangle.Theyfoundthathigh-energycoaststendtohavesmallershoalsthanonthoseonlow-energycoastswithasimilarmagnitudetidalprism.Therearelinksbetweentidalprismandtheextent(bothseawardanddowndrift)oftheebbshoalcomplex( Carr-Bettsetal. 2012 )andtheminimumdepthovertheebbshoalcrest( BuonaiutoandKraus 2003 ). Carr-Bettsetal. ( 2012 )foundthattheseawardanddowndriftextentoftheebbshoalremainsconstantfortidalprismslessthat108m3andincreaselinearlywithtidalprismfortidalprismsgreaterthan108m3.Thisrelationshipbetweentidalprismandebbshoallocationwashighlycorrelatedformildlyorhighlywave-exposedinlets,buttherewasnocorrelationformoderatelyexposedcoasts.Astidalprismincreases,theebbshoalspreadsfurtheroffshoreandinthedowndriftdirection,andtheshoaloccupiesadeeperwaterdepth( BuonaiutoandKraus 2003 ; Carr-Bettsetal. 2012 ). 1.4SaltMarshes 1.4.1TypesofSaltMarshesSaltmarshesinhabittheupperintertidalregionbetweenthetidalatsandtheuplandenvironment,andaredominatedbyavarietyofhalophytic(salt-tolerant)vegetation.Mostmarshmorphologiescanbeclassiedasrampedorplatform,dependingontherelativeamountofsupratidal(highmarsh)andintertidal(lowmarsh)vegetation.Marshsystemswithlargeamountsofhighmarshesplantsexhibitaplatform 26

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morphology,thosewithanevenlydistributedamountofhighandlowmarsheshavearampedprole.Thedistributionoflowmarshvegetationspeciesarecontrolledbyphysicalstressestothesystem,suchasoodingandanoxia,whilethedistributionofhighmarshvegetationiscontrolledbyinterspecicplantcompetition( DonnellyandBertness 2001 ).Netverticalaccretioninmarshesisdependentonthebalanceoftidalrange,wind-waveclimate,sedimentsupply,relativesealevelrise,sedimentcompaction,subsidence,andvegetationproductivity( Reed 1990 ).Marshsedimentscanhavetwomodesoforigins:allochthonous(mineral,negrainparticlesbroughtfromoodingwateroutsidethemarshes)andautochthonous(deadorganicmatterproducedfromthesaltmarshvegetation).Therelativeamountofsedimenttypesdependsontheavailabilityofmineralsediments,tidalrange,storminess,vegetationtype,andvegetationproductivity,factorswhichvaryspatiallyacrossthemarsh( deGrootetal. 2011 ). 1.4.2SaltMarshResponsetoSeaLevelMarshescanrespondtosealevelriseby:(1)activelyexpandingverticallyandlaterallyifaccretionratesarefasterthanlocalsubmergence,(2)maintainingastableelevationbytrappingsedimentsandaccretingverticallyatthesamerateaslocalsubmergence,or(3)themarshsystemdrownsbynotbeingabletoaccreteverticallyatthesamerateofsubmergence( Orsonetal. 1985 ).Whenanon-aquaticplanthasitsrootssubmergedforprolongedperiodsoftime,theplantisnotsuppliedwithsufcientoxygenandwillbecomewaterloggedanddrown.Asthedrowningofindividualplantsoccur,themarshsystemwilllosebiomassandtheamountofinsitusedimentproductionwillbecomereduced.Thisfurtherretardstheabilityofthesystemtoaccretevertically,andtheentiremarshsystemmaydrown( Orsonetal. 1985 ).Marshplantshavesomenegativefeedbackmechanismswhichgivethemtheabilitytomaintainelevationwithmoderatelevelsofrelativesealevelrise. Morrisetal. ( 2002 )completedastudyonSpartinaalterniorainSouthCarolinatoinvestigatehowthemarshcordgrassrespondstoanincreaseinsealevel.Theyfoundthatthebiomass 27

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ofthiscordgrassincreaseswithdepthbelowhightide(uptoalimit).Higherbiomassincreasesaggradationratesonadeeperplatform,allowingtheplantstoequilibratetoaslightincreaseintherateofsealevelrise.Theyfoundthatthereisanoptimalrateofrelativesealevelriseforplantgrowth,whichalsorepresentstheupperlimitatwhichthecommunityisabletosustaintheelevation.Numerouseldstudiesandnumericalmodelshavebeenusedtoshowthatthestabilityofamarshsystemishighlydependentonthemagnitudeofthetidalrangeofthesystem( KirwanandGuntenspergen 2010 ; Kirwanetal. 2010 ; Reed 1995 ; Simasetal. 2001 ).Lossofmarshvegetationcanvarygreatlybetweenregions,withlowtidalrangeareas(suchastheAtlanticcoastofNorthandCentralAmerica,theBaltic,andtheMediterranean)beingparticularlyvulnerable( Reed 1995 ). Kirwanetal. ( 2010 )compiledtheresultsofvenumericalmodelsofmarshevolutiontondthresholdratesofsealevelriseatwhichmarsheswouldnotsurviveunderavarietyofsuspendedsedimentconcentrationsandtidalranges.Theyfoundthatforagivensuspendedsedimentconcentration,theabilityofamacrotidalmarsh(TR>4m)wasabletoadapttoasealevelriserateuptoanorderofmagnitudegreaterthanamicrotidalmarsh(TR<2m).Themodelresultsindicatethatforsuspendedsedimentconcentrationsover20mg/Landatidalrangeover1m,thethresholdrateofrelativesealevelwouldbeapproximately10mm/yr.Theypredictthatthisconversionofmarshtosubtidalenvironmentwouldoccurabout30-40yearsafterthethresholdratewasmet. DonnellyandBertness ( 2001 )tookcoresamplesfromaNewEnglandmarshsystemtoseetheevolutionofplantzonalboundariesovertime.Theyfoundthatthelowermarshes,dominatedbycordgrasses(Spartinaalterniora),slowlymovedlandwardattheexpenseofhighermarshspecies,dominatedbymarshhay(Spartinapatens),spikegrass(Distichlisspicata),andblackrush(Juncusgerardi).Thetimingoftheonsetofthisboundarymigrationwasshowntomatcharegionalincreaseofsealevelriserate(from2.4mm/yrto4.2mm/yr)recordedbyaNewYorktidegage.The 28

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abilityofthecordgrasstooxygenatethesubstrateallowedthespeciestosurviveduringthehigherrateofsealevelrise.Themarshhay,spikegrass,andblackrushwerenotabletotoleratetherelativelyhighriserates.Thevariationinverticalaccretionandtolerancetosealevelrisebetweenplantsspeciesindifferencezonesofthemarshtransformedthedistributionofplantsacrossthemarshsystem. DonnellyandBertness ( 2001 )predictthattheNewEnglandmarshwilllikelybecomeacordgrass-dominatedsysteminthefutureifrelativesealevelratesremainconstant. Nicholls ( 2004 )usedaclimatemodeltoshowthatunderanIPCCSRESA1FIworld,thatthepotentialcoastalwetlandlossduetosealevelriseis5-20%bythe2080s. Nicholls ( 2004 )alsoinvestigatesthesocio-economicinuenceoncoastalwetlands,ndingthatthewetlandlossduetosealevelriseissmallincomparisontothepotentialhuman-induceddirectandindirectinuencesthatincreasewithpopulationgrowth.HendsthatcoastalwetlandsaremuchmoreatriskunderIPCCscenarioswithlowersocialenvironmentalconsciousness;thisfactorcangreatlyinuencethemarshsystem'svulnerabilitytosealevelrise.Globalcoastalwetlandshavebeendecliningatarateofapproximately1%peryearduringthelate20thcentury,primarilyduetohumanreclamation( Hoozemansetal. 1993 ). 29

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Table1-1. Inletmorphologicvariables(from Hubbardetal. ( 1979 )) InletType VariablesWaveDominatedTransitionalTideDominated PrincipalshoallocationsInsidethebay,asamulti-lobateooddeltaInthethroatSeawardoftheinletaslonglinearchannelmarginbars Ebb-tidaldeltaSmallandclosetothebeachVariableLargeextendsfarfromshore Flood-tidaldeltaLarge;lobateordigitatePoorlydevelopedorabsentGenerallyabsent ChannelcharacterPoorlydened:oftenmultipleVariable;oftenonemainchannelandoneormoresecondarychannels.Unstableinshallowerportions5-10mdepthsTendstowardstability.Depthsgreaterthan10m. Width/depthratioModerateVerylargeSmall LagoonWide;openFringingmarsh;marsh-lledMarsh-lledandchannelized SwashbarsPoorlydevelopedVariableVariable SwashplatformsPoorlydevelopedVariableWelldeveloped ChannelmarginbarsAbsentVariableLarge SandbodycharacterTabularVariablePod-like;connedtonearchannels Sandby-passingBarby-passingVariable;ofteninpackets;channelabandonmentimportantPrimarilybyebbcurrentsinthemainchannelandlandwardtransportbywaves 30

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Figure1-1. Tidalinletelementsshownonatypicalmixed-energytidalinletsystem. 31

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Figure1-2. Morphologyofatypicaloodshoal(reproducedfrom Hayes ( 1980 )).Arrowsindicatedominantdirectionoftidalcurrents Table1-2. Empiricalparametersforthetidalprism-inletarearelationshipsdevelopedby Jarrett ( 1976 )(formetricunits) LocationAllinletsNooroneJettyTwoJetties CqCqCq AllInlets2.4110)]TJ /F7 7.97 Tf 6.58 0 Td[(40.933.6510)]TJ /F7 7.97 Tf 6.59 0 Td[(51.041.4810)]TJ /F7 7.97 Tf 6.59 0 Td[(30.83 AtlanticCoast6.0410)]TJ /F7 7.97 Tf 6.58 0 Td[(51.021.9810)]TJ /F7 7.97 Tf 6.59 0 Td[(51.086.7010)]TJ /F7 7.97 Tf 6.59 0 Td[(40.87 GulfCoast9.3010)]TJ /F7 7.97 Tf 6.58 0 Td[(40.846.9410)]TJ /F7 7.97 Tf 6.59 0 Td[(40.861.4310)]TJ /F7 7.97 Tf 6.59 0 Td[(30.81 PacicCoast4.7510)]TJ /F7 7.97 Tf 6.58 0 Td[(40.888.8310)]TJ /F7 7.97 Tf 6.59 0 Td[(61.101.8810)]TJ /F7 7.97 Tf 6.59 0 Td[(30.82 32

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Figure1-3. Conceptualmodelsofsedimentbypassing(from FitzGeraldetal. ( 2000 )). 33

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Figure1-4. Coastalclassication(reproducedfrom Hayes ( 1979 )). Table1-3. Numberofinletsandcorrelationsforthetidalprism-inletarearelationshipsdevelopedby Jarrett ( 1976 )(formetricunits) LocationAllinletsNooroneJettyTwoJetties No.ofInletsr2No.ofInletsr2No.ofInletsr2 AllInlets1080.90710.92370.88 AtlanticCoast590.92400.94190.81 GulfCoast240.87210.8730.88 PacicCoast250.92100.97150.93 34

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Figure1-5. PatternsinthenumberandspacingoftidalinletsasafunctionofwaveversustidalenergyalongtheGeorgiaBight(from FitzGerald ( 1996 )). Table1-4. Empiricalparametersforthetidalprism-ebbshoalvolumerelationshipsdevelopedby WaltonandAdams ( 1976 )fordifferentwaveenergyregimes. WaveRegimeNo.ofInletsab HighlyExposed78.710)]TJ /F7 7.97 Tf 6.58 0 Td[(51.23 ModeratelyExposed1810.510)]TJ /F7 7.97 Tf 6.59 0 Td[(51.23 MildlyExposed1613.810)]TJ /F7 7.97 Tf 6.59 0 Td[(51.23 AllInlets4410.710)]TJ /F7 7.97 Tf 6.59 0 Td[(51.23 35

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Figure1-6. TidalinlettypesintheGeorgiaembayment(reproducedfrom Hubbardetal. ( 1979 )),includingA)tide-dominatedinletsB)wave-dominatedinletsandC)transitionalinlets. 36

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Figure1-7. Escoferstabilitycurve(from Escofer ( 1940 1977 )). 37

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CHAPTER2HOWDOESVERTICALMARSHACCRETIONCONTROLHYDRODYNAMICANDMORPHOLOGICRESPONSESOFATIDALINLETTOSEALEVELRISE?Sedimentaryaccretioninback-barriermarshesexertsacontrolonthemorphologicresponseoftidalinletsystemstorelativesealevelrise.Weinvestigatethisphenomenonbyapplyinganumericalhydrodynamicmodel,pairedwithempiricallyderivedmorphologicrelationships,toaninletsystemtypicalofamixed-energy,tidedominatedbarrierislandsystem.Weconsidertwoend-member,marshaccretionscenarios:(A)noverticalmarshaccretion,whereinmarshislandsbecomesubmerged,changingboththeoodedbasinareaandthespatialpatternoftidalwaveattenuation,and(B)amarshaccretionrateequaltotherateofsealevelrise,whereinmarshtidalchannelsdeepenbutmaintaintheircoursesandtheassociatedfrictionreductionleadstoamoreefcienttidalexchangebetweentheoceanandback-barrierbasin.Modelresultsshowatidalprismincreaseforbothscenarios,leadingtoincreasesinchannelcross-sectionalareaandebbshoalvolumes.Underbothmarshaccretionscenarios,themechanismofimprovedtidalexchangeefciencythroughchanneldeepening,producesincreasesoftidalprismthataresimilarinmagnitude.Underconditionswithnomarshaccretion,anadditionalmechanism,namelytheexpansionofoodedbasinarea,furtherincreasesthemagnitudeofthetidalprism.ScenarioA(noaccretion)producedatidalprism,inletcross-sectionalarea,andebbshoalvolumeincreasedoublethatoftheincreasecalculatedforscenarioB(pace-keepingaccretion).Theincreaseinequilibriuminletchannelcross-sectionalarea,arisingfromscourprocesses,exceedstheincreaseduetosealevelrisealone,illustratingtheinuenceofmarshtidalowprocesses.Ourresultsindicatethatprocessesthatretardback-barriermarshaccretionwillhavetheinadvertentconsequencesofincreasingbothinletchannelcross-sectionalareasandebbshoalvolumes.Increasesinebbshoalvolumescouldprofoundlyimpactregionalsedimentbudgetsandleadtochangesintheerosion-depositionpatternsofadjacentshorelines. 38

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2.1IntroductionAtidalinletactsasthepassagewayforexchangeofwaterandsedimentbetweentheoceanandaback-barrierbasin.Theinletsystemiscomposedoftheinletchannel,ebbandoodshoalcomplexes,adjacentbarrierislands,andthecontiguouswetlands,witheachcomponentparticipatinginasandsharingsystem,whichisassimilatedintotheregionalsedimentbudget( Dean 1988 ; Hayes 1979 ).Despitetheimportanceofincludingtheinuenceoftidalinletsinregionalsedimentbudgets,fewstudieshaveinvestigatedthemorphologicresponseoftidalinletsystemstochangesinrelativesealevel( FitzGeraldetal. 2008 ).Themorphologyoftheinletsystemiscontrolledbylocalriverinow,tidalexchange,andwaves.Aswaterlevelsintheoceanincreasewiththerisingtide,waterandsedimentistransportedthroughtheinletchannelandintothebasin,anduponowexpansioninthebasin,transportcapacitydecreasesandsedimentisdepositedonoodshoals.Asoceanwaterlevellowerswiththefallingtide,waterandsedimentfromthebasinowsbackouttotheoceananddepositssedimentonebbshoalsseawardoftheinletchannel.Ebbshoalsalterwavetransformationandinterruptlongshorecurrents,leadingtoasedimentexchangebetweentheshoalsandadjacentshorelines.Increasestothetidalprism,thetotalvolumeofwaterexchangedduringatidalcycle,canincreasethestorageofsedimentinebbshoals,whichcausestheshoalstoactasalocalsedimentsink,alteringthewaveenergyux,andtherefore,theerosional-depositionalpatternsoftheadjacentbarrierislandshorelines( Dean 1988 ; FitzGerald 1988 ).Figure 1-1 illustratessomeofthecomponentsofatypicalmixed-energytidalinletsystem.TwomodelingstudiesexploringinletresponsetosealevelrisehavebeenundertakenforinletsystemsoftheWestFrisianIslandsintheNorthSea,whichconsistoflarge,un-vegetatedtidalatsthatconnecttheopenoceantotheWaddenSea( Dissanayakeetal. 2009 ; VanGooretal. 2003 ).Theirresultspredictincreases 39

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forinletchannelcross-sectionalareasandoodtidaldeltas,butdecreasesinvolumesofebbshoalcomplexes.ThesepredictionsconictwiththechangesrecordedineldstudiesperformedalongtheLouisianacoast( FitzGeraldetal. 2004 2007 ; Listetal. 1994 1997 ).TheinletsintheseeldstudiesconnecttheGulfofMexicotoBaratariaBay,whichhasexpansiveregionsofwetlandsconnectedbyacomplexnetworkoftidalchannels.Highrates(approximately10mm/yr)ofrelativesealevelrisehaveledtomarshdegradation,resultinginanincreaseinbasinarea,tidalprism,cross-sectionalarea,andebbshoalvolumes( FitzGeraldetal. 2004 2007 ; Listetal. 1994 1997 ).Thelossofmorethan1,100km2ofwetlandareahasledtoanincreaseinbarrierislandsegmentationandbreakup( FitzGeraldetal. 2007 ).Thisstudyexplorestheroleofwetlandstabilityonthehydrodynamicandmorphologicresponseofatidalinletsystemtochangesinsealevel.WehaveperformedtwosetsofexperimentsusingtheDelft3Dnumericalmodel:(A)sealevelriseinabasinwithnoverticalmarshaccretion,and(B)sealevelriseinabasinwhereverticalmarshaccretionratesareequaltotherateofsealevelrise.Therstexperimentrepresentsamarshsystemwhichisunabletokeeppacewithsealevelrise,whereasthesecondexperimentrepresentsasystemthatisable.Weusethesetwoscenariostobracketthepotentialshort-term(decadal)responseofthesystem,andtohighlighttheroleofwetlandvegetationinthisresponse.Wedonotinvestigatemarshedgeerosionsinceitwouldbeexpectedtooccurmultipledecadesafterthresholdrateswereachieved( Kir-wanetal. 2010 ).ThenumericalexperimentsarerunfortheSt.MarysRiverentrance,ontheFlorida-Georgiaborder,asystemthatistypicalofthoseseenintheSeaIslandchainofbarrierislandslocatedonthesoutheastcoastofNorthAmerica.Wedonotinvestigateascenarioofmarshexpansionforthissitebecausethewetlandscovermostofthelocalundevelopedlandandthereislittlespaceforlateralexpansion. 40

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2.2BackgroundWetlandvegetationresponsetosealevelriseiscomplex,withmanyfactorscontributingtotheresilienceofthesystem.Wetlandscanrespondtosealevelriseby:(1)activelyexpandingverticallyandlaterallyifaccretionratesarefasterthanlocalsubmergence,(2)maintainingastableelevationbytrappingsedimentsandaccretingverticallyatarateequaltotherateoflocalsubmergence,or(3)drowningduetoaninabilitytoaccreteverticallyattherateofsubmergence( Orsonetal. 1985 ).Ifvegetationissubmerged,itmaybecomewaterloggedanddie.Thiscanleadtomarshplatformedgeerosion,whichisexpectedapproximately30-40yearsafterthresholdratesofsealevelrisearereached( Kirwanetal. 2010 ).Therateofmarshaccretionisabalancebetweenstorm,ice,andtidalsedimentation,bioproductivity,decomposition,compaction,andsubsidence.Theseprocessesarecontrolledbyfactorsthatincludeclimatechange,sealevelrise,andregionaltectonics( ArgowandFitzGer-ald 2006 ).Numerouseldstudiesandnumericalmodelshavebeenusedtoshowthattheresilienceofawetlandsystemtoachangeinrelativesealevelisdependentonthemagnitudeofthetidalrangeandsedimentsupplyofthesystem( KirwanandGuntenspergen 2010 ; Kirwanetal. 2010 ; Reed 1995 ; Simasetal. 2001 ).Marshecosystemshavetheabilitytoregulatetheirelevationwithinanarrowrangeoftheintertidalzonebyincreasingsedimenttrappingandbioproductivitywhenthevegetationisatalowerelevationinthetidalrange,leadingtofeedbacksinthesystemthatpromoteverticalaccretionwithincreasesinsealevel( Boormanetal. 2001 ; MendelssohnandMorris 2000 ; Morris 2007 ; Morrisetal. 2002 ).Thesefeedbackshavelimitations,giventhattheoptimalrateofplantproductivityoccursatasubmergencedepthequaltothedrowningpoint( Morrisetal. 2002 ).AtmostinletsontheU.S.Atlanticcoast,wetlandvegetationcoversabroadarealextentaroundtheback-barrierbasinchannels.Ifthewetlandsystemisunabletomaintainverticalaccretionratessufcienttokeeppacewithsealevelrise,thosebroad 41

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areasmaybecomesubmerged.Thiswouldleadtoincreasesinoodedbasinarea,allowingforanincreasedtidalprism.Thedeepeningofchannelsshouldreducesomeofthetidalwaveattenuationinthesystemandleadtoamoreefcienttidalexchange.Bothofthesechangeswouldincreasethetidalprismandleadtoanincreaseininletchannelcross-sectionalareaandebbshoalvolume.Ithasbeensuggestedthatthesizeofsomemorphologicfeaturesofatidalinletsystemcanbepredictedusingempirically-derivedrelationshipsbasedonthehydrodynamiccharacteristicsofthesystem. O'Brien ( 1931 1969 )comparedinletchannelcross-sectionalareatotidalprismforstableinlets,whichwerethoughttobeinastateofequilibrium,andrevealedapowerlawrelationshipbetweenthetwovariables.Alargertidalprismimpliesthatlargerowvolumesmustbeexchangedduringatidalcycle.Thecross-sectionalareaofthechannelgovernstheconstrictionofowandthecurrentvelocitiesthatoccurduringtheexchange.Accordingto O'Brien ( 1931 1969 ),anequilibriumowrateexists,atwhichthecurrentexhibitsnonettransportinthechannel.Iftheowvelocityexceedstheequilibriumrate,scourwilloccuruntiltheequilibriumowrateisattained.Iftheowvelocityisbelowtheequilibriumrate,channelsedimentationwilloccuruntilthecross-sectionalareareestablishestheequilibriumowrate. Jarrett ( 1976 )expandedtheinvestigationperformedby O'Brien ( 1931 1969 )bycompilingdatafrom108inlets,59fromtheAtlanticcoast,24fromtheGulfofMexico,and25fromthePaciccoast,andseparatedtheinletsintothreecategories:(1)allinlets,(2)inletswithnojettiesorasinglejetty,and(3)inletswithtwojetties.Withineachcategory,theywerefurtherseparatedaccordingtothefollowinggeographiclocations:(a)inletsonallthreecoasts,(b)InletsontheAtlanticcoast,(c)inletsontheGulfcoast,and(d)inletsonthePaciccoast.Foreachofthesetwelvecombinations,powerlawrelationshipsweret,and95%condenceintervalsforthepowerlawconstantswereestablished.Duringtidalexchange,sedimenttransportedlandwardduringtheoodinglimbisdepositedonoodshoal,andsedimenttransportedseawardduringtheebbinglimb 42

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isdepositedonebbshoal.Asebbshoalsgrow,thewaterdepthstheyoccupybecomeshallowerandmorestronglyinuencedbytheassailingwaveeld.Waveactionentrainssedimentandlongshorecurrentstransportsedimentofftheshoalandbacktothenearshoresystemadjacenttotheshoal( Kraus 2000 ).Therefore,ebbtidalowandwaveactionacttogethertobalancethegrowthoftheshoal. WaltonandAdams ( 1976 )exploredthisrelationshipbycomparingebbshoalvolumesunderthreewaveenergyregimesdenedbywaveheightandperiod.Theyfoundthattheirdatacouldbettoapowerlawrelationshipbetweentidalprismandebbshoalvolumeforeachofthethreewaveenergyregimes. 2.3Methodology 2.3.1StudySiteTheSaintMarysEntrance(SME)isatidalinletlocatedontheborderofFloridaandGeorgiainsoutheasternNorthAmericathatconnectstheCumberlandSoundtotheAtlanticOcean.TheinletisborderedonthenorthbyCumberlandIslandandonthesouthbyAmeliaIsland.BothAmeliaandCumberlandislandsarepartofthebarrierislandstringknownasSeaIslandsshowninFigure 2-1 .Theinletsinthisareafallintothemixed-energytide-dominatedrangeoftheclassicationsystemdevelopedby Hayes ( 1979 ),whichcategorizesthemorphologicfeaturesoftidalinletsbasedontheirrelativestrengthoftideandwaveforces,aconceptfurtherexploredby FitzGerald ( 1996 ).Ingeneral,thisislandchaincharacterizedbyfrequentlyspacedinlets,withwell-developedebbshoalcomplexes.Thesebarrierislandsareseparatedfromthemainlandbyacomplexnetworkoftidalcreeksandmarshislands.ThebanksoftheCumberlandSoundandattachedchannelsaremostlyborderedbycoastalmarshvegetation,coveredpredominatelybythesmoothcordgrass,Spartinaalterniora.Theareaofwetlandcoverageinthebasin,calculatedfromdataavailablefromtheNWI,isapproximately197km2,whichisapproximately80%ofthebasinareathatliesbelowthespringhightidewaterelevation. 43

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Thelowmarshrepresentsapproximately60%ofthetotalarealextentinGeorgiasaltmarshes,whereapproximately80-96%ofthenetprimaryproductionisduetoSpartinaalterniora( FreyandBasan 1985 ).Approximatelytwo-thirdsoftheproductionofSpartinaalternioraoccursasrhizomesbelowthesurface,makingitphysicallyinaccessibletograzingherbivores( Fogeletal. 1989 ).Georgiasaltmarshesexhibitlittleornopeatduetotheextensiveraftingofmaterialoutofthemarsh,thehighmeantemperatures,intensebacterialdegradation,andhighlevelsofbioturbation;alayerofsediment30cmthickmayremainintheactivebioturbationzoneforuptoseveraldecades( Fogeletal. 1989 ).AveragesedimentationratesalongtheGeorgiacoasthavebeenestimatedas3-5mm/yr( Hattonetal. 1983 ).Fieldmeasurementsperformedby Craft ( 2007 )indicateawidevariationinboththespatialandtemporalverticalaccretionratethroughoutthemarshsystem,withshort-termratesvaryingbetween5.30.5and9.91.1andlongtermratesvaryingbetween1.30.3and3.40.6.Thisvariationislikelyduetothemixtureofsedimentsources,bothexternalandinternaltothemarshsystem,whicharenotsuppliedatanunsteadypaceand/orinanonuniformspatialpattern( NicholsandBoon 1994 ).Theproportionsofsand,silt,andclayvarythroughoutthemarshsystem;thecreekbanksarecomposedofamixtureofsilt-andclay-sizedsediment,whereasthehighmarshescontainmostlysand-sizedsediment( FreyandBasan 1985 ).TheSt.Marys,Cumberland,Crooked,North,Jolly,BellandAmeliaRiversowintotheestuarybasin,withtheSt.MarysRiverbeingtheprimarycontributoroffreshwater.TheriverdischargeatUSGSstation02231254(located30.7439N,81.6544W),approximately20kminlandfromtheinletentrance,isgenerallytidallydominated,punctuatedwithrainevents,whichtemporarilyincreasedischargevalues.Twoharborsarelocatedintheestuary,whichserveasabaseforsubstantiallocalcommercialandshingeets.TheKingsBayNavalbase,locatedapproximately14kmnorthoftheinletintheCumberlandSound,servesasaportfornavalsubmarines.Insupportofthe 44

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defense,commercial,andrecreationalnavigation,theinletisstabilizedwithtwojettiesandisregularlydredgedtomaintainadepthofapproximately14m( Parchure 1982 ).Channelsbetweentheinletandthenavalbase(northoftheinlet),aswellasbetweentheinletandFernandinaBeachMarina(southoftheinlet),aredredgedtomaintainnavigation.BathymetryobtainedfromtheNationalGeophysicalDataCenter(NGDC)3arc-secondCoastalReliefModelisdisplayedinFigure 2-2 .Thetideispredominatelysemi-diurnalwithameanrangeof1.75mandspringrangeof2.5m.Tidalprismmeasurementforthisinlethavebeenreportedas1.75108m3,1.58108m3,1.70108m3,and3.3108m3by Bruunetal. ( 1978 ), O'BrienandClark ( 1974 ), EnvironmentalScienceandEngineering,Inc. ( 1980 ),and Powelletal. ( 2006 ),respectively.Figure 2-3 showsthebasinhypsometriccurve,thedistributionofbasinelevation,illustratingthat25%ofthebasinresideswithinthespringtidalrange.Usingthedistributionofbasinelevations,andthetemporalobservationsofwaterlevels(takenover40tidalcycles),anestimateoftheoodedportionofbasinareacanbecalculated.Figure 2-4 displaysthetemporaldistributionofoodedbasinareaovertherangeoftidalelevations(shadedarea)andthetemporallyaveragedbasinarea(blueline).Thedistributionofelevationsisbimodalrepresentingthemarshchannelsandthemarshplatforms.Duringthetransitionfromebbtooodtide,themarshchannelsarethersttoexperienceinundationuntilthemarshplatformedgeisovertopped(ZoneA),afterwhichtimetheoodedbasinarearapidlyexpandswhilethemarshplatform(ZoneB)continuestobeinundated.Duringthehigherportionoftherisingtidelimb,theregionofoodedmarshplatformenlargesuntilmaximumtidalelevationisreached(ZoneC).Thetemporallyaverageoodedbasinsizeis178km2,butthatpreciseamountofbasinareaissubmergedforonlyashortduration. 2.3.2TidalFlowModelandExperimentalDesignDelft3DisamodelingsuitedevelopedbyDeltaresandiscapableofsimulatingthree-dimensionalunsteadyoweldsresultingfromwaves,tides,rivers,winds,and 45

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othercoastalcurrents.Thesystemofequationsconsistsofthehorizontalmomentumequation,thecontinuityequation,thetransportequation,andaturbulenceclosuremodel,describedindetailby Lesseretal. ( 2004 ).Themodelusescurvilinear,boundary-ttedgrids,andcanbeusedtoprovideowpredictionsforareaswithcomplexbathymetry.Inoursimulations,themodelisforcedwithwaterlevelsproscribedbyasetofastronomicaltidalconstituentsderivedfromNOAAtidalstations.Themodeldoesnotincorporatefreshwaterinowfromlocalriversourcessincethenetdischargethroughtheinletchannelduetoriverinputintothesystemislessthan5%ofthetotalinletdischargeattributabletothetides( Parchure 1982 ).Themodeldomainisacurvilinearsetof419x319x8gridcells,withanaveragehorizontalgridspacingof100mx100mintheestuary,increasinginthex-directiontowardsdeeperoceancells.Themodelusesasigmacoordinatetransformationintheverticaldirection,dividingthedepthintoanevenlyspaced,constantnumberofverticalslices,varyinginthicknesswithchangesinwaterlevel.Thisresultsinasmoothrepresentationofthelocalbathymetryandhighcomputingefciency.Watersurfaceelevationsandowvelocitiesfromonemodelrun,simulatinga52-dayperiodwascomparedwithavailableinsitudata,inordertoconductamodelvalidationstudy.Subsequently,twoseriesofmodelrunswereconductedforeachofthewetlandaccretionscenarios.Therstexperimentalseries,withnomarshaccretion,wasexecutedbyloweringthebaselevelofthebathymetryevenlythroughoutthemodeldomain.Inthesecondexperimentalset,withwetlandaccretionequaltosealevelrise,thebaselevelwasloweredinareasofthebathymetrythatarenotclassiedbytheNationalWetlandInventory(NWI)asvegetatedarea.Eachseriesofmodelrunsranthroughthefollowingsetofsealevelrisemagnitudes:5,10,20,30,40,50,60,70,80,90,and100cm.Allofthesimulationswererunusingtidalelevationconditionsduringthesamesixdayinterval,fromNovember08,2011toNovember14,2011,whichcomprised10fulltidalcycles.Thismodeldoesnotincorporatesedimenttransportinto 46

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thesystembecausethereisnotsufcientdatausedforcalibrationtocondentlymodelmorphologychangetothesystem.Inordertoaccuratelymodelsedimenttransportatthislocation,detailedinformationaboutthesedimentdistribution,longshoretransport,andriverineinputwouldberequired.Sincethemodeldoesnotincorporatesedimenttransport,themagnitude,ratherthantherateofsealevelrise,isusedinthisstudy.Therateofsealevelrisedictatesthetimetowhicheachsealevelrisemagnitudewouldbereached.Forexample,asealevelriserateof2mm/yrwouldrequire250yearstoreach50cmofsealevelrise,whilearateof10mm/yrwouldrequire50yearstoreachthismagnitude. 2.3.3EmpiricallyDerivedHydrodynamic-MorphologicRelationshipsInthisstudy,weusethemodeloutputoftheinstantaneousdischargethroughtheinletchanneltocalculateameantidalprismoverthe10modeledtidalcycles,inordertomakeestimatesaboutchangestotheinletcross-sectionalareaandebbshoalvolume.Therelationshipbetweenthetidalprismandtheinletchannelcross-sectionalareathatweapplyinthisstudywasestablishedby Jarrett ( 1976 )forU.S.Atlanticcoastinletswithtwojetties: A=1.584010)]TJ /F7 7.97 Tf 6.59 0 Td[(4P0.95(2)wherePisthetidalPrism(m3)andAistheminimumcross-sectionalarea(m2).Similarly,weuseanempiricalrelationshiptoinvestigatechangestotheequilibriumebbshoalvolumeusingarelationshippublishedby WaltonandAdams ( 1976 ).Wechosetherelationshipdevelopedformoderatelyexposedcoasts,basedonthewaveenergyregimeintheareaoftheSaintMarysEntrance: V=6.610)]TJ /F7 7.97 Tf 6.59 0 Td[(3P1.23(2)whereVistheebbshoalvolume(m3).Weapplytheseformulastothetidalprismmodelcalculationsforbothmarshplatformaccretionscenariosandallsealevelrise 47

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magnitudesinordertounderstandthecontrolofmarshprocessesontheresponseoftheinletmorphologytochangesinrelativesealevel. 2.3.4ModelTestingandCalibrationPriortoexecutingthefullsuiteofnumericalexperiments,themodelwasrunforpurposesoftestingandcalibration,tosimulatetidalconditionsfora52-dayperiodfromNovember08,2011toDecember30,2011.ComparisonsitesincludedpointsclosesttotheNOAAtidalstationandADCPlocations.TheNOAAFernandinaBeachCurrentsProjectbottom-mountedworkhorseADCPlocationsanddeploymentperiodsareshowninFigure 2-5 .Watersurfaceelevationcomparisonwithtidestation8720030isshowninFigure 2-6 ,withthelengthoftherecordbrokenintofourpanels.Displayedare(1)thetidalstationdata(redline),(2)theDelft3Dmodelresults(blue),and(3)thedifference(green)betweenobservationandmodelresults-underpredictionshavepositivevaluesandoverpredictionshavenegativevalues.Thephaseofthesignalappearstobeaccuratelypredicted,withmostofthedifferencesarisingfromdiscrepanciesinmagnitude.Thewaterelevationdifferencesforthisrecordpassedat-testofthenullhypothesisthattheyfollowanormaldistributionwithameanof-2.1cmandastandarddeviationof19.7cm.Thestandarddeviationisapproximately8%oftherangeoftidalelevationsinthisrecord.Someofthisdifferentislikelyduetothelackofwindinducedset-upandset-downincorporatedintothemodel.Timeseriesplotsofobservedandmodeledsurfacecurrentspeeds,foreachofthesixstations,areshowninFigure 2-7 .Thedatadurationdisplayedisfortherstthreefulldaysofdeploymentateachstationinordertoexploreameaningfulcomparison.AplotofthesurfacecurrentsfortheentiredeploymentofeachstationareshowninFigure 2-8 asU-Vscatterplotsalongwiththe95%condenceellipsesoftheADCPcurrentmeasurementsandtheco-locatedmodeledcurrents.TheUandVvelocitiesaretheeastingandnorthingcomponentsofvelocity,respectively.Theaxesarestretched 48

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toshowvariability(axisexaggerationsindicatedonplots).Forbothplots,thecoloreddatarepresenttheADCPobservationdata,coloredbystation,andtheblackdatapointsaretheco-locatedmodelresults.Figure 2-9 showsthecalculatedmeanspeed,speedstandarddeviation,andprincipalaxiscalculatedoverthedeploymentperiodateachofthesixstations.ThemajorityofthemodelstationshaveaphasesimilartothereportedADCPcurrents,withtheexceptionofFEB1108,whichislocatedclosetothesouthernjetty.Thislocationmayhavesomemodelinginaccuraciesduetotheproximityofthehardstructure(jetty).Thislocationmayalsobeinuencedbyacombinationofchannelandalongshorecoastalow;themodeloutputexhibitsgreaterchanneldirectedowandsmallermagnitudesthantheADCPobservationsatFEB1108.Longshorecurrentsarenotincludedinthemodelcalculations,makingthisaplausiblesourceofthediscrepancy.ThemodeltendstounderpredictcurrentspeedsduringoodtideatstationFEB1101,whichislocatedinthecenterofthejettystructuresontheoceansideoftheinlet.Thismaybeduetotheinuenceofthejetties,whichconstrictowandincreasecurrentvelocitythroughtheinlet.Thejettiesareincludedinthemodelasshallowregions,ratherthanthindams,becausethejettiesdoallowsomepassage(overtopping)ofwaterduringhightide.Experimentalrunsusingthindamjettiesreducedtheowthroughthechannelandthecurrentsinthebasinweresignicantlyunderpredicted.ThemodeloverpredictscurrentspeedsatstationFEB1104,apointinanarrowingsectionoftheAmeliaRiver,2.5kmsouthoftheinletchannel,byapproximately20cm/s.TherealsoexistsadepthdiscrepancybetweentheNOAAADCPdataandtheNGDCCoastalReliefModeldatausedtoconstructthemodelbathymetryatthatlocation;theADCPdepthisreportedat12m,whiletheNGDCdepthis8.3m.ThisareaisintheQuarantineReach,adredgedsectionofthebasin,maintainedatapproximately11meters.ThedatescorrespondingtothebathymetricsurveyandADCPdeployments 49

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maybeseparatedbyadredgingeventleadingtothisdepthdiscrepancy,whichwouldcertainlyinuencecurrentvelocities.ThetwoADCPsinthechannelthroat(FEB1102andFEB1103)arelocatedoneithersideofwherethemodeltidalprismcalculationsaremade.Thisminimumcross-sectionoftheinletchannelwaschosenbecausethetotalvolumeuxthroughthisplaneovereachtidalcycleisequivalenttothetidalprism.Themodelmakesthemostaccuratevelocitypredictionsinthisarea;theco-locatedmodeloutputshavemeanspeedswithin2.2cm/s,standarddeviationswithin4.4cm/s,anddirectionwithin2.8degreesoftheADCPdata.Modelcalculationsoftidalprismsduringthe52-daysimulationrangefrom1.3108m3to2.7108m3.Modeledinletchannelwaterelevations,modeledinstantaneousdischargesthroughtheinlet,andmodeledtidalprismvalues,foreachtidalcycle,areshowninFigure 2-10 .Themeanofthetidalprismduringthismodelsimulationwas1.87108m3,comparingwellintherangeofreportedvaluesof1.75108m3,1.58108m3,1.70108m3,and3.3108m3publishedin Bruunetal. ( 1978 ), O'BrienandClark ( 1974 ), EnvironmentalScienceandEngineering,Inc. ( 1980 ),and Powelletal. ( 2006 ),respectively.Thesevaluesareshown,forcomparisonpurposes,inthebottompanelofFigure 2-10 asthedashedhorizontallines. 2.4ResultsBelow,wepresentthemodelingresultsofsimulatedsealevelriseandthemorphologiceffectsorganizedintofoursectionscorrespondingtothevariablesofinterest.Wedescribethesimulatedchangesinbasinarea,tidalprism,inletcross-sectionalarea,andebbshoalvolumefortheincrementedsealevelrisescenariosinthetwo,end-membermarshaccretionscenariosdescribedabove:nomarshaccretionandmarshaccretionatarateequaltothatofsealevelrise. 2.4.1BasinAreaThechangeintemporallyaveragedoodedbasinareawascalculatedforeachsealevelrisemagnitudeunderthetwoendmembermarshaccretionscenarios.Figure 2-11 50

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displaysthechangeinthetemporaldistributionofoodedbasinareaandthechangeinthetemporallyaveragedbasinarea(verticallines)withsealevelriseforeachmarshaccretionscenario.Theblacklinesshowinitialbasinareadistribution,thebluelinesare10cmincrementalsealevelrisestepsbetweenzeroand100cm,withasealevelriseof50cmand100cmhighlightedasgreenandredlines,respectively.Inthecaseofnomarshaccretion,boththechannelsandmarshplatformareoodedwithincreasedfrequencyandduration.Inthecaseofsealevelrise-pacedmarshaccretion,thechanneledgesbecomeoodedmorefrequentlywithsealevelrise,buttheplatformisoodedwiththesamefrequencyandduration.Eventually,thechannelsidesbecomesteepandarecontinuouslysubmerged.Figure 2-12 displaystherelationshipbetweensealevelrisemagnitudeandtemporallyaveragedsubmergedbasinareaforbothofthemarshaccretionscenarios. 2.4.2TidalPrismTheidealtidalprism,consideredtobethatwhichwouldoccuriftidalexchangewereinstantaneousanduniformthroughoutthebasin,iscalculatedasthetemporallyaveragedsubmergedbasinareamultipliedbythemeantidalrange.Themodeledtidalprism,averagedforthetentidalcyclessimulated,wascalculatedfromtheinstantaneousdischargethroughtheinletchannelforbothofthemarshaccretionscenariosandforeachofthesealevelrisemagnitudes.TheupperpanelinFigure 2-13 displaysthecalculatedidealtidalprisms(circles)andmodeledtidalprism(squares)forthescenarioofzeromarshaccretion(red)andmarshaccretionequaltosealevelrise(blue).Inallcases,theidealandmodeledtidalprismsexhibitanincreasewithrisingsealevel.Forthestaticmarshscenario,thetidalprismincreasesatagreaterratethanforthepace-keepingmarshaccretionscenario,becausethebasinareaincreasesatagreaterratewithrisingsealevel.Thetidalexchangeefciencywascalculatedastheratioofmodeledtoidealtidalprism,andisshowninthelowerplotinFigure 2-13 overtherangeofinvestigated 51

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sealevelrisevalues.Theincreaseinthisratioindicatesthatthetidalprismexchangebecomesmoreefcientwithincreasesinsealevelduetoareductionintidalwaveattenuation.Theincreaseisslightlygreaterinthemarshaccretionscenariobecausetheonlyadditionalbasinareathatisbecomingoodedisinthechannels.Inthecaseofastaticlandscape,shallowareasthatwerenotpreviouslywithinthetidalrangearenowaccessible;theseshallowareasretardexchangeowmoreseverelythandothebasinchannels.Thetidalprismincreasesduetoacombinationoftheincreasedbasinareaandincreasedtidalexchangeefciency.InFigure 2-14 weseparatetheincreasedmodeledtidalprismintothesetwo,aforementioned,componentsforboththestaticmarsh(red)andpace-keepingmarshaccretion(blue)scenarios.Thetotalmodeledtidalprismincreasesareshownassolidlines,andthecomponents,fromthebasinareaincreaseandfrommoreefcientexchange,areshownascirclesanddashedlines,respectively.Theincreaseintidalexchangeefciencycontributesasimilaramounttoeachofthesystems,regardlessofmarshaccretionrates,duetochanneldeepening.Theincreasedefciencyisresponsibleforapproximatelytwo-thirdstheincreaseintidalprisminthemarshaccretionscenario,whereasitisonlyone-thirdinthecaseofastaticmarshsystem. 2.4.3Cross-SectionalAreaSealevelriseincreasesthecross-sectionalareaoftheinletchannelduetoincreasingwaterlevelandoodingofadjacentshoreline.Theequilibriumvalueofthechannelcross-sectionalarea,theareanecessarytoconveytidalows,alsoincreaseswithsealevelriseduetothescourassociatedwiththeincreaseintidalprism.Theempiricalrelationshipbetweentidalprismandcross-sectionalareadevelopedby Jar-rett ( 1976 )isusedtocalculateequilibriumcross-sectionalareaforeachsealevelrisescenario.TheupperpanelofFigure 2-15 showsthechangeincross-sectionalareaduetosealevelriseinthechannel(green)andthechangeinequilibriumcross-sectional 52

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areaduetoscourfromtidalprismincreaseforastaticlandscape(red)andforabasinwithpace-keepingmarshaccretion(blue).Theapproximaterateofincreaseis61m2and28m2per1cmofsealevelriseforstaticmarshesandaccretingmarshes,respectively.Atpresent-daysealevel,themeasuredcross-sectionalareaisgreaterthantheequilibriumprediction,likelyduetochanneldredgingregularlyperformedatthissite( Johnstonetal. 2002 ).Assealevelrises,theequilibriumareaincreasesatafasterpacethantheincreaseinthecross-sectionalareaduetosealevelriseinthechannel.Forsealevelrisemagnitudesatwhichtheequilibriumcross-sectionalareaexceedsthecross-sectionalareacreatedbysealevelriseinthechannel,scourshouldoccurtoenlargethechannelbywideningordeepening,untilsufcientareaisachievedtoaccommodatetheincreasedtidalprism. 2.4.4EbbShoalVolumeUsinganempiricallyderivedequilibriumrelationshipdevelopedby WaltonandAdams ( 1976 ),weexploretheimpactofsealevelriseontheebbshoalvolumeoftheinletsystem.Aplotofthechangeinebbshoalvolumeovertherangeofsealevelrisemagnitudesforstaticmarshes(red)andpace-keepingmarshes(blue)isprovidedinthelowerpanelofFigure 2-15 .Thisguredisplaysthesensitivityofebbshoalstochangesinmarshaccretionrates;staticmarshenvironmentsshowanincreaseinebbshoalvolumemorethandoubletheamountcalculatedwhenmarshesaccreteatthesamerateassealevelrise.Forevery1cmofsealevelrise,increasesintheequilibriumvolumeofsedimentstoredinebbshoalsof0.66km2and0.30km2arepredictedtooccurforstaticandpace-keepingaccretingmarshes,respectively. 2.5DiscussionInthissection,weconsiderthepotentialimpactsofsealevelriseonebbshoalvolumeandtheinuencethatsuchachangemightexertonlocallongshoretransportpatterns.Wecompareourmodelingresultswithpreviousstudiesfocusedontidalinletresponsetosealevelriseandspeculateonwhythereisdisagreementwithmodeling 53

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studiesofinletsalongtheWestFrisianIslandsintheNorthSea.Finally,wediscussthequalitativeagreementofourmodelresultswitheldstudiesfromtheLouisiana(U.S.)Gulfcoast. 2.5.1RegionalImpactsThecurrentrateofsealevelriseatNOAAtidalstation8720030(locationshowninFigure 3-1 ),calculatedusingdataovera110yearrecordbetween1897and2006,is2.020.2mm/yr( Zervas 2009 ).Assumingasteadyrate,themagnitudeofsealevelriseshouldbe5cmin22.7years.Resultsofthismodelingstudypredictanincreaseintheebbshoalvolumeatthissiteofbetween3.6106and6.83106m3(2.23%to4.24%increase),forthepace-keepingmarshaccretionandstaticmarshscenarios,respectively;nearlyadoublingoftheebbshoalvolumeifaccretionhalts.Thelocallongshoresedimenttransportratehasbeenreportedtobeapproximately3.8105m3/yr( Dean 1988 ),totaling8.63106m3overthe22.7years.Thepredictedincreaseinequilibriumebbshoalvolumeisbetween41and79%ofthislongshoretransport.Astidalprismincreases,theebbshoalspreadsfurtheroffshoreandinthedowndriftdirection,andtheshoaloccupiesadeeperwaterdepth( BuonaiutoandKraus 2003 ; Carr-Bettsetal. 2012 ).Thischangeinlocationreducestheimpactofwave-inducedtransportoffoftheshoals.Ifall16inletsintheseaislandchainweretoexperiencesimilarincreasesinebbshoalvolume,thelongshoretransportalonecouldnotprovideadequatesedimenttosustainthisgrowth.ThisdeciencyinthesedimentbudgetcouldtriggershorelineretreatandbeachvolumelossfromthebarrierislandswithintheSeaIslandChain.Althoughthismodelwassetupforaparticularsite,theSt.MarysEntrance,theresultssuggestthattherelationshipsandconsequencesoftheseinterrelatedprocessesareapplicabletobarrierislandsystemsworldwide. 54

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2.5.2ComparisonwithPreviousModelingStudiesTherehavebeentwo,previouslypublished,modelingstudies,whichinvestigatetheinuenceofsealevelriseontidalinletslocatedalongtheWestFrisianIslandsintheNorthSea.Therststudy,by VanGooretal. ( 2003 )usesathree-elementsemi-empiricalequilibriummodelandthesecondstudy,by Dissanayakeetal. ( 2009 ),usesDelft3D,thesamemodelusedinourstudy.Bothpreviousmodelingstudiesconcludethatanincreaseinsealevelwoulddriveanincreaseincross-sectionalareaandadecreaseinebbshoalvolume. Dissanayakeetal. ( 2009 )hypothesizedthatthedecreaseinebbshoalvolumeismostlikelyduetothedecreasedbedfrictionfrominletchanneldeepening,allowingforhigheroodcurrentvelocitiesthroughtheinlet.Theinletsinthisareahaveexpansiveregionsofunvegetatedtidalats,withdifferentbasinhypsometriestothoseseenontheU.S.Atlanticcoast.Thismayaccountforthedifferenceinebbshoalchangepredictionsbetweenstudiesatthatlocationandtheresearchconductedinthisstudy.Ourresultsareinagreementwitheldobservationsreportedby Listetal. ( 1994 1997 )and FitzGeraldetal. ( 2004 2007 )atsiteslocatedwithinBaratariaBay,Louisiana,whichfoundanincreaseinbothinletchannelcross-sectionalareaandebbshoalvolume.StudiesoftheBaratariatidalinletshavebeenperformedtoshowhowamultipletidalinletsystemevolveswithhighratesofrelativesealevelrise(approx.10mm/yr)mixedwithsubstantialmarshloss( FitzGeraldetal. 2004 2007 ; Listetal. 1994 1997 ).TheBaratariaBayisconnectedtotheGulfofMexicobyfourtidalinlets:Abel,Barataria,Caminada,andQuatreBayou. Listetal. ( 1994 1997 )performedacomparativestudyofthebathymetricevolutionofa157kmreachofthisbarrierislandschain,locatedofftheLouisianacoastwestoftheMississippiRiverdelta,overthreesurveyperiods(1880s,1930s,and1980s),withdepthsoundingsbetween7kmlandwardoftheislandstoanoffshoredepthof12m(3000km2totalarea).Theirassessmentrevealedincreasesinebbshoalvolumeandtidalprismthatfollowedtherelationshipsdevelopedby Walton 55

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andAdams ( 1976 ).Theyconcludedthatthechangesinbarrierislandsandtidalinletsystemscannotbeconsideredindependentofthehydrodynamicandmorphologicbehavioroftheback-barrierwetlands. FitzGeraldetal. ( 2007 )lookedattheevolutionofthecross-sectionalareaofthefourtidalinletsconnectedtoBaratariaBayandfoundconsistentincreasesovertimeduetotheincreasedtidalprism,likelydrivenbylocalwetlandloss.Notably,thetotalcross-sectionalareaoftheinletshasquadrupledsince1880.ADCPswereusedtocalculatethetidalprismforeachoftheinlets,andtheresultingcomparisonswiththe Jarrett ( 1976 )equation,whichrelatestidalprismandinletcross-sectionalarea,showedthatthemeasuredtidalprismsof3(outof4)inletsfellwithinthe95%condenceintervalpublishedby Jarrett ( 1976 ).Theoneinletthatdidnotmatchthepredictedrelationship(BaratariaPass)hasasmallercross-sectionalareathanpredicted,which,theauthorspostulate,maybeduetothestratigraphyofthearea;theinletmaybetryingtocutintoconsolidatedclaysthatresisterosion.Measurementsfromtheeldstudies,describedabove,followasimilarqualitativetrendtothemodelingresultspresentedinthispaper. 2.6ConclusionsBecauseoftheircriticalroleinthecoastallandscape,theresponseoftidalinletsystemstosealevelriseisimportanttoconsideroverthecourseofthenextcentury.Inthispaper,wehavedemonstratedthattheaccretionarybehaviorofback-barrierwetlandsexertsignicantcontrolonthegeomorphicresponseoftheinletsystemsandtheirmorphologiccharacteristics(e.g.inletchannelcrosssectionsandebbshoals).Assealevelrises,marshesmustaccreteverticallyatacomparablerateinordertocounteractsubmergence.Ifmarshesdonotmaintainsufcientverticalaccretion,thesubmergedportionoftheback-barrierbasinwillincreaseinarealextent,whichleadstoanincreaseinthetidalprism.Ifthemarshvegetationaccretesatapacesufcienttokeepupwithsealevelrise,thenonlythemarshchannelswilldeepenandunvegetated 56

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coastlinewillbecomeooded.Weusedthetwoend-memberscenariosofzeromarshaccretionandpace-keepingmarshaccretiontobrackettherangeofpotentialinletsystemresponses.Aftersatisfactorycalibration,themodelingprocedureusedinthisstudycalculatesthatsealevelrise,inboththenon-accretingandpace-keepingmarshcases,drivesanincreaseintidalprismthroughtwomechanisms:(1)anincreaseinsubmergedbasinareaand(2)anincreaseinthetidalexchangeefciencyfromchanneldeepening.Sealevelrise,affectingalandscapewithnon-accretingmarshes,increasesthetidalprismapproximatelytwiceasmuchasalandscapewithmarshesmaintaininganaccretionarypacecomparabletorisingsealevel.Themorphologicconsequencesofthisincreasedtidalprismincludechangestotidalinletchannelcross-sectionalareaandebbshoalvolume.Equilibriuminletchannelcross-sectionalareaincreasesinboththenon-accretingandpace-keepingmarshexperiments.Inasystemexperiencingmarshaccretionequaltosealevelrise,theincreaseinequilibriumchannelareaisapproximately1.5timestheincreaseduetochanneloodingalone(i.e.elevatedwaterlevelsinthechannelduetosealevelrisealone).Inanon-accretingmarshlandscape,theincreaseinequilibriumchannelareaisapproximately3timestheincreaseduetooodingalone.Ebbshoalvolumesincreaseduetosealevelriseinbothnon-accretingandaccretingmarshes.Theebbshoalvolumeapproximatelydoublesforasystemwithnomarshaccretioncomparedtoasystemofpace-keepingmarshaccretion.Increasesinebbshoalvolumescouldprofoundlyimpacttheregionalsedimentbudgetandleadtochangeswithintheerosional-depositionalpatternsofadjacentshorelines. 57

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Figure2-1. MapoftheSeaIslandChainwithaninsetoftheSaintMarysRiverEntrancebasin.Thismapdisplaysvegetatedarea,NOAAtidalstation8720030,andADCPdeploymentlocations. 58

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Figure2-2. ContourmapoftheSaintMarysEntrancebasinbathymetryfromdataavailablefromtheNationalGeophysicalDataCenter(NGDC)CoastalReliefModelat3-arcsecondresolution. 59

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Figure2-3. ThecumulativedistributionoftheelevationswithintheSt.MarysRiverbasinmodeldomain(greenshadedarea).Barsontheleftrepresentthepercentageofsurfaceareawithineach1minterval,showingapeakaroundMSL.Theyellowareahighlightstheelevationsthatarewithinthespringtidalrange. 60

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Figure2-4. ThetemporaldistributionofoodedbasinareaintheSaintMarysRiverEntrancebasin(shadedarea)andthetemporallyaveragedoodedbasinarea(blueline).Therearetwodistinctregionsofelevations:themarshchannelsandthemarshplatform.Fromlowtohightide,themarshchannelsexpanduntilthemarshplatformedgeisreached(ZoneA).Asthemarshplatformisovertopped,thebasinarearapidlyexpands(ZoneB).Slowlytheoodedareaofmarshplatformexpandsuntilmaximumtidalelevationisreached(ZoneC). 61

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Figure2-5. AmapoftheNOAAFernandinaBeachCurrentsProjectbottom-mountedworkhorseADCPdeploymentlocationsandcorrespondingdeploymentdates.Thecoloredlocationdotsmatchthecoloredbarsforeachlocation.NameswereretainedfromtheNOAAproject,beginningwithFEBfollowedbythetwodigityear11andtheprojectstationnumber(01-04,07,and08). 62

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Figure2-6. WaterelevationsatNOAAtidestation8720030andtheco-locatedDelft3Dmodeledwaterlevels.Themodeldataisshowninblack,thetidalobservationsarered,andthedifferenceisshowningreen.Underpredictionshavepositivevaluesandoverpredictionshavenegativevalues. 63

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Figure2-7. TimeseriesplotsofsurfacecurrentspeedsfromADCPdataandco-locatedmodeldatafortherst3fulldaysofdeploymentateachstation.TheADCPdataiscoloredaccordingtothestationandthemodeldataisblack. 64

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Figure2-8. ScatterplotsofsurfacecurrentUandVcomponentswiththe95%condenceellipseandprincipalaxesfromthesixNOAAADCPstationsandco-locatedmodeldata.TheADCPdataiscoloredaccordingtostation,theco-locatedmodeldataisblack,andtheprincipalaxesaredashedlines.Noteunequalsizeaxestohighlightdifferencesinellipses. 65

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Figure2-9. ModelcomparisonswithNOAAADCPdata.A)Themeansurfacecurrentspeed,B)thestandarddeviationofthesurfacecurrentspeed,andC)theprincipalaxisdirectionforthesixNOAAADCPstations(red)andtheco-locatedmodeldata(blue). 66

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Figure2-10. Modeloutputofwaterlevel,instantaneousdischarge,andcalculatedtidalprism.A)Thewaterelevationsintheinletchannel,B)themodeloutputofinstantaneousdischargethroughtheinlet,andC)thecalculatedtidalprismforeachtidalcycleduringa52daysimulation.Tidalprismcalculationsarebetween1.3108m3and2.7108m3forthissimulation,withameanof1.87108m3.Reportedvaluesby Bruunetal. ( 1978 ), O'BrienandClark ( 1974 ), EnvironmentalScienceandEngineering,Inc. ( 1980 ),and Powelletal. ( 2006 )areplottedin(C)ashorizontaldashedlines. 67

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Figure2-11. Thechangeinthetemporaldistributionofoodedbasinareaandthechangeinthetemporallyaveragedbasinarea(verticallines)withsealevelrise.Theblacklinesshowinitialbasinareadistribution,thebluelinesare10cmincrementalsealevelrisestepsbetweenzeroand100cm.Asealevelriseof50cmisshowningreen,and100cmisshowninred.Thechangesinbasinareawithsealevelintheaccretingmarshplatformscenarioarelimitedtochanneledges.Inthemodelscenarioswithastaticmarshplatform,allareasofthebasinthatareoodedbecomeoodedforalongerportionofthetidalcycle. 68

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Figure2-12. Thechangeintemporallyaveragedoodedbasinareaduetosealevelrise,forastaticmarshplatformandamarshplatformaccretingatthesamepaceassealevelrise. 69

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Figure2-13. Theidealtidalprism,themodeledtidalprism,andtheratioofmodeledtoidealtidalprism.A)Theidealtidalprism(circles)andmodeledtidalprism(squares)forstaticmarshes(red)andaccretingmarshes(blue),andB)theratioofmodeledtoidealtidalprism.Theincreaseinthisratioindicatesthatthetidalprismexchangebecomesmoreefcientwithincreasesinsealevelduetoareductionintidalwaveattenuation. 70

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Figure2-14. Thechangeinmodeledtidalprism(solidlines)fromthebasinareaincrease(circles)andfrommoreefcienttidalexchange(dashed),forstaticmarshes(red)andaccretingmarshes(blue). 71

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Figure2-15. Changeincross-sectionalareaandebbshoalvolumeduetosealevelrise.Thechangeincross-sectionalareaduetochannelooding(green)andthechangeintheequilibriumcross-sectionalareaforstaticmarshes(red)andaccretingmarshes(blue)isshownin(A).Thechangesinequilibriumebbshoalvolumewithsealevelriseforstaticmarshes(red)andaccretingmarshes(blue)isshownin(B).Thegreyareashighlighttherangeofpredictivechangesifmarshverticalaccretionwerebetweentheend-memberscenarios. 72

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CHAPTER3ECOGEOMORPHICFEEDBACKSBETWEENSEALEVELRISE,ESTUARYHYDRODYNAMICS,ANDVERTICALMARSHACCRETIONThemorphologicresponseofatidalinlettosealevelriseisdependentonthemarshplatformresponseintheback-barrierbasin.Theverticalaccretionrateofthemarshsystemcontrolstheoodedbasinareaandthetidalwaveattenuationintheestuary,regulatingthetidalprism,inletcross-sectionalarea,andebbshoalvolumes.Alterationsofthehydrodynamicswithintheestuaryleadtochangesinthespatialdistributionofmarshsubmergence.Submergencedurationimpactstheaccessofoxygenbyhalophyticvegetationand,therefore,thestabilityofthemarshplatform.Deviationoftemporalsymmetryofthetidalcurrentvelocitythroughtheinletchannelresultsinadifferenceinnettransportbetweenthebasinandocean.Nettransportinuencestheavailabilityofsedimentforthemarshplatform,acriticalcomponentofmarshverticalaccretion.Inthisstudyweusedanumericalmodeltoinvestigatetheroleofmarshverticalaccretiononthehydrodynamicresponseintheback-barrierbasintochangesinsealevelrisebyinvestigatingtwomarshaccretionend-memberscenarios:(A)noverticalmarshaccretion,and(B)marshaccretionatarateequaltotherateofsealevelrise.Weransimulationsforasuiteofsealevelrisescenariosbetween0and100cmat10cmincrementfortheSaintMarysEntrance,aninletrepresentativeofamixed-energy,tidedominatedsystem.Modelresultsindicateforastaticmarshplatform(scenarioA),sealevelrisecausesareasfarfromtheinletchanneltobesubmergedforlongerperiodsoftimethanareasclosetotheinletchannel,duetoareductionindrainageefciencyduringtheebbtidalexchange.Thetidalasymmetryforthissystembecomesmoreooddominantwithsealevelrisebecausethedifferenceinstoragecapacitybetweenlowandhightideisreduced.Theinletsystemtransitionsfromebbtoooddominanceathighlevelsofsealevelrise(>70cm).Whentheplatformisabletoaccreteverticallyatthesamerateassealevelrise(ScenarioB),thesystembecomesslightlylessebbdominant,withmoregrosssedimenttransportthroughtheinlet, 73

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butsimilarnettransport.Sealevelrisealterstheback-barrierbasinhydrodynamics,changingthedistributionofallochthonoussedimentsandthesubmergenceofthemarshplatform,leadingtofeedbacksbetweenmarshaccretion,hydrodynamics,andinletmorphology. 3.1IntroductionTheresponseofbarrierislandcoastalsystemstosealevelriseiscriticallyinuencedbytidalinletmorphologyandhydrodynamics.Inletsactaspartofasandsharingsystem,inwhichtheinletchannel,ebbandoodshoalcomplexes,andadjacentbarrierislandsareinterconnected( Dean 1988 ; Hayes 1979 ).Chapter 2 explorestherelationshipbetweenmarshverticalaccretionintheback-barrierbasinandthetidalprism,cross-sectionalarea,andebbshoalvolumeforarangeofrelativesealevelrisescenarios.Resultsofthatstudyshowthatmarshplatformswithnoverticalaccretionleadtoanampliedincreaseintidalprism,inletcross-sectionalarea,andequilibriumebbshoalvolumewithsealevelrise.Increasesintheequilibriumebbshoalvolumemayprovideasinkforlongshoresedimenttransportinthevicinityofaninlet,leadingretreatofadjacentshorelines.Sealevelriseinducedchangesinthehydrodynamiccharacteristicsofaninletsystemcanchangetheresilienceofamarshplatformbyalteringtheavailabilityofsedimentandthedurationofvegetationsubmergence.Inthisstudy,weusedanumericalmodeltoinvestigatehowsealevelandmarshplatformelevationinuencethespatialdistributionoftidalrangeandmarshsubmergencedurations,aswellasthetidalinletvelocityasymmetry,inordertounderstandhowchangesinsealevelwouldinuencefactorsthatcontrolmarshplatformresilience. 3.2BackgroundMarshverticalaccretionrateisafunctionoftidalrange,sedimentavailability,andvegetationproductivitysincethemarshplatformaccretesthroughtheaccumulationofautochthonousplantmaterialandallochthonoussediment( ArgowandFitzGerald 2006 ; D'Alpaosetal. 2011 ; KirwanandGuntenspergen 2010 ; Kirwanetal. 2010 ; 74

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Mudd 2011 ; Reed 1995 ; Simasetal. 2001 ).Changesinthehydrodynamicsofaninletsystemduetosealevelrisemayimpactthesefactors,leadingtofeedbacksbetweenthemarshvegetation,hydrodynamics,andmorphodynamics.Assumingnonetsedimentaccumulationduetoareductioninowvelocity,increasedwaterdepthdecreasesthefrictionintheinletandbasinchannels,modifyingthespatialdistributionofowthroughoutthebasin,thetidalcurrentvelocityasymmetry,andthedurationofsubmergenceofthemarshplatform( SeeligandSorensen 1978 ; SpeerandAubrey 1985 ).Changesinthetidalvelocityasymmetryalterthenetowofallochthonoussedimentsintoandoutofthebasin,aswellastheavailabilityofsedimentforaccretionofthemarshplatform( Gardineretal. 2011 ).Therearetwoprincipalcontrolsontidalinletvelocityasymmetryalteredbychangesinrelativesealevel:(1)frictionalinteractionbetweenthetidalcurrentandchannelbottoms,and(2)theintertidalwaterstorage.Highratiosoftidalamplitudetochanneldepthcorrespondtoshortebbdurationswithhighoodvelocitiesandooddominantsedimenttransport( FriedrichsandAubrey 1988 ; SeeligandSorensen 1978 ; SpeerandAubrey 1985 ).Channeldeepening(andthereforefrictionreduction)shouldmakeasystemlessooddominant(moreebbdominant).Ahighratioofintertidalstoragevolumetobasinchannelvolumeprolongsooddurationwithhigherebbvelocitiesandebbdominantsedimenttransport( BoonandByrne 1981 ; DiLorenzo 1988 ; FriedrichsandAubrey 1988 ; NummedalandHumphries 1978 ; SpeerandAubrey 1985 ).Athightide,thelargeroodedsurfaceareadoesnotdrainefcientlythroughtheinlet,leadingtoasubstantiallagtimebetweentheoceanandbasintidalpeaks.Duringlowtide,thesurfaceareaissmallerandthereisashorterlagtimebetweentheoceanandbasintidalpeaks.Thesedifferencesinlagtimesresultinprolongedooddurationsandhigherebbowvelocities/shearstresses( FitzGeraldandNummedal 1983 ). 75

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Ifmarshaccretionrateisnotsufcienttokeeppacewithsealevelrise,themarshplatformwillbecomesubmergedforprolongedperiodsoftimesandthevegetationwillbedeniedadequateoxygen,leadingtoplantwaterlogginganddrowning( D'Alpaosetal. 2011 ; Kirwanetal. 2010 ; MariottiandFagherazzi 2010 ; Morrisetal. 2002 ; Orsonetal. 1985 ).Localplantdrowningalterstheproductivityofthemarshplatformsystemandreducestheavailabilityofautochthonoussediments,makingtheentiresystemmorevulnerabletosubmergencewithsealevelrise( Orsonetal. 1985 ). 3.3Methods 3.3.1StudySiteThestudysiteforthisresearchistheSaintMarysEntrance(SME,Figure 3-1 ),aninletlocatedonsoutheasternAtlanticcoastoftheNorthAmerica,atthesouthernendofaregionreferredtoastheSeaIslandChain,whichextendsfromsouthernNorthCarolinatonorthernFlorida.TheSMEislocatedonthestateborderbetweenFloridaandGeorgia,atthesouthendofCumberlandIslandandthenorthendofAmeliaIsland.Theinlethascharacteristicsthataretypicalofamixed-energytidedominatedsystem( Hayes 1979 ),withalargeebbshoalcomplexandanexpansiveregion(197km2)ofwetlandsintheback-barrierbasin.Theback-barrierbasinconsistsofalarge,atmarshplatformdissectedbytidalchannels.Figure 3-2 showsthe3arc-secondresolutionbathymetryofthebasinderivedfromthefreely-available,NationalGeophysicalDataCenter(NGDC)CoastalReliefModel,withthemeanhighwater(MHW)andmeanlowwater(MLW),at0.88mand-0.95mrelativetomeansealevel(MSL),shownasthinandthickblackcontourlines,respectively.ThecumulativedistributionofelevationwithinthebasinisshowninFigure 3-3 asthegreenshadedregion.Theelevationsaredividedinto1mintervals,andthepercentageofthebasinthatresideswithineachofthoseintervalsinshowninthebargraphontheleft.Theproportionofbasinareathatlieswithinthespringtidalrangeisshowninyellow. 76

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Giventhatasubstantialfractionofthebasinhasanelevationwithinthespringtidalrange,thesizeoftheoodedbasinareamorethandoublesduringatidalcycle.Thetemporaldistributionoftheoodedbasinareacalculatedusingmodelsimulationsdescribedinsection 3.3.2 isshown,astheshadedarea,inFigure 3-4 .Asthebasinllsduringtherisinglimbofthetidalcycle,theslopedchanneledgesbecomesubmerged,then,asthemarshplatformedgeisovertopped,thefractionofthebasinsubmergedquicklyincreasesdrasticallyinsize.Asthetidecontinuestorise,theoodedareaoftheplatformcontinuestoexpand,untilthemaximumelevationisreached.Thereversepatterniswitnessedduringtheebbingportionofthetidalcycle. 3.3.2ModelSetupThethree-dimensionalhydrodynamicnumericalmodelingsuite,Delft3D,wasusedtoinvestigatetheroleofverticalmarshaccretiononthehydrodynamicresponseoftheback-barrierbasintoincreasesinsealevelrise.Weappliedtwoend-memberresponsesofmarshaccretiontothemodel:(A)noverticalmarshaccretion,and(B)verticalmarshaccretionthatkeepspacewithsealevelrise.AreasofmarshcoverageweredeterminedusingvegetationcoverageinformationavailablefromtheNationalWetlandsInventory(NWI)providedbytheU.S.FishandWildlifeService.Inmodelsimulationsusinganaccretingmarshplatform(scenarioB),onlythebasinchannels,unvegetatedshorelines,andoceandeepenedwiththerisingsealevel.Insimulationsusingastaticplatform(scenarioA),increasestomeansealevelwereappliedevenlythroughouttheentiremodeldomain(i.e.ocean,basinchannels,marshplatforms).Aseriesofmodelsimulations,coveringarangeofsealevelrisemagnitudes,between0and100cmat10cmincrements,wereconductedforbothmarshaccretionscenarios.Themodelgridiscurvilinear,consistingofahorizontalgridof419x319cells,whichisfurtherexpandedverticallyinto8layers.Theaveragegridspacinginthebasinis100mx100m,increasinginthex-direction(eastward)intothedeepeningoceandomain.Weutilizedasigmacoordinatetransformationintheverticaldirection, 77

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whichdivideswaterelevationintoevenlyspacedslices,varyinginthicknesswithchangesinwaterelevation.Inthesemodelsimulations,wedonotincorporatesedimenttransportormorphologicchanges,becauseofalackofsufcientinsituobservationstoadequatelycalibratesimulationsofsedimenttransportwithinthesystem.AcalibrationandvalidationstudywasperformedusingNOAAADCPdata,tidalstationwaterelevations,andpreviouslydocumentedtidalprismmeasurements.DetailedinformationandresultsofthisstudycanbefoundinChapter 2 3.4Results 3.4.1SpatialDistributionofTidalRangeandMarshSubmergenceAsmentionedabove,forsimulationsinwhichthemarshplatformisabletomaintainverticalaccretionatthesamepaceassealevelrise,onlythebasinchannelsandtheiradjacentunvegetatedshorelinehaveincreaseddepth.Deeperbasinchannelsreducethedegreeoftidalwaveattenuationwithinthebasin,leadingtoanincreaseinthetidalrangeinareasfar(10-20km)fromtheinletchannel.ThiscanbeseenintheFigure 3-5 ,wherethechangeintidalrange,withrespecttoitsvalueforpresentsealevel,isshownfor10,20,40,60,80,and100cmofsealevelrise.Channellocationsclosetothethroatshowsmallincreasesintidalrange(e.g.1-5cmpermeterofsealevelriseforsiteswithina10kmalong-channelpathoftheinletthroat),butthetidalrangeincreasegrowswithgreateralong-channeldistances.Theincreaseintidalrangeatdistalregionsofthebasinraisestheeffectivebasinareacontributingtothetidalprism.Anincreaseintidalrangealsooccursonunvegetatedsectionsofthechanneledgesassealevelrisecausesthoseareastoresidelowerwithinthetidalrange.Forsimulationsinwhichmarshplatformelevationisstatic,sealevelrisecausesadecreaseinthetidalrangeinchannelreacheswithinapproximately15kmoftheinletthroatbecausewaterisredistributedontothemarshplatform.Oncetheowisallowedtoexpandhorizontally,theverticalchangeinwaterelevationisreduced.Figure 3-6 78

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showsthechangeintidalrangethroughoutthebasinonastaticmarshplatform.Tidalrangesforallareasofthemarshplatformincrease,withthegreatestincreaseforlocationsclosetotheinletchannel,probablybecausethesearethelocationswheretidalexchangeismostefcient.Figure 3-7 showsthechangeintidalrangeforsevenlocationswithinbasinchannelsinordertohighlightthedifferenceintidalrangechangebetweenthemarshaccretionscenarios.Thefourpointswithin15kmfromtheinletchannelexperienceaslightincreaseintidalrangewithsealevelrisewhenthemarshplatformisaccretingverticallyatthesamepaceassealevelrise.Pointsinmoredistalregions,withlongeralong-channeltraveldistances,experiencemoredramaticincreasesintidalrangewithsealevelrise.Asimilartrendisseeninthecaseofastaticmarshplatform,wherethesedistalpointshaveincreasedtidalrangesduetoareductioninfrictioninthechannelsallowingmorewatertoaccessthisportionofthebasin.Whenthemarshplatformisstatic,thecloserpointsdecreaseintidalrangeduetothedistributionofwaterontotheadjacentmarshplatform.Whenthemarshvegetationisabletoaccreteverticallyatthesamepaceassealevelrise,littlechangeinsubmergencedurationshouldoccursincetheplatformmaintainsasteadyelevation,relativetosealevelrise,withinthetidalrange.Underpresentsealevelconditions,themarshplatformissubmergedapproximately50%ofthetimethroughoutthebasin.Modelresultsshowthatwhenmarshplatformelevationisstatic(non-accreting),thesubmergencedurationincreasesnon-uniformly,inspiteofanearlyuniformmarshplatformelevationthroughouttheback-barrierbasin.Figure 3-8 showsthespatialdistributionofsubmergencefrequencyforsealevelrisemagnitudesof0,20,40,60,80,and100cmonastaticmarshplatform.Distalmarshplatformareas,locatedfarfromtheinletchannel,experiencelongerdurationsofsubmergence,foragivensealevelrise,ascomparedtoproximalareas. 79

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Figure 3-9 displaysthechangeinthewaterdepthatthreepoints(SiteA,SiteB,andSiteCshowninthegurefromtoptobottom)onthemarshplatformforsealevelriseconditionsof0,20,40,60,80,and100cm,onastaticmarshplatform.SitesA,B,andCareapproximately18,13,and9kmalong-channelfromtheinletthroat,respectively.Whilethereareincreasingmaximumdepthsduringhightidewithsealevelriseatallthreelocations,SiteAshowsincreasinglowtidelevelsbecausethewaterdoesnotfullydrainingfromtheplatformduringlowtide.Theseplotsillustratethenon-uniformspatialdistributionofdrainageefciency.Areasofthemarshplatformsthatarefartherfromtheinletchanneldonotfullydrainduringatidalexchangeand,therefore,haveaslightlylowerincreaseintidalrangeandmaintainalayerofwaterforalargerproportionofthetidalcycle. 3.4.2TidalVelocityAsymmetryFigure 3-10 (A)showsavelocity-stageplotforresultsfromthreenumericalmodelsimulations:(i)forthepresentsealevelcondition,(ii)forasealevelriseof60cmonastaticmarshplatform,and(iii)for60cmonanaccretingmarshplatform.Theplotillustratestheowspeedatdifferenttimesduringthetidalcycle.ThetimeseriesofwaterelevationinthechannelandowspeedsareshowninFigure 3-10 (B).Thevelocity-stageplotdemonstratesthatthereisareversalfromoodingtoebbingow(negativetopositivevelocityvalues),referredhereinashighwaterowreversal(HWFR),thatoccursnearlytwohoursafterhightide,duringthefallinglimbofthetidalcycle.Thisdelayisduetothephaseshiftbetweenthetideinthebasinandoceancausedbytheinertialeffectofthewaterintheinlet.HWFRisobservedtooccurattwodiscretewaterlevels.Theowalsoreversesfromebbingtoooding(positivetonegativevelocityvalues),referredtohereinaslowwaterowreversal(LWFR),duringtherisinglimbofthetidalcycle,alsoattwowaterlevels.Thetwowaterlevels,occurringduringeachowreversal,arecausedbydiurnalinequalityproducedbytheeffectofthemoon'sdeclination,whichcontributetochangingthewaterlevelofhighandlowtideoccurrence. 80

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Forpresentsealevelconditions,owintothebasin(tidalooding)occursforalongerportionofthetidalcyclethanowoutofthebasin(tidalebbing);thiscausesthepeakowspeedstobegreaterduringtheebbexchangethanduringtheoodexchange.Thisdifferenceinowdurationsiscreatedbytheinteractionofthetidalharmoniccontsituentsoftheforcingtides.Sealevelrisecausespeakcurrentvelocities,duringbothebbandoodexchange,toincreaseinboththestaticandaccretingmarshscenarios,thoughtheeffectisdemonstrablygreaterinmodelsimulationsforthestaticmarshplatform.Thepositionwithinthetidalcycleatwhichtheowreversesfromoodingtoebbingdoesnotchangesignicantlywithsealevelriseineitherofthemarshaccretionscenarios.Thereversalfromebbtooodtidalexchangeisdelayedinthesimulationswithastaticmarshplatform,causingtheebbingowtooperateoveranincreasedportionofthetidalcycle.Theinstantatwhichthewaterelevationonthebasinsideoftheinletchannelisequaltotheelevationontheoceansideoftheinletchannelrepresentsattimeatwhichthereisnotidalowthroughtheinletchannel-identiedaboveasthereversals(HWFRandLWFR).ThechangeinthetimingofHWFRandLWFRasafunctionofsealevelriseisshowninFigure 3-11 .Figure 3-11 (A)showsthischangeforanaccretingmarshplatformandFigure 3-11 (B)showsthischangeonastaticmarshplatform.AnincreaseinthelagduringHWFRshouldprolongoodtidalexchangeandanincreaseinthelagduringLWFRshouldprolongebbtidalexchange.Therelativedurationsofeachlagchangedeterminesifthesystemisintransitiontoamoreoodorebbdominantsystem.Onamarshplatformthatkeepspacewithsealevelrise,theLWFRlagincreasesandtheHWFRlagdecreases,leadingtoanoverallincreaseinthedurationoftheebbtidalexchange.SealevelriseonastaticmarshplatformincreasesthelagofboththeLWFRandHWFR.Inthiscase,theLWFRlagisgreaterthantheHWFRlag,andtherefore,thesystemhasincreasedebbtidalexchangedurations. 81

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Atpresentsealevel,theinletisclassiedasanebbdominantsystembecauseofthehigherebbdirectedcurrentvelocities.Bedloadsedimenttransportisproportionaltothecubeofthespatially-averagedvelocityacrosstheinletchannelresultinginanetseawardsedimenttransportinebbdominantsystems( Bagnold 1963 ; FryandAubrey 1990 ).Figure 3-12 and 3-13 showmodelresultsofthespatiallyaveragedvelocity,thecubeofthespatiallyaveragedvelocity,andcumulativesumofthecubeofthespatiallyaveragedvelocityfortheaccretingmarshplatformandthestaticmarshplatform,forsealevelrisemagnitudesrangingbetween0and100cmat10cmintervals.Positivevaluesrepresentowintheebbdirection.Forbothmarshaccretionscenarios,themagnitudeofthespatiallyaveragedvelocityincreasesintheebbandooddirectionwithsealevelrise.Thisincreaseisampliedwhenthemarshplatformisstatic.Thevelocitycubedisusedasanestimateofnettransportinordertoestimatedominantdirection.Resultsfortheaccretingmarshplatformshowanoverallslightincreaseinthegrosstransportthroughtheinlet,andaslightshifttowardthebalanceoftransportintheooddominantdirection.Forastaticmarshplatform,thegrosstransportthroughtheinletincreases,andthenettransporttransitionsfrombeingdominantlyintheebbdirectiontotheooddirectionwithincreasesinsealevel.Figure 3-14 displaysmodelresultsoftheratioofoodtoebbtransport,estimatedasthespatially-averagedvelocitycubedfortherangeofsealevelmagnitudesinvestigatedonanaccretingandastaticmarshplatform.Onanaccretingmarshplatform,theratioofoodtoebbtransportslightlyincreaseswithhighermagnitudesofsealevelrise,implyingthatthesystembecomesslightlylessebbdominant.Whentheplatformisstatic,theratioofoodtoebbtransportincreases,becomingaooddominantsystemathighlevelsofsealevelrise(>70cm).Oncethetransitiontoooddominanceoccurs(ratioofoodtoebbsedimenttransportgreaterthan1),theratioofoodtoebbsedimentexchangebecomeslesssensitivetosealevelrise. 82

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3.5DiscussionInourmodelresults,werevealnon-uniformincreasestothevegetation(marshplatform)submergencedurationwhenthemarshwasstatic(non-accreting),despitetherelativelyattopographyontheplatforms.Itisnotablethat,holdingotherfactorsconstant(sedimentdistribution,vegetationtypes,etc.),marshvegetationatgreaterdistancesfromtheinletchannelmay,surprisingly,bemorevulnerabletodrowningfromanincreaseinlocalsealevel.Thisphenomenonarisesbecauseofthedecreaseddrainageefciencyatdistalregionsofthebasin.Whenanareaofvegetationdiesoff,theplantsceasetocontributetotheallochthonoussedimentsandthemarshmaybecomelessefcientatverticalaccreting.Verticalaccretionatarateslowerthantherateofsealevelrisewillleadtoanincreasethesubmergencedurationsthatthesystemexperiencesduringincreasesinlocalsealevel,leadingtoafeedbackthatputstheentiremarshsystematriskofsubmergenceanddie-off.TheSMEback-barrierbasinhasalargeportionofmarshplatformatanelevationclosetopresentmeansealevelandisdissectedbynumeroustidalchannels.Theoodedareaofthebasinapproximatelydoublesinsizewhencomparingbetweenlowandhightide.Thistypeofbasinhypsometryisinlinewiththosedescribedtobeebbdominant,whichisseeninmodelresultsbytheprolongedooddurationandhigherquantitiesofnetsedimenttransportoutofthebasin,seaward.Boththefrictioninthechannelsandthedrainageefciencyofthesystemarealteredbychangestolocalsealevelandbytherateofverticalmarshaccretion.Inmodelexperimentswithaccretingmarshes,thebasinchannelsdeepen,therebyreducingthefrictionaldragwithinthesystem,whichwouldbeexpectedtoleadtoanincreaseintheebbdominanceofthesystem( FriedrichsandAubrey 1988 ; SeeligandSorensen 1978 ; SpeerandAubrey 1985 ).Thisisnotseeninourresults,possiblyduetotheoodingofunvegetedareasadjacenttothebasinchannelsimposingagreaterinuenceonthesystem.Thereis 83

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onlyaslightchangeinthetidalvelocityasymmetryinthissystem(approximately1%increaseintheratioper10cmofsealevelrise).Inmodelsimulationswithastaticmarshplatform,theoodedbasinareaincreasesduringlowertidalstagesandthedifferenceinthewaterstoragebetweenhighandlowtideisreduced.Thisreducesthedifferenceinthelagtimebetweentheoceanandbasinhighandlowtideoccurrencetimes,decreasingtheebbdominanceofthesystem.ThischangeisillustratedbytheincreaseintheLWFRlagshowningure 3-11 .Atsealevelriseover70cm,thechangeinstoragecapacityduetosealevelriseisreducedbecausethemarshplatformisoodedforthemajorityofthetidalcycle.Atthatpointfrictionalchangesbecomeamoresignicantforceforchangeinthesystem'sbehavior.Tidalasymmetryhasbeenfoundtobeanimportantfactorinthetransportandaccumulationofsedimentinaninletsystem.Whenthemarshplatformisstatic,thenetsedimenttransporttransitionsfromebbtoooddominance.Thisincreaseintransportintothebasinprovidesmoreallochthonoussedimenttothemarshplatform,increasingtheabilityoftheplatformtoaccretevertically.Acorrelationbetweenoodtidaldominantsystemsandhighratesofmarshaccretionhasbeendocumented( Gardineretal. 2011 ).Thisfeedbackcouldhelptoprotectthemarshsystembyallowingittomaintainverticalaccretionratesequaltosealevelrise.Increasesinsedimenttransportintothebasinmayhaveimplicationsforlongshoresedimentmovementandaccumulationonadjacentshorelines.Thesechangestothebalanceoftheinletsystemcouldalterthealongshoreerosional-depositionalpatternandleadtolocalshorelineerosion.Thisimpactmaybeampliedbychangestotheequilibriumebbshoalvolume,leadingtoalocalsedimentsinkinboththemarshplatformandtheebbshoal( LoveringandAdams inreview ). 84

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3.6ConclusionsInthisresearch,weaimtounderstandtheroleofverticalmarshaccretionandsealevelriseonsomeofthesedimentfeedbackwithintheestuary,specicallysubmergencedurationandtidalvelocityasymmetry.Submergencedurationisacriticalfactorinthevegetation'sabilitytomaintainadequateaccesstooxygenandtheplant'ssusceptibilitytodrowning.Ifthevegetationdrownsthenthereisdecreasedinsitusedimentproductionandtheentiremarshsystemwillhavelessautochthonoussedimentforverticalaccretion.Thetidalvelocityasymmetryintheinletsystemcontrolsthenettransportofsedimentintoandoutoftheestuary,impactingallochthonoussedimentdeliverytothemarshplatform.Usingtheresultsofournumericalmodelingstudy,weconclude: Submergencedurationincreasesnon-uniformlythroughoutthebasinwithsealevelrise,despitetherelativelyatmarshplatformtopography,duetoadecreaseindrainageefciencythroughoutthebasinandinletchannels.Sealevelrisecausesdistalreachesofthemarshplatformtomaintainalayerofwatercoverforalongerportionofthetidalcyclethanregionsmoreproximaltotheinletchannel,makingtheseareasmoresusceptibletowaterlogginganddrowning. Tidalvelocityasymmetryshiftsintheooddominantdirectionwithsealevelriseduethedecreaseinthedifferenceinstoragecapacitybetweenhighandlowtideforbothverticalmarshaccretionscenarios.Thiseffectisampliedwhenthemarshplatformisstatic. Ashiftinthetidalvelocityasymmetryintheooddominantdirectioncausesanincreaseinthenetsedimenttransportinthebasindirectionleadingtobasininllingandmoresedimentavailabilitytothemarshplatformforverticalaccretion.Thesedimentdeliveredtothemarshplatformisattheexpenseofothermorphologicelementsoftheinlet,includingtheebbshoalcomplexandadjacentbarrierislands,whichcouldleadtoerosionofthelocalshoreline. 85

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Figure3-1. MapofSaintMarysEntrancewithmarshvegetatedareahighlighted,insetonamapoftheSeaIslandChain.SMEisthesouthernmostinletintheSeaIslandchainlocatedontheAtlanticcoastoftheUS. 86

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Figure3-2. MapofelevationsintheSaintMarysEntrancereferencedtoMSL,withtheMLWandMHWelevationscontoursshown.ElevationsarefromtheNationalGeophysicalDataCenter(NGDC)CoastalReliefModelat3-arcsecondresolution. 87

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Figure3-3. ThedistributionofelevationsintheSaintMarysEntrancebasinisshowninthebargraph.Theelevationsthatliewithinthespringtidalrangearehighlightedintheyellowzone.Thegreyshadedregionsisthecumulativedistributionofelevations,indicatingthepercentageofthebasinthatisaboveeachelevation.ThereisapeakinthebasinareaisaroundMSL,withapproximately20%ofthebasinresidingwithin0.5mofMSLandapproximately25%withinthespringtidalrange. 88

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Figure3-4. ThetemporaldistributionofoodedbasinareaintheSaintMarysEntrancebasinforpresentsealevelconditions.Theoodedareaofthebasinisalways100km2orlarger.Asthetiderisesfromlowtide,thechannelbanksaresubmergedandtheoodedareaincreasestoapproximately150km2.Asthemarshplatformisovertopped,theoodedareagrowsquicklytonearly225km2.Atthatpoint,thetiderisestoitsmaximumelevationandtheoodedbasinareacontinuestoexpanduntilitreachesamaximumof240km2. 89

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Figure3-5. Thespatialdistributionofthechangeintidalrangefrompresentsealevelconditionsasaresultofasealevelriseonanaccretingmarshplatform.Increasesintidalrangeoccurinareasofthebasinchannelsthatarefartherfromintheinletandalongnon-vegetatedareasofthechanneledges.Littlechangeoccursonthemarshplatformorinthebasinchannelsthatareclosetotheinlet. 90

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Figure3-6. Thespatialdistributionofthechangeintidalrangefrompresentsealevelconditionsasaresultofasealevelriseonastaticmarshplatform.Increasesinthetidalrangeonthemarshplatformoccurovertheentireplatform,butthereisanampliedincreaseinareasthatareclosertotheinlet.Tidalrangeinthechannelsdecrease,likelyduetotheredistributionofwaterontotheadjacentplatforms. 91

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Figure3-7. Thechangeintheaveragetidalrangeover10tidalcyclesduetosealevelriseforsevenchannellocations,indicatedonthemapin(A).Thechangeisshownforanaccreting(B)andastatic(C)marshplatform.Whenthemarshplatformaccretesvertically,thetidalrangeinallofthechannellocationsincreaseduetoareductionintidalwaveattenuationwithchanneldeepening.Inthestaticmarshplatform,moreproximallocationsdecreaseintidalrangebecausetheowisdistributedbetweenthechannelsandthemarshplatform. 92

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Figure3-8. Thespatialdistributionofthesubmergencedurationduetosealevelriseonastaticmarshplatform.Thedurationisshownasthepercentageoftimeduringa10tidalcycleperiod.Initially,themarshplatformissubmergedapproximately50%ofthetime.Thesubmergencedurationsincreasethroughoutthebasinassealevelincreases,withmoredramaticincreasesatmoredistalareasofthebasin. 93

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Figure3-9. Timeseriesofwaterdepthatthreepointslocatedonthemarshplatformforsealevelriseof0to100cmat20cmintervalsforastaticmarshsystem.Thelocationofthepointsareindicatedonthemap,labeledassiteA,B,andC.Theyareatapproximately18,13,and9kmalong-channeldistancesfromtheinletchannel,respectively.Thetwoclosersites(BandC)tendtodrainmoreefciently,withamorerapiddecreasesinwaterlevel,reachingzeroatlowtideforsealevelriseupto60cm. 94

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Figure3-10. Thevelocitystageplotandthetimeseriesofthewaterlevelsandthespatiallyaveragedvelocitythroughtheinletforpresentsealevelandasealevelriseof60cmonastaticandanaccretingmarshplatform.Thetopplotshowsthevelocitystageplotforthespatiallyaveragedcurrentacrosstheinletcross-sectionforpresentsealevel(black)andforasealevelincreasesof60cmonanaccreting(blue)andstatic(red)marshplatformforthetidalsignalshowninthelowerplot.Onthelowerplot,thegreenlineisthetimeseriesofwaterelevationsandtheblack,blue,andredlinescorrespondwiththetopplot.Positivevaluesofcurrentspeedrepresentowoutofthebasin(ebbcurrents)andnegativevaluesrepresentowintothebasin(oodcurrent).Thechangefromebbtooodandfromoodtoebbareindicatedasthelowwaterowreversal(LWFR)andhighwaterowreversal(HWFR),respectively. 95

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Figure3-11. ThechangeintimeatwhichtidalowreversalsoccurduetosealevelriseforA)anaccretingandB)astaticmarshplatform.Thisisshownforthehighwaterowreversal(HWFR)andthelowwaterowreversal(LWFR).Thetimechangeofthereversalsindicatethechangeindurationoftheoodandebbtidalexchange,withanincreaseintheHWFRindicatinglongerooddurations,andanincreaseintheLWFRindicatinglongerebbdurations. 96

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Figure3-12. Thespatiallyaveragedvelocityacrosstheinlet,thecubeofthespatiallyaveragedvelocity,andthecumulativeofthespatiallyaveragedvelocitycubedforsealevelriseonanaccretingmarshplatform.Positiveowvaluesindicateowoutofthebasin(ebbcurrent)andnegativevaluesindicateowintothebasin(oodcurrent).Thecubeofthevelocityisusedasaproxyforthenetbedloadsedimenttransport,withthecumulativeofthecubeindicatingthedominanttransportdirection. 97

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Figure3-13. (Thespatiallyaveragedvelocityacrosstheinlet,thecubeofthespatiallyaveragedvelocity,andthecumulativeofthespatiallyaveragedvelocitycubedforsealevelriseonastaticmarshplatform..Positiveowvaluesindicateowoutofthebasin(ebbcurrent)andnegativevaluesindicateowintothebasin(oodcurrent).Thecubeofthevelocityisusedasaproxyforthenetbedloadsedimenttransport,withthecumulativeofthecubeindicatingthedominanttransportdirection. 98

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Figure3-14. Theratiooftheoodtoebbsedimenttransportproxyisshownforanaccretingmarshplatform(blue)andastaticmarshplatform(red)foranincreaseofsealevelbetween0and100cm.Thespatiallyaveragedvelocitycubedisusedasaproxyforsedimenttransport.Avalueofonerepresentsequaloodandebbtransport,withvalueslessthanoneindicatingebbdominanttransport,andgreaterthanonerepresentingooddominanttransport. 99

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CHAPTER4THEROLESOFMARSHCONFIGURATIONANDMARSHMARGINRETREATONTIDALINLETMORPHOLOGYMorphologicevolutionoftidalinletsdependsontheecogeomorphicbehavioroftheback-barrierbasin,andexertsastronginuenceonlocalshorelineresponsetosealevelrise.Atidalinletchannelactsastheprincipalvalveforwaterandsedimentexchangeinabarriersystem,butchangestoback-barrierbasinecology,hypsometry,andownetworkcongurationcanalterdischargeconveyedthroughtheinletchannel.Wetlandvegetationlosscanchangethetidalprismforaparticularinletby:(1)increasingthemap-viewareaofopenwaterexchangedbetweentheback-barrierbasinandtheoceanduringatidalcycleand(2)reducingthespatialrateoftidalwaveattenuationwithinthebasin.WeuseasimpleconceptualmodeltoexplorethegeomorphicresponseoftwoFloridainlets,ofcontrastingwetlandcongurations,touniformbackbasinvegetationlossthatmightresultfromcurrentprojectionsofsealevelrise.Allresultsshowthatvegetationlosscausesanincreaseintidalprism,inletcross-sectionalarea,andebbshoalvolume,butinletswithwetlandcongurationsthatstronglyincreasetidalwaveattenuationintheback-barrierbasinhaveanampliedresponsetovegetationloss.Usingempiricalrelationships,wendthataonepercentlossofback-barrierbasinvegetatedarearesultsinanincreaseofebbshoalvolumebyanamountapproximatelyequivalenttoannualtobienniallongshoresedimenttransportratesalongtheFloridaAtlanticcoast.Theconceptualmodeldevelopedinthisstudycanbeusedtoexaminemorphologicresponseoftidalinletsystemstowetlandvegetationlossatsimilarbarrierislandcomplexesworldwide. 4.1IntroductionTheresponseofatidalinlettosealevelrisehasbeenshowntobehighlydependentontheecogeomorphicresponseofvegetationintheadjoiningback-barrierbasin.TheBaratariaBay,locatedinsoutheasternLouisiana,hasexperiencedmarshlossduetosealevelriseandhighenergystormwaves( Barras 2006 ; Barrasetal. 100

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1994 ; BritschandDunbar 1993 ),whichhasledtoanincreaseinthetidalprismoftheinterconnectedfourinletcomplex,anincreaseinthecross-sectionalareaoftheinletchannels,andanincreaseinebbshoalvolumes( FitzGeraldetal. 2004 2007 ; Listetal. 1994 1997 ).Studiesoftheareahaveshownthatduringthepast100yearstherehasbeenarapidincreaseinthenumberandsizeofinlets( Levin 1993 ; McBrideetal. 1992 ),whichmaybeadirectresponsetoincreasesintidalprismvolumes.Theincreaseinebbshoalvolumeresultingfromincreasedtidalprismisinagreementwiththepredictiverelationshipdevelopedby WaltonandAdams ( 1976 )( Listetal. 1997 ). FitzGeraldetal. ( 2007 )foundthatthefourtidalinletshavequadrupledinsizesince1880.Threeofthefourinletsfellwithinthe95%condenceintervalofthetidalprismandcross-sectionalarearelationshipdevelopedby Jarrett ( 1976 ).Relationshipsbetweentidalprismandmorphologyhavebeenextensivelystudiedandquantied,however,theprocessbywhichwetlanddegradationandconversiontoopenwaterexertscontrolonthetidalprismofasystemmustbefurtherexplored.StudiesusingtheHadCM3climatemodelpredictthat,underanIPCCSRESA1FIworld,thepotentialworldwidecoastalwetlandlossduetosealevelriseisestimatedtobe5-20%bythe2080s( Nicholls 2004 ).Thisstudyexaminestheinuenceofback-barrierbasinvegetationlossontransformationofthetidalprismand,subsequently,cross-sectionalareaandebbshoalvolume.Weinvestigatetwomechanismsfortidalprismchangeresultingfromwetlandareaconversiontoopenwater:(1)thecontributionofincreasedback-barrierbasinopenwaterareatotidalprismvolume,and(2)reductionintidalwaveattenuationwithintheback-barrierbasin.Weinvestigatetwoinletswithsimilartidalrangesandwaveclimatesbutwithstronglycontrastinginitialecogeomorphicconditionsintheiraccompanyingback-barrierbasins,inordertohighlightthecontroloftheinitialwetlandcongurationontheevolutionofthetidalinletduetovegetationdeterioration.Weconcludewithadiscussionoftheimplicationsofcontinuedsealevelriseonthemorphologicevolution 101

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oftidalinlets,ebbshoal,andadjacentbeach/dunecomplexesandcommentontheapplicationofthisconcepttobarriersystemsworldwide. 4.2ModelDetailsWehavedevelopedaconceptualmodeltoexploretheprocesslinkagesamongback-barrierbasinwetlandvegetation,hydraulicsofatidalinlet,andthegeomorphicevolutionoftheinletsystemunderascenarioofwetlandconversiontoasubtidalenvironment.Figure 4-1 organizestheprocessesandlinkages,whicharedescribedinsomedetail,below.Iftherateofsealevelriseisrapidenoughtooutpaceverticalaccretionofthevegetation,non-aquaticplantsmayexperiencerootsubmergenceforprolongedperiods,preventingaccesstooxygen,whichwillpromotewaterloggingandsubsequentdrowning(Figure 4-1 ,ProcessA).Asplantdrowningoccurs,thewetlandsystemlosesbiomass,decreasingtheamountofinsitusedimentproduction.Thisinhibitsthebasin'sabilitytoaccretevertically,andtheback-barrierecosystemmaybecomemorevulnerabletoinundationfromsealevelrise( Muddetal. 2009 ; Orsonetal. 1985 ).Thesusceptibilityofsaltmarshestoinundationhasbeenshowntobedependentonthesedimentsupplyandtidalrangeofthesystem;systemswithgreatersedimentavailabilityandhighertidalrangeareabletoaccreteverticallyatamorerapidpace( D'Alpaosetal. 2011 ; KirwanandGuntenspergen 2010 ; Kirwanetal. 2010 ; Reed 1995 ; Simasetal. 2001 ).Thereexistsathresholdrateofsealevelriseforwhichmarshesfailtomaintainasufcientverticalaccretionrate;ifthisthresholdvalueisreached,thendegradationcanbeexpectedtocommenceapproximately30-40yearslater( Kirwanetal. 2010 ).Mangroveforestsrespondsimilarlytosealevelriseandaresensitivetotheavailabilityofallochthonoussediments( EllisonandStoddart 1991 ).Therelationshipbetweensealevelriseandvegetationdegradationisnotquantitativelyaddressedinthisstudy,butisakeycomponentinthesequenceofback-barrierbasinexpansion.Sealevelrisecouldleadtosubmergenceoflow-lying,unvegetatedland,generatingincreasedbasinareaandtidalprism(Figure 4-1 ,ProcessB).Inthis 102

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study,thisisconsideredanegligibleincreasesincecoastalstructuresbordermostunvegetatedsectionsofthebasinboundariesinourstudysites,butthisshouldbeaddressedinundevelopedlocations.Sealevelriseincreasesdepthintheback-barrierchannelstherebyreducingthespatialrateoftidalwaveattenuation(Figure 4-1 ,ProcessC),acomponentwhichissignicantlysmallerthantheeffectsofvegetationontidalwaveattenuation( MollerandSpencer 2002 )andisignoredinthisstudy.Theactualtidalprismofaninlet(P)canbeestimatedastheidealtidalprism,wherethetidalexchangeisinstantaneousanduniformthroughoutthebasin,lessthelossintidalprismduetotidalwaveattenuation.Ateachofourstudysites,theinletconnectsalong,narrow,shore-parallelbasintotheocean.Weparameterizebasingeometries,bydeningtwosectionsofbasinseparatedatthelocationoftheinletchannel,andbycalculatingthelengths(L1andL2)andmeanwidths(w1andw2)ofeachsection(Figure 4-2 ).Formorecomplexbasingeometries,thebasinmaybesubdividedintomoresections.Weassumethatthetidalwaveheightattenuatesataspatially-uniformrate(R)withinthebasin.Undertheseassumptions,thetidalprismcanbecalculatedas P=H(L1w1+L2w2))]TJ /F9 11.955 Tf 13.15 8.09 Td[(1 2R(L21w1+L22w2),(4)whereHisthetidalrange.Itisexpectedthatthevegetationlosswouldoccurfrommarshedgeerosion( Allen 1997 ; D'Alpaosetal. 1993 ; FitzGeraldetal. 2007 ; Kirwanetal. 2008 )orseawardedgeretreatofmangroves( Ellison 1991 ).Areductioninwetlandareawould,therefore,increasechannelwidthandreducethetortuosityofthesystem;wetlandvegetationlossshouldreducetidalwaveattenuationintheback-barrierbasin(Figure 4-1 ,ProcessD).Decreasedtidalwaveattenuationincreasestheactualtidalprism,P,orthevolumeofwatermovingthroughthebasinduringatidalcycle(Figure 4-1 ,ProcessE).Initialmeanattenuationratescanbeestimatedusingequation 4 ifbasingeometryandtidalprismareknown.Weassumethattidal 103

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waveattenuationratevarieslinearlybetweeninitialmeanattenuationrateandtheratecalculatedwithinanunvegetatedend-memberversionofthebasin,aswetlandvegetationlossvariesfrom0to100%.Areductioninvegetatedwetlandareawouldlikelyincreasetheopen-waterback-barrierbasinarea,resultinginanincreasedtidalprism(Figure 4-1 ,ProcessF).Inpractice,thischangeinvegetationareacanbecalculatedusinginformationfromtheU.S.FishandWildlifeServicesNationalWetlandsInventory(NWI),forexample.Wetlandareascanbedividedintotwocategories:highvegetationzoneandlowvegetationzone,classiedthroughtheNWIasareasthatareirregularlyoodedandregularlyooded,respectively.Inthisstudy,weestimatethatlowvegetationzones,wherethetidalwatersalternatelyoodandexposelandsurfacesatleastoncedaily,effectivelycontributetheirareatothetidalprismduringhalfofthetidalcycle.Highvegetationzonesoodlessfrequentlyand,therefore,donotsignicantlycontributetothetidalprism.Inthisstudy,weestimatethatvegetationconversiontoasubtidalenvironmentoccursatarateproportionaltotheinitialcoveragebyeachofthetwozones.Thisisnotalwaysthecase,however,asevidencedbysitesinsouthernNewEnglandwherereplacementofhighmarshvegetationwithlowmarshvegetationhasoccurredbecauseoftheabilitypossessedbysomecordgrassplantspecies(inlowmarshareas)towithstandhighratesofsealevelrise( DonnellyandBertness 2001 ).Itisassumedthatthelossoccursuniformlythroughoutthebasin,butwenotethatvegetationlossoccurringclosetotheinletshouldincreasethetidalprismmoresignicantlythanlossoccurringatdistalsiteswithinthebasin,wheretheinuenceoftidalwaveattenuationislow.Thecross-sectionalareaoftheinletchannel(AC)increaseswithtidalprisminordertoconveyalargervolumeofwaterduringatidalcycle( D'Alpaosetal. 2010 ; Jarrett 1976 ; O'Brien 1931 ; Powelletal. 2006 )(Figure 4-1 ,ProcessG).Inthisstudy,weemploytherelationshipdevelopedby Powelletal. ( 2006 ),whichwasderivedfrom 104

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observationsofFloridainlets, AC=6.2510)]TJ /F7 7.97 Tf 6.58 0 Td[(5P1.00.(4)Inadditiontotheinuenceoninletmorphology,tidalprismhasbeenshowntocorrelatewithgrossandnetsedimenttransportthroughtheinletandwithdepositionvolumeonebbshoals(Figure 4-1 ,ProcessH)( FitzGerald 1988 ; MarinoandMehta 1987 ; WaltonandAdams 1976 ).Inthisstudy,weestimateebbshoalvolume(VE)fromanempiricallyderived,power-lawrelationshipby MarinoandMehta ( 1987 ),thatdependssolelyupontidalprismsize: VE=5.5910)]TJ /F7 7.97 Tf 6.59 0 Td[(4P1.39.(4) 4.2.1StudySitesWechosetwositesfromtheFloridaAtlanticcoasttowhichweapplytheconceptualmodel.SaintAugustineInlet(SAI)andPoncedeLeonInlet(PLI)areseparatedbyapproximately100kmandarebothsubjecttosemi-diurnal,micro-tidal(range<2m)conditions.Someofthehydraulic,morphologic,andecogeomorphicpropertiesoftheinletsystemsareshowninTable 4-1 .Inthisstudy,weusethemeanofthemeasureddata,derivedfrom WaltonandAdams ( 1976 )and Powelletal. ( 2006 )fortidalprisms,inletcross-sectionalareas,andebbshoalvolumes.Theback-barrierbasinofSAIisanorderofmagnitudesmallerinspatialextentthanthatofPLI,andthecongurationsofthesebasinsareillustratedinFigure 4-3 .Despitethesignicantlylargerbasinarea,PLIhasasmallermeasuredtidalprism,whichislikelyduetothepresenceofanextensivenetworkofchannelsseparatedbyislandsofwetlandvegetationbetweentheinletandMosquitoLagoon.SAIhasadistinctmainchannelborderedbymarshvegetation,whereasPLIhasamixtureofmarshvegetationandmangroveforestoccupyingthesidesofthebasinaswellasthebasinislands,whichcharacterizetheanastomosednetworkofsmallchannels.Thevegetatedislandsattenuatethetidalwaveasitmovesthroughthebasin,reducingthetidalprismofthesystem. 105

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ThemeasuredtidalprismatPLIisapproximately11%oftheidealtidalprism,whichiscalculatedbymultiplyingtidalrangebyopen-waterbasinarea.Usingequation 4 ,ameanattenuationrateof4.7cm/kmthroughoutthebasinisrequiredinordertocausethisdegreeoftidalwaveattenuation.Forcomparison,studiesofwaterlevelsthroughanunimpededsectionoftheIndianRiverclosetotheinletatPLIdeterminedanattenuationrateofapproximately1.1cm/km( MilitelloandZarillo 2000 ).SAItidalprismmeasurementsyieldvaluesthatareclosertotheideal(88%),requiringameanrateofonly1.6cm/kmthroughoutthebasintoaccountforthedifferencefromideal.PLIhasasmallercross-sectionalareaandebbshoalvolumethanSAI,aswouldbeexpectedtoaccompanythesmallerobservedtidalprism.Atbothstudysites,thepredictiverelationshipdevelopedby Powelletal. ( 2006 )(equation 4 )and MarinoandMehta ( 1987 )(equation 4 )underpredictsthecross-sectionalareaandebbshoalvolumesmeasurementspresentedin Powelletal. ( 2006 )and WaltonandAdams ( 1976 ).ThisisshowninFigure 4-5 asthegreen(SAI)andblue(PLI)stars.AtPLI,thecross-sectionalareaandebbshoalvolumesare23%and158%largerthanpredictedusingthetidalprism.AtSAI,thecross-sectionalareaandebbshoalvolumesare82%and320%largerthanpredictedusingthetidalprism.Theunderpredictionofthecross-sectionalareaatthesestudysitesmaybeduetothedynamicnatureoftheseinlets;untilSAIwasjettiedinthe1940sandPLIwasjettiedinthe1960s,theyshowedhighvariabilityininletwidth.AerialphotographsavailablefromtheU.S.ArmyCorpofEngineersCoastalInletResearchProgram(CIRP)showthatthewidthofSAIhasvariedbetween450mand250moverthe24yearintervalfrom1975to1999uctuatingbyasmuchas50mwithina6monthperiod.WhilefeweraerialphotographsareavailableforPLI,theyshowasimilarrangeofvariability,witha65muctuationinwidthbetweenphotographstakenoveratwo-yearinterval.Thedifferencebetweenactualandpredictedvaluesforebbshoalvolumeatthestudysitesmaybeduetothedifcultyinmeasurement(reportedvaluesvarygreatlybetweenstudies,asshowninTable 4-1 ),or 106

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theinuenceofotherfactorssuchas,channeldepthtowidthratio,inletcross-sectionalarea,orlongshorecomponentofwaveenergyux,allofwhichhavebeenshowntoexertinuenceonebbshoalvolume( MarinoandMehta 1987 ).Weusetheserelationshipstoinvestigatetrendsthatareseeninnaturebetweenthemorphologyofaninletanditshydrodynamicproperties,inordertoshoworderofmagnitudechangesfromvegetationloss-nottomakepredictionsforagivensite. 4.3ResultsWeuseequation 4 tocalculatechangestotidalprism,whichshouldariseduetoaconversionofwetlandvegetationtoopenwaterintheback-barrierbasin,thenweuseequations 4 and 4 tocalculatethecorrespondingchangestocross-sectionalareaofinletchannel,andebbshoalvolume.Thisconversionisconsideredtorepresentasituationinwhichbasinvegetationcannotmaintainasufcientlyhighaccretionratetokeepupwithsealevelrise.Overtherangeofcalculations,itisevidentthatwetlandlossleadstoanoverallincreaseintidalprismforbothstudysites(Figure 4-4 ).Table2presentsthechangeinvegetatedarea,tidalprism,cross-sectionalarea,andebbshoalvolumeforeachinletbasedonthe5-20%wetlandlosspredictedby Nicholls ( 2004 )underIPCCSRESA1FIscenariobytheyear2080.DespitePLIhavingasimilaramountofwetlandareatoSAI,itismoresensitivetochangesinwetlandareapercentage.Wecalculatethattheseinletsystemsshouldexperienceanincreaseintidalprismof3.02m3and1.47m3forevery1m2ofvegetationlossatPLIandSAI,respectively.Figure 4-4 illustratestherelativeinuenceoftheincreaseinbasinarea(rstterminequation 4 )andthereductionintidalwaveattenuation(secondterminequation 4 )onthetidalprismofeachinlet.DashedlinesrepresentPLIandsolidlineswithcircularmarkersrepresentSAI.Theblacklinesarethetidalprism(P),whichistheidealtidalprism(greenline),dependentsolelyonbasinarea,lesstheattenuatedtidalprism(blueline),dependentonbasinareaandattenuationrate.PLIshowedanincreaseof1.24m3per1m2lossduetoanincreaseinbasinarea,and1.77m3per1m2lossdueto 107

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adecreaseintheamountoftidalprismreductionfromtidalwaveattenuation.AtSAI,thebasinareaincreasecausesatidalprismincreaseof1.51m3per1m2loss.Giventhatthemeantidalwaveattenuationrateissimilartotherateinun-vegetatedareas,theincreaseinopen-waterarea(overwhichthetidalwaveattenuates)causesadecreaseinthetidalprismby0.4m3per1m2.Figure 4-4 highlightsthesignicanceofthedecreaseintidalwaveattenuationwithwetlandlossforsomeinletsystems,suchasPLI,whichhavewetlandcongurationsthatprovideahighdegreeoftidalwaveattenuation.Thisisnotthecaseatallinlets,asseenintheSAIexample,wherechangestothetidalwaveattenuationratehaverelativelylittleinuenceonhowthetidalprismrespondstochangesinmarsharea.Initially,anincreasedtidalprismshouldincreasethemeangrossdischargethroughtheinletchannelduringeachtidalcycle,increasingtheowvelocity,shearstress,andsedimenttransportcapacitythroughthethroatoftheinlet.Thishastheeffectofscouringthechanneluntilthecross-sectionalareaofthethroataccommodatesthedecreasedowsuchthatthereisnonettransportthroughthechannel;anewequilibriumcross-sectionalareaisachievedatthatpoint( O'Brien 1931 ).Usingtherelationshippresentedby Powelletal. ( 2006 )(equation 4 ),wendthattheincreaseincross-sectionalareaforevery1m2ofvegetationlossis1.78cm2and0.92cm2,atPLIandSAI,respectively(Figure 4-5 ).Thepredictiverelationshipof MarinoandMehta ( 1987 )revealsthat1m2ofvegetationlossshouldresultinanincreasedebbshoalvolumeof2.98m3forPLI,and1.29m3forSAI(Figure 4-5 ). 4.4Discussion 4.4.1TwoMainMechanismsforTidalPrismChangeThisstudyexaminestheinuenceofchangesincongurationofvegetatedwetlands,whichmayarisefromsealevelchange,onthemorphologicevolutionofatidalinletsystem.Theresultsarenotintendedtobeusedasapredictivetoolforeitheroftheexampletidalinletsystemspresented,butrathertoidentifyandexplore 108

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thetwomainfactorsgoverningtidalprismresponsetochangesinwetlandvegetationarea:(1)map-viewareaoftheback-barrierbasin,and(2)thespatialrateoftidalwaveattenuationwithinthebasin.Herein,weinvestigatedasimplescenarioofuniformwetlandvegetationretreatwithintheback-barrierbasininordertohighlighttherelativeimportanceofthetwofactorsatPLIandSAI,stemmingfromtheirdifferencesininitialwetlandconguration.Whilethetwostudysiteshavesimilartotalwetlandareaintheirback-barrierbasins,thecongurationsofthesewetlandsystemsdiffer.SAIhasfringingwetlandsalongthesidesofthebasin,creatingonemainbasinchannel,whereasPLIhasacombinationoffringingwetlandsandanetworkofwetlandislandswhichcreatesacomplexwebofhighlysinuousbasinchannels.TheintricatechannelnetworkatPLIreducesthetidalwaveasittravelsthroughthebasinbyincreasingtheowresistancebywetlandvegetationandincreasingthepathdistancethroughwhichthetidalwavetravels.AreductioninwetlandareaatPLIwouldincreasethemapviewopenwaterareaanddecreasethespatialrateoftidalwaveattenuation.SuchachangewouldcausethetidalprismatPLItorespond(increase)moresensitivelythanwouldbeexpectedtooccuratSAI,wherewetlandlosswouldhaveanegligibleimpactontidalwaveattenuationrate.Theseresultsindicatethataninletwhoseback-barrierbasinhasahigherinitialspatialrateoftidalwaveattenuationholdsgreaterpotentialfortidalprismchangeduetovegetationloss. 4.4.2MarshLossSpatialDistributionInourconceptualmodel,weassumethat,aswetlandlossoccurs,thewaveattenuationratechangeslinearlybetweentheinitialestimatedaverageattenuationinthebasinandthemeasuredattenuationthatoccursinanunvegetatedbasin.Ifwetlandlossoccursinareasfarfromtheinletchannel,itwouldnothavethesameimpactonwaveattenuationaslossofawetlandislandclosetotheinletchannel.Thisisduetothefactthatatdistalbasinregions,thetidalwaveissmallincomparisontoareasproximaltotheinletchannel.Theassumptionoflinearratechangewithwetlandlosswilloverpredict 109

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tidalprismchangewherewetlandlossoccursatafringingmarshinthebackofthebasin,andwillunderpredictinthecaseofnear-channelwetlandloss.Giventhatwetlandlosspatternscannotbereliablypredicted,weoptforaconservativemethod(linear)toestimatewaveattenuationchangeasafunctionofwetlandloss. 4.4.3InuenceonAdjacentShorelinesEbbshoalvolumechangescanimpactadjacentenvironments,suchasbeachanddunecomplexesoneithersideoftheinlet.Shorelinechangeisparticularlysensitivetoinletsystemmorphologyasebbshoalsinterruptlongshoresedimenttransport(LST)andgradientsinLSTleadtobeacherosionandaccretion.Forinletsystemscomparabletothosepresentedinthestudy,avegetationlossof1%,shouldincreaseebbshoalvolumeby6105m3,byincorporatingafractionofthesteadyowofLSTpassingtheinlet.Inthesand-sharingconceptof Dean ( 1988 )and Kraus ( 2000 ),theebbshoalcomplexconsistsofamainebbtidalshoal,aseriesofbypassingbars,andattachmentbars.Iftheebbshoalcomplexisoutofequilibriumduetoachangeinhydrodynamicproperties,suchasashiftinthetidalprism,itwilladjustitsvolumebysequesteringsandfromthepassingowofLSTuntilanewequilibriumvolumeisachieved.Inthisscenario,theebbshoalactsasalocalsedimentsinkandinterruptstheowofLSTpasttheinletchannel.Alongthecoastalreachinthevicinityofthetwoexamplesitespresentedherein,theLSTratesareapproximately3.8105m3/yr( Dean 1988 ),implyingthatsuchachangeinebbshoalwouldbeequaltoapproximately19monthsofLSTinthearea.Therearelinksbetweentidalprismandtheextent(bothseawardanddowndrift)oftheebbshoalcomplex( Carr-Bettsetal. 2012 )andtheminimumdepthovertheebbshoalcrest( BuonaiutoandKraus 2003 ).Astidalprismincreases,theebbshoalspreadsfurtheroffshoreandinthedowndriftdirection,andtheshoaloccupiesadeeperwaterdepth. 110

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4.4.4OtherInuenceonMarshLossAlthoughwehavechosentoidentifysealevelriseasthemostlikelydriverofvegetationlossinback-barrierbasins,anthropogenicdisturbancescanplayamajorroleinexacerbatingsealevelriseeffects( Mudd 2011 ; Nicholls 2004 ).Naturalandanthropogenicprocesses,suchasinvasivespeciesestablishment,overshing,nitrogeneutrophication,risingwatertemperatures,increasedatmosphericcarbondioxide,alteredhydraulicandsedimentationregimes,drainage,reclamation,andshorelinedevelopment,mightalsocontributetowetlandlossandthereforeinuencemorphologicchangesinthesesystems( Sillimanetal. 2009 ).Furtherresearchintotherelationshipsbetweenwetlandvegetationandtidalinletmorphologywillprovidevaluableprogresstowardourunderstandingofthelong-termmorphologicalevolutionofsandycoastalsystemsglobally. 4.4.5ApplicationtoBarrierSystemsWorldwideWhilethefocusofthisstudywasoncontrastingwetlandcongurationsinthebasinsoftwoFloridainlets,theconceptualmodelcanbeappliedtootherbarrierislandsystems.Forthetwostudysitesusedhere,thebasingeometriescouldbeparameterizedintotwomainsections,whichmayneedtobemodiedformorecomplexbasinsystems.Wewereabletoneglectthechangeinbasinareaduetosealevelriseoodingadjacentshorelinesbecauseofthehighlyurbanizedandmodiedcoastalareasurroundedthesebasins.Wenotethatbasinareachangeatthemarginsshouldnotbeneglectedincaseswithbasinedgesaregentlyslopedandunmodiedbyseawalls.Therelationshipsbetweentidalprismandcross-sectionalareawaschosenfromastudyofFloridainletsforoursites,butcouldbemodiedtomoregeneralrelationship,suchasthosepresentedby Jarrett ( 1976 ),forothersites.Ourconceptualmodel,whichincludestheinuenceofthewetlandvegetationchangesontidalinletresponsetosealevelrise,canprovideinsightintothemorphologicresponseofotherinletsystems,including 111

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changestothechannelcross-sectionalareaandthevolumeandpositionoftheebbshoalcomplex. 4.5ConclusionsInthispaper,weshowprogresstowardunderstandinghowtheecogeomorphicpropertiesofatidalinletsystemcontroltheevolutionoftheinletandadjacentshorelinemorphologyduetolossinwetlandarea.Usingoursimpleconceptualmodel,weconclude: Atbothstudysites,wetlandvegetationlossthatleadstobankdestabilizationanderosioncreatesanincreaseintidalprism,increaseincross-sectionalarea,andincreaseinebbshoalvolume. Initialwetlandcongurationcontrolstheresponseofthetidalinletmorphologytowetlandloss;inletswithwetlandcongurationsthatimposeahigherspatialrateofwaveattenuationhavegreaterpotentialfortidalprismchangeduetovegetationlossthatleadstobankerosion. Fortheinletsinthisstudy,smallamountsofmarshplatformloss(1%)canincreasetheequilibriumvolumeoftheassociatedebbshoalcomplexbyanamountequivalenttoonetotwoyearsofaccumulatednetlongshoretransportinthearea.Figure 4-6 showsthechangestothetidalinletmorphologythatwouldoccurduetoalossinwetlandvegetation,including:(1)anincreaseincrosssectionalareaoftheinlet,(2)anincreaseinthevolumeoftheebbshoalcomplex,and(3)anincreaseinthedowndriftandseawardextentofthemainebbshoal.PlotAandBofFigure 4-6 illustratesauniformwetlandvegetationlossthatcouldoccurinbasinssimilartoSAIandPLI,respectively. 112

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Figure4-1. Conceptualmodeloftidalinletgeomorphicresponsetosealevelrise.Lettersrepresentspecicprocesseslinkingkeyvariables(showninblueboxes)asdescribedinthetext. Figure4-2. Diagramillustratinghowthebasinsareparameterizedintotwosectionsoneithersideoftheinletchannel. 113

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Figure4-3. Mapsoftheback-barrierbasinsexaminedinthisstudy:(A)thebasinassociatedwithSaintAugustineInlet(SAI),andthe(B)northand(C)southsectionsofbasinassociatedwithPoncedeLeonInlet(PLI).BothsitesarelocatedalongtheNorthFloridaAtlanticOceancoast,withinapproximately100kmofoneanother.ThislocationisshownastheredboxintheinsetmapofFlorida.Thescalebarandnortharrowapplytoallthreebasinmaps. 114

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Figure4-4. ThechangeintidalprismduetowetlandvegetationlossforPLIandSAI.Theblacklinesarethetotalchangeintidalprism,whichiscalculatedastheidealtidalprism(greenlines)lessthelossintidalprismduetotidalwaveattenuationinthebasin(bluelines).Thepercentlossforeachinletinshownbelowthegureforeachinletandthegreyhighlightedareascorrespondtotheextentofworldwidewetlandloss,aspredictedby Nicholls ( 2004 )underIPCCSRESA1FIscenarioby2080.Thisgurehighlightstherelativeimportanceofthereductionintidalwaveattenuationandincreaseinbasinareaonthehydrodynamicsresponseoftheinletsystemstochangesinwetlandarea. 115

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Figure4-5. Theimpactofmarshvegetationlossontidalprism,cross-sectionalareaofinletchannel,andebbshoalvolume.SaintAugustineInlet(SAI)isshowningreen,andPoncedeLeonInlet(PLI)isshowninblue.Starsindicatetheaveragemeasurementsofcross-sectionalareaandebbshoalvolumepublishedin Powelletal. ( 2006 )and WaltonandAdams ( 1976 ).Grayshadingshowsextentofworldwidewetlandloss,aspredictedby Nicholls ( 2004 )underIPCCSRESA1FIscenarioby2080. 116

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Figure4-6. SchematicIllustrationofwetlandvegetationlossintwobasinswithecogeomorphiccongurationssimilartoSAIandPLI.Vegetationlosswithineachbasinincreaseschannelcross-sectionalarea,ebbshoalvolume,andthedowndriftandseawardextentofthemainebbshoal.Decreaseinthetidalwaveattenuationinbasin(B)leadstoahigherchangeintidalprismofthesystemandanintensicationoftheseeffects. 117

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Table4-1. Studysiteshydraulic,ecologic,andgeomorphicproperties SaintAugustinePoncedeLeonInlet,FLInlet,FL TidalRange(m)1.61.3Meas.TidalPrism(m3)2.51071.71073.711071.63107IdealTidalPrism(m3)3.521071.56108Cross-SectionalArea(m2)4600150024611068EbbShoalVolume(m3)4.31071.71078.11071.45107BasinArea(m2)2.21071.2108HighVegetationArea(m2)4.691075.02107LowVegetationArea(m2)5.821064.38106N.BasinLength,L1(km)2637S.BasinLength,L2(km)1852N.BasinAvg.Width,w1(m)495550N.BasinAvg.Width,w2(m)5001860Avg.Att.Rate(cm/km)1.64.7 Firstvaluesofmeasuredtidalprism,cross-sectionalarea,andebbshoalvolumesarefrompublisheddatain Powelletal. ( 2006 )andthesecondlistedvaluesarepublishedin WaltonandAdams ( 1976 ).WetlandareavaluescalculatedbasedonNWIestuarineenvironmentdata.Thebasinareaisclassiedassubtidal.Highandlowvegetationareaareclassiedasintertidalwithemergentvegetationorscrub-shrub,andirregularlyandregularlyoodedwaterregimes,respectively. Table4-2. Inletmorphologicandhydraulicresponsetowetlandloss SaintAugustinePoncedeLeonInlet,FLInlet,FL VegetationLoss(km2)2.64-10.542.73-10.92P(107m3)0.38-1.530.72-2.93AC(m2)238-955448-1834VE(107m3)0.25-1.070.39-1.89 118

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APPENDIXADELFT3DMODELSETUPThisappendixisintendedtoactasaguideforthesetupandexecutionoftheDelft3D-FLOWmodulewithintheDelft3DmodelingsuiteforsimulationssimilartothosepresentedinChapter 2 andChapter 3 .ThesemodelrunsusedDelft3DutilitiesandtheDelft3D-FLOWmodulewithoutwindorwaveinputsanddidnotcalculatesediment,temperature,orsalinitytransport.ThisappendixwillgiveabriefdescriptionofthephysicalprocessesthatcanbemodeledusingDelft3D-FLOWandtoactasaguideforthegeneralstepsofmodelsetup.MoredetailedinformationisprovidedintheDelft3D-FLOWusermanual( Deltares 2009 ). A.1ModelPhysicalProcessesTheDelft3D-FLOWmodeliscapableofsimulatingtwo-dimensional(depthaveraged)orthree-dimensionalowusingtheunsteadyshallowwaterequations.Theequationsarederivedfromthethree-dimensionalNavierStokesequationsforincompressiblefreesurfaceowundertheshallowwaterandBoussinesqassumptions.Detailedhydrodynamicequationsarepresentedin Deltares ( 2009 ).Themodelisforcedattheopenboundariesbytides,atthefreesurfacebywindstress,andbypressuregradientsduetogradientinthefreesurfaceelevationanddensity.Delft3D-FLOWiscapableofsimulationthefollowingphysicalphenomena: Freesurfacegradients(barotropiceffects). TheeffectoftheEarth'srotation(Coriolisforce). Waterwithvariabledensity(equationofstate). Horizontaldensitygradientsinthepressure(barocliniceffects). Turbulenceinducedmassandmomentumuxes(turbulenceclosuremodels). Transportofsalt,heatandotherconservativeconstituents. Tidalforcingattheopenboundaries. Spaceandtimevaryingwindshear-stressatthewatersurface. 119

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Spacevaryingshear-stressatthebottom. Spaceandtimevaryingatmosphericpressureonthewatersurface. Timevaryingsourcesandsinks(e.g.riverdischarges). Dryingandoodingoftidalats. Heatexchangethroughthefreesurface. Evaporationandprecipitation. Tidegeneratingforces. Effectofsecondaryowondepth-averagedmomentumequations. Lateralshear-stressatwall. Verticalexchangeofmomentumduetointernalwaves. Inuenceofwavesonthebedshear-stress(2Dand3D). Waveinducedstresses(radiationstress)andmassuxes. Flowthroughhydraulicstructures. Winddrivenowsincludingtropicalcyclonewinds. A.2Delft3D-FLOWModelSetupBeforebeginningmodelsetup,theusershouldselecttheworkingdirectoryforthemodelsimulation.Thiscanbedonebyselectingthe`Selectworkingdirectory'buttononthebottomofthemainDelft3Dmenu.Itisimportanttonotethatalluserinputlesandattributelesforamodelsimulationshouldbestoredinthesamedirectory.ThegeneralstepsthatwillbepresentedinthisappendixforthesetupandexecutionoftheDelft3D-FLOWmodule,are: 1. Creationofalandboundaryle 2. Generationofmodelgridandenclosureles 3. Generationofabathymetryleusingsampleles 4. CreationofanMDF-lewhichspecies: 120

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Modeldomain Timeframe Processes Initialconditions Boundaryconditions Physicalparameters Numericalparameters Operations Monitoring Output 5. Executionofmodelsimulations 6. Viewingmodeloutput A.2.1LandBoundaryFileGenerationThelandboundaryleconsistsofclosedpolygonswhichrepresenttheland-waterinterface.Theselescanbeusedforgridgenerationandinthecreationofoutputimages.ThelesmustbecreatedbytheuserinautilityoutsideoftheDelft3Dmodel,suchasMATLAB.Thelesareasciitextleswiththeextension`.ldb.'Intheseles,eachpolygonhasaheaderwiththepolygonlabelontherstline,followedonthenextlinebythenumberofpolygonpointsandthenumberofcoordinatesspecied(usually2forX,Ycoordinates),followedonthelinesbelowasalistofXandYpoints.Thisisrepeatedforeachpolygonthatmakesuptheentirelandboundaryofinterest.EachpolygonmusthavethesamerstandlastsetofX,Ycoordinates.Exampleoftheleformatusingasphericalcoordinatesystemforalandboundaryisshownbelow: L00162-81.49231030.647717-81.49265330.647631-81.49341630.647675 121

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-81.49280530.648373-81.49216530.647991-81.49231030.647717L00242-81.49533130.649523-81.49433130.649611-81.49353830.649931-81.49533130.649523L00382-81.48694630.633556-81.48673230.633736-81.48673230.634113-81.48719830.635128-81.48742730.635008-81.48758730.634333-81.48751830.633995-81.48694630.633556 A.2.2GridGenerationThemodelgridcanbecreatedusingthebuilt-inutility,Delft3D-RGFGRID,developedbyDeltares.ThisprogramcanbelaunchedthroughthemainDelft3Dmenu,byclickingonthe`Grid'buttonandthenthe`RGFGRID'button.Thisapplicationiscapableofgeneratingcurvilineargridsusingeitheraspherical(indecimaldegrees)orcartesian(inmeters)coordinatesystem.AsimplerectangulargridcanbecreatedbyinputtingtheXandYorigins,gridcellspacing,andthenumberofgridcellsintheXandYdirection.Morecomplexgridscanbecreatedbyimportingalandboundaryletouse 122

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asareferenceforgridboundarylocations.Individualgridcellscanbemanuallymovedordeleted,gridlinescanbesnappedtolandboundarylocations,andgridsectionscanbesmoothed,allowingforcompleteusercontrolovereachgridcelllocation.Gridlinesshouldbesmoothedalonglandboundaries,reducingthestaircaseboundariesandreducingarticialdiffusion.Theoutputofthisprogramisagridlewiththeextension`.grd'andagridenclosurelewiththeextension`.enc.'Theenclosureleisgeneratedautomaticallywhenthegridleisexported. A.2.3BathymetryGenerationOnceamodelgridhasbeencreatedusingtheDelft3D-RGFGRIDutility,abathymetrymaybeinterpolatedontothegridusingtheDeltf3D-QUICKINutility.ThisutilitycanbelaunchedthroughthemainDelft3Dmenu,byclickingonthe'Grid'buttonandthenthe`QUICKIN'button.Oncetheprogramisopened,thegridmustbeimportedintotheprogrambyselectingFile!Import!Grid.Abathymetrycanbecreatedusingasamplele,anasciitextle,withalistof(X,Y,Z)coordinates.Thesetofcoordinatesforeachsamplepointareonaline,andareseparatedbyaspaceortab.Insphericalcoordinates,theX,YcoordinatesareindecimaldegreesandtheZcoordinatesareinmeters.Incartesiancoordinates,allcoordinatesareinmeters.DepthsinDelft3Darepositivevalues.Thesesamplepointsdonotneedtobeevenlyspaced,andmultiplelescanbeimported.ThesamplelescanbeimportedintheprogrambyselectingFile!Attributes!OpenSamples.Oncethesamplesareimportedintotheprogram,abathymetrycanbecreatedtocorrespondwiththeimportedgridbyeithertriangularinterpolation,gridcellaveraging,oracombinationofthetwo.Gridcellaveragingrequireshigherresolutionofsamplepointsthantriangularinterpolation,andmaynotbeanoptionsfornegridresolutionsrelativetosampleresolution.ThesetwomethodsareavailableundertheOperationstab.Polygonscanbebecreatedandusedtoisolatedindividualgridareastoapplytheseinterpolations,whichisusefulforlargegridsorgridswithmanysampleinputles 123

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withdifferentresolutions.Internaldiffusioncanbeusedtopopulategridcellsthatareontheedgesofthegridwhichmaynothaveenoughsamplessurroundingthecelltoestimateavalueforthatlocation.Thisdiffusionwillassignthedepthvalueoftheclosestcelltoallthecellswithnotdepth.Thedepthofindividualgridcellscanbemanuallyalteredinthisprogramandlargeareascanbesmoothed.TheparametersforsmoothingandinterpolationofsamplestothegridcanbechangedintheSettings!GeneralParameters.Onceadesireddepthvaluehasbeenfoundforeachgridcell,thebathymetryleshouldbeexportedinFile!Export!Depth.Itwillbesavedasa`.dep'andmustbeusedinconjunctionwiththegridlefromwhichiswascreatedbecauseitdoesnotcontainhorizontalcoordinatedata. A.2.4CreatinganMDF-FileTheMasterDenitionFlowle,orMDF-File,isthemaininputleusedtoruntheDelft3D-FLOWmodule.ItcanbecreatedbylaunchingauserinterfacethroughtheDelft3Dmainmenu,byselecting`Flow'andthenselecting`Flowinput.'Auserinterfacelauncheswithtabsontheleftwhichopenadifferencesetofinputoptionsontheright.Thetabsshouldbeselectedfromtoptobottomandtheappropriateinformationforeachtabshouldbecompletedbeforecontinuingontothenextsection.Belowarebasicinstructionsforeachtab.FordetailedinstructionseetheDelft3D-FLOWusermanual( Deltares 2009 ) Description.Thedescriptioninputisusedonlyforthereferenceoftheuseranddoesnotinuencethemodelrun. Domain.Inthissectiontheusershouldselect`Gridparameters'andthenopenthegridandenclosurelescreatedintheprevioussteps.Theco-ordinatesystemandnumberofgridcellsshouldbereadfromthegridle.Theuserthenneedstospecifythenumberoflayersinthez-direction.Avalueofoneindicatesatwo-dimensional,depthaveragedmodelrun.Forathree-dimensionalmodelsimulation,avaluegreaterthan 124

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oneshouldbeselected.Anoptionforlayerthicknesswillpopulatetheuserinterfaceandtheusercanspecifythelayerthickness(asapercentageofthewatercolumn)foreachlayer.Thedefaultisforevenlyspacedlayers.Theusershouldselectthe`Bathymetry'buttonatthetopandopenthebathymetrylecreatedintheprevioussteps.Drypointsandthindamsmaybeaddedinthissectiontorepresentjettiesandareaswithnoow. Timeframe.Herethemodelsimulationdaterangeandtimestepshouldbespecied.Generally,thereferencedateisthesameasthesimulationstartdate.ThedefaulttimezoneisGMT,butcanbemodiedinthissection. Processes.Thistaballowstheusertospecifywhichprocessestoincludeinthemodelsimulation.Forthisexample,noneoftheconstituentsorphysicalprocessesareselected.Iftheseareselectedthenmoreinputinformationinthefollowsectionsbecomeavailable.Ifnooptionsareselected,asinthisexample,onlythehydrodynamicpropertiesarecalculatedwithoutwindorwaveforces. Initialconditions.Thissectionallowsuserstospecifyauniformwaterlevelthroughoutthedomainastheinitialcondition,toincludeaninitialconditionsle,toincludearestartle,ortoincludeamaple.Usinginitialconditionsorrestartlescanreducethespin-uptimeofthemodel,butarenotnecessary.Thedefaultforthissectionisauniformwaterlevelofzerometersthroughoutthedomain. BoundaryConditions.Asetofinitialandboundaryconditionsforwaterlevelsandhorizontalvelocitiesmustbespecied.Initialverticalvelocitiesarenotnecessarytospecify,astheyarecomputedthroughthecontinuityequation.Boundariesofthemodelareclassiedasopenedorclosedboundaries.Closedboundariesarelocationswithoutow,suchasland-waterlines(riverbanks,coastlines).Openboundariesarealwayswater-waterboundariesthatintersecttheoweld.Theseboundariesshouldalwaysbesituatedasfarfromtheareaofinterestaspossible.Reectionatopen 125

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boundariesshouldbeminimalsincetheopenboundariesshouldnothamperlongwavepropagation.Tospecifytheboundaryconditions,rstindividualboundarysegmentsmustbedenedbyclickingthe`add'button.Eachsegmentmusthaveanuniquenameandtheusermustspecifytheindices(m,n)ofeachendpoint.Thevisualizationareacanbeusedtohelpwiththisprocess.ItcanbeopenedthroughthetopmenubyselectingView!Visualizationarea.Inthiswindow,boundarysegmentscanbeaddedmanually.Theboundariescanbebrokenintonumeroussegments,andshoulddependonthedomainsize.Allareasofopenwaterattheborderofthegridshouldbedenedasaboundary.Closedboundaries,whichborderland,donotneedtobespeciedasaboundaryhere.Onceeachboundaryisdenedinspace,theboundaryconditionsmustbespecied.Thetypeofboundariesthatcanbespecied,include:Waterlevel,Current,Neumann,Totaldischarge,Dischargepercell,orRiemann.Forthisexampleweusewaterlevels,butdetailsofeachofthesetypesofboundariescanbefoundin Deltares ( 2009 ).Theforcingtypeforwaterlevelscanbeastronomic,harmonic,QH-relation,ortimeseries.Forthisexamplewechoseastronomic,whichisconvenientiftidalconstituentscanbederivedfromlocaltidalgauges.Oncetheappropriateselectionshavebeenmade,theuserneedstoeditthedetailsoftheboundarybyselectingthe`Editowconditions'button.Anewboxwillopenwherethedetailsoftheboundarycanbeinput.Differentsetsofconditionscanbespeciedforeachendofeachoftheboundaries.Thesesetsofconditionscanbespeciedbyselectingthe`Add'buttonandinputtingeachsetofconstituents.Thecomponentsetislinkedtoeachendofeachboundarysegmentbythedropdownmenusontherightside.Oncetheboundarydetailshavebeeninput,theuserclosestheboxbyclickingthe`close'buttoninthebottomrightcorner.Oncethisprocesshasbeencompletedforeachboundarysegment,thelesneedtobesavedbyselectingthe`Open/Save'button.Theboundarydenitionsle(withtheextension`.bnd')containsthecoordinatesofeach 126

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boundarysegmentandtheastronomicowconditionsle(withtheextension`.bca')containstheconstituentsforeachendofeachboundarysegment. Physicalparameters.Inthissectiontheuserspeciestheconstantsforgravityandwaterdensity,thebottomandwallroughness,theviscosity/diffusivity,andthree-dimensionalturbulenceclosuremodeltobeusedinthesimulation.Theroughnessandviscosity/diffusivitycanbespeciedusingauniformvaluethroughoutthedomainorasalethatspeciesavalueateachgridcelllocation.Formoreinformationonthesevaluesandhowtocreatetheseles,referto Deltares ( 2009 ). Numericalparameters.Inthissectiontheusercanspecifyparametersrelatedtodryingandoodingandsomeotheradvancedoptionsfornumericalapproximations.Thesmoothingtimeisthetimeintervalatthestartofthemodelsimulationthatisusedtocreateasmoothtransitionbetweentheinitialandboundaryconditions.Longersmoothingtimeperiodscreatesmootherresultsinthebeginningofthesimulationbutincreasethecomputationtimeperiod. Operations.Dischargevaluescanbespeciedheretorepresentowintothesystembyasourcesuchasariver.Thedischargeateachgridcelllocationmustbespecied,soowacrossarivermustbedividedintosegments. Monitoring.Differentobservationtypesforoutputcanbespeciedinthissection.Observationsareindividualpoints,droguesmonitorparticlepaths,andcross-sectionsareshownforalldepthsalonganm-orn-gridindexsegment.Morethanonespecicobservationpointorcross-sectionmustbespeciedorthemodelwillnotrun(i.e.therecanbeoneobservationaslongasthereisalsoonecross-sectionspecied). Additionalparameters.ThissectionprovidesaccesstoadditionalfunctionsthatarenotsupportedbytheFLOW-GUI,allowingformoreexibilitywithoutalteringtheFLOW-GUI.Unlesstheuserhasaccesstoadditionaloptions,itshouldremainblank. Output.Thetimeinterviewformodeloutputandthedetailsoftheoutputcanbespeciedinthissection.Themapresultsarethesnapshotsofthecomputedquantities 127

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fortheentiremodeldomain,thehistorylestorestheresultsforthespeciedmonitoringobservationpoints,drogues,andcross-sections,andthecommunicationlestoresdatarequiredforotherDelft3Dmodules.Thestarttimeandendtimemustbeintherangeofthemodeltimeframe,butdonothavetocovertheentirerange.Theintervalsetsthetimestepofoutputforthemapleandthehistoryintervalsetsthetimestepforoutputofthehistoryle.Bothofthesevaluesmustbeamultipleofthemodeltimestep.Unlessothermodulesarebeingused,theintervalforthecommunicationlecanbesettozero.Onlinevisualizationshouldgeneralbeuncheckedunlessitisneededfortroubleshooting.Bydefaultallmodeloutputdetails(underthe`Details'button)areselected.Someofthesemaybeunselectedinordertoreduceoutputlesize. A.2.5ExecutingmodelrunAfterallthedetailsoftherunhavebeenspeciedthroughtheFLOW-GUI,theMDF-leshouldbesavedbyselectingFile!SaveMDF.Thiscreatesanasciitextlewiththeextension`.mdf'thatcontainsinputinformationandthenamesoflestoreferenceduringthemodelsimulation.Alllesforthesimulationneedtobesavedinthesamefolder.Oncethelehasbeensaved,theFLOW-GUIcanbeclosed.Whenthemodelisreadytoberun,selectthe`Start'buttonfromthemainDelft3DmenuandselecttheMDF-lethathasbeencreatedandselectOK.Aboxshouldappeartoshowthatthemodelisrunning. A.2.6ViewingmodeloutputTheQUICKPLOTutilitycanbeusedtoopen,view,andexportmodeloutput.Itreadsthemapoutputle(trim-name.dat)andthehistoryle(trih-name.dat).Oncetheseleshavebeenloadedintotheprogram,specicdaterangesandmodeldatacanbeexportedinavarietyofformatsformanipulationoutsideofthepargram,includingMATLABmat-les. 128

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APPENDIXBMODELINPUTPARAMETERSThisappendixincludesthemodelinputparametersforthe52-daymodelsimulationdescribedinChapter 2 .ThissimulationwasusedformodelcalibrationandcomparisonwithavailableADCPdata.ThelistsarebrokenintogroupswhichcorrespondtothetabsintheFLOW-GUIdescribedinAppendix A Domain. CoordinateSystem:Spherical GridpointsintheM-direction:420 GridpointsintheN-direction:302 Numberoflayers:8(12.5%ofdeptheach) TimeFrame. Referencedate:08112011 Simulationstarttime:08112011000000 Simulationstoptime:30122011000000 Timestep:0.5min Localtimezone:0+GMT Processes. Noconstituentorphysicalprocessesselected(hydrodynamicsonly) InitialConditions. Uniformvalues Waterlevel:0m Boundaries. 3boundarysegments:North,East,andSouth Typeofopenboundary:Waterlevel 129

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Forcingtype:Astronomic Reectionparameteralpha:0s2 TidalconstituentsIncluded(Name,Amplitude(m),Phase(deg)): M2,8.0269704e-001,1.5706319e+001 S2,1.5658684e-001,1.3463423e+001 N2,1.6423517e-001,3.5913640e+002 K2,2.5928995e-002,8.6506397e+000 K1,1.0109143e-001,1.9361364e+002 O1,7.7357689e-002,2.0546273e+002 P1,3.7856681e-002,1.9961633e+002 Q1,1.7017450e-002,2.0305634e+002 MF,7.5714709e-003,3.4363395e+002 MM,2.9204701e-003,3.2804466e+002 M4,7.1590335e-003,3.4327001e+002 MS4,4.6285343e-003,2.4064482e+002 MN4,1.8140395e-003,1.3922591e+002 PhysicalParameters. Gravity:9.81m/s2 Waterdensity:1025kg/m3 Roughnessformula:Chezy,UniformU=65,V=65 Wallroughnessslipcondition:Free Backgroundhorizontalviscosity/diffusivity:Uniform1m2horizontaleddyviscosity Backgroundverticalviscosity/diffusivity:Uniform0m2verticaleddyviscosity Turbulencemodelfor3D:k-Epsilon NumericalParameters. Dryingandoodingcheckat:gridcellcentresandandfaces Depthspeciedat:Gridcellcorners 130

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Depthagridcellcentres:Max Depthatgridcellfaces:Mean Thresholddepth:0.1m Marginaldepth:-999m Smoothingtime:60min Advectionschemeformomentum:Cyclic Operations. Nodischargesincluded Monitoring. Observations:oneattidalstation8720030andoneininletchannel Drogues:nonespecied Cross-section:twothroughinletchannel,oneatminimumcross-section AdditionalParameters. Noadditionalparametersincluded Output. Mapstoragestarttime:08112011000000 Mapstoragestoptime:30122011000000 Mapstorageinterval:30min Historyinterval:6min Communicationinterval:0min Restartinterval:0min 131

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BIOGRAPHICALSKETCH JessicaLoveringwasborninMarylandandmovedtotheFloridaKeysinlateelementaryschool.ShelivedonBigPineKeyandgraduatedfromKeyWestHighSchoolin2001.ShebeganherundergraduatecareerattheUniversityofMarylandandcompletedherdegreeincivilengineeringwithaspecializationingeotechnicalengineeringattheUniversityofFlorida.Shewentontocompleteamaster'sdegreeincoastalandoceanographicengineering.SheremainedattheUniversityofFloridainordertopursueherPh.D.intheGeologicalSciencesDepartmentwithPeterAdams.ShewasawardedtheSMART(ScienceMathandResearchforTransformation)fellowshipandwillbeworkingfortheDepartmentofDefenseaftergraduation.ShewillbeginhercareerasaphysicaloceanographerattheNavalOceanographicOfcesattheStennisSpaceCenterinMississippi. 140