PredictingRiparianHabitatQuantityandDiversityUsing2DLandscapeEvolutionModeling

KaitlynHammond

EnvironmentalStudiesSeniorSynthesis

SeattleUniversity

March10,2015

Abstract

Alterationofriversystemshasresultedinmorphologicallysimplerivers,and

poor-qualityriparianhabitat.Astherelationshipbetweenhabitatdiversityand

ecosystemfunctionbecomesmoreapparent,managementhasbeguntofocuson

restoringnaturalhabitat-creatinggeomorphicprocesses.Wideningtheerodible

rivercorridorisonerestorationstrategy,butdeterminingthecorridorwidth

neededtofacilitateanincreaseinhabitatcanbechallenging.Thisstudyexploresthe

useofCAESAR-Lisflood,a2Dcellularhydraulicmodel,asatoolforquantifyingsite-

specificdifferencesresultingfromdifferenterodiblecorridorwidths.TheNorth

ForkoftheSnoqualmieRivernearNorthBend,Washingtonwasusedformodeling.

Non-erodiblerockrevetmentsweremodeledonthebanksofthemainchanneland

setbackoneriverwidth.After100yearsofsimulatedflow,theresulting

morphologywascomparedtoanunconstrainedcondition.Theunconstrained

conditionhadmoreactivesidechannelsattheendof100yearsthanthe

constrainedconditions,andmoresidechannelactivationthroughoutthedurationof

modeling.Theseresultssuggestthatawidererodiblecorridordoesfacilitatehabitat

formation.Additionally,thesuccessfultranslationofmodeloutputtohabitatquality

providesastartingpointtheuseof2Dmodelingasatoolforrestoration.Further

studiesshouldfocusondevelopingappropriatehabitatassessmentindicestomake

thisanaccessibletoolformanagers.

Introduction

Habitatheterogeneity,definedasaspatiallydiversedistributionofphysical

andbiologicalhabitatcomponentsinanenvironment,hasbeenshowntoinfluence

thelevelofbiodiversitythatcanbesupportedbyariverecosystem(Wardand

Tockner2001).Therelationshipbetweenhabitatheterogeneityandbiological

diversityisparticularlyevidentinripariansystems,astheinterfacebetween

aquaticandterrestrialecosystemsisassociatedwithavarietyofmicrohabitatsthat

supportmorebiologicalniches,andthereforemorespecies(Ward,Tockner,and

Schiemer1999,Malmqvist2002).Studieshaveexpressedtheimportanceof

biodiversityasafacilitatorofecosystemproductivityandresilience(Isbell,Polley,

andWilsey2009,Mace,Norris,andFitter2012),andforthisreason,many

restorationeffortsaimtoincreaselocalbiodiversity.

Humanmodificationstoriversystems,includingalterationofflowregimes,

canalization,andbankstabilization,haveeliminatedmuchofthespatialand

temporaldiversityassociatedwithriparianhabitat(BunnandArthington2002,

Ward,Tockner,andSchiemer1999).Manyofthesemodifications,particularlyriver

channelizationthroughuseofbankstabilizationstructures,destroybothsmall-scale

habitatfeaturesandthegeomorphicprocessesthatpromotehabitatheterogeneity

atalargerscale(AbbeandMontgomery1996;SeguraandBooth2010).Because

erosionandfloodingcandamagepropertyandotherpublicandprivateassets,

managementtendstofocusheavilyonbankstabilization.Whetheraccomplished

usingtraditionalrockriprap,orusingsofterapproaches,likeengineeredwoodor

bankplanting,bankstabilizationcaneventuallynarrowtherivercorridor,

diminishingthepotentialfornaturalhabitatcreatingprocessesandecological

succession(Piégayetal.2005).Findingtherightbalancebetweenstabilityandthe

ecologicalbenefitsassociatedwithinstabilityisachallengefacedinmanagement.

Managersmayconsidertheremovalofbankstabilizationstructuresand

wideningoftheerodiblecorridorasmeanstoreactivategeomorphicprocessesand

enhancebiodiversity,butassessingthepotentialoutcomesofdifferentplansis

difficult.Studiessuggestthatwideningtheerodiblecorridor,themanagement-

definedareathatarivercanerode,isbeneficialintermsofhabitatformation.Itis,

however,unclearhowwidethecorridormustbetoallowformeasurablehabitat

improvement(Buijseetal.2002;Palmeretal.2007).Additionally,variation

betweensitesmakesitdifficulttoapplya“onesizefitsall”managementstrategy

(Piégay2005).

Hydraulicmodelinghasbeenproposedasawaytoevaluatepotential

morphologicformsresultingfromdifferentmanagementstrategiesataparticular

site(Richards,Brasington,andHughes2002).However,beingpredictiveisdifficult,

andmodelingiscomputationallydemanding;therefore,hydraulicmodelinghasnot

yetbeenusedforthispurpose.Recentchangesto2Dcellularhydraulicmodels,a

classofgrid-basedmodels,havemadethemmoreefficientandbetterableto

representinstreamhydraulicconditions(Coulthard,Hicks,andVanDeWiel2007).

Becauseoftheefficiencyofthesemodels,theyprovideafeasibleoptionfor

exploringpredictivemodeling.

CAESAR-Lisflood,anumeric2Dcellularmodel,waschosenforuseinthis

study.ThisprojectseekstoutilizetheCAESAR-Lisfloodmodelto:

1. DeterminewhetherCAESAR-Lisfloodcanreasonablymodelchangesin

morphologyover100simulatedyears,andwhethertheprogramcanmodel

theareaofatypicalrestorationsitequicklyenoughtobeapracticaltoolfor

management.

2. Evaluatepotentialhabitatdifferencesresultingfromtheplacementof

modeledburiedrockrevetments(acommonlyusedbankstabilization

structure)atvaryinglevelsofsetbackfromthemainriverchannel.

Alow-cost,predictivetoolthatcanoperatequickly,andquantifydifferencesin

potentialoutcomes,wouldgiverestorationprojectmanagers,engineers,andthose

involvedinconservationmanagementabetterframeworkformakingdecisions

aboutprojectimplementation.

LiteratureReview

Determiningamethodforimprovingecologicalintegrityisacritical

challengefacedbyrestorationmanagers.Thisreviewwillexplorethebodyof

literaturesurroundingrestorationplanning,andpossibilitiesforinformingthe

decision-makingprocess.First,Iwillsummarizetheliteraturepertainingtoriver

restorationstrategies,focusingonthebenefitsassociatedwiththerestoration

geomorphicprocesses.Then,Iwilldiscussthepotentialuseofmodelingasatoolfor

restoration.Finally,Iwillevaluateseveralmetricsforhabitatassessment,and

suggesthowtheycouldbeincorporatedwithamodeltoprovideaneffectivetoolfor

enhancingdiversity.

Riverrestorationgoalsandmethods

Riverandstreamrestorationhasbecomeanincreasinglycriticalundertaking

aspeoplebegintounderstandriversystemservices(Palmeretal.2005).Rivers

provideavarietyofecosystemservices,includingwaterfiltration,nutrientcycling,

andclimateregulation,andmorebiodiversesystemsarebetterabletoprovide

thesefunctions(Isbell,Polley,andWilsey2009;Mace,Norris,andFitter2012).As

thisrelationshipbecomesclearer,restorationprojectshaveemphasizedthe

improvementofecologicalintegrityasaprinciplefocus.

Restorativeeffortsaremovingfroma“state-based”approachthatfocuseson

achievingaparticularsetofcharacteristicstoa“process-based”approachthat

emphasizestheimportanceoflarge-scaledriversofriparianfunction(Beechieetal.

2010).Ratherthaninstallinginstreamhabitatfeatures,likespawninggravelor

logjams,contemporaryprojectsseektobeself-sustainingbyremoving“barriers”

(bothliteralandfigurative)tonaturalriverevolution.Beechieetal.(2010)argue

thatripariandynamicsareinfluencedby“hierarchicallynested”physical,chemical

andbiologicalprocessesactingatbroadspatialandtemporalscales.Theydescribe

theimportanceofdesigningrestorationeffortstoaddresslarge-scaleprocesses,like

sedimenttransportandseasonalflowregimes,ratherthantheindividualsymptoms

oflargerissues.Restorationatanecosystemscalemaynotbepossibleatallsites

duetoeconomicconstraints,buteffortsbasedontheseprinciplescanleadto

successevenatasmallerscale(Beechieetal.2010).

Oneofthemainissueswith“state-based”strategiesisthedifficultyof

definingareferencestate(DufourandPiégay2009).Inthepast,mostrestoration

effortsfocusedonrestoringarivertoahistoricalstate,butidentifyingthedesired

stateproveddifficult.DufourandPiégay(2009)argueforanapproachsimilarto

thatofBeechieetal.(2010)thatfocusesonfunctionoverstate.However,Dufour

andPiégaydonotbelievethataprocess-basedapproachwillalwaysleadtodesired

outcomes,andsuggestintegratinghumanandsocietalneedsintodesigntoensure

success.

Restorationofgeomorphicprocessesiscomplicatedbysocietaldesiresfora

stableriverchannel.Whilebeneficialforpropertyandothersocietalassets,river

regulationandbankstabilizationcaneliminateprocessesthatcreatemorphologic

diversity(SeguraandBooth2010;Collins,Montgomery,andHaas2002).Processes

likeerosionhavebeenshowntoincreasemorphologicaldiversity,andbydoingso,

providehabitatbenefitstoriparianspecies.Forexample,sidechannelshavebeen

showntoprovidevaluablehabitatforlivingandbreedingformanyspecies(Stellaet

al.2011).Riverswithbraidedflowpatterns,orvariouschannelsofactiveflow

weavingaroundislands,areassociatedwithgreaterpopulationsoffishspecies

(Montgomeryetal.1999).Ingravel-beddedstreams,thepool-rifflesequencewith

areasoflowvelocitiesandhighdepthsalternatingwithhighvelocitiesandlow

depthshavebeenshowntobeespeciallyimportantforfish,bothforbreeding

spawning(Beechieetal.2005).Otherphysicalelementsplayseasonalroles.For

instance,overhangingbanksprovideshadeandcoolerwaterforfish,andoxbow

lakesprovideslow-waterrefugeinhigh-flowevents(Beechieetal.2005,Ishidaet

al.2010).Thesebenefitsmustbeweightedagainstthecostsassociatedwithan

activeerodiblecorridor,particularlythethreatofpropertydamage,andprojects

mustberesponsivetosocietalneedstoensuresuccess.

Modelingasatoolforrestoration

Currently,mostdecisionsregardingriverrestorationstrategiesarebasedon

informationgainedfromotherrestorationprojects,andresearchaboutrestorative

tools(Buijseetal.2002).Thisinformationisvaluableinguidingdecisions,butitis

notsite-specific,andtendstobe“fragmented,”onlyevaluatingtheeffectsofa

strategyononeparticularcomponentoftheriparianzone(Buijseetal.2002,889).

Itcanbechallengingtocompareproposeddesigns,particularlywhenthe

approachesutilizeavarietyoftoolsandareintendedtoaffectmultiplecomponents

oftheriparianzone.Thisbecomesevenmorechallengingwhenevaluatingsimilar

designs.Ateammaybedecidingbetweenimplementationofburiedrevetmentsset

backoneortwochannelwidthsfromthemainchannel.Awaytocomparethe

habitatqualityandquantitythatwouldresultfromthesedifferentrestoration

strategieswouldbeusefulforhelpingdistinguishbetweentwoapproaches.

Therearemanystrategiesforevaluatingexistinghabitatdiversityand

complexity,includingstreamcategorization,hydraulicmodeling,andspatial

variabilityindicies(Yarnell,Mount,andLarsen2006;Benjanker,Koenig,andTonina

2013),butevaluatingfutureoutcomesofspecificmanagementplansislimitedto

evidencebasedonthesuccessesandfailuresofotherrestorationprojects(Buijseet

al.2002).Thereisneedforasite-specificassessmentstrategy,particularlyonethat

canquantifythedifferencesinhabitatresultingfromdifferentstrategies.

Richards,Brasington,andHughes(2002)proposethatitcouldbepossibleto

usehydraulicmodelstoevaluatefuturesituations,notjustcategorizecurrent

conditions.Nosubstantialworkhasbeendoneonthetopicsince,asmodelingis

computationallydemanding,andchallengingtovalidate(VandeWieletal.2011).

However,recentupdatestocellularhydraulicmodelshaveimprovedtheir

computationalefficiency,andasthebodyofknowledgeaboutmodelcalibration

expands,theyhavebecomeanincreasinglyviableoptionforuseinpredicting

habitat(Coulthard,Hicks,andVandeWiel2007).

2Dcellularhydraulicmodelsuseagrid-basedmapofelevationandsediment

sizesaccompaniedwithwaterandsedimenttransportequationstosimulateriver

flowanderosionprocesses(Coulthard,Hicks,andVandeWiel2007).Coulthard,

Hicks,andVandeWiel(2007)identifytwomajorcategoriesofcellularmodels:

LandscapeEvolutionModels(LEMs),whichusesteadyflowequations,andnon-

steadyflowhydraulicmodels.LEMsareusefuloverlongspatialandtemporalscales,

butneglectimportanthydraulicinformation.Non-steadyflowmodelsaremuch

morecomputationallydemanding,butareclosertorealityintheirrepresentationof

in-channelflow.

Coulthardetal.(2013)combinedbothtypesofmodelsintoanewmodel

calledCAESAR-Lisflood.Thismodelinparticularisagoodoptionforpredicting

futurehabitatconditions,asmanagersmustevaluatebothlong-termchangesthat

resultfromamanagementchoice,aswellastheimmediatehydraulicconditions,as

theyarerelevanttohabitat.Additionally,becauseitismorecomputationally

efficientthanother2Dcellularmodels,itispossibletosimulate50-100yearsof

flow(animportanttime-scaleformanagers)inashortenoughtimeperiodtobe

usefulformanagers.

Themodelisrunusinganelevationmapfortheareatobemodeled,daily

flowvolumesandvelocities,andasedimentsizedistributionfromthesite.Foreach

cellinthemodel,sedimentandwaterareaddedfromupstream.Ifthecapacityfor

sedimenttransport(whichiscalculatedbasedonflowvelocity)exceedsthesupply,

sedimentistakenfromthebed,andthebedislowered.Ifthesedimentsupplyis

greaterthanthetransportcapacity,thebedraises.Themodelalsoallows

specificationofcellsasbedrockthatcannotbeeroded.Thisfunctionprovidesan

easywaytomodelbankstabilizationstructures.Thesourcecodeforthemodelis

alsofreelyavailable,whichallowsuserstointegratemodifications,andpresentsno

financialburdentomanagersseekingtousethemodel.

Intheirreviewof2Dhydraulicmodels,Coulthard,Hicks,andVandeWiel

(2007)notedthatwhilecellularmodelsareausefultypeofmodel,theydohave

certaintechnicalproblemsthatmeantheyshouldnotbeusedforexactprediction,

butinsteadtopredictsetsofpossiblefutures,ormorphologicalforms.Oneofthe

mainissuestheyidentifyisthedifficultyassociatedwithmodelinglateralerosion.

However,theequationsusedinthesemodelsmakesthemmoreeffectiveat

representingbraidedriversystemsthanothermorphologicalpatterns(Coulthard,

Hicks,andVandeWiel2007).Zilianietal.(2013)supplementedthesefindingsby

comparingtheCAESARmodeltoarealsystem,andfoundthatthemodeleffectively

simulatedgeneralmorphologicchangesandsedimentoutput,butwaslesseffective

atrepresentingfinerscalefeatures,likebraidingintensity.Thesestudiescollectively

indicateCAESAR-Lisfloodisappropriateoptionformodelingfuturehabiat

conditions.

Frommodeloutputtohabitatcomparison

Whilemethodologiesexistforevaluatingspatialvariationandhabitat

heterogeneityinrivermorphology(Yarnell,Mount,andLarsen2006),thereis

currentlynometricincorporatingbothbioticpreferencesandspatialvariation.

Creatinganindexforassessmentbasedonspeciespreferenceswouldallow

managerstobetterevaluatehowamanagementplanaffectsimportantfocalspecies

inanarea.

InthePacificNorthwest,salmonidscanbeausefulindicatorofbiological

integrity.Becauseofthedirectuseandculturalvaluesattachedtosalmonids,they

areoftenthedrivingforcebehindrestorationefforts.Thesespecieshavecomplex

lifehistorystrategiesthatrequireavarietyofmicrohabitats(Beechieetal.2014;

SaraevaandHardy2009),makingthemagoodindicatorofhabitatdiversity.They

arealsoanimportantgroupofspecieseconomically.Salmonidssitatthe

intersectionbetweenecologicalandsocialrestorationgoals,makingthema

particularlyusefulfocalspeciesforthisproject.

Conclusions

Habitatmodelingcouldprovideextremelyusefulinformationtomanagers,

andisnowpossiblewithupdatedmodels.Thesemodelsshouldnot,however,be

usedtopredictexactfuturesduetothestochasticnatureofriversystems.Agood

habitatindextoassessmodeloutputwilltakeintoaccountmanyofthediverse

featuresoftheriparianlandscape,includingoffchannelhabitat,geomorphological

features,likeoff-channelpoolsandgravelbars,aswellashydraulicinformation,

includingwaterdepthandvelocity.Theimportanceofthesefeatureshasbeen

evaluatedindividually,butcombiningthemprovidesanewwayofassessinghabitat

quality.Thepredictionsbasedonmodelassessmentcouldbetterallowmanagersto

worktowardrestoringnaturalprocessesthatcouldenhancehabitatinthelongrun,

ratherthanartificiallycreatinghabitatfeatures.

Methodology

StudySite

Iperformedmodelingona2.5kmstretchoftheNorthForkofthe

SnoqualmieRivernearNorthBend,Washington.Thisisagravel-bedded,braided

riversystem.Thesitecontainsabridgethatmaybeatriskoffailureiferosionon

thesouthbankcontinues(Ruebel,personalcommunication).KingCountyis

developingaplantoprotectthebridge,butintendstousesofterengineering

approachesinordertoactivategeomorphicchangeattheprojectsite(Ruebel,

personalcommunication).Whilemodelingcannotbeusedtopredictexactlywhat

theriverwilllooklikeinthefuture,theexplorationofdifferentmorphologicforms

andtheresultinghabitatconditionsfromdifferentmanagementdesignstrategies

maybeofuseasthecountydeliberatesbetweenplans.Because2Dmodelsaremost

accuratewhenrepresentingbraidedriversystems(Coulthard,Hicks,andVanDe

Wiel2007),thisisanappropriatechoiceforaprojectsite.

ExperimentalDesign

Isimulatedthreedifferentconditionsrepresentingincreasingerodible

corridorwidthusingthebedrockfunctionintheCAESARmodel:buriedrevetments

alongthebanksofthemainchannel,buriedrevetmentssetbackoneriverwidth

fromthemainchannel,andanunconstrainedcondition(Figure1).ADigital

ElevationMap(DEM)obtainedfrom2009KingCountyLIDARwasusedastheinitial

conditionformodeling.Iobtainedaveragedailyflowvaluesforthepast50years

fromUSGSstreamgauge12142000,agaugelocatedupstreamfromtheprojectsite,

andduplicatedthedatatorepresent100yearsofflow.Tominimizeruntime,only

thetop2%offlowvolumeswereused,ascalculationsusingtheBedload

AssessmentinGravel-beddedStreams(BAGS)calculatorindicatedthat98%of

sedimenttransportoccurredwiththetop2%offlows(WilcockandCrowe2003).A

sedimentdistributionforthesiteincluding9sedimentsizeswasinputtedtothe

model,andsedimentwasrecirculatedthroughthemodel.Twoadditionaltestruns

includingthelowflowswereperformedtoevaluatethedifferencebetweenthe

narrowrevetmentsandtheunconstrainedcondition.Theserunsusedinputted

sedimentcalculatedbasedonflowvelocitiesusingBAGS.4sedimentsizeswere

usedinthesesimulations.Theserunsincorporateduseofthevegetationand

sedimentdepositionparameters.Allothermodelparametersaredescribedin

appendix1.

Aftersimulating100yearsofflow,theresultingDEMsweremodeledfortwo

dayswithanaveragesummerlowflow(seeappendix1)todeterminewhich

channelswereactiveduringnon-floodconditions.Modeloutputwasanalyzedin

ArcGIS.

Ateverymomentofsimulatedtime,themodelrecordsavalueforeachcell

forwaterdepth,velocity,andaveragesedimentsize.Aftersimulating100yearsof

flowandrunningasummerlowflowthroughtheresultingDEM,IusedArcGISto

findcellsthatmetdepthandvelocityconditionscorrespondingwithhabitat

preferencesforCohoandChinookpresmoltasdescribedbyGoodmanetal.(2014).

WhileSnoqualmieFallsblocksthepassageofanadromousfish,definedasthosefish

thatmigratefromtheoceantofreshwatertospawn,studiesindicaterainbowtrout,

aspeciesthatispresentatthesite,havethesamehabitatrequirementsasCohoand

Chinooksalmon(Quinn2005,202-203).Thisagegrouptendstobelimitedby

habitatavailability,makingitanappropriate,albeitnotentirelyinclusive,indicator

ofhabitatquality(Goodmanetal.2014).

Results

Thesimulationof100yearsofhighflowstookapproximately11hours(see

appendix1forcomputerspecifics).After100simulatedyears,theunconstrained

conditionshowedsmallsidechannelsactivatedevenduringasummerlowflow

(Figure2).ComparisonwiththeoriginalDEMsuggeststhattheriverisreoccupying

abandonedchannels.Theconstrainedconditionsdidnothaveanyactiveside

channelssummerflow,withtheexceptionofonechannelsplitpresentinthe

narrowconditionthatwaspresentintheinitialcondition(Figures3and4).

Across-sectionalanalysisoftheunconstrainedconditionshowedarelatively

widechannelwithgentlyslopedbanks.D50,theaveragesedimentdiameter,was

loweronthefloodplainandhigherinthemiddleofthechannel(Figure5).Thisis

consistentwithnormalriverconditions.Thenarrowconditionhadasharper

channelslopeandanirregularsedimentsizepatternthroughthecross-sectionthat

wascoarserthanseenintheunconstrainedposition(Figure6).Thesetback

conditionresultedinawiderchannelthanboththeunconstrainedandnarrow

conditions,butthesedimentsizeprofilewassimilartothatoftheunconstrained

run(Figure7).

Thecumulativetimeinundatedforeachcellovertheperiodof100yearscan

beseeninFigures8,9,and10.Thesefiguresshowthatthesidechannelactivation

intheunconstrainedrunwasmoreconsistentoverthedurationofthesimulation

thantheconstrainedruns.Ontherightrideofthemapoftheunconstrained

condition(Figure8),thereareseveralredtoorangecoloredchannelsbraidedina

waythatistypicalforabraidedriversystem.Thereisalsooneredtoorange

coloredchannelnearthetopofthemap.Thiswasahistoricchannel,anditappears

asthoughtheriverhasreoccupiedthischannelmanytimesduringthesimulation.

Infigures9and10,thesidechannelsvisibleonthebottomofthemaps,closertothe

leftside,arelocatedclosertogether,andwouldnotbeconsistentwithapatternof

multiplechannelsactivatedsimultaneously.

Figure11showstheriverprofilethroughthecenterofthemainchannelof

theunconstrainedrunduringthelowflowsimulation.Thepatternofhighvelocities

associatedwithlowdepthsandlargeraveragesedimentsize(D50)isconsistent

withwhatwouldbeexpectedforapool-rifflegravel-beddedriver.Sedimentsizes

foreachoftheselocationsareappropriate,giventhesedimentsizeinputs.

Thecumulativeamountofsedimentfluxwasplottedovertimeforallthree

scenarios(Figure12).Allthreeconditionsproducedfairlylinearoutputs,butthe

mostsedimentfluxoccurredinthesetbackconditionandtheleastinthenarrow

condition.ComparisontoUSGShistoricalrecordsstatinghistoricalsedimentflux

revealsthevaluesfortheunconstrainedandsetbackconditionsarewithinan

appropriatesedimentfluxrange,butthevalueforthenarrowconditionistoosmall.

Forthetrialrunsincludingthelowflows,modeltimewasapproximately15

hours.Cross-channelelevationandsedimentprofileswereconsistentwithexpected

results.Thenarrowconditionhadasharpinclineandcoarsesedimentinthemiddle

ofthechannel.Theunconstrainedconditionhadawiderchannel,slightlywider

thantheinitialchannel,andsedimentsizeinthemiddleofthechannelwaslarger

thanonthefloodplain,butstillsmallerthanintheconstrainedrun.

Thevelocityoutputofthelowflowtrialrunswasmapped,andvelocities

werecharacterizedbasedontypicaltransitionsbetweenmorphologicunitsas

identifiedbyPasternakandSenter(2011).Planebedisdefinedasavelocityless

than0.3m/s,insetchannelsasbetween0.3and0.6m/s,steepinsetchannelsas

greaterthan0.6m/s.Thefinalcategory,theareaswithvelocitiesmorethan0.9m/s,

aredefinedastherunmorphologicunit.Inthenarrowrun(Figure13),thechannel

isverynarrowandthererangeofmorphologicunitsisdifficulttodistinguish.Inthe

unconstrainedrun(Figure14),thechanneliswider,andthespatialpatternis

recognizable,andconsistentwithwhatwouldbeexpectedforagravel-beddedriver.

Thefastareas(blue)areontheinsideofbends,andtheslowerparts(greenand

yellow)areinthesidechannelareas.

Salmonidhabitatarea(definedbyGoodmanetal.2014)wasmappedforthe

highflowruns(Figures15and16).Thehabitatareas(Table1)foreachrunwere

fairlyconsistent.Therewaslessareaintheunconstrainedrunthaninthenarrow

run.Themosthabitatareawasinthesetbackrun.However,muchofthehabitat

areaintheunconstrainedrunwasinthesidechannels.

Insummary,physicaldiversitywasmoreintheunconstrainedrunsthanin

theconstrainedruns.Whilehabitatmeasurementssuggestmorehabitatinthe

constrainedrun,muchofthehabitatintheunconstrainedrunwasintheside

channels.

Discussion

Theunconstrainedconditionhadthemostsidechannelactivityoutofthe

threetrials,bothattheendofthetrialandcumulativelyduringsimulation.Thisis

consistentwiththeliteraturesuggestingawidererodiblecorridorcanenhance

morphologicdiversity.Asexpected,inthenarrowcorridor,themainchannelwas

stationarythroughoutthedurationoftherun.Thecross-channelprofileofthe

narrowcorridorconditionsrevealedthatthechannelbecamenarroweranddeeper,

whichisconsistentwithobservationsinrealsystems(Beagleetal.2015).However,

thesedimentprofilesuggeststhattoomuchfinesedimentmaybeerodingfromthe

system.Addinganappropriateamountofsedimenttothesystem,ratherthan

recirculatingsediment,mayresultinamorerealisticsedimentprofile.

Inthesetbackcondition,thechannelwidened,andcumulativesedimentflux

washigherthanintheunconstrainedcondition.Judgingbythecross-sectional

profileandcomparisonofthefinalelevationmaptotheinitialcondition,itappears

thatthechannelerodeduntilitcametotherevetments,and“bouncedoff,”running

intotherevetmentsontheotherside.Becausetheerodiblecorridorwasrelatively

narrow,thisprocesscontinued,resultinginawideractivechannelandmore

sedimentfluxthanfortheunconstrainedcondition(Figure12).Timeconstraints

preventedmodelingofthesetbackconditionwithallflows,butthisresultwould

likelybeimprovedbysupplyingsediment.

Thehabitatareaintheunconstrainedrunwaslessthanthesetbackrun,and

allthreerunswerefairlysimilarincalculatedhabitatarea.However,theside

channelareadidappeartobeanimportantcontributortohabitatarea(Figure14).

Themodeloutputsvelocityanddepthateachtimestep,meaningthatthisissimply

asnapshotofwhathabitatexistsatasinglepointintime.Amodificationtothe

modelallowingthetrackingofcumulativetimeacellmeetsthespecifiedhabitat

conditionwouldlikelybemorerepresentativeofthelong-termhabitatchanges

associatedwithdifferentmanagementstrategies.

Theallflowmodelresultssuggestthatthisstrategymaybeabetterindicator

offuturehabitatconditionsthanthesolelyhighflowcondition.Originally,Itrieda

fewtrialswithallflows,butbecauseIwasusing9grainsizes,itwasextraordinarily

slow.However,reducingthenumberofgrainsizesdecreasedruntimesignificantly.

Whileitispossibletorunthemodelwithalltheflowsandgrainsizes,itwouldtakea

verylongtime,andmaynotbesuitableformanagement.However,thiswouldbea

necessarytestforthetheoreticalexperimentsabouttheimportanceofriver

corridorwidth.

Thehabitatparametersusedinthisstudywereverylimited.Developingan

indexforassessingthephysicaloutputofthemodelspatially,similartotheuseof

Shannon’sdiversityindexperformedbyYarnelletal.in2006wouldbethefirststep

inturningtheoutputofthemodelintoausefultoolforrestoration.Thiscouldbe

appliedtothemapsforallflowsclassifyingcertainhabitatunits.Theuseofanindex

likeShannon’sdiversityindexwouldbeanotherusefultoolforexploringhabitat

quantity.Incorporatingotheravailableparameters,likesedimentsize,wouldalso

increaseitsutility.Connectingcurrentlyexistingrivermorphologiestolocal

biologicalintegrityestimateswouldbeanimportantwayoffieldvalidatingthe

results.

ThesepreliminarytestsindicatethattheCAESAR-Lisfloodmodelhasthe

potentialtoquantifydifferencesbetweenpossiblerestorationstrategies,andina

reasonableamountoftime.Thechannelprofilefordepth,averagesedimentsize,

andvelocityindicatedthatthemodeliscapableofrepresentingthepool-riffle

sequenceexpectedinagravel-beddedriversystem.Whilethevalidityofthe

constrainedconditionswouldbeimprovedbyaddingsedimenttothesystem,the

modeliscapableofproducingreasonablerivermorphologyandappropriately

distributingsediment.

Futurestudiesshouldexploreothermodelparameters,andincorporate

moresedimentsizes,anduseofacommonbiologicalindex.Furtherexplorationof

themodel’soperationcouldresultinausefulandapproachabletoolforrestoration.

Figure1.Positionsofnon-erodiblerockrevetmentsusedforCAESARmodelruns.Revetmentsareplacedalongthebanksoftheexistingchannel.

Figure2.Unconstrainedconditionafter100yearsofsimulatedflow.ResultingDEMismodeledwithasummerlowflow(4cms).Colorsrepresentvelocitywithdarkerblueindicatinggreatervelocity.Redlineindicatespositionofcross-section(Figure5).

TablesandFigures

Figure3.Narrowconditionafter100yearsofsimulatedflow.ResultingDEMismodeledwithasummerlowflow(4cms).Colorsrepresentvelocitywithdarkerblueindicatinggreatervelocity.Redlineindicatespositionofcross-section(Figure6).

Figure4.Setbackconditionafter100yearsofsimulatedflow.ResultingDEMismodeledwithasummerlowflow(4cms).Colorsrepresentvelocitywithdarkerblueindicatinggreatervelocity.Redlineindicatespositionofcross-section(Figure5).

Figure5.Cross-sectionofunconstrainedconditionafter100years.Averagesedimentdiameterislargerinthemiddleofthechannelthanthefloodplain.

Figure6.Cross-sectionofnarrowconditionafter100years.Averagesedimentdiametershowsnopatternacrossthechannelprofile.

Figure7.Cross-sectionofsetbackconditionafter100years.Averagesedimentdiameterislargerinthemiddleofthechannelthanthefloodplain,andchanneliswiderthanintheunconstrainedcondition(Figure5).

Figure8.Cumulativetimeinundatedduring100-yearsimulationforunconstrainedcondition.Colorsrangefrompurpletoredforincreasingtimeinundated.Sidechannels(orange)visibleonthebothsidesofthemainchannel(red)wereinundatedforlongerthanthesurroundingfloodplain.

Figure9.Cumulativetimeinundatedduring100-yearsimulationfornarrowcondition.Colorsrangefrompurpletoredforincreasingtimeinundated.Sidechannels(orange)canbeseenprimarilyonthesouthsideofthemainchannel(red).

Figure10.Cumulativetimeinundatedduring100-yearsimulationforsetbackcondition.Colorsrangefrompurpletoredforincreasingtimeinundated.Veryfewareasoutsidethemainchannel(red)wereinundatedforasignificantportionofthesimulation.

Figure11.Depth,velocity,andaveragesedimentdiameter(D50)profileforthelengthofthemainchanneloftheunconstrainedconditionafter100yearssimulation.Sedimentsizeandvelocityareinverselycorrelatedwithdepth,asexpectedforapool-rifflesequence.

Figure12.Cumulativesedimentfluxovertimefortheunconstrained,narrow,andsetbackconditions.

Figure15.HabitatareainunconstrainedconditionforCoho/Chinookpresmoltafter100yearsofflow(Depth<1m,velocity<1m/s).

TestConditions HabitatArea

Unconstrained 2970m2

Narrow 2410m2

SetBack 3140m2

Table1.Habitatareacalculatedduringsummerlowflowafter100simulatedyears.

Figure16.HabitatareainconstrainedconditionforCoho/Chinookpresmoltafter100yearsofflow(Depth<1m,velocity<1m/s).

Figure13.Velocityduringlowflowinconstrainedrunafter100simulatedyearswithallflows.Lowvelocitiescanbeseenalongtheedgesofthechannel,andthereislittleareaofhighvelocities(blue).

Figure14.Velocityduringlowflowinunconstrainedrunafter100simulatedyearswithallflows.Velocityisproperlysortedalongedges,andthereisaconsistentdistributionofmorphologicunits.

Appendix1ModelInformation

CAESAR-Lisfloodisa2DcellularmodelthatintegratestheCAESARlandscapeevolutionmodel(LEM)withtheLISFLOOD-FPhydraulicmodel(Coulthardetal.2013).Combiningthemodelsprovidesgreaterefficiencyforlargerspatialandtemporalscaleswithoutthelossofprecisionprovidedbynon-steadyflowhydraulicequations,makingthismodelanappropriatechoiceforthisstudy.

Inadditiontothemodelefficiency,themodelwasselectedbecause:• Itusessize-specificsedimenttransportequations(WilcockandCrowe,2003)

torepresentfluvialerosionanddeposition,therebyallowingsimulationofchangesinbedtexture

• Outputprovideswaterdepth,velocity,andaveragesedimentparticlesizevaluesforeverycellonthegrid,whichcanbeusedtocalculatehabitatareaatanypointinthesimulation

• Sourcecodeisavailableforcustomization,allowingustotrackcellsmeetingconditionsforhabitatranges

ComputerUsed4core3.5ghzXeonPCDEM:18,012cellgrid(114x158),10mcellsModelInputHydrology AveragedailyflowvalueswereobtainedfromUSGSstream

gage12142000.Flowentersthemodelatthreearbitrarilychosenpointsclosetothenorthedgeofthemap.Lowflowsusedaflowof9cms.

DigitalElevationMap(DEM)

Themapusedwasobtainedfrom2009KingCountyLIDAR.Itwascorrectedforwaterdepthbasedoncolorinanaerialimage,resampledat10mresolution,andmodifiedinArcGIStopreventflowfromleavingthenorthernboundary.

Sediment Distributionwascalculatedfromabar-toppebblecount.Thesupplyisspecifiedbyrecirculatingsedimentleavingthelowerboundaryofthemap.

Revetments ThesearerepresentedbyabedrockfilecreatedbymodifyingtheoriginalDEM

Lateralerosion Thisisaparameterthatmustbecalibratedforaparticularstudysitebyexperimentation.Itestedarangeofvaluesfrom0.01to0.00001,andfoundthatforthissite,avalueof0.0002resultedinanappropriatemorphologywithcurvatureexpectedgiventhecurrentandhistoricalconditionsofthesite.

HydraulicRoughness

Thisparameteraffectsthevelocityofthein-channelflow.Manning’snwasfoundbycalibrationtohighwatermarks.

Allothermodelparameterswereleftunaltered.