delineation of riparian habitats from high resolution...

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JeffBakerGEO565

3/14/2009

DelineationofriparianhabitatsfromhighresolutionLiDARdata:theWillamette

Riverfloodplain

Introduction

Riverfloodplainsdependuponperiodicfloodingtomaintainecosystemfunctionsrelatedto

disturbance,nutrientcycling,vegetativecommunities,andfishandwildlifehabitat.Butinmanyplaces

floodplainshavebeenalteredbyregulationofriverflows,conversiontoagriculture,anddevelopment

forindustrialandurbanuses,whichhasdegradedecosystemprocessesandservicesassociatedwith

riverfloodplains.Asaresultthereisincreasinginterestinrestoringphysicalandecologicalprocessesto

floodplains,wherepossible.

IntheWillametteBasin,Oregongovernmentagenciesandconservationorganizationshave

identifiedopportunityareasalongtheWillametteRiverforconservationandrestorationofphysicaland

ecologicalprocessesandservices(Floberg2004,Hulseetal.2002,ODFW2006).Theseconservation

opportunityareas(COA)wereidentifiedataregionalscaleasplaceswheretherearegoodopportunities

toconservehighpriorityhabitatsandspecies(ODFW2006).However,sitespecificassessmentsand

prescriptionshavenotbeencompletedfortheCOAs.

Theobjectivesofthisprojectweretobegintoidentifyandprioritizehabitatswithinthefloodplain

oftheWillametteRiverbetweenCorvallisandAlbanythatmaybesuitableforconservationor

restoration.Ageographicinformationsystem(GIS)wasusedtoanalyzetopographyandvegetationto

determinethelocationsofstreamchannelsandriparianvegetation.Theresultswillcontributeto

conservationplanningbytheGreenbeltLandTrustbasedinCorvallis,Oregon.

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StudyArea

Thestudyarea(Figure1)islocatedinthe500‐yearfloodplainofareachoftheWillametteRiver

betweenCorvallisandAlbany,Oregon.ItiswithintheconservationopportunityareaidentifiedasWV‐

04intheOregonConservationStrategy(ODFW2006)andencompasses4,438ha.Themeanannualriver

flowis4,561m3/sasmeasuredbyaUSGSstreamflowgage(14174000)locatedatthedownstreamend

ofthestudyareanearAlbany.Thedrainageareaupstreamofthegaugeis12,536squarekilometers.

Thereare9floodcontroldamslocatedupstreamofthestudyareathatregulateflowsthroughthestudy

reach.Primarylandusesincludeagriculture,sandandgravelmining,ruralresidences,openspace,and

recreation.Themajorityofthelandisprivatelyownedwithafewparcelsalongtheriverownedbythe

StateofOregonandmanagedasgreenways.

Figure1.Thestudyareaislocatedwithinthe500‐yearfloodplainoftheWillametteRiverbetweenCorvallisandAlbany,Oregon.Thestudyextentisshownasrectangleasitwasusedtoconducttheinitialrasteranalyses.Imageryis2009DOQfromOregonGeospatialEnterpriseOffice.

Corvallis

Albany

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Methods

Data

Highspatialresolutionelevationdataacquiredbylightdetectionandranging(LiDAR)wasusedto

analyzeforstreamchannelsandvegetationheightsandpatcheswithinthestudyarea.TheLiDARdata

werecollectedbyWatershedSciences,Inc.in2008and2009fortheOregonDepartmentofGeologyand

MineralIndustries(DOGAMI).Horizontalgridcellsmeasure0.9144mby0.9144mandmeanvertical

offsetsvaryfrom0.009mto0.033masmeasuredbycomparingtheLiDARelevationswithmeasured

ground‐controlpoints(DOGAMI2009a,DOGAMI2009b,DOGAMI2009c).Dataweredownloadedfrom

theOregonGeospatialEnterpriseOfficeFTPserverat

ftp://159.121.106.159/elevation/lidar/WillametteValley_LiDAR/.

AdditionalGISlayersusedforthisprojectincluded100and500yearfloodplainsandaerialimagery.

ThefloodplainlayerwasderivedfromtheFederalFloodInsuranceRateMapsandwasdownloaded

fromtheOregonGeospatialEnterpriseOfficewebsiteat

http://www.oregon.gov/DAS/EISPD/GEO/sdlibrary.shtml.Aerialimageryflownin2009wasobtained

fromtheOregonGeospatialEnterpriseOfficeFTPserverftp://159.121.106.159/imagery/CCM2009/.

AlldatalayerswereprojectedusingtheNAD1983LambertConformalConiccoordinatesystem.

StudyExtentandArea

TheextentofthestudyareawasdefinedintheGISwitharectanglethatencompassedthe500year

floodplainbetweenCorvallisandAlbanywiththeeastandwestboundariesplacedattheapproximate

locationsoftheVanBurenStreetBridgeinCorvallisandtheHighway20BridgeinAlbany.Therectangle

studyextentwasusedforclippingandanalysisoftherasterlayersderivedfromtheLiDARdata.The

studyareawasthenfurtherrefinedbyclippingresultstotheboundariesofthe500yearfloodplain.The

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500yearfloodplainwasclippedtothestudyrectangleextentandeditedinArcGIS9.3.1toremove

tributaryfloodplainsoftheWillametteRiver.

Processing

TheLiDARdatawereprovidedasbareearthandhighesthitmodelsinrasterformatinsixtiles

coveringdifferentpartsofthestudyarea.Forthisprojectthebareearthmodelisreferredtoasadigital

elevationmodel(DEM)andthehighesthitmodelisreferredtoasadigitalsurfacemodel(DSM).The

DEMsandDSMswereclippedtothestudyareaandthenarastermosaicDEMandDSMwerecreated

usingModelBuilderinArcGIS9.3.1(Figure2).

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Figure2.ThisflowchartshowstheprocessofcreatingaDSMandDEMforthestudyextent.Blueovalsrepresentinputdata,yellowrectanglesrepresenttheoperationperformed,andgreenovalsaretheoutputdatawiththefinaloutputbeingtheStudyDSMandStudyDEM.

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Analysis

AfterprocessingtheDEMandDSMtothestudyextent,streamchannelsandvegetationwere

derivedandanintersectionoverlaywascompletedtodeterminewherestreamchannelsarevegetated.

AllanalysisoperationswereperformedinArcGIS9.3.1usingModelBuilder.

StreamchannelswerederivedfromthestudyDEMusingtheWatershedDelineationModelthatis

partoftheWatershedDelineationToolboxavailablefordownloadfromESRIat

http://support.esri.com/index.cfm?fa=downloads.geoprocessing.filteredGateway&GPID=16.Thesteps

forderivingthestreamchannelsareshowninFigure3.Thethresholdforcontributingareainorderfor

astreamtobecreatedwas>=10,000cellsor9,144m2.Streamswereoutputasavectorlinefile.

Figure3.ThisflowchartshowsthestepstoderivestreamchannelsfromtheDEM.

VegetationwasderivedbysubtractingtheDEMfromtheDSMandthenreclassifyingtheresults

basedonheight.Vegetationwasclassedasheights<or>3.048m.Vegetation<3.048mwasassumed

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tobeagriculturalcropswhilevegetation>3.048mwasassumedtobenaturalormostlynative

vegetation.Thereclassifiedvegetationrasterwasconvertedtoapolygonfeatureclassandthennatural

vegetationfeatureswereselectedandoutputasaseparatefeatureclass.Thestepsforderiving

vegetationareshowninFigure4.

Figure4.ThisflowchartshowsthestepsusedtoderivevegetationfromtheDSMandDEM.

Afterderivingstreamchannelsandvegetationanintersectionoverlaywasperformedtodetermine

wherevegetationandstreamchannelsintersected.Onlyvegetation>3.048mwasusedinthisanalysis

becauseitwasassumedtobenaturalvegetationandnotagriculturalcrops.Thismodelwasconstructed

tooutputbothstreamlinesthatintersectwithvegetationpolygonsandvegetationpolygonsthat

intersectwithstreamlines,sothatbothcouldbeviewedsimultaneouslyinresultingmaps.Figure5

showsthestepsusedfortheintersectionoverlay.

Figure5.Thisflowchartshowsanintersectionoverlayofstreamsandvegetation.

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Results

Theresultsindicatethatthereareapproximately884hectaresofriparianvegetationand110

kilometersofvegetatedstreaminthefloodplainstudyarea(Table1,Figures6,7,and8).

Table1.Thelengthandareaofstreamandvegetationfeaturesinthestudyarea.

feature length(m)area(ha)

%oftotal

riparianvegetation 883.64 85%non‐riparianvegetation 154.13 15%vegetatedstreams 110,573.40 25%unvegetatedstreams 331,477.37 75%

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Figure6.Vegetatedandunvegetatedstreamsdelineatedfroma0.9144mdigitalelevationmodel.

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Figure7.Riparianandnon‐riparianvegetationderivedfrom0.9144mdigitalelevationanddigitalsurfacemodels.

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Figure8.Riparianvegetationthatintersectswithstreamchannelstotals884hectares.Theseareasmaybethemostsuitableforconservingfloodplainecologicalprocesses.

Discussion

Theresultsindicatethatmuchofthetallervegetation(>3.048m)inthefloodplainisassociated

withstreamchannels(~85%),whichforthepurposesofthisprojectisconsideredtoberiparian

communities.Theseareas,showninFigure8,wouldbethehighestpriorityforconservationbecause

theycontainstreamchannelsandintactvegetativecommunities.Streamswithoutvegetationand

vegetationwithoutpolygonswouldbeconsideredalowerprioritybecausetheaquaticandvegetative

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featuresdonotintersect.Theremainingareaofthefloodplainthatdoesnothavevegetation>3.048m

oraquaticfeatureswouldbethelowestpriorityforconservationbecauseithaslessvaluableecological

featurespresentandwouldrequirethegreatestlevelofrestoration.Theseareasaretypicallyin

agriculturalproduction.

Thereareseveralassumptionsandcaveatsthatshouldbeconsideredwiththisanalysis.Thestream

channelsdelineatedweredonesoatarelativelyfinescaleusinghighresolutionelevationdatasothat

subtledifferencesintopographyresultedinstreamsshowinginareasthatarenottypicallyconsidered

tobestreams.Insomecasesitmightbebettertoconsiderthestreamnetworkasdrainagepatterns.

Forthisanalysisithasbeenassumedthatanyvegetation>3.048misnaturalvegetationandisof

conservationinterest.However,furtheranalysismayshowthatsomepolygonscontainsomething

otherthannatural,mostlynativevegetation.Onelastimportantcaveatisthatnogroundtruthinghas

beenconductedandlittleeditinghasbeendonetoremovefeaturesfromtheanalysisthatmaynotbe

ofinterest,suchastelephonepoles.

Sourcesoferrorinthestudycouldincludemisclassificationofvegetation,incorrectdelineationof

thestreamnetwork,orerrorsintherawLiDARdata.Thereareobviouslocationswherevegetation

polygonsalongtheedgeoftheWillametteRivershouldbeclassifiedasriparianbutwerenotdueto

howtheriverwasdelineated.Theriverwasdelineatedasalinethatmeanderedbetweentheriver

bankssothatinsomeplacestherewasnointersectionofvegetationandstreamchannelswhenthere

shouldhavebeen.Essentially,theriverismuchwiderthanthelinethatwasdelineated.Therecouldbe

verticalorhorizontalerrorsassociatedwiththeLiDARdatahowevertheLiDARdatahadextensive

qualitycontrolanalysisandtheverticalerrorreportedinthemethodssectionaboveappearstobe

acceptable.

Additionalworkshouldfocusonimprovingtheaccuracyofresultsgeneratedbythisproject,adding

additionalanalysis,andprioritizingwithadditionalparameters.Editingofsomestreamchannelsand

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reclassifyingsomevegetationpolygons(e.g.theriveredgeboundaryandadjacentvegetation)using

aerialphotosorfieldvisitswouldimproveaccuracy.Additionalanalysisshouldlookatinundationlevels

andfrequenciesusingsatelliteimageryorhydrologicmodelssuchasHEC‐RAS(Ackermanetal.2009)

andaddadditionalfeatureclassessuchassoiltypes,permanentwaterbodies,andhistoricvegetation

typestohelpfurtheridentifyecologicallyimportantfeaturestoconserveorrestore.Addingaprivate

versuspublicownershiplayerwouldidentifyalreadyprotectedareastouseascoreconservationareas.

Editingandimprovingtheresultsandaddingfurtheranalysiswouldcontributetowardsadditional

prioritizationsothatconservationinvestmentscanbeoptimized.

Conclusion

TheuseofLiDARdatatoanalyzestreamchannelsandriparianvegetationintheWillametteRiver

floodplainrevealedcomplexdrainagepatternsaswellasthelocationandheightsofvegetation.With

thisnewinformationover800hectaresoffloodplainhasbeenidentifiedaspotentiallysuitablefor

restoringecologicalandphysicalprocessesintheWillametteRiverfloodplain.Furtheranalysisshould

helptonarrowthefocustotheverybestareasinwhichtoinvestlimitedconservationresources.

ReferencesCited

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DOGAMI(OregonDepartmentofGeologyandMineralIndustries).2009a.WillametteValleylidarproject,2009–delivery2and3QCAnalysis.OregonDepartmentofGeologyandMineralIndustries.

DOGAMI(OregonDepartmentofGeologyandMineralIndustries).2009b.WillametteValleylidar

project,2009–delivery4and5QCAnalysis.OregonDepartmentofGeologyandMineralIndustries.

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DOGAMI(OregonDepartmentofGeologyandMineralIndustries).2009c.WillametteValleylidarproject,2009–delivery6and7QCAnalysis.OregonDepartmentofGeologyandMineral

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