Delineation of riparian habitats from high resolution...
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1 Jeff Baker GEO 565 3/14/2009 Delineation of riparian habitats from high resolution LiDAR data: the Willamette River floodplain Introduction River floodplains depend upon periodic flooding to maintain ecosystem functions related to disturbance, nutrient cycling, vegetative communities, and fish and wildlife habitat. But in many places floodplains have been altered by regulation of river flows, conversion to agriculture, and development for industrial and urban uses, which has degraded ecosystem processes and services associated with river floodplains. As a result there is increasing interest in restoring physical and ecological processes to floodplains, where possible. In the Willamette Basin, Oregon government agencies and conservation organizations have identified opportunity areas along the Willamette River for conservation and restoration of physical and ecological processes and services (Floberg 2004, Hulse et al. 2002, ODFW 2006). These conservation opportunity areas (COA) were identified at a regional scale as places where there are good opportunities to conserve high priority habitats and species (ODFW 2006). However, site specific assessments and prescriptions have not been completed for the COAs. The objectives of this project were to begin to identify and prioritize habitats within the floodplain of the Willamette River between Corvallis and Albany that may be suitable for conservation or restoration. A geographic information system (GIS) was used to analyze topography and vegetation to determine the locations of stream channels and riparian vegetation. The results will contribute to conservation planning by the Greenbelt Land Trust based in Corvallis, Oregon.
Transcript of 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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