A Compendium of Ecological Information on Australia’s Northern
TropicalRivers
REPORT 1
Geomorphicclassification
M.J.SaynorA,WayneErskineBandJLowryA
AEnvironmentalResearchInstituteoftheSupervisingScientist,GPOBox461,Darwin,NT
0801,Australia
BCentrefortheSustainableUseofCoastsandCatchments,SchoolofEnvironmentalandLife
Sciences,TheUniversityofNewcastle,POBox127,Ourimbah,NSW2258,Australia.
Authors
M.J.Saynor-EnvironmentalResearchInstituteoftheSupervisingScientist,GPO Box461,Darwin,NT0801,Australia
W.Erskine-CentrefortheSustainableUseofCoastsandCatchments,Schoolof EnvironmentalandLifeSciences,TheUniversityofNewcastle,PO Box127,Ourimbah,NSW2258,Australia.
J.Lowry-EnvironmentalResearchInstituteoftheSupervisingScientist,GPO Box461,Darwin,NT0801,Australia
Thisreportshouldbecited asfollows:
Saynor,M.J.,Erskine,W.andLowry,J.2008.Report:Geomorphology.InG.P.Lukacsand C.M. Finlayson (eds) 2008. A Compendium of Ecological Information on Australia’s NorthernTropicalRivers.Sub-project 1ofAustralia’s TropicalRivers–anintegrateddata assessment andanalysis(DET18).AreporttoLandWaterAustralia.NationalCentrefor TropicalWetlandResearch,Townsville,Queensland.
Contactinformation
NCTWR
C/ AustralianCentreforTropicalFreshwaterResearch
JamesCookUniversity
Townsville4811
QueenslandAustralia
Fundingstatement
ThisprojectwasfundedbytheNaturalHeritageTrustPhase2(NHT2)andLandWater
Australia(LWA)aspartoftheTropicalRiversInventoryandAssessmentProject(TRIAP).
Disclaimer
Theviewsandopinionsexpressedinthisreportdonotnecessarilyreflect thoseofthe NationalCentreforTropicalWetlandsResearchanditspartners.Whilereasonableefforts havebeenmadetoensurethatthecontents ofthisreportarefactuallycorrect,someessential data rely on the referencescited and the NCTWRdo not accept responsibilityfor the accuracy,currencyorcompletenessofthecontentsofthisreport,andshallnotbeliablefor anylossordamagethatmaybeoccasioneddirectlyorindirectlythroughtheuseof,or relianceon,thereport.Readersshouldexercisetheirownskillandjudgment withrespectto theiruseofthe materialcontainedinthisreport.
Acknowledgments
Wethank DrC.TaylorandDrA.Brooksforhelpful discussiononmethodologyandmapped reaches.ProfessorWayneErskinegratefullyacknowledges thesupportoftheEnvironmental ResearchInstituteoftheSupervisingScientistforhisinvolvementinthisproject.
TABLE OF CONTENTS
1. / Executive Summary / 42. / Background / 5
3. / Geomorphic Classification - Continental Scale / 6
4. / TropicalRiversGeomorphicClassification:Focus
CatchmentScale / 12
4.1 DalyRiver / 13
4.2 FitzroyRiver / 16
4.3 FlindersRiver / 17
4.4 AllFocusCatchments / 17
5. / PredictedClimateChangeImpacts / 18
6. / SummaryandConclusions / 19
7. / References / 20
Figure 1 Location of the three focuscatchments for the Tropical Rivers Inventory
and Assessment project………………………………………………………………………………5
Figure 2 The nine mainriver types andtheir important variants found on Australian
tropical rivers…………………………………………………………………………………………...6
Figure 3 Continental geomorphic classification of rivers across northern Australia……...…..11
Figure 4 Continental classification (7classes) for theDaly River, NT…………………...…….11
Figure 5 Mapped river types for river reaches of theDaly Rivercatchment, NT...….….……15
Figure 6 Mapped river types for river reaches of the Fitzroy River catchment, WA…….……16
Figure 7 Mapped river types for river reaches of the Flinders River catchment, Qld…….…..17
Table 1 Comparison of initial focus-catchment classification and initial
broadscale geomorphic classification .…………………………………………………………….7
Table 2 Continental-scalegeomorphic typology of rivers………………………….……………10
Table 3 Length of Continental Geomorphic Classes…………………………………………….10
Table 4 River types identified in the DalyRiver, Fitzroy River and Flinders River
catchments, Qld and mapped as homogeneous river reaches in eachcatchment…………..13
Table 5 Percentage of total river length for each river type in each focus catchment….……15
1.ExecutiveSummary
ThepreliminarytypologyofAustralian tropicalriversproposedbyErskineetal.(2005)has beenrevisedtoprovideacontinental-scale geomorphicclassificationofalltheriversin northernAustraliarepresentedonthe1:2,500,000 drainagedataset,andacatchment-scale classificationto the complete channelnetwork(namedand majorrivers)shownon the
1:250,000topographicmaps forthree large drainagebasinsinnorthernAustralia(Daly River, NT;Fitzroy River,WA;Flinders River,Qld).ThisworkispartoftheTropical Rivers InventoryandAssessment ProjectfundedbyLandandWaterAustraliaandtheNatural Heritage Trust. The continental-scale typology used continental-scalesoil and landform informationtocategorise riversintothefollowing sevenbroadgeomorphicrivertypesacross northernAustralia (1)bedrockchannel;(2)bedrock confined; (3)levelalluvialplain;(4) undulatingalluvialplain;(5)rollingalluvialplain;(6)lake/swamp; (7)estuarine.The catchmentscaleclassificationissignificant asthisisthefirsttimethatthewholechannel networkofallthreecatchmentshasbeenclassifiedintohomogeneousriverreachesbasedon geomorphic criteria.Previousriverclassificationexercisesontheserivershaveonly investigatedaminorcomponentofthetotalchannelnetwork.TheninerivertypesofErskine etal.(2005)wererevisedbyadditions,amalgamationsanddeletionsto12toaccommodate thefullrangeofriver typespresent.The12river types mappedashomogeneousriver reaches were:(1)bedrockrivers;(2)confinedandconstrained rivers;(3)lowsinuosityrivers;(4) meanderingrivers;(5)wanderingrivers;(6)anabranching rivers;(7)chainofponds;(8) gullies;(9)floodouts;(10)lakes,swampsorbillabongs;(11)non-channelised valleyfloors; and(12)estuarinerivers.Thefloodplainsassociatedwitheachrivertypearealsodifferent andareincludedintheclassification.Atscaleslargerthan1:250,000,subdivisionofeach rivertypeisrecommended. IntheDalyRivercatchment,confinedandconstrainedrivers dominate,withbedrock,meanderingandanabranching riverssubdominant. IntheFitzroy Rivercatchment,confinedandconstrainedriversandanabranching riversdominate,with bedrock,meanderingandlowsinuosityriverssubdominant. IntheFlindersRivercatchment, anabranching rivers predominate, with confined and constrained rivers also present. Wanderingrivers,floodoutsandnon-channelised valleyfloorswererareforthe1:250,000 channelnetwork.PredictedclimatechangefortheAustralian tropicsincludeshigher temperatures, a more intense monsoon, general increase in rainfall intensities, possible markedincreaseinheavyrains,morefloodsanddryspells,increasedpotentialevaporation and enhancedtopographiceffectsonrainfall.Irrigatedagricultureisalsochangingfocusfrom temperatetotropicalAustraliawheretherearecurrentlymanyproposeddevelopments. To predict river response to climate change and agriculturaldevelopmentit is essential to benchmark thelocationandcondition ofexistingrivertypesintheAustraliantropicsand understandtheirstructureandfunction.Theproposedriverclassification schemeenablesthe identificationof the major river types present and the prioritisationof research on the structureandfunctionofthedominantrivertypes.Itisunlikelythatthedominantrivertypes intropicalAustralia aresensitivetoclimatechangebecauseofeitherextensive floodplains (anabranching and meandering rivers) to dissipate flood power or resistant channel boundaries(confinedandconstrainedriversandbedrockrivers).Nevertheless, riparian vegetation is an important control on channel stability and climate-inducedchanges in riparianvegetation willhavesignificant implicationsforthecharacteristicsoftheidentified rivertypes.
2.Background
Anumberofattemptshavebeenmadeatdevelopingageomorphic classificationscheme whichcouldbeappliedatthecontinental scaleegRosgen(1994)andBrierlyandFryirs (2005).However,atpresentthereisnoconsensusonwhatwouldconstitute auniversally acceptedgeomorphic riverclassificationschemeatthecontinentalscalethatcouldbeeasily repeatedbydifferentoperators(Naiman,1992;Kondolf,1995,Parsonset al2004).
Basedontheirexperience withtropicalriversintheNorthernTerritory,Erskineetal.(2005) proposedapreliminarytypologyofAustraliantropicalriversforsubsequent applicationto riverreachmappingandclassification.A geomorphologicalapproachto rivercharacterization andclassificationwasadoptedbecauseitistheonlyonepossiblebasedonthelimited existinginformation forAustraliantropicalrivers.Riverreachesarehomogeneouslengthsof streamchannelwithinwhichhydrological, geological,andadjacentcatchmentsurface conditionsaresufficientlyconstantsothatauniformrivermorphologyoraconsistentpattern ofalternatingrivermorphologies isproduced(Erskine,2005a).Channelreachesconsistof relativelyhomogeneous associationsoflandformsandhabitattypes,whichdistinguishthem fromadjoining reachesandaretypically10kmtogreaterthan100kminlength(Bissonand Montgomery,1996).Whilethecore lengthofareachiseasytoidentify,itismore difficultto definepreciselythetransitionalboundariesfromonerivertypeorreachtoanother(Erskine,
2005a).
Thegeomorphic classificationfortheTropicalRiversInventoryandAssessment Project (TRIAP)wasundertakenattwoscales,acontinentalscale(nominally1:2,500,000) andata catchment scale (1:250,000). At the continental scale, all rivers represented on the
1:2,500,000drainagedatasetsproducedbyGeoscienceAustraliahavebeenclassifiedusing thecontinental geomorphic classification.Acatchmentscaleclassificationwasappliedtothe majorandnameddrainagefeaturesextractedfromthe1:250,000Geodatadrainagedatasets forthreecatchments(Daly-NT,Flinders-QLD andFitzroy–WA)which wereselectedas
focuscatchments(Figure1).
Fitzroy
River
Daly
RiverFlindersRiver
Figure 1:LocationofthethreefocuscatchmentsfortheTropicalRiversInventoryandAssessment project.
3.GeomorphicClassification- ContinentalScale
Erskine et al (2005) originally proposed that nine broad tropical river types could be identifiedwithin northernAustralia.Importantly,someoftheproposedcategoriesareunique, inthattheydescriberivertypesthathavenotpreviouslybeencategorized /classifiedin Australiaorinsimilarenvironmentsoverseas.Theninerivertypesare:
1. BedrockChannels
2. Bedrock-ConfinedRivers
3. AvulsiveRivers
4. MeanderingRivers
5. Lowsinuosityrivers(StraightRivers)
6. Floodouts
7. Island-andRidge-AnabranchingSand-BedRivers
8. Co-ExistentMudBraidedandAnabranchingRivers
9. ExtensiveWetlandsandBillabongs
Whiletheproposedrivertypescouldrepresenttheprogressivedownstream changein geomorphologyofariver from theheadwaterstothemouth,itisimportantto understandthat notalltypeswillnecessarilybeobservedonthesamestreamorriver.Figure2illustratesthe
nineproposedrivertypes;furtherdetail iscontainedinErskineet al(2005).
1.RESISTANT BEDROCKRIVER
PlungePool
Waterfall
Cascade
Pool
1AUpland1BTransition1CGorge
2.BEDROCK-CONFINEDRIVER3.AVULSIVERIVER
Natural
LeveeAbandoned
Channel
In-Channel
Bench
4.MEANDERING RIVER
4AConfined4BLaterallyMigratingUnconfined
PointBar
4CLaterallyStable
Unconfined
5.STRAIGHTRIVER6.FLOODOUT
Intersection
Point
7.ISLANDRIDGE ANABRANCHING
8.CO-EXISTENT MUD9.FRESHWATER WETLANDS BRAIDEDANABRANCHINGANDBILLABONGS
BraidBar
BED- ROCK
LARGE GRAVEL
SAND
SILTY SAND
Waterhole
Channel
Billabong
GRAVEL
MUD
Figure 2: Thenine main rivertypes and their important variants found onAustralian tropical rivers.
The nine classes were developedto provide a geomorphicclassificationfor Australia’s tropicalrivers.Howeveratthebroad,continental scaleitbecameapparentthatitwasnot possibletoidentifyordelineateeachoftheindividual classesusingexisting,availabledata sets. This was particularly evident with regard to floodplain reaches that had multiple channelsorthosewithahighsinuosity.AworkshopwasheldinJuly2005(Darwin)whereit was agreed that a broader scale classification was required at the continentalscale, to complement thenine-class classification,whichwouldbeappliedtoindividual focus catchments. Table1shows thebroadscaleclassificationandhowitrelatestothenineclasses ofErskineetal (2005)originallyintendedfor use atthefocus-catchmentlevel.Avulsiveriver typeshavebeentakenoutoftheclassificationasitwasdecidedthatitwasadescription ofa processratherthanatypeofriver.Initially,TidalandEstuarinewerealsonotconsidered by Erskineetal2005buthavebeenaddedtoTable1toallowforconnectivity totheocean. Furtherclassificationoftidal andestuarineclasseswillbecompletedelsewhere.
Table 1: Comparison of initial focus-catchment classification and initial broadscale geomorphic classification
Initialfocus-catchmentscaleclassificationInitialbroad-scaleclassification
(1)BedrockChannel(1)BedrockChannel
(2)Bedrock-confined(2)Bedrock-confined
(3)Lowsinuosityrivers(StraightRivers) (4)Meanderingrivers
(5)Floodouts
(6)Multiplechannelrivers(Island-andRidge-
Anabranching& Co-ExistantMudBraidedand
AnabranchingRivers)
(7)Wanderingchannelrivers(Newcategory) (8)Non-channelised(ExtensiveWetlandsand
Billabongs)
(9)Swamp/waterbodydominatedzone(Extensive
WetlandsandBillabongs) (10)Tidal
(3)Alluvial
(4)Lake/Swamp
(5)Estuarine
Bedrock channels represent environments with highly resistant lithologies ie quartz sandstone, quartziteandgranite,whichhavebeenerodedbyverylargefloods. Theymaybe represented asuplandbedrockchannels,whichoccurinchannelscabland,oronplateau surfacesupstreamofwaterfalls.Channelscablandconsistsofextensivebedrockanabranching channels and scour pools eroded by catastrophic floods on bedrock uplands. Bedrock channelsmayalsoberepresented asdeepbedrockchannels,whichareincisedintoresistant bedrock,andare alsoformedaftervery large floods.Erosionbycatastrophicfloodsproducea rangeofchannel unitswhichinclude deeppools(upto30metresdeep),andboulder riffles, cascadesandbars(BakerandPickup1987;Wohl1992a,1992b).
Bedrockconfinedriversareusuallyfounddownstream ofgorgeswheretheconstraining mediumislesseffectiveinpreventing valleywidening,andtheslopedeclinessothatgravel and/orsandbedmaterial isdeposited.Poolsareoftensandfloored,andrifflesarecomposedof gravels(boulders)and/orbedrock.Riparianvegetationis importantfor stabilizingthese rivers,andlargewoodstartstoaccumulateinthechannel, although thehighstreampower meanstheloadingsarelow.Themainchannelunitsareacombination ofstillandfast-water habitats. Turbulent fast-water habitats can restrict fish passage due to vertical steps,
turbulence andhighvelocity.Poolsusuallypersistduringthedryseason,wherestreamsare seasonal.
Alluvialriversareusuallyfoundbetweenthebedrockconfined reaches andtheEstuarine sectionsdownstream.Thisclasscontainsthefivefocuslevelclassificationscontainedin Table1.Theseriversoccuronlevelorgentlyundulating plainsandcanhaveeithersingleor multiplechannelsofvariouscurvaturesorsinuosity’s. Theseriverswouldusuallybe characterised bysandybedmaterialandriparianvegetation alongthebanks.Thechannels wouldusually compriseofpoolsandrifflesandwhennotinfloodconditionsthewaterwould beslowmovingwhichallowsforeasyfishpassage.Manyofthesechannels coulddryout duringdryseasonconditionsleavinglimitedpoolrefugesforfish.
Lake/swamp.Thedominantchannelunitsarechannelandfloodplainbillabongs, butthere arealsoabandonedchannelsandseasonalbackswampwetlandsthat supporta rangeof different plant communities.Swamps are perennial, although the area extent may vary seasonally.Factorswhichaffectthedistribution ofswampsincludetherelativereliefofthe land,andthewaterloggingcharacteristics ofthesoils.Lakesmaybeperennialorseasonal. AcrossnorthernAustralia,perenniallakes arelargelytheresult ofhumanactivity,suchasthe dammingofrivers.LakeArgyleintheKimberley,producedbythedammingoftheOrd River,isanexampleofthis.Naturally-occurringlakestendtobe seasonalinnature.
Estuarine riversarethosesectionsthatareinfluenced bytidalmovementandthushave brackishorsaltywater.Theestuarinesectionsoftheriversarebeingexaminedseparately.
Unfortunately,manyofthedatasetswhichwouldbeidealformappingthedistributionof thesecharacteristicsacrossnorthernAustraliaeitherarenotavailable,areincomplete,donot extendoverthewholeofnorthernAustralia,oronlyexistatscaleswhicharenotuseful.It wasthereforenecessarytotryandidentifythesegeomorphic classesusingexistingsurrogate datasetswhichcoulddelineate andidentifythedifferentgeomorphicclasses.
Theinitialbreakdownintotheproposedgeomorphicclassesatthecontinentalscalewasdone inaGISenvironment,usingthe1:2,000,000 DigitalAtlasofAustralianSoils,whichisitself basedontheclassificationbyNorthcoteetal(1960-1968).Thedescriptions ofall513soil typesthatoccurredwithin a200-metrebufferofthecenterlineoftheriversrepresentedinthe
1:2,500,000 drainagedatasetweredownloadedasatextfileandthenimportedintoaspread sheet.Thesedescriptionscontainedinformationofthesurroundinglandformandrocktypes, as well as depth and soil characteristics.The soil typeswere sortedalphabeticallyand subjectivelyassignedtooneofthebroadgeomorphicclasseslistedinTable1.
Theattributesofthesoildatasetwereintersectedwiththelinearfeaturerepresenting the drainageline,andthesoilattributes–includingthegeomorphicclassification–assignedto thedrainagefeature.Thisenabledthedrainage featuretobeclassified intothedifferent geomorphicclassesdescribedearlier.
Anydescriptions withthewordsplateau,dissectedandotherindicationsofbedrockorany references torockyoutcropsetcwereassignedasBedrockChannel(class1).Soiltypes describedashilly,orwhichreferredtoareasofundulating plainswereassignedasBedrock Confined(class2).TheAlluvialcategory(class3)wascomposedofalldescriptions withthe word“plain/s”orthatweredescribedas“gentlyundulating”or“gentlysloping”. Classes4
(Lake / swamp) and 5 (Estuarine)were reasonably self-evident when looking at the descriptions,with floodplainsand swampyplainsassignedcategory4 and coastaldune systemsassignedcategory5.Compared totheothercategories therewererelativelyfew descriptionsincategories4and5.
Whenthedistributionofthealluvial classalongthe1:2,500,000drainagenetworkwas mapped,itbecameapparent,throughinitialfeedback,thatfurtherdifferentiation withinthis classwasrequired. Thenumberofrelevantdatasetswhichhavebeencompiledtoasimilar scalelimitedthenumberofdatasets whichcouldbeusedtodifferentiate thisdata.Intheend, thedatasetrepresentingthedominantgeomorphic landformcharacteristicsoftheregion, compiledtoa scale of1:2,000,000wasusedtodifferentiateandidentifyalluvialsub-classes.
Usingthelandformcharacteristicsdataset,thealluvialclass wasdividedintothree categories, basedonthefollowingcriteria:
•level alluvial plain(composedofthoselandformsclassifiedas'levelplains;)
•undulating alluvial plain (those landforms classified as 'gently undulating', or
'undulating'plains)
•rolling alluvial plain (the remainder of the landforms that occurred within the previous'alluvial floodplain'classification- includesrollingplains,rollinghills, undulatingrisesetc) -effectivelytoidentifyareaswithgreaterrelief.
Usingthesecategories, whichreflectedrelativereliefandelevationinthelandscape,hadthe effectofdividingthepre-existingalluvialcategoryintolower,middleanduppersections.
Asaresultofthisprocess,afinal7-classtypologywasgeneratedforapplicationatthebroad (continental) scale.Acomparisonoftheinitial,andthefinalbroad-scaleclassesisshownin Table2.The7-classtypologywasappliedtoall riverswithinthetropicalnorthrepresentedon the1:2,500,000drainagedatasetproducedbyGeoscienceAustralia(Figure3).Figure4 showstheapplication ofthe7-classestotheDalyRiverNT.Theriverreacheshavebeen classifiedusingonlytheexistingbroad-scaledatasetsreferredtoearlierandtherehasnot beenanygroundtruthingtovalidatetheseclassifications. Thelengthofthedifferent geomorphicclasseswithin theproject areaofeachstateinthestudyarea,andthetotallength ofeachclassisshowninTable3.
Table3showsthelengthofthemappeddrainage foreachofthecontinental geomorphic classes.Overall,‘undulatingalluvialplains’arebestrepresentedoftheclassesacrossthe entirestudyarea.However,thedistribution isextremelyuneven,withmorethantwo-thirds classifiedasoccurringinQueensland, withcomparatively fewoccurrences inWestern Australia. Similarly, level alluvial plains are also found predominantly in Queensland. Bedrock channel and bedrock confined channels are next best represented,the greatest distribution inbothcasesbeingintheNorthernTerritory.Rollingalluvialplainsarefound primarilyinWA.Theclasseswiththeshortestriverlengths,‘lake/swamp’and‘estuarine’are foundprimarilyintheNorthernTerritory.Onastate-by-statebasis,theundulating alluvial plainclassificationdominaterivers inQueensland,whilst bedrockconfined/bedrockchannel classificationsdominatethe NorthernTerritory.WesternAustraliahas the lowestoverallriver length,withthebedrockconfinedclassthedominantclasspresent.Interestingly, Western Australiaistheonlystateinwhichnoneoftheriversareclassifiedaslake/swamp,andhas thelowestlengthofriverclassifiedas‘estuarine’.
Againitshouldbestressedthatthisclassificationwasdevelopedfrom1:2,000,000 Digital Atlas of Australian Soils and that the differences described above may be reflecting differencesin soiltyperatherthandifferencesinchannelcharacteristics.
Table 2: Continental-scale geomorphic typology of rivers
Initialbroad-scaleclassificationFinalbroad-scaleclassification
(1)BedrockChannel(1)BedrockChannel
(2)Bedrockconfined(2)Bedrock-confined
(3)Alluvial(3)Levelalluvialplain
(4)Undulatingalluvialplain
(5)Rollingalluvialplain
(4)Lake/Swamp(6)Lake/ Swamp
(5)Estuarine(7)Estuarine
Table 3: Length of Continental GeomorphicClasses.
Geomorphic classification / LengthofclassifiedriverWA (km) / Lengthof classifiedriverNT (km) / Lengthof classifiedriver QLD(km) / Total(km)
BedrockChannel / 4905.6 / 5109.5 / 2071.7 / 12086.8
Bedrock-confined / 2244.3 / 5879 / 3363.8 / 11487.1
Estuarine / 119.1 / 1679.9 / 951.2 / 2750.2
Lake/ swamp / - / 1673.4 / 395.4 / 2068.8
Levelalluvialplain / 2513.5 / 1381.6 / 9771.2 / 13666.3
Rollingalluvialplain / 1945 / 1336.6 / 1394.1 / 4675.7
Undulatingalluvial plain / 518.2 / 5195.3 / 10062.7 / 15776.2
TotalperState / 12245.7 / 22255.3 / 28010.1 / 62511.1
Figure 3:Continental geomorphic classification of rivers across northern Australia
Figure 4:Continental classification (7 classes) for the Daly River, NT
4.TropicalRiversGeomorphicClassification:Focus
CatchmentScale
Itisessentialtoknowwhatrivertypescurrentlyexistincatchmentsifthey are to bemanaged effectivelyandifappropriateactionsaretobeproposedandimplemented toaddresscurrent andfuturethreats,suchaslanddevelopmentandclimatechange.Theworkreportedbelow canbecompletedinabout2daysfora110,000km2catchmentiftopographicandgeological mapsandremotelysenseddataarereadilyavailable.
Theapproach adoptedhereisthatasimpledescriptivenamebasedonthedistinguishing geomorphiccharacteristicsofthereachisused,suchas‘Meandering River’.Greater terminologicalprecisioncanbeusedwhentheuniquecharacteristics ofeachtypeare determined (Erskine,1999).Thiswillallowsubdivision ofmajortypesintomore homogeneouscategoriesasmoreinformationisobtainedandasmappingprogressestolarger scale.Channelreachesaretheappropriate spatialscaletomapspecificrivertypes,suchas thosedefinedbyRosgen(1994;1996),Brierleyand Fryirs(2000;2005),Brierleyetal(2002) andErskineetal(2005).TheErskineetal(2005)typologyappliestoreachesatleast5km butusuallygreater than10kmlong.Previousassessmentsof streamconditionin theDalyand Roper catchments in the Northern Territory were based on stream order as shown on
1:250,000topographic maps(Faulks,1998;2001)whichareofanappropriatescalefor applicationofthepresenttypology.
Erskineetal’s(2005)preliminarytypology(Figure 2)wasappliedtothecompletechannel networkwhichhadbeenclassifiedaseitheranamedand/oramajorriver)extractedfromthe
1:250,000GeoDatadigitaltopographicdatasetsforthethree largedrainagebasinsinnorthern Australia (Daly River, NT; Fitzroy River, WA; Flinders River, Qld) which had been previouslyidentifiedas so-called ‘focuscatchments’for the TRIAPprogram.Remotely senseddata,topographic andgeologicalmapsandrelevantpublishedliteraturewereusedto supplement andenhancethedelineation ofthesechannels.Significantlythisisthefirsttime thatthewholemappedchannelnetworkofallthreerivershasbeenclassified into homogeneous riverreaches.Previousriverclassificationexercisesontheserivershavenot investigatedthetotalchannelnetworkbutonlyasubjectivelydeterminedsubset(Faulks,
1998;BrennanGardiner,2004).
However,itwasfoundthat someof the rivertypesillustratedin Figure2weretoo detailedfor mappingatascaleof1:250,000andthatthepreliminaryschemeneededexpansiontoinclude rivertypesthathadnotbeenincorporated intotheinitialtypology.Therefore,theinitial schemeshowninFigure2wasrevisedbyadditions,amalgamationsanddeletionsto12river typestoaccommodate thefullrangeofrivertypespresent.The12rivertypesmappedas homogeneous riverreacheswere:(1)bedrockrivers;(2)confinedandconstrainedrivers;(3) lowsinuosityrivers;(4)meanderingrivers;(5)wandering rivers;(6)anabranchingrivers;(7) chain of ponds;(8) gullies;(9) floodouts;(10) lakes, swampsor billabongs;(11) non- channelisedvalleyfloors;and(12)estuarinerivers.The floodplainsassociatedwitheachriver typearealsodifferentandareincludedintheclassification. Table4outlinestherevised classification.Atscaleslargerthan1:250,000,subdivisionof eachrivertypeisrecommended, asshownbythevariantsinTable4.However, noattemptwasmadetomapthevariantsfor thisproject.AswithBrennan andGardiner (2004),thiswasadesktopexercisethatdidnot involveanyfieldwork.
Thechangefromoneriverreachtoanothercanbeabruptbutcanalsobetransitional.Care was taken to check boundariesin bedrock confinementfor changes in geology, where possible.Nevertheless, itmustberealisedthatbetterqualitydataontopography,landforms andgeologymaynecessitaterevisionsofthepresentreachboundaries. Importantly, itshould berecognised thatallclassesmaynotbepresentineverycatchment. Theresultsofthe classificationoftheindividualfocuscatchmentsaredescribedbelow:
4.1DalyRiver
ThetotalcatchmentareaoftheDalyRiverdrainage basinis52577km2andFaulks(1998), Jolly(2001;2002),Jollyetal (2000),Beggetal.(2001),BeggandLowry(2003)and Erskine etal(2003)alldiscussthechannelnetwork,wetlands,hydrology, waterbalanceand environmentalwater requirementsofthecatchment. Figure5shows thespatialdistributionof rivertypesandTable5showsthepercentage ofthemappeddrainage occupied byeachriver type. Thetotallengthofchannelsclassifiedas‘namedormajor’ atascaleof1:250,000inthe DalyRivercatchmentis4861km.
IntheDalyRivercatchment,confinedandconstrainedriversdominated (48.5%ofthetotal lengthofthechannelnetwork),withanabranching rivers(17.4%),chainofponds(9.33%), meanderingrivers(8.88%)andbedrockrivers(7.66%)subdominant. Onlyshortreachesof lowsinuosityrivers,non-channelised valleyfloors,billabongsandestuarineriverswere mapped.Wanderingrivers,floodoutsandgullieswereabsent.
TheKatherine, Fergusson, EdithandDalyRiversareeitherbedrockchannelsorbedrock confinedandconstrainedchannelsformostoftheirlength.Thelowreliefcatchmentofthe Dry Riverischaracterisedbylowenergyrivertypeswithnon-channelisedvalleyfloors,chain ofpondsandanabranchingriversdominating.Billabongsandnon-channelisedvalleyfloors arecommonontheestuarinefloodplain.
Table 4: River types identifiedin the DalyRiver catchment, NT, FitzroyRiver catchment, WA and Flinders River catchment, Qldand mapped ashomogeneous river reachesin each catchment. See Figures 3, 4 and 5 for the spatial distributionof river types ineach catchment.
RivertypeCharacteristicsVariants
1.BedrockRiverChannelexcavatedintobedrockwithessentially nofloodplain.
iv) UplandBedrockChannel ii)SteepBedrockCascades
iii)DeepBedrockGorge
2.Confinedand
ConstrainedRiver
Channelimpingesagainstand/orflowsacross materialsoflimitederodibility,suchascolluvium, bedrockorterracesediments(Schumm,2005). Limiteddevelopmentoffloodplainaspocketsin localisedexpansions.Barsandbenchesoften formwhereitistoonarrowforafloodplain.
iv) Closelateralconfinement ii)Closelateralandvertical
confinement
iii)CloseVerticalConfinement iv)PartialLateralConfinement v)PartialLateralandVertical
Confinement
vi)PartialVerticalConfinement
3.LowSinuosityRiverSinglechannelwithasinuosity< 1.35.Floodplain usuallyhasa well-developednaturalleveewith crevassesandsplays.
i)Straightchannelswitha sinuosity<1.05
ii)Lowsinuositychannelwitha sinuositybetween1.05and1.4.
4.MeanderingRiverSinglechannelwithasinuositygenerally>1.5.
Shortsectionsofstraighterchannelwitha sinuosityof>1.35areincluded.Pointbarsusually well=developedontheinsideofbends.
Floodplainformeddominantlybylateralaccretion andoftenconsistsoffloodplainridges.
5.WanderingRiverUsuallygravel-bedbutcanbesand-bed.
Intermediateformbetweenmeanderingand braidedriverswithislandsandbars.
6.AnabranchingRiverMultiplechannelsseparatedbyridges,islands and/orfloodplain.Diversityof different anabranchingriversandfloodplains,manyof whichhavestillnotbeeninvestigated.
iv) ConfinedMeanderingRiver
ii)LaterallyMigratingUnconfined
MeanderingRiver
iii)LaterallyStableUnconfined
MeanderingRiver
Overseasresultsmaynotbe applicabletoAustraliabecause therearefewbraidedrivers.
iv) RidgeAnabranchingRiver ii)IslandAnabranchingRiver
iii)Co-existentMud-Braidedand
AnabranchingRiver
iv)FloodplainAnabranching
River
v)MultipleMainChannels
AnabranchingRiver
7.ChainofPondsAdiversedrainageformrangingfrom disconnectedpools/pondsinvalleyfloorstolarge poolsinsmallcontinuouschannelstoextensive wetlands.
8.GullyRelativelydeep,recentlyformed,eroded channelsthatarecutintounconsolidated materialswhereno well-definedchannel previouslyexisted.
Requiresfurtherinvestigation.
i)ValleyFloorGully ii)ValleyHeadGully iii)Valley-SideGully
9.FloodoutFormofchannelfailurewherebedloadis deposited.DiscussedbyErskineetal.(2005).
i)TerminalFloodout
ii)IntermediateFloodout
10.Lakes,Swampsand
Billabongs
11.Non-ChannelisedValley
Floors
Poolsinformerchannelsofestuariesandrivers, backswampsanddammedtributaryvalleys. DiscussedbyErskineetal.(2005)
Swampy,unchanneledvalleyfloorsthatcan extendupslopeintoalluvialfans,hillslopehollows andpercolines.Usuallywellvegetatedand characterisedbyhighwatertables,atleast
duringthe wetseason.Mudsheetscharacterise thefloodplain.
i)ChannelBillabongs
ii)FloodplainBillabongs iii)BackflowBillabongs iv)Backswamps
Requiresfurtherinvestigation
12.EstuarineRiversWoodroffeetal.(1989)definefourreachesfor macrotidal estuarieswhichareincludedas examples i)toiv)inthenextcolumn.Floodplains differ between different reaches. Newly developing tidalchannelsarecalled‘Developing SalineChannels’ andarediscussed byKnighton etal.(1991;1992)
i)EstuarineFunnel
ii)SinuousMeanderingReach iii)CuspateMeanderingReach iv)UpstreamReach
v)DevelopingSalineChannels
Figure 5: Mapped river typesfor river reaches of the DalyRiver catchment, NT.
Table 5: Percentageoftotalriverlengthfor each river typein each focus catchment.
Rivertype / %oftotalchannel length–DalyRiver / %oftotalchannel length– FitzroyRiver / %oftotalchannel length– Flinders River / %oftotalchannel length– Overall1.BedrockRiver / 7.65 / 7.48 / 1.94 / 3.64
2.Confinedand
ConstrainedRiver / 48.45 / 38.52 / 13.22 / 22.01
3.LowSinuosityRiver / 4.17 / 2.14 / 1.50 / 1.93
4.MeanderingRiver / 8.88 / 3.70 / 2.63 / 3.54
5.WanderingRiver / 0 / 0 / 0.9 / 0.63
6.AnabranchingRiver / 17.41 / 44.68 / 77.77 / 64.66
7.ChainofPonds / 9.33 / 0.49 / 0.32 / 1.38
8.Gully / 0 / 0.30 / 0 / 0.06
9.Floodout / 0 / 0.49 / 0 / 0.09
10.Lakes,Swamps andBillabongs / 0.96 / 0.07 / 0 / 0.12
11.Non-Channelised
ValleyFloors / 1.50 / 0.76 / 0.80 / 0.87
12.EstuarineRivers / 1.65 / 1.37 / 0.92 / 1.09
4.2FitzroyRiver
The total catchment area of the Fitzroy River catchment is about 90,000 km2 and the catchmentiscomposed ofbedrockuplandsintheupperone-thirdofthecatchmentand lowlandsinthelowertwo-thirds ofthecatchment(Figure6).Taylor(1999)discussesthe anabranching reachesinthelowlandsbutanabranching reachesalsooccurinpartsofthe uplands. Figure4showsthespatialdistribution ofrivertypesandTable5showsthe percentage ofthemappeddrainageoccupiedbyeachrivertype.Thetotallengthof major/namedchannelsmappedatascaleof1:250,000inthe FitzroyRivercatchmentis8145 km.
IntheFitzroyRivercatchment,anabranching rivers(44.68%)andbedrockconfinedand constrainedrivers(38.52%)dominate,withbedrock(7.48%),meandering(3.70%)andlow sinuosityrivers(2.15%)subdominant.Onlyshortreachesofnon-channelised valleyfloors, billabongs, chainofponds,gullies,floodoutsandestuarineriversweremapped.Wandering riverswerenotpresent.
Anabranchingriversdominate inthelowercatchment,andbedrockandbedrockconfinedand constrainedriversdominateintheuppercatchment(Figure6).Exceptfortheestuary,all otherrivertypeshavea veryrestrictedspatial distribution(Figure6;Table5).
Figure 6:Mapped river typesfor river reaches of the Fitzroy River catchment, WA.
4.3FlindersRiver
Thetotalcatchment areaoftheFlindersRivercatchment isabout109,400km2.Brennanand Gardiner(2004) mapped riverstylesontheFlinders,Stawell,Cloncurry,Corella,Dugald and WilliamsriversandJuliaCreek.Figure7showsthespatialdistribution ofrivertypesinthe FlindersRivercatchmentfromthepresentworkandTable5showsthepercentage ofthe mappeddrainageoccupiedbyeachrivertype.Thetotallengthofmajor/named channels mappedat a scale of1:250,000in theFitzroyRivercatchmentis29,927km.
IntheFlindersRivercatchment,anabranching riverspredominate(77.77%),withbedrock confined and constrained (13.22 %), meandering (2.63 %) bedrock (1.94 %) and low sinuosityrivers(1.50%)alsopresent.Wandering rivers,chainofponds,non-channelised valleyfloorsandestuarineriverswererareforthe1:250,000mappedchannelnetwork.
AsshowninFigure7,anabranchingriversdominatethroughoutthecatchment,exceptforthe uplandsinthesouthwestern cornerandtheeasternpartofthecatchment.Intheuplands, bedrockconfinedandconstrained andbedrockchannelsdominate.Exceptfortheestuary,all otherfiverivertypeshavea restricteddistribution.
Figure 7:Mapped river typesfor river reaches of the Flinders River catchment, Qld.
4.4AllFocusCatchments
Table5showsthepercentageof themappeddrainageoccupiedbyeachrivertypeforallthree focuscatchmentscombined. Thetotallengthofchannelsmappedat1:250,000 inthethree focuscatchmentsis42,933km.Anabranching riversclearlydominateoccupying64.66%of thetotallengthofmappeddrainageinallthreecatchments. Confinedandconstrained rivers occupythenextgreatestlengthofmappeddrainageat22.01%.Bedrock (3.64%)and meanderingchannels(3.54%)arethenextmostsignificant,withlowsinuosityrivers(1.93
%),chainofponds(1.38%)andestuarinerivers(1.09%)beingtheonlyotherstooccupy morethan1%ofthetotalmappeddrainagelength.Therefore, billabongs, non-channelised valleyfloors,floodouts, gulliesandwandering riversarerelativelyrarerivertypesforthe mappeddrainageonthe1:250,000datasetsinthefocuscatchments.
5.PredictedClimateChangeImpacts
PredictedclimatechangefortheAustraliantropicsincludeshighertemperatures, amore intensemonsoon, generalincreaseinrainfallintensities,possiblemarkedincreaseinheavy rains,morefloodsanddryspells,increased potentialevaporation andenhancedtopographic effectsonrainfall.Irrigatedagriculture isalsochangingfocusfromtemperatetotropical Australiawherethereare currentlymanyproposeddevelopments.To predictriverresponseto climatechangeandagriculturaldevelopment itisessentialtobenchmarkthelocationand conditionofexistingrivertypesinthe Australiantropicsandtounderstandtheir structureand function.Theriverclassification schemeusedforthepresentstudyenablestheidentification ofthemajorriver typespresentandtheprioritisationofresearchonthestructureandfunction ofthedominantrivertypes.Clearly,ourresultsindicatethatanabranching andbedrock confinedandconstrained riversarethemostimportrivertypesinthefocuscatchments.Itis unlikelythatthesedominant rivertypesintropicalAustralia aresensitivetoclimatechange becauseofeitherextensivefloodplains(anabranching rivers)todissipatefloodpoweror resistantchannelboundaries (bedrockconfinedandconstrained rivers).Theeffectsofmore variablestreamflows ontheirresilienceandsensitivityrequiresfurtherinvestigation. Nevertheless, riparianvegetationisanimportantcontrolonchannelstabilityandclimate- induced changes in riparian vegetation will have significant implications for the characteristicsoftheidentifiedrivertypes.
Riverclassification isalsoimportantfortheidentification ofrarerivertypesthatshouldbe conserved and/orprotectedfromknownthreats, suchasclimatechange.Ourresultsindicate thatbillabongs,non-channelised valleyfloors,floodouts,gulliesandwanderingriversare relativelyrarerivertypesthatshouldbeassessedfortargettedconservation efforts.While gulliesand floodoutsare hardlysignificantlandformsand ecosystems,non-channelisedvalley floorsandbillabongsaremoreimportantintermsofpreventing theonsetofgullyerosion whichcangeneratehighsedimentyields(Erskine, 2005b)anddrainbillabongs. Saynoretal (2004)haveemphasised thatitispossibletoreversegullyinitiationiftheearlystagesare identifiedandappropriatecorrectivemeasuresaretaken.
Theextensive freshwater wetlands (220km2)onlowerMagelaCreekwereformedatleastin part bysedimentationduringthelateHoloceneraisingtheMagelawetlandsabovethelevelof tidal inundation,hencecausingatrophyofestuarinechannels,theremnantsofwhichstillexist asbillabongs insomeplaces(Wasson,1992).Russell-Smith (1985)andMulrennen and Woodroffe(1998a)alsodocumentedasimilardismembermentoftheSouthAlligatorand Maryrivers,respectively, immediatelyupstreamoftheirestuariesduringthelateHolocene. However,in the latter cases, there has been recent saline intrusioninto the freshwater wetlands,forreasonsthatarestillunclear(Mulrennen andWoodroffe, 1998b)butprobably includeshortperiodchangesinsealevel.Nevertheless, ontheMaryRiver,theatrophied formertidalchannelshaverapidlyextendedbackintothewetlandsbyacombination of headwardextension alongmainchannelsandbytributarydevelopment(Knightonetal1991;
1992). Wedidnotidentifysalineintrusion inourfocuscatchments.Nevertheless,billabongs,
lakes andswampsaresensitivelandformsandecosystemsthatwillrespondtoanychangesin tidal hydrodynamicsandwaterbalance,bothofwhichcanbeinfluencedby climate change.
6.Summaryand Conclusions
Apreliminarynine-class typologyofAustraliantropicalriverswasproposed byErskineetal (2005)toprovideageomorphicclassification forAustralia’stropicalrivers.However,atthe broad,continentalscaleitbecameapparentthatitwasnotpossibletoidentifyordelineate eachoftheindividualclassesusingexisting,availabledatasets. Throughaprocessof consultation, thetypologywasrevisedtoproduceaseven-classtypology.Consequently,this typologywasappliedtoalltheallriversrepresentedonthe1:2,500,000digitaldrainage datasetinthe51catchmentsinthestudyarea. Theclassificationwasbasedonquerying existing soils and landform datasets in a GIS environment. No ground surveys were undertakentovalidate thetypologyandtherehasnotbeenanyonthegroundvalidation.
Whenapplied atthefocuscatchmentscale,specificallytothecompletechannel network (namedandmajorrivers)extractedfromdigital1:250,000hydrological datasetsforthethree focuscatchments (DalyRiver,NT;FitzroyRiver,WA;Flinders River,Qld),thepreliminary typologyproposedbyErskineetal.(2005)requiredmajorrevisions.Theinitialnineriver typeswererevisedbyadditions,amalgamations anddeletionsto12toaccommodatethefull rangeofrivertypespresent.The12rivertypesmappedashomogeneous riverreacheswere: (1) bedrock rivers; (2) confined and constrained rivers; (3) low sinuosity rivers; (4) meanderingrivers;(5)wanderingrivers;(6)anabranching rivers;(7)chainofponds;(8) gullies;(9)floodouts;(10)lakes,swampsorbillabongs;(11)non-channelised valleyfloors; and(12)estuarinerivers.Thefloodplainsassociatedwitheachrivertypewerealsoincluded in the classification.At scales larger than 1:250,000,subdivisionof each river type is recommended. IntheDalyRivercatchment,confinedandconstrainedriversdominate,with bedrock,meanderingandanabranching riverssubdominant.IntheFitzroyRivercatchment, confinedandconstrainedriversandanabranchingriversdominate,withbedrock,meandering andlowsinuosityriverssubdominant. IntheFlindersRivercatchment,anabranching rivers predominate,withconfinedandconstrained riversalsopresent.Wanderingrivers,floodouts andnon-channelisedvalleyfloorswererareforthe1:250,000channelnetwork.
Thegeomorphicclassificationsatboththecontinentalandfocus-catchment scalearean essentialandintegralelementofaGISwhichhasbeencompiledaspartoftheinventory of datausedinthedevelopmentofanecologicaltypologyfornorthAustralianrivers.
PredictedclimatechangefortheAustralian tropicsissignificant.Topredictriverresponse to climatechangeandagriculturaldevelopment itisessentialtobenchmarkthelocationand conditionofexistingrivertypesintheAustraliantropicsandunderstand theirstructureand function.Themodifiedriverclassificationschemeenablestheidentificationofthemajorriver typespresentandtheprioritisation ofresearchonthestructureandfunctionofthedominant rivertypes.Itisunlikely thatthedominant rivertypesintropicalAustraliaaresensitive to climatechangebecauseofeitherextensivefloodplains (anabranchingandmeandering rivers) todissipatefloodpowerorresistantchannelboundaries (confinedandconstrained riversand bedrockrivers).Nevertheless, riparianvegetationisanimportantcontrolonchannelstability andclimate-inducedchangesinriparianvegetationwillhavesignificant implications forthe characteristicsoftheidentifiedrivertypes.
7.References
Baker VR Pickup G 1987. Flood geomorphologyof the Katherine Gorge, Northern
Territory,Australia.GeologicalSocietyofAmericaBulletin 98,635-646.
Begg,G.Lowry,J.(2003)Landcapabilityandtopographic dataasasurrogateforthe mappingandclassificationofwetlands: acaseexamplefromtheDalybasin,Northern Territory,Australia.WaterScienceandTechnology48(7):49-56.
Begg,G.W.,vanDam,R.A.,Lowry,J.B.,Finlayson, C.M.Walden,D.J.(2001).Inventory and risk assessmentofwaterdependentecosystemsinthe Dalybasin,NorthernTerritory, Australia.SupervisingScientistReport162,SupervisingScientist,Darwin.
Bisson,P.A.andMontgomery, D.R.(1996).Valleysegments,streamreaches,andchannel units.In:‘MethodsinStreamEcology’. (EdsF.R.Hauer,andG.A.Lamberti.) pp.23-52. (AcademicPress:SanDiego,USA.)
Brierley,G.J.andFryirs,K. (2000).Riverstyles,a geomorphicapproachto catchment characterization: implicationsfor river rehabilitationin Bega catchment, New South Wales,Australia.EnvironmentalManagement25,661-679.