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TRANSCRIPT
Lake Eyre Basin14 Lake Eyre Basin ........................................................ 2
14.1 Introduction ........................................................ 2
14.2 Key information .................................................. 3
14.3 Description of the region .................................... 4
14.3.1 Physiographic characteristics.................. 6
14.3.2 Elevation ................................................. 7
14.3.3 Slopes .................................................... 8
14.3.4 Soil types ............................................... 9
14.3.5 Land use ............................................. 11
14.3.6 Population distribution .......................... 13
14.3.7 Rainfall zones ....................................... 14
14.3.8 Rainfall deficit ....................................... 15
14.4 Landscape water flows ................................... 16
14.4.1 Rainfall .................................................. 17
14.4.2 Evapotranspiration ............................... 20
14.4.3 Landscape water yield ......................... 23
14.5 Surface water and groundwater ....................... 26
14.5.1 Rivers ................................................... 26
14.5.2 Streamflow volumes ............................. 26
14.5.3 Flooding ............................................... 29
14.5.4 Wetlands .............................................. 29
14.5.5 Hydrogeology ....................................... 32
14.5.6 Watertable salinity ................................. 32
14.5.7 Groundwater management units ........... 32
Lake Eyre Basin
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14 Lake Eyre Basin14.1 Introduction
ThischapterexamineswaterresourcesintheLakeEyreBasinregionin2011–12andoverrecentdecades.Itstartswithsummaryinformationonthestatusofwaterflowsandstores.Thisisfollowedbydescriptiveinformationfortheregionincludingthephysiographiccharacteristics,soiltypes,population,landuseandclimate.
Spatialandtemporalpatternsinlandscapewaterflowsarepresentedaswellasanexaminationofthesurfaceandgroundwaterresources.ThedatasourcesandmethodsusedindevelopingthediagramsandmapsarelistedintheTechnicalSupplement.
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14.2 Keyinformation
Table14.1givesanoverviewofthekeycomponentsofthedataandinformationinthischapter.
Table 14.1 Key information on water flows and groundwater quality in the Lake Eyre Basin region
Landscape water flows
Evapo-transpiration
Landscapewater yield
Rainfall
Regionaverage Differencefrom1911–2012long-termannualmean
Decilerankingwithrespecttothe1911–2012record
337mm +42% 9th—aboveaverage
327mm +45% 10th—verymuchaboveaverage
25mm +150% 10th—verymuchaboveaverage
Streamflow (at selected gauges)
Annualtotalflow:
Aboveaverageflowinthreegaugesintheeast.Averageflowsononeofthegaugesinthecentre
Flooding: MajorfloodsintheupstreampartoftheCooperCreekbasin,decreasinginseveritydownstreamandsomefloodingintheDiamantinaandBulloorivers
Groundwater (in selected aquifers)
Salinity: Mostlynon-saline(<3000mg/L)groundwaterinthenorthandsaline(≥3000mg/L)inthesouth
Lake Eyre Basin
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Lake Eyre salt lake | iTobi (iStockphoto)
14.3 Descriptionoftheregion
TheLakeEyreBasinregioncoversapproximately1.2millionkm²ofaridandsemi-aridCentralAustralia.Itrepresents17%ofthecontinentandstretches,northtosouth,fromjustbelowMountIsainQueenslandtoMarreeinSouthAustralia.Fromwesttoeast,itextendsfromAliceSpringsintheNorthernTerritorytoTamboandBlackallincentralQueensland.
Landformsintheregionmainlyconsistofplains,inlanddunes,sandplains,floodplains,andlowreliefhillsandplateaus.Highlyvariableandonaveragelowrainfallhasresultedinsparsevegetationcoverandintermittentriversystems.Subsections14.3.1–14.3.4providemoreinformationonthetopographyandsoilscover.
Withapopulationofapproximately59,000,theLakeEyreBasinaccountsforlessthan0.25%ofthenation’stotalpopulation(AustralianBureauofStatistics[ABS]2011b).
AliceSpringsisthemajorpopulationcentrealongwithanumberofremoteandregionalcentres(Figure14.1)includingCooberPedy,Birdsville,Winton,LongreachandPeterbourough.Furtherdiscussionoftheregion’spopulationdistributioncanbefoundinsubsection14.3.6.
Mostofthelandusewithintheregionisforgrazingandnatureconservation.Therearenumerousdrylakesthatformasubstantialpartoftheregion.Onlyasmallpatchinthefarsouthincludessomedrylandagriculture.
Theregion’sclimateisgenerallyquitearid,withrainfallmuchbelowpotentialevaporation.Theregionisdriestinthenortheast,butthisareadoesreceivesomemonsoonalrainand,althoughbeinghighlyvariable,itcansupplylargeamountsofwater,inparticularintotheupperreachesoftheDiamantinaandGeorginarivers.
Theregionisdividedintoseveralmajorriverbasins.ThemajorriversaretheGeorgina,Diamantina,ThomsonandBarcooriversandCooperCreek,whichflowfromcentralandwesternQueenslandintoSouthAustralia,aswellastheFinke,ToddandHughriversinCentralAustralia.ThesewaterwaysalldrainintoLakeEyre.Theriversandcreeksarecharacterisedbyhighvariabilityandunpredictabilityintheirflow,andhightransmissionlossesandverylowgradients.
ThehydrogeologyoftheregionisdominatedbythesedimentsoftheGreatArtesianBasinwithporoussandstoneaquifers.Thisgroundwaterbasinunderliestheregionfromthenortheast.ItisoneofAustralia’smostsignificantgroundwaterbasins.Thereisnotableextractionofgroundwaterforstockanddomesticpurposes.
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Figure 14.1 Major rivers and urban centres in the Lake Eyre Basin region
Lake Eyre Basin
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Figure 14.2 Physiographic provinces of the Lake Eyre Basin region
14.3.1Physiographiccharacteristics
ThephysiographicmapinFigure14.2indicatesareaswithsimilarlandformevolutionaryhistories(Painetal.2011).Thesecanberelatedbacktosimilargeologyandclimaticimpactswhichdefinetheextentoferosionprocesses.Theareashavedistinctphysicalcharacteristicsthatcaninfluencehydrologicalprocesses.
TheLakeEyreBasinregionhasthreesuchdominantphysiographicprovinces,namely:
• CentralLowlands(72%):undulatingclayplains,sandplainswithlowsandstone,shaleandsilcretehills;
• CentralAustralianRanges(11%):rangesandhillsofigneousrock,sandstoneandquartzitesurroundedbyhardpanwashplainsandsomedunefields,sandandstonyplainsandsaltlakes;and
• Barkly–TanamiPlains(10%):blackclay,sandandlimestoneplainsandsandstonerisesandplateaussomewithferruginousmantles.
Theremainingsixprovinces(seeFigure14.2)occupyonly7%oftheregionandcontainavarietyofphysiographicfeaturesfromplainstoprominentranges.
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Figure 14.3 Ground surface elevations in the Lake Eyre Basin region
14.3.2Elevation
Figure14.3presentsgroundsurfaceelevationsintheLakeEyreBasin.InformationwasobtainedfromtheGeoscienceAustraliawebsite(www.ga.gov.au/topographic-mapping/digital-elevation-data.html).Theregionconsistsofenclosedriverbasinsastheriversdonotflowtothesea.MostoftheregiondrainsintoLakeEyre,providedenoughwaterisavailabletoreachthelake.ThelakeitselfisthelowestpointinAustralia.Thebottomofthelakeis15mbelowsealevelandtheshoresare9mbelowsealevel.
ThemajorriversthatfillLakeEyrearetheDiamantinaandGeorginarivers,whichreceivemostoftheir(monsoonal)wateronthenorthernmountainranges.
ThewatertravelsthroughChannelCountry,wherethelandformsaretypicalofdesertconditions.Theareamainlyconsistsofplains,inlanddunes,sandplains,floodplains,andlowreliefhillsandplateaus.
ThehighestmountainsintheregionarelocatedaroundAliceSprings,withpeaksexceeding1,000mabovesealevel.ThenortherntipoftheFlindersRangesinthesouthalsohassomehighpeakscloseto1,000mabovesealevel(Figure14.3).
Lake Eyre Basin
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Figure 14.4 Surface slopes in the Lake Eyre Basin region
14.3.3Slopes
Areaswithsteepslopesprovidehigherrun-offgeneratingpotentialthanflatareas.TheLakeEyrebasinregionisgenerallyflat,withsomeminorareaswithsteephills(Table14.2andFigure14.4).Theslopeswerederivedfromtheelevationinformationusedintheprevioussection.
Table 14.2 Proportions of slope classes for the region
Slopeclass(%) 0–0.5 0.5–1 1–5 >5
Proportionofregion(%) 61.2 20.1 16.8 1.9
ThesteepslopesinthemapinparticularhighlighttheFlindersRangesinthesouthandtheMacDonnellRangesinthewest.
ThelargeareasofminorslopesinthecentreoftheregionarethesanddunesoftheSimpsonDesert.
AscanbenotedinFigure14.4,theriversintheregionrunthroughvastareaswithhardlyanygradient,whichmeansthatlargeamountsofwaterareneededtomaketheriversflow.
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Figure 14.5 Soil type in the Lake Eyre Basin region
14.3.4Soiltypes
Soilsplayanimportantroleinthehydrologicalcyclebydistributingwaterthatreachestheground.Watercanbetransportedtoriversandlakesviathesoilsurfaceasrun-offorenterthesoilandprovidewaterforplantgrowthaswellascontributingtogroundwaterrecharge.
Thenatureofthesehydrologicalpathwaysandthesuitabilityofthesoilsforagriculturalpurposesareinfluencedbysoiltypesandtheircharacteristics.SoiltypeinformationwasobtainedfromtheAustralianSoilResourceInformationSystemwebsite(www.asris.csiro.au).
About90%oftheLakeEyreBasinregioniscoveredbyfivetypesofsoil,namelyvertosols,rudosols,kandosols,sodosolsandtenosols(Figure14.5andFigure14.6).Thesoilsarecommoninareasusedforgrazingandnatureconservationinthisregion.
Vertosolsaremostlydistributedintheeasternhalfofthisregion.Theyareclayrichsoilswhichhaveatendencytocrackwhendryandswellwhilewetting.Theyarehighlyfertileandhavealargewater-holdingcapacity.Theydo,however,absorbasignificantamountofwaterbeforeanybecomesavailabletoplants.
Rudosolsaremostcommoninthewesternhalfoftheregion.Rudosolsaswellastenosols,whicharescatteredinthenorthwestandeastoftheregion,
arecharacterisedbyhavingaweakandminimaldevelopment.Theyshownoorlittlechangeintextureandcolourandareoftenshallowindepth.Tenosolsandrudosolsarelowinchemicalfertilityandinwater-holdingcapacityandthustheiragriculturalpotentialislow.
Kandosolsarestructurelesssoilswhichareoftenverydeep(uptothreemetresormore),buttheydonothaveastronglycontrastingtextureandtheydonotcontaincarbonatethroughouttheirprofile.Theyarelowinchemicalfertilityandarewell-drained;withonlymoderatewater-holdingcapacitycomparedwithothersoiltypes,thustheyonlyhavelowtomoderateagriculturalpotential.Kandosolsarescatteredacrosstheregion,exceptinthecentralpart.
Sodosolsaredominantinthecentral-westandscatteredinsmallpatchesacrossotherpartsoftheregion.Thesesoilshaveacleartexturecontrast,withanimpermeablesodicsubsoilduetoelevatedsodiumconcentrationsaswellasincreasingclaycontents.Theyaresusceptibletodrylandsalinityaswellaserosion,ifvegetationisremoved.Sodosolsareusuallylowinnutrientstatus.
TheothersoiltypesthathaveminimalrepresentationintheLakeEyreBasinregionincludedermosolsandchromosols(1–6%ofthetotalarea).
Lake Eyre Basin
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Figure 14.6 Soil type distribution in the Lake Eyre Basin region
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Figure 14.7 Land use in the Lake Eyre Basin region
14.3.5Landuse
Figure14.7presentslanduseintheLakeEyreBasinregion.Mostofthelandisusedforgrazingandnatureconservation(datafromdata.daff.gov.au/anrdl/metadata_files/pa_luav4g9abl07811a00.xml).
Therearenumerousdrylakeswhichformasubstantialpartoftheregion.Onlyasmallpatchinthefarsouthincludessomedrylandagriculture(Figure14.8).
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Figure 14.8 Land use distribution in the Lake Eyre Basin region
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Figure 14.9 Population density and distribution in the Lake Eyre Basin region
14.3.6Populationdistribution
LakeEyreBasinregionisamongsttheleastpopulousareasinAustralia.Figure14.9showsthepopulationdensitiesfortheregionandillustratesthesparsenatureofitspopulation(ABS2011b).
ItsmajorpopulationcentreofAliceSpringsislocatednearitsboundaryinthenorthwest.Otherremotecommunitiesarelocatedonorneartheregion’sbordersinthesouthandwest.
Outsideofthemajorurbancentres,miningleases,Indigenouscommunitiesandanumberofsmalltownsandsettlementslocatedadjacenttomajorroadsaccountformuchofitsremainingpopulation.
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Figure 14.10 Rainfall zones in the Lake Eyre Basin region
14.3.7Rainfallzones
TheLakeEyreBasinregion’sclimateisaridthroughout.Theregionreceivesmonsoonalrainacrossthebasin,inparticularintheupperreachesoftheDiamantinaandGeorginarivers.Medianrainfalldoesnotexceed650mmperyearanywhereintheregion(Figure14.10).
Theregionconsistsofoneofthedriestpartsofthecontinent,withlargeareasinthecentrenotexceeding200mmofrainfallonaverage.
Thefarnortheasthasapronouncedwetseason,withannualaveragesofabout400mm.Inthefarsouth,someconsistencyinwinterrainfallispresent,althoughannualmedianrainfalldoesnotexceed500mm.
Formoreinformationonthisandotherclimateclassifications,visittheBureauofMeteorology's(theBureau's)climatewebsite:www.bom.gov.au/jsp/ncc/climate_averages/climate-classifications/index.jsp
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Figure 14.11 Rainfall deficit distribution in the Lake Eyre Basin region
14.3.8Rainfalldeficit
Therainfalldeficitindicator,thatis,rainfallminuspotentialevapotranspiration,givesageneralimpressionaboutwhichpartsoftheregionarelikelytoexperiencemoisturedeficitsovertheperiodofayear.TheLakeEyreBasinregionhasauniformpatternofveryhighpotentialdeficitsoverthewholeregion(Figure14.11),althoughrainfallishighlyvariablefromyeartoyear.
Mostoftheregionconsistsofdesertlandandephemerallakes,includingLakeEyreitself.Streamflow,oftencomingfromthenortheastasaresultofmonsoonalrainfallandtropicalstorms,
occasionallyfeedstheselakesandformslargefloodplains.
Otherthangrassesandsomeshrubsusedforsparselystockedfarming,noreallanduseoccursinthisdrylandscape.
Themoisturedeficitdoes,however,providemanyareaswithauniquefloraandfauna,mostlypreservedinthemanynatureconservationareasintheregion.
Formoreinformationontherainfallandevapotranspirationdata,seetheBureau’smapsofaverageconditions:www.bom.gov.au/climate/averages/maps.shtml
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Figure 14.12 Landscape water flows in 2011–12 compared with the long-term record (July 1911–June 2012) for the Lake Eyre Basin region
14.4 Landscapewaterflows
Thissectionpresentsanalysesofthespatialandtemporalvariationoflandscapewaterflows(rainfall,evapotranspirationandlandscapewateryield)acrosstheLakeEyreBasinregionin2011–12.Nationalrainfallgridsweregeneratedusingdatafromanetworkofpersistent,high-qualityrainfallstationsmanagedbytheBureau.EvapotranspirationandlandscapewateryieldswerederivedusingthelandscapewaterbalancecomponentoftheAustralianWaterResourcesAssessmentSystem(VanDijk2010).ThesemethodsandassociatedoutputuncertaintiesarediscussedintheIntroductionandaddressedinmoredetailintheTechnicalSupplement.
Figure14.12showsthattheLakeEyreBasinregionhasaseasonalrainfallpatternwithawetterspringtoearlyautumnandalargelydrywinterperiod.Evapotranspirationinthedrywinterperiodgenerallyexceedsrainfall.Afterthewetperiodthesoils
normallycontainplentyofmoisturethatisavailableforevapotranspiration.Themonthlylandscapewateryieldhistoryfortheregionshowsastablepatternofverylowyieldthroughouttheyear,althoughitmarginallyincreasesbetweenJanuaryandMarch.
The2011–12yearwasarelativelywetyear,withthemonthsofNovemberandMarchreceivingverymuchaboveaveragerainfall.AnactivemonsooninthenorthoftheregionandLaNiñaandwetterIndianOceaninfluencescontributedtohighrainfalltotals,particularlyforthemonthofMarch.
EvapotranspirationwasparticularlyhighinNovember,DecemberandMarch.InMarch,evapotranspirationwasthesecondhighestonrecordforthe1911–2012time-series.
Thelandscapewateryieldfor2011–12wasfifthhighestonrecordinNovemberandthirdhighestonrecordinMarch.
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Figure 14.13 Spatial distribution of (a) annual rainfall in 2011–12, and (b) their decile rankings over the 1911–2012 period for the Lake Eyre Basin region
14.4.1Rainfall
RainfallfortheLakeEyreBasinregionfor2011–12isestimatedtobe337mm.Thisis42%abovetheregion’slong-termaverage(July1911–June2012)of237mm.Figure14.13ashowsthatthehighestrainfalloccurredinthenortheastwithannualtotalsexceeding600mmin2011–12.Rainfallinthecentreoftheregiondidnotexceed200mmoverlargeareas.
Rainfalldecilesfor2011–12indicateaveragetoaboveaveragerainfallfortheentireregionoverthecourseoftheyear(Figure14.13b).Thesoutheastoftheregionreceivedverymuchaboveaveragerainfall.TheDiamantina–Georginariverbasinsinthenorthwestoftheregionreceivedpredominantlyaveragerainfallonly.
Lake Eyre Basin
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Figure 14.14 Time-series of (a) annual rainfall, and (b) five-year retrospective moving averages for the summer (November–April) and winter (May–October) periods for the Lake Eyre Basin region
Rainfall variability in the recent past
Figure14.14ashowsannualrainfallfortheregionfromJuly1980onwards.Overthis32-yearperiodtheannualaveragewas264mm,varyingfrom156mm(2007–08)to616mm(2010–11).Temporalvariabilityandseasonalpatternssince1980arepresentedinFigure14.14b.
Thegraphsindicatethepresenceofcyclicalpatternstypicalintheregion’sannualrainfall,whichareparticularlynoticeableinthesummerperiod.ThispatterniscloselylinkedtotheSouthernOscillationIndexandtheoccurrenceofElNiñoandLaNiñaperiods(seetheNationalOverviewchapter).AstrongLaNiñaperiodtypicallydeliversaboveaveragerainfall,particularlytothenortheastoftheregion,clearlyseenintherecentverystrong2010–11LaNiñaevent.
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Figure 14.15 Spatial distribution of (a) trends in annual rainfall from 1980–2012, and (b) their statistical significance at 90% (weak) and 95% (strong) confidence levels for the Lake Eyre Basin region
Recent trends in rainfall
Figure14.15apresentsthespatialdistributionofthetrendsinannualrainfallforJuly1980–June2012.Thesearederivedfromlinearregressionanalysesonthetime-seriesofeachmodelgridcell.ThestatisticalsignificanceofthetrendsisprovidedinFigure14.15b.
Figure14.15bshowsthatsince1980anincreaseinrainfallhasoccurredinlargepartsoftheregion,particularlytowardsthenorth;however,thetrendsareonlystronglystatisticallysignificantin6%oftheregion.Thetrendsarelargelyaresultofthemulti-annualcyclicrainfallpatternshowninFigure14.14andtheparticularlyhighrainfallof2011–12.
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14.4.2Evapotranspiration
ModelledannualevapotranspirationfortheLakeEyreBasinregionfor2011–12isestimatedtobe327mm.Thisis45%abovetheregion’slong-term(July1911–June2012)averageof226mm.Thespatialdistributionofannualevapotranspirationin2011–12(Figure14.16a)issimilartothatofrainfall(Figure14.13a).
Evapotranspirationdecilesfor2011–12indicateaboveaveragetotalsacrossmostoftheregion(Figure14.16b).Around23%oftheregionevenrecordedverymuchaboveaverageevapotranspiration,scatteredthroughout.TheLakeEyredistrictinthesouthwestistheexception,wheregenerallyaverageevapotranspirationisestimated.
Figure 14.16 Spatial distribution of (a) modelled annual evapotranspiration in 2011–12, and (b) their decile rankings over the 1911–2012 period for the Lake Eyre Basin region
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Figure 14.17 Time-series of (a) annual evapotranspiration, and (b) five-year retrospective moving averages for the summer (November–April) and winter (May–October) periods for the Lake Eyre Basin region
Evapotranspiration variability in the recent past
Figure14.17ashowsannualevapotranspirationfortheregionfromJuly1980onwards.Overthis32-yearperiodtheannualevapotranspirationaveragewas250mm,varyingfrom153mm(2004–05)to543mm(2010–11).Temporalvariabilityandseasonalpatternssince1980arepresentedinFigure14.17b.
Summerperiodsshowedconsistentlyhigherevapotranspirationthanthewinterperiodduetothehighertemperaturesandthehigherrainfallinthenorthofthearea.Alsotheannualvariabilityismainlycausedduringthesummerperiod,whichagainfollowsthepatternofrainfall(Figure14.14b).
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Recent trends in evapotranspiration
Figure14.18apresentsthespatialdistributionofthetrendsinmodelledannualevapotranspirationfor1980–2012.Thesearederivedfromlinearregressionanalysesonthetime-seriesofeachmodelgridcell.ThestatisticalsignificanceofthetrendsisprovidedinFigure14.18b.
Figure14.18ashowsthatsince1980trendsaremostlyrisingwithastrongersignalinthenorthoftheregion.Figure14.18bconfirmsthatthesestrongernortherntrendsarestatisticallymoresignificant.
Figure 14.18 Spatial distribution of (a) trends in annual evapotranspiration from 1980–2012, and (b) their statistical significance at 90% (weak) and 95% (strong) confidence levels for the Lake Eyre Basin region
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14.4.3Landscapewateryield
ModelledlandscapewateryieldfortheLakeEyreBasinregionfor2011–12isestimatedtobe25mm.Thisis150%abovetheregion’slong-term(July1911–June2012)averageof10mm.Figure14.19ashowsthespatialdistributionoflandscapewateryieldfor2011–12,whichissimilartotheannualrainfalldistribution(Figure14.13a,notethedifferenceinthescalesbetweenthetwofigures).
Thedecile-rankingmapfor2011–12(Figure14.19b)showsaboveaveragetoverymuchaboveaveragelandscapewateryields.Thedecilerankingsoflandscapewateryieldaresubstantiallyhigherthanthoseofrainfallduetothehigherinitialsoilmoisturelevels,causedbythestrongwetseasonin2010–11.
Figure 14.19 Spatial distribution of (a) modelled annual landscape water yield in 2011–12, and (b) their decile rankings over the 1911–2012 period for the Lake Eyre Basin region
Lake Eyre Basin
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Figure 14.20 Time-series of (a) annual landscape water yield, and (b) five-year retrospective moving averages for the summer (November–April) and winter (May–October) periods for the Lake Eyre Basin region
Landscape water yield variability in the recent past
Figure14.20ashowsannuallandscapewateryieldfortheLakeEyreBasinregionfromJuly1980onwards.Overthis32-yearperiod,annuallandscapewateryieldwas13mm,varyingfrom4mm(1985–86)to51mm(2010–11).Temporalvariabilityandseasonalpatternssince1980arepresentedinFigure14.20b.
LandscapewateryieldishighlyvariableintheLakeEyreBasinregionwiththesecondhighestcoefficientofvariation(standarddeviationdividedbymean)ofallregions,behindthePilbara–Gascoyneregion.Thevariabilityinlandscapewateryieldintheannualtotalsaswellasthelandscapewateryieldofthesummerperiodisdirectlyrelatedtorainfall.
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Recent trends in landscape water yield
Figure14.21ashowsthespatialdistributionofthetrendsinmodelledannuallandscapewateryieldfor1980–2012.Thesearederivedfromlinearregressionanalysesonthetime-seriesofeachmodelgridcell.ThestatisticalsignificanceofthetrendsisprovidedinFigure14.21b.
ThepatterninFigure14.20aandtheparticularlyhighpeakof2010–11makesthelandscapewateryieldtrendsstandoutasrisingthroughouttheregion,withtheexceptionoftheverylowlandscapewateryieldareaintheLakeEyredistrictinthesouthwest.Figure14.21bshowsthatinlargepartsoftheregiontrendsarestatisticallysignificant.
Figure 14.21 Spatial distribution of (a) trends in annual landscape water yield from 1980–2012, and (b) their statistical significance at 90% (weak) and 95% (strong) confidence levels for the Lake Eyre Basin region
Lake Eyre Basin
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14.5 Surfacewaterand groundwater
ThissectionexaminessurfacewaterandgroundwaterresourcesintheLakeEyreBasinregionin2011–12.Rivers,wetlandsandstoragesarediscussedtoillustratethestateoftheregion’ssurfacewaterresources.Theregion’swatertableaquifersandsalinityaredescribed.NodatawasavailableattheBureauinasuitableformatforadetailedanalysisonindividualaquifers.
DatawasnotavailableforstreamflowsalinityintheLakeEyreBasin.
TherearenostoragesystemsintheLakeEyreBasin.
14.5.1Rivers
Theregionistheworld’slargestinternallydrainingsystemandLakeEyreisthefifthlargestterminallakeintheworld.Therearethreeriverbasinsintheregion,varyinginsizefrom106,000to699,000km2(Figure14.22).
ThemajorriversintheregionflowfromcentralandwesternQueenslandinthenortheastintoSouthAustraliainthesouth.Thesouthwestcorneroftheregion(LakeEyre)isupto15mbelowsealevelanditisthefinalreceivingareaforallmajorwatercoursesinthebasinifthefloodextentislargeenough.
Theriversandcreeksarecharacterisedbyhighvariabilityandunpredictabilityintheirflowwithhightransmissionlossesandverylowgradients.Allcreeksandriversofthebasinareephemeralwithrelativelyshortperiodsofflowfollowingrain,andoftenlongperiodswithnoflow.
14.5.2Streamflowvolumes
Figure14.23presentsananalysisofflowsatfivemonitoringsitesduring2011–12relativetoannualflowsfortheperiodfromJuly1980–July2012.Monitoringsiteswithrelativelylongrecordsacrossfourgeographicallyrepresentativeriverswereselected(seeTechnicalSupplement).Theannualriverflowsfor2011–12arecolour-codedaccordingtothedecilerankateachsiteoverthe1980–2012period.
TheflowsgenerallyreflectthemostlyaveragetoaboveaveragemodelledlandscapewateryieldresultsshowninFigure14.19b.OnlythemonitoredflowsintheDarrRiverpresentaslightlydifferentpatternofbelowaverageflows(reddotinFigure14.23).
AboveaverageflowswereobservedatthreesitesintheregionwhichwerelocatedonriversintheeastoftheLakeEyreBasinregion.Averagetotalflowswererecordedatonemonitoringsite.ThiswasontheDiamantinaRiverinthecentreoftheregion.
Flowdecilesinthesummer(November2011–April2012)wereverysimilartototalannualflowsfor2011–12asshowninFigure14.23.Thisistobeexpectedgiventhebulkofflowsintheregion,particularlyinthenortheast,occurredoverthesummerperiod.Itisalsotheconsequenceofthesummer-dominatedrainfallinthatpartoftheregion.
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Figure 14.22 Rivers and catchments in the Lake Eyre Basin region
Lake Eyre Basin
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Figure 14.23 Average annual and summer period flow volumes of selected gauges for 2011–12 and their decile rankings over the 1980–2012 period in the Lake Eyre Basin region
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14.5.3Flooding
Figure14.24givesanoverviewofthelocationswheretheBureauismonitoringfloodlevelsintheLakeEyreBasinregionthroughtheNorthernTerritoryGovernment.TheselevelsarefurtherspecifiedintheTechnicalSupplement.
Asequenceofwetanddryspellshasbeenobservedinthelakeoveryears,whichisverymuchrelatedtotheElNiño—SouthernOscillationIndex.MajoreventsoffillingtheLakeEyreareassociatedwithrarecasesofannualrainfallinexcessof500mm.SeveralofthetributariestothelakewerefloodedduringthemonthsbetweenJanuaryandMarch2012.Inearly2012,majorfloodsoccurredintheBullooRiver.
LaterinFebruary,themaintributarytoLakeEyre,theDiamantinaRiver,wasflooded;thiswasconcurrentwithmajorfloodsinseveralsegmentsoftheBarcooRiver.SomemoderatefloodswerealsoregisteredintheThomsonandBullooriversduringFebruary.
InMarch2012andfollowingheavyrainfallsinthecatchmentalltributariesofthelakewereflooded,themostsignificantofwhichwastheDiamantinaRiverwhichhadmajorfloods.Moderatefloodsoccurredinothertributariesofthelake.InApril,thefloodsgraduallysubsidedandwerelimitedtosomemoderateandminorfloodsintheDiamantinaandThomsonrivers,respectively.
14.5.4Wetlands
TherearetwoRamsar-listed,internationallyimportantwetlandsintheLakeEyreBasinregionaswellasanumberofwetlandsofnationalimportancementionedintheAustralian Directory of Important Wetlands (www.environment.gov.au/water/topics/wetlands/database/diwa.html)
Thewetlandsmainlyconsistofephemeralriverfloodplainsandlakes(Figure14.25).Theyplayimportantrolesinthesurvivalofmanyrarespeciesofplantsandanimals.Theyalsoattractlargenumbersofcommonwaterbirdswhenthelakesandfloodplainsareflooded.
Nodetailedassessmentontheinflowsofselectedwetlandshasbeenperformedforthisregion.
Coongie Lakes wetlands | Paul Wainwright
Lake Eyre Basin
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Figure 14.24 Flood occurrences in the Lake Eyre Basin region
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Figure 14.25 Location of important wetlands in the Lake Eyre Basin region
Lake Eyre Basin
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14.5.5Hydrogeology
ThehydrogeologyoftheregionisdominatedbythesedimentsoftheGreatArtesianBasinwithporoussandstoneaquifers.Figure14.26showsthattheGreatArtesianBasinunderliestheregionfromthenortheast,wheretheboundariesofbothbasinscloselyapproximateeachother,andextendsthroughtothecentralandsouthwestmargins.ThisbasinisoneofAustralia’smostsignificantgroundwaterbasins.TheareasidentifiedasPalaeozoicfracturedrock(lowpermeability)inthenorthwestofthisregiontypicallyofferrestrictedlowvolumegroundwaterresources.
Incontrast,theareasidentifiedasfracturedandkarsticandPalaeozoicfracturedrock(consolidatedandpartlyporous)provideausablegroundwaterresourceinsomeparts.Theseunitsprovide95%ofthetownwatersupplyforAliceSprings.
Groundwatersystemsthatprovidemorepotentialforextractionarelabelledas:
• FracturedandKarsticRocks(regional)and(local);and
• MesozoicGAB(porousmedia—consolidated).
14.5.6Watertablesalinity
Figure14.27belowshowstheclassificationofwatertableaquifersasfresh(totaldissolvedsolids<3,000mg/L)orsaline(TDS≥3,000mg/L)wateraccordingtowatertablesalinity.Therearesmallareasofnodatarepresentedingrey.Ingeneral,groundwaterhasbeenclassifiedasmainlyfreshalongthebordersoftheNorthernTerritoryandNewSouthWales,andmainlysalineintheSouthAustralianborderarea.
14.5.7Groundwatermanagementunits
Thegroundwatermanagementunitswithintheregionarekeyfeaturesthatcontroltheextractionofgroundwaterthroughplanningmechanisms.Figure14.28showsthemajorgroundwatermanagementunitsthataresuperimposedontheGreatArtesianBasin,thatis,NorthernTerritory,GreatArtesianBasinWaterControlDistrict;SouthAustralia:FarNorthPrescribedWellsArea;Queensland:GreatArtesianBasin;NewSouthWales:GreatArtesianBasinCapRock,andtheKarsticandFracturedRocksresources,thatis,NorthernTerritory:AliceSpringsandQueensland:MountIsa.
Aerial view, Lake Eyre with water | Edstock (iStockphoto)
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Figure 14.26 Watertable aquifers of the Lake Eyre Basin region; data extracted from the Groundwater Cartography of the Australian Hydrological Geospatial Fabric (Bureau of Meteorology 2012)
Lake Eyre Basin
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Figure 14.27 Water table salinity classes in the Lake Eyre Basin region; data extracted from the Groundwater Cartography of the Australian Hydrological Geospatial Fabric (Bureau of Meteorology 2012)
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Figure 14.28 Groundwater management units in the Lake Eyre Basin region; data extracted from the National Groundwater Information System (Bureau of Meteorology 2013)