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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

2 Australian Water Resources Assessment 2012

14 Lake Eyre Basin14.1 Introduction

ThischapterexamineswaterresourcesintheLakeEyreBasinregionin2011–12andoverrecentdecades.Itstartswithsummaryinformationonthestatusofwaterflowsandstores.Thisisfollowedbydescriptiveinformationfortheregionincludingthephysiographiccharacteristics,soiltypes,population,landuseandclimate.

Spatialandtemporalpatternsinlandscapewaterflowsarepresentedaswellasanexaminationofthesurfaceandgroundwaterresources.ThedatasourcesandmethodsusedindevelopingthediagramsandmapsarelistedintheTechnicalSupplement.

3Australian Water Resources Assessment 2012

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


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.


Figure 14.1 Major rivers and urban centres in the Lake Eyre Basin region

Lake Eyre Basin


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.


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).

http://www.ga.gov.au/topographic-mapping/digital-elevation-data.html

http://www.ga.gov.au/topographic-mapping/digital-elevation-data.html

Lake Eyre Basin


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.


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).

http://www.asris.csiro.au

http://www.asris.csiro.au

Lake Eyre Basin


Figure 14.6 Soil type distribution in the Lake Eyre Basin region


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).

data%20from.adl.brs.gov.au/anrdl/metadata_files/pa_luav4g9abl07811a00.xml

http://data.daff.gov.au/anrdl/metadata_files/pa_luav4g9abl07811a00.xml

http://data.daff.gov.au/anrdl/metadata_files/pa_luav4g9abl07811a00.xml

Lake Eyre Basin


Figure 14.8 Land use distribution in the Lake Eyre Basin region


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.

Lake Eyre Basin


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

http://www.bom.gov.au/jsp/ncc/climate_averages/climate-classifications/index.jsp

http://www.bom.gov.au/jsp/ncc/climate_averages/climate-classifications/index.jsp


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

http://www.bom.gov.au/climate/averages/maps.shtml

http://www.bom.gov.au/climate/averages/maps.shtml

Lake Eyre Basin


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.


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


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.


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.

Lake Eyre Basin


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


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).

Lake Eyre Basin


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


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


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.


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


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.


Figure 14.22 Rivers and catchments in the Lake Eyre Basin region

Lake Eyre Basin


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


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

www.environment.gov.au/water/topics/wetlands/database/diwa.html

www.environment.gov.au/water/topics/wetlands/database/diwa.html

Lake Eyre Basin


Figure 14.24 Flood occurrences in the Lake Eyre Basin region


Figure 14.25 Location of important wetlands in the Lake Eyre Basin region

Lake Eyre Basin


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)


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


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)


Figure 14.28 Groundwater management units in the Lake Eyre Basin region; data extracted from the National Groundwater Information System (Bureau of Meteorology 2013)

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