North Western Plateau - Bureau of Meteorology · The North Western Plateau region is located in...

North Western Plateau12 North Western Plateau ............................................... 2

12.1 Introduction ....................................................... 2

12.2 Key information .................................................. 3

12.3 Description of the region .................................... 4

12.3.1 Physiographic characteristics.................. 6

12.3.2 Elevation ................................................. 7

12.3.3 Slopes .................................................... 8

12.3.4 Soil types ............................................... 9

12.3.5 Land use ............................................. 11

12.3.6 Population distribution .......................... 13

12.3.7 Rainfall zones ...................................... 14

12.3.8 Rainfall deficit ....................................... 15

12.4 Landscape water flows ................................... 16

12.4.1 Rainfall ................................................. 17

12.4.2 Evapotranspiration ............................... 20

12.4.3 Landscape water yield ......................... 23

12.5 Surface water and groundwater ....................... 26

12.5.1 Rivers .................................................. 26

12.5.2 Flooding ............................................... 26

12.5.3 Wetlands .............................................. 26

12.5.4 Hydrogeology ...................................... 30

12.5.5 Watertable salinity ................................. 30

12.5.6 Groundwater management units ........... 30

North Western Plateau

2 Australian Water Resources Assessment 2012

12 North Western Plateau12.1 Introduction

ThischapterexamineswaterresourcesintheNorthWesternPlateauregionin2011–12andoverrecentdecades.Itstartswithsummaryinformationonthestatusofwaterflows,storesanduse.Thisisfollowedbydescriptiveinformationfortheregionincludingthephysiographiccharacteristics,soiltypes,population,landuseandclimate.

Spatialandtemporalpatternsinlandscapewaterflowsarepresentedaswellasanexaminationofthesurfaceandgroundwaterresourcestofinishthechapter.ThedatasourcesandmethodsusedindevelopingthediagramsandmapsarelistedintheTechnicalSupplement.

3Australian Water Resources Assessment 2012

12.2 Keyinformation

Table12.1givesanoverviewofthekeycomponentsofthedataandinformationinthischapter.

Table 12.1 Key information on landscape water flows, floods and groundwater quality in the North Western Plateau region

Landscape water flows

Evapo-transpiration

Landscapewater yield

Rainfall

Regionaverage Differencefrom1911–2012long-termannual

mean

Decilerankingwithrespecttothe1911–2012record

319mm +65% 10th—verymuchaboveaverage



Streamflow (at selected gauges)

Flooding: MajorfloodingintheDeGreyRiverbasin

Groundwater (in selected aquifers)

Salinity: Scatteredareasofsalinegroundwater(≥3000mg/L)mainlysurrounding(dry)riverbedsandlakes



Gibson Desert, Western Australia | Airspeed (iStockphoto)

12.3 Descriptionoftheregion

TheNorthWesternPlateauregionislocatedinnorthwestAustraliaandincludesmajorpartsoftheGreatSandyandGibsondeserts.Theregioncovers716,000km²oflandareaandonlyhassomelimitedsurfacewaterresourcespresentinthenorthernandeasternpartsoftheregion(seeFigure12.1).

Thecoastlineconsistsoftide-dominatedplainsandtidalcreeks.Drylakesarescatteredacrosstheregion,butaeolianlandformsincludingdunesandsandplainsdominatethelandscape.Subsections12.3.1–12.3.4providemoreinformationonthephysicalcharacteristicsoftheregion.

Withapopulationof13,100people,theNorthWesternPlateauishometolessthan0.1%ofthenation’stotalpopulation(AustralianBureauofStatistics[ABS]2011b).

Figure12.1showstheonlymajortownoftheregion,MarbleBar.Subsection12.3.6providessomeadditionalinformationonthepopulationanddistributionacrosstheregion.

Theareaisimportantformineralresourcesandthereareseveralminingoperationsintheregion.

Mostoftheregionisinarelativelynaturalstateand77%isassociatedwithnatureconservation.

Afurther22%oftheregionisusedforgrazing,particularlyalongthewesternandnorthernboundaries(Figure12.1).Irrigatedagricultureandurbanareasaccountforlessthan0.01%oftheregion’sarea.

Theclimateisaridandisaffectedbyerraticmonsoonalrainfall,particularlyinthenorth.Subsections12.3.7and12.3.8providemoreinformationontherainfallpatternsanddeficitsacrosstheregion.

Alltheriversintheregionareephemeralandonlyflowafteraheavyrainfall.

Thehydrogeologyisdominatedbyalargeareaofoutcroppingfracturedbasementrockinthewestandeastoftheregion.Theassociatedgroundwatersystemstypicallyofferlimitedlowvolumewaterresources.OtherimportanthydrogeologicalgroupsaretheMesozoicsedimentsthroughthecentreoftheregionandthesurficialsedimentsin-fillingpaleovalleys.Thesegroupsarelikelytooffermorereliablegroundwaterresources.Giventheirregularnatureofsurfaceflows,waterisgenerallysuppliedbygroundwater.

Amoredetaileddescriptionoftheriversandgroundwaterstatusintheregionisgiveninsubsection12.5.


Figure 12.1 Major rivers and urban centres in the North Western Plateau region



Figure 12.2 Physiographic provinces of the North Western Plateau region

12.3.1Physiographiccharacteristics

ThephysiographicmapinFigure12.2showsareaswithsimilarlandformevolutionaryhistories(Painetal.2011).Thesecanberelatedbacktosimilargeologyandclimaticimpactswhichdefinetheextentoferosionprocesses,andhavedistinctphysicalcharacteristicsthatcaninfluencehydrologicalprocesses.

TheNorthWesternPlateauregionisdominatedbytheSandlandphysiographicprovincewhichoccupies73%ofitsarea.Thisprovincecomprisesmainlyeast-westlongitudinalduneswithminorsaltlakes.Therearesomesandyorstonyferruginousplainsandlowsandstonehills.Theremainingfiveprovincesoccuralongtheregion'ssouthwestandnortheastborders.

Theseprovincesare:

• Pilbara(14%):largelydissectedflat-toppedhillsofgranitic,volcanicandmetamorphicrocksinterspersedbystonyplainsongranite;

• Barkly–TanamiPlains(7%):mainlysandplainswithscatteredlowrangesandtablelandswithoccasionalgraniteandsedimentaryhills;

• YilgarnPlateau(3.5%):sand,gravelandhardpan-washplainswithsaltlakes,brokenbyridgesofmetamorphicrocksandgraniteandmesas;

• CentralAustralianRanges(2%):dunefieldsandsandplainswithsandstone,graniticandvolcanicranges,saltlakesandcalcreteplains;and

• Kimberley(0.5%):scatteredtablelands,rangesofsedimentaryrocksandplainswitheast-westlongitudinaldunes.


Figure 12.3 Ground surface elevations in the North Western Plateau region

12.3.2Elevation

AspresentedinFigure12.3,aeolianlandforms,includingdunesandsandplains,dominatethelandscapeoftheNorthWesternPlateau.Theregionhasnosignificantmountainrangeswithinitsborder.InformationwasobtainedfromtheGeoscienceAustraliawebsite(www.ga.gov.au/topographic-mapping/digital-elevation-data.html).

Thesouthwestoftheregionhassomehigheraltitudeswithplateausexceeding600minaltitude.

TheregionhassomeofthelargestpaleodrainagesystemsinAustralia.Theycurrentlyincorporateanumberofalignedlakes.Thetopographyclearlydepictsthevalleystheserivershaveformedinthepast.

ApartfromtheDeGreyRiverinthefarwest,theregionhasnosurfacewaterflowtotheIndianOcean.Underheavyrainfall,themanyclosedriverbasinsfillupthelakesthathaveformedovertime;however,rainfallisveryunreliableandlakesarenormallydry.

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

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



Figure 12.4 Surface slopes in the North Western Plateau region

12.3.3Slopes

Areaswithsteepslopesprovidehigherrunoffgeneratingpotentialthanflatareaswhicharemorefavourableforverticalinfiltration.TheNorthWesternPlateauregionhasgenerallyaflattopography,withoutanydistinctslopes(Table12.2andFigure12.4).

Table 12 2. Proportions of slope classes for the region

Slopeclass(%) 0–0.5 0.5–1 1–5 >5

Proportionofregion(%) 50.6 31.7 16.9 0.8

TheslightlysteeperslopesparticularlyaroundMarbleBarinthewestprovidesomegradientforstreamflowtobegenerated(Figure12.4).TheseheadlandstreamsoccasionallyreachtheDeGreyRiver,whichflowsintotheIndianOcean.Theslopeswerederivedfromtheelevationinformationusedintheprevioussection.

Theabsenceofslopesandreliablerainfallmakesthisregionhighlyreceptiveforaeolianinfluences.Formerhillshavebeenlevelledoutbywinderosionandplainsarevastandcoveredwithsanddunes.

Apartfromthenorthernpart,theborderoftheregionisnotanaturaltopographicwaterdivide.Manysmallandlargeinternallydrainingriverbasinsexistonbothsidesoftheborderoftheinlandregion.


Figure 12.5 Soil types in the North Western Plateau region

12.3.4Soiltypes

Soilsplayanimportantroleinthehydrologicalcyclebydistributingwaterthatreachestheground.Watercanbetransportedtoriversandlakesviathesoilsurfaceasrunofforenterthesoilandprovidewaterforplantgrowthaswellascontributingtogroundwaterrecharge.

Thenatureofthesehydrologicalpathwaysandthesuitabilityofthesoilsforagriculturalpurposesareinfluencedbysoiltypesandtheircharacteristics.SoiltypeinformationwasobtainedfromtheAustralianSoilResourceInformationSystemwebsite(www.asris.csiro.au).

About90%oftheNorthWesternPlateauareaiscoveredbythreesoiltypes,namelytenosols,rudosolsandkandosols(Figure12.5andFigure12.6).

Tenosolsandrudosolsaretypicallysandy,andshowlittlechangeintextureandcolourthroughtheprofileandareoftenshallowindepth.Tenosolsandrudosolshavelowchemicalfertilityandhavealowwater-holdingcapacity,thustheiragriculturalpotentialislow.Bothsoiltypesaremostlypresentinareasusedfornatureconservationratherthanagriculture.

Tenosolscovermorethan50%ofthetotalareaofthisregion.Theyaredominantinallpartsoftheregion,exceptforthenortheasttosoutheastwhererudosolsaredominant.

Kandosolsarestructurelesssoilswhichareoftenverydeep(uptothreemetresormore),buttheydonothaveastronglycontrastingtextureandtheydonotcontaincarbonatethroughouttheirprofile.Theyarelowinchemicalfertilityandarewell-drained,withonlymoderatewater-holdingcapacitycomparedwithothersoiltypes;thustheyonlyhavelowtomoderateagriculturalpotential.Theyaremostlyusedforgrazinginthisregion.

TheothersoiltypesthathaveminimalrepresentationintheNorthWesternPlateauregionaresodosols,calcarosols,hydrosols,vertosolsandchromosols(0.8–3%).

www.asris.csiro.au



Figure 12.6 Soil type distribution in the North Western Plateau region


Figure 12.7 Land use in the North Western Plateau region

12.3.5Landuse

AspresentedinFigure12.7andFigure12.8,mostoftheregionisinarelativelynaturalstatewith77%associatedwithnatureconservation.Afurther22%

oftheregionisusedforgrazingalongthewesternandnorthernboundaries.Irrigatedagricultureandurbanareasaccountforlessthan0.01%ofthearea(datafromdata.daff.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



Figure 12.8 Land use distribution in the North Western Plateau region


Figure 12.9 Population density and distribution in the North Western Plateau region

12.3.6Populationdistribution

Withapopulationdensityinmuchoftheregionbeingzero,theNorthWesternPlateauregionistheleastpopulatedoftheregions.ThescarcityofthepopulationisclearlyillustratedinFigure12.9(ABS2011b).

ThelargestofthepermanentpopulationcentresisMarbleBar,located200kmsouthwestofPortHedland.Miningleases,remoteIndigenouscommunitiesandanumberofsmallsettlementslocatedadjacenttomajorroadsintheregion(includingtheGreatNorthernHighwayandMarbleBarRoad)accountfortheremainingpopulation.



Figure 12.10 Rainfall zones in the North Western Plateau region

12.3.7Rainfallzones

Theregion’sclimateissemi-aridtoarid.Thenorthernpartisaffectedbyoccasionalmonsoonalrainfallinsummer.Medianrainfalldoesnotexceed650mmperannum(Figure12.10).

Inthenorthernpartoftheregion,rainfallisveryirregular.Relativelylowrainfallamountscanoccuroverthewetseason,duetothelimitedextentofthemonsoonandtropicaldepressions,andstormsoftenbypasstheregion.

Thearidsouthreceivesaverageannualrainfalltotalsgenerallynotexceeding300mm.Aswithmanyaridzones,rainfallisveryunreliableandhighlyvariablebetweenyears.

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 12.11 Rainfall deficit distribution in the North Western Plateau region

12.3.8Rainfalldeficit

Therainfalldeficitindicator,thatis,rainfallminuspotentialevapotranspiration,givesageneralimpressionofwhichpartsoftheregionarelikelytoexperiencemoisturedeficitsovertheperiodofayear.TheNorthWesternPlateauregionhasauniformpatternofseriouspotentialdeficits(Figure12.11).

Mostoftheregionconsistsofdesertlandwithsomeephemeralstreamsandlakes.Themoisturedeficitsinthisareaallowsanddunesandplainstodominatethelandscape.

Inthenorth,theunreliablesupplyofrainfallandthelongdryseasoncreateaharshenvironment.MarbleBarhastheworld’slongestrecord(161consecutivedays)ofabove37.8°C.Themajorityoftheregionisdeclaredasnatureconservationland,containingsomeuniquefloraandfauna.

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



Figure 12.12 Landscape water flows in 2011–12 compared with the long-term record (July 1911–June 2012) for the North Western Plateau region

12.4 Landscapewaterflows

Thissectionpresentsanalysesofthespatialandtemporalvariationoflandscapewaterflows(rainfall,evapotranspirationandlandscapewateryield)acrosstheNorthWesternPlateauregionin2011–12.Nationalrainfallgridsweregeneratedusingdatafromanetworkofpersistent,high-qualityrainfallstationsmanagedbytheBureau.EvapotranspirationandlandscapewateryieldswerederivedusingthelandscapewaterbalancecomponentoftheAustralianWaterResourcesAssessmentSystem(VanDijk2010).ThesemethodsandassociatedoutputuncertaintiesarediscussedintheIntroductionandaddressedinmoredetailintheTechnicalSupplement.

Figure12.12showsthattheregionhasahighlyseasonalrainfallpatternwitharelativelywetsummerandadrywinterperiod.Evapotranspirationinthedrywinterperiodgenerallyexceedsrainfall.Afterthewetperiodthesoilsnormallycontainanaboveaveragewatervolumethatisavailableforevapotranspiration.Themonthlylandscapewateryieldhistoryfortheregionshowsastablepatternofverylowyieldinthedryperiod.Itonlyincreasesmarginallyduringthesummerperiod(NovembertoApril).

The2011–12yearwasarelativelywetyear,particularlybetweenOctober2011andMarch2012,whenrainfallwasmuchhigherthanthehistoricmedian.In2011,theregionrecordedthehighestNovemberrainfallonrecord(1911–2012).Infact,theperiodbetweenOctober2011andJanuary2012wasthewettestonrecordforthisfour-monthperiod.InMarchthepassageoftropicalcycloneLuaalsocausedheavyfallsandflooding.

WithwetconditionspresentatthestartoftheyearandtheexcessofrainfallinNovemberandJanuary,evapotranspirationwasparticularlyhighthroughouttheyear.EvapotranspirationwashighestonrecordfortheNovembermonth,andsecond-highestonrecordintheOctober–Januaryperiod.

Landscapewateryieldfor2011–12startedtoincreaseinJanuary.Marchhadthehighestmonthlylandscapewateryieldfortheyear.


Figure 12.13 Spatial distribution of (a) annual rainfall in 2011–12, and (b) their decile rankings over the 1911–2012 period for the North Western Plateau region

12.4.1Rainfall

RainfallfortheNorthWesternPlateauregionfor2011–12isestimatedtobe319mm.Thisis65%abovetheregion’slong-termaverage(July1911–June2012)of193mm.Figure12.13ashowsalargeproportionofuncertaintyofrainfalldataintheregion.Thisisduetoalowraingaugedensityandexplainsthelowrainfallinthecentreoftheregion.Forconsistencyreasons,however,thisareaincludedforcalculatingtotalsandstatistics.

Rainfallin2011–12marginallyexceeded600mmperyear,generallyintheareasthatshowverymuchaboveaveragerainfallinFigure12.13b.Fortheremainderoftheregionwithreasonabledatareliability,rainfalldecilesfor2011–12indicatepredominantlyaboveaveragerainfall.



Figure 12.14 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 North Western Plateau region

Rainfall variability in the recent past

Figure12.14ashowsannualrainfallfortheregionfromJuly1980onwards.Overthis32-yearperiodtheannualaveragewas264mm,varyingfrom119mm(1989–90)to502mm(1999–2000).Temporalvariabilityandseasonalpatterns(overthesummerandwinterperiods)since1980arepresentedinFigure12.14b.

Thegraphsindicatethedependencyofannualrainfallontheamountofrainfalloccurringinthesummer

period.Rainfallinthewinterperiodisgenerallylowandrelativelystablebetweenyearswhilstrainfallinthesummerperiodishighlyvariable.Consequentlyannualrainfallishighlyvariableaswell(Figure12.14a).Infact,theNorthWesternPlateauhasthesecondhighestcoefficientofvariation(standarddeviationdividedbythemean)forannualrainfallcomparedtootherreportingregionsofAustralia,onlybehinditsneighbour,thePilbara–Gascoyneregion.


Figure 12.15 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 North Western Plateau region

Recent trends in rainfall

Figure12.15apresentsthespatialdistributionofthetrendsinannualrainfallforJuly1980–June2012.Thesearederivedfromlinearregressionanalysesonthetime-seriesofeachmodelgridcell.ThestatisticalsignificanceofthetrendsisprovidedinFigure12.15b.

Figure12.15ashowsthatsince1980anincreaseinrainfallhasoccurredinlargepartsoftheregion.Thesignificanceofthetrendsisparticularlystronginthesouthoftheregion.



12.4.2Evapotranspiration

ModelledannualevapotranspirationfortheNorthWesternPlateauregionfor2011–12isestimatedtobe291mm.Thisis61%abovetheregion’slong-term(July1911–June2012)averageof181mm.Thespatialdistributionandmagnitudeofannualofevapotranspirationin2011–12(Figure12.16a)issimilartothatofrainfall(Figure12.13a).

Evapotranspirationdecilesfor2011–12indicateaboveaverageorverymuchaboveaveragetotalsacrossmostoftheregion(Figure12.16b).ItalsoresemblestherainfallpatternsofFigure12.13bratherclosely,whichindicatesthatwateravailability,throughrainfall,limitstheamountofevapotranspirationoccurring.

Figure 12.16 Spatial distribution of (a) modelled annual evapotranspiration in 2011–12, and (b) their decile rankings over the 1911–2012 period for the North Western Plateau region


Figure 12.17 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 North Western Plateau region

Evapotranspiration variability in the recent past

Figure12.17ashowsannualevapotranspirationfortheregionfromJuly1980onwards.Overthis32-yearperiodtheannualevapotranspirationaveragewas242mm,varyingfrom140mm(1985–86)to411mm(1999–2000).Temporalvariabilityandseasonalpatterns(overthesummerandwinterperiods)since1980arepresentedinFigure12.17b.

Summerperiodsshowconsistentlyhigherevapotranspirationthanthewinterperiod.Thehighertemperaturesandthehigherrainfallamountsduringtheseperiodsarethemaincontributingfactors.Comparedwithseasonalrainfall(Figure12.14b),evapotranspirationexceedstheinputofrainduringthewinterperiod.Thisisduetothehigheravailabilityofsoilmoistureaftertherelativelywetsummerperiod.



Recent trends in evapotranspiration

Figure12.18apresentsthespatialdistributionofthetrendsinmodelledannualevapotranspirationfor1980–2012.Thesearederivedfromlinearregressionanalysesonthetime-seriesofeachmodelgridcell.ThestatisticalsignificanceofthetrendsisprovidedinFigure12.18b.

Figure12.18ashowsthatsince1980,trendsaremostlypositivethroughouttheregion.Similarareasofstatisticalsignificance(Figure12.18b)areidentifiedascomparedtotherainfalltrendsignificanceinFigure12.15b,thoughtheareasofstatisticallysignificantevapotranspirationincreasearesomewhatlarger.

Figure 12.18 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 North Western Plateau region


12.4.3Landscapewateryield

ModelledlandscapewateryieldfortheNorthWesternPlateauregionfor2011–12isestimatedtobe26mm.Thisis136%abovetheregion’slong-term(July1911–June2012)averageof11mm.Figure12.19ashowsthespatialdistributionoflandscapewateryieldfor2011–12,whichissimilartotheannualrainfalldistribution(Figure12.13a,notethedifferenceinthescaleofthelegend).

Thedecile-rankingmapfor2011–12(Figure12.19b)showsaboveaveragetoverymuchaboveaveragelandscapewateryields,similartowhatcanbeseenintherainfallpatternsofFigure12.13b.Verymuchaboveaveragewateryieldsarefoundacrossmuchofthedata-sparsesoutheast,buttheseresultsshouldbeusedwithcautionastheyaremodelresultsgeneratedwithhighlyuncertainrainfalldata.

Figure 12.19 Spatial distribution of (a) modelled annual landscape water yield in 2011–12, and (b) their decile rankings over the 1911–2012 period for the North Western Plateau region



Figure 12.20 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 North Western Plateau region

Landscape water yield variability in the recent past

Figure12.20ashowsannuallandscapewateryieldfortheNorthWesternPlateauregionfromJuly1980onwards.Overthis32-yearperiod,annuallandscapewateryieldwas21mm,varyingfrom4mm(1989–90)to64mm(1999–2000).Temporalvariabilityandseasonalpatterns(overthesummerandwinterperiods)since1980arepresentedinFigure12.20b.

Landscapewateryieldisconsistentlyhigherduringthesummerperiodcomparedtothewinterperiod.Rainfallobviouslyisthemajorforcebehindlandscapewateryieldandthetemporalvariabilitycloselyresemblesthevariabilityinrainfall.Again,thecoefficientofvariation(standarddeviationdividedbythemean)oftheannualdataishighcomparedtomostotherregions.


Recent trends in landscape water yield

Figure12.21ashowsthespatialdistributionofthetrendsinmodelledannuallandscapewateryieldfor1980–2012.Thesearederivedfromlinearregressionanalysesonthetime-seriesofeachmodelgridcell.ThestatisticalsignificanceofthetrendsisprovidedinFigure12.21b.

Figure12.21ashowsthatthereisnoobvioustrendinmostoftheregionwiththeexceptionofthefarnortheastwherelandscapewateryieldincreasestowardstheeasternborderoftheregion.Figure12.21bconfirmsthesignificanceofthesetrendsandshowssomestrongsignalsmainlyinthesouthwestoftheregion;however,trendshereonlyjustreach1mm/year.

Figure 12.21 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 North Western Plateau region



Birdlife on the Eighty Mile Beach, Western Australia | Gayle Partridge

12.5 Surfacewater andgroundwater

ThissectionexaminessurfacewaterandgroundwaterresourcesintheNorthWesternPlateauregionin2011–12.Riversandwetlandsarediscussedtoillustratethestateoftheregion’ssurfacewaterresources.Theregion’swatertableaquifersandsalinityaredescribed.NodatawasavailableattheBureauinasuitableformatforadetailedanalysisonindividualaquifers.

Therearenomajorstorageslocatedintheregion.

12.5.1Rivers

TherearetworiverbasinsintheNorthWesternPlateauregion.TheDeGreyRiverbasincoversanareaof477,000km2andtheSandyDesertbasinis239,000km2insize.

Theregionhassomelimitedsurfacewaterresourcespresentinthewesternpartoftheregion(Figure12.22).Thecoastlineconsistsoftide-dominatedstrandplainsandtidalcreeks.Somedrylakesarescatteredovertheregion,butaeolianlandformsincludingdunesandsandplainsdominatethelandscape.

Almostallriversareephemeral,endingupindesertcountryorsaltlakes,exceptfortheDeGreyRiverbasin.Allstreamsflowonlyafterheavyrains,whichoccurinfrequently.

12.5.2Flooding

HeavyrainfallinJanuaryassociatedwithanactivemonsoonbroughttropicalcyclonesHeidiandIggytotheregion.ThesetropicalcyclonescausedmoderatetomajorfloodingparticularlyintheShawandCoonganrivers.MajorfloodsaffectedtheNallagineandDeGreyriversinMarchwiththepassageoftropicalcycloneLua(Figure12.23).

12.5.3Wetlands

ThereisoneRamsar-listed,internationallyimportantwetlandintheNorthWesternPlateauregionandthereareanumberofwetlandsofnationalimportanceintheregionmentionedintheAustralian Directory of Important Wetlands (www.environment.gov.au/water/topics/wetlands/database/diwa.html).Thewetlandsvaryfromcoastalfloodplains,lakesandtidalflatstoinlandephemerallakesandriverfloodplainsystems(Figure12.24).

TheEightyMileBeachRamsarsitemainlyconsistsoftidalflats,whichsometimesextendupto5kminwidth.Itisahighlyimportantretreatformanyspeciesof(migrating)shorebirds.

Nodetailedassessmentontheinflowsofselectedwetlandshasbeenperformedforthisregion.

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

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


Figure 12.22 Rivers and catchments in the North Western Plateau region



Figure 12.23 Flood occurrence in 2011–12 for the North Western Plateau region


Figure 12.24 Location of important wetlands in the North Western Plateau region



12.5.4Hydrogeology

Thehydrogeologyisdominatedbyalargeareaofoutcroppingfracturedbasementrockinthewestandeastoftheregion.Theassociatedgroundwatersystemstypicallyofferrestrictedlowvolumewaterresources.OtherimportanthydrogeologicalgroupsaretheMesozoicsedimentsthroughthecentreoftheregionandthesurficialsedimentsin-fillingpalaeovalleys.Thesegroupsarelikelytooffermorereliablegroundwaterresources(Figure12.25).

ThewatertableaquiferspresentintheregionaregiveninFigure12.25below.Groundwatersystemsthatprovidemorepotentialforextractionarelabelledas:

• Mesozoicsedimentaquifer(porousmedia—consolidated);and

• surficialsedimentaquifer(porousmedia—unconsolidated).

12.5.5Watertablesalinity

Figure12.26showstheclassificationofwatertableaquifersasfresh(totaldissolvedsolids(TDS)<3,000mg/L)orsaline(TDS≥3,000mg/L)accordingtowatertablesalinity.Asshown,mostpartsoftheregionareconsideredtohavefreshgoundwater.Salinegroundwateroccursinlocalisedareasalongthemajordrainagelinesinthealluvialsediments.

12.5.6Groundwatermanagementunits

Thegroundwatermanagementunitswithintheregionarekeyfeaturesthatcontroltheextractionofgroundwaterthroughplanningmechanisms.Figure12.27showsthatthegroundwatermanagementunitswithintheregionincludeCanning–Kimberley,EastMurchison,GoldfieldsandPilbara.


Figure 12.25 Watertable aquifers of the North Western Plateau region; data extracted from the Groundwater Cartography of the Australian Hydrological Geospatial Fabric (Bureau of Meteorology 2012)



Figure 12.26 Watertable salinity classes of the North Western Plateau region; data extracted from the Groundwater Cartography of the Australian Hydrological Geospatial Fabric (Bureau of Meteorology 2012)


Figure 12.27 Groundwater management units in the North Western Plateau region; data extracted from the National Groundwater Information System (Bureau of Meteorology 2013)

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