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Historical stream salinity trendsand catchment salt balancesin the Murray–Darling Basin

Final Report – NRMS D5035

G.R. Walker, I.D. Jolly, D.R. Williamson, M. Gilfedder, R. Morton,L. Zhang, T. Dowling, P. Dyce, R. Nathan, N. Nandakumar,G.W.B. Gates, G.K. Linke, M.P. Seker, G. Robinson, H. Jones,R. Clarke, V. McNeill, and W.R. Evans

Technical Report 33/98, September 1998

HISTORICAL STREAM SALINITY TRENDSAND CATCHMENT SALT BALANCES INTHE MURRAY–DARLING BASIN

FINAL REPORT – NRMS D5035

G.R. Walker1, I.D. Jolly1, D.R. Williamson1, M. Gilfedder1,R. Morton2, L. Zhang1, T. Dowling1, P. Dyce1, R. Nathan3,N. Nandakumar3, G.W.B. Gates4, G.K. Linke4, M.P. Seker4,G. Robinson4, H. Jones4, R. Clarke5, V. McNeill5, and W.R. Evans6

1 CSIRO Land and Water2 CSIRO Biometrics Unit3 Sinclair Knight Merz Pty Ltd4 NSW Department of Land and Water Conservation5 Qld Department of Natural Resources6 AGSO

Technical Report 33/98September 1998CSIRO Land and Water

Executive SummaryStream salinisation is one of the largest off-siteeffects of dryland salinity. As a result, an increas-ing salinity trend provides an early warning sign ofimpending dryland salinity and gives an indicationof the general health of a catchment. In 1987, theMurray-Darling Basin Commission’s Salinity andDrainage Strategy established a key basin-widestrategy to control salinity, which uses the streamsalinity at Morgan (South Australia) as a key indi-cator of the management of stream salinisation inthe Basin. The Strategy highlights the impacts ofirrigation areas, with an assumption of nominalinput from dryland areas. Recent studies have sug-gested that the effect of dryland salinity on streamsalinisation will be much greater than wasoriginally estimated for the Strategy. This Basin-wide assessment of stream salinisation proposes todetermine the magnitude of the dryland areas onstream salinisation and the areas where targetedfunding for remediation should be focused.

Statistical trends and catchment salt andwater balances were used to reconstruct the historyof stream salinisation across the Murray-DarlingBasin. Establishment of historical stream salinitytrends and catchment salt balances was seen as anecessary pre-condition for the development ofapproaches to predict likely future trends. Analysisof these trends highlight a distinct region of streamsalinity and catchment salinisation ‘hot-spots’within the Basin. These hot-spots are of highpriority for detailed investigation and their identi-fication will assist in targeting future remedialwork.

For many areas of the Basin, the streamsalinity data set was generally quite limited, withfew locations of long record, particularly in thedryland areas. In order to derive historical trendsfrom the intermittent data, a new statistical methodwas developed. This approach has enabled thedetermination of historical trends over time at87 sites distributed across the Murray-DarlingBasin. The resulting non-linear trends with timewill allow stream salinity to be related to processessuch as changes in land management, climaticvariables, or salt mitigation schemes. Salt andwater balances were conducted for 101 streamgauging stations throughout the Murray-DarlingBasin. This analysis provided a separate method ofanalysing the stream salinity data with anassessment of the salt output/input (O/I) ratio forthese locations. This technique provided a meansto identify areas of salt imbalance, high salt load,

and high salt load per unit area. However, becauseof the sparse nature of the data-set, these trendsand balances should be used as an indication ofgeneral behaviour only, and not considered exactfor any given individual location.

Large areas within the Basin showed sig-nificant rising trends in stream salinity and saltloads, and generally high catchment O/I ratios,particularly in the eastern and southern drylandregions with annual rainfall of 500 – 800 mm. Thisfinding was consistent with previously mappeddryland salinity areas in New South Wales andVictoria, and consistent with the areas of knownrising groundwater trends, and with previous localstudies. Streams in the irrigation areas of the Basinalso showed consistent rising salinity trends, butwith salt O/I ratios close to a balance. This may beexplained by the large volumes of water and saltthat are diverted in these areas, and means thattrends in salt loads may actually be decreasing insome cases. Further detailed analysis at a smallerscale is required to account for these diversions.Neither trends or salt O/I ratios were significant inthe northern and western Darling Basin drylandarea, perhaps due to the summer dominance ofrainfall and slower rates of land clearing. TheLower Murray also failed to show a significanttrend suggesting that the salt interception schemesin this region are currently effective.

The analysis indicates that the time lag forresponse by groundwater may be much shorter inthe southern part of the Basin (about 50 years) thanin the northern part (greater than 80 years).Although reliable indication of future stream sal-inity and salt load can not be obtained from histori-cal trend analysis, there seems little to suggest thatcurrent trends will decrease substantially in thefuture. This project highlights the difficulties of us-ing the salinity at Morgan as the only measure ofthe effects of the Salinity and Drainage Strategy,especially since future stream salinisation arisingfrom dryland areas will be first felt in the upstreamirrigation areas.

Future work should concentrate in moredetail on catchments identified as having ‘hot-spots’. This will enable the determination of thereasons for the increasing salinisation. Thesesmaller-scale studies will aid in the understandingof the links between stream salinisation and factorssuch as land use, river management and climaticeffects. A particularly attractive methodology forthis purpose is catchment categorisation.

BackgroundIn addition to being an indicator of the environ-mental health of catchments, stream salinisation isone of the major off-site costs of dryland salinity.Studies over the last decade suggest that drylandsalinity will increase dramatically in the Murray-Darling Basin over the coming years, causingsignificant increases in stream salinisation. Forexample, conservative estimates suggest that theeffects from the Victorian Riverine Plains willcontribute an increase of up to 140 µS cm–1 atMorgan over the next 50 to 100 years (Allison &Schonfeldt, 1989). Moreover, preliminary resultsfrom recent work supported by the Murray-DarlingBasin Commission suggest that stream salinitieshave been rising in many catchments in southernNew South Wales, presumably in response to theincreasing outbreaks of dryland salinity in theregion.

In response to the need to managepredicted increases in stream salinisation in thebasin over the next few decades, the Murray-Darling Basin Commission established the Salinityand Drainage Strategy in 1987. Underpinning theStrategy was the recognition that there would be anincrease in stream salinities for several decades asa result of current land management practices. Itwas assumed that much of the increase in salinityin the lower Murray River would be the result ofdeep drainage from the large irrigation areas ratherthan from the upstream-dryland areas of the Basin.Based on this assumption, the impact of landmanagement practices and the success of theupstream salinisation control measures weregauged by salinity levels of the lower Murray Riverat Morgan.

However, the impact of dryland salinitywas assumed to be only a minor contributor, withthe Strategy estimating its effect on River Murraysalinity to be only 40 µS cm–1 at Morgan over thenext 50 years (Williamson et al., 1997). Recentstudies have questioned this estimation, suggestingthat dryland salinisation will increase significantly,resulting in higher stream salinities thanpreviously estimated (e.g. Earl, 1988; Evans,1994). Allison and Schonfeldt (1989) suggestedthat Victorian riverine plains alone could result inan increase of 140 µS cm–1 at Morgan over thenext 50 years. In light of an upcoming review ofthe Salinity and Drainage Strategy, improvedestimates of Basin-wide dryland inputs to streamsalinisation are needed.

Establishment of historical trends instream salinity and catchment water and saltbalances across the Murray-Darling Basin has beenseen as a necessary precondition for the develop-ment of approaches to predict future trends. ThisBasin-wide approach will provide a framework forfuture small-scale studies and enable possible

remediation activities to be prioritised. Analysis ofhistorical trends and catchment balances will alsoallow the targeting of key salinisation ‘hot-spots’throughout the Basin.

ObjectivesThe principal objectives of this project are givenbelow. The original objectives have undergonemodification at various Steering Panel meetings.

• Establish historical trends for stream salinityand salt loads in the Murray-Darling Basin.

• Prioritise catchments within the Basin forfuture smaller-scale studies.

• Review the stream salinity monitoring networkwithin the Murray-Darling Basin.

• Undertake preliminary analysis of factorscontributing to stream salinity trends.

MethodologyThe study established historical trends in streamsalinity and calculated catchment water and saltbalances at stream-gauging stations across theMurray-Darling Basin. Long-term stream salinitymonitoring was infrequent, which made theestablishment of salinity trends difficult. Therefore,it was necessary to develop a new statisticalmethodology which could deal with theintermittent nature of the data, and to establishreliable historic stream salinity and salt loadtrends. Confidence in the salinisation trends wasimproved, with good correlation between thetrends, and separately analysed catchment saltbalance results.

This section will describe the metho-dology for both the historical trend analysis and thecatchment water and salt balance analysis. Detailsof the flow correction procedure are also discussed.

Stream Salinisation Trend AnalysisHistorical trend analysis was carried out for 87stream gauging stations distributed throughout theBasin. A new statistical method was developed toovercome concerns over high autocorrelationin the salinity data and their effect on the accuracyof trend estimates (Morton, 1996). As well asproviding an estimate of the trend and itsconfidence interval, the relationship between thetrend and physical processes was considered in thedevelopment of the new method. This new methodconsisted of two statistical approaches, andprovided non-linear trends, incorporated flowcorrection and could be used on much sparser datasets than conventional methods (such asKendall’s tau technique). The method was de-veloped using the GENSTAT package (Payne et al., 1993; Morton, 1997) which can be used on

UNIX, DOS, and Windows platforms.The first approach used in the statistical

method was an Ordinary Least Squares (OLS)regression using a generalised additive model. Thisapproach was used when autocorrelation was low(<0.2). In this approach, additive regression termsare fitted to logEC, the exploratory variables beingtime (years), logflow (log ML day–1), and sinu-soidal seasonal terms. The non-linear OLS modelrepresented the response of logEC to time andlogflow by arbitrary smooth curves using cubicsplines with knots at each data point. The mathe-matical form of the regression was:

επγπβ

)2cos()2sin(

);();(

dflogflowSdftSlogEC ft

where logEC was the natural logarithm of EC,logflow was the natural logarithm of flow + 1, twas time in years, S1(t;dft) was a smoothing splineof logEC versus time with dft degrees of freedom,S2(logflow;dff) was a smoothing spline of logECversus time with dff degrees of freedom; α, β, γwere linear regression coefficients and ε was theresidual error. In using this approach, Morton’s(1997) recommendations that values of 4 for dft

and 2 for dff respectively were appropriate for datasets of the length used in this project. The aim ofthe fitting procedure was to define S, as itrepresented the non-linear trend in time (excludingflow and seasonal effects which were accounted forin the remaining terms). Standard errors from thestatistical output were adjusted for the magnitudeof the autocorrelation and for the amount ofmissing data by multiplying by the following factor(Morton, 1996):

( ) 2/1)1/()2(1 ARpAR −+

where p was the proportion of available data andAR was the first order autocorrelation coefficient.

When autocorrelation was high (>0.2), asecond approach was used; a Time Series Model(TSM) which used an auto-regressive integratedmoving-average model. However if the number ofmissing months was too large (>20%), then theTSM approach failed and it was necessary to usethe OLS approach with a multiplier applied to thestandard errors. The TSM approach carried out theabove fits with auto-regressive parameters. The95% confidence intervals for the linear time trendswere estimated as ±2 standard errors. Standarderrors for the TSM approach were taken directlyfrom the statistical output. The first order auto-regressive model with Ctime and Clogflow as the expl-

oratory variables could be represented mathemat-ically as:

επξ

πωψυτζλ

)2cos(

)2sin(

tClogflowCtimelogEC

logflow

where λ,ζ,τ,ν,ψ,ω and ξ were linear regressioncoefficients.

This statistical method did not include thetrend of flow directly, and hence flow was assumednot to vary over the longer period. It was difficultto statistically remove these trends because of theinherent high variability of Australia’s streamflow. However, if diversions or other changes inflow are known, they may be incorporated into theanalysis for each station. It was not possible to dothis within the scope of this study, which meantthat trends in salt loads were the product of thetrend in stream salinity and mean stream flow.Thus, decreases in the trend of salt load due todiversions were not included in this analysis.

Catchment Water and Salt BalancesSalt balances were calculated for each catchment ofthe Basin to estimate its net contribution to Basin-wide stream salinisation. The ratio of salt output toinput (O/I) is a key indicator of catchment salinitystatus (Peck and Hurle, 1973). Calculation of O/Iratios allowed ‘hot-spots’ to be identified,indicating locations where catchments are not in asalt equilibrium.The O/I ratio is usually close to unity prior to theclearing of native vegetation, which indicates a saltequilibrium. However, vegetation clearing resultsin a disturbance in the original salt equilibriumthrough increased recharge and runoff, which canresult in a flushing of stored salt from the area andlead to high salt O/I ratios. Salt O/I ratios havebeen observed as high as 20 in highly salinisedcatchments (Peck and Hurle, 1973). Eventually anew salt equilibrium will be reached, however itmay take from 20 years up to thousands of years tooccur. Figure 1 shows an example of the responseof catchment salt O/I ratio to clearing over time forboth high and medium rainfall catchments. Thisfigure shows the relevance of a departure of the saltO/I ratio from a balance, as an indicator for ident-ifying both the salinity status of the catchment andan indication of impending salinisation.

Catchment water and salt balances werecarried out at 101 stream gauging stations acrossthe Murray-Darling Basin. The stations wereselected so as to obtain balances at the outlets of,and at a number of sites within each sub-basin. Inaddition, four of the sub-basins (Campaspe River,

200 years

MEDIUM RAINFALL

20 years

HIGH RAINFALL

Time since clearing

Oldequilibrium

Risinggroundwater

pressures

Newgroundwaterequilibrium

New saltequilibrium

Leaching ofsalt fromcatchments

Figure 1 Salt Output/Input (O/I) ratio variationwith time since vegetation clearing for medium and

high rainfall catchments

Loddon River, Murrumbidgee River, Namoi River)were analysed in more detail at a greater number ofstations, with attempts being made to correct forthe effects of water (and hence salt) diversions forboth urban and irrigation supplies. Salt balanceratios, total salt output (in both tonne km–2 and intonne day–1) were also calculated within these sub-basins. The following assumptions were implicit inthe analysis:

• Water and salt diverted from a stream forirrigation and other uses do not contribute tothe return flow to the stream within the 10-year analysis period.

• Salt and water transferred into the catchmentwere accounted for as being added directly tothe streamflow rather than being included as acomponent of the salt and water input to thecatchment.

• No attempt was made to include an estimate ofthe net movement of water and salt out of acatchment in groundwater flow.

Input of water and salt to catchments from rainfallwere estimated using a GIS-based approach whichutilised available coverage of interpolated rainfalland existing measurements of salt in rainfall from18 sites within the Basin (Blackburn and McLeod,1983). Only the sites to be uncontaminated byresuspended terrestrial dust were used for rainfallsalt concentrations (Simpson and Herczeg, 1994).Digital maps of the boundaries of the Murray-Darling Basin and its 26 sub-basins were obtainedfrom the Murray-Darling Basin Commission on anAlbers projection, and used as the base map for the

project. Detailed digital catchment boundary mapsfor New South Wales sub-basins were obtainedfrom the New South Wales Department of Landand Water Conservation, Victorian sub-basinboundaries were digitised from 1:100,000topographical maps. Monthly rainfall surfaces forthe Basin were obtained from the QueenslandDepartment of Primary Industries DroughtResearch Centre for the period 1980–95. Thesewere available on a 0.01 degree (approximately5 km) grid resolution in units of 0.1 mm. Rainfallsurface data were summed to provide annualrainfall, then projected and clipped to the requiredcatchment boundary. An ARC/INFO MacroLanguage (AML) routine was then used tocalculate the area-weighted annual rainfall for eachsub-basin or catchment of interest.

The annual output of water from the sub-basins was calculated by summing the daily flowdata from each station. Stream salt load wasestimated using one of the following methods,depending upon the frequency of the salinity dataat a gauging location. If the gap between salinitymeasurements was less than 7 days, the missingdata was interpolated (taking into account the flowregime during the period) and daily salt load wascalculated as the product of daily flow and saltconcentration. However, where the gaps betweensalinity measurements were greater than 7 days aregression analysis was undertaken to establish arelationship between salinity and stream flow rate,based on intermittent data sets. The regressionanalysis generally exceeded 50 points and was usedto calculate daily salt loads (in units of tonne day–1)from continuous streamflow data. For most stations, the relationships between salt load and stream flow were very good,with coefficients of determination usually greaterthan 0.90. However, in some cases with less distinctrelationships it was necessary to:

• fit the data with both a low-flow and high-flowregression line to reflect clear differencesbetween the two flow cases;

• separate the data set into 4 sub-sets andconstruct a regression for each of the four toavoid an extremely poor correlation at somestations in Victoria;

• use a non-linear regression (log–log) in a fewvery special cases where the above methodswere unsuccessful.

Finally, estimated daily salt loads were summed toprovide annual salt loads for each station.

Attempts were made to incorporate theeffects of water diversions on the water and saltbalances. In the case of the Victorian stations,Sinclair Knight Merz provided diversion data(flow, and some salinity for the period 1988–94)and maps (with location reference numbers) for theBroken, Goulburn, Campaspe, Loddon and Avoca

River sub-basins from the Victorian GovernmentBulk Carriers database. The data were annual flowin ML for 1988–94. The major diversionsaccounted for were from the Goulburn andCampaspe Rivers for the Waranga Western MainChannel, which is then distributed into theCampaspe, Loddon, and Avoca River basins. Thediversions from the Coliban River (via the ColibanMain Channel) and the Ovens River for irrigation,domestic, stock, industrial and town water supplieswere obtained from MDBC Annual Reports for1985 – July 1991. Diversions from the RiverMurray were obtained from both Sinclair KnightMerz (for the Yarrawonga Channel, and theNational Channel at Torrumbarry), as well asMDBC Annual Reports. Data were not availablefor diversions in the Eppalock–Bendigo pipeline(Campaspe River), or from Laanecoorie, CairnCurran and Tullaroop Reservoirs (Loddon River).The Gunbower Creek system could not be analyseddue to the absence of data for the input to KowSwamp and the upper reaches of the GunbowerCreek from the National Channel nearTorrumbarry Weir, and the diversion at CohunaWeir into No. 3 Channel. However, the MDBCAnnual reports gave data (1985 – 1990/91) fordiversions into the National Channel and also theirrigation returns to the River Murray viaGunbower Creek at Koondrook.

For New South Wales, the Department ofLand and Water Conservation provided data andassociated maps over the period 1985–94, fordiversions in reaches of the Murrumbidgee,Lachlan, Macquarie–Castlereagh, Namoi, Gwydir,Border Rivers, and the Darling Rivers. MDBCAnnual Reports provided diversion data from theRiver Murray into NSW, in some NSW riverbasins for 1985 – 90/91, as well as the diversionsfor the Jemalong and Wyldes Plains IrrigationDistricts.

In the case of the Snowy MountainsScheme, the MDBC provided good data for theperiod 1985–95 for the transfers of water withinthe Snowy Mountains Scheme and specifically thenet contributions to the River Murray and theMurrumbidgee River (including the Tumut River).Water is transferred into the Upper Murray at

Swampy Plains River, from the Tooma River (inthe Upper Murray) and Lake Eucumbene into theTumut River at Tumut Pond Reservoir, and fromthe Upper Murrumbidgee via Tantangara Reservoirto Lake Eucumbene. The Snowy MountainAuthority provided limited recent salinity data forsome reservoirs, and some documented data fromthe early construction phases of the scheme. Thesalinity of the reservoirs was quite variable, with arange in measured values of about an order ofmagnitude, which may reflect the location or depthof sampling rather than a representative salinity ofthese water bodies. In the absence of measuredsalinity in the 1985–94 period, the salinity of thewater transferred from the Snowy Scheme wastaken to be 25 mg L–1.

ResultsThis section presents a summary of the results fromboth the historical stream salinity trend analysis,and the catchment water and salt balance compon-ent of the project. The correlation between theresults of both methods of data set analysis pro-vided increased confidence in the stream salini-sation conclusions, given the intermittent nature ofmuch of the historical stream salinity data.Detailed results for each station can be found intechnical reports by Jolly et al. (1997a, 1997b).

In order to simplify the summary of thestream salinisation trends and catchment water andsalt balances, the Murray-Darling Basin wasdivided into four geographically similar regions.The results and trends for each of these regionshave been discussed separately. These regions areshown in Figure 2 and have been described as:

1) the northern and western dryland region,2) the eastern and southern dryland region3) the irrigation region,4) the Lower Murray region.

Figure 3 then shows the stream salinity trends interms of an annual percentage change at locationsthroughout the Murray-Darling Basin, whileFigure 4 shows the catchment salt output/input(O/I) ratios for the period 1985–94.

1. Northern-Western Dryland

4. Lower Murray

3. Irrigation

2. Southern-Eastern Dryland

Stream gauging station

Zone boundary

Legend

Figure 2 Map showing this study’s division of the Murray-Darling Basin into four regions

Decreasing 1% per year

Increasing 3% per year

No trend

Trend less than error range

Legend

(1)(1)

0(1)(1)0

(1)(1)

(3)0(3)

Figure 3 Annual percentage change in stream salinity trend at stream gauging stationswithin the Murray-Darling Basin

1.51.4

0.50.32.0

2.51.2

1.53.0

5.44.4

2.60.9

1.21.42.6

1.72.9

4.33.0

1.10.4

3.73.0

1.31.9

2.41.91.5

4.13.6

Ratio < 1.0

Ratio 1.0 - 1.5

Legend

Figure 4 Catchment salt output/input ratio for stream gauging stations within the Murray-Darling Basin

Summaries of the results for each of these4 regions of the Murray-Darling Basin are asfollows:

1) The northern and western region of the Basinwas found to have no significant trends or saltimbalances. The lack of response for thisregion may be partially due to the summerdominance of the rainfall, the heavier soilsfound in the higher rainfall areas, and also therelative lateness of agricultural land-usechanges. The results substantiate earlierconclusions that the Darling Basin was likelyto develop salinity more slowly than thesouthern parts of the Murray-Darling Basin.Jolly (1989) came to those conclusions on thebasis of an analysis of the soils, land use,vegetation, rainfall and groundwater. Thereshould be preventative action to avoid the onsetof salinisation as in the Murray Basin, howeverthe quality and chemistry of the groundwaterhas meant that groundwater pumping is likelyto be able to control groundwater levels andsalinisation. Such measures in similarenvironments in Queensland have beeneffective.

2) In the southern and eastern dryland region ofthe Basin, uniformly rising stream salinitytrends were found in most of the tributaries (seeFigure 5 for an example of the rising trends inthis area). The change in salt balance wasminimal in areas of high rainfall (> 800 mmyr–1) and hence trends were not as noticeable,even when the salt O/I ratio was in a risingphase. Through the medium rainfall zones(500–800 mm yr–1), all of the trends were

significant and rising, with catchment saltoutput/input (O/I) ratios generally high.Figure 6 shows the catchment salt balance forthe Namoi River catchment, giving the salt bal-ance and salt output estimates (in tonne km–2

and tonne day–1) for the catchment. Thismedium rainfall zone coincided with theknown areas of dryland salinisation in NSW(Bradd and Gates, 1995) as well as with knownareas of groundwater rise. The stream salinityin the dryland area of Victoria was confused byriver regulation, with only 3 stations showing asignificant trend. Despite the overall lack ofstream salinity trend, catchment salt O/I ratioswere consistently high in the unregulatedUpper Loddon–Campaspe catchment.

3) The irrigation region of the Basin lies mainly inthe lower reaches of the river systems, withannual rainfall of less than 500 mm. Streamsalinity trends were uniformly rising in the irri-gation areas. This was likely to be the result ofmore saline irrigation returns to the rivers, andin some cases groundwater input from moundsbelow irrigation areas. Despite these risingstream salinity trends, catchments were close toa salt balance. It was likely that this balancewas due to the effect of large diversions ofwater (and salt) in the area, which result intemporary storage of large amounts of salt thatmay have otherwise contributed to a catchmentsalt export. The effects of this storage are likelyto result in salt export in the medium to longterm, however it was not possible to undertakethis full diversion-corrected analysis within thescope of this project.

65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95

Lachlan R@Forbes (412004)

Lachlan R@Condoblin Bridge (412006)

Lachlan R@Cowra (412002)

Lachlan R@Hillston Weir (412039)

Figure 5 Flow and seasonally corrected non-linear salinity trends at 4 stations along the Lachlan River

Walget Narrabri

Gunnedah

Namoi River@Goangra (9)

1.2 Salt O/I RatioSalt Output (tonnes km )

Salt Output (tonnes day )

LEGEND

Namoi River@Mollee (9) Namoi River

@Boggabri (5)

Namoi River@Keepit (5)

Namoi River@Manila (4)

Peel River@Carrol Gap (6)

Mooki River@Breeza (7)

Mooki River@Caroona (6)

Namoi River@Gunnedah (9)

Cox’s Creek@Boggabri (5)

50 100km0

Figure 6 Salt output/input (O/I) ratio and salt output within the Namoi River Catchment

4) In the Lower Murray River region, most of thestations showed no significant stream salinitytrend (although one case had a significantdecreasing trend). This result suggests that thesalt interception schemes implemented as partof the Murray-Darling Basin Commission’sSalinity and Drainage Strategy are currentlyeffective.

Discussion of Outcomes

The pattern of catchment salt balances exhibitsbehaviour which appears to correlate well with ourunderstanding of land salinisation. The resultsindicate that the areas in the Murray-DarlingBasin which are presently (or already) exper-iencing the onset of stream salinisation aregenerally those in the medium rainfall zone (500–800 mm yr–1), and that the significant trends areoccurring in the same places where there are saltimbalances. This suggests that these catchmentshave not yet reached a new hydrologic equilibriumand there is potential for further increases instream salinity. The results are also consistent inthat the salt balance results show that salinisationis much further advanced in the Murray Basinthan it is in the Darling Basin.

Salt imbalances are not apparent in thehigh rainfall zones (>800 mm yr–1), with nosignificant trend in stream salinisation presumably

due to less clearing of native vegetation. This,combined with the strong possibility that thesesystems may have already reached a newhydrologic balance, means that trends are notobvious. However, the lower salt output/input (O/I)ratios may also be the result of the smaller relativeincrease in recharge which occurs in the highrainfall areas following widespread clearing. Thelower rainfall (<500 mm yr–1) downstream regionsof many of the catchments appear to be in close tosalt balance due to the large diversions of water(and hence salt) from the rivers. However,increasing trends are still present, as a result ofboth the high salinity irrigation return flows andenhanced groundwater inflows.

Trends are apparent in the drylandstreams and in the flow-corrected stream salinitiesfrom the irrigation areas; however it is not clearhow these will impact on River Murray salinity inthe medium term. Diversions, and mitigationmeasures such as evaporation basins orgroundwater pumping, are likely to decrease saltload trends in the short term by removing waterand salt from the streams. This off-stream storageof salt acts as a temporary buffer that can preventincreasing stream salt-load trends, but which mayeventually lead to medium-long term increases instream salinity.

While historical trends are useful forextrapolating into the future to a limited extent, it

is important to know how these trends will changeinto the future and how they may be impacted byland use or river management change. Thedevelopment of a new statistical approach tostream salinity non-linear trend estimation is seenas a highlight of this project, as previous methodshave generally only been able to provide lineartrends. Determination of the non-linear trend withtime will enable the analysis of the relationshipbetween trends and factors such as climaticvariability, operation of salt mitigation schemes,changes in stream operation, or known trends ingroundwater or land salinisation. Moreover, thecorrelation of stream salinity with flow canindicate whether the salt arrives at the stream as aresult of base flow or runoff.

The results from the salt-trendscomponent of the project are consistent with thesalt balance results in the general basin-widepattern. The analysis indicates that the time lag forresponse by groundwater may be much shorter inthe southern part of the Basin (about 50 years)than in the northern part (greater than 80 years).Although reliable indication of future streamsalinity and salt load can not be obtained fromhistorical trend analysis, there seems little tosuggest that current trends will decreasesubstantially in the future. This project highlightsthe difficulties of using the salinity at Morgan asthe only measure of the effects of the Murray-Daring Basin Commission’s Salinity and DrainageStrategy, especially since future stream salinisationarising from dryland areas will be first felt in theupstream irrigation areas.

Future RecommendationsThe results of this project provide a framework forincluding knowledge gained in other studies, oftensite-specific, regarding stream salinisation. At thisstage, it is difficult to specify the catchment worknecessary for the amelioration of stream salinity,although future work is needed to betterunderstand the role of stream interaction with theweathered, fractured rock and alluvial groundwatersystems that contribute to the Deep Leadequivalents around the Basin. This knowledge isnecessary to devise appropriate land managementoptions which will ensure that funds for catchmentplans can be targeted on the key areas which arethe most critical for Basin salinisation.

AcknowledgmentsThe Murray-Darling Basin Commission, throughits Natural Resources Management StrategyInvestigation and Education Program (Grant No.D5035), have provided significant funding for thiswork. Funding was also provided by the CRC forCatchment Hydrology. The support of bothorganisations is greatly appreciated.

Ken Brook and Neil Flood of the Queens-land Department of Primary Industries providedrainfall data. Janice Green of the Department ofLand and Water Conservation provided flow,salinity, and diversion data for New South Wales.Tim Vass of Sinclair Knight Merz Pty Ltdprovided flow, salinity, and diversion data forVictoria. Kit Dyer and Andrew Close of theMurray-Darling Basin Commission also providedadditional flow and salinity data.

References

Allison, G.B. and Schonfeldt, C.B. (1989).Sustainability of water resources of the Murray-Darling Basin. 12th Invitation Symposium:Murray-Darling Basin – A Resource to beManaged, Preprint No. 8, Australian Academyof Technological Sciences and Engineering,149-161.

Blackburn, G. and McLeod, S. (1983). Salinity ofatmospheric precipitation in the Murray-DarlingDrainage Division, Australia. AustralianJournal of Soil Research, 21, 411-34.

Bradd, J. and Gates, G. (1995). The Progressionfrom Site Investigations to GIS Analysis to MapDryland Salinity Hazard in NSW. Murray-Darling 1995 Workshop, Australian GeologicalSurvey Organisation Record 1995/61.

Jolly, I.D. (1989). Investigation into the potentialfor increased stream salinisation in the DarlingBasin. Report 10, Centre for GroundwaterStudies, CSIRO Land & Water, Adelaide,103pp.

Jolly, I.D., Dowling, T.I., Zhang, L, Williamson,D.R. and Walker G.R. (1997). Water and saltbalances of the catchments of the Murray-Darling Basin. Technical Report 37/97,November, CSIRO Land and Water.

Jolly, I.D., Morton, R., Walker, G.R., Robinson, G,Jones, H., Nandakumar, N., Nathan, R.J.,Clarke, R. and McNeill, V (1997). Streamsalinity trends in catchments of the Murray-Darling Basin. Technical Report 14/97, August,CSIRO Land and Water.

Morton, R. (1996). Statistical Methodology forStream Salinity Trends. CSIRO Biometrics Unit,Canberra, 9 pp.

Morton, R. (1997). Instructions for the use of thetrend estimation program. CSIRO BiometricsUnit, Canberra, 7 pp.

Payne, R.W. et al. (1993). Genstat 5 Release 3Reference Manual. Clarendon Press, Oxford,797 pp.

Peck, A.J. and Hurle, D.H. (1973). Chloridebalance of some farmed and forested catchmentsin south western Australia. Water ResourcesResearch, 9(3), 648-57.

Simpson, H.J. and Herczeg, A.L. (1994). Deliveryof marine chloride in precipitation and removalby rivers in the Murray-Darling Basin,Australia, Journal of Hydrology, 154, 323-350.

Williamson, D.R., Gates, G.W.B., Robinson, G.,Linke, G.K., Seker, M.P. and Evans, W.R.(1997). Salt Trends: Historic Trend in Salt Con-centration and Saltload of Stream Flow in theMurray-Darling Drainage Division. DrylandTechnical Report No. 1, Report to NRMS ofMDBC by the Project 5043 Steering Committee.

Project Publications

Reports

Jolly, I.D., Morton, R., Walker, G.R., Robinson, G,Jones, H., Nandakumar, N., Nathan, R.J.,Clarke, R. and McNeill, V (1997), Streamsalinity trends in catchments of the Murray-Darling Basin. Technical Report 14/97, August,CSIRO Land and Water.

Jolly, I.D., Dowling, T.I., Zhang, L, Williamson,D.R. and Walker G.R. (1997). Water and saltbalances of the catchments of the Murray-Darling Basin. Technical Report 37/97,November, CSIRO Land and Water.

Williamson, D.R., Gates, G.W.B., Robinson, G.,Linke, G.K., Seker, M.P. and Evans, W.R.(1997), Salt Trends: Historic Trend in SaltConcentration and Saltload of Stream Flow inthe Murray-Darling Drainage Division. DrylandTechnical Report No. 1, Report to NRMS ofMDBC by the Project 5043 Steering Committee.

Conference Proceedings

Jolly, I., Zhang, L, Dowling, T., Williamson, D.and Walker, G. (1997), Estimation of HistoricalSalt Balances for Various Catchments of theMurray-Darling Basin. Murray Darling BasinWorkshop, August, Toowoomba, 24-29.

Jolly, I.D., Walker, G.R., Dowling, T.I., Zhang, L.,Morton, R., Williamson, D.R. (1997), Recon-structing Historical Salt Balances and StreamSalinity Trends in Catchments of the Murray-Darling Basin, Australia. Water/Land Wai-Whenua – 24th Hydrology and Water ResourcesSymposium, Auckland, December, 423-428.

Walker, G., Jolly, I., Morton, R., Robinson, G.,Jones, H., Nathan, R.J., Nandakumar, N.,Clarke, R. and McNeill, V. (1997), Estimationof Historical Trends in Stream Salinity forVarious Catchments of the Murray-DarlingBasin. Murray Darling Basin Workshop, 26-28August, Toowoomba, 125-129b.

Walker, G., Jolly, I., Zhang, L., Dowling, T.,Dyce, P., Williamson, D., Morton, R., Robinson,G., Jones, H., Nathan, R., Nandakumar, N.,Evans, R. (1997), Trends in salt loads andconcentrations of stream flow in the Murray-Darling Basin, 1997 Dryland Forum, October,North Adelaide, Murray-Darling Basin Com-mission, 75-78.

Historical stream salinity trends - CSIRO · Historical stream salinity trends and catchment salt...

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