Whole-of-catchment Water and Salt Balance

WHOLE-OF-CATCHMENT WATERAND SALT BALANCEIdentifying potential water saving and managementoptions in the Murrumbidgee catchment

N AT I O N A L R E S E A R C H

FLAGSHIPS

water for a healthy country

NSW GOVERNMENT

2


KEY OPPORTUNITIES

The opportunities are based on research by the Water for a HealthyCountry National Research Flagship quantifying actual losses inthe river and the major irrigation areas. Decisions to realise savingsat any level must follow a full benefit–cost analysis.

Water saving options will also need to take into account climatevariability and its impacts on water allocation for consumptive andenvironmental purposes.

KEY OPPORTUNITIES FOR IMPROVEMENTS

❚ Better ordering, measuring and metering systems whenintroduced will assist in overcoming apparent measurementand end-of-system escape flows.

❚ Peak summer crop demand should be spread and seasonality offlows improved by encouraging growth of winter crops and byconstructing storages to better manage river flows. It would alsohelp overcome system constraints and provide better security ofsupply.

❚ Conjunctive use of surface water and groundwater should bepromoted for sustainable water management at the catchmentscale.

❚ Potential for artificial recharge using good quality water anddedicated or existing bores should be investigated to reducesalinisation of deeper aquifers and provide an evaporation-freesecure underground storage. Any artificial recharge efforts needto consider both the elastic and inelastic recovery behaviour ofclay layers and related land subsidence issues.

❚ Agronomic and engineering solutions need to be examined formanaging rootzone salinity and drainage in low groundwateroutflow areas such as south of Coleambally, Yenda, Wah Wahand Lakeview since these irrigation areas are net importers ofsalts.

❚ At sites with high seepage rates (>10 mm/day), use of EM andgeophysical methods is a prerequisite for targeted investmentsaimed at controlling losses from the supply systems.

❚ New insights into the nature and contribution of differentsubcatchments demand a through investigation to pinpointclearly which subcatchments and surface–groundwaterinteractions provide the best opportunity to manage drylandsalinity.

NOTE TO READER

Water-saving figures in these summary booklets differfor the following reasons.

❚ The WHOLE-OF-CATCHMENT WATER ANDSALT BALANCE: identifying potential water savingand management options in the Murrumbidgeecatchment used existing knowledge (data and models)to obtain a first-cut understanding of possible watersaving volumes across the catchment. A number ofknowledge gaps and the need for further analysisare highlighted.

❚ The OFF- AND ON-FARM SAVINGS OFIRRIGATION WATER: Murrumbidgee valley waterefficiency feasibility project followed the initialcatchment water balance. During this study, targeteddata gathering, analysis and modelling were carriedout to refine the values for water saving volumesand conduct a cost–benefit analysis within irrigationareas. This study showed that greater and more cost-effective water savings are possible if the correctknowledge investments can be made.

3


INTRODUCTION

Understanding water use, water use efficiency, water productivity,water savings and water losses is essential in ensuring that we haveenough water to meet both irrigation and river needs. Before wecan approach these issues with any real certainty we need tounderstand and be able to track water pathways.

A whole-of-catchment hydrologic assessment of the MurrumbidgeeCatchment was made as part of the Pratt Water Initiative. It usedexisting hydrological data plus additional analysis to evaluate thepotential for water savings. Specific objectives were to:

❚ provide a description of the major features of the hydrologicsystem relevant to potential water savings;

❚ quantify potential water savings; and

❚ identify information gaps.

The assessment distinguishes between apparent and true or actualwater losses, and examines unaccounted water flows.

Figure 1. Location of the Murrumbidgee River Valley.

II

Wah Wah Irrigation District

Benerembah Irrigation Area

Mirrool Irrigation Area

Yanco Irrigation Area

Coleambally Irrigation Area

Lowbidgee Irrigation Area

Balranald

Deniliquin

Albury

Canberra

Hay

Griffith

Leeton

Narrandera

Wagga WaggaJerilderie

Towns

Water courses

Dams

Roads

Murrumbidgee and Murray irrigation areas

Murrumbidgee catchment boundary100

Distance (km)

2001000

N

Water pathways are a key to tracking andmaking water savings

4


HYDROLOGIC SYSTEM

The Murrumbidgee River has a catchment area of around84 000 km2. It flows 1600 km from the alpine mountains at itssource in the Snowy Mountains to flat alluvial plains at its junctionwith the Murray River (Figure 1).

Flow constraints. Main flow constraints occur in the Tumut River(< 9 GL/day) and Gundagai Choke (< 32 GL/day).

Rainfall. Precipitation decreases from east to west: from1500 mm/yr near Tumut, to 600 mm/yr near Gundagai, andbetween 500 mm/yr and 300 mm/yr between Darlington Pointand Balranald (Figure 2).

Evapotranspiration. Potential evapotranspiration varies from1000 mm/yr in the east to over 1600 mm/yr in the west.

Temperature. In the east, average daily maximum and minimumtemperatures are 21°C and 6°C. During the hottest month in thewest, average daily maximum and minimum temperatures are 32°Cand 16°C.

Figure 2. Murrumbidgee annual rainfall distribution (1950–2001).

Upper catchments are characterised by steepslopes and fractured discontinuous underlying

aquifers

142 143 144 145 146 147 148 149 150

-36.8

-35.8

-34.8

-33.8

300

500

700

900

1100

1300

1500

Griffith

Wagga Wagga Canberra

NarranderaYass

Balranald Leeton Temora

Junee

Rainfall (mm)

Darlington Point

NLo

ng

itu

de

(o

)

Latitude (o)

5


Figure 3. Hydrogeology of the Murrumbidgee Catchment.

Geology. The catchment has three major hydrogeological units(Figure 3).

❚ The Upper Murrumbidgee Fractured Rock consists of hardconsolidated rocks that have limited groundwater pumpingpotential and provide base flows to the upper Murrumbidgeecreeks (e.g. the Goodradigbee River).

❚ The Mid Murrumbidgee Alluvium is a deep v-shaped aquifersystem over weathered bedrock. Alluvium consists broadly ofsands, gravel, clays, and granite. It has a very strong hydraulicresponse and reduction in seepage from the river in this reachwill have a direct negative impact on groundwater available tousers including irrigation and town water supplies. Total annualrecharge is around 127 GL/yr; current entitlements are55 GL/yr; town water supplies for 1998/99 were 21 GL.

❚ The Lower Murrumbidgee Alluvium consists of unconsolidatedalluvial deposits consisting of layers of sands, silts, clays andpeat. Water movement through the deep aquifers is generallyfrom east to west. Recharge to the deep aquifers is mainly fromthe Murrumbidgee River downstream of Narrandera and fromthe irrigation areas, and salinity increases from east to west, butis generally low. Deep bore yields may exceed 400 L/s andaquifers may store 250 000 GL of low salinity groundwater.Average annual recharge is 335 GL/yr; safe yield is 270 GL/yr.Losses downstream of Hay can be 370 GL/yr but flows anddiversion statistics in this reach need to be validated.

Strong hydraulic connection between river andaquifer in the Mid Murrumbidgee Alluvium

BalranaldHay

Griffith

Narrandera

Canberra

Wagga Wagga

Towns

Major water courses

Murrumbidgee catchment boundary

Lower Murrumbidgee Alluvium

Mid Murrumbidgee Alluvium

Unincorporated area: Lachlan Fold Belt Province

N

Murrumbidgee River

Yanco Creek

Billabong Creek

6


WATER ALLOCATION

Water is allocated according to the following entitlements:

❚ water availability and flows (total inflow is 4360 GL/yr);

❚ riparian rights requirements (4.5 GL/yr);

❚ licensed domestic and stock requirements (36 GL/yr);

❚ local water utility requirements (23 GL/yr);

❚ any water carried forward in water accounts (variable amounteach year);

❚ high security (298 GL/yr) ;

❚ general security (2043 GL/yr); and

❚ conveyance allowance within the irrigation corporations (up to373 GL/yr depending on total allocation).

Water allocation is moderated by:

❚ a cap on diversions that sets them at the volume that wouldhave been used with 1993/94 levels of irrigation developmentunder similar climatic conditions; and

❚ environmental flow rules.

Rules for translucency state that when general water allocations areabove 80%, the flow past Balranald must be 300 ML/d; when theyare below 80%, the flow past Balranald must be 200 ML/d. Theserules have effectively reduced water supply to irrigators by between4 and 5% of entitlements.

Allocations for general security have fallen by 30% since 1995 dueto the introduction of the Murray–Darling Basin Cap,environmental flows, activation of sleeper and dozer licences,increased water trading, and dryer than average seasonalconditions. The August 2003 general security allocation was thelowest on record at 23% of entitlement.

Analysis of historic data shows that the catchment has a very secureavailability of water (e.g. January allocations less than 80% wouldhave occurred in the drier periods from 1900 to the mid 1940s;and they would have been greater than 90% for most years since1948).

Historic data show a secure availability ofwater

Total inflow – 4360 GL/yr

Total water allocation – 2778 GL/yr


7


SALT BALANCE

Around 140 000 tonnes of salts were exported from the river tofarmers’ fields in the Murrumbidgee and Coleambally irrigationareas in 1992. Amounts will increase, with increasing river salinityand will need to be managed within the irrigation areas ifsustainable irrigated agriculture is to be achieved.

A paucity of salinity data means that a comprehensive salt balancecould not be calculated. It is known that less salt per unitcatchment area and per volume of runoff is contributed by theTumut River as compared to the Murrumbidgee River upstream ofBurrinjuck Dam (see Table 1).

❚ The Tumut catchment contributes 38% of the water but only11% of the salt.

❚ The Murrumbidgee catchment upstream of Burrinjuck alsocontributes 38% of water but 37% of the salt.

Most salts are derived from small tributaries of the MurrumbidgeeRiver and surface–groundwater interaction between BurrinjuckDam and Wagga Wagga. Management of dryland salinity wouldhave the greatest effect on reducing salt loading to the river in thesesubcatchments and then reducing the salt load into the irrigationareas.

Management of salt should include:

❚ dealing with local sources of salt;

❚ developing guidelines for operating bores between Gundagaiand Narrandera;

❚ in-depth studies on managing salinity between Gundagai andNarrandera; and

❚ catchment repair of key tributary catchments of theMurrumbidgee River.

Table 1. Comparison of water and salt yield per subcatchment.

Subcatchment Contributing Average 1992 water Percentage Percentage Percentagearea salt yield yield contributing water salt

area yield yield(km2) (tonnes) (GL/yr) (%) (%) (%)

Tumut* 11 540* 50 671 1 914 10 38 11

Murrumbidgee upstream of Burrinjuck 13 100 164 354 1 928 50 37 37

Dam Walls to Wagga Wagga 10 760 231 189 1 269 40 25 52

Total 26 400 446 214 5 111 100 100 100

* The Tumut subcatchment includes the NSW Snowy river area of 9000 km2 and 2540 km2 of the Tumut subcatchment.

About 140 000 tonnes of salt are exported tofarmers’ paddocks each year


8


WATER BALANCE

Water balance is calculated using inflows, outflows, evaporation,diversions, and unaccounted and apparent losses from the river.Apparent losses are less in dry years than in wet years. Most reacheslose water during high demand periods (September to February)due to high volumes of flow in the river and higher pumping ratesfrom the adjoining groundwater bores. Most apparent losses andunaccounted flows occur below Narrandera.

The only true losses from the system are evaporation and seepagelosses to saline groundwater. Hundred year average annual waterinflows and outflows are:

❚ river flow from Burrinjuck and Blowering dams (2900 GL/yr);

❚ net gain between the dams and Wagga Wagga (1460 GL/yr);

❚ apparent loss from Wagga Wagga to Darlington Point(170 GL/yr);

❚ aquifer recharge from Darlington Point to Hay (120 GL/yr);

❚ apparent loss from Hay to Balranald (190 GL/yr); and

❚ total evaporation from the river (70 GL/yr) (see also Figure 4,Table 3).

1000

500

0

-500

-1000

-1500

-2000

Net changes (

GL)

+ve values = loss from the river reach

1991: a wet year

1994: a dry year

1995: an average year

Dams to Wagga

Narrandera to

Darlington Pt

Darlington Pt to

DS Hay WeirDS Hay Weir to

DS Maude Weir

Wagga to Narrandera

-ve values = gain to the river reach

Table 2. Murrumbidgee water balance (100 years average).

Reach Reach length Inflow Outflow Diversions Unaccounted flows(km) (GL) (GL) (GL) (GL)

Upstream to Burrinjuck 1 300

Upstream to Blowering 1 600

Dams to Wagga 260 4 360 16 26

Wagga to Darlington Pt 466 4 360 2160 2010 170

Darlington Pt to Hay 214 2160 1840 170 120

Hay to Balranald 280 1840 1190 425 190


Figure 4. Yearly net gain/loss along the Murrumbidgee River forselected years.

9

water for a healthy countrywater for a healthy country

Table 3. Yearly water balance.

Year Inflow Outflow Diversions Evaporation Net apparentGain/Loss

(Gl) (Gl) (Gl) (Gl) (Gl)

Burrinjuck Dam Wet – 1991 1880 1945

Dry – 1994 380 921

Average – 1995 1860 1784

Blowering Dam Wet – 1991 1830 2216

Dry – 1994 1908 2468

Average – 1995 1555 980

Dams – Wagga Wagga Wet – 1991 4161 5125 14 17 -995

Dry – 1994 3389 3719 25 16 -371

Average – 1995 2764 4165 12 14 -1427

Wagga Wagga – Narrandera Wet – 1991 5125 3924 1096 15 90

Dry – 1994 3719 2447 1221 14 37

Average – 1995 4165 3294 895 13 -37

Narrandera – Darlington Point Wet – 1991 3924 2536 1217 7 164

Dry – 1994 2447 1063 1278 7 99

Average – 1995 3294 2017 1109 7 161

Darlington Point – D/S Hay Weir Wet – 1991 2536 2038 194 22 282

Dry – 1994 1063 580 237 22 224

Average – 1995 2017 1571 293 21 132

D/S Hay Weir – D/S Maude Weir Wet – 1991 2038 1619 278 8 133

Dry – 1994 580 460 158 7 -45

Average – 1995 1571 1161 356 6 48

D/S Maude Weir – D/S Balranald Weir Wet – 1991 1619 1181 190 13 235

Dry – 1994 460 442 19 10 -11

Average – 1995 1161 793 166 9 193

Figure 5. Water balance (1995).

#

Net change (GL)

Evaporation (GL)

Inflow/outflow (GL)

Diversions (GL)

Balranald Weir

Burrinjuck Dam

Hay Weir

Darlington Point

Narrandera

Wagga Wagga

Blowering Dam

15

161

1784

-14271860

980

1555

12

3294

-37

895

1571132

293

2017

1109

241

522793

4165

1413

7

21

N

10


GROUNDWATER

Matching and not exceeding groundwater outflow is the key tosustainability in any inland, high evaporation environment,irrigation area.

Reported groundwater pumping in the lower Murrumbidgee is lessthan sustainable yield. It has rapidly increased since 1994/95 (seeFigure 6). In the last 10 years, the deeper groundwater pressureshave declined by 10 to 20 m over most of the deeper aquifersbetween Narrandera and Hay. Groundwater downstream of Hay istending to rise—possibly due to increased rice growing adjacent tothe river and/or losses from the river (see Figure 7). Declininggroundwater levels may result in ingress of saline groundwater fromshallow aquifers to deep aquifers and lateral movement of deepsaline groundwater towards better quality groundwater.

Residual groundwater drawdowns in deeper aquifers offer apotential for these aquifers to be artificially recharged using goodquality water from either new dedicated bores or existing bores.This can help reduce salinisation of deeper aquifers as well as offerevaporation-free secure underground storage.

Figure 6. Groundwater entitlements and use in the Lower Murrumbidgee.

Figure 7. Overall change in deeper groundwater levels betweenNarrandera and Hay (1990 – 2003).

600

400

300

200

100

0

Volu

me

(G

L/y

r)

Entitlement (GL/yr)

Use (GL/yr)

500

19

82

/83

1983/8

4

1984/8

5

1985/8

6

1986/8

7

1987/8

8

1988/8

9

1989/9

0

1990/9

1

1991/9

2

1992/9

3

1993/9

4

1994/9

5

1995/9

6

1996/9

7

1997/9

8

1998/9

9

1999/0

0

2000/0

1

200000 250000 300000 350000 400000 450000

6050000

6100000

6150000

6200000

6250000

Narrandera

Griffith

Hay

Change in

GWL (m)

Easting

No

rth

ing

-10

0

-5

-15

-20

11


WATER BALANCE IN THEIRRIGATION AREAS

Crop water demand in the irrigation areas is dominated by summercrops especially rice. This has created environmental and supplyproblems and altered the natural flow regime.

❚ The limited capacity of the Tumut River means that in someyears it may not be possible to meet high summer demands.

❚ Irrigation demand needs to be spread to better mimic the‘natural’ flow variability in the river.

This could be achieved by growing more winter crops andconstructing storages for winter flows that provide a bufferagainst peak summer demand. Coleambally IrrigationCo-operative Limited together with Australian BioFuels PtyLtd, for example, are considering a joint venture to build anethanol plant. It would require approximately 200 000 tonnesof grain per year from both winter and summer crops.

Total true losses for the river and major irrigation (MIA and CIA)areas are approximately 345 GL/yr. Potential true water savings inthe river (from evaporation) and the losses in the MurrumbidgeeIrrigation Area and Coleambally Irrigation Area are around295 GL/yr (170 GL in the Murrumbidgee Irrigation Area + 45 GLfor the Coleambally Irrigation Area and 80 GL evaporation fromthe river) if the present cropping regimes are maintained. Thisleaves 50 GL for rootzone leaching recharge.

Ne

t w

ate

r re

qu

ire

me

nt

(GL

)

120

100

80

60

40

20

0

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

Dry

Average

Wet

Figure 8. Net monthly crop water requirements (GL) in the Coleambally Irrigation Area (2000/01) under three climateconditions.

12


Murrumbidgee Irrigation Area

Average diversions to the Murrumbidgee Irrigation Area are around1000 GL/yr; average annual rainfall is around 400 mm (equivalentto 850 GL/yr).

OFF-FARM LOSSES

The difference between intake from the river and on-farm suppliesis between 173 and 225 GL.

Over 200 GL/yr of water are lost between the point of withdrawalfrom the Murrumbidgee River to the delivery at farm boundaries.Of this, true losses (evaporation from channels and swamps andlakes and channel seepage losses) are approximately 100 GL/yr:

❚ approximately 60 GL is from true losses in the supply system(see Table 3); and

❚ approximately 40 GL is from evaporation from Barren BoxSwamp and Lake Wyangan (see Table 4).

Low seepage losses compared to other areas are a result of shallowwatertable conditions and heavy soils. Less than 5 mm/day seepsfrom over 80% of the channels. The total surface area of theirrigation supply system is around 1000 ha. Our estimates ofseepage losses using a surface and groundwater interaction modelare between 25 and 30 GL/year. In order to justify conveyanceefficiency gains by reducing seepage it is necessary to target channelreaches with seepage rates greater than 10 mm/day which arearound 10% of the area.

Remaining losses from the supply systems (42 GL) are eitherreturned to the river (32 GL drainage to the river) or are used onfarm (~10 GL leaks).

Up to 14% of delivery can be attributed to unaccounted flows dueto underestimation of flows by the Dethridge wheels that meterdelivery to the farm. It may be possible to better understand andreduce these flows by introducing better ordering, measuring andmetering systems.

ON FARM LOSSES

On-farm water is lost from farm supply systems, from drains andthrough deep percolation. However, little data are available todistinguish between them.

Deep percolation losses are around 110 GL/yr (20 GL/yr asseepage from channels, and 90 GL/yr from on-farm irrigation).Some 80 GL of this recharge is either re-used by the plants throughcapillary upflow or is evaporated through the soil surface. Theremaining 30 GL/yr either flows out of the region as the regionalgroundwater outflow (depending on the capacity of the aquifers—estimated total is 20 GL/yr) or causes local net accessions adding tothe shallow watertable.

The rate of groundwater outflow is between 0.2 and 1.0 ML/ha/yr.This wide range is mainly caused by localised hydrogeologicalinteractions due to the closed nature of some local groundwatersystems.

Table 4. Reported transmission losses for theMurrumbidgee Irrigation Area (2000/01).

Source of loss Volume (GL)

True losses (100 GL/yr)

Seepage from main system 21

Seepage from Wah Wah supply system 20

Evaporation from channels 20

Evaporation from Barren Box and Lake Wyangan 37

Remaining losses (42 GL/yr)

Surface water drainage back to river 32

Miscellaneous (leaks) 10

Total 140

Unaccounted flows (Dethridge wheels) 120

1850 GL is supplied to the MIA through rainand irrigation water

Off-farm losses are 200 GL/yr

On-farm losses are around 110 GL/yr


SALINITY

A significant proportion of the land is subject to salinity (Table 5).Shallow groundwater salinity varies from less than 2 dS/m to over20 dS/m. In limited regional groundwater outflow situations(e.g. Yenda), the major deep percolation is discharged throughcapillary upflow and presents a risk of land salinisation. The slowresponse of aquifers in many areas is due to the presence of claylayers at various depths exacerbating salinisation risk.

WATER SAVING POTENTIAL

Potential total water savings are around 170 GL and are made upof:

❚ 60 GL from supply systems;

❚ 40 GL evaporation from the storages; and

❚ around 70 GL from on-farm savings.

On-farm water use efficiency needs to be improved by around70 GL/yr to enable a balance between recharge and dischargecapability of the regional groundwater. This will be a true watersaving under the present cropping and climate regime.

Murrumbidgee Irrigation has conducted a savings exercise whichfound a total saving of 90 to 100 GL (see Table 6). The potentialwater savings at Barren Box Swamp are mainly due to a reductionof its area by 60% and therefore reducing evaporation loss.

Table 5. Percentage of land affected by salinity in various sub Murrumbidgee Irrigation Area districts based on previousstudies.

Subdistrict % of land > 2 dS/m % of land > 4 dS/m % of land > 8 dS/m1990–94 1998 1990–94 1998 1990–94 1998

Gogeldrie 8.6 7.4 0.0 0.0 0.0 0.0

South Ben 17.3 32.8 3.6 4.2 1.3 2.2

North Ben 30.0 44.4 11.6 9.6 6.3 2.5

Hanwood 33.8 31.1 12.7 18.9 2.9 3.2

Kooba 4.8 10.0 2.2 1.5 0.9 0.0

Yenda 35.3 39.1 16.6 12.2 6.3 0.0

Murrami 11.0 27.6 8.9 4.0 5.3 2.1

Murrumbidgee Irrigation Area 22.0 27.6 8.8 8.1 2.9 1.5

Wah Wah 53.5 70.1 11.1 12.5 5.1 5.1

Table 6. Murrumbidgee Irrigation’s water saving proposals prior to this study.

Water saving (GL)

Barren Box Swamp Splitting the swamp with an internal levee providing an active cell and a wetland.Present area of 3000 ha and reducing the surface area by 40 to 60%. 20 – 30

En route storages Providing 1 or 2 storages within Murrumbidgee Irrigation’s system, collecting (subject to modelling)rainfall runoff and irrigation rejection flows.

Wah Wah stock and Replacement of existing open channel system with pipes 18*domestic systems,Northern Hay Plains

Horticulture farm Providing high-tech water system for 900 farms in Leeton, Griffith and Yendarefurbishment areas on the basis of 3 ML/ha savings ~50

Total ~88 – 98

* Recent advice from Murrumbidgee Irrigation suggests that this water saving may be only 10 GL.

Potential water savings of ~ 170 GL/yr

13

14


Coleambally Irrigation Area

Total water deliveries to the Coleambally Irrigation Area are615 GL/yr.

OFF-FARM LOSSES

True losses from the supply channels are 30 GL/yr—half fromseepage and half from evaporation. Part of the escape flows andchannel emptying flows are re-used in the Coleambally OutfallDrain District.

Seepage losses are not uniform. The best value for investment toaffect water savings will be obtained by locating channel seepagesites with rates greater than 10 mm/day using electromagnetic(EM) and geophysical methods.

Operational losses (escape and channel emptying) can be improvedconsiderably by using Rubicon System’s FlumeGates® farm outletflow measurement technology—more than 15% (~20 GL/yr)reported savings in conveyance access losses during 2000/01.Where possible two Dethridge outlets are being replaced with asingle, larger 30 ML/day FlumeGate. The new technology aims fortotal channel control by:

❚ integrating ordering, flow regulation and measurement to thefarm outlet and the supply channel system;

❚ providing automated and virtually on-demand deliveries to thefarm; and

❚ eliminating escape flows from the channel system.

ON-FARM LOSSES

On-farm losses are caused by recharge from irrigation and rainwater below the root zone and are approximately 60 GL/yr. Aroundhalf of this leaves the shallow groundwater system as deep leakageand lateral regional groundwater outflow; 15 GL/yr is dischargedthrough capillary upflow in shallow watertable areas and may resultin land salinisation. Groundwater outflow rates are lowest in thesouth of the Coleambally Irrigation Area.

Figure 9. Annual groundwater outflow rates in the Coleambally Irrigation Area.

615 GL/yr is supplied to the ColeamballyIrrigation Area

On-farm losses are ~60 GL/yr

True off-farm losses are 30 GL/yr

370000 380000 390000 400000 410000 420000 430000

6120000

6130000

6140000

6150000

6160000

0

0.25

0.50

0.75

1.00

1.25

ML/ha


15


SALINITY

An overall decline (0.5 to 1.5 m) has occurred in shallowwatertables in the past two years due to low water allocations and arelatively dry climate. The low groundwater outflow rates, shallowwatertables and high groundwater salinity in the south pose a riskto productivity and environmental quality. In this area there is aneed for on-farm and regional drainage investments.

WATER SAVING POTENTIAL

Total losses for the Coleambally Irrigation Area are around75 GL/yr (real channel supply losses seepage + evaporation~ 30 GL/yr, and recharge below the root zone from on-farm losses~ 45 GL/yr). If these losses are reduced to 30 GL/yr, there will beno net recharge as they will be balanced by the groundwateroutflow of 30 GL/yr resulting in a potential water saving of45 GL/yr.

Table 7. Water Balance of the Coleambally IrrigationArea (GL/yr).

SUPPLY SYSTEM IN OUT

Diversions 615

Rain on supply 3

Channel seepage 15

Channel Evaporation 15

Escapes 90

Deliveries 494

Channel empty 11

Channel evaporation 15

RAINFALL

Rainfall 346

Rain on supply 3

Rain on drains 3

Rainfall runoff 38

DRAINAGE SYSTEM

Rain on drains 3

Irrigation runoff 30

Escapes 90

Channel empty 11

Rainfall runoff 38

Town 1

ET drains 4

Drainage in creeks 160

Seepage from drain 1

ROOTZONE IN OUT

Supply system 464

Rainfall 310

Capillary rise 15

Trees 6

Evaporation crop ET 736

Recharge 59

SHALLOW GROUNDWATER SYSTEM

Channel seepage 15

Recharge 59

Seepage from drains 1

Trees 6

Capillary rise 15

Deep leakage 16

Lateral outflow 14

DEEP GROUNDWATER SYSTEM

Deep leakage 16

Lateral outflow 20

Deep pumping 5

16


Water for a Healthy Country National Research Flagship

The Water for a Healthy Country National Research Flagship is a research partnership between CSIRO,state and Australian governments, private and public industry, and other research providers. TheFlagship was established in 2003 as part of the CSIRO National Research Flagship Initiative.

This booklet on salt and water balance in the Murrumbidgee catchment is derived from Whole ofcatchment water and salt balance: identifying potential water saving and management options in theMurrumbidgee catchment. Research for this report was conducted by Shahbaz Khan, Tariq Rana, RedhaBeddek, John Blackwell, Zahra Paydar and Jason Carroll. The research was part of a partnership betweenCSIRO and the Pratt Water Group. Two associated reports are Hydrologic economic ranking of watersaving options: on-farm savings of irrigation water and Hydrologic economic ranking of water saving options:off-farm savings of irrigation water.

The Department of Infrastructure, Planning and Natural Resources, Department of Primary Industries,NSW Agriculture, the Cooperative Research Centre of Sustainable Rice Production and Murrumbidgeeand Coleambally Irrigation Ltd provided much of the data used in the development of these reports.Discussion in this booklet represents the views of the authors not the funding agents.

Copyright

© Commonwealth of Australia 2005. All rights reserved.

This work is copyright. Apart from any use as permitted under theCopyright Act 1968, no part may be reproduced by any processwithout prior written permission from the Commonwealth.

Disclaimer

You accept all risks and responsibility for losses, damages, costs andother consequences resulting directly or indirectly from using thisreport and any information or material available from it.

To the maximum permitted by law, CSIRO excludes all liability toany person arising directly or indirectly from using this report andany information or material available from it.

Further information

For further information contact:

Dr Shahbaz Khan

Phone: 02 6933 2927Email: [email protected]

<www.csiro.au/healthycountry/>

Publishing details

Photographs: CSIRO

Design: Themeda

Printing: Elect Printing


Documents

Whole-of-catchment Water and Salt Balance