Managing irrigation demand to improve seasonality of river flows

IRRIGATION AND DRAINAGE

Irrig. and Drain. 58: 157–170 (2009)

Published online 17 July 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ird.405

MANAGING IRRIGATION DEMAND TO IMPROVE SEASONALITY OFRIVER FLOWSy

SHAHBAZ KHAN1,2*, AFTAB AHMAD1,2 AND HECTOR M. MALANO2,3

1International Centre of Water for Food Security, Charles Sturt University, Wagga Wagga, Australia2Cooperative Research Centre for Irrigation Futures, Wagga Wagga, Australia

3University of Melbourne, Melbourne, Australia

ABSTRACT

Human interventions often lead to unsustainable river systems. There is always a trade-off between level of

socio-economic gains from consumptive use in the river system and the need to maintain the natural seasonality of

river flows supporting the ecosystem function. In the case of the Murrumbidgee River, Australia, irrigation demand

is concentrated in the summer season while natural inflows to the river occur during the winter season. The

summer-dominated irrigation water demand has created environmental and supply problems by altering the natural

flow regime. This paper presents a hydrologic assessment of a range of irrigation demand management options for

improving the natural seasonality of the river flow. Among the possible alternatives, change of cropping pattern by

achieving a better mix of summer and winter crops is recommended as the most feasible alternative, which can also

save up to 211 million m3 of water yearly. This water can then be released during the winter time to augment the

environmental flows of the river. Other irrigation demand management options explored in this paper include

aquifer storage and recovery, on-farm and off-farm water savings and construction of intermediate surface water

storages. Copyright # 2008 John Wiley & Sons, Ltd.

key words: seasonality of river flows; hydrologic assessment; irrigation demand management; environmental flows; Murrumbidgee River;Australia

Received 6 May 2007; Revised 18 January 2008; Accepted 18 January 2008

RESUME

Les interventions humaines menent souvent a des regimes de riviere non durables. Il y a toujours un arbitrage entre

le niveau des gains socio-economiques pour les usages consommateurs dans la riviere et le besoin de maintenir la

repartition saisonniere des debits qui favorise les fonctions de l’ecosysteme. Dans le cas de la riviereMurrumbidgee

en Australie, la demande d’irrigation est concentree dans la saison d’ete tandis que les apports normaux a la riviere

se produisent pendant la saison d’hiver. La demande estivale pour l’irrigation a cree des problemes environne-

mentaux et d’approvisionnement en eau en changeant le regime normal d’ecoulement. Cet article presente

l’evaluation hydrologique d’une gamme d’options de gestion de la demande d’irrigation pour ameliorer la

saisonnalite normale des debits de la riviere. Parmi les alternatives possibles, le changement de l’assolement en

proposant une meilleure repartition des cultures d’ete et d’hiver est recommande comme l‘alternative la plus

faisable, ce qui peut egalement economiser chaque annee jusqu’a 211 million m3. Cette eau peut alors etre liberee

pendant l’hiver pour augmenter les ecoulements environnementaux du fleuve. D’autres options de gestion de la

demande d’irrigation explorees dans cet article sont le stockage en aquifere, les economies sur et en dehors de

*Correspondence to: Shahbaz Khan, Professor of Hydrology, International Centre ofWater for Food Security, Charles Sturt University; ProgramLeader, Cooperative Research Centre for Irrigation Futures; and Senior Principal Scientist, CSIRO Land and Water, Locked Bag 588, WaggaWagga, NSW 2678, Australia. E-mail: [email protected] la demande d’irrigation pour ameliorer la saisonnalite des debits de riviere.

Copyright # 2008 John Wiley & Sons, Ltd.

158 S. KHAN ET AL.

l’exploitation et la construction de stockage intermediaires pour les eaux de surface. Copyright# 2008 JohnWiley

& Sons, Ltd.

mots cles: saisonnalite des debits de riviere; evaluation hydrologique; gestion de demande d’irrigation; debits environnementaux; riviereMurrumbidgee; Australie

INTRODUCTION

Rational decisions on quantity and timing of water to be held by in-stream reservoirs and how much water is to be

taken off-stream for consumptive and non-consumptive seasonal uses are a challenge for water resource managers

and river flow regulators in a river catchment. Physical constraints of the system and the environmental impacts

must be considered along with the economic benefits of river flow regulation. Flows in major rivers of the

Murray-Darling Basin (MDB) are highly regulated. The MDB is located in the south-east of Australia and covers

1 061 469 km2, equivalent to 14% of the country’s total area. The basin is defined by the catchment areas of the

Murray and Darling Rivers and their many tributaries (Figure 1). Most of the basin is composed of extensive plains

and low undulating areas, mostly below 200m above sea level. Of greatest extent are the vast plains, the Darling

Plain in the north, drained by the Darling and its tributaries, and the Riverine Plain in the south, drained by the

Rivers Murray and Murrumbidgee and their tributaries. The MDB is spread over five states and territories of

Australia with areas in: New South Wales (57%), Victoria (12%), Queensland (25%), South Australia (6%) and the

Australian Capital Territory (less than 1% of the basin). The MDB contains more than 20 major rivers as well as

important groundwater systems. It is also an important source of fresh water for domestic consumption, agricultural

production and industry. Although the MDB receives only 6% of Australia’s annual rainfall, around 40% of the

value of the nation’s agricultural production is generated here, and 70% of the value of Australian irrigation occurs

in the region, which has 2 million residents.

Increasing water scarcity and high demands on existing supplies have brought the river systems under great

pressure (Lovett et al., 2002). Due to soaring water demand, the physical characteristics of the river systems within

the basin have been extensively and significantly modified through a range of interventions; the most significant of

these are associated with flow regulation (King and Brown, 2003). Such is the case with the Murrumbidgee River. It

is the major river in the state of New South Wales and the Australian Capital Territory originating from the Snowy

Figure 1. Map of major rivers and their tributaries of the Murray Darling Basin (Source: adopted from Khan et al., 2007a)

Copyright # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: 157–170 (2009)

DOI: 10.1002/ird

IRRIGATION DEMAND MANAGEMENT 159

Mountains, part of the Australian Alps near Mount Kosciusko. The main stream of the river is 1600 km long and is

the major tributary of the Murray River in MDB. The geographic boundaries of the Murrumbidgee catchment

include the Great Dividing Range in the east, the Lachlan River Valley to the north and the Murray River Valley to

the south. The total annual turnover of economic activity in the Murrumbidgee Valley is A$ 8 billion, contributing

A$3.8 billion to the gross domestic product (Pratt Water, 2004). (1 A$¼ 0.74 US$ in 2004.)

The Murrumbidgee River is a highly regulated stream incorporating eight weirs (Ebsary, 1992), over 10 000 km

of irrigation canals and draining 84 000 km2 of catchment area from its source to its confluence with the Murray

River (Khan et al., 2004). The weirs were constructed for domestic water supply, stock water supply, irrigation,

diversion to irrigation areas and diversion to effluent streams. The total catchment area above Burrinjuck Dam is

13 000 km2. The storage capacity of Burrinjuck Dam is 1026 million m3. Below Burrinjuck Dam, the river flows

initially through a narrow reach and then a widening valley near Gundagai. The Tumut River joins the

Murrumbidgee River upstream of Gundagai. The total catchment area of the Tumut River is 4000 km2. Blowering

Dam is the major storage on the Tumut River; it stores both natural river flows and water that has been released from

the Snowy Mountains Hydroelectric Scheme. The overall capacity of Blowering Dam is 1632 million m3. The two

storages release water based on seasonal allocations, with flows mostly released between September and March

when all weir operations are based on irrigation demand. The main flow constraints in the Murrumbidgee system

include the limited conveyance capacity of the Tumut River (<9 million m3 day�1) and the Gundagai Choke

(<32 million m3 day�1) (Khan et al., 2004).

The catchment is divided into three climatological zones – upper, middle and lower Murrumbidgee. Average

annual rainfall (1950–2000) in the upper part of the Tumut catchment is 768mm. In the middle reach at Gundagai it

is around 584mm and in the lower reach between Darlington Point and Balranald the average annual rainfall is

428mm. Rainfall in the Murrumbidgee catchment decreases from east to west. The potential evapotranspiration

varies from 1000mm in the east to over 1600mm per annum in the west. In the lower zone, January is the hottest

month with average daily maximum and minimum temperatures of 32 and 168C. In the upper zone, the average

daily maximum and minimum temperatures are 21 and 68C. July has average maximum and minimum

temperatures of 14 and 48C for the lower zone and 4 and�48C for most parts of the upper zone (Khan et al., 2004).

The major hydrological issues in this catchment include altered flow regimes and their impacts on river and

wetland ecosystems, water quality and high salinity in dryland and irrigation areas. Many irrigators are fearful of

losing valuable entitlements and access to water supplies. There is also concern about groundwater depletion and

the risk of groundwater contamination (Khan, 2004). Moreover, the impacts of these altered flow regimes on

wetlands along the watercourses are significant, and vary markedly depending on the nature and extent of the

alteration to the flow regime (Ritchie and James, 2000). Since irrigation is the main user of water in the catchment,

the aim of this paper is to investigate a range of hydrologic and management solutions for irrigation demand that

can ultimately improve or augment the restoration process of the seasonality of natural flows in the Murrumbidgee

River. This paper provides the details of a hydrologic framework to assess water demand management options

which is a new way of visualising river flow augmentation options for the restoration of the seasonality of natural

flows in the Murrumbidgee River.

STUDY AREAS

This study focused on two main irrigation areas (Figure 2) which are major users of water in the Murrumbidgee

catchment: the Murrumbidgee Irrigation Area (MIA) and the Coleambally Irrigation Area (CIA) and which can

bring about significant change in the system. The water year in this area starts on 1 July and ends on 30 June each

year. Water for these two irrigation areas is stored in the Burrinjuck and Blowering reservoirs. The key

characteristics of these irrigation areas are given below:

Murrumbidgee Irrigation Area (MIA)

TheMIA is located in middle to the lower reach of theMurrumbidgee River covering approximately 3624 km2. It

consists of the Yanco, Mirrool, Benerembah, Wah Wah and Tabbita irrigation districts. The topography is a


DOI: 10.1002/ird

Figure 2. Map of the Murrumbidgee River catchment

160 S. KHAN ET AL.

relatively flat open plain at an elevation of 100–135 m above sea level. Metered water is delivered onto farms and

farmers pay for the volume of water supplied which is used for crops such as grapes, citrus, rice, wheat, barley, oats,

canola, soybeans, maize, sunflowers, lucernes and pastures for sheep and cattle. Drainage water from irrigation

farms flows through the Mirrool Creek to Barren Box Swamp and then flows into the irrigation districts of

Benerembah, Tabbita and Wah Wah.

Coleambally Irrigation Area (CIA)

The CIA is located to the south of the Murrumbidgee River. The irrigation area was developed during the 1960s

to make use of water diverted westward as a result of the Snowy Mountains Hydroelectric Scheme. Water is

diverted to the area from the Murrumbidgee River at the Gogeldrie Weir. Drainage water flows via Yanco and

Billabong creeks before entering the Murray River. Irrigation water is used for crops such as rice, wheat, barley,

oats, canola, soybeans, maize, sunflowers, lucernes, grapes, prunes and pastures for sheep and cattle. Irrigation has

turned what used to be less productive land into highly productive land, which produces a diverse range of food that

ends up on the dinner tables of many Australians. Export of produce is also important for the regional economy as

over 80% of rice is destined for overseas markets.

DATA ANALYSIS

Currently water users in theMurrumbidgee Valley (Table I) have a combined entitlement (upper limit of the volume

of water which can be allocated during a given year depending on the availability of water) of 2754 million m3,

which is close to 65% of the average annual flow volumes of 4300 million m3, of the Murrumbidgee River past the

regional city of Wagga Wagga (Pratt Water, 2004). Clearly, irrigation is the main user of surface water (63% of


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Table I. Water entitlementsa in the Murrumbidgee catchment

Category Volume (million m3)

Basic landholder rights 4 500Native title rights 0Local water utility access licences (towns) 23 400Domestic and stock access licences 35 600Murrumbidgee Irrigation Ltd total supply 1 253 000Coleambally Irrigation Cooperative Ltd total supply 630 000Private irrigators 808 000Total 2 754 500

aUpper limit of the volume of water which can be allocated during a given year depending on theavailability of water.Source: adopted from Khan (2004).


average annual flow at 100% allocation level) in the valley. The estimated annual recharge to the Middle

Murrumbidgee aquifer is around 127 million m3. The current entitlements are around 55 million m3. The estimated

annual recharge to the Lower Murrumbidgee aquifer system is 335 million m3 and the ‘‘safe yield’’ is 270

million m3 (Kumar, 2002). Although the reported groundwater pumping is still less than the ‘‘sustainable yield’’,

there has been a rapid increase in the use of groundwater since 1994/95 with an overall decline in groundwater level

of the deeper aquifers by 10–20m over the main groundwater pumping area. Groundwater salinity is the most

significant factor limiting its use for irrigation. It varies substantially throughout the catchment, from

<400mS cm�1 in some areas upstream of Narrandera to values of around 80 000mS cm�1 near Balranald.

Approximately 270 000 million m3 of groundwater in the basin is of low salinity (<1500mS cm�1), although the

distribution of this low-salinity groundwater throughout the catchment is uneven (Department of Land and Water

Conservation (DLWC), 1995).

Irrigation water demand of the Murrumbidgee River catchment is mainly concentrated in the dry period

(summer) due to dominant summer cropping, while the wet period occurs in the winter season in this region.

Therefore, inflows to the river during the wet period are stored in the two main reservoirs which are regulated to

supply irrigation water during the summer. Balranald station is the most downstream barrier on the Murrumbidgee

River before it joins theMurray River. Long-termmonthly natural and current flows modelled by IQQM (integrated

quantity and quality model) at Balranald are shown in Figure 3 for 1907 to 2005. The river flow pattern has been

altered by flow regulation as a consequence of the irrigation demand pattern in the valley. The near-zero flow during

Figure 3. Long-term natural and current flows (modelled) in Murrumbidgee River at Balranald station just upstream of the confluence with theMurray River


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Table II. Crop coefficients for selected crops in NSW (Meyer, 1996)

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

Rice 15 Oct 0.20 0.30 0.40 1.00 1.10 1.10 1.10 1.10 1.00 0.40 0.20 0.20 15 MarWheat 15 May 0.90 1.05 1.05 0.80 0.50 0.20 0.20 0.20 0.20 0.30 0.40 0.60 13 NovOats 20 Apr 1.00 1.05 1.05 0.70 0.30 0.20 0.20 0.20 0.20 0.30 0.50 0.80 20 NovBarley 31 May 0.80 1.00 1.00 0.90 0.50 0.20 0.20 0.20 0.20 0.30 0.35 0.50 15 NovMaize 1 Nov 0.40 0.40 0.30 0.35 0.50 0.70 0.85 0.85 0.60 0.30 0.30 0.40 10 MarCanola 30 Apr 0.70 0.75 0.75 0.70 0.40 0.20 0.20 0.20 0.20 0.30 0.40 0.60 30 OctSoybean 30 Nov 0.40 0.40 0.30 0.30 0.30 0.45 0.75 1.05 1.00 0.50 0.30 0.40 15 AprSummer pasture 1 Sep 0.80 0.80 0.80 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.80 0.80 PerennialWinter pasture 25 Mar 0.80 0.80 0.80 0.60 0.40 0.20 0.20 0.20 0.20 0.40 0.60 0.70 PerennialLucerne 1 Oct 0.65 0.65 0.90 1.20 1.30 1.30 1.30 1.30 1.20 1.20 1.00 0.65 PerennialVines 1 Sep 0.40 0.40 0.45 0.50 0.50 0.50 0.60 0.50 0.50 0.40 0.30 0.30 PerennialCitrus 1 Jul 0.70 0.70 0.70 0.60 0.60 0.60 0.60 0.60 0.70 0.70 0.70 0.70 PerennialStone fruit 1 Sep 0.40 0.40 0.50 0.65 0.75 0.80 0.80 0.80 0.80 0.80 0.70 0.40 PerennialSummer vegetables 30 Aug 0.40 0.40 0.50 0.60 0.65 0.65 0.65 0.60 0.40 0.30 0.30 0.40 PerennialWinter vegetables 1 Apr 0.55 0.50 0.50 0.30 0.30 0.20 0.20 0.20 0.20 0.40 0.50 0.55 Perennial

162 S. KHAN ET AL.

winter months (May to July); whereas the natural flows would be increasing during this period, has created severe

environmental issues including impacts on the ecosystem and biodiversity of the riparian zones. The high daily

flows during the summer period cause flooding along the low conveyance capacity reaches of the upper part of the

catchment near Tumut and Gundagai. For example, the Tumut Land Holders Group is concerned about river

channel erosion and flooding of adjacent land caused by flows greater than 6millionm3 day�1. During the irrigation

season, flows can be as high as 9.3 million m3 day�1. These high flows have been attributed to the widening of the

river up to 20 m on each side. The lower-lying properties are flooded in times of high flows, therefore restricting

their ability to farm. High irrigation demand concentrated in summer and almost no irrigation demand in winter has

effectively altered the role of the river to an irrigation supply channel.

The effects of characteristics that distinguish field crops from the reference grass crop in terms of water

requirement are integrated into the crop coefficient Kc. Kc data based on Meyer (1996) at Griffith Laboratory of

CSIRO for selected crops grown in NSWare given in Table II. The crop coefficients are used later in the analysis to

determine irrigation demand using a reference evapotranspiration on a monthly basis.

METHODOLOGY

The overall framework of the approach used in this study is shown in Figure 4.

For each management option, the overall impact on irrigation demand, reduction of peak water demand and shift

of demand from summer to winter are assessed. In this analysis alternative irrigation demand is computed based on

the assumed spatial and temporal distribution of crops, better use of groundwater and adoption of water-saving

technologies.

In the following sections key components of analysing irrigation demand are assessed.

Reference evapotranspiration (ETo)

The reference crop evapotranspiration is the evapotranspiration rate from a reference surface with no shortage of

water. The reference surface is a hypothetical grass reference crop with specific characteristics. The only factors

affecting ETo are climatic parameters. The FAO Penman-Monteith model (Allen et al., 1998) was selected for ETocalculation as it closely approximates grass ETo and explicitly incorporates both physiological and aerodynamic

parameters.


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Figure 4. General framework for assessing impact of irrigation demand management options


The Penman-Monteith approach includes all parameters that govern energy exchange and corresponding latent

heat flux from uniform expanses of vegetation. Most of the equation parameters are directly measured or can be

readily calculated from weather data. The Penman-Monteith model to estimate ETo is given by Equation (1):

Table

Month

ETo (mETo (m

Copyri

ETo ¼0:408D Rn � Gð Þ þ g 900

Tþ273u2 es � eað Þ

Dþ g 1þ 0:34u2ð Þ (1)

where

ETo¼ reference evapotranspiration (mm day-1),

Rn¼ net radiation at the crop surface (MJm�2 day�1)

G¼ soil heat flux density (MJm�2 day�1)

T¼mean daily air temperature at 2 m height (8C)u2¼wind speed at 2m height (m s�1)

es¼ saturation vapour pressure (kPa)

ea¼ actual vapour pressure (kPa)

es� ea¼ saturation vapour pressure deficit (kPa)

D¼ slope of the vapour pressure curve (kPa 8C�1)

g ¼ psychrometric constant (kPa 8C�1).

The equation uses standard climatological records of solar radiation (sunshine), air temperature, humidity and wind

speed. To ensure the consistency among all irrigation areas, ETo data based on Equation (1) for the Griffith station

(Table III) is taken from a website (http://www.nrw.qld.gov.au/silo/) that is a joint effort of the Bureau of

Meteorology and the Department of Natural Resources, Queensland, Australia.

III. Reference crop evapotranspiration (ETo) at Griffith weather station (Lat: 34.32S, Long: 146.06E, Elev.: 126.0m)

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

m day�1) 9.1 8.1 6.3 3.9 2.3 1.5 1.8 2.9 4.3 6.1 7.9 8.9m) 282 227 195 119 73 47 56 91 131 191 238 275 1930

ght # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: 157–170 (2009)

DOI: 10.1002/ird

164 S. KHAN ET AL.

Total crop water requirement

Crop water requirement (CWR) or crop evapotranspiration of a given crop is obtained by multiplying reference

crop evapotranspiration with suitable crop coefficients as given by Equation (2):

Copyri

ETc ¼ ETo � Kc (2)

where ETc¼ crop evapotranspiration (mmday�1) and Kc¼ crop coefficient (dimensionless).

The total crop water requirement over the growth cycle (annual basis) of a crop can be given by Equation (3):

ETcð Þper crop¼Xn

i¼1

ETcð Þi�di (3)

where di¼ number of crop days in a given month i and n¼ last month of crop life.

Net crop water requirement

Subtraction of the amount of effective rain (if any) that falls direct on to a crop field from the total crop water

requirement gives the net (potential) crop water requirement as given by Equation (4). The effective rainfall is

computed by the USDA method (Kassam and Smith, 2001).

CWRnet ¼ ETcð Þper crop�Reff (4)

where CWRnet¼ net crop water requirement (mm) and Reff¼ total effective rain (mm).

The net crop water requirement calculated in this paper does not include the leaching fraction which is almost 5%

in the study area. The actual irrigation requirement of a given crop is calculated by incorporating leaching fraction,

irrigation efficiency and irrigation scheduling criteria.

A wide range of engineering and management options were explored to investigate their direct or indirect

hydrological impact on river flows in terms of increased peak flows, increase in total flow or shift in flow pattern.

The option with most positive and ultimate impact on the river environment was recommended as a possible way

forward for the irrigation community.

RESULTS AND DISCUSSION

Using data given in Tables II and III and Equation (4), monthly net potential water requirement calculated for

selected crops in MIA and CIA for average climatic conditions in 2000/01 is given in Tables IVand V, respectively.

The typical net crop water requirement pattern of the two major irrigation areas, the MIA and CIA, for dry

(1994), wet (1991) and average (1995) climatic conditions shown in Figure 5 indicate that irrigation water demand

of the Murrumbidgee River catchment is mainly concentrated in the dry season (November–February) due to

dominant summer cropping peaking up to 310 million m3 while the wet season occurs in the winter (May–August)

when the irrigation demand is as low as zero in this region.

The hydrological impacts of different irrigation demand management options are discussed below.

Groundwater substitution

Some fraction of surface water can be substituted by groundwater during the months of peak daily irrigation

demand to release pressure on the surface water supply and avoid flooding in certain reaches of the river. Figure 6

shows the amount of monthly groundwater pumped to keep the demand so it does not exceed 200 million m3

month�1. In this case, the total amount of groundwater pumped is 200 million m3 over a period of four months,

resulting in a saving of the same amount of surface water that can be contributed to the environmental flow of the

river. This 200 million m3 of water can be contributed from the existing groundwater entitlements in the Lower

ght # 2008 John Wiley & Sons, Ltd. Irrig. and Drain. 58: 157–170 (2009)

DOI: 10.1002/ird

Table

IV.Net

potential

water

requirem

ents

(millionm

3)forcropsin

theMIA

fortheyear2000/2001under

averageclim

ateconditions

Crop

Area(ha)

Jul

Aug

Sep

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

Jun

Total

Rice

46120

00

062262

97590

117975

131073

97662

00

00

506562

Wheat

39215

1882

12353

31980

39450

23581

00

00

00

2588

111835

Oats

2896

290

912

2362

2415

824

00

00

64

188

458

7512

Barley

3034

0850

2306

3574

1824

00

00

00

61

8615

Maize

2924

00

00

1598

4462

6322

4842

1588

00

018813

Canola

2685

0282

1296

2239

649

00

00

00

177

4643

Soybean

2881

00

00

1118

2538

5445

6327

2955

00

018383

Summer

pasture

3929

0550

2114

4290

6192

7516

8494

6506

5145

2680

1045

621

45154

Winterpasture

24184

03386

13011

16010

7790

00

00

4305

3192

2709

50403

Lucerne(uncut)

2468

086

1602

4181

6288

7587

8357

6486

4847

2651

987

220

43291

Vines

13635

00

2038

6681

11181

13771

20207

12272

8931

2427

00

77508

Citrus

8700

0609

3715

5759

9013

11032

12893

9709

8952

4472

1731

974

68859

Stonefruit

934

00

191

699

1270

1666

1892

1446

1136

585

186

09071

Wintervegetables

1500

00

308

219

233

00

00

098

65

923

Summer

vegetables

1500

00

0993

1716

2096

2427

1674

00

00

8906

Lucerne(cut)

00

00

00

00

00

00

00

Total

156605

2172

19028

60922

148773

170869

168643

197111

146924

33555

17182

7428

7872

980477

Table

V.Net

potential

water

requirem

ents

(millionm

3)forcropsin

theCIA

fortheyear2000/2001under

averageclim

ateconditions

Crop

Area(ha)

Jul

Aug

Sep

Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

Jun

Total

Rice

26820

00

036207

56751

68606

76222

56793

00

00

294579

Wheat

12388

595

3902

10102

12462

7449

00

00

00

818

35329

Oats

1290

129

406

1052

1076

367

00

00

28

84

204

3346

Barley

2689

0753

2044

3168

1617

00

00

00

54

7635

Maize

2888

00

00

1579

4407

6244

4783

1569

00

018581

Canola

1951

0205

941

1627

471

00

00

00

129

3373

Soybean

4551

00

00

1766

4009

8601

9994

4668

00

029039

Summer

pasture

00

00

00

00

00

00

0Winterpasture

9880

01383

5315

6541

3183

00

00

1759

1304

1107

20591

Lucerne(uncut)

00

00

00

00

00

00

0Vines

00

00

00

00

00

00

0Citrus

00

00

00

00

00

00

0Stonefruit

112

00

23

84

152

200

227

173

136

70

22

01088

Wintervegetables

00

00

00

00

00

00

0Summer

vegetables

00

00

00

00

00

00

0Lucerne(cut)

200

077

178

378

518

619

653

518

411

246

121

51

3771

Total

62769

724

6727

19655

61543

73854

77841

91947

72262

6785

2104

1531

2361

417333

Copyright # 2008 John Wiley & Sons, Ltd.


Irrig. and Drain. 58: 157–170 (2009)

DOI: 10.1002/ird

Figure 5. Combined net crop water requirement of the MIA and CIA for the year 2000/01

166 S. KHAN ET AL.

Murrumbidgee Valley. A possible management intervention may be to promote groundwater use during the

summer months while the surface water use is made available during the winter months.

Summer–winter crop mix

As the cropping patterns of the MIA and CIA are dominated by the summer crops requiring more irrigation

water, an appropriate alternative mix of crops grown in summer and winter can effectively reduce the high water

demand during hot months. An alternative mix of summer and winter crops obtained from optimisation in a system

dynamics environment (Khan et al., 2007b) using the Vensim software package (Ventana Systems, 2004) is given in

Table VI for an average year. The objective of the optimisation was to reduce total water requirement while change

in any crop area must not exceed 15% while maintaining the same economic returns. The new alternative crop mix

spares 211 million m3 of summer water demand and reduces the total water demand from 1390 to 1179 million m3.

Figure 7 shows the comparison of current cropping pattern water demand and that of alternative crop mix for the

average climatic conditions. To further explore this option, sensitivity analysis (Figures 8 and 9) was undertaken

using the Vensim software package. Sensitivity of total monthly CWR to the area under rice and vine crops

indicates that CWR is understandably more sensitive to rice than vines (Figures 8 and 9). For example, within 95%

Figure 6. Groundwater substitution to keep surface water demand of the MIA and CIA below 200 million m3 month�1


DOI: 10.1002/ird

Table VI. Current and alternative mix of summer and winter crops in the MIA and CIA fora season with average climatic conditions

Crop Current crop areaa (%) Alternative crop areaa (%)

Maize 2.65 6.00Wheat 23.52 25.00Barely 2.61 2.61Canola 2.11 2.00Oat 1.91 4.00Soybean 3.39 3.39Summer vegetables 0.68 0.68Winter vegetables 0.68 2.00Rice 33.25 18.25Summer pasture 1.79 1.79Winter pasture 15.53 15.53Citrus 3.97 8.00Lucerne (cut) 0.09 0.09Lucerne (uncut) 1.13 0.00Stone fruit 0.48 0.48Vines 6.22 10.00

aPer cent of the total irrigated area in the MIA and CIA.


confidence limits, change in the rice area by�15 (current per cent area � 15) affects a change in peak (in January)

of CWR between 205 and 335 million m3 as compared to the peak CWR of around 285 million m3 under the current

cropping pattern. Hence it can be envisaged that reduction in the rice area by 15% will reduce the peak summer

water demand for the month of January by 28% and an overall demand reduction by 15%.

A similar sensitivity analysis carried out for vines shows that the total monthly CWR is less sensitive to the

reduction in area under vines (Figure 9).

Aquifer storage and recovery

Aquifer storage and recovery (ASR) sometimes referred to as ‘‘water banking’’ stores water (when available) in

existing natural aquifers and when needed, recovers water from the same aquifer, potentially offering timely

Figure 7. Comparison of current crop water demand and that of new proposed alternative crop mix for the average climatic conditions


DOI: 10.1002/ird

Figure 8. Sensitivity of monthly CWR of the MIA and CIA to percentage change in area of rice within 50, 75, 95 and 100% confidence bounds

168 S. KHAN ET AL.

seasonal water supply and more effectively managing peak supply and demand for productive use, reducing the

need to construct surface reservoirs and reducing evaporation losses.

From preliminary feasibility work by Pratt Water (2004), the introduction of ASR in the Murrumbidgee Valley,

specifically the Lower Murrumbidgee Groundwater Area, creates the opportunity for significant water saving. This

may include up to 47 million m3 of avoided evaporative losses and some 181 million m3 of stored water.

Improving end-use efficiency

By improving the on-farm water use efficiency, less water will be required by farmers to maintain the same level

of production. Use of two on-farm water-saving irrigation technologies, a drip irrigation system (DIS) and a

sprinkle irrigation system (SIS), was investigated for on-farm water use efficiency. DIS was selected for

horticultural crops, vines and citrus, and SIS for the other crops. Analysis for a typical 220 ha farm in the catchment

indicated that with the adoption of these water-saving irrigation technologies, the farm will save 0.416 million m3

Figure 9. Sensitivity of monthly CWR of theMIA and CIA to percentage change in area of vines within 50, 75, 95 and 100% confidence bounds


DOI: 10.1002/ird


of water which is 35% of the total water use of the farm. Adoption of such technology at wider scale in the

catchment will reduce the total irrigation demand and help augment flows in the river.

Improving delivery efficiency

Canal and channel lining is another option to improve conveyance efficiency. Currently, the delivery efficiency in

the MIA and CIA is about 80% and there are about 2050–2566 km of unlined canals in the MIA and 516 km in the

CIA (Australian National Committee on Irrigation and Drainage (ANCID), 2004). There is potential for saving 168

million m3 of water (115 million m3 in the MIA and 53 million m3 in the CIA) through increased investment in

conveyance systems (Pratt Water, 2004).

En route storages

Differences in the timing of irrigation and environmental demands raise the requirement for infrastructure that

can increase the reliability of irrigation supplies by reducing the likelihood that peak season delivery constraints

will become binding and reregulation of spills, for either consumptive or environmental purposes. One option is the

construction of en route storages at suitable locations along the river. After accounting for seepage and evaporation

losses, it was estimated that three above-ground storage reservoirs of 50 million m3 each would help reduce the

peak demand by 119 million m3; whereas a single 250 million m3 en route storage will minimise the peak demand

by 203 million m3. However, this option may require significant infrastructure investment which needs to be further

explored using economic analysis.

CONCLUSIONS

The irrigation industry is the major user of water in the Murrumbidgee River catchment. Increased summer

irrigation demand and flow regulation by major storages have changed the natural flow regime of the river both in

terms of timing and volume of flows. This has resulted in environmental degradation and flow conveyance problems

in some parts of the catchment.

Spreading water demand through a better summer–winter crop mix seems to be the most attractive and feasible

irrigation demand management option for improving the seasonality of flow with a water-saving potential of up to

211 million m3 yr�1. However, it may take time to win acceptance of the farmers to adopt the new alternative

cropping pattern. Groundwater substitution during the summer high demand with the allocated surface water (from

the summer period to the winter period) is another possible option to make additional surface water available for the

environment during the peak irrigation demandmonths. However, there is a need to further investigate groundwater

quality and sustainability issues.

Other demand management options such as construction of intermediate surface water storage and investment in

irrigation efficiency at the farm and the catchment levels require substantial investments and need further

investigations in terms of their economic feasibility.

ACKNOWLEDGEMENT

The authors wish to acknowledge the funding support from the Cooperative Research Centre for Irrigation Futures,

Australia.

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Documents

Managing irrigation demand to improve seasonality of river flows