hydrologic and economic evaluation of water-saving options in irrigation systems

IRRIGATION AND DRAINAGE

Irrig. and Drain. 57: 1–14 (2008)

Published online 31 October 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ird.336

HYDROLOGIC AND ECONOMIC EVALUATION OF WATER-SAVINGOPTIONS IN IRRIGATION SYSTEMSy

S. KHAN1,2,3*, A. ABBAS3, H. F. GABRIEL1,4, T. RANA3 AND D. ROBINSON3

1Charles Sturt University, Wagga Wagga NSW, Australia2UNESCO IHP-HELP, Australia

3CSIRO Land and Water, Wagga Wagga NSW, Australia4NIT, National University of Sciences and Technology (NUST), Risalpur Campus, Pakistan

ABSTRACT

This paper investigates a range of water savings options at irrigation system level and ranks these options according

to the potential savings of each option and the economic return in terms of water saved (ML – megalitres) for each

dollar invested. Most of the work was conducted on large-area farms of the Murrumbidgee Irrigation Area (MIA)

and Coleambally Irrigation Area (CIA) in the Murrumbidgee River catchment, New South Wales, Australia.

Field-based on-farm water savings for scenarios analysed ranged from 0.1 ML ha�1 up to 3.9 ML ha�1

(10–390 mm). As capital can be a limiting resource to farmers, options that have the lowest cost per ML saved

may be more appealing than options that have a higher cost but may also have higher net benefits over time. The

water savings that derived the highest net benefit per megalitre saved were conversion to drip and subsurface drip

for the case study farms and laser levelling which had net benefits ranging from A$ 164 to A$ 344 ML�1 saved per

year. All of the other options had net benefits ranging from A$ 4 to A$ 37 ML�1 saved per year. All of the options

that had a low annualised cost also had a relatively low net benefit (less than A$ 24 ML�1 saved per year). Marginal

costs of off-farm water savings increase with the volume of water saved. In the MIA up to 20 GL (1

gigalitre¼ 1 MCM million cubic metres) of potential water savings are possible at a marginal capital cost of

around A$ 1500–2000 ML�1. Marginal capital costs then rise rapidly, reaching A$ 4000 ML�1 at around 38 GL

reflecting the lower volumes saved at higher costs. Copyright # 2007 John Wiley & Sons, Ltd.

key words: water use efficiency; water saving; economic evaluation; irrigation methods; channel losses; on-farm and off-farm water losses

Received 16 December 2006; Revised 21 June 2007; Accepted 22 June 2007

RESUME

Cet article etudie une serie d’options d’economie d’eau au niveau des systemes d’irrigation et les classe selon

l’economie potentielle de chaque option et la rentabilite economique en termes d’eau economisee (en ML, Mega

Litres) pour chaque dollar investi. La majeure partie du travail a ete conduite sur de grandes exploitations des

regions d’irrigation de Murrumbidgee (MIA) et de Coleambally (CIA) dans le bassin versant du fleuve

Murrumbidgee en New South Wales (Australie). Les economies concretes realisees pour les scenarios analyses

allaient de 0,1 a 3,9 ML ha�1 (10–390 mm). Comme le capital peut etre une ressource limitative pour les exploitants

agricoles, les options qui ont le cout le plus bas par ML economise peuvent etre plus attrayantes que les options qui

ont un cout plus eleve mais peuvent rapporter des benefices nets plus eleves avec le temps. Les economies d’eau qui

ont degage le benefice net le plus eleve par ML economise ont ete le passage au goutte a goutte et a l’irrigation

* Correspondence to: S. Khan, Charles Sturt University, CSIRO Land and Water, Locked Bag 588, Wagga Wagga, NSW 2678, Australia.E-mail: [email protected] hydrologique et economique des economies d’eau dans les systemes d’irrigation.1A$¼Australian dollar. 1 A$¼ 0.81 US$ (2007).

Copyright # 2007 John Wiley & Sons, Ltd.

2 S. KHAN ET AL.

souterraine pour les exploitations etudiees, ainsi que le planage au laser qui a rapporte de 64 a 344 AUD (dollar

australien) par ML economise par an. Toutes les autres options ont eu des benefices nets compris entre 4 et 37 AUD

par ML economise par an. Toutes les options qui avaient un cout annualise faible ont aussi eu un benefice net

relativement bas (moins de 24 AUD par ML par an). Les couts marginaux de l’economie d’eau hors exploitation

augmentent avec le volume d’eau economise. Dans le MIA, un potentiel d’economie d’eau pouvant aller jusqu’a

20 GL (1 Giga Litre¼ 1 MCM ou million de metre cube) est possible a un cout marginal du capital de 1500 a 2000

AUD ML�1. Ce cout augmente ensuite rapidement jusqu’a 4000 AUD ML�1 pour environ 38 GL, refletant ainsi la

tendance des couts a augmenter pour des volumes inferieurs economises. Copyright # 2007 John Wiley & Sons,

Ltd.

mots cles: efficience de l’irrigation; economie d’eau; evaluation economique; methodes d’irrigation; pertes en ligne (canaux); pertes a laparcelle et hors exploitation

INTRODUCTION

The worst drought in Australian history continues to affect farmers, businessmen and individuals and is posing a

threat to the sustainability of the irrigated farming systems. At the national level, the Council of Australian

Governments (COAG) and the State Government water reforms resulted in reduction in water supplies for irrigated

farming and have implemented an increase in water delivery charges. There is a great need to save every possible

drop of water for better outcomes for agriculture, the environment and rural communities. More efficient water

application technologies and saving system losses can help the irrigation industry and the environment in coping

with drought and fulfil water reform needs. Since it is hardly possible to withdraw more water from existing

resources, the present irrigation practices and future irrigation developments should focus on improvement of water

use efficiency at both field and regional levels (Khan et al., 2005).

Possible means of more efficient use of available water supply for irrigation include:

1. A

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doption of on-farm water-saving methods (from soil water monitoring to pressurised irrigation systems) to

improve water productivity;

2. R
educing conveyance losses in the water delivery systems through canal lining and piping;
3. M
atching water-saving investments with higher-value cropping systems;
4. R
emoving salinity constraints from farm to regional levels through efficient leaching of soils and promoting
sustainable multiple use of water.

The relative economic and environmental merits of adopting these alternative water-saving options on the overall

water saving and water productivity at the irrigation system or catchment levels are largely unknown due to a lack

of integration of existing data sets and identifying and filling in vital gaps.

The key to promoting different water-saving options lies in their economic and hydrologic assessment. This

study adopted a targeted data gathering, modelling and integration approach to evaluate alternative technologies for

reducing on- and off-farm losses within the Coleambally and the Murrumbidgee irrigation areas (New South Wales,

Australia) overlying different subsoil and hydrogeological conditions.

STUDY AREA

The Murrumbidgee River (Figure 1) has a catchment area of around 84 000 km2 and a length of 1600 km from its

source in the Snowy Mountains to its junction with the Murray River. 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.

Rainfall in the Murrumbidgee catchment decreases from east to west. In the middle reach at Griffith it is around

400 mm and annual evaporation is 1797.4 mm. The maximum daily temperature is 30.18C with highest maximum

of 43.98C in January and minimum daily temperature is 2.98C with lowest minimum of �5.48C in July (Bureau of

ght # 2007 John Wiley & Sons, Ltd. Irrig. and Drain. 57: 1–14 (2008)

DOI: 10.1002/ird

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Coleambally Irrigation Area

Murrumbidgee Irrigation Area

Figure 1. Location of the Murrumbidgee River Valley

WATER-SAVING OPTIONS IN IRRIGATION SYSTEMS 3

Meteorology, 2006). The topography is a flat open plain at an elevation of 100–135 m above sea level. The main

irrigation areas are the Murrumbidgee Irrigation Area (MIA) and the Coleambally Irrigation Area (CIA). The MIA

is a mix of horticultural and broad acre cropping farms whereas the CIA is mainly a broad acre cropping area. From

the right bank of the Murrumbidgee River, water is diverted at Berembed weir and further downstream at Gogeldrie

weir for the MIA. From the left bank downstream to Yanco weir, water is diverted to the CIA. Horticulture and rice

are the main irrigated crops in the MIA while broad acre crops are the main land use in the CIA.

STUDY APPROACH

Cropping system savings

In most of the Murrumbidgee catchment, the surface irrigation system is built and designed specifically for field

crops to meet water needs of both summer and winter crops. The major irrigated broad acre crops sown in the MIA

and CIA are wheat, barley, maize, rice, sunflower, soybean, fababean, lucerne, pasture and vegetables. The MIA is

also one of the major contributors to horticultural crops, i.e. citrus, vineyards and stone fruits. An agro-hydrological

model (SWAP – ‘Soil–Water–Atmosphere–Plant’ model) was combined with GIS analysis of soils and

groundwater depths to illustrate potential water savings under the MIA and CIA agro-climatic conditions. SWAP

simulates vertical transport of water, solutes and heat in variably saturated, cultivated soils (Kroes and van Dam,

2003). SWAP includes versatile modules for simulating irrigation practices and crop yields. Examples include

design and monitoring of field irrigation and drainage systems, surface water management, soil and groundwater

Copyright # 2007 John Wiley & Sons, Ltd. Irrig. and Drain. 57: 1–14 (2008)

DOI: 10.1002/ird

4 S. KHAN ET AL.

pollution by salts and pesticides and crop water use and crop production studies. The upper boundary condition is

determined by the potential evapotranspiration, irrigation and precipitation fluxes. The groundwater depth is used

as the lower boundary condition. The other model parameters are irrigation water salinity, soil type, irrigation

method and irrigation timing criteria. The detailed methodology is described in Khan et al. (2005) and Khan and

Abbas (2007).

Assessment of near-farm losses

Many studies carried out by various researchers (Smith and Turner, 1982; Lawler, 1990; Strong and Barron,

1994; Van der Lely, 1994; Tiwari, 1995; McLeod, 1996; Watts and Thompson, 2002; Akbar, 2002) indicate

that an estimate of channel seepage is an essential component in the management of earthen channel systems.

Seepage losses from channels or drains must be located and quantified to establish their economic and

environmental importance. Seepage from farm channels and drains of nine rice farms in the MIA and CIA was

monitored. The electromagnetic inductance EM31 survey was used to identify priority seepage investigation sites.

ECa (apparent electrical conductivity) survey results from the EM31 survey were mapped and the interpolated

values were used in relation to three seepage sample points at each location. Low EM data indicated high seepage

rates at those locations. There are many factors that may influence the interpretation of ECa values from EM31

surveys. These include soil variability, channel history, construction techniques, presence of sediments and weeds,

and any slope or bend within the middle part of the channel (Khan et al., 2005).

Eight piezometers were installed in each farm prior to the commencement of the irrigation season. Calibrated

DF392 (http://www.odysseydatarecording.com/) data loggers were installed in three piezometers adjacent to the

channel and drains for recording water pressure at 6 hourly intervals. The remaining five piezometers were

configured to monthly intervals for data recording. The soil texture at each piezometer set location was assessed by

the ribbon method at 500 mm intervals to a depth of 3.0 m. The electrical conductivity of soil samples taken at

500 mm intervals down the soil profile at piezometer locations was measured in a 1: 5 soil: water solution using a

DiST 4 salinity meter (http://www.instrumentation2000.com/catalog/water/0902.html).

Assessment of off-farm losses

Monitoring seepage loss in irrigation supply channels involved four steps:

1. E

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lectromagnetic (EM31) survey of the channels for identifying critical sections of the irrigation system for

quantitative seepage measurements;

2. I
nflow–Outflow method to measure total water losses in measured lengths of channels. Water flow
measurements (using Flow Tracker) in selected channels to determine overall water losses, including

evaporation, leakage and seepage;

3. I
daho Seepage Meter to measure seepage rate at the selected spots identified as of low electromagnetic
conductivity and reflected by Inflow–Outflow measurements;

4. A
rtificial neural network model for extrapolation of seepage data.
Economic evaluation

Comparison of the relative economic performance of irrigation technologies is undertaken using partial

budgeting. Partial budgeting involves a process of valuing all the costs and benefits that the project generates over

the life of the project in today’s monetary terms and then discounting these future costs and benefits to take into

account the opportunity cost of capital. In addition to the cost–benefit curves, this study also derived three economic

parameters in which the various on-farm water-saving technologies can be compared. They were:

1. N
et benefits (i.e. NPV) per megalitre water saved per year;
2. A
nnualised cost per megalitre water saved;
3. B
reakeven year.

DOI: 10.1002/ird


The net present value (NPV) is the sum of the discounted future annual cash flows attributed to the investment

decision, over a time frame of 25 years, i.e.

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NPV ¼X25

t¼1

Bt � Ct

ð1 þ rÞt (1)

where B¼ project benefits (A$), C¼ project costs (A$), r¼ discount rate (%) and t¼ project period (years).

To compare the different water-saving technologies, the NPV becomes net benefit per megalitre water saved per

year. The annualised cost per megalitre water saved is used when projects have similar net benefits per megalitre

water saved. This economic parameter will determine the project that has the lowest annual cost of saving one unit

of water and would be a useful ranking parameter when capital is a limiting resource to agricultural production. The

annual cost of a water-saving technology is the annual operating cost (operation and maintenance and cost of skilled

manpower) plus the annualised capital cost of the technology where the annuity of the capital cost is determined by:

Va ¼ Vnr

1 � ð1 þ rÞ�n (2)

where Va¼ annuity value (A$), Vn¼ nominal value (A$), r¼ discount rate (%) and n¼ period of annuity (years).

The breakeven year is the year when the cumulative discounted cash flow (i.e. the NPV) becomes positive. The

breakeven year indicates how long an investment takes to repay itself. Projects that have low breakeven years might

be considered less risky, particularly when the project incorporates some key variables that are uncertain.

Water productivity at system level

Water productivity analysis is a useful tool at irrigation system level (Molden, 1997; Molden et al., 2003) where

the main emphasis is on increasing on-farm water use efficiency and farm profitability for situations where water is

the most limiting factor. A comprehensive water productivity analysis is conducted at the irrigation system level for

both ‘‘before and after’’ adopting the water-saving options (Khan et al., 2005) The components of irrigation

efficiency are: conveyance efficiency (farm supply/water source), farm efficiency (field application/farm supply),

field efficiency (root zone storage/field application) and the overall irrigation efficiency (root zone storage/water

source). Water use efficiency covers water consumptively used in ET divided by total water supply including

surface water diversions, groundwater abstractions, effective rainfall and capillary uptake. Water productivity

(t ML�1 water used) is the crop yield divided by total water supply. Water productivity is also quantified as

economic return (A$ ML�1 water used).

RESULTS AND DISCUSSION

The exercise of individual crop and technology water saving was to quantify water use (ML ha�1) for different

scenarios of soil types and depth to groundwater table. The cropping systems of wheat–maize, barley–sunflower

and fababean–soybean combinations were used in modelling. Ten types of soils and three groundwater tables were

tested for irrigation needs of the field crops. The range of water use (ML ha�1) in surface and sprinkler irrigation

technologies are given in Table I.

The conversion from surface irrigation to high-tech irrigation technologies, e.g. sprinkler and drip irrigation

systems, means a higher water-saving potential. Model simulations shows water-saving potential on a per unit area

(hectare) basis of 7% for maize, 15% for soybean, 17% for wheat, 35% for barley, 17% for sunflower and 38% for

fababean.

The main capital investment profile for tested crops and overall investment curves are given in Figure 2 for the

MIA and Figure 3 for the CIA. These investments range from less than A$ 2000 ML�1 saved to over A$ 6000 ML�1

saved.

Rice is the major user of water in the Murrumbidgee valley (over 50% of the total water use in the CIA and MIA),

therefore there are possibilities to improve overall water use efficiency by growing rice on suitable land with lower


DOI: 10.1002/ird

Table I. Water use and savings (ML/ha�1) for selected crop under different irrigation technologies using SWAP model

Irrigation method Surface Sprinkler Water Ssavings

High Low Average High Low Average High Low Average

Maize 10.6 4.3 8.3 9.2 4.0 7.7 1.4 0.3 0.6Soy bean 6.6 3.6 5.4 5.6 3.2 4.6 1.0 0.4 0.8Wheat 4.2 0.5 2.4 2.8 0.5 2.0 1.4 0.0 0.4Barley 4.3 0.7 1.7 2.4 0.7 1.1 1.9 0.0 0.6Sunflower 7.0 3.5 4.6 4.8 3.1 3.8 2.2 0.4 0.8Fababeans 4.9 1.5 3.2 3.3 1.4 2.0 1.6 0.1 1.2

6 S. KHAN ET AL.

soil hydraulic permeability and minimum groundwater outflow rates. A three-stage classification scheme of rice

land suitability is proposed in Australia including EM31 soil mapping and measurement of soil sodicity as key

components (Beecher et al., 2002). Modelling results using ‘‘SWAGMAN Farm1’’ (Edraki et al., 2003) show that

if rice is grown on shallow groundwater table soils (less than 2 m depth to groundwater table) with lower

groundwater outflow rates (less than 0.25 ML ha�1yr�1) the total soil filling and groundwater outflow requirements

can be reduced to less than 1 ML ha�1 and therefore rice water use can be reduced to less than 11–12 ML ha�1 in an

average year. The reported rice water use varies between 12 and 16 ML ha�1. If rice is relocated to more suitable

soil and groundwater conditions there is a potential to reduce soil filling and groundwater outflow requirement

‘‘allowance’’ by around 3 ML ha�1 allowing around 1–3 ML ha�1 savings on the current rice water use (Khan et al.,

2003). This can lead to over 50 000 ML water savings (on the average 1 ML ha�1 over 50 000 ha) under a full

allocation year.

0

1000

2000

3000

4000

5000

6000

7000

9000080000700006000050000400003000020000100000

Total Water Saving (ML)

Cap

ital

Co

st (

$/M

L)

Subsurface Drip

Lateral Move

Central Pivot (towed)

Central Pivot (fixed)

Figure 2. Capital investment and total water savings by high-tech irrigation technologies in MIA


DOI: 10.1002/ird

0

1000

2000

3000

4000

5000

6000

7000

1600014000120001000080006000400020000

Total Water Saving (ML)

Cap

ital

Co

st (

$/M

L)

Subsurface Drip

Lateral Move

Central Pivot (towed)

Central Pivot (fixed)

Figure 3. Capital investment and total water savings by high-tech irrigation technologies in CIA


For quantification of near-farm losses, seepage was measured at 408 locations in different channels and drains of

9 farms in the irrigated areas of MIA and CIA. There was a large degree of variability in the mean seepage rates,

between sections within the same channels and drains. Tables II–IV show the number of measurements, the mean

seepage rate and the standard deviation from the mean for each site. Mean seepage rates varied from 0 to 108 mm

day�1. Very high rates were encountered and the coefficient of variation for drains was accordingly high, values

ranging from 5 to 1034%. The seepage volume (ML yr�1) as a proportion of annual farm water delivery ranges

between 1 and 4%. The cost of reducing seepage losses can be directly related to the value of the resource. When

water is bought by farmers for a low price the cost of losses due to seepage is not considered to be very important

compared to the very high capital cost of repairing leaks.

Table II. Seepage meter measurements at farms A, B, and C

Combined batters and bed Farm A Farm B Farm C

Channel Channel Drain Channel Channel Drain Channel Channel Channel

Number of readings 17 12 12 14 5 8 11 10 11Minimum (mm day�1) 0.89 0.75 0.37 0.86 1.49 1.46 1.46 0.55 1.12Maximum (mm day�1) 24.30 2.99 45.99 16.08 4.86 7.80 37.53 46.55 6.6Median (mm day�1) 3.12 1.50 3.18 13.47 2.00 2.05 15.45 40.55 3.70Mean (mm day�1) 6.22 1.62 12.12 7.75 3.06 4.02 11.50 21.32 2.97Standard deviation 5.87 0.64 13.36 5.13 0.74 2.34 9.29 14.59 1.44Coefficient of variation (%) 94 40 110 66 24 58 81 68 48


DOI: 10.1002/ird

Table III. Seepage meter measurements at farms D, E, and F

Combined batters and bed Farm D Farm E Farm F


Number of readings 23 14 9 23 18 11 13 8 12Minimum (mm day�1) 4.49 2.24 12.96 1.50 1.50 1.25 1.99 7.48 2.24Maximum (mm day�1) 36.15 43.88 108.20 7.48 14.21 8.23 9.97 38.64 53.60Median (mm day�1) 13.46 15.71 70.80 3.49 4.36 2.24 5.98 17.95 12.59Mean (mm day�1) 16.71 18.25 60.52 3.86 5.74 2.65 5.94 18.57 17.26Standard deviation 9.34 14.63 32.16 1.63 3.80 2.24 2.83 11.33 15.42Coefficient of variation (%) 87 155 1034 3 14 5 8 128 238

8 S. KHAN ET AL.

Irrigation scheduling to meet soil water deficit is a recommended irrigation practice where ‘measuring and

monitoring soil water status is important part of an integrated management program to avoid the economic losses

and effects due to under irrigation and over irrigation’. There is a wide range of equipment to measure soil moisture

(e.g. tensiometers, gypsum block, neutron probes and capacitance probes e.g. Enviroscan1) at a range of costs from

approximately A$ 3 ha�1 to A$ 22 ha�1. Assuming the marginal value of water savings is A$ 55 ML�1, the

sensitivity of the annualised cost of five types of soil moisture monitoring equipment for a 50 ha block, showed the

net benefit per megalitre saved per year would range from �A$ 76 to A$ 25 ML�1 saved per year. These results

show that if the annualised cost of the soil moisture monitoring equipment is relatively high and water savings are

low, then investment in this technology is not viable.

Significant water savings can also be made with adjustments to the flow rate and/or change in length of the water

run in flood or furrow irrigation systems. The cost–benefit curves of improving flow rates in flood irrigation

systems for four water- saving scenarios are illustrated in Figure 4. The cost–benefit curves of improving flow rates

in flood irrigation systems showed that if the marginal value of water is A$ 55 ML�1 then the NPV is A$ 5,700 when

water savings are 0.3 ML ha�1 and the NPV is A$ 75, 600 when water savings are 2.5 ML ha�1. Consequently, the

net benefit per megalitre saved is A$ 15 ML�1 and A$ 24 ML�1 with the breakeven year occurring in Year 7 and

Year 1 respectively. When the marginal value of water is reduced to A$ 30 ML�1, the NPV decreases significantly,

the NPV becoming A$ 1,300 when water savings are 0.3 ML ha�1 and A$ 39, 500 when water savings are

2.5 ML ha�1.

The volume and marginal capital costs of water use savings from off-farm investment are summarised in

Figure 5. The information indicates that there could be up to 20 GL of potential savings at a marginal cost of around

A$ 1,500–2,000 ML�1. Costs then rapidly rise, reaching A$ 4,000 ML�1 at around 38 GL, reflecting the lower

volumes of water saved at higher cost of Bentonite. The above information also indicates that there could be up

to 20 GL of potential savings at a marginal cost of around A$ 400–A$ 500 ML�1. Costs then rise, reaching

A$ 600 ML�1 at around 28 GL for rice hull ash to 32 GL for water sludge.

Table IV. Seepage meter measurements at farms G, H, and I

Combined batters and bed Farm G Farm H Farm I


Number of readings 12 9 6 10 11 7 13 7 —Minimum (mm day�1) 1.75 1.99 12.71 1.50 2.99 4.74 1.25 4.74 —Maximum (mm day�1) 91.25 25.68 84.52 11.97 14.21 11.47 14.71 9.97 —Median (mm day�1) 8.35 8.23 51.36 8.73 10.97 7.98 3.99 7.73 —Mean (mm day�1) 19.69 10.19 52.98 7.88 9.65 8.30 5.43 7.48 —Standard deviation 26.76 7.51 24.75 3.07 4.23 2.69 4.47 1.61 —Coefficient of variation (%) 716 57 612 9 18 7 20 3 —


DOI: 10.1002/ird

-20

0

20

40

60

80

100

2520151050

Year

NP

V (

'000

)

w ater savings: 2.5 ML/ha @ $55/MLw ater savings: 2.5 ML/ha @ $30/MLw ater savings: 0.3 ML/ha @ $55/MLw ater savings: 0.3 ML/ha @ $30/ML

Figure 4. Cumulative NPV of improving flow rates in flood irrigation systems


Figures 6 and 7 represent an example of a supply channel, Sturt Canal, with average wetted width of 16.15 m for a

channel length of 1 km. The estimated losses are equal to 73 ML per irrigation season (270 days). Values on the Y

axis in Figures 6 and 7 are the threshold values that the saved water needs to be for the channel lining investment

options to break even with in the following three effectiveness scenarios:

� B

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entonite 65–80% effectiveness;

� W
ater sludge 55–65% effectiveness;
� R
ice hull ash 50–60% effectiveness.
Table V lists the breakeven cost of technologies with their effective life. The analysis is based on a number of

assumptions that include: (i) all capital works occur in year 1; (ii) channel maintenance costs are constant over the

analysis period, and independent of the channel capacity; (iii) asset residual values are based on straight

line depreciation and include only earthworks cost (not the structures); (iv) a 270 days yr�1 seepage duration

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

40000 32000 24000 16000 8000 0

Total (ML) Saved

Cap

ital

Co

st (

$/M

L S

aved

)

Bentonite

Rice Hull Ash

Water Sludge

Figure 5. Capital investment curves for saving seepage losses

ight # 2007 John Wiley & Sons, Ltd. Irrig. and Drain. 57: 1–14 (2008)

DOI: 10.1002/ird

Figure 6. Capital investment of lining materials for $/ML saved in supply channels

Figure 7. Capital investment and effective life of lining materials in supply channels

10 S. KHAN ET AL.

(irrigation time per year); (v) a minimum seepage rate of 1.0 mm day�1 has been allowed for clay lining; (vi)

channel cross-section parameters have been estimated using Manning’s equation; (vii) capital cost unit rates for

short project lengths (0–l00 m) have been calculated.

RELATIVE EVALUATION OF WATER-SAVING OPTIONS

Field- based on-farm water savings for scenarios analysed ranged from 0.1 ML ha�1 up to 3.9 ML ha�1. As capital

can be a limiting resource to for farmers, options that have the lowest cost per ML saved may be more appealing

Table V. Breakeven cost of technologies with effective life

Technology ML saved 20 years 10 years 5 years

A$ ML�1 A$ ML�1 A$ ML�1

Rice hull ash 57 31 49 88Water sludge 62 28 46 81Bentonite 73 147 237 423


DOI: 10.1002/ird

Tab

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and

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enta

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(ML

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Copyright # 2007 John Wiley & Sons, Ltd. Irrig. and Drain. 57: 1–14 (2008

DOI: 10.1002/ir


)

d

12 S. KHAN ET AL.

than options that have a higher cost but may also have higher net benefits over time. Based on the annualised cost

per ML saved, changing irrigation management by improving scheduling with soil moisture monitoring (some

equipment only) and/or improving inundation times in irrigation bays as well as recycling had annualised costs less

than A$ 44 ML�1 saved. Expensive soil moisture monitoring equipment, laser levelling and conversion to

pressurised systems for broad acre farms range between A$ 50 and A$ 200 ML�1. Conversion to drip for

horticulture farms were slightly more expensive, ranging from A$ 220 to A$ 390 ML�1, and the most expensive

was the storage evaporation cover costing between A$ 330 and A$ 530 ML�1 saved.

Measuring and monitoring soil moisture have a number of economic and environmental benefits. There is a wide

range of equipment to measure soil moisture (e.g. tensiometers, gypsum block, neutron probes and capacitance

probes) at a range of costs from approximately A$ 3 ha�1 to A$ 22 ha�1. The sensitivity of the annualised cost of the

above monitoring equipment shows water savings of 0.2–3 ML ha�1 depending upon the crop type and associated

yield benefits.

On-farm recycling provides an alternative source of water supply and consequently increasing water use

efficiency. For a typical farm (200 ha) in the MIA, a recycle system has the potential to capture 56 ML–224 ML

year�1. Assuming a pumping cost of A$ 7 ML�1 and maintenance costs equivalent to 1% of the capital cost, the

annualised cost per ML saved is approximately A$ 22–A$ 44 ML�1 (Table VI).

Average annual evaporation from storages in MIA is 1,990 mm. The surface area required to save 1 MLyr�1 of

evaporation is approximately 500 m2 at an annualised cost of A$ 530 ML�1 to A$ 296 ML�1 for a lifespan of 10

to 25 years respectively. After conducting the NPS analysis, the results show the marginal value of water as

A$ 295–A$ 530 ML�1 (Table VI).

Laser levelling would increase irrigation efficiency by 25%. The study compared the net benefits of land forming

for various volumes of soil moved on rice farms in the MIA (Marshall and Jones, 1992). The land forming generates

a high return on investment and priority and should be given to areas with relatively low volumes of earth to be

moved if capital is limiting.

The water savings that derived the highest net benefit per megalitre saved were conversion to drip and subsurface

drip for the case study farms and laser levelling which had net benefits ranging from A$ 64 to A$ 344 ML�1 saved

per year. All of the other options had net benefits ranging from A$ 4 to A$ 37 ML�1 saved per year. All of the

options that had a low annualised cost also had a relatively low net benefit (less than A$ 24 ML�1 saved per year).

Table VI presents a summary of water- saving economic parameters and environmental benefits using the case

study approach.

Ranking for off-farm water saving options through lining of supply channels is performed. The rating of

alternative water water-saving technologies from cheapest to most expensive as cost for lining with water sludge to

piping channels is determined in terms of NPV. NPVof cost of saving water by using different technologies varies

from less than A$ 50 to A$ 2,000 ML�1 yr�1.

Table VII shows the possible impacts of the adoption of the water use efficient management options and

technologies. These results are based on the whole-of-system analysis (further details are available in a detailed

report by Khan et al., 2005) under current practice of water use and for a possible future scenario with uptake of the

Table VII. ‘‘Before and after’’ adopting water efficiency for the whole of irrigation system

Efficiency Coleambally Irrigation Area Murrumbidgee Irrigation Area

Now After possibleadoption of

WUE technologies

Now After possibleadoption of

WUE technologies

Conveyance efficiency Farm edge/water source (%) 80 85 90 95Farm efficiency Field edge/farm edge (%) 94 96 88 90Field efficiency Root zone storage/field edge (%) 92 97 89 95Water use efficiency ETactual/water supply (%) 77 85 88 91Water productivity Yield/water supply (t GL�1) 343 374 798 836Economic return Profit/water supply (A$ GL�1) 91 000 99 200 198 000 207 150


DOI: 10.1002/ird


identified water- saving options. The outputs of these models show the water saving and economic benefits that may

occur in the MIA and CIA with the adoption of the water use efficient management options and technologies.

CONCLUSIONS

Essentially, real water savings in agriculture sector mean increasing its productive use, freeing up water from

non-beneficial uses and releasing water for the environment, cities, or industries. At farm level, improving

irrigation efficiency is the most appropriate way to save water. However, implementing strategies for saving water

with reduced risks of negative impacts on the environment should focus on a system perspective. This study

encompasses possible target areas for saving water from farm to irrigation system level. Irrigation scheduling is

recommended as an irrigation practice to avoid the economic losses and effects due to under- irrigation and over-

irrigation. Seepage losses from supply canals and drains are quantified by combining in situ seepage monitoring

with EM31 surveys. The losses from an off-farm earthen supply channel vary widely and can be from 1 to 30% of

the water supplied. The occurrence pattern is not seen uniform along the channel reaches and is more noticeable in

hot spots, for example, up to 9% of losses in one channel occurred in a single kilometre length. The on-farm supply

losses are varied from 1 to 4%. There exists potential for water savings from recycle and storage systems; for

example, a 220 ha farm could save between 56 and 224 MLyr�1 in the Murrumbidgee Irrigation. Optimising flow

rates across fields can reduce losses due to deep percolation. Rice is best grown on soils with low soil hydraulic

permeability, low groundwater outflow rates (<0.25 ML ha�1 yr�1) and shallow groundwater tables (<2 m depth to

groundwater table) by reducing the total soil filling and groundwater outflow requirements to less than 1 ML ha�1.

Conversion to pressurised irrigation can potentially save water when growing both broad acre as well as

horticultural crops. This study clearly shows that substantial water savings can be made by improving management

practices or adopting new practices. The benefits can be extended to other irrigation regions providing greater

potential for water savings and increased economic returns at the irrigation system level.

ABBREVIATIONS

A$ A

Copyright # 2007

ustralian dollar

CIA C
oleambally Irrigation Area
COAG C
ouncil of Australian Governments
ECa A
pparent electrical conductivity
EM31 E
lectromagnetic inductance 31
ET E
vapotranspiration
GL G
igalitres¼million cubic metres¼ 1000 ML
MIA M
urrumbidgee Irrigation Area
ML M
egalitres¼ 1 000 000 litres
ML ha�1 1
00 mm per hectare
NPV N
et present value
SWAP S
oil–Water–Atmosphere–Plant Model
SWAGMAN S
alt Water And Groundwater MANagement Model
WUE W
ater use efficiency
ACKNOWLEDGEMENTS

The authors wish to acknowledge funding support by Pratt Water Group, Australia and the Water for a Healthy

Country Flagship. Technical support provided by CSIRO scientists D. Dassanayake, I. Hirsi, J. Blackwell and E.

Xevi is greatly appreciated.

John Wiley & Sons, Ltd. Irrig. and Drain. 57: 1–14 (2008)

DOI: 10.1002/ird

14 S. KHAN ET AL.

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hydrologic and economic evaluation of water-saving options in irrigation systems

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