ECONOMICS OF CONJUNCTIVE W ATER MANAGEMENT UNDER CROP SALINITY TOLERANCE CONSTRAINTS ISMAIL HIRSI B.Sc. (Honours) Agriculture M.Sc. (Honours)) Agricultural Economics A thesis submitted for the degree of Doctor of Philosophy in Environmental Sciences International Centre of Water for Food Security Faculty of Science, School of Environmental Sciences Charles Sturt University
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A thesis submitted for the degree of Doctor of Philosophy in Environmental Sciences
International Centre of Water for Food Security Faculty of Science, School of Environmental Sciences
Charles Sturt University
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February 2008
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CERTIFICATE OF AUTHORSHIP
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AGREEMENT FOR THE RETENTION & USE OF THE THESIS
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I Mr. Ismail Hirsi S/O Farah Hirsi
Hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree or diploma at Charles Sturt University or any other educational institution, except where due acknowledgment is made in the thesis. Any contribution made to the research by colleagues with whom I have worked at Charles Sturt University or elsewhere during my candidature is fully acknowledged. I agree that the thesis be accessible for the purpose of study and research in accordance with the normal conditions established by the University Librarian for the care, loan and reproduction of the thesis.*
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ACKNOWLEDGEMENT
In the Name of Allah, the Merciful, the Compassionate All praises and thanks be to Allah (S.W.T), we praise Him, seek His aid, forgiveness, and His protection against our evil-self and wrong doings. My deep sense of gratitude is due to Allah (S.W.T), Who enabled me to complete this study. The efforts made with trust in Allah (S.W.T) and faith in His Prophet (may the blessings and peace of Allah be upon him) always bear fruit. May Allah (S.W.T) accept this humble effort as a reflection to His sayings: “Say: “Have you ever considered that if all the water you have, sink down in the ground, who then can bring you the clear-flowing water?”. (Sûrah 67, verse 30). “Mentioning (speaking of) the favours of Allah is (a show of) gratefulness. Leaving it (the favour) is ingratitude. Whoever does not thank (for) the little will not thank the much. And he who does not thank the people does not thank Allah...”(On the authority of Nu’man Ibn Basheer. Hadith No. 5325 in Al Jami’ Assaghir). With feelings of great pleasure and deep sense of profound gratitude, my acknowledgement also goes to my supervisor Professor Shahbaz Khan for his intelligible guidance and moral support during the course of this study. The benefits from many helpful discussions with Dr. Tom Nordblom, Dr. Richard Culas, and the members of International Centre of Water for Food Security, Charles Sturt University, Wagga Wagga must not be left unacknowledged. I am greatly indebted to the Australian Cooperative Research Centre for Irrigation Future (CRC IF). I am sincerely thankful for the cooperation from the officials of the Coleambally Irrigation Cooperative Limited (CICL), Coleambally, and the hospitality offered by the members of staff of the CICL during my field study tour to Coleambally Irrigation Area. Thanks are due to my wife, children, brothers, sister and other family members for their unreserved love, benevolent prayers, and sacrifices in sustaining my efforts during the studies. Sincere thanks are due to all my friends from Somalia, Pakistan, Australia, Egypt, Indonesia, China, Palestine, Oman, India, Bangladesh, Iran, Saudi Arabia, Lebanon, Djibouti, Ethiopia, and Ghana. I am indebted to all the members of the Islamic Students’ Association Riverina of Charles Sturt University during my study period. It was an unforgettable experience to see these companions as a profound reflection of the following verse of Al-Qur’an: “O mankind! We created you from a single (pair) of a male and a female and made you into nations and tribes that you may know each other (not that you may despise each other). Verily the most honoured of you in the sight of Allah is (he who is) the most righteous of you. And Allah has full knowledge and is well acquainted (with all things)” (Sûrah 49, verse 13). My greatest and ultimate gratitude is due to Allah (S.W.T), the Creator of the heavens and the earth. May He forgive my failings and weaknesses, strengthen and enliven my faith in Him and endow me with knowledge and wisdom, Aameen!
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Ismail Hirsi
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ABSTRACT
The negative effect associated with soil salinisation has been an issue of
irrigated agriculture for centuries. The agricultural impacts associated with
excess soil salinity levels cause decrease in crop yield and other off farm
impacts such as damages to infrastructure and build environment. The main
goal of this dissertation was to study the economics of conjunctive water
management under crop salinity tolerance constraints. The specific
objectives were to: determine the possibilities of increasing gross margins
by taking optimal mix of crops under crop salinity tolerance constraints;
develop a hydrologic economic model and employ different mathematical
optimisation techniques using GAMS environment to determine the ways of
best use of conjunctive water for irrigation; and estimate and compare the
cost of irrigation and the resulting gross margins from using surface water,
groundwater and conjunctive water use with respect to optimal crop mix
under crop salinity tolerance constraints.
This study extended previous work on SWAGMAN Farm models, which
are a range of models of salt and water balance at the plant, farm and
catchment scale. However, this study integrated the Mass and Hoffmann
Model accounting for crop-soil groundwater salinity interactions in the
standard SWAGMAN Farm version. This was the key conceptual
contribution of this dissertation and an advance into the standard
SWAGMAN Farm model. It involved mixed integer programming in
GAMS (General Algebraic Modeling System) environment to model the
nonlinearities in the Mass and Hoffmann equation. This advance enables a
more scientific and accurate assessment of the impact of salinity on crop
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yield via-a-vis land and water management strategies to enhance
productivity and environmental sustainability in an economic decision
making environment. The nonlinearities and crop yield response to salinity
as defined by Mass and Hoffman cannot be captured by conventional
biophysical modelling techniques alone due to complex relationship.
The model was successfully validated on selected farms in two mature
irrigation areas in Pakistan and Australia. The overall model result show
that the yield and profitability response to salinity and groundwater depth
varies across farms within the same irrigation system. For a given level of
canal water allocation the gross margin per ha is lowest with the
groundwater use only, and highest for the canal water use only for current
salinity levels in the studied systems. The lowest economic returns under
groundwater use only mean those crop yields are adversely impacted due to
higher salinity of groundwater, lowering economic returns. In limiting
salinity areas, mixing of canal water with groundwater to achieve a specific
target salinity level enables farmer to achieve higher economic return per ha
and enhance total return from available water resources. This has
implications for allocating more canal water to saline environments such as
the tail ends, better groundwater mapping, and for public investments and
APPENDIX I .................................................................................................................... 164
APPENDIX II .................................................................................................................. 176
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LIST OF FIGURES
FIGURE 2.1 RELATIONSHIP BETWEEN RELATIVE PLANT YIELD AND SOIL ROOT ZONE
SALINITY (MASS AND HOFFMAN, 1977). ......................................................... 35 FIGURE 4.1 THE COLEAMBALLY IRRIGATION AREA. ......................................................... 63 FIGURE 4.2 MONTHLY RAINFALL FIGURES DURING 2006-07 (AER 2007). ........................ 64 FIGURE 4.3 MONTHLY EVAPOTRANSPIRATION FIGURES DURING 2006-07 (AER 2007). .... 65 FIGURE 4.4 CIA GROUNDWATER MANAGEMENT ZONES (KHAN ET AL., 2008)................... 69 FIGURE 4.5 FARM 1 - TOTAL GROSS MARGIN FOR VARIOUS WATER ALLOCATION LEVELS
AND WATER MANAGEMENT SYSTEMS.............................................................. 71 FIGURE 4.6 FARM 6 - TOTAL GROSS MARGIN FOR VARIOUS WATER ALLOCATION LEVELS
AND WATER MANAGEMENT SYSTEMS.............................................................. 73 FIGURE 4.7 FARM 9 - TOTAL GROSS MARGIN FOR VARIOUS WATER ALLOCATION LEVELS
AND WATER MANAGEMENT SYSTEMS. ............................................................. 76 FIGURE 4.8 FARM 11 - TOTAL GROSS MARGIN FOR VARIOUS WATER ALLOCATION LEVELS
AND WATER MANAGEMENT SYSTEMS.............................................................. 77 FIGURE 4.9 COMPOSITE SALINITY OF CONJUNCTIVE USE ................................................... 82 FIGURE 5.1 LOCATION MAP OF RECHNA DOAB IRRIGATION SYSTEM................................ 85 FIGURE 5.2 GROUNDWATER SALINITY IN RECHNA DOAB (ΜS/CM)................................... 88 FIGURE 5.3 TOTAL GROSS MARGIN FOR VARIOUS WATER ALLOCATION LEVELS AND WATER
MANAGEMENT SYSTEM IN UPPER RECHNA DOAB............................................ 92 FIGURE 5.4 TOTAL GROSS MARGIN FOR VARIOUS WATER ALLOCATION LEVEL AND WATER
MANAGEMENT SYSTEMS IN THE MIDDLE RECHNA DOAB................................. 93 FIGURE 5.5 TOTAL GROSS MARGIN FOR VARIOUS WATER ALLOCATION LEVEL AND WATER
MANAGEMENT SYSTEMS IN THE LOWER RECHNA DOAB.................................. 94 FIGURE 5.6 EFFECT OF MIXING RATIO OF SURFACE WATER AND GROUNDWATER ON THE
GROSS MARGINS IN UPPER RECHNA DOAB. ..................................................... 95 FIGURE 5.7 EFFECT OF MIXING RATIO OF SURFACE WATER AND GROUNDWATER ON THE
GROSS MARGINS IN MIDDLE RECHNA DOAB .................................................... 97 FIGURE 5.8 EFFECT OF MIXING RATIO OF SURFACE WATER AND GROUNDWATER ON THE
GROSS MARGINS IN LOWER RECHNA DOAB..................................................... 98 FIGURE 6.1 ANNUAL GENERAL SECURITY ALLOCATIONS SINCE 1982/83 (AER 2007)..... 101 FIGURE 6.2 ANNUAL DIVERSION AND LICENSED ENTITLEMENT (AER 2007). .................. 101 FIGURE 6.3 LOCATION MAP OF GROUNDWATER BORES IN COLEAMBALLY IRRIGATION
AREA (CICL, 2006). ..................................................................................... 103 FIGURE 6.4 GROUNDWATER USAGE IN COLEAMBALLY IRRIGATION AREA (AER 2007).. 106 FIGURE 6.5 ANNUAL COST OFF PUMPING ELECTRIC. ....................................................... 112 FIGURE 6.6 ANNUAL COST OF PUMPING DIESEL............................................................... 113 FIGURE 6.7 ANNUAL COST OF PUMPING TRACTOR........................................................... 113 FIGURE 6.8 MIXING RATIO OF SURFACE WATER AND GROUNDWATER FOR THE FARM 1. . 116
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FIGURE 6.9 LAND USE IN FARM 1 .................................................................................... 116 FIGURE 6.10 MIXING RATIO OF SURFACE WATER AND GROUNDWATER FOR THE FARM 6.. 117 FIGURE 6.11 MIXING RATIO OF SURFACE WATER AND GROUNDWATER FOR THE FARM 9. . 118 FIGURE 6.12 MIXING RATIO OF SURFACE WATER AND GROUNDWATER TO INDIVIDUAL FARM.
...................................................................................................................... 119 FIGURE 6.13 MIXING RATIO OF SURFACE AND GROUNDWATER FOR THE UPPER RECHNA
DOAB ............................................................................................................ 122 FIGURE 6.14 MIXING RATIO OF SURFACE AND GROUNDWATER FOR THE MIDDLE RECHNA
DOAB ............................................................................................................ 123 FIGURE 6.15 MIXING RATIO OF SURFACE AND GROUNDWATER FOR THE LOWER RECHNA
DOAB ............................................................................................................ 123 FIGURE 6.16 MIXING RATIO OF SURFACE WATER AND GROUNDWATER TO INDIVIDUAL FARM
TABLE 2.1 SALT TOLERANCE LEVELS OF GRAINS (ANZECC AND ARMCANZ, 2000). . 36 TABLE 3.1 LANDUSES CONSIDERED IN THE MODEL FOR A FARM. (MADDEN AND
PRATHAPAR, 1999; JEHANGIR AND KHAN, 2003)............................................ 45 TABLE 3.2 SOIL TYPES CONSIDERED IN THE MODEL FOR A FARM. (MADDEN AND
PRATHAPAR, 1999; JEHANGIR AND KHAN, 2003)............................................ 45 TABLE 4.1 AREAS (HA) OF EACH CROP TYPE IRRIGATED IN CIA, AND THE KERARBURY
CHANNEL AND OUTFALL DISTRICT, AND EACH CROP’S RELATIVE PERCENTAGE
TO TOTAL IRRIGATED AREA 2004 (COLEAMBALLY IRRIGATION CO-OPERATIVE
LIMITED 2005). ............................................................................................... 65 TABLE 4.2 AREAS (HA) OF EACH CROP TYPE IRRIGATED IN CIA, AND THE KERARBURY
CHANNEL AND OUTFALL DISTRICT, AND EACH CROP’S RELATIVE PERCENTAGE
TO TOTAL IRRIGATED AREA 2005 (COLEAMBALLY IRRIGATION CO-OPERATIVE
LIMITED 2006). ............................................................................................... 66 TABLE 4.3 A COMPARATIVE OVERVIEW OF THE MODELLED FARMS.................................. 70 TABLE 4.4 SCENARIO 1..................................................................................................... 79 TABLE 4.5 SCENARIO 2..................................................................................................... 79 TABLE 4.6 SCENARIO 3..................................................................................................... 80 TABLE 5.1 AREA UNDER MAJOR CROPS GROWN ON FARMS ACROSS IRRIGATION SUB-
DIVISIONS (HA)................................................................................................ 86 TABLE 5.2 NUMBER OF GROWING DAYS FOR PARTICULAR LAND USES. ............................ 87 TABLE 5.3 A COMPARATIVE OVERVIEW OF THE MODELLED FARMS IN PAKISTAN............. 89 TABLE 5.4 COMPOSITE EC OF CONJUNCTIVE WATER MANAGEMENT. ............................... 95 TABLE 5.5 COMPOSITE EC OF CONJUNCTIVE WATER MANAGEMENT. ............................... 96 TABLE 5.6 COMPOSITE EC OF CONJUNCTIVE WATER MANAGEMENT. ............................... 97 TABLE 6.1 SALINITY OF GROUNDWATER EXTRACTED FROM COLBORE- 2004/07 (CICL,
2005-2007) ................................................................................................... 103 TABLE 6.2 MONTHLY GROUNDWATER EXTRACTIONS FROM COLBORE 1994/95 TO
2006/07......................................................................................................... 104 TABLE 6.3 INPUT DATA USED FOR CALCULATING CAPITAL AND OPERATING COSTS IN AN
AUSTRALIAN CONTEXT (AFTER ROBINSON, 2002). ....................................... 109 TABLE 6.4 NET PRESENT VALUES OF DEEP GROUNDWATER BORES................................ 110
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ACRONYMS AND ABBREVIATIONS
ANZECC Australian and New Zealand Environment and Conservation Council
ARMCANZ Agriculture and Resource Management Council of Australia and New Zealand
CIA Coleambally Irrigation Area
CICL Coleambally Irrigation Cooperative Limited
ColBore CICL augmentation bore (Bore no. 39406)
CSIRO Commonwealth Science and Industry Research Organisation
CSU Charles Sturt University
CW Canal Water
CWM Conjunctive water management
DNR NSW Department of Natural Resources (now DWE)
DPI NSW Department of Primary Industry
dS/m Deci Siemens per metre
EC Electric conductivity (a standard term used to refer to salinity as measured by micro Siemens per centimetre, µS/cm, at 25oC)*
GAMS General Algebraic Modeling System
GWSP Water Sharing Plan for the Lower Murrumbidgee Groundwater Sources
LCC Lower Chenab Canal
LWMP Land and Water Management Plan
LRDIS Lower Rechna Doab Irrigation System
MDB Murray-Darling Basin
MDBC Murray-Darling Basin Commission
MENA Middle East and North Africa
Mha Million hectare
ML Meggalitre
MRDIS Middle Rechna Doab Irrigation System
NPV Net Present Values
NSW New South Wales
SAR Sodium absorption ratio
SWAGMAN Salt Water And Groundwater Management
TGM Total Gross Margin
TW Tubewell
UCC Upper Chenab Canal
URDIS Upper Rechna Doab Irrigation System
µS/cm Micro Siemens per centimetre; the standard unit used to measure salinity (see EC)
WSP Water Sharing Plan
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CHAPTER ONE
1 Introduction
This chapter explains key issues in using the term “Conjunctive Water
Management – the joint management of groundwater and surface water”,
and expands this definition to capture its relationship in association to: (i)
conjunctive use, (ii) link between groundwater and surface water, (iii)
irrigation system management, and (iv) interpretation and implications in
water governance. Global issues of groundwater use and its key challenges
are also discussed in brief. In the context of conjunctive water management
in Australia and Pakistan, research question is defined and research
objectives are formulated to address this research question. Thesis structure
is also presented in this chapter.
1.1 Background
Surface water is an increasingly scarce commodity, particularly in arid and
semi-arid regions of the world (Falkenmark, 1986). In these regions,
groundwater (being used alone or in conjunction with limited surface water
supplies) has become an unprecedented reality to fill the gap between
demand and supply of consumptive and environmental users (Ward et al.,
1996, 2006, 2007; Chermak et al., 2005; Ding, 2005). In practice, the
conjunctive water management can be envisioned at the farm and irrigation
system levels (Houk et al., 2005; Karlberg et al., 2006; Schoups et al.,
2006). Although the scope and scale of conjunctive water management
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differ in these two levels, but it helps improve the overall availability and
reliability of water (Hussain et al., 2004; Shah and Singh, 2004; Peterson
and Ding, 2005; Sekar and Randhir, 2007; Syaukat and Fox, 2004).
Generally, the term ‘conjunctive water management’ refers to the joint
management of groundwater and surface water (Murray-Rust and Velde,
1994). This section introduces and expands on the definition of ‘conjunctive
water management’ to capture the concept of managing groundwater and
surface water as a single resource. It recognizes the hydrological and
agronomic link between surface and groundwater and juxtaposes the issues
from the management and governance perspective in the context of mature
large scale irrigation system across two diverse settings in Australia and
Pakistan. Within this context, key issues in the use of the term are associated
with its relationship to:
o Conjunctive use,
o Link between groundwater and surface water,
o Irrigation system management, and
o Interpretation and implications in water governance.
Conjunctive use: It is necessary to distinguish between conjunctive use (of
groundwater and surface water) and conjunctive water management because
conjunctive use has emerged as an on-farm practice based on institutions
which do not recognise hydraulic link between groundwater and surface
water. The term ‘conjunctive use’ refers to the practice of using multiple
resources for individual outcomes, while ‘conjunctive water management’
refers to the management of water resources for public welfare (Murray-
Rust, 2002; Merritt et al., 2005).
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Link between groundwater and surface water: The “conjunctive water
management” refers explicitly to management across hydraulically
connected groundwater and surface water systems (Sahuquillo and Lluria,
2003; Sharda et al., 2006; Sheng, 2005). This definition leaves unclear the
capacity to use the term in reference to realising public goals where there
may be no measurable natural connectivity, such as may be the case in
developing aquifer storage and recovery management options.
Irrigation system management: In this context ‘conjunctive water
management’ refers to managing and accounting for aquifer recharge as a
tool to realise efficiencies across the complementarities of groundwater and
surface water (Blomquist et al., 2004; Diodato and Ceccarelli, 2006). The
reference to complementarities implies utilisation of natural efficiencies
whether they are associated with the link or not.
Interpretation and implications in water governance: The term ‘conjunctive
water management’ has different meanings and interpretation in water
governance literature. In settings with legally enforceable private property
rights in surface and groundwater, the use of both surface and groundwater
for private benefit are sanctioned by the law, and the water is defined a
public good (Colby, 1988; Orr and Colby, 2004). Else the private use of
groundwater is permissible within limits but there are no formal institutional
or legal rules to enforce the property rights (Meinzen-Dick, 1996; Bennett,
2005). Still in other settings where groundwater may be the only resource
available for human needs such as drinking and subsistence production, it
may be regarded as a basic human right and equal access for all may be
sanctioned by local norms and customs (Laamrani et al., 2000).
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1.1.1 Global issues
There was a rapid growth in groundwater use especially since 1950.
Shallow wells and manual lifting devices were in use since the millennia. It
was used mainly for domestic needs and livestock (Shat et al., 2003).
Groundwater wells played little role in agriculture of most ancient
civilisations which grew in river valleys (Mosse, 1997). Studies on
individual ancient wells in the Middle East and North Africa (MENA)
regions speak to the limited scale of its use (Giordano, 2006).
The belt stretching from Spain to Persia to the Punjab was an exception
where wells supported an agrarian society during the medieval era (Hunt
and Hunt, 1976). For example, the Persian Wheel revolutionised the
irrigation agriculture in Mughal India (Mosse, 1997). In British India wells
accounted for about 1/3rd of irrigated land even in 1903 when irrigated was
limited to only 14 percent of cropped area (Shah et al 2003).
With the introduction of the tubewell and diesel and electric pumps in
1970’s, groundwater use soared. Despite this massive growth in
groundwater use in agriculture, global groundwater use is a quarter of total
global water withdrawals. Yet its contribution to agricultural production,
food security and poverty reduction is huge. Nearly half the world’s
population relies on groundwater as a drinking water supply (Shah et al
2006; Qadir et al., 2007; Barber, 2007). Irrigated agriculture remains the
major user of groundwater. The groundwater abstracted for agriculture is
generally of a high quality and often good for human use.
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There is intense competition for high quality water (Kim, 1999). The
demand is huge for shallow groundwater that can be easily accessed at low
cost by irrigators and rural communities for sustaining their livelihoods and
food security (Hussain and Hanjra, 2002; Hussain and Hanjra, 2003;
Hussain et al., 2004b). Over abstraction of groundwater is often noticeable
in major groundwater basins, and this presents a complex challenge for
sustainable resource management (Hussain et al, 2004a). The groundwater
use in agriculture is high and increasing in developing countries, and the
associated challenges of sustainable management are the greatest both
because of the importance of the resource for sustaining livelihoods and
generally poor or often lacking laws and policies to protect its over use
(Shah et al. 2003; Chowdary et al., 2005; Gomann et al., 2005). The key
challenges include:
o Over exploitation of the resource beyond sustainable recharge
limits,
o Deterioration in quality through over use, and pollution from
agriculture and domestic and industrial uses,
o Arsenic poisoning of groundwater,
o Fall in watertable and inefficient use of energy for pumping,
o Use of poor quality groundwater for irrigation and human use and
associated impacts on productivity and human health,
o Instances of land subsidence and salt intrusion,
o Increase in salts in the root zone and impaired drainage due to
falling watertable, and
o Potential for social instability.
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There is a general lack of data on groundwater use. Data on the impact of
agricultural groundwater use on food security and ecological systems are
rare (Nickum, 2003). Groundwater is becoming increasingly important for
agriculture in many parts of the world. For instance, the first wave of
groundwater irrigation began in the US, Spain, Italy and Mexico in early
parts of 1900’s (Garrido et al., 2006; Goesch et al., 2007; Llamas and
MartAnez-Santos, 2005a, 2005b; MacKay, 2006; Narayan et al., 2007). In
South Asia, parts of the North China plains, and of the MENA regions
groundwater use has now nearly peaked, while such revolution is not in
sight in much for the sub-Saharan Africa.
Over the years, conjunctive water management has emerged as a common
wisdom for ensuring plausible consumptive and environmental gains in
irrigated agricultural areas; particularly across parts of Central America,
South America, North America, the Middle East, South Asia, Central Asia
and Australia (O’Mara, 1988; Shah et al., 2003). During the periods of
limited surface water supplies, individual farmers make decisions of using
groundwater (alone or conjunctively with surface water) at farm level
(Qureshi et al., 2004); whereas at irrigation system level, a group of water
users take collective actions to manage the underlying aquifer for ensuring
the sustainable use of available groundwater resource (Pulido-Velazquez et
al., 2004, 2006; Griffin, 2006).
Surface water and groundwater typically have a natural hydrologic
connection, and conjunctive water management tries to utilize this
connection to use the already existing water resources more efficiently but
with convenience (Dudley and Fulton, 2006; Marques, et al., 2005, 2006;
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Hafi, 2003, 2006). In irrigated agricultural areas when quantity or quality of
the primary source of water is of concern (Zhu et al., 2003; Watanabe et al.,
2006); conjunctive water management allows an individual (at farm level)
or a group of water users (at irrigation system level) to sustain (or increase)
crop production or productivity by being able to substitute or supplement
the primary source of water (i.e., surface water) with groundwater. While
conjunctive water management may prove successful for an individual or a
group of water users to cope with immediate changes and shortages, it is
also possible for conjunctive water users to deplete and/or deteriorate the
groundwater aquifer, and to harm other groundwater users who are not
involve in conjunctive water management but are reliant on the same
groundwater aquifer.
1.1.2 Conjunctive water management in an Australian context
Competition of surface water is growing, within and between consumptive
and environmental uses, while its resources are generally limited in
Australia (Elmahdi et al., 2006; Khan, 2007; Khan and Abbas, 2007; Khan
et al., 2006). Groundwater may help fulfilling the gap between supplies and
demands (Hafeez et al., 2007; Khan, 2007b). The allocation of groundwater
entitlements in Australia (that is, the volume of groundwater that irrigators
are entitled to extract in a given year) is based on annual groundwater
sustainable yield, with extractions restricted to long term average recharge
adjusted for discharge to dependent ecosystems. While groundwater
extractions (actual use) in the Murray Darling Basin were only half the
8
groundwater sustainable yield in 2000-01 (1250 gigalitres), increasing
demand for irrigation water combined with restrictions on access to surface
water are likely to lead to the activation of licences that are currently unused
or partially used within groundwater systems (Qureshi et al., 2006).
The goal of water resource management is to maximise the net social
benefits from water use (Khan et al., 2008; Oelmann , 2007). These benefits
from water use are the private and external benefits derived from water use
less any private and external costs. As is the case for many natural
resources, there are external costs associated with groundwater use
(Gonzalez et al., 2006). For example, over pumping may lead to land
subsidence, loss of habitat or ecological diversity, or increased groundwater
contamination through the inability of the resource to dilute and assimilate
contaminants. In the absence of price signals that reflect the external costs
of groundwater use, irrigators will have little or no incentive to reduce
consumption (Serra et al., 2006). As a result governments may intervene to
ensure that at least some of these costs are accounted for by irrigators. Thus,
for ensuring the sustainability of conjunctive water use of surface and
groundwater is an irrigated area, there is a need to understand the economics
of different promising conjunctive water management opportunities.
1.1.3 Conjunctive water management in a Pakistani context
Pakistan is fortunate enough because its soils, topography and climate are
generally suitable for farming but its agriculture sector faces the problem of
scarcity of the irrigation water. The designed cropping intensity of the
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irrigation system was pitched low, in the order of 60-70 percent at the start,
but now the cropping intensity is more than 120 percent, indicating the
increased water demand (Jehangir et al. 2003). This paucity of irrigation
supplies has forced the farmers to use the groundwater to augment their
surface supplies. In most cases, farmers are using groundwater in
conjunction with limited surface water supplies on their farms.
In Pakistan, the literature review shows that all of the previous studies
conducted in the arena of water management reported the management
problems leading to the inefficiencies in irrigation application and reduction
in crop productivity, (Kijne and Velde 1991,2006; Mustafa 1991; Siddiq
1994 and Prathaper et al., 1994). Few of the studies took into consideration
the impact of waterlogging and salinity on productivity at farm level
(Prathaper et al., 1997; Traintafilis et al., 2004; Pannell and Ewing, 2006;
Steppuhn et al., 2005; Hajkowicz et al., 2002, 2005a, 2005b; and Young
Meyer et al., 1996; Sakkhati and Chawala 2002; Feng et al., 2005; John,
2005). None of these studies have taken into consideration the alternate
modes of irrigation and farmer returns under conjunctive water
management.
1.2 Problem statement
The negative effect associated with soil salinisation has been an issue of
irrigated agriculture for centuries. The soil salinity problem exists when the
build up of salts in a crops root zone is significant enough that a loss in crop
yield results. Although, waterlogged and saline soils are found naturally,
10
irrigated areas these salts typically originate from either a saline high
watertable or from salts in the applied water. The agricultural impacts
associated with excess soil salinity levels will be derived from the
corresponding decrease in crop yield. Additional plant symptoms associated
with high salinity levels are similar in appearance to those of drought, such
as wilting (Ayers and Westcot 1985; Brumbelow and Georgakakos 2007).
Conjunctive water use may help to improve water security, sustain
agricultural growth, and achieve higher economic returns; but due to the
increased salinity of irrigation water, long-term environmental sustainability
of irrigated agriculture may prove too questionable if conjunctive water use
is not managed appropriately. Proper accounting of crop salinity tolerance
constraints can help maximise benefits with lower environmental footprints
of agriculture from conjunctive water management under limited water
supplies both at the farm and irrigation system levels.
1.2.1 Research question
The main research question to be answered though this research is:
What is the role of crop salinity tolerance constraints to determine the
promising options of conjunctive water management practices for
irrigation purposes which would result in maximum gross margin
while meeting environmental requirements?
1.2.2 Research objectives
The objectives of this research are to:
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o Determine the possibilities of increasing gross margins by taking
optimal mix of crops under crop salinity tolerance constraints,
o Develop a hydrologic economic model and employ different
mathematical optimisation techniques using the GAMS
environment to determine the ways of best use of conjunctive
water for irrigation,
o Estimate and compare the cost of irrigation and the resulting gross
margins from using surface water, groundwater and conjunctive
water use with respect to optimal crop mix under crop salinity
tolerance constraints, and
o Propose different policy interventions to maximise the socio-
economic and environmental benefits from conjunctive water
management.
1.3 Structure of the thesis
Chapter 1 introduces the conjunctive water management issues at global
level as well as in the context of irrigated agriculture situations in Australia
and Pakistan. Keeping in view the conjunctive water management issues
both at the farm and irrigation system levels, research question and
objectives are also outlined in this chapter. Chapter 2 outlines the lesson
learned from the literature reviewed related to hydrologic-economic
modeling of conjunctive water management in irrigated agricultural areas.
Chapter 3 describes different components of the conjunctive water
management model developed in this research. Modeling testing results are
12
also presented in this chapter. Chapter 4 and 5 present the modeling results
regarding the economics of conjunctive water management under crop
salinity tolerance constraints at the farm level, respectively. Separate case
studies are presented in this chapter for the selected irrigated agricultural
areas from Australia and Pakistan. Chapter 6 introduces the case study of
conjunctive water management at irrigation system level in Coleambally
Irrigation Area, Australia. However, this chapter also presents the cost of
conjunctive water management for a range of water use scenarios for the
case study areas in Australia and Pakistan. Chapter 7 presents conclusions
from this research and a possible way forward to improve the conjunctive
water management understanding and how to further adopt the modeling
tool developed under this research for the benefit of wider farming
community dependent on conjunctive water use in Australia, Pakistan and
elsewhere around the world.
13
CHAPTER TWO
2 Literature Review
This chapter reviews the practices, problems and prospects of conjunctive
water management at both the farm and irrigation system levels in various
irrigated agricultural areas around the world. However, main emphasis is
given to present an overview of the studies presenting hydrologic-economic
modeling of conjunctive water management in irrigated agricultural areas.
2.1 Introduction
Surface water is an increasingly scarce commodity, particularly in arid and
semi-arid regions of the world that cover about one-third of the total globe
land mass. In these regions, groundwater has become an unprecedented
reality, in these regions, to fill the gap between demand and supply of
consumptive and environmental users. Over the years, conjunctive use of
surface water and groundwater has emerged as a common wisdom for
ensuring plausible consumptive and environmental gains in irrigated
agricultural areas; particularly across parts of Central America, South
America, North America, the Middle East, South Asia, Central Asia and
Australia (O’Mara, 1988; Shah et al., 2003).
In practice, the conjunctive water use can be envisioned at farm level where
individuals make decisions of using groundwater to supplement limited
surface water supplies (Qureshi et al., 2004), and at irrigation system level
where water users take collective actions to replenish aquifer storage during
14
high rainfall periods for aquifer recovery to use groundwater during low
rainfall periods (Pulido-Velazquez et al., 2007). Although the scope and
scale differ in these two levels, but both are using surface water and
groundwater together to improve the overall availability and reliability of
water.
Usually, the surface water use has a benefit on the groundwater resource
through recharge (which can replenish aquifer storage, and in most cases
improve groundwater quality), or an adverse effect through contamination
(if the surface water is of poor quality). The groundwater use usually has a
benefit on the surface water resource through baseflow (which sustains
stream flows in low rainfall years, and in some cases improve stream flows
quality), or an adverse effect through stream flows depletion (if the
groundwater pumping induce the increase in seepage from the stream).
More often than not, the bulk of the groundwater use was developed after
most of the surface water use had been established, and if there is an
imbalance between benefits and adverse effects, it tends to favour the
groundwater users at the expense of the surface water supply. It is often the
case that users of one resource are not fully aware of the costs and benefits
of users of other water resource.
Surface water and groundwater typically have a natural hydrologic
connection, and conjunctive water use tries to utilize this connection to use
the already existing water resources more efficiently but with convenience
(Dudley and Fulton, 2006). In irrigated agricultural areas when quantity or
quality of the primary source of water is of concern; conjunctive water use
allows an individual (at farm level) or a group of water users (at irrigation
15
system level) to sustain (or increase) crop production or productivity by
being able to substitute or supplement the primary source of water (i.e.,
surface water) with groundwater. While conjunctive water use may prove
successful for an individual or a group of water users to cope with
immediate changes and shortages, it is also possible for conjunctive water
users to deplete and/or deteriorate the groundwater aquifer, and to harm
other groundwater users who are not involve in conjunctive water use but
are reliant on the same groundwater aquifer.
Conjunctive water management, on the other hand, is the management of
different water resources to create conducive environment for conjunctive
water use by an individual and a group of water users simultaneously, so
that wider ranging goals of equity, production and protection of different
water resources can be accomplished (Murray-Rust, 2002; Marrett, 2005). It
engages the principles of conjunctive water use, where surface water and
groundwater are used in combination to improve water availability,
reliability and convenience at farm level or irrigation system level; and can
be done with and without interventions from some external organisation(s).
and the socio-political climate are also important when implementing
conjunctive water management policies at both the farm and irrigation
system levels.
There clearly is no “one-size-fits-all” approach to conjunctive water
management, but it should include components like monitoring the status of
underlying aquifer at both the farm and irrigation system levels, evaluation
of the monitoring data to develop (or verify) management objectives, and
16
use of monitoring data to establish and enforce the management policies
(Lecina et al., 2005; Theodossiou and Latinopoulos, 2006). Primarily,
conjunctive water management should occur at farm levels where the unique
set of conditions is well understood and where interested water users can
participate and remain informed (Bredehoeft and Young, 1983). Monitoring,
the status of underlying aquifer at both the farm and irrigation system levels,
can help validating the conjunctive water management practices and policies
that are being implemented at these two levels (Shah et al., 2003). An
integrated approach can address these issues by considering these varied
dimensions of conjunctive water management to enhance overall
production, environmental achievements and social benefits for all (Khan et
al., 2007; Khan and Tariq, 2005; Fraiture, 2006).
2.2 Conjunctive water management
Conjunctive water management is often suggested as a means of taking
short-term actions that may come at some cost, in order that the water
supply will be more sustainable and/or more reliable in the long-term. Just
as surface reservoirs were built at some cost in order to improve the
availability of surface water supplies; conjunctive water management
usually includes some use of aquifer storage as a key in the long-term
management of water supplies. The most common objectives are to
physically increase water supplies, to increase supply reliability, or to
improve the flexibility in supply allocation.
17
For conjunctive water management, the cyclic nature of aquifer storage and
recovery is a critical operational consideration. Depending upon the water
cycle processes, three modes of operations can be categorised: short cycle1
annual cycle2 and long cycle3. Usually, long cycle approach is more efficient
and productive when the underlying aquifer is highly permeable, and is
practiced at the irrigation system level. Short cycle and possibly annual
cycle approaches are more appropriate when underlying aquifer is less
permeable, and are practiced at the farm level.
2.2.1 At the irrigation system level
There is no one standard set of issues or needs that motivates conjunctive
water management; this concept can take many forms and have many
objectives at the irrigation system level.
First, a large irrigation system exists where the surface water and
groundwater resources are jointly managed and/or regulated at the irrigation
system level by the public or private institution. In this case, conjunctive
water management typically involve: (i) the recharge of surface water into
the underlying groundwater aquifer and resulting in increase of aquifer
storage, (ii) the groundwater pumping as a supplement to surface water
1 Short cycle may spread over a course of days, weeks or perhaps months. This approach has been used to service peak daily and maximum monthly water demands in some areas. 2 In an annual cyclic approach, surface water is stored during the months when surface water supplies become available, and then recovered during periods of peak demand. In this approach, the aquifer storage and recovery are typically done with the same year to sustain a balance. The approach may or may not be coupled with the operation of surface water resources. 3 In a long cycle approach, the aquifer system is typically recharged during years of abundant surface water availability and recovery is done is a year or consecutive years of drought when there is a surface water shortage.
18
supply or to augment stream flow, and/or (iii) the substitution of one type of
water supply for another to make use of additional water in the future (e.g.,
surplus surface water may be supplied to a user who then foregoes the use
of groundwater in effect the groundwater is left in the underlying aquifer for
future use).
Second, a large irrigation system exists, which is managed and/or regulated
by the public or private institutions; however, there is no legal system in
place for conjunctive water management, and/or there is no public or private
institution with such responsibility. In this case, the aquifer storage is a
coincidental outcome of a surface water irrigation system. An example of
such irrigation systems is Indus Basin Plains in Pakistan.
Third, a large irrigation system exists, which is managed and/or regulated by
the public or private institution; but the management of groundwater is less
extensive and/or engaged in by a different institution. In this case, the
aquifer storage is also a coincidental outcome of a surface water irrigation
system. Examples of such irrigation systems are Coleambally, Murray and
Murrumbidgee irrigation areas in Australia.
2.2.2 At the farm level
Similar to the irrigation system level, there is also no one standard set of
issues or needs that motivates conjunctive water management; this concept
can take many forms and have many objectives at the farm level.
Firstly, a large irrigation system exists, which is managed and/or regulated
by the public or private institution. There are risks associated with uncertain
19
surface water supplies and their fluctuations, especially during low rainfall
years. The underlying aquifer has potential for pumping of groundwater that
is suitable for irrigation purposes. Surface water users, at the farm level,
look for conjunctive water use to increase the reliability of their supplies for
irrigation purposes. The groundwater resource is free (except for physical
supply costs) and is subjected to minimal or no regulations, especially that
limit pumping quantity. Users of groundwater may see no individual
benefits from any efforts to manage the aquifer, unless there are obvious
problems from watertable drawdown. Their motivation for participating for
conjunctive water management often comes from some external regulatory
pressure.
Secondly, a large irrigation system exists, which is managed and/or
regulated by the public or private institution. However, the underlying
aquifer has potential for groundwater pumping but its quality is marginally
suitable for irrigation. Not only, there are risks associated with uncertain
surface water supplies and their fluctuations, but groundwater quality is also
an issue. Surface water users, at the farm level, look for conjunctive water
use to increase the reliability of their supplies, as well as, to make the
quality of water suitable for irrigation purposes. The groundwater resource
is free (except for physical supply costs) and is subjected to minimal or no
regulations, especially that limit pumping quantity and quality. Users of
groundwater may see no individual benefits from any efforts to manage the
aquifer, unless there are obvious problems from watertable drawdown and
groundwater quality impacts. Their motivation for participating for
20
conjunctive water management also comes from some external regulatory
pressure.
2.2.3 Key messages
The key messages from the literature on conjunctive water management at
both the farm and irrigation systems levels, include, but may not be limited
to:
o Primarily, conjunctive water management should occur at farm
levels where the unique set of conditions is well understood and
where interested water users can participate and remain informed,
o Monitoring the status of underlying aquifer at both the farm and
irrigation system levels can help validate the conjunctive water
management practices and policies that are being implemented at
these two levels, and
o There is a need for analytical tools to: (i) quantify the impacts of
conjunctive water management at both the farm and irrigation
system levels, (ii) identify the consequences, particularly
pertaining to the hydrologic-economic aspects, of the specific
practices and policies that are proposed (or being implemented),
and (iii) compare these to the consequences of a future in which
there is no conjunctive water management.
2.3 Hydrologic-economic models for water management
In the past, decision-makers generally ignored the economic considerations
involved in water allocation, water use and water management (Krawczyk
21
and Tidball, 2006; Peterson et al., 2005; Wang et al., 2007). As water
scarcity increases and new sources of supply (e.g. groundwater) become
increasingly costly, decision-makers (including individuals at the farm level
as well as the managers at the irrigation system level) are beginning to
incorporate economic consideration into their decision making process.
Often, the balance between irrigation profitability and water resource
management has been stated as a policy goal but not defined in any
quantitative way (Acreman, 2005; Hellegers, 2006; Holmes et al., 2005;
Janssen and van Ittersum, 2007). This section presents an overview of the
hydrologic-economic modeling studies aimed at conjunctive water
management at the farm and irrigation system levels in various irrigated
agricultural areas around the world.
2.3.1 At the irrigation system level
Conjunctive water use plays an important hydrologic-economic role at
irrigation system level, as it reduces risks associated with uncertain surface
water supplies and their fluctuations. In other words, groundwater brings
stability in water supplies to meet the demands of consumptive and
environmental users. The economic value of the stabilisation role of
groundwater has significant implications for employing, managing and
promoting conjunctive water use, both in developing and developed
countries (Burt, 1964; Dains and Pawar, 1987; Tsur, 1993; FAO, 1994;
Meinzen-Dick, 1996; Hernandez-Mora, et al., 2001). During the drought
years, economic impacts can be minimal on irrigated agriculture if farmers
22
are able to switch from unreliable surface supplies to conjunctive water use
(Gleick and Nash, 1991). In fact, the stabilisation role, associated with the
flexibility of groundwater supplies, can boost agricultural productivity as it
will allow intensification and diversification of agricultural production in
otherwise inflexible surface-irrigation schemes. The stabilisation role of
groundwater is even important, through higher yields, in normal water years
(Tsur, 1990).
Lefkoff (1990) constructed a model of an irrigated, saline stream aquifer
system to simulate economic, agronomic, and hydrologic process. The
model is used to examine the effect of crop-mixing strategies on long term
profits. The hydrologic component of the model, which uses regression
equations to simulate salt transport, was verified with a method-of-
characteristics solution. The model was built on assumptions that simplify
the complex interactions between physical processes and human activity
which occur in the Arkansas Valley.
Different approaches have been used to understand hydrologic-economic
role of conjunctive water use at irrigation system level. (Provencher and
Burt, 1994) used the stochastic approaches while evaluating conjunctive
water management for three interrelated aquifers in California. The
conventional stochastic approach becomes infeasible when dealing with
large spatial dimension; however, this was not the case with the use of
Monte Carlo and Taylor series approximations. Results indicated that both
approaches perform well, providing almost identical estimates of the
optimal pumping policy for maximising hydrologic-economic benefits from
the three interrelated aquifers in California. The Taylor series approximation
23
was found to be particularly promising to decision-makers, because it is
user-friendly and is much less computer-intensive as compared to Monto
Carlo approach; all that is required is a software package (like GAMS)
capable of solving a set of nonlinear equations.
Belaineh et al. (1999) presented a linear programming-based
simulation/optimisation model, which integrates linear reservoir operation
rules along with the detailed stream aquifer system flows, conjunctive use of
surface and groundwater and delivery to water users via branching canals.
Groundwater flow was simulated using the MODFLOW program, which
solves the quasi three-dimensional groundwater flow equations.
Cai (2003) developed an integrated hydrologic-agronomic-economic model
in the context of a river basin in which irrigation is the dominant water use
and irrigation-induced salinity presents a major environmental problem. The
model is applied to problems of water management in the Syr Darya River
basin in Central Asia, providing environmental and economic information
If DIFRC,S ≤ 0, DIFRC,S = 0, and if DIFRC,S ≥ 1, DIFRC,S = 1
Where,
WEXCESSC,S Water in excess of actual
evapotranspiration (ML/ha)
52
LFRACC,S Leaching fraction for a landuse C on
soil type S during cropping (-)
WAVAILC,S Total water available for a landuse C on
soil type S during cropping (ML/ha)
Note: In this model, groundwater pumping is considered from shallow
watertable aquifer; therefore, GWIRRN is set equal to CGWATER.
SCUFLOW -salt brought into root zone by capillary upflow during fallow,
is estimated as under:
∑=S,C
S,CS,C CGWATER*BUCB*X*SFACTSCUFLOW
(9)
Where,
SCUFLOW Salt brought into root zone by capillary upflow during
fallow (t)
SFACT 0.64 – a factor for converting salt concentration from dS/m
to t/ML
XC,S Area of a landuse C on soil type S (ha)
BUCBC,S Capillary upflow for a landuse C on soil type S during
fallow (ML/ha)
This parameter is estimated as under:
SCS,C BFLOW*BPERIODBUCB =
Where,
BPERIODC Fallow period after each crop (d)
BFLOWS Capillary upflow corresponding to soil
53
type S and depth to the watertable on a
farm during fallow (ML/ha/d)
CGWATER Salt concentration of capillary upflow from shallow
groundwater aquifer at the farm (dS/m)
SRAIN -salt brought onto the farm by rain water, is estimated as under:
( )SFACT*CRAIN*AREA*RAINSRAIN = (10)
Where,
SRAIN Salt brought onto the farm by rain water (t)
RAIN Annual amount of rain water (ML)
AREA Area of the farm (ha)
CRAIN Concentration of rain water (dS/m)
SFACT 0.64 – a factor for converting salt concentration from dS/m
to t/ML
DDSALT1 and DDSALT2 -salt removed with leaching water during
cropping and fallow, respectively, are estimated as under:
∑=S,C
S,CS,CS,C CDWATER*VOLLF*X*SFACT1DDSALT
∑=S,C
S,CS,CS,C CDWATER*BRAIN*X*SFACT2DDSALT
(11)
Where,
DDSALT1 Salt removed with leaching water during cropping (t)
DDSALT2 Salt removed with leaching water during fallow (t)
SFACT 0.64 – a factor for converting salt concentration from dS/m
54
to t/ML
VOLLFC,S Water available for leaching of salt for a landuse C on soil
type S during cropping (ML/ha)
This parameter is estimated as under:
S,CS,CS,C AVAILLF*WAVAILVOLLF =
Where,
WAVAILC,S Total water available for a landuse C on
soil type S during cropping (ML/ha)
AVAILLFC,S Excess water fraction (water in excess
of actual evapotranspiration divided by
total water available for a landuse C on
soil type S during cropping (-)
BRAINC,S Rainfall for a landuse C on soil type S during fallow
(ML/ha)
CDWATERC,S Salt concentration of leaching water to shallow
groundwater aquifer for a landuse C on soil type S (dS/m)
SDSALT -salt removed by surface drainage during cropping, are estimated
as under:
∑ ⎟⎟⎠
⎞⎜⎜⎝
⎛=
S,C S,CS,C
S,CS,C
DSALINITY*PERDRAIN*IRRN*X
*SFACTSDSALT (12)
Where,
SDSALT Salt removed by surface drainage during cropping (t)
SFACT 0.64 – a factor for converting salt concentration from
55
dS/m to t/ML
XC,S Area of a landuse C on soil type S (ha)
IRRNC,S Total irrigation water (ML/ha)
PERDRAINC,S Fraction of total irrigation water that is surface drained for
a landuse C on soil type S during cropping (-)
DSALINITYC,S Salt concentration of surface drainage for a landuse C on
soil type S during cropping (dS/m)
Note: If a farm has a recycling system, SDSALT can be set as zero.
Salinity of leaching water
The salt concentration of leaching water to shallow groundwater aquifer is
estimated under the following conditions:
If water in excess of actual evapotranspiration (WEXCESS) is greater than
or equal to leaching fraction for a landuse C on soil type S during cropping
(LFRAC), then
S,CS,CS,C LFRAC/CWAVAILCDWATER = (13a)
Where,
CDWATERC,S Salt concentration of leaching water to shallow
groundwater aquifer for a landuse C on soil type S during
cropping (dS/m)
CWAVAILC,S Salt concentration of total water available for a landuse C
on soil type S during cropping (dS/m)
LFRACC,S Leaching fraction for a landuse C on soil type S during
cropping (-)
56
If water in excess of actual evapotranspiration is less than leaching fraction
for a landuse C on soil type S during cropping, then the salinity of leaching
water is adjusted in proportion to leaching fraction and amount of total
water available for a landuse C on soil type S. This condition allows salt
build up in the root zone due to inadequate amount of leaching water; and
the resulting equation is given as under:
S,CS,CS,C AVAILLF*CWAVAILCDWATER = (13b)
Where,
CDWATERC,S Salt concentration of leaching water to shallow
groundwater aquifer for a landuse C on soil type S during
cropping (dS/m)
CWAVAILC,S Salt concentration of total water available for a landuse C
on soil type S during cropping (dS/m)
AVAILLFC,S Excess water fraction (water in excess of actual
evapotranspiration divided by total water available for a
landuse C on soil type S during cropping (-)
3.3.4 Constraints on pumping from shallow watertable aquifer
Pumping from shallow watertable aquifer is an option in the model;
however, the model can be run in two modes: pumping or no pumping.
Using pumping constraints, the model calculates the new depth to
watertable. However, in case of no pumping, the model calculates the
volume of groundwater that is required to be pumped to maintain initial
depth to watertable (i.e., to obtain zero net recharge).
57
Under both the modelling mode: pumping or no pumping, the new depth to
water is estimated as under:
WTDWTNDWT ∆−= (14)
Where,
NDWT New depth to watertable (m)
DWT Initial depth to watertable (m)
∆WT Change in depth to watertable (m)
This parameter is estimated as under:
( )( )( ) 10/
AREA*SOILWATERTHETAS/PUMPNRECH
WT⎭⎬⎫
⎩⎨⎧
+−−
=∆
Where,
NRECH Net recharge at the farm (ML)
PUMP In pumping mode, it represents the volume of
pumped groundwater from shallow watertable
aquifer (ML), and
In no pumping mode, it represents the volume
of groundwater that is required to be pumped
(ML) to maintain initial depth to watertable
(i.e., to obtain zero net recharge)
THETAS Weighted average of saturated volumetric soil
water content of the farm (-)
SOILWATER Average volumetric soil water content of the
farm (-)
AREA Total area of the farm (ha)
58
Net recharge at the farm
The amount of net recharge to shallow groundwater aquifer is estimated as
under:
( )AREA*LEAKAGERECHBRECHGNRECH −+= (15)
Where,
NRECH Net recharge at the farm (ML)
RECHG Recharge under a landuse C on soil type S during cropping
(ML)
RECHB Recharge under a landuse C on soil type S during fallow
(ML)
LEAKAGE Amount of groundwater moved to deeper aquifer layers
(ML/ha)
AREA Total area of the farm (ha)
RECHG – recharge under a landuse C on soil type S during cropping is
estimated as under:
∑=S,C
S,CS,C WEXCESS*XRECHG
if WEXCESS ≥ 0 (16a)
∑=S,C
S,CS,C CUCB*XRECHG
if WEXCESS < 0 (16b)
Where,
RECHG Recharge under a landuse C on soil type S during cropping
(ML)
XC,S Area of a landuse C on soil type S (ha)
CUCBC,S Capillary upflow for a landuse C on soil type S during
59
cropping (ML/ha)
WEXCESSC,S Water in excess of actual evapotranspiration (ML/ha)
RECHB – recharge under a landuse C on soil type S during fallow is
estimated as under:
∑ −=S,C
2RECHF1RECHFRECHB
(17)
Where,
RECHB Recharge under a landuse C on soil type S during fallow
(ML)
RECHF1 Rain water during fallow (ML)
This parameter is estimated as under:
( )∑=S,C
S,C BFRAIN*BRAIN*X1RECHF
Where,
RECHF1 Rain water during fallow (ML)
XC,S Area of a landuse C on soil type S (ha)
BRAIN Rain water at the farm during fallow
(ML/ha)
BFRAIN 0.4 – a factor for adjusting rain water at
the farm during fallow (-)
RECHF2 Capillary upflow during fallow (ML)
This parameter is estimated as under:
∑=S,C
S,CS,C BUCB*X2RECHF
Where,
60
RECHF2 Capillary upflow during fallow (ML)
XC,S Area of a landuse C on soil type S (ha)
BUCBC,S Capillary upflow for a landuse C on soil
type S during fallow (ML/ha)
3.3.5 Constraints on net recharge
The amount of net recharge to shallow groundwater aquifer is constrained
by the maximum allowable annual change in depth to watertable, which is
set by the user:
ADWTWT ≤∆
Where,
∆WT Change in depth to watertable (m)
ADWT Maximum allowable annual rise in depth to watertable (m)
3.4 Summary
This study extends previous work of SWAGMAN series models, and
develops a customised version of the SWAGMAN Farm model, which
integrates the Mass and Hoffmann equation in the standard SWAGMAN
version and includes the modeling constraints on area of a landuse, water
allocation, root zone salinity, watertable changes, pumping from shallow
watertable aquifer, and net recharge. This customised version of the
SWAGMAN Farm model enables a more scientific and accurate assessment
of the impact of salinity on crop yield via-a-vis land and water management
strategies to enhance productivity and environmental sustainability.
61
It can be used to: (i) provide farmers with a tool to simulate and assess
various farm cropping scenarios in terms of economic return and
environmental effects, (ii) determine environmentally optimal irrigation
intensity and encourage water use efficiency through water and salinity
auditing in an integrated manner, and (iii) assist irrigation authorities (public
and private) for developing policies to achieve improved economic and
natural resource sustainability.
62
CHAPTER FOUR
4 Conjunctive Water Management at the Farm Level: Case
Studies in Australia
This chapter captures the heterogeneity in the basic resource characteristics
across farms, and modeling its impact on crop mix, yield, and gross returns
from conjunctive water management at farm level for the selected irrigated
agricultural areas from Australia. Depending upon the quality and aquifer
yields, the decision of installing deeper or shallower groundwater bore is
made. For instance, if deep aquifers have better quality (less saline) water
than the shallow aquifers and are high yielding, a deep bore becomes an
attractive option for farmers who want to supplement their existing
irrigation allocation, even though the capital cost is high. The chapter
presents the comparison of crop gross margins at the same farm under
various simulation scenarios to capture the impact of change in water
allocation and related salinity levels on the gross margin.
4.1 Description of the study area
The Coleambally Irrigation area was selected for this research study in
Australia (Figure 4.1). This irrigation area is located in western New South
Wales. It covers about 80,000 ha of irrigated land, practicing conjunctive
use of surface and groundwater for broadacre agriculture. Rice is the
principal crop. Other crops include winter cereals, wheat, maize, soybean,
hay lucerne, canola and barley etc. Irrigation farms within this irrigation
63
area are not identical. They vary in basic resource characteristics such as
size of landholding, mix of soil types, depth to watertable (that is current
impact of salinity and waterlogging), rice quota held (related to property
size and soil type). There will also be variation between farms based on
individual landholder preferences, farming technologies and other factors.
The focus, in these sections, is therefore on capturing the heterogeneity in
the basic resource characteristics across farms, and modeling its impact on
crop mix, yield, and gross returns. In order to capture the impacts of
variation in resource characteristics a pragmatic trade-off was made between
the complexity and difficulty in assembling information across more than
300 farm units in the Coleambally Irrigation area and adequately estimating
the scale impacts on productivity and gross margin.
Figure 4.1 The Coleambally Irrigation Area.
64
In Coleambally Irrigation Area, total average rainfall lies between 400 – 450
mm/year, which can generally be described as a semi-arid climate. Total
rainfall for 2006/07 was 239.5 mm. This figure is 156.9 mm or 40 percent
less than the long term average of 396.4 mm. As displayed in Figure 4.2, in
9 out of 12 months the rainfall was lower than the long term average. Only
in the months of July 2006, February and April 2007 the monthly rainfall
was greater than the long term average. Monthly evapotranspiration figures
for 2006/07 are represented in Figure 4.3. Based on data from CSIRO
Griffith, the total evapotranspiration of 2182 mm is 341mm higher or 18.5
percent higher than the long term average of 1841 mm. Almost every month
of the year, the monthly evapotranspiration exceeded the long term average.
0
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Jun-
07
Rain
fall
(mm
)
2006/07 rainfall Long Term Average
Figure 4.2 Monthly rainfall figures during 2006-07 (AER 2007).
65
0
50
100
150
200
250
300
350
Jul-0
5
Aug
-05
Sep
-05
Oct
-05
Nov
-05
Dec
-05
Jan-
06
Feb-
06
Mar
-06
Apr
-06
May
-06
Jun-
06
Evap
otra
nspi
ratio
n (m
m)
2006/07 Long-term average
Figure 4.3 Monthly evapotranspiration figures during 2006-07 (AER 2007).
Table 4.1 and Table 4.2 outline the different types of land uses and their
respective areas in the CIA over the period of the research.
Table 4.1 Areas (ha) of each crop type irrigated in CIA, and the Kerarbury Channel and Outfall District, and each crop’s relative percentage to total irrigated area 2004 (Coleambally Irrigation Co-Operative Limited 2005).
Table 4.2 Areas (ha) of each crop type irrigated in CIA, and the Kerarbury Channel and Outfall District, and each crop’s relative percentage to total irrigated area 2005 (Coleambally Irrigation Co-Operative Limited 2006).
There were some exceptions about the area where vegetables, oil seed and
millets were grown. Some of the above combinations are effected by soil
type because some Kharif crops were sensitive to soil like rice show good
87
growth in finer soils while light soils are good for cotton. Rabi crops like
wheat and barseem (Rabi Fodder) can survive on wide range of soils. The
model uses the growth period of crops. Regarding the growing period of
crops, (Table 5.2) provides a summary of number of growing days for
specific cropping patterns.
Table 5.2 Number of growing days for particular land uses. Land use Growing Season Growing
period (Days) Bare season Bare periods
(days) Wheat-Rice Jun-Mid May 359 May 15 Sugarcane Annual 365 None None Wheat-Maize Nov-Sept 319 Oct 46 Wheat-Cotton Full Year 365 None None Wheat-Kharif Fodder Nov-Sept 319 Oct 46 Rabi Fodder-Cotton Nov-May 212 Jun-Oct 153 Rabi Fodder-Rice Full Year 365 None None Wheat Nov – Mid May 192 June – Oct 173 Fallow Seasonal 365 None None
Figure 5.2 presents groundwater salinity in Rechna Doab. There are two
distinct zones in the Rechna Doab: (i) the Upper zone with low salinity and
underlain with good quality groundwater; and (ii) the Lower zone with
higher salinity and poor quality groundwater.
88
3150000 3200000 3250000 3300000 3350000 3400000
750000
800000
850000
900000
950000
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
13000
14000
15000
16000
Figure 5.2 Groundwater salinity in Rechna Doab (µS/cm)
5.2 Case studies in conjunctive water management
In the Rechna Doab, surface water allocation is done by weekly rotational
system called Warabandi (Chaudhry and Shah, 2003). The canal water is
normally delivered by turns which start from head of water course and end
at tail. Water supply is thus rotational and proportional but not volumetric.
The way system operates the maximum amount water delivered is about 2/3
of the water allowance. This means that farmer operate under condition of
deficit irrigation. This is why conjunctive use of groundwater is so
important in the system.
Groundwater is widely used in the Doab particularly in the upper and the
middle reaches where groundwater is of good quality. Conjunctive use of
surface water and groundwater is common on medium and large farmers;
small farmers may practice conjunctive use but to a lower extent because of
89
their smaller farm size, high cost of groundwater and infrastructure
constraint as water courses are basically designed for canal water delivery.
Farmers lift groundwater generally using shallow bores or skimming well
technologies. (Qureshi et al., 2004; Kahlown et al., 2005, 2007; Kirsch and
Characklis, 2006). Diesel pump electric engine or tractor may be use for
lifting water.
In order to capture variation in resource allocation across the Rechna Doab,
three representative farms were selected from a data set of actual farms
within the system. One farm each from Upper, Middle and Lower Rechna
Doab was selected (Appendix II). The three representative farms reflect the
variation in soil types and cropping pattern across the system. Small
adjustments were made to individual farms in order to reflect the mix of
different soils and variability in groundwater salinity. This was required for
extrapolation purposes as soil type and salinity plays a significant role on
crop mix and recharge amounts. The physical characteristics for each
representative farm and modelling parameters for salinity sensitivity
analysis are given in (Table 5.3).
Table 5.3 A comparative overview of the modelled farms in Pakistan.
Upper Middle Lower Rainfall (mm) 600 360 211 Allowable rise in groundwater level (m) 0.1 0.1 0.1 Allowable rise in salt concentration. (dS/m) 2.25 2.25 2.25 Price of surface water ($ ML-1) 0.46 0.24 0.3 Price of groundwater ($ ML-1) 3.32 3.42 3.3 Area of farm (ha) 10 10 10 Leakage (mm/year) 20 20 20 Initial depth to watertable (m) 1.5 1.65 1.75 Initial average root zone salinity (dS/m) 1.5 1.5 1.5 Concentration of surface water (dS/m) 0.14 0.45 0.75
90
Concentration of groundwater (dS/m) 0.7 2.5 2 Concentration of watertable in (dS/m) 1.5 5.5 7.5 Surface water allocation per farm (ML) 70 70 70 Groundwater allocation per farm (ML) 0 0 0 Concentration of rain water (dS/m) 0.01 0.01 0.01 Rainfall recycling yes yes yes Pumping from shallow watertable aquifer yes yes yes
The three farms represent the variation in groundwater depth, salinity
concentration of groundwater and concentration of soils in watertable and
concentration of soils in the Upper, Middle and Lower reaches of the
system. For instance, initial watertable depth is 1.5, 1.65, and 1.75 meter in
upper, middle and lower system respectively the concentration of salts in
surface water is 0.14, 0.45 and 0.75 dS/m reflecting that the salt
concentration rises as water moves down the system. The concentration of
salt in groundwater is 0.7, 2.5, and 2 dS/m in the three farm respectively.
The concentration of salts in watertable is 1.5, 5.5 and 7.5 dS/m
respectively.
For Upper Rechna Doab the selected representative farm has a shallower
initial watertable depth and lower concentration of salts surface and
groundwater than the farm selected from the middle and lower part of the
system. For the selected from the middle of the system the values of these
parameters are in the middle ranges compared to farm 1 and farm 3. The
representative farm selected from middle Rechna Doab has high level of
groundwater salinity and surface water salinity and higher concentration of
salt in watertable and a bit more depth of watertable. For the lower Rechna
Doab all salinity related parameter are worse than the representative farm as
explain earlier.
91
5.3 Modeling results and discussion
5.3.1 Upper Rechna Doab
The modelling result for various water allocation levels and water
management system in Upper Rechna Doab is given in Figure 5.3. It shows
that:
o surface water has the highest gross margin per ha
o groundwater has lowest gross margin per ha
o the total gross margin per ha for conjunctive use is in middle
And
o the total gross margin rises as total water allocation increases
o rise in total gross margin slows down for allocation level beyond
60 ML.
These result suggest that farmer with good access to surface water can take
advantage of the groundwater for conjunctive use to earn highest gross
margin.
92
0
50
100
150
200
250
300
0 20 40 60 80Total water allocation (ML)
Gro
ss m
argi
n ($
/ha)
Surface water Groundwater Conjunctive
Figure 5.3 Total gross margin for various water allocation levels and water management system in upper Rechna Doab
5.3.2 Middle Rechna Doab
The modelling result for various water allocation levels and water
management system in Middle Rechna Doab is given in Figure 5.4. It shows
that:
o surface water has highest gross margin per ha
o groundwater has lowest gross margin per ha
o the total gross margin per ha for conjunctive use is in middle
And
o the total gross margin rises as total water allocation increases
o rise in total gross margin begins to fall for allocation level beyond
60 ML.
These result suggest that farmer with good access to surface water can take
advantage of the groundwater for conjunctive use to earn highest gross
93
margin. For water allocation levels beyond 60% the use of groundwater or
conjunctive use does not increase gross margin. This means that their upper
limit for groundwater use is reached.
0
50
100
150
200
250
300
0 20 40 60 80Total water allocation (ML)
Gro
ss m
argi
n ($
/ha)
Surface water Groundwater Conjunctive
Figure 5.4 Total gross margin for various water allocation level and water management systems in the middle Rechna Doab
5.3.3 Lower Rechna Doab
The modelling result for various water allocation levels and water
management system in Middle Rechna Doab is given in Figure 5.5. For the
lower Rechna Doab all salinity related parameter are worse than the
representative farms the upper Rechna Doab areas as explain earlier.
Therefore, the expected gross margin per ha for same allocation level will
be lower. This study result confirms this expectation. Further the result
show that total gross margin per ha is lower for groundwater use only than
surface water use only where as conjunctive use gives a gross margin higher
than groundwater use only.
94
0
50
100
150
200
250
0 20 40 60 80Total water allocation (ML)
Gro
ss m
argi
n ($
/ha)
Surface water Groundwater Conjunctive
Figure 5.5 Total gross margin for various water allocation level and water management systems in the lower Rechna Doab.
5.4 Groundwater salinity impacts
For upper Rechna Doab, farmer can practice conjunctive use to mix canal
water with groundwater in different mixing ratios (Table 5.4). If the farmer
is able to achieve the same composite groundwater salinity, would gross
margin per ha be the same for different mixing ratio? This study result
shows this is not the case (Figure 5.6). Appropriate mixing ratio is required
for good conjunctive use management. When irrigation water is available,
groundwater with high salinity could be used. As irrigation water available
becomes lower such that one moves from left to right on the curve only
lower salinity groundwater could be used. The mixing ratio 1:1 gives a total
gross margin $ 252 /ha. As mixing ratio increases to 2:1 and 3:1 total gross
margin per ha increases due to more use of canal water. As mixing ration
95
changes 1:2 to 1:3 the total gross margin falls because of higher used of
groundwater, even if the target salinity is the same.
This suggests that the gross margin would increase due the dilution effect
and would decrease due to the concentration effect. This is a very strong
conclusion. We suggest that farmer with lowest supply of canal water will
achieve a lower gross margin than may be possible when more canal water
is available and appropriate mixing ratio could achieve. It also means that
where canal water supply is short such as at tail ends and groundwater is a
poor quality the return from conjunctive use will be lower.
Table 5.4 Composite EC of conjunctive water management. Ratio Surface water Groundwater) Surface water Groundwater Conjunctive Composite TGM
EC EC EC
(dS/m) (dS/m (ML) (ML) (ML) (dS/m) ($/ha)
3:1 0.14 1.26 53 18 70 0.420 257
2:1 0.14 0.98 47 23 70 0.420 255
1:1 0.14 0.70 35 35 70 0.420 252
1:2 0.14 0.56 23 47 70 0.420 248
1:3 0.14 0.51 18 53 70 0.420 236
Conjunctive w ater -Electric
225
230
235
240
245
250
255
260
3:1 2:1 1:1 1:2 1:3
Mixing ratio (SW:GW)
Gro
ss M
argi
n ($
/ha)
Figure 5.6 Effect of mixing ratio of surface water and groundwater on the gross margins in upper Rechna Doab.
96
For middle Rechna Doab, farmer can practice conjunctive use to mix canal
water with groundwater in different mixing ratios (Table 5.5). The upper
limit to groundwater use is also clear from the analysis of composite salinity
level and associated gross margin per ha as shown below.
Table 5.5 Composite EC of conjunctive water management. Ratio Surface water Groundwater) Surface water Groundwater Conjunctive Composite TGM
EC EC EC
(dS/m) (dS/m (ML) (ML) (ML) (dS/m) ($/ha)
3:1 0.45 4.55 53 18 70 1.475 225
2:1 0.45 3.53 47 23 70 1.475 223
1:1 0.45 2.50 35 35 70 1.475 220
1:2 0.45 1.99 23 47 70 1.475 216
1:3 0.45 1.82 18 53 70 1.475 214
My result show that when the mixing ratio 1:1 gives a total gross margin of
$ 220 /ha. As mixing ratio increases to 2:1 and 3:1 total gross margin per ha
increases due to more use of canal water. As mixing ration changes 1:2 to
1:3 the total gross margin falls because of higher use of groundwater, even
if the target salinity is the same.
The analysis of irrigation water available and groundwater salinity shown
below suggest that when water supplies are lower only low salinity
groundwater could be used (Figure 5.7). The optimum level of groundwater
salinity for this farm is 2.50 dS/m. For salinity higher than this more canal
water is required for conjunctive use. For highest level canal water
availability it may be possible to use groundwater with salinity level up to 5
dS/m.
97
Conjunctive water -Diesel
208210212214216218220222224226
3:1 2:1 1:1 1:2 1:3
Mixing ratio (SW:GW)
Gro
ss M
argi
n ($
/ha)
Figure 5.7 Effect of mixing ratio of surface water and groundwater on the gross margins in middle Rechna Doab
For lower Rechna Doab, farmer can practice conjunctive use to mix canal
water with groundwater in different mixing ratios (Table 5.6). The results
for the mixing ratios shown below are similar to the previous two farms
although gross margin are lower. This study result show that the mixing
ratio 1:1 gives a total gross margin $ 201 /ha. As mixing ratios increases to
2:1 and 3:1 total gross margin per ha increases due to more use of canal
water. As mixing ratio changes from 1:2 to 1:3 the total gross margin falls
because of higher used of groundwater, even if the target salinity is the
same.
Table 5.6 Composite EC of conjunctive water management. Ratio Surface water Groundwater) Surface water Groundwater Conjunctive Composite TGM
EC EC EC
(dS/m) (dS/m (ML) (ML) (ML) (dS/m) ($/ha)
3:1 0.75 3.25 53 18 70 1.375 206
2:1 0.75 2.63 47 23 70 1.375 204
1:1 0.75 2.00 35 35 70 1.375 201
1:2 0.75 1.69 23 47 70 1.375 197
1:3 0.75 1.58 18 53 70 1.375 196
98
This study results again show that when irrigation water availability is low
only low salinity groundwater could be use for conjunctive use. For
instance, for lower farm the desirable salinity limit is to 2 dS/m, as shown in
Figure 5.8. Beyond this level the gross margin would fall sharply. If more
irrigation become available it may be possible to use this saline groundwater
to achieve same target salinity. This may expand production but will reduce
per ha gross margin.
Conjunctive water -Diesel
190192194196198200202204206208
3:1 2:1 1:1 1:2 1:3
Mixing ratio (SW:GW)
Gro
ss M
argi
n ($
/ha)
Figure 5.8 Effect of mixing ratio of surface water and groundwater on the gross margins in Lower Rechna Doab.
5.5 Summary
In order to capture variation in resource allocation across the Rechna Doab,
three representative farms were selected from a data set of actual farms
within the system. One farm was selected from Upper, Middle and Lower
reaches of the Rechna Doab. These three representative farms reflect the
variation in soil types and cropping pattern across the system. Small
adjustments were made to individual farms in order to reflect the mix of
99
different soils and variability in groundwater salinity. This was required for
extrapolation purposes as soil type and salinity plays a significant role on
crop mix and recharge amounts.
For Upper Rechna Doab the selected representative farm has a shallower
initial watertable depth and lower concentration of salts surface and
groundwater than the farm selected from the middle and lower part of the
system. The representative farm selected from middle Rechna Doab has
high level of groundwater salinity and surface water salinity and higher
concentration of salt in watertable and a bit more depth of watertable. This
suggests that the gross margin per ha would be lower than the previous farm
from the upper Rechna Doab. The comparison of total gross margin across
the upper and lower Rechna Doab shows total gross margin are in fact lower
in the middle Rechna Doab farm and this is the case for all levels of surface
water supply as estimated by the model runs. A comparison of surface water
only and groundwater only shows that total gross margin per ha is lower for
groundwater only case.
For the lower Rechna Doab all salinity related parameter are worse than the
representative farm as explain earlier. Therefore, the expected gross margin
per ha for same allocation level will be lower. My result confirms this
expectation. Further the result show that total gross margin per ha is lower
for groundwater use only than surface water use only where as conjunctive
use gives a gross margin higher than groundwater use only.
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CHAPTER SIX
6 Conjunctive Water Management at the Irrigation System
Level
This chapter first introduces the case study of conjunctive water
management at irrigation system level in Coleambally Irrigation Area using
a ColBore (community bore) and other deep groundwater bores (farmers’
bores). To help select the type of pumping, the cost of pumping is described
for electric and diesel pumps by using a procedure of discounting all the
costs (capital and variable) over the life of tubewell, taking into account the
opportunity cost of investment. This chapter concludes with the cost of
conjunctive water management for a range of water use scenarios for the
case study areas in Australia and Pakistan.
6.1 Case study in Australia
This section presents an overview of the surface water and groundwater
resources in Coleambally Irrigation Area.
6.1.1 Surface water resources
Maximum annual general security allocations since 1982-83 are shown in
Figure 6.1. Since 1994/95 there has been a continual downward trend in
allocations. Reduced allocations over the past ten years have adversely
affected landholders’ capabilities to invest in LMWP options. In 2006/07
214,113.3ML was diverted by CICL. This was 60 percent less than the
101
benchmarked average of 551,477 ML. Annual diversions, shown in Figure
6.2, continued to show a declining trend.
Figure 6.1 Annual general security allocations since 1982/83 (AER 2007).
Figure 6.2 Annual diversion and licensed entitlement (AER 2007).
102
6.1.2 Groundwater resources
During the 1990s, the Murray Darling Basin (MDB) Governments,
including NSW, were encouraging the development and use of groundwater
in the southern MDB on the understanding that it was an underutilised
resource (MDBC, 1998). In the Murrumbidgee Valley, this was evident by
State groundwater allocation announcements between 1991 and 1996 of
150% of annual entitlement (Lawson, 1996). During this time, the NSW
Government was also issuing conjunctive conditions on groundwater
licences as a default (Fullagar et al., 2006, 2007)
The existence of good quality deep groundwater under the CIA had already
been established, not least as the basis of town water supply. It was
proposed the pumping deep aquifers would induce downward leakage. The
associated potential to reduce the shallow groundwater mound in the CIA
that had been created by rice flooding was attractive to both the NSW
Government of the time, and the CIA community.
To test this proposition, a deep bore was constructed in 1988 in the centre of
the CIA, on the intersection of Channels 9 and 9b (Lawson and van der
Lelij, 1992). The location of the ColBore is indicated by a black star in
Figure 6.3. In terms of salt mobilisation, the groundwater from the bore of
about 650 µS/cm is shandied into channel water typically 100-200 µS/cm
(Table 6.1). Table 6.2 presents the monthly groundwater extractions from
ColBore 1994/95 to 2006/07. ColBore originally augmented only Channel
9b flows, with downstream farms subsequently incurring the salt cost of an
activity undertaken for public good.
103
Figure 6.3 Location map of groundwater bores in Coleambally Irrigation Area (CICL, 2006).
Table 6.1 Salinity of groundwater extracted from ColBore- 2004/07 (CICL, 2005-2007)
2006/07 2005/06 2004/05
Average Average Average
Salinity Salinity Salinity
(µS/cm) (µS/cm) (µS/cm)
August 420
September 670
October 612 671
November 574 452
December 578 609 698
January 562 631 698
February 515 669 615
March 507 484
April 551 631
May 579
Average 554.3 606.4 617.5
Pumping tests conducted between 1990 and 1992 showed her drawdown in
the Calivil was evident within a 12 km radius of the bore, and a decline in
watertables was also evident (Lawson and van der Lelij, 1992). However,
104
dry climatic conditions of this period saw watertables decline in control
areas also, and it was not possible to distinguish whether the additional
decline of 0.4-0.5m around ColBore to the bore was appropriately attributed
to the bore or to changes in surrounding land management practices.
Table 6.2 Monthly groundwater extractions from ColBore 1994/95 to 2006/07.