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Review of Recharge Mechanisms for the Great Artesian Basin Andrew L. Herczeg and Andrew J Love November 2007
Report to the Great Artesian Basin Coordinating Committee under the auspices of a Consultancy Agreement: Commonwealth Dept of Environment and Water Resources, Canberra
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2
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Cover Photograph:
From CSIRO Land and Water Image Gallery: www.clw.csiro.au/ImageGallery/File: ASA_STRZ002_011.jpg.
Description: Sunrise on wildflowers in the sand dunes of the Strzelecki Desert near Montecollina, SA.
2004.Photographer: Greg Rinder
© 2006 CSIRO
Water for a Healthy Country report series
ISSN: 1835-095X
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CONTENTS
EXECUTIVE SUMMARY............................................................................................ 6
1. INTRODUCTION................................................................................................ 8
1.1 Scope ..................................................................................................... 8
1.2 Objectives.............................................................................................. 8
1.3 Recharge and sustainable yield .......................................................... 9
2. SITE CHARACTERISTICS.............................................................................. 11
2.1 Western margin................................................................................... 12
2.2 Coonamble Embayment ..................................................................... 17
3. LITERATURE REVIEW OF RECHARGE MECHANISMS .............................. 21
3.1 Overview.............................................................................................. 21
3.2 Comparison of Recharge Techniques .............................................. 22
3.3 Surface Water Techniques................................................................. 24
3.4 Unsaturated zone................................................................................ 26
3.5 Saturated Zone Techniques............................................................... 30
3.6 Groundwater Age of the Great Artesian Basin waters .................... 35
4. REVIEW OF EXISTING RECHARGE STUDIES IN THE GAB........................ 37
4.1. Western Margin (SA & NT)...................................................................... 37
4.2. Coonamble Embayment (NSW).............................................................. 37
5. RECHARGE MECHANISMS IN THE WESTERN GAB AND COONAMBLE
EMBAYMENT .......................................................................................................... 40
5.1 Conceptual models of recharge.............................................................. 40
4
5.2 Diffuse recharge.................................................................................. 41
5.3 Localized Recharge. .......................................................................... 41
5.4 Mountain Block Recharge. ................................................................ 42
5.5 Modern and Palaeo-Recharge in the GAB ....................................... 43
5.6 Model Recharge rates in the Great Artesian Basin......................... 44
6. EVALUATION OF APPROPRIATE TECHNIQUES TO ESTIMATE RECHARGE
IN THE GAB............................................................................................................. 46
7. PROPOSALS FOR ESTIMATING RECHARGE.............................................. 52
7.1 Desktop study ..................................................................................... 52
7.2 Well survey.......................................................................................... 53
7.3 Transects in the unconfined part of the GAB................................... 53
7.4 Unsaturated zone profiles of soil water properties and chloride
mass balance.................................................................................................. 54
7.5 Estimation of direct and localised recharge..................................... 55
8. REFERENCES AND BIBLIOGRAPHY ........................................................... 56
5
LIST OF FIGURES
Figure 1. Delineation of the project areas considered as part of this review. Also shown are the recharge areas of the Great Artesian Basin not investigated in this review (see Kellett, et al., 2003). ................................................. 9
Figure 2. Topography, aquifer outcrop and extent of the artesian region and unconfined/confined boundary for the western margin of the GAB. No data for NT portion for this map........................................................................... 13
Figure 3. Location map of the south west margin of the Great Artesian Basin, showing location of sampling wells along the northern and southern transect as well as the potentiometric contours (denoted as AHD – Australian Height Datum). The dashed line representing the unconfined/confined boundary indicate where the standing water level in the aquifer is below the overlying Bulldog Shale (i.e, unconfined west of the boundary) or above the Shale (east of the boundary). ................................................................................................................................ 14
Figure 5. Land use and tenure for the western margin of the GAB........................................................................ 16
Figure 6. Map showing the inferred recharge zone within the Coonamble Embayment (after DWR as cited in Brownbill, 2000)..................................................................................................................................................... 18
Figure 7. Map showing the geological formations, topography and present day potentiometric head of the Pilliga sandstone within the Coonamble Embayment (after Wolfgang, 2000) .................................................................. 19
Figure 8. Shaded areas show the extent of flowing bores in the NSW portion of the GAB in 1920 and 1995. ..... 20
Figure 9. Stable isotope data plot for an arid region of Australia (Ti-Tree basin, NT) showing the relationship between amount of rainfall and isotopic composition. The extrapolated groundwater trend shows that recharge occurs predominantly from high rainfall events, indicative of monsoonal systems. ............................................... 26
Figure 10. Schematic diagram, showing the hydrological balance for the conceptual, one-dimensional recharge system for using the chloride mass balance technique. ........................................................................................ 28
Figure 11. Schematic diagram showing different soil water chloride profiles under conditions of a fresh water table (a); saline water table (b) and diffusion to a very deep fresh water table (c) (after Phllips, 2000........................... 29
Figure 12. Cumulative soil water profiles for different land elements showing changes in recharge rates where there is a break in slope (after Leaney et al., 1999)............................................................................................... 29
Figure 13. ............................................................................................................................................................. 32
A list of various groundwater dating methods and the approximate time intervals for which they are valid........... 32
Figure 14. Conceptual flow paths under two recharge scenarios (a) constant recharge over the entire landscape and (b) preferential recharge over an unconfined aquifer becoming confined down-gradient. .............................. 33
Figure. 15. Flood map showing boundaries of a major flood in the Macquarie and Castlereagh catchments (after DWR, 1991)........................................................................................................................................................... 38
Figure 16. Diagrammatic representation of recharge process in the Great Artesian Basin (reproduced from Radke et al., 2000)............................................................................................................................................................ 40
Figure 17 Conceptual diagram showing mountain block recharge which is a likely mechanism within the GAB, particularly the Coonamble zone. .......................................................................................................................... 42
Figure 18. Stable isotope data for the western flow systems (data from Love etal., 200; Zhang et al., 2007) and Coonamble Embayment (data from Radke et al., 2000)........................................................................................ 44
LIST OF TABLES
Table 1. Summary of different techniques to estimate recharge. Data complied from review of existing literature as well as author’s knowledge - Note much of the data in this table comes from detailed reviews found in Scanlon and Cook (2004). Note Recharge rates in mm/yr, - Spatial scales in m2 and temporal scale in years unless otherwise specified in the table.............................................................................................................................. 48
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EXECUTIVE SUMMARY
Scope and objectives
The Great Artesian Basin (GAB) covers about one-fifth of the Australian continent and contains about 8.7 x 106
GL of groundwater in the Jurassic sandstone aquifers. Although there is widespread use of many thousands of
artesian bores throughout the GAB, relatively little is known of the water balance, particularly recharge.
The review is provided within the context of a very large aquifer system where recharge rates have varied
considerably over the time scale of development of the aquifer system. The large reservoir of fresh groundwater
has developed during much wetter climatic conditions in the past that those prevailing over the last 10 000 years
or more. There is no consensus that the water balance of the GAB is currently ‘in balance’ – that is that recharge
rates equal total of discharge via natural discharge and pumping or exploitation of artesian wells.
The objectives of this review commissioned by the Commonwealth Dept. of Environment and Water Resources
on behalf of the Great Artesian Basin Coordinating Committee are:
1. To provide a literature review of methods to estimate recharge
2. To develop conceptual models for the recharge mechanisms of the GAB and advise on appropriate
methodologies for the quantification of recharge in the GAB
3. Develop costed recharge investigation projects in the Coonamble Embayment NSW and the western
GAB in SA and NT.
Review of methods to estimate recharge
4. The various methods for recharge estimation that are relevant to semi-arid and arid regions are described.
These include water balance methods, piezometric methods, unsaturated zone and saturated zone
environmental tracers. The most commonly used methods to estimate diffuse recharge in semi-arid
regions is using chloride profiles in the unsaturated zone. The technique is most accurate when surface
runoff is low, and where estimates of long-term chloride deposition from atmospheric aerosols are
available. Methods to estimates of recharge from direct or localized recharge rates rely of both
unsaturated zone and saturated zone water balance and tracer methods and yield recharge rates that are
one to two orders of magnitude greater than the diffuse recharge estimates.
Previous studies in the GAB
A major recharge study was undertaken in the Queensland intake beds of the GAB (Kellett et al.,
2003) where 14 unsaturated zone profiles were collected. Recharge estimates from that study indicated
diffuse recharge rates of 0.03 – 2.4 mm yr-1 and preferred pathway recharge of 0.5 – 28.2 mm yr-1.
7
Western margin (incorporating SA and NT)
The western margin is in the driest portion of the GAB and has relatively low hydraulic gradients. This region
has little development and has predominantly pastoral leases. Saltbush and blue bush with patchy acacia are the
dominant land cover. There have been no specific recharge studies done in this area. However, estimates based
on chloride mass balance in the unconfined aquifers in the SA portion of the western GAB suggest recharge rates
of 0.16 ± 0.08 mm yr-1 (Love et al., 2000).
Coonamble Embayment, NSW
The Coonamble embayment is thought to be an isolated part of the GAB, with discharge and recharge occurring
within the Embayment and little if any connection to the remainder of the GAB outside of NSW. There have
been widely disparate estimates of the water balance of the Pilliga Sandstone aquifer system, with estimates of
recharge ranging over nearly two orders of magnitude. The most recent compilation and assessment given by
Wolfgang (2000) is based predominantly on chloride mass balance estimates and an approximate area of the
recharge zone and provides and estimate of recharge of 970 ML yr-1 (median ~6mm yr-1).
Recharge mechanisms in the GAB
Recharge mechanisms are generally a combination of widespread diffuse (or local) recharge and direct (or
localised) recharge. Recharge is though to occur via direct infiltration to the soil into the outcropping regions of
the Jurassic (J-) aquifers, downward hydraulic movement through aquifers above the J-aquifer where the
hydraulic conditions permit, direct recharge through ephemeral creeks and rivers, and recharge on mountain
block alluvial fan systems, particularly within the Coonamble Embayment. The relative importance of the
different recharge mechanisms will vary from place to place and given the very long residence time of
groundwater within the GAB.
Costed Recharge proposals
A series of recharge investigation proposals are presented in a hierarchical manner. These are as follows: a)
desktop study evaluation and analysis of existing information ($65 000) b) sampling of existing artesian bores
and new nested bores located near to proposed localised recharge sites ($350 000 - $600 000) c) detailed
unsaturated soil profiles and measurement of environmental tracers ($850 000). In additional to these site
specific studies, there would need to be parallel studies that can scale up the point estimates (using remote
sensing and GIS methods) as well as hydrological modelling.
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1. INTRODUCTION
1.1 Scope
Increasing demands on the limited availability of global water supplies has resulted in a dramatic increase in the
amount of studies focused on estimating groundwater recharge (eg., Gee and Hillel, 1988; Allison et al, 1994;
Scanlon et al, 2006), particularly in semi-arid and arid zones. This is largely because surface water resources are
scarce and unpredictable in dry areas and groundwater often provides the only reliable source of water for
consumptive use. In many semi-arid to arid zone aquifer systems around the world the groundwater is very old
and may have been recharged under a different climate than that of the present. As a result these systems contain
“fossil” water and groundwater exploitation may not be indefinitely sustainable under the current recharge
regime.
Whilst there have been some investigations to estimate recharge in the Great Artesian Basin (Radke et al., 2000;
Kellett et al., 2003), there is relatively little information about recharge to the western margin (Love et al., 2000)
nor the NSW portion of the Basin (Wolfgang, 2000; Brownbill, 2000). Increased demands on the GAB resources
through mining and irrigation, and the need to sustain the enterprises that depend on the water as well as protect
groundwater dependent ecosystems, means that a better estimate of recharge is seen as an important component
of sustainable water allocation and use within the GAB as a whole. This is clearly the situation in the western
margin of the GAB where groundwater recharge is estimated to be at least three times greater in the Pleistocene
compared to today (Love at al., 2000). This is also implicitly true for groundwater in the majority of the
Coonamble Embayment in NSW.
The project area for this review, as shown in Figure 1, is the western margin of the Great Artesian Basin,
stretching from near Woomera in South Australia, north, then north-east across the south-east of the Northern
Territory and into south-western Queensland and the Coonamble Embayment within the NSW portion of the
GAB. The recharge zones are those areas where the GAB aquifer either outcrops or where overlying aquifers
have higher head than the main GAB aquifer.
The report is organised according to the activities that are outlined in the project brief. Namely:
5. Literature review of recharge approaches and those studies carried out in the GAB to date;
6. Presentation of appropriate methods for quantification of recharge;
7. Costed proposal for priority recharge sites in NSW and the western GAB;
8. Report on the above activities.
1.2 Objectives
The objectives of this review as defined in the project brief are:
9. To provide conceptual models for the recharge mechanisms of the GAB;
9
10. Advise on appropriate methodologies for the quantification of recharge;
11. Develop costed recharge investigation projects in NSW and the western GAB.
DUBBO
MACKAY
TAMWORTH
GLADSTONE
ROCKHAMPTON
ROMA
MOREE
COBAR
DALBY
MILES
MONTO
BOURKE
NYNGAN
MARREE
CEDUNA
TAROOM
BOULIA
WINTON
IVANHOE
WOOMERA
QUILPIE
BILOELA
EMERALD
MITCHELL
BLACKALL
WINDORAH
WILCANNIA
ST GEORGE
LONGREACH
HUGHENDEN
CUNNAMULLA
INNAMINCKAOODNADATTA
AUGATHELLA
BARCALDINE
BIRDSVILLE
BROKEN HILL
COOBER PEDY
GOONDIWINDI
CHARLEVILLE
PORT AUGUSTA
WHITE CLIFFS
THARGOMINDAH
ALICE SPRINGS
LIGHTNING RIDGE
Figure 1
Legend
Project Areas
Recharge Areas
Great Artesian Basin
Figure 1. Delineation of the project areas considered as part of this review. Also shown are the recharge areas of the Great Artesian Basin not investigated in this review (see Kellett, et al., 2003).
1.3 Recharge and sustainable yield
Estimates of recharge rates are arguably the most difficult component of the water budget to quantify (Scanlon
2004; Scanlon et al., 2006). This is even more so in semi-arid and arid environments where one is often dealing
with low water fluxes that vary considerable over both spatial and temporal scales. Estimation of recharge rates
and identification of the important recharge mechanisms are important for a number of reasons. These include
the following:
12. Recharge rates are often used as a benchmark for determining groundwater allocation volumes, where the
amount of water extracted is determined from a percentage of modern day recharge. Whilst it is
recognised that this policy is flawed, the concept of “safe-yield” determined from recharge rate alone
perpetuates in practice.
13. Following on from the above, there is a need to balance the demands of groundwater pumping whilst
maintaining groundwater dependent ecosystems (such as the GAB mound springs) and therefore
understanding all components of the water balance is required.
10
14. Recharge rates are a critical input to numerical groundwater models that are used for developing
groundwater management policies in both time and space.
Just as important as estimating recharge is the need to predict the impact that groundwater extraction may have
on declining pressures and consequent reduced discharge to GAB Mound Springs. This requires:
Knowledge of magnitude, location and timing of groundwater extraction;
Measurements of the magnitude and location of natural recharge;
Measurement of the magnitude and location of natural discharge from the aquifer;
Determination of the degree to which each natural discharge will be reduced when the system reaches a
new balance, and the timescale over which this will occur.
Very large groundwater resources have usually evolved over thousands to hundreds of thousands of years.
Current recharge rates may be much less than in the past, and the water storage within the aquifer may be a
legacy from higher recharge rates that were prevalent during much wetter periods many tens to hundreds of
thousands of years ago. Discharge, on the other hand, is driven by head gradients, aquifer properties and their
configuration that determine flow rates. The change in discharge rate will rarely be in concert with recharge due
to the lag time (especially in the GAB) because of very large distance and complex flow systems that propagate
changes in rainfall to recharge and then through the aquifer.
Exploitation of such resources will invariably alter the balance between recharge and discharge, by adding a
discharge term and altering the head gradient. By definition, therefore, pumping or intercepting water and
discharging by artesian pressure has no relationship to current recharge rates in terms of maintaining a desired
water level or pressure in any given point. This can be explicitly defined by the water balance expression:
Volume = recharge – discharge = 0 at steady-state
or
Volume = recharge – (discharge + pumping) > 0
It is self evident that there will be a consequent reduction in storage, but the rate of decline will decrease over
time. Further, if exploitation is greater than the recharge rate, then eventually the water will be entirely depleted.
The real limitation, however, will be ingress of poorer quality water from aquitards or other adjacent aquifers, or
a drop in water pressure/level until the cost of pumping is prohibitive. In the case of the GAB, the amount of
water removed annually is a small fraction of total storage.
The total volume of water in the GAB is listed in the GABCC website (see references) as:
Total volume = 64 900 million ML (mega litres) or 6.5 x 1013 m3. Although the uncertainty is not given, one
would expect this number to have an error range of at least 1.5 x 1013 m3.
Estimated annual recharge in the Queensland intake beds of the GAB to the Hutton and Hooray sandstone
11
aquifers is estimated to be 3.8 x 108 m3 yr-1, (Kellett et al., 2003). The amount of recharge to the Cadna-owie
formation is perhaps an additional 5-10% of this number [ibid]..
Total discharge is estimated as 9 ± 1.5 x 108 m3 yr-1, divided equally between natural discharge, by springs and
vertical leakage (4.5 ± 1 x 108 m3 yr-1) and bore discharge (4.5 ± 0.5 x 108 m3 yr-1)(Kellett et al., 2003). Of the
natural discharge, vertical leakage probably accounts for 90% of losses through upward leakage to phreatic
aquifers. Under ‘natural’ conditions, the ratio of storage to total discharge (6.5 x 1013 m3 divided by the natural
annual discharge of 4.5 x 108 m3 yr-1) yields a water residence time of about 1.44 x 105 years for the entire GAB.
Similarly, if we assume that bore discharge is about the same as natural discharge, the ratio of storage to total
discharge (6.5 x 1013 m3 divided by the annual discharge of 9 x 108 m3 yr-1) yields a residence time of about 7.22
x 104 years.
Even if the main pressurized J-K aquifers store 10% of the total water, and they are about 150 million years old,
then at least one thousand pore volumes of water have passed though the basin since deposition of the basin. The
fraction of bore discharge divided by the total storage volume = 7 x 10-6 which means that about 0.0007 percent
of the total storage is exploited every year. While this is a very small fraction of the total resources, the confined
nature of the aquifer results in considerable pressure head decline. Indeed, of 4900 bores that have been installed
since the 1860s, about 25% have ceased to flow (i.e., are now sub-artesian).
The most obvious surface manifestations of GAB artesian water are the more than 600 spring complexes that are
scattered through the Basin (GABCC, 1998). These support a unique flora and fauna in an otherwise arid
landscape. Some of the most notable and unique of these are the so-called mound springs in the SA portion of
the GAB which extend along a SE-NW transect from the edges of Lake Frome, near Innaminka, to the
remarkable Dalhousie Springs, which account for about 40% of all SA spring flow near Oodnadatta. It is
estimated that the springs have decreased in flow by about 30% since development of the basin and some have
dried out completely. In the Coonamble Embayment in NSW, there has been up to a 50 metre pressure head
decline (Brownbill, 2000).
If the maintenance of current or natural spring flows is desired, then the bore discharge rates up-gradient of these
systems need to be reduced, or eliminated, to restore pressure heads. The lag times in transfer of water pressure
through such a large system will be important in managing the resource from the point of view of these fragile
dependent ecosystems.
About 90% of the natural GAB discharge is thought to occur by diffuse upward leakage through the overlying
water tables, and ultimately by evaporation though the soil (GABCC, 1998). The rates of upward leakage
estimated for a portion of the basin in the southern part of Lake Eyre are 3 ± 1 mm yr-1 (Woods, 1990). The
interaction between the upward movement of GAB artesian water, and the overlying aquitards, aquifers and
surface water systems are not well known. There are numerous ephemeral and perennial streams, rivers and
water holes throughout the surface water catchment (e.g. Lake Eyre Basin in SA). The extent to which the GAB
leakage is connected to these is not well known.
2. SITE CHARACTERISTICS
12
2.1 Western margin
Mean annual rainfall in the western margin areas of the GAB is between 170 –220 mm/yr with mean relative
humidity around 40% in the SA portion. The region is relatively flat with gradual increase in elevation towards
the west (Fig. 2) with ephemeral surface drainage toward Lake Eyre to the east. Also shown in Figure 2 are
zones of aquifer outcrop as well as the extent of the artesian area and the approximate unconfined/confined
boundary.
Nomenclature of the main artesian aquifer along the western margin is yet to be resolved. The main aquifers
have been named as various units including the De Souza Sandstone, Algebuckina Formation, Cadna-owie
Formation and Hooray Sandstone. For the purpose of this review we name the main artesian aquifer as the J-K
as it contains units of both Jurassic and Cretaceous age.
The J-K aquifer comprises unconsolidated gravels, sands and silts and consolidated sandstones with inter-bedded
shales and mudstones (Habermehl, 1980; Habermehl & Lau, 1997). The aquifer ranges in thickness from
approximately 250m in SA up to 1,000m in the NT (Love at al., 2000, Matthews, 1997). Salinity of groundwater
varies considerable from 550 mg/L in the Finke River region to >3,500 mg/L along the southwest margin (Radke
et al 2000). The J-K aquifer outcrops in portions of the northwest and southwest of the study area as well as
adjacent to the Proterozoic inlier of the Peake and Dennison Ranges in the central portion of the study area (Fig.
2).
13
Figure 2. Topography, aquifer outcrop and extent of the artesian region and unconfined/confined boundary for the western margin of the GAB. No data for NT portion for this map.
Overlying the J-K is the Bulldog Shale and its equivalent, the Rumbalara Shale, in the NT. These units form a
regional aquitard over much of the region and can reach a maximum thickness of 400 metres. A cross section of
the major units in the SA portion of the GAB is shown in a more detailed review of the geology and
hydrogeological units by Habermehl (1980) and references therein.
14
The potentiometric surface (Fig. 3) indicates that the major direction of groundwater flow in the study area is
towards the south – east and east with hydraulic gradients ranging from 2 x 10-4 to 8 x 10-4. In the western
portion of the study area, the aquifer either outcrops, or is unconfined. Further east, the aquifer is confined by
the overlying Bulldog Shale and eventually becomes artesian. Minor discharge from the system occurs via a
series of springs to the south west of Lake Eyre. These springs are often associated with faulting. The majority of
discharge is by diffuse vertical leakage through the confining bed at the down flow end of the system where the
hydraulic gradient is favourable for upward leakage.
Figure 3. Location map of the south west margin of the Great Artesian Basin, showing location of sampling wells along the northern and southern transect as well as the potentiometric contours (denoted as AHD – Australian Height Datum). The dashed line representing the unconfined/confined boundary indicate where the standing water level in the aquifer is below the overlying Bulldog Shale (i.e, unconfined west of the boundary) or above the Shale (east of the boundary).
The predominant vegetation for the western area is saltbush, blue bush and Acacia (Fig. 4). The land-use in the
recharge zone of SA is a mixture of pastoral leases, Aboriginal freehold and nature conservation park, whilst in
the NT it is mainly pastoral leases and some Aboriginal freehold (Fig. 5).
15
Figure 4. Natural vegetation map for the western margin of the GAB.
16
Figure 5. Land use and tenure for the western margin of the GAB.
17
2.2 Coonamble Embayment
The Coonamble Embayment lies in the NSW portion of the GAB and is located west of the Warrumbungle
mountain range (Fig. 6). The area of the GAB that is within NSW is ~207 000 km2 (~11% of GAB).The general
topography declines from 300m in the eastern portion at the foot of the Warrumbungles to ~125m at Carinda in
the north-west part of the area (Fig. 7). The main aquifer, the Jurassic Pilliga sandstone, outcrops at higher
elevations further to the east (250m to 600m). Most of the surficial cover in the area is classified as
undifferentiated Quaternary cover.
The climate is described by Wolfgang (2000) as sub-humid to semi-arid. Rainfall is ~900mm yr-1 in the SE part
(uplands) to <400 mm yr-1 in the north-west. In general, rainfall is 450 – 550 mm yr -1 throughout most of the
area, dominated slightly by summer rainfall but also with significant winter falls. Rainfall trends show a
markedly drier first half of 20th century compared to the 2nd half of the century as is commonly observed in SE
Australia (Bureau of Meteorology data: http://bom.gov.au). Annual potential evapotranspiration (PET) ranges
from 1300mm in the east to 2000mm in the western area.
The area considered incorporates the Bogan-Macquarie and Castlereagh catchments of northern NSW; part of
the larger Darling Basin. These areas include development for cotton, grazing, and other cropping systems. The
region includes the Ramsar-listed Macquarie marshes. Wolfgang, 2000 describes a conceptual model for
recharge to the this portion of the GAB as via the Pilliga sandstone aquifer along the western slopes of the Great
Dividing Range through alluvial fans on the Warrumbungle Ranges in the south and eastern portions of the
Coonamble Embayment. Groundwater moves in a north and north-westerly direction along a low gradient (Fig.
7), with Darcy flow rates range from 0.1 m/yr to 0.8 m/yr. Discharge is thought to be predominantly within an
area of mound springs, many of which are extinct, located at the western edge of the embayment. It is not clear
whether the mound springs were active prior to development of the basin after the late 1800s. The interaction
between the Pilliga sandstone aquifer and other groundwater and surface water systems is unknown.
The geological model for the GAB system in this area as outlined by Wolfgang (2000) is as follows:
15. The aquifer is within an alluvial fan splaying out from the Warrumbungle Ranges towards the west
16. Recharge is predominantly within the easterly portion of the region
17. The flow regime is isolated from the rest of the GAB
18. Discharge is to the overlying aquifers at the west of the embayment
The commonly expressed view is that the Coonamble Embayment is an isolated part of the GAB. That is,
recharge and discharge occurs within the embayment and little water if any flows outside to the other States
(Brownbill, 2000).
The soils are described by Sleeman and Downes (1950) as brown – reddish-brown surface, of light-medium
texture with red – red-brown subsoil and CaCO3 concretions. They are highly weathered and leached (Taylor,
1994). Natural vegetation in the upper catchment is eucalypt hardwood forests. In lower elevations: Yellow box;
red gum; she-oak and introduced willows (Downes and Sleeman, 1955). Further west is savannah swamp and
some mallee and red gum on the floodplains. Land clearing of native vegetation commenced in late 1880s in the
18
low lying areas immediately west of the Ranges. There has been a significant shift from dryland to irrigation
farming that occurred in the 1960s – 70s. The predominant current land-use is dryland cropping (wheat),
pastures and irrigated cotton and also some oats and barley. The total agricultural area ~ 8,250,000 ha.
Figure 6. Map showing the inferred recharge zone within the Coonamble Embayment (after DWR as cited in Brownbill, 2000).
The first artesian bores were drilled in the late 1880s and a number of weirs were constructed along the
Macquarie River in the 1890s. The early 1900s saw rapid increase in the rate of development. Major land
clearing in the eastern and southern portion may have caused rising water tables and dryland salinity and stream
bank erosion (Wolfgang, 2000).
One of the first major overview papers on the NSW portion of the GAB was published by Abbott (1884). He
showed that the flow systems in the Jurassic aquifers are recharged directly through outcrops in the eastern
highlands of Queensland and flow in a westerly to SW direction. It also showed a distinct hydrochemical
character, with bicarbonate dominated waters in the flow systems emanating from the eastern part of the Basin.
There has been an estimate pressure loss over 80% of the NSW portion of the GAB and now <50% of the total
NSW portion of the GAB has artesian pressures (Brownbill, 2000). Decrease in pressure had already been
noticed in 1893. The pressure head near the recharge zone, west of the Warrumbungle Ranges was ~200m (pre
1910) and had declined to ~160m by the mid 1980s (Fig. 8). In the north-west part of Coonamble Embayment
the pressure head has fallen from 150m to 130m while in the south-eastern the decline is from 230m to 160m.
The greatest rate of change was observed from 1900-1920. There are estimated to be ~6000 bores in the entire
area in both the phreatic and artesian systems (Fig. 8). Mean pressure from the Pilliga Sandstone aquifer had
dropped from 180m to 145m by 1935, followed by a relatively slow decline since then to the present.
The chemical composition of the Pilliga sandstone aquifer is Na+-HCO3- type. This is similar to other eastern
19
margin flow-paths, and salinity ranges from 1000 – 1600 EC (Wolfgang, 2000). Total dissolved solids (TDS)
increase from 500 – 700 mg/L west of Warrumbungle Ranges to higher TDS in the NW. The shallow aquifer
salinity tends to be higher than that of the Pilliga sandstone (Radke et al., 2000).
Figure 7. Map showing the geological formations, topography and present day potentiometric head of the Pilliga sandstone within the Coonamble Embayment (after Wolfgang, 2000)
20
Figure 8. Shaded areas show the extent of flowing bores in the NSW portion of the GAB in 1920 and 1995.
21
3. LITERATURE REVIEW OF RECHARGE MECHANISMS
3.1 Overview
Over the past 20 years there has been a rapid increase in the number of papers on groundwater recharge in the
literature. The need to know recharge rates is driven by such things as the need for improved water resource
management, better defining the extent and transport of groundwater contamination and the safe disposal of
nuclear waste in underground repositories. As a result of these activities there are now text books dedicated to
recharge studies (Simmers 1988 & 1997, Sharma 1989, Lerner et al., 1990, Robbins 1998, Zhang 1998, Hogan
et al., 2004) as well as a number of review articles in the international literature (Scanlon et al., 2002, Scanlon et
al., 2006 and references therein). In the following review we examine the previous literature and its potential
application to the Great Artesian Basin.
Australia has the most variable and unpredictable rainfall pattern of any continent on earth (Pigram 2006). This
large variation of rainfall in both time and space has resulted in groundwater recharge varying temporally and
spatially. This variability is particularly pronounced in the semi-arid and arid regions of the continent. The
development of a number of geochemical and isotopic techniques that attempt to integrate different spatial and
temporal scales (Hogan et al 2004) are often the only reliable techniques in regions where low net water fluxes
dominate.
In this review we firstly examine the background information required to develop a conceptual model of
recharge mechanisms in the study area. This is followed by a brief examination of the water budget equation as it
applies to many recharge studies. We then present a brief overview of environmental tracers as they are widely
applied in all areas of recharge investigations. The review is then organised into surface water, soil water (the
unsaturated zone) and groundwater (the saturated zone). We discuss a variety of both physical and chemical
techniques for estimating recharge. We deliberately place greater emphasis on the chemical and isotopic
approaches as they can integrate over larger scales and are more relevant for the sub-humid to semi-arid regions
of the GAB intake areas.
The first stage of any recharge investigation requires the collection of existing data. This is important for two
primary reasons:
19. To develop an initial conceptual model of recharge process, and
20. Provide a range of what the likely recharge rates might be.
These two factors have important implications for the selection of which recharge techniques should be used in
any study. As discussed by many previous authors, there is a need to have an idea of what the answer may be
before we can design a recharge study. This is critical for the selection of recharge technique. For example, some
techniques, such as artificial tracers, only work well in high rainfall areas; lysimeters, that measure the actual
water movement through a soil profile, are expensive, difficult to construct and require regular field visits for
monitoring and are not considered suitable for remote areas of the GAB. In contrast, environmental tracers are a
more useful technique in arid and semi-arid regions.
22
Background information is used to assess the potential controls on recharge rates and mechanisms. Useful
information to collate includes: topography, geology, geomorphology, soil type, rainfall, evaporation,
transpiration, vegetation, and land-use. The better the conceptual model of the hydrology and hydrogeology in a
region, then the better the accuracy and precision of recharge estimates. Whilst the use of a good
hydrogeological conceptualisation to guide and help the recharge assessment seems obvious, it has been ignored
in many previous studies. Basic hydrogeological data should include: depth to the water table, or hydraulic
head, groundwater chemistry and geological constraints, such as folds and faults. Basic conceptualisations can
then include:, water table and potentiometric surfaces, aquifer type and aquifer geometry. When the existing data
is complied a conceptual hydrogeological model of groundwater recharge can be developed, as well as
preliminary estimates of what the recharge rate may be.
It is important to clarify a number of terms regarding recharge, used in this report:
Infiltration is the amount of water per unit area that enters the soil profile over a given time period.
Deep drainage is the amount of water per unit area that moves vertically downwards below the zone of evapo-
transpiration (or root zone) over a given period of time.
Recharge is the amount of water per unit area that reaches the aquifer over a given period of time.
Diffuse recharge is defined as recharge derived from precipitation that occurs fairly uniformly across the
landscape (Scanlon et al 2002). It is the recharge that enters the water table resulting from deep drainage.
Localised Recharge is the recharge that results from run-off, streams and lakes where water moves laterally to
the point where it recharges. This includes recharge from ephemeral rivers.
Mountain Block Recharge describes the contribution of mountains regions to the recharge of adjacent aquifers
(Wilson and Guan 2004).
3.2 Comparison of Recharge Techniques
3.2.1 Water Balance Techniques
The water budget equation can be used in all recharge studies, whether for surface water, unsaturated or
saturated zones. In its simplest form the water budget equation is expressed as:
inflow = outflow change in storage.
Specifically, in terms of recharge:
ROETPR (1)
23
Where: R = recharge, P = precipitation, ET = evapotranspiration and RO = runoff. The water balance technique
often estimates recharge by the residual difference of the estimates of P, ET and RO. The difficulty of this
approach is that it relies on accurate measurements of the other components in the water budget equation. Some
authors suggest that this difference technique is not particularly useful in semi-arid and arid regions because the
values of recharge would be smaller than the errors associated with measurements of P, ET and RO (Gee and
Hillel 1988, Hendrix and Walker 1997).
Another major limitation of the technique is the temporal scale over which the water balance is applied. If one
uses average annual values of P and ET it is easy to see from Equation 1 that no recharge would occur in the arid
zone as (ET >> P). As a result this approach using large time steps dampens out extreme precipitation events that
may cause recharge. In the arid zone, recharge is most likely to occur from very large events, where P >> E. If
measurements were taken daily, the water budget technique may offer some promise, particularly in zones of
ephemeral recharge from creeks.
3.2.2 Environmental Tracers
A very brief overview of environmental tracers is presented below. The objective here is to provide the reader
with background information before a discussion of the separate recharge techniques for the various hydrological
zones. Environmental tracers are “natural, or anthropogenic, compounds, or isotopes, that are widely distributed
in the near-surface environment of the Earth, such that variations in their abundances can be used to determine
pathways and timescales of environmental processes” (Cook and Bohlke, 2000).
Fundamental to recharge studies is an appreciation of the age of groundwaters that can then constrain the rate of
recharge. There are a number of environmental tracers that can be used as tools to estimate the age of water in
the unsaturated and saturated zones. These include:
a) Radioactive tracers;
b) Accumulating tracers; and,
c) Event Markers.
Radioactive tracers are naturally-occurring radioactive tracers have been used extensively over the past 30 years
to provide information on residence time and groundwater flow rates. The groundwater age is calculated by the
expression:
0
1 lnC
Ct
(2)
where t = time since water entered the saturated zone, C and C0 are the measured and initial concentration of the
radioactive isotope and is the decay constant. The most commonly used tracers in regional scale groundwater
systems are 14C with a half life of 5,730 years and 36Cl with a half life of 301,000 years.
24
Accumulating tracers increase in concentrations with increasing residence times. The most commonly used
accumulating tracer is 4He which has a very low initial concentration that increases with time due to release of 4He by alpha decay of uranium and thorium decay-series isotopes within the aquifer matrix. Often such a tracer
provides only semi–quantitative information on the groundwater residence time.
In rare cases, chemical species can be used as accumulating tracers if their accumulation rates in the sub-surface
can be quantified. Recently, Purtschert et al (2007) have applied the in-situ, sub-surface production rate of 39Ar
to estimate recharge rates in fractured rock aquifers in the Clare Valley of South Australia.
Event markers are elevated levels of a particular tracers injected into the environment as a result of
anthropogenic activities in the past. Such activities include contaminant spills or atmospheric nuclear weapons
testing. Commonly used event makers include 36Cl, 3H, 14C and chlorofluorocarbons (CFCs). The presence of an
event marker in a parcel of water indicates that it was recharged at a particular time. Event markers can be used
both in unsaturated and saturated zones and have been used to estimate recharge rates during the last 50 years.
Conservative tracers such as Cl- and Br- have wide application in the hydrological field. Many studies have used
Cl- to estimate recharge (see below). Bromide is often used as an applied tracer in recharge studies.
3.3 Surface Water Techniques
The role that surface water plays in groundwater recharge depends upon the interconnection between the two
water bodies. Throughout most of the GAB, the potentiometric head is upwards and as a result no recharge from
the surface water bodies is possible. There is the potential, however, for groundwater recharge from surface
water bodies in the recharge zones of the GAB, where the aquifer is outcropping, or unconfined. A number of
ephemeral, braided streams cross the potential recharge zones of both the Western Margin and Coonamble
Embayment.
3.3.1 Estimation of ephemeral stream recharge
Historically, ephemeral recharge has been estimated from channel loss between gauging stations. This approach,
however, does not allow for the uptake of water by riparian vegetation. The recharge rate, R, for a channel reach
can be estimated using the water budget equation. This approach assumes that recharge equals channel
transmission losses less the abstraction of water from evaporation in the channel and transpiration (Goodrich et
al 2004):
STEPQQQR Li 1 (3)
where, Qi and Q1 are measured flow at gauging stations at the inflow and outflow of the reach; QL is lateral,
overland and tributary flow; P is direct precipitation; E is evaporation; T is transpiration and S is chance in
storage.
The importance of ephemeral stream recharge on the basin scale depends upon the size of the landscape
occupied by streams. For example, if we assume that diffuse recharge is 10 mm/y, and that the stream recharge
25
features cover 1% of land area, then to be comparable, recharge through stream bed features must be 1,000
mm/yr. Alternatively, if the streams occupy 10% of the landscape then recharge through the stream bed must be
100 mm/yr. As is evident from the above example, the two important factors for basin scale recharge from
streams are the amount of diffuse recharge and the geographical size of the streams in comparison to the zones of
diffuse recharge.
3.3.2 Hydraulic and Geophysical approach.
Another method to estimate groundwater recharge under localized zones such as ephemeral creeks is to estimate
recharge from the shape of any mounding of the water table. This is a useful approach in areas where there is a
lack of well coverage. A number of techniques have been applied in the desert environments of the southwest
USA, including: gravity, electromagnetic induction and ground penetrating radar (Hogan et al 2004). Electrical
topographic methods have the advantage of being able to trace water movement in 2 and 3 dimensions and
maybe very useful for evaluating focused recharge beneath ephemeral streams. If a groundwater mound can be
established, an estimate of recharge can be achieved by using the groundwater mound equation of Hantush
(1967).
3.3.3 Stable Isotopes
Natural variations in the stable isotopes of the water molecule (18O/16O and 2H/1H) can provide valuable
information on the source and history of water in the hydrologic cycle (Clark and Fritz, 1997). The primary
advantage of stable isotopes is that as part of the water molecule they trace the actual movement of water. In
contrast, when one uses a solute to infer water transport one assumes that the tracers either moves with the water,
or corrections need to be made for dispersion, diffusion and any chemical interactions.
Although rarely used to estimate recharge rates, the stable isotopes of water have been shown to be particularly
useful in distinguishing different recharge mechanisms in arid and semi-arid zones (Coplen et al., 2000 and
references therein). Both unsaturated and saturated water in arid zones often display enrichment in stable
isotopes of the water molecule due to evaporation in the upper few meters of the soil zone. These will tend to
plot to the right of a Meteoric Water Line (MWL) on a stable isotope plot, indicating evaporation. In contrast,
localised recharge from flood events through ephemeral streams often has a more depleted signature indicative
of more direct recharge as it by-passes the zone of evaporation. These waters will not only be more depleted, but
will plot closer to the MWL. In ideal situations the relative proportion of localised recharge versus diffuse
recharge can be determined by simple mixing calculations.
An example of stable isotope data in an arid zone groundwater system in central Australia (Fig. 9) shows that the
groundwaters tend to plot to the right of the local meteoric water line (in this case represented by local rainfall).
Evapo-transpiration in the upper part of the soil zone causes this trend and is typical of groundwater in semi-arid
and arid zones. The stable isotope compositions also tend to be considerably more negative than that of mean
annual rainfall and indicate recharge is primarily from episodic high rainfall events as a result of summer
dominated tropical storms. These data could also represent rainfall from past cooler and wetter climates, such
data, however, would tend to plot closer to the meteoric water line. This will be discussed for the GAB system in
sections 4.1 and 4.2.
26
Figure 9. Stable isotope data plot for an arid region of Australia (Ti-Tree basin, NT) showing the relationship between amount of rainfall and isotopic composition. The extrapolated groundwater trend shows that recharge occurs predominantly from high rainfall events, indicative of monsoonal systems (Harrington, 1997).
3.4 Unsaturated zone
3.4.1 Darcy’s law
Unsaturated zone techniques to estimate recharge rates are often used where the unsaturated zone is relatively
thick, such as in arid and semi-arid regions. Detailed reviews of unsaturated zone techniques can be found in Gee
and Hillel (1988), Zhang (1998), Scanlon et al (1997; 2006). In essence, unsaturated zone techniques estimate
the drainage rate below the root zone and provide a point estimate of recharge. Unsaturated techniques can also
provide information on temporal variability. They generally do not provide detailed information on spatial
variability.
It is important to note that unsaturated techniques actually measure deep drainage and not recharge. It is often
assumed that this deep drainage will reach the water table and become recharge. This assumes vertical flow only
beneath the root zone. This assumption is not always correct, however, due to heterogeneity in the unsaturated
zone. For example, a sandy horizon overlying a low permeability clay has the potential to perch water and result
in lateral flow.
Physical methods for estimating water fluxes in semi–arid and arid zones are generally very difficult to apply
because water fluxes are very low. Chemical tracers have an advantage over physical methods as they can
provide information on both current and historical recharge rates. Both physical and chemical techniques are
used for determining soil water velocities, which can then be related to drainage rates and, ultimately, recharge
rates. A number of unsaturated zone techniques, such as lysimeters and applied tracers, have limited application
27
to the GAB and are not discussed here (see Scanlon et al 1999 and Scanlon 2004 for detailed reviews).
Darcy’s Law can be used to calculate recharge, R, in the unsaturated zone using the following (Scanlon 2004):
1
dz
dhKzh
dz
dK
dz
dHKR
(4)
Where K() is the unsaturated hydraulic conductivity at the ambient water content , H is the total head, h is the
matric pressure head and z is the elevation. In thick, unsaturated zones with a porous medium the matric
pressure gradient is often close to zero and drainage is driven by gravity (Scanlon, 2004). Under this scenario the
total head gradient can be assumed to be unity, negating the need to measure the matric pressure gradient. One of
the main limitations to using Darcy’s Law in the unsaturated zone, however, is that it requires accurate
measurements of unsaturated hydraulic conductivity. Scanlon (2004) concluded that considering problems with
sample disturbance, drying and spatial variability the method has a limited applicability to recharge rates of 20
mm/yr or higher. The recharge rates for much of the GAB intake areas are estimated to be <20 mm/yr, therefore
this technique has limited use here.
3.4.2 Chloride Mass Balance
The Chloride Mass Balance (CMB) technique has been used extensively over the past 40 years to estimate
recharge rates in both humid and arid climates (Fig. 10). The technique is suitable for both the unsaturated and
saturated zones (see Scanlon et al, 1997; Herczeg and Edmunds, 2000 for comprehensive review). As water,
containing chloride, enters the soil zone, water is lost by transpiration from plants and evaporation leaving
residual Cl- in the soil water. Thus, the concentration of Cl- is proportional to the amount of water removed.
Below the root zone the chloride signature is transported to the water table. In humid regions, with high
downward water fluxes, the Cl- concentration is relatively constant below the root zone. In contrast in arid zones
with low water fluxes the Cl- concentration below the root zone will be balanced by the downward moving Cl- in
the soil water against any diffusive flux across the unsaturated/ saturated boundary.
In the following we combine the basic water balance equation (Equation 5) to include the solute Cl- (Equation
6):
QREP (5)
rivswpptn QClRClEClPCl (6)
Clpptn, Clsw and Clro refer to Cl concentration in precipitation, soil water and runoff respectively and Q is runoff.
Here we assume that Cl- is neither gained, nor lost, from weathering or anthropogenic impacts. Note that this
equation applies equally to the unsaturated and saturated zones. In the saturated zone the chloride concentration
in soil water is replaced by Cl- concentration in groundwater at the top of the water table.
In many arid areas surface runoff, Q, is not significant and, assuming there are no other source or sinks of Cl-,
then recharge maybe estimated from Equation 7:
28
sw
pptn
Cl
ClPR
(7)
rainfall
evaporation
recharge
transpiration
run off
Modified from Val SnowModified from Val Snow
Natural water balance
Figure 10. Schematic diagram, showing the hydrological balance for the conceptual, one-dimensional recharge system for using the chloride mass balance technique.
This equation is applicable to both the unsaturated and saturated zones. In the unsaturated zone, however, we
measure deep drainage and not recharge. This technique has been used extensively in semi-arid and arid zones
because it can measure recharge at low water fluxes. Water fluxes as low as 0.05 mm/yr have been measured in
the arid zone of Australia (Allison and Hughes 1983, Cook et al 1994).
If the interest is in establishing a chronological history of recharge, then in addition to measuring Cl-
concentrations, measurements of 36Cl and 2H and 18O should be obtained. CMB in the unsaturated zone
provides point estimates of recharge, but over large temporal scales. Examples of ideal chloride profiles, shown
in Fig. 11, are for situations of varying groundwater chloride concentration and depth to water table. One can
also use the data to evaluate changes in recharge rate with time if cumulative [Cl-] and water content are plotted
(Fig. 12).
29
Figure 11. Schematic diagram showing different soil water chloride profiles under conditions of a fresh water table (a); saline water table (b) and diffusion to a very deep fresh water table (c) (after Phllips, 2000).
Figure 12. Cumulative soil water profiles for different land elements showing changes in recharge rates where there is a break in slope (after Leaney et al., 1999).
3.4.3 Event Markers
The most commonly used event markers in the unsaturated zone are 3H and 36Cl. Chlorine-36 has a half-life of
301,000 years and is primarily produced in the atmosphere via cosmic ray spallation of argon-40. Tritium (3H) is
the radioactive isotope of hydrogen, has a half-life of 12.43 years, and is also produced in the atmosphere, by the
30
bombardment of nitrogen by the flux of neutrons in cosmic radiations. In the 1950s and 1960s thermonuclear
testing caused a large increase in the concentration of 3H and 36Cl in precipitation. This has resulted in these
isotopes being excellent markers in the hydrological cycle for recharge events in the last 50 years. The peak
concentration of these event markers in the unsaturated zone can be used to estimate groundwater from Equation
8:
t
zvR
(8)
where v is the tracer velocity, z is the depth to the peak of the tracer concentration, t is time difference
between the tracer the peak of the tracer fallout in the atmosphere and the time of sampling, and is the average
water content above the tracer peak.
A limitation to this technique in semi arid zones is potential low water fluxes, which can result in the peak
concentrations not being transported past the root zone. This technique, however, may have applications in zones
of localised recharge in arid zones due to potentially larger water fluxes.
3.5 Saturated Zone Techniques
3.5.1 Darcy’s Law
Many of the unsaturated zone techniques provide only point estimates of recharge. In contrast, saturated
techniques have the potential to integrate over much larger spatial scales. Furthermore, saturated techniques have
the advantage in that we are measuring water that has actually reached the water table. Darcy’s Law can be used
to estimate groundwater recharge by relating the groundwater flow rate through a cross-sectional area of the
aquifer to the surface area that contributes to recharge. Darcy’s Law (Equation 4, above) states that, in saturated
media, the groundwater flux (q) is equal to the product of hydraulic conductivity (K) and hydraulic gradient (i):
Kiq (9)
The groundwater flux, q, can then be converted to a recharge rate from the following:
AS
qAR
(10)
where, R = recharge, q = groundwater flux A = cross sectional area of aquifer, and SA = surface area that
contributes to flow. The method assumes steady flow with minimal pumping. The cross-sectional area should be
aligned such that the groundwater flow direction is normal to the water table contours. The method suffers
significantly from reliable estimates of hydraulic conductivity, which can vary by several orders of magnitude.
Considering the natural variation in hydraulic conductivity and the difficulty in scaling up regional scale values
of hydraulic conductivity, the method at best would provide order of magnitude estimates of recharge.
3.5.2 Groundwater Hydrographs
Variations in groundwater hydrographs can provide valuable information on the timing and amount of recharge
31
(see Healey and Cook (2002) for a comprehensive review). The rise of groundwater levels in an unconfined
aquifer is an indication of a recharge event. Often referred to as the water table fluctuation method (WTF)
recharge can be estimated from Equation 11:
t
hSR Y
(11)
where Sy is the specific yield and h/t is the change in height of the water table over a certain period of time.
The largest uncertainty is the estimation of specific yield, which can vary considerably and is difficult to
measure. Many previous applications of the technique use specific yield values for various lithologies from text
book examples. Another disadvantage of the method is that it cannot account for lateral flow. Under certain
situations, however, groundwater hydrographs can provide a rapid estimate of recharge before applying more
sophisticated technology. This method has the advantage that it actually estimates change in recharge over time
of the hydrograph record. As the method represents an integration of deep drainage by porous media and by-pass
flow it can integrate over large spatial scales. This method is best applied to shallow water tables that display
sharp water-level rises and declines. In areas of low water fluxes and a deep water table, there is a long delay, up
to 105 years, for current soil water infiltration to reach the water table. Under these situations the hydrograph
technique is not very useful.
3.5.3 Groundwater age dating
Age dating of groundwater can be used for determining groundwater velocities, which in certain situations can
sometimes be related to recharge rates. The main advantage of using groundwater dating techniques is that they
can provide information about the groundwater systems over time scales ranging from 10 to > 500,000 years.
This is a powerful advantage over hydraulic techniques that provides information on the potential groundwater
flow regime operating today and does not provide any temporal information. Furthermore, groundwater ages
have the advantage of not relying on estimates of hydraulic conductivity that can vary by many orders of
magnitudes in groundwater systems. The following section summarizes the work of Vogel (1967), Appelo and
Postma (1993) and Cook and Bohlke (1999). The principle of age dating relies on using a suitable radionuclide
or anthropogenic tracer that has a half-life (or accumulation time) commensurate with the groundwater residence
time (Fig. 13).
32
Figure 13. A list of various groundwater dating methods and the approximate time intervals for which they are valid.
3.5.4 Unconfined aquifers
In the following we consider a unconfined aquifer receiving uniform recharge, R, with constant thickness, H,
constant porosity, , and uniform horizontal velocity with depth, bounded below by an impermeable aquiclude
(Figure 14). The vertical and horizontal distances travelled by a parcel of water entering the aquifer are related
by Equation 12:
zH
H
x
x
o
(12)
Where, xo is the location where the water parcel enters the unconfined aquifer, x is the horizontal distance and z
is the vertical distance of travel.
time (years)
10-1 100 101 102 103 104 105 106 107 108
3He/3H
226Ra14C
36Clfreons, SF6
85Kr
3H
39Ar
81Kr4He
40Ar/36Ar
33
Figure 14. Conceptual flow paths under two recharge scenarios (a) constant recharge over the entire landscape and (b) preferential recharge over an unconfined aquifer becoming confined down-gradient.
The age of the groundwater, t, can be calculated from the following
zH
H
R
Ht ln
(13)
In this case the groundwater age, t, will increase from zero at the water table (z = 0) to infinite at the base of the
aquifer (z = H). The vertical component of groundwater velocity will decrease from R/ at the water table (z = 0)
to zero at the base of the aquifer. It is interesting to note that in this simplified system that the groundwater
isochrones are horizontal.
If the groundwater age is measured at a discrete depth then the recharge rate can be estimated from,
zH
H
t
HR ln
(14)
In relatively thick, unconfined aquifers, and if the groundwater is sampled close to the water table, such that z/H
is small, then the horizontal component of groundwater flow will be small and the recharge rate can be estimated
from the following expression.
t
zR
(15)
3.5.5 Confined Aquifers
Here we build upon the previous model and consider an unconfined aquifer that becomes confined down
gradient (Fig. 14B). In the unconfined portion the aquifer receives uniform recharge, R, and receives no recharge
in the confined portion of the aquifer. The aquifer is of constant thickness, H, and constant porosity, , and
bounded below by an impermeable aquiclude. In the confined portion, the aquifer is also bounded above by an
34
impermeable aquiclude. In this scenario, the groundwater flow lines will be convex downward, as in the
unconfined example above, until they reach the unconfined – confined boundary, where the flow lines will
become horizontal. The isochrones in the unconfined portion of the aquifer will be constant and horizontal. In
the confined portion, however, the isochrones will become concave upwards towards the top aquiclude
boundary. In this situation groundwater ages will increase with distance along the flowline. If samples are
obtained from the same depth, then the horizontal groundwater flow velocity can be determined from
groundwater ages between two wells along a flow path.
12
12
tt
xxvh
(6)
Where vh = horizontal velocity, x2 –x1 is the horizontal distance between the wells and t2 – t1 is the age difference
between the two wells. As discussed by Cook and Bohlke (2000), the horizontal velocity is directly proportional
to the length of the recharge area and the recharge rate, and inversely proportional to the height and porosity of
the aquifer such that:
x
HhR v
(17)
The advantage of calculating recharge rates from horizontal flow velocities is that there is less reliance on
obtaining an accurate initial isotopic value of the recharging water.
3.5.6 Chloride Mass Balance
The principles of the chloride mass balance approach were discussed previously. As with the unsaturated zone,
CMB can be used to calculate recharge from Equation 7. Eriksson & Khunakasem (1969) was the first published
study to use chloride mass balance to calculate recharge to groundwater, from the coastal plain of Israel. Since
that time this method was had wide application in groundwater studies in both humid and arid zones (See
Scanlon and Cook 2002 and reference therein).
The main advantage of using CMB in the saturated zone is that recharge can be estimated over larger spatial
scales. Furthermore, if water residence times are known then recharge can be determined over larger temporal
scales. A potential limitation of using this technique are additional sources of chloride in the subsurface,
resulting in minimum calculated recharge rates. This chloride may come from diffusion of chloride through
aquitards, or the addition of Cl- from the dissolution of halite. Dissolution of halite can be easily checked by
using the ratio of bromide to chloride. Bromide is sparingly incorporated into halite minerals during
precipitation; groundwater that has dissolved halite will evolve to a very low bromide to chloride ratio as
dissolution progresses.
Cook and Bohlke (2000) have shown that for unconfined aquifers, if the Cl- concentrations change along the
direction of groundwater flow and if they can be attributed to changes in the concentration of recharge, then
recharge can be estimated from the following:
x
Hv
c
cc
c
PCR P
2
12
2
(18)
35
In the above, R is the recharge rate; Cp is the concentration of Cl- in precipitation; P is the annual precipitation; c1
and c2 are the Cl- concentrations measured from two wells along a flow line separated by a distance x; v is the
mean groundwater velocity between these two points; H is the aquifer thickness and is the porosity.
3.5.7 Modelling
Theoretically, groundwater modelling can be used to estimate recharge over a wide range of spatial and temporal
scales. Application of numerical models to recharge estimation, however, should be treated with extreme
caution. If the prime objective of an investigation is to estimate recharge it is far more accurate to measure
recharge directly through other methods than to estimate it indirectly from modelling applications.
In principal, groundwater models use an inversion approach to back calculate recharge. Model calibration using
hydraulic head data alone provides an estimate of the ratio of recharge to hydraulic conductivity. Considering the
very large variation in hydraulic conductivity in the sub surface this approach is not recommended. It has been
shown, however, that the use of groundwater age dating incorporated into models can better constrain the
recharge value (Sanford et al., 2004).
3.6 Groundwater Age of the Great Artesian Basin waters
Calculations of groundwater age in the GAB, and its conversion to groundwater flow rates is important for a
number of reasons including, but not limited to:
(1) It provides the basis of a conceptual model of system behaviour, and horizontal flow rates should be
compared to recharge and discharge rates to determine the relative water budget of the GAB; and (2)
Groundwater flow rates provide critical input into numerical models.
Estimating groundwater age in such a large system as the GAB is not straightforward as there is often a myriad
of assumptions required, no matter what approach is used. The two most common techniques to estimate
groundwater age are the application of Darcy’s Law and groundwater dating techniques using natural
environmental tracers. Darcy’s Law requires estimates of both hydraulic conductivity and hydraulic gradient.
Estimates of hydraulic conductivity are difficult due to a number of reasons including: sparse array of wells;
scaling up to regional values and corrections for the affects of partial penetration. Furthermore, estimate of the
potentiometric surface only represents hydraulic conditions today and does not reflect the groundwater flow
system under past climatic conditions where it is likely that the majority of recharged occurred.
There are only two suitable natural radionuclides for dating old groundwater in a system the size of the GAB: 81Kr and 36Cl. 81Kr has a half-life of 2.3 x 105 yr and been proposed as the ideal tracer isotope for dating old
water (Lehmann et al., 2003). Unfortunately, the use of this isotope is only in its development stage and is
currently not available for commercial application. Chlorine-36 has a half life of 3.01 ± 0.04 x 105 years and is
produced primarily in the atmosphere via cosmic ray spallation of argon-40. Because of its hydrophilic nature, it
is thought to be an ideal tracer to date groundwater on timescales of up to 1.5 x106 years, provided that sources
and sinks of 36Cl and stable Cl can be accounted for. The advantage of using 36Cl is that the chloride anion
behaves conservatively, where, in the absence of any Cl- bearing mineral such as halite, it is neither added, nor
removed, from solution via water rock interaction and moves at approximately the same velocity of the water.
36
Although 36Cl and Cl- concentrations may be modified after recharge by mixing with other aquifers, or by
diffusion from adjacent aquitards within a system, these problems may be overcome by incorporating
supplementary chemical and isotopic data to account for these added contributions. The reader is referred to
Love et al., (2000) who provide a detailed discussion of the relative importance of Cl- accession via rainfall and
acquitard diffusion, as well as a methodology to account for the different sources and sinks of 36Cl and Cl- and
appropriate modifications to the radioactive decay equation.
Flow rates are determined from both hydraulic calculations (Darcy’s law) and from 36Cl measurements. They
range from 0.2 m yr-1 to 5 m yr-1, with higher rates being recorded in the up-gradient parts in the Queensland
flow systems (2 – 5 m yr-1) , and the lower rates recorded in the western flow systems emanating from the SA
part of the basin and flowing westwards (0.2 – 0.5 m yr-1). The flow rates derived from the above methods are
complementary. The hydraulic age is determined from the current hydraulic gradient and a mean hydraulic
conductivity, while the isotopic age records a mean flow rate over the entire history of the flow systems, but is
subject to modification of the isotopic concentration and also subject to large errors.
37
4. REVIEW OF EXISTING RECHARGE STUDIES IN THE GAB
Despite its obvious importance there are very few detailed recharge studies throughout the GAB. The potential
recharge zones of the GAB are relatively well known. Recharge can occur where the GAB intake beds are
exposed at or close to the land surface or anywhere in the unconfined parts of the Basin. This zone, where there
is recharge potential, has been estimated to be 10 % of the Basin area (GABCC, 1998).
4.1. Western Margin (SA & NT)
There is no published paper or report that deals specifically with groundwater recharge along the Western
Margin. Love et al., (2000) investigated the relative importance of a number of processes that affect Cl- and 36Cl
distribution in the south-western flow systems to provide more precise estimates of age and flow and recharge
rates. In situ production of 36Cl, secular variations in the rate of production of 36Cl, and its subsequent fallout as
well as rates of diffusion of stable Cl- from adjacent aquitards masks the interpretation of rates of 36Cl/Cl decay
along the along hydraulic gradients and can preclude estimating absolute groundwater ages. Mean flow
velocities of 0.24 .03 m yr-1 were calculated from absolute 36Cl concentrations, however, and are a more
reliable parameter than calculated ages, because fewer assumptions and approximations are required. These flow
rates are an order of magnitude lower than others recorded in the basin (Bentley et al 1986; Torgersen et al.,
1991).
Recharge rates to the main J-K aquifer estimated from chloride mass balance in the unconfined aquifers are 0.16
0.08 mm yr-1 and were probably up to a factor of 3 higher > 30 kyr ago as indicated by decreasing Cl- and 18O
concentrations along the head gradient. Note, however, that the study area did not include any flood out zones
associated with ephemeral streams, where it is possible than higher rates of recharge may occur.
Matthews (1997) summarised the hydrogeology of the NT portion of the GAB. Data in that study included 14C, 36Cl, major ions and 2H and 18O, with important implications for recharges process associated with ephemeral
creeks and is discussed in detail in Section 5.
4.2. Coonamble Embayment (NSW)
The most recent studies of the water fluxes, water balance and recharge of the GAB within the Coonamble
Embayment are by Brownbill (2000), Radke el al. (2000) and Wolfgang (2000). The former report considers the
groundwater status of the region with respect to analysis of hydrographs and potential impacts of irrigation and
other. The Pilliga sandstone has been exploited since the early 1900s and significant hydraulic pressure declines
were noted at least 50 years ago when the NSW government started regular monitoring of key artesian bores.
Periodic flooding occurs along river valleys of the Macquarie and Castlereagh Rivers, although the extent and
frequency of flooding has declined due to the dams and impoundments built along the Macquarie River in the
20th century (Fig. 15). There are records of 10 or more floods in the region (Keshwan, 1995) with up to ~25% of
the area flooded and about 3-4 major floods per century. The last major floods were in the 1950s and 1970s (in
the latter years only on the Castlereagh, due to dams on the Macquarie).
38
Figure. 15. Flood map showing boundaries of a major flood in the Macquarie and Castlereagh catchments (after DWR, 1991).
Estimates of recharge rate are highly variable, in part due to widely-ranging estimates of the area of recharge
(local recharge). The estimated recharge area as documented by Wolfgang (2000) ranges from 453 – 35 000 km2
with a ‘best’ estimate of ~1,625 km2. This translates to an annual recharge volume estimate of ~9740 ML/yr or 6
mm/yr. This is higher than the 0.2 – 1.1 mm/yr estimates derived from 36Cl data by Radke et al., (2000) and at
the lower end of recharge estimates derived from the Queensland recharge beds derived from soil water chloride
mass balance by Kellett et al., (2003) i.e., 6 – 30 mm/yr.
The chloride mass balance estimates (see section 3) derived by Wolfgang (2000) use input chloride values from
rainfall from Dubbo ([Cl]rain = 3.25 mg/l) and mean annual rainfall of 520 mm yr-1. The rainfall amount may be
an underestimate of that received in the recharge zone. Due to the inverse relationship between rainfall amount
and chloride concentration in rainfall, however, the overall deposition rate of chloride based on the Dubbo data
may be reasonable. Wolfgang has reported data from ~20 boreholes from the recharge zone where measured
chloride in groundwater range from 47 – 2,000 mg/L. Using the mass balance equation given in section 3, the
recharge rate estimates range from 2 – 51.2 mm/yr with a mean value of 9.5 mm/yr and log mean of 6 mm/yr.
This translates to a recharge volume that range in estimates from 3000 – 50000 ML/yr.
39
Estimates of recharge from the Macquarie River along the Buddah fault (north of Narromine) range from
160,000 – 730,000 ML/yr while leakage may have increased due to higher stream water levels and groundwater
pumping (Keshwan, 1995). The importance of the flooding event to the recharge of the Pilliga Sandstone is not
certain, however, with claims of it being far greater than that of diffuse widespread recharge (Keshwan, 1995).
Wolfgang (2000) suggests that its importance is overstated due to the Pilliga Sandstone having a greater head
than the river systems in the larger portion of the flooded river valley areas. Furthermore, the major ion
chemistry in the underlying Pilliga Sandstone aquifer is very different from Macquarie River.
Brownbill (2000) suggested that there is likely to be connectivity between the Jurassic GAB aquifer and the
overlying Cainozoic aquifer because the former responds to pumping, infiltration and ET from the overlying
Cainozoic system. He considered there is a need to obtain better estimates of recharge in the Border
Rivers/intake bed region, where there is also extensive groundwater extraction. Radke et al., (2000) also suggest
that the Cainozioc aquifer recharges Pilliga Sandstones in the northern part of the study area where the head
gradient is higher and where the chemistry of the two systems are similar.
The extinct, or ‘palaeo’, mound springs along northern Bogan River imply wetter conditions at some time in the
past resulting in higher artesian pressures. It is not established whether the sinking of artesian bores has lowered
the pressure that has resulted in the decline in mound spring flow. Most are reported to be not flowing now but
may have been active until the early 20th Century.
Rising water tables in the Cainozoic aquifer systems is thought to be caused by river regulation and land-use
change. Current recharge to Pilliga from the unconfined aquifer is unlikely, as there is higher head in the Pilliga
than in the phreatic water table throughout most of the region. Potentiometric heads of the Jurassic aquifer are
40-60m higher than the watertable (unconfined) in the Cainozoic and Mesozoic parts of the Macquarie and
Castlereagh catchments. It is not known, however, what the relative head gradient conditions were like over the
past several tens to hundreds of thousands of years.
Isotopic data documented by Radke et al., (2000) show that 36Cl data for the NSW portion of the GAB indicate
flow systems increasing in age along the inferred hydraulic gradient, with indicative groundwater ages <5,000
years within the highland areas and river alluvial valleys in the recharge zone to >200 000 years in the western
portion of the Embayment, with horizontal flow rates decreasing to <1 m/yr as groundwater traverses from the
alluvial fans and move towards the plains.
40
5. RECHARGE MECHANISMS IN THE WESTERN GAB AND COONAMBLE EMBAYMENT
5.1 Conceptual models of recharge
The three predominant recharge mechanisms to occur in both the Western Margin and Coonamble Embayment
are:
a) Diffuse Recharge,
b) Ephemeral creek recharge, and
c) Mountain block recharge.
These are represented diagrammatically for the various settings of the GAB in Figure 16. The relative
importance of the three will vary from place to place, and over time, due to the very long time frame of
groundwater flow systems in GAB flow systems.
Figure 16. Diagrammatic representation of recharge process in the Great Artesian Basin (reproduced from Radke et al., 2000).
As potential evapo-transpiration substantially exceeds precipitation in the Western margin it is only the extreme
rainfall events that will result in groundwater recharge. As a result it is unlikely that any seasonal recharge will
occur under the current climate regime. These large episodic events result in large and often unpredictable
temporal variability in recharge. Recharge has the potential to occur when the aquifer is outcropping or sub
41
cropping and throughout the unsaturated zone overlying the unconfined aquifer. This represents a potential
recharge zone from the basin margin up to 50 to 300 km wide. Recharge also has the potential to occur from
elevated regions of the Peake and Dennison Ranges.
5.2 Diffuse recharge
Diffuse recharge has the potential to occur across the landscape from these large episodic events. There is
evidence, however, to suggest that diffuse recharge is extremely small or non-existent under the current climate
(Matthews, 1997, Love et al., 2000). This evidence comes from sampling unconfined wells not associated with
the drainage pattern of ephemeral creeks. Carbon-14 activities for these wells are generally at background levels
indicating the groundwater is >30 000 years old. It should be noted that this interpretation should only be
considered as a working hypothesis at this time. The reason for this is that there is only a paucity of data from
unconfined wells in the recharge zones. Not only is there a lack of age dating data; many wells do not have basic
hydrogeological information such as depth to the water table and salinity.
If we assume the current “working hypothesis” is correct, and that no diffuse recharge is occurring today along
the western margin, this does not imply that diffuse recharge did occur in the past. The climate in the Western
Margin was considerably wetter during parts of the Holocene and Pleistocene (Wasson and Clark 1988) and as a
result there would have been more favourable conditions for recharge. Love at al (2000) suggested that that
recharge rates were at least a factor of 3 greater in the Pleistocene. Although not referred to in their manuscript
much of this recharge would have occurred as diffuse recharge.
5.3 Localized Recharge.
In times of high rainfall events surface water run-off accumulates in topographic depressions, such as playas and
ephemeral water courses and their associated flood plains. During such events, saturated conditions, combined
with the high permeability of river bed sediments, has the potential to drive infiltration, deep drainage and
recharge through ephemeral creeks. The first mention of recharge occurring under ephemeral creeks was by
Vine, (Vine 1969) who postulated it as the major mechanism for recharge in the northern Eromanga Basin.
There is evidence to suggest that ephemeral creek recharge is occurring today along the western margin. The
most compelling evidence comes from the Finke and Goyder River region in the NT (Matthews 1997). Stable
isotopes of the water molecule are significantly more depleted with 18O values < – 9.3 ‰, in the catchment
zone of the Finke River. Carbon –14 activities of > 90 %MC indicate a thermonuclear component and that
groundwater has recharged within the last 40 years. Matthews (1997) mapped a groundwater mound along a
transect near the Finke and postulated that a 3H-36Cl peak could occur in the unsaturated zone at depths of
approximately 50 m below the ground surface mirroring the groundwater mound.
In contrast, in areas away from the possible influence of the braided streams, catchment zone 18O values are > -
6.8 ‰ suggesting diffuse recharge in these zones. Carbon –14 activities for these wells range between 3-22
%MC indicating recharge between 10,000 to 30,000 years ago. Corrections for the addition of dead carbon
would help determine a more accurate chronology of these .
It is also possible that recharge occurs along a number of braided streams along the western zone, such as the
Alberga. Unfortunately, there is no available hydraulic or isotopic data from these regions to support this.
42
Clearly to develop a consistent conceptual model for groundwater recharge, additional data such as stable
isotopes (2H, 18O) and groundwater age indicators (14C, 36Cl, 4He) as well as depth to groundwater and any
aquifer characteristics are required.
Because diffuse recharge is low or non existent today, the current day inputs to the water budget must be
dominated by ephemeral creek recharge. As well as obtaining values of ephemeral creek recharge, the spatial
extent of the braided streams needs to be known. In order to understand the relative importance of palaorecharge
from ephemeral creeks, however, a chronology of the history and spatial extent of the drainage pattern is
required.
Craddock et al., (2007) produced a digital elevation model for part of the Simpson Desert that identified a
number of palaeo-drainage patterns underlying the sand dunes. It is unlikely that palaeo-drainage patterns would
have significant impact on recharge as the majority occur in zones of upward hydraulic head gradient. This
technique, however, could be useful in other zones of the western margin that are covered in sand dunes with
favourable hydraulic conditions. A potential target zone for this could be to the west and north-west of Pedirka in
SA.
5.4 Mountain Block Recharge.
There is some potential for so-called Mountain Block Recharge (Fig. 17) from the elevated Peake and Dennison
Ranges into the adjacent aquifer. Mountain Block Recharge is considered to be an important recharge
mechanism in semi-arid and arid catchments of the southwestern USA (Wilson and Guan 2004). As no
hydrolgeological data exits throughout the Peake and Dennison Ranges, however, it is difficult to speculate what
the recharge mechanism and rates may be. The potential pathways for Mountain Block Recharge are discussed
in greater depth under the Coonamble Embayment where it is potentially far more important than the Western
Margin (see Section 4.2).
Figure 17 Conceptual diagram showing mountain block recharge which is a likely mechanism within the GAB,
particularly the Coonamble zone.
43
5.5 Modern and Palaeo-Recharge in the GAB
The only evidence for modern recharge along the western margin is near the Finke River in the NT and near
Marla in northern SA (Matthews 1997, Beyerle et al 1999). Recharge through the Finke system occurs via
ephemeral creek recharge through highly permeable sediments and associated flood out events. As discussed
previously this has been identified on the basis of modern 14C activities. Modern recharge has been identified
near Marla based on a relatively shallow depth to the water table and the presence of modern 14C and tritium
(Beyerle et al 1999). The recharge mechanism near Marla is most likely associated with preferential flow from
basement rocks adjacent to the GAB aquifer sequence. On the western margin the two pre-requests for modern
recharge appear to be a relative shallow depth to the water table and a mechanism that allows for preferential
flow. Along the eastern margin of the Coonamble Embayment the potential for modern recharge has also been
identified in certain locations by elevated 14C activities (Radke et al 2000).
Based on a thick unsaturated zone (up to 100 m) and chloride mass balance (CMB) recharge estimates of ~ 0.16
mm/yr., diffuse recharge is extremely low along the Western Margin in SA (Love et al., 2000). Residence time
in the unsaturated zone could be on the order of 10-80 kyr depending upon the depth to the water table and
porosity of the unsaturated zone.
A greater understanding of palaeo-recharge rates and mechanisms is not only important in developing a
conceptual model of the GAB, but quantification of recharge is required for input to numerical models. Extinct
Mound Springs with topographic elevations higher than active springs today clearly suggest higher aquifer heads
in the past. From this we can infer both wetter climates and higher recharge rates in the past. This also suggests
that the boundaries of the GAB were possibly more extensive in the past, where the depth to the water table
would have been shallower and the boundary between the unconfined/confined aquifer would have migrated
outwards towards the edge of the basin.
The only reference in the literature to quantifying palaeo-recharge rates is from Love and co-workers who
suggested that recharge rates were likely to be factor of at least 3 greater, approximately 30 kyr ago along the
western margin of SA. This was based on a decrease in chloride concentrations and depletion of the stable
isotopes of the water molecule along groundwater flow paths.
Estimating rates of palaeo-recharge is complex and remains a challenge for future research in the GAB and other
large arid sedimentary basins. This requires not only an accurate estimate of the recharge rate but also an
associate chronology. The most common method used to estimate recharge rates in arid and semi-arid zones as
discussed previously is the chloride mass balance (CMB) technique. Extreme care should be used when applying
the CMB at large temporal scales. The use of modern Cl- deposition rates and Cl- concentration from the aquifer
can lead to erroneous estimates of palaeo-recharge. As precipitation and Cl- depositional rates vary temporally,
there is a requirement to obtain information from archival records (such as unsaturated zones, lake sediments
etc). Much of this data, however, can often only be used in a proxy manner with limited quantitative data.
Groundwater systems can some times contain archival data from the time of recharge, but it is often difficult to
determine the recharge signature because of mixing processes within the aquifer system. This is particularly true
for large time scales.
The stable isotopic composition of the groundwater for the western margin and Coonamble Embayment regions
(Fig. 18) shows 2H ranges from -51 to -24 (‰, VSMOW) and 18O ranges from -7.4 to -2.6 (‰, VSMOW).
The data for the Coonamble Embayment suggest two clusters around -40‰ and -6.7‰ and -25‰ and -3.3‰
for 2H and 18O, respectively. The former data lie on the Global meteoric water Line (GMWL), while the latter
lie slightly to the right of the line and are generally from an area at the most south-eastern most part of the
44
Coonamble Embayment and may not be related to the rest of the GAB groundwater in the region. Stable isotope
data for the western flow systems lie on a linear trend to the right and parallel to the meteoric water line with a
mean value about -46‰ and -6.1‰ for 2H and 18O, respectively, which is considerably more negative than
present day rainfall in Alice Springs (-33.7‰ and -6.3‰ repectively; GNIP,2008). These data indicate that
recharge to the aquifer occurred during a climate that was both wetter and or cooler than the present day climate
regime in the respective recharge areas.
-55
-50
-45
-40
-35
-30
-25
-20
-8 -7 -6 -5 -4 -3 -2
GAB Stable isotopes
W estern flow systemsCoonamble Embayment
2 H (
‰, V
SM
OW
)
18O (‰ , VSMOW )
GMW L
Figure 18. Stable isotope data for the western flow systems (data from Love etal., 200; Zhang et al., 2007) and Coonamble Embayment (data from Radke et al., 2000).
5.6 Model Recharge rates in the Great Artesian Basin
Numerical models of the GAB have been attempted in both steady-state and transient modes (Welsh 2000 and
2006). The steady-state model GABFLOW was constructed using the MODFLOW code to predict changes in
artesian pressure as a result of bore rehabilitation throughout the basin. Recharge rates used in this study are
generally higher than recharge rates predicted from field studies. This is especially so on the western margin
where modeled recharge rates range from ~ 5-70 mm/yr, compared to field results of < 1 mm/yr (note field
results only represent diffuse recharge). In the transient groundwater flow model recharge rates varied between <
2.2 – 33 mm/yr throughout. The average recharge rate for all designated recharge cells is 2.4 mm/ yr which is a
factor 2 lower than the average recharge rates used in the steady state GABFLOW model. The recharge values
used in the transient simulation are more closely aligned to previous field studies (Love at al 2000, Kellett et al
2003). Welsh (2006) concluded that the water balance of the basin is not in equilibrium, with discharge 70 %
greater than inflows over a calibration period of 1965-2000. This supports the results of Love and co workers
45
(2000) who suggested that discharge to the system under the current day climate exceeds recharge. Clearly
changes in the hydrodynamic equilibrium of the GAB are effected not only by anthropogenic impacts, but also
long term changes in climatic regime. Changes in climate not only effect recharge rates but will have a
significant impact on changing boundary conditions throughout the Basin. To obtain a greater conceptual
understanding of the basin, there is a need to develop transient numerical models over long time scales
(~millions of years). We would recommend this be done in a step-wise approach using simple cross-sectional
numerical models to obtain a greater understanding of changing flow dynamics with time, rather than attempting
a basin wide modeling approach.
46
6. EVALUATION OF APPROPRIATE TECHNIQUES TO ESTIMATE RECHARGE IN THE GAB
In essence, hydraulic approaches for estimating recharge provide information on recharge rates and mechanism
occurring today. The GAB groundwaters, however, are essentially a fossil resource, hence these approaches have
limited application. An alternative and more applicable approach to investigating recharge in the GAB is to use
chemical and isotopic tools, as they can integrate over a wide range of temporal scales. A summary of the
advantages and disadvantages of different recharge techniques is presented in Table 1.
Water balance approaches have a high level of uncertainty in the GAB because they rely on accurate
measurements of precipitation, evaporation, transpiration and runoff to estimate recharge as the residual of the
water balance. Increasing the number of time steps to calculate daily water balances can reduce these errors. This
approach is considered to be extremely limited in most applications in the GAB. The only potential use could be
in the estimation of localised recharge from ephemeral creeks. There are many disadvantages, however, and it
would be very expensive both in terms of instrumentation and detailed and regular monitoring in the field. It also
relies on the unpredictability of large fold events.
Methods that rely on estimating hydraulic conductivity such as Darcy’s Law and unsaturated and saturated
modelling at best will only provide an order of magnitude estimate of the recharge rate due to the large spatial
variability in hydraulic conductivity. However, groundwater modelling that incorporates groundwater tracer data
has the potential to constrain the recharge rate and should be attempted.
The water table fluctuation method (WTF) from groundwater hydrographs is unlikely to be useful due to the
large depth to the water table often > 80 m. In these situations groundwater hydrographs are likely to the
constant over time and will not show any seasonal variations required to estimate recharge. It should be noted,
however, that in certain scenarios it is possible that groundwater hydrographs may be in decline due to extraction
from a fossil groundwater resource. Alternatively, a rising hydrograph may indicate a change in land use as has
occurred in the Murray Basin. Application of this technique may provide valuable data under zones of localised
recharge such as the Finke river system and other ephemeral creek systems.
There is a need to update maps of water table and potentiometric surface in both the Western Recharge Zone and
the Coonamble Embayment. Monitoring of water levels in the GAB largely occurs in the artesian portion of the
basin. For recharge studies, however, it is important to obtain data on the unconfined portion of the aquifer. This
could be achieved in a two-step process: (1) Examination of existing databases and other archives in the State
agencies of SA, NT and NSW; (2) surveying and water levels measurements via a field survey.
The most promising methodologies to estimate recharge in the Western GAB and Coonamble Embayment are
those that use environmental tracers. Environmental tracers have the ability to provide information on a wide
range of spatial and temporal scales. Due to uncertainties in all methods for estimating recharge, it is strongly
recommended to use a multiple approach using a range of environmental tracers such as (Cl, 36Cl, 14C, 3H, CFC’s 4He, 2H, 18O). Stable isotopes of the water molecule will not provide estimates of recharge rates but can
provide valuable information on recharge mechanisms to improve the conceptual model.
Unsaturated zone profiles estimate deep drainage over a small spatial scale, but provide invaluable data over
different time scales throughout the Holocene and late Pleistocene. This is important, as the majority of
groundwater recharge in the GAB occurred under past climates. Tracers sampled in the saturated zone measure
47
actual recharge, and not deep drainage, as water has reached the water table. These techniques are extremely
beneficial for estimating recharge over much larger spatial scales.
48
Table 1. Summary of different techniques to estimate recharge. Data complied from review of existing literature as well as author’s knowledge - Note much of the data in this table comes from detailed reviews found in Scanlon and Cook (2004). Note Recharge rates in mm/yr, - Spatial scales in m2 and temporal scale in years unless otherwise specified in the table.
Scale
Method Recharge Range
(mm/yr)
Spatial
(m2)
Temporal
(yrs)
Advantage Disadvantage
Background Information
– Hydro geomorphic
mapping
Can provide order
of magnitude
estimate of
recharge
Local to
regional
Generally provides
process information
A pre requisite for any recharge study.
Develops conceptual model of recharge
processes. Iterative approach should be
used as more data is gathered
throughout the recharge study to
improve the conceptual model
None
Water Budget Order of magnitude
at best
Local to
regional
Generally yearly Useful as a check on other methods. Requires accurate estimates of
evaporation, transpiration and run off.
Surface Water
49
Channel loss 5 - > 50 Local to
intermediate
Daily Only application under ephemeral
creeks and flood out zones.
Requires daily estimates of
evaporation, transpiration and run off.
Expensive
Unsaturated Zone
Darcy –Richards Law 20 -400 Point < 300 yrs Does not accurately estimate low water
fluxes
Expensive: requires accurate estimates
of K()
Lysimeters 5 - >100 20 m2 Length of test 2-3
yrs
Can provide accurate estimates of deep
drainage.
Expensive field instrumentation and
monitoring. Difficult to represent
natural conditions.
Applied Tracers 10 - >1000 100 m2 Length of test < 5
yrs
Very accurate estimates of recharge
under ideal situations
Needs approval from environmental
agencies. Requires high water fluxes
Chloride Mass Balance
(CMB)
0.01 - 200 point 5 - > 10, 000 y Very accurate for low recharge rates.
Has wide application in semi-arid and
arid zones
Requires estimates of the total Cl- flux,
under present and past climates
Event Markers 10 – 60 Point < 50 yrs Potentially useful technique assuming
high water fluxes under ephemeral
creeks
Under low water fluxes the bomb peak
is still in the root zone Requires
sufficient water fluxes
Radiotracer Decay 0.1 - 30 Point 500 - > 100,000 yrs Used in combination with CMB to
provide palaeo recharge rates
Need to account for subsurface
sources and sinks of tracers. Requires
specialised interpretation
50
Unsaturated Modelling Infinite <100 m2 All time scales Can constrain recharge provided
reliable field data is available
Relies on reliable estimates of K(),
Order of magnitude at best
Saturated Zone
Darcy’s Law Order of magnitude Local to
regional
short None in arid zones dominated by
palaeo recharge
Requires accurate estimates of
hydraulic conductivity and gradient
Hydrographs 5 - 400 50 –10,000 m2 Length of record Useful technique if water table is
shallow. May be useful under
ephemeral streams. In certain situations
may detect change in land use or
climate.
Has limited application for diffuse
recharge in GAB due to deep water
tables that do not reflect seasonal
recharge
Chloride Mass balance
(CMB)
0.01 - 400 5- 10,000 m2 10 – > 10,000 Integrates preferential flow in
unsaturated zone. Can provide sub-
regional estimates of recharge. Very
useful in arid zones as it can measure
low water fluxes
Must ensure there are no addition
sources or sinks of Cl other than
atmosphere
Event Markers 20 -1000 5- 10,000 m2 < 50 yrs Potentially useful technique assuming
high water fluxes under ephemeral
creeks
Requires accurate estimates of input
functions. Requires expert
interpretation in isotope hydrology
Accumulating
Tracers
Semi – qualitative
only
5- 10,000 m2 1000 - >10,000 May provide estimates of residence
time to back-calculate recharge.
Improves conceptual understanding of
system.
Often requires sophisticated sampling
methods. Data can be difficult to
interpret. Requires expert
interpretation in isotope hydrology
51
Radiotracer Decay 1-100 5- 10,000 m2 14C 500 –25,000
36Cl 50,000 >
300,000
Integrates recharge process. Very
useful for low water fluxes
Need to account for subsurface
sources and sinks of tracers. Data can
be difficult to analyses requires
expertise in dating methodologies
Groundwater Modelling Infinite (in theory) Local to
regional
All time scales Use should be restricted to constraining
recharge rates with additional isotopic
and chemical data
Relies on accurate estimates of K;
order of magnitude at best
Geophysics and Remote
Sensing
N/A Local to
regional
At the time of
measurement
Non-invasive. Good spatial resolution.
Provides data for scaling recharge.
Generally requires expensive ground-
truthing
52
7. PROPOSALS FOR ESTIMATING RECHARGE
Estimation of groundwater recharge is an iterative process. Firstly an examination of all existing data is required
to develop a conceptual model of the system and provide a likely range of recharge values. This is important in
the selection of specific recharge techniques. Below we present a staged approach to recharge estimation. It is
important that after each stage the conceptual model is re examined in light of new information. The proposed
program is organised in a hierarchical manner starting from the basic desktop study of compilation of existing
information through to detailed field programs involving drilling of soil profiles and groundwater sampling and
chemical and isotopic analyses.
7.1 Desktop study
A desktop study is a recommended starting point in any recharge study to compile available information in a
coherent manner to provide first-pass estimates of recharge rates.
Compile all available data:
Land-use, soil type, vegetation
Hydrological data: river discharge, rainfall (long-term trends) evapo-transpiration
Hydrogeology: aquifer units, unsaturated zone thickness, aquifer properties [aquifer architecture], total sediment
thickness or depth to basement; potentiometric head; hydrographs
Flow system analysis: conceptual model to give zones of potential recharge [plan and cross-section]. Preliminary
recharge rate estimates based on chloride mass balance from existing groundwater data (e.g., Wolfgang, 2000).
Analyse the suitability of using the water table fluctuation method to estimate recharge from bore hydrographs in
the unconfined portion of the aquifer.
Costing:
8 weeks professional $40 000
6 weeks GIS $25 000
Total $65 000
Limitations:
Limited data sets available for the SA and NT unconfined system, which is required to constrain water table
contours.
53
Limited chloride data in unconfined aquifer in western margin and imprecise data for rainfall chloride
concentrations.
7.2 Well survey
The well survey would be the next level of activity that would require some fieldwork and laboratory analysis.
Measure potentiometric head and land elevation to provide RSWL data for the recharge zones.
Sample the wells for major ion chemistry, isotopes and other tracers.
Carry out geophysical logging at selected wells to estimate aquifer properties.
Costing:
Sampling of 60 wells in SA/NT and 40 wells in the
Coonamble embayment of NSW
$120 000
Analysis costs $50 000
Geophysical logging $50 000
Data evaluation and reporting $30 000
Total $250 000
Limitations:
Potential poor coverage in critical areas and unknown well integrity.
7.3 Transects in the unconfined part of the GAB
Conduct sampling of wells along transects along inferred flow lines (perpendicular to isopotentials determined
from 1 & 2 above).
Use information gathered from 7.1 & 7.2 to ensure hydrologic and hydraulic continuity.
Collect 6 – 8 wells per transect – 2 transects in SA; 2 in NT and 2 in NSW
Costing:
54
Sampling of ~28 wells in SA/NT
and 12 wells in NSW
$75 000
Analyses costs $40 000
Data evaluation and reporting $20 000
Total $135 000
Limitations:
Hydraulic and hydrological continuity needs to be established.
Cost assumes no new drilling is required.
7.4 Unsaturated zone profiles of soil water properties and chloride mass balance
The use of unsaturated zone profiles has been used extensively to estimate recharge rates in the Murray-Darling
Basin and in the Queensland portion of the GAB (Kellett et al., 1998).
Carry out drilling and coring through the unsaturated zone in various land units that cover the different land-units
(creek beds, open scrubland, dunes etc).
Analysis of core samples for soil moisture content, soil suction, chloride content, stable isotopes of water, (some) 36Cl
Profiles at 20 sites in SA/NT and 10 sites in NSW, in some cases to the water table: costing based on 10 m
coring per day with average depth of 50 metres.
Costing:
Coring and drilling $400 000
Analyses costs $350 000
Data evaluation and reporting $100 000
Total $850 000
Limitations:
Availability of contractor to carry out specialized drilling and coring
55
Scaling up of data over very large area
7.5 Estimation of direct and localised recharge
This component complements information for 7.4 above, but provides estimates from flood and localised
recharge, which in arid areas are sometimes equal to, or greater than, local or diffuse recharge across the entire
landscape.
Compile all available data on flooding records for the Lake Eyre basin and the Macquarie; Castlereagh and
Bogan rivers.
Collect soil profiles below surface water drainage systems in both the unsaturated and saturated zones (as per for
7.4 above).
Digital elevation and remote sensing to identify buried palaeochannels.
Costing:
Coring and drilling (3 sites in
SA/NT and 2 sites in NSW)
$200 000
Analyses costs $75 000
Data evaluation and reporting $25 000
Total $300 000
Limitations:
Flood records are limited to last 100 years in NSW. Data for Lake Eyre Basin also limited, and may not be
applicable to the western margin.
Access to suitable sites for drilling, particularly in NSW, need to be determined.
56
8. REFERENCES AND BIBLIOGRAPHY
Abbott, WE, 1884. Water supply in the interior of NSW. J. Proc. Royal Soc. NSW, 18, 85-111.
Airey, PL, Calf, GE, Campell, BL, Habermehl, MA, Hartley, PE, Roman, D, 1979. Aspects of the isotope
hydrology of the Great Artesian Basin, Australia. In: Proceeding of Intl. Symp., Isotope Hydrology and Water
Res. Devt., Intl. Atomic Energy Agency, Vienna, 1979.
Airey, P L, Bentley, HW, Calf, GE, Davis, SN, Elmore, D, Gove, H, Habermehl, MA, Phillips, F, Smith, J,
Torgersen, T, 1983. Isotope hydrology of the Great Artesian Basin, Australia. In: Proceeding of Intl. Symp.,
Isotope Hydrology and Water Res. Devt., Intl. Atomic Energy Agency, Vienna, 12-16 Sep, 1983.
Allison GB & Hughes MW, 1983 The use of natural tracers as indicators of soil-water movement in a temperate
semi-arid region. J. Hydrology, 60:157-173.
Allison, GB, Gee, GW ,Tyler, SW, 1994. Vadose-zone techniques for estimating groundwater recharge in arid
and semiarid regions. Soil Science Soc. America J., 58:1
Appelo, CAJ & Postma, D, 1993. Geochemistry, Groundwater and Pollution. Rotterdam: A.A. Balkema.
Bentley, HW, Phillips, FM, Davis, SN, Habermehl, MA, Airey, PL, Calf, GE, Elmore, D, Gove, HE, Torgersen
T, 1986. Chlorine-36 dating of very old groundwater. The Great Artesian Basin, Australia. Water Resour, Res.
22(13), 1991-2001.
Bethke, CM, Xiang Z, Torgersen, T, 1999. Groundwater flow and the 4He distribution in the Great Artesian
Basin of Australia. J. Geophys. Res. 104 B6, 12, 999-13 011.
Beyerle, U, Aeschbach-Hertig, W, Peeter, F, Kipfer, R, Purtschert, R, Lehmann, BE, Loosli, HH, Love, AJ,
1999. Noble gas data from the Great Artesian Basin provide a temperature record of Australia on time scales of
105 years In: Proceeding of Intl. Symp., Isotope Hydrology and Water Res. Devt., Intl. Atomic Energy Agency,
Vienna, 19-24 May, 1999.
Bierwirth, PN & Welsh, WD, 2000. Delineation of recharge beds in the Great Artesian basin using airborne
gamma radiometrics and satellite remote sensing. Bureau of Rural Sciences, Canberra.
Brownbill, R. 2000. NSW Great Artesian Basin Status Report. NSW Dept. of Land and Water Conservation,
37pp + 2 Appendices.
Calf, GE & Habermehl, MA, 1984. Isotope hydrology and hydrochemistry of the Great Artesian basin. In:
Proceeding of Intl. Symp., Isotope Hydrology and Water Res. Devt., Intl. Atomic Energy Agency, Vienna, 12-
16 Sep, 1983.
Clark, ID & Fritz, P, 1997. Environmental Isotopes in Hydrogeology. Lewis Publishers. Boca-Raton,
57
Collon, P, Kutschera, W, Loosli, HH, Lehmann, BE, Purtschert, R, Love, A, et al., . 2000. 81Kr in the Great Artesian Basin, Australia: a new method for dating very old groundwater. Earth Planet Sci. Lett., 182,
103-113.
Cook, PG & Herczeg, AL (editors). Environmental Tracers in Subsurface Hydrology. Kluwer Academic
Publishers, Boston Ma, 16 Chapters, November 1999 552 pp., 1999.
Cook PG and Herczeg AL, 1999. Environmental Tracers in Subsurface Hydrology. Kluwer Academic Press,
Boston, 529 pp.
Cook PG & Bohlke JK, 1999. Determining timescales for groundwater flow and solute transport. In: PG Cook
and AL Herczeg (ed.) Environmental Tracers in Subsurface Hydrology. Kluwer AP, Boston, pp.1-30.
Cook PG & Herczeg AL 1998. Groundwater Chemical Methods for Recharge Studies. Part 1 of 2. L.. Zhang and
GR Walker (ed.) The Basics of Recharge and Discharge. CSIRO Publishing.
Cook, PG & Herczeg, AL 1998. Groundwater chemical methods for recharge studies. Part 2 of 2: Zhang, L.
(editor), Studies in Catchment Hydrology: The Basics of Recharge and Discharge, Melbourne, Vic.CSIRO
Publishing: 17 pp.
Cook PG, Jolly ID, Leaney FW, Walker GR, Allan GL, Fifield L.K & Allison GB 1994. Unsaturated zone
tritium and chlorine-36 profiles from southern Australia: their use as tracers of soil water movement. Water
Resour. Res., 30, 1709-1719.
Coplen, T, Herczeg, AL, and Barnes, CB, 1999. Isotope Engineering - using stable isotopes of the water
molecule to solve practical problems. Cook, PG & Herczeg, A. (eds), Environmental Tracers in Subsurface
Hydrology, Boston, USA :Kluwer Academic Press: 79-110.
Cox R & Barron, R. Eds. 1998. Great Artesian Basin Resource Study, GABBC.
Craddock R, Hutchinson M, Stein J, Tooth S, Maxwell T, 2007, Evidence for Buried River Channels in the
Simpson Desert, XVII INQUA Congress 2007.
David, TWE, 1983. Artesian water in NSW and Qld. J Proc. Royal Soc. NSW. 27, 408-443.
DWR, 1991. Water resources in the Castlereagh, Macquarie and Bogan valleys. Depatrment of Water Resources,
NSW Report.
Downes, RG & Sleeman, JR 1955. Soils of the Macquarie region, NSW. Soil Publ. No.4, CSIRO, Melbourne.
Dyce, PH & Dowling, TI. 1997. Mapped biophysical themes produced for reconstructing historical salt balances
and stream salinity trends in the catchments of the Murray-Darling basin. CSIRO Land and Water Tech. Rep.
19/97
Eriksson E. & Khunakasem V, 1969 Chloride concentration in groundwater, recharge rate and rate of
deposition of chloride in the Israel Coastal Plain. J. Hydrol. 7, 178-197.
58
Evans, WR, Hillier, J, & Woolley, DR, 1994. Hydrogeology of the Darling River Drainage basin: Qld/NSW,
Australia. 1:1 000 000 Map Sheet, AGSO Canberra.
(GABCC) Great Artesian Basin Consultative Council, 1998. Great Artesian Basin Resource Study. R. Cox and
A. Barron, eds., 235p.
Gee GW & Hillel D, 1988. Groundwater recharge in arid regions: review and critique of estimation methods.
Hydrol Proc 2, 255-266.
Goodrich DC, Williams DG, Unkrich CL, Hogan JF, et al., 2004, Comparison of methods to estimate ephemeral
channel recharge, Walnut Gulch, San Pedro River Basin, Arizona In: JF Hogan, FM Phillips, & BR Scanlon,
(eds.), Groundwater recharge in a desert environment: the southwestern United States: Washington, D.C.,
American Geophysical Union, Water Science and Applications Series, v. 9, p. 77-100.
Habermehl, MA 1980. The Great Artesian Basin, Australia. BMR J. Geol. Geophys. 5, 9-38.
Habermehl, MA & Lau, L 1997. hydrogeology of the Great Artesian Basin, Australia (1:250 000). Australian
Geological Survey Organisation, Canberra.
Hantush MS 1967, Growth and decay of groundwater mounds in response to uniform precipitation. Water
Resour. Res. 3, 227-2334.
Harrington, GA 1997. Recharge mechanisms and chemical evolution in an arid groundwater system, central
Australia. PhD thesis, Flinders University of SA, 333pp.
Harrington, G.A., Cook, P.G. and Herczeg, A.L. 2002. Spatial and temporal variability of ground water recharge
in central Australia: A tracer approach. Ground Water, 40: 518-528.
Healy RW & Cook PG 2002. Using groundwater levels to estimate recharge. Hydrogeology J. 10(1), 91-109.
Hendrickx J & Walker GR 1997. Recharge from precipitation. In: I. Simmers (ed) Recharge of phreatic aquifers
in (semi-) arid areas. AA Balkema, Rotterdam, 19-98.
Herczeg, AL & Edmunds, WM 1999. Inorganic ions as Tracers. In PG Cook & AL Herczeg (eds.),
Environmental Tracers in Subsurface Hydrology, Boston, USA :Kluwer Academic Press: 31-78.
Herczeg, AL, Torgersen, T, Chivas, A. Habermehl, MA 1991. Geochemistry of groundwater from the Great
Artesian Basin, Australia. J. Hydrol. 126, 225-245.
Hogan, JF, Phillips, FM, Scanlon, BR 2004. (eds.) Groundwater recharge in a desert environment; the
southwestern United States. Water and Science Application 9, American Geophysical Union, Washington, DC,
ISSN 1526-758X
Kellett, JR., Ransley, TR., Coram J., Jaycock, J., Barcaly, DF., McMahon, GA, Foster LM, Hillier JR. 2003.
Groundwater Recharge in the Great Artesian Basin Intake Beds, Queensland Department of Natural Resources
and Mines Technical Report.
59
Keshwan, M. 1995. River loss investigation in the Macquarie River downstream of Narromine. Dept. Land &
Water Cons. Dubbo, NSW.
Leaney, FWJ, Herczeg, AL, & Walker, GR 2003. Salinisation of a fresh palaeo-ground water resource by
enhanced recharge. Ground Water 41, 84-93.
Lehmann, BE, Love, AJ, Purtschert, R, Collon, P, Loosli, HH, Kutschere, W, Beyerle, U, Aeschbach-Hertig, W,
Kipfer, R, Frape, SK, Herczeg, AL, Moran, J, Tolstikhin, IN, Groening, M. 2003. A comparison of groundwater
dating with 81Kr, 36Cl and 4he in four wells of the Great Artesian Basin, Australia. Earth Planet Sci. Lett., 211,
237-250.
Lerner DN, Issar, AS, Simmers I 1990 Groundwater recharge. A guide to understanding and estimating natural
recharge. IAH. Int Contrib Hydrgeo 8. Heinz, Heise, Hannover, 325pp.
Love, AJ, Herczeg, AL, Sampson, L, Cresswell, RG, Fifield, LK 2000. Sources of chloride and implications for 36Cl dating of old groundwater, south-western Great Artesian basin, Australia. Water Resour. Res. 36(6), 1561-
1574.
Matthews, I, 1997. Hydrogeology of the Great Artesian Basin in the Northern Territory, Water Resources
Division Darwin Report No 52/96A
Mazor, E 1995. The stagnant aquifer oncept part 1. large scale Artesian systems – Great Artesian basin,
Australia. J. Hydrol., 173, 219-240.
McKenzie, NJ 1992. Soils of the Lower Macquarie Valley, NSW. CSIRO Div. Soils rep. No. 117. CSIRO
Mulholland, C StJ 1950. Review of southern intake beds, NSW and their bearing on on artesian problems. In:
Geol. Surv. Geological Reports 1939-1945, Dept. of Mines, NSW p. 125-127.
Phillips, FM 2000. Chlorine-36 In:
Pigram, JJ 2006. Australia’s Water Resources, From Use to Management CSIRO Publishing. 226 pp.
Radke, BM, Ferguson, J, Cresswell, RG, Ransley, TR Habermehl, MA. 2000. Hydrochemistry and implied
hydrodynamics of the Cadna-owie – Hooray Aquifer, Great Artesian Basin. Bureau of Rural Sciences, Canberra
ISBN 0 642 47554 7 Commonwealth of Australia report.
Robbins NS 1998 Groundwater pollution, aquifer recharge and vulnerability. Geol Soc Lond Spec Publ
130:224.
Sanford, WE, Plummer, LN, McAda, DP, Bexfield, LM, Anderholm, SK. 2004. Hydrochemical tracers in the
middle Rio Grande Basin, USA: 2. Calibration of a groundwater flow model. Hydrogeol. J., 12, 389-407.
Scanlon, BR, 2004, Evaluation of methods of estimating recharge in semiarid and arid regions in the
southwestern U.S., In: JF Hogan, FM Phillips, & BR Scanlon, (eds.), Groundwater recharge in a desert
environment: the southwestern United States: Washington, D.C., American Geophysical Union, Water Science
60
and Applications Series, v. 9, p. 235–254.
Scanlon, BR., Tyler, SW, Wierenga, PJ 1997, Hydrologic issues in arid, unsaturated systems and implications
for contaminant transport: Rev. Geophys. 35, no. 4, 461–490.
Scanlon, BR, Healy, RW, Cook, PG, 2002, Choosing appropriate techniques for quantifying groundwater
recharge: Hydrogeology J. 10, 18–39.
Scanlon, BR, Keese, KE, Flint, A , Flint, LE, Gaye, CB, Edmunds, WM, Simmers, I, 2006. Global synthesis of
groundwater recharge in semiarid and arid regions: Hydrol. Proc., 20, 3335–3370.
Sharma ML (ed) 1989 Groundwater Recharge AA Belkema Rotterdam. 323pp.
Shepherd, RG 1978. Underground water resources of South Australia, Bulletin 48, South Australian Dept of
Mines and Energy, South Australian Govt. 66pp.
Simmers I (ed) 1988 Estimation of natural groundwater recharge. NATO ASI Ser C 222 Reidel, Dordrecht, 510
pp.
Simmers I (ed) 1997 Recharge of phreatic aquifers in semi –arid areas. IAH Int Contrib Hydrogeol 19, AA
Belkema. Rotterdam. 277 pp.
Sleeman, JR, & Downes, RG 1950. Part 1: Soil survey of proposed irrigation area – Narromine, NSW. Div. Soils
Rept. 3/50 CSIRO, Adelaide.
Taylor, S. 1994. Macquarie River catchment land management proposal for the integrated treatment and
prevention of land degradation, Macquarie River catchment – CaLM, Sydney.
Torgersen, T., Habermehl, MA, Phillips, FM, Elmore, D, Kubik, P, Jones, BG, Hemmick, T, Gove, HE 1991.
Chlorine-36 dating of very old groundwater 3. Further studies in the Great Artesian basin, Australia. Water
Resour. Res.
Vine RR, 1969 Hydrological implications of recent geological work in the Great Artesian Basin. BMR Research,
1969/56
Vogel JC 1967 Investigation of groundwater flow with radiocarbon. In: Isotopes in hydrology. International
Atomic Energy Agency, Vienna pp 355-369.
Wasson RJ, & Clark RL, 1988 The Quaternary in Australia – past, present and future. Quaternary Australasia
6(1):17-22.
Welsh, WD, 2000. GABFLOW: A steady state groundwater flow model of the Great Artesian Basin. Bureau of
Rural Science, Canberra
Welsh WD, 2006, Great Artesian Basin transient groundwater model. Bureau of Rural Science, Canberra.
61
Wilson JL, & Guan H, 2004 Mountain-Block Hydrology and Mountain-Front Recharge. In: Hogan, J. F.,
Phillips, F. M., and Scanlon, B. R., eds., Groundwater recharge in a desert environment: the southwestern United
States: Washington, D.C., American Geophysical Union, Water Science and Applications Series, v. 9, p. 113-
137.
Wolfgang, C. 2000. Hydrogeology of the Pilliga sandstone, Coonamble Embayment and water resource
management. PhD Thesis, Fenner School of Environment, The Australian National University.
Woods, PH 1990. Evaporative discharge of groundwater from the margin of the Great Artesian Basin near Lake
Eyre, South Australia. PhD Thesis, Flinders University of SA.
Woods, P.H., Walker, G.R., Allison, G.B. 1990. Estimating groundwater at the southern margin of the Great
Artesian Basin near Lake Eyre, South Australia. Proc. Intl. Conf. Groundwater in Large Sedimentary Basins,
Perth WA 9-13 July, 1991, AWRC.
Zhang L (Ed) 1998. The basics of recharge and discharge. CSIRO Publishing, Collingwood, Australia
Zhang, M., Frape, SK, Love, AJ, Herczeg, AL, Lehmann, BE, Bayerle, U, Pertschert, R. 2007. Chlorine stable
isotope studies of old groundwater, southwestern Great Artesian Basin, Australia. Applied Geochem. 22, 557-
574.
Websites that have information on the GAB
http://www.gab.org.au/
http://www.affa.gov.au/content/output.cfm?ObjectID=D2C48F86-BA1A-11A1-A2200060B0A05660
http://www.atse.org.au/index.php?sectionid=404 (Lance Endersbee)
