SCHOOL OF NATURAL RESOURCE SCIENCES
QUEENSLAND UNIVERSITY OF TECHNOLOGY
HYDROGEOLOGY, CONCEPTUAL MODEL AND
GROUNDWATER FLOW WITHIN ALLUVIAL
AQUIFERS OF THE TENTHILL AND MA MA
CATCHMENTS, LOCKYER VALLEY,
QUEENSLAND
ANDREW SCOTT WILSON
B. App. Sc. (QUT)
SUPERVISOR: Dr Malcolm Cox
ASSOCIATE SUPERVISOR: Dr Vivienne McNeil
A thesis submitted in partial fulfilment of the requirements for the
award of the degree of Master of Applied Science
February 2005
KEY WORDS
hydrogeology, conceptual model, groundwater, alluvial aquifers,
Lockyer Valley, Queensland
ABSTRACT
The study focuses on the adjacent Tenthill and Ma Ma catchments which
converge onto the heavily cultivated alluvial plain of Lockyer Creek.
Groundwater extracted from the alluvial aquifers is the primary source of
water for intensive irrigation. Within the study the hydrogeology is
investigated, a conceptual groundwater model produced and a numerical
groundwater flow model is developed from this. The hydrochemistry and
stable isotope character of groundwater are also investigated to determine
processes such as recharge and evaporation.
Examination of bore logs confirms the Quaternary alluvium comprises a
laterally continuous gravel aquifer with an average thickness of 4.5 m,
overlain by mixed sands and clays which form a semi-confining layer with
an average thickness of 22 m. Variations in long term groundwater
hydrographs indicate the aquifer changes from confined to unconfined in
some locations as water levels drop, while bores adjacent to creek banks
display a rapid response to a flood event. Pump testing of bores screened in
the gravel produces estimates of hydraulic conductivity ranging from 50-80
m/day and storativity of 0.00166 which are both within realistic bounds for
this aquifer material.
Major ion chemistry of surface water collected during a flood is Mg-
dominated, similar to alluvial groundwater in the Tenthill catchment and the
Lockyer plain, suggesting a strong connection between surface and
groundwater in these locations. Alluvial groundwater salinity in Tenthill
catchment is typically less than 3500 µS/cm but may approach 6000µS/cm
on the Lockyer plain. By contrast Ma Ma catchment alluvial groundwater is
Na-dominated with conductivity up to 12000 µS/cm and more associated
with groundwater from the underlying sandstone bedrock. Stable isotope
analyses of alluvial groundwater from throughout both catchments and the
Lockyer plain are compared with basalt and sandstone groundwater. A
range of processes have been identified including recharge to alluvium from
basalt groundwater and evaporated surface water; and alluvial-bedrock
groundwater mixing at some locations.
Integration of the components of the study enabled the production of a
conceptual hydrogeological model of the Lockyer alluvial plain, proposing
two hydrostratigraphic units; the gravel aquifer and the overlying mixed
sand and clay which acts as a semi confining unit. Hydrochemical and stable
isotopic evidence suggests seepage from creek channels as the dominant
recharge process. A single layer groundwater flow model using
MODFLOW was developed, based on groundwater extraction data, to
represent flow in the gravel aquifer. The model was calibrated to transient
conditions with groundwater fluctuations, incorporating both drought and
flood conditions. A sensitivity analysis for each of the aquifer properties
demonstrates the model is insensitive to variations within realistic bounds
for the gravel aquifer material, however, the model is highly sensitive to
changes in the chosen boundary conditions. Predictive simulations with
several annual extraction scenarios ranging from 1.75 to 0.5 ML/ha indicate
the resulting minimum saturated aquifer thickness ranges from 0.03 to 1.4
m.
TABLE OF CONTENTS
1. INTRODUCTION 1
Background 1
Purpose and Scope of the Investigation 1
Aims and Objectives 2
2. PHYSICAL SETTING 3
Location 3
Climate 3
Geomorphology 6
Soils 6
Land Use 8
Water Use 8
3. GEOLOGICAL SETTING 10
Regional Geology 10
Geological Units of the Tenthill and Ma Ma catchments 11
Marburg Subgroup 11
Walloon Coal Measures 15
Main Range Volcanics 16
Quaternary Alluvium 16
4. HYDROGEOLOGICAL BACKGROUND 17
Occurrence of Groundwater in the Lockyer Valley 17
Types and Features of Alluvial Aquifers 17
Features of Bedrock Aquifers 19
Previous Groundwater Investigations in the Lockyer Valley 20
NRM&E Database 24
5. HYDRAULIC INVESTIGATIONS 27
Background 27
Methods 27
Hydrograph Interpretation 27
Pumping Tests 28
Results 32
Hydrograph Interpretation 32
Pumping Tests 37
Discussion of Hydraulic Investigations 37
6. HYDROCHEMISTRY AND STABLE ISOTOPES 43
Background 43
Methods 45
Water Chemistry 45
Stable Isotopes 45
Results 46
Water Chemistry 46
Stable Isotopes 55
Discussion of Hydrochemistry and Stable Isotopes 56
7. DEVELOPMENT OF GROUNDWATER MODEL 70
Introduction 70
Background 71
Conceptualisation 80
Calibration 91
Prediction 125
Discussion of Groundwater Modelling 127
8. CONCLUSION 131
9. REFERENCES 135
APPENDICES after 141
LIST OF FIGURES
Figure 1. Location of the study area in southeast Queensland.
Figure 2. Monthly rainfall recorded at Gatton from 1960-2003.
Figure 3. Monthly rainfall and evaporation recorded at Gatton for 1992-
2002.
Figure 4. Structural setting of the Laidley Sub basin in the Clarence
Moreton Basin.
Figure 5. Surficial geology of the study area .
Figure 6. Locations of 8 bores with regular water level records for 1988-
2003.
Figure 7. Hydrographs of 8 monitoring bores with regular records for 15
year period from 1988 – 2003.
Figure 8. Bore hydrographs at different distances from creeks compared
with monthly rainfall residual mass from 1988-2003.
Figure 9. Locations of 3 pumping tests conducted on alluvial bores,
Figure 10. Plot of drawdown versus log time for pumping test 1.
Figure 11. Plot of residual drawdown versus (t/t’) for pumping test 2.
Figure 12. Plot of drawdown data from Macleod (1998) for pumping test 3.
Figure 13. Daily measurements recorded by bore 516 on bank of Tenthill
Creek during flood event of early May 1996.
Figure 14. Locations of bores sampled for hydrochemistry and stable
isotopes in the study area.
Figure 15. Locations of bores sampled for hydrochemistry and stable
isotopes outside the study area.
Figure 16. Piper diagram utilising the Davies and De Wiest (1966)
classification system for identifying groundwater types.
Figure 17. Piper diagram of surface and alluvial groundwater samples 1996.
Figure 18. Schoeller diagram showing relative proportions of major ions
1996.
Figure 19. Piper diagram of alluvial groundwater samples 2003.
Figure 20. Logarithmic plot of Ca (mg/L) vs TDS (mg/L) for groundwater
samples in 2003.
Figure 21. Logarithmic plot of HCO3 (mg/L) vs conductivity (µS/cm) for
groundwater samples in 2003.
Figure 22. Stable isotope plot of all samples.
Figure 23. Detailed stable isotope plot of surface water and alluvial and
basalt groundwater in 2003.
Figure 24. Semi logarithmic plot of δ2H ‰ VSMOW vs conductivity
(µS/cm) for groundwater samples in 2003.
Figure 25. Location of model extent and the 32 bores used to define the
hydrogeological framework for the conceptual model of the Lockyer plain.
Figure 26. Cross section A-A’
Figure 27. Cross section B-B’
Figure 28. Hydrograph of bore 516 adjacent to Tenthill Creek for period
1993-1996.
Figure 29. Conceptual hydrogeological model for cross section A-A’
Figure 30. Model grid orientated at 62.68 degrees from east showing active
cells (white), inactive cells (grey) and fixed head cells (green).
Figure 31. Top of layer contours interpolated from bore logs with 1 m
interval.
Figure 32. Bottom of layer contours interpolated from bore logs with 1 m
interval.
Figure 33. Initial heads interpolated from 10 head measurements in March
1993 with 1 m contour interval.
Figure 34. Locations of Tenthill Creek (east) and Lockyer Creek (north)
and Ma Ma creek (west) in the model grid.
Figure 35. Locations of 7 recharge zones relative to observation bores.
Figure 36. Extraction cells applied to entire model grid.
Figure 37. Head time graphs of observed and calculated heads.
Figure 38. Water budget for each stress period of the model.
Figure 39. Correlation of derived recharge volumes and rainfall for each
stress period of the model.
Figure 40. Graph of RMS error vs hydraulic conductivity.
Figure 41. Graph of RMS error vs specific yield.
Figure 42. Graph of RMS error vs specific storage.
Figure 43. Head time graphs for simulation with no groundwater extraction
for entire model.
Figure 44. Head time graphs for simulation with all time variant specified
head boundaries replaced by constant head boundaries set at initial heads.
Figure 45. Head time graphs for simulation with western time variant
specified head boundary only replaced by no flow boundary.
Figure 46. Head time graphs for two layer model with derived recharge
rates applied to creek cells in layer 2 and recharge applied as 1% of rainfall
for layer 1.
Figure 47. Graph of minimum saturated thickness of aquifer at end of stress
period 11 versus annual extraction rate applied for entire simulation.
LIST OF TABLES
Table 1. Summary of the pump test specifications, analysis methods
and estimated aquifer properties compared with literature
values for gravel.
Table 2. Stable isotope data related to EC, TDS and aquifer geology.
Table 3. Summary of aquifer geology, EC and water chemical type.
Table 4. Summary of bore logs used to define the thickness of the
gravel aquifer in the study area.
Table 5. Summary of temporal data
Table 6. Summary of groundwater extraction data adapted for the
Lockyer plain.
Table 7. Parameter variations used in the sensitivity analysis.
LIST OF APPENDICES
Appendix 1. Example of bore record from NRM&E database.
Appendix 2. Pumping test data.
Appendix 3. Hydrochemical analytical methods.
Appendix 4. Hydrochemical data.
LIST OF ABBREVIATIONS
NRM&E Natural Resources and Mines and Energy
TMMC Tenthill and Ma Ma catchments
ICP-OES Inductively Coupled Plasma Optical Emission Spectroscopy
CSIRO Commonwealth Scientific and Industrial Research
Organisation
EC Electrical Conductivity
TDS Total Dissolved Solids
VSMOW Vienna Standard Mean Ocean Water
GNIP Global Network for Isotopes in Precipitation
K Hydraulic conductivity
Ss Specific Storage
Sy Specific yield
PMWIN Processing Modflow for Windows
RMS Root Mean Square
QUT Queensland University of Technology
STATEMENT OF ORIGINAL AUTHORSHIP
The work contained in this thesis has not been previously submitted
for a degree or diploma at any other higher education institution.
To the best of my knowledge and belief, the thesis contains no
material previously published or written by another person except
where due reference is made.
Signature: Andrew Wilson
Date: 25 / 2 / 05
I
ACKNOWLEDGEMENTS
I would like to thank the following people for the ways they have
contributed to this study:
Dr Malcolm Cox: supervision, funding, good humour and giving me the opportunity to attempt this project.
Dr Vivienne McNeil: associate supervision and providing access to the
NRM&E groundwater database, maps, reports and sharing her knowledge.
Dr Miceala Preda: GIS and visualisation software “technical support”. Tim Ezzy: acting as an “unofficial associate supervisor” on this
project. Thanks mate for all our discussions of fish, cricket and the meaning of life.
John Harbison: groundwater modelling advice and hydrochemistry
advice. Tim Armstrong: assistance with pumping tests both in the field and at
uni. Peter Cochrane: assistance with locating bores in the field and use of
the NRM&E compressor for water sampling. Wathsala Kumar: assistance with laboratory work. NRM&E staff: Andrew Durick, Ashley Bleakley, Rob Ellis, Gerard
McMahon, Matthew Stenson, Mike Mikillop, Chris Strachotta for providing access to data, maps, reports and sharing their knowledge.
Thank you to the many friendly and co-operative landholders I’ve met in the
Lockyer Valley for their assistance.
Thanks to all my fellow students at QUT NRS.
Thanks to my friends for their help with both uni and non uni stuff.
I would especially like to thank my parents and my brother for their
continual support and interest in my studies.
1
1. INTRODUCTION
Background
The Lockyer Valley is an intensively irrigated agricultural region in
southeast Queensland and is of high economic significance, producing one
third of the vegetables in that state. Groundwater is the primary source of
irrigation water and is extracted from the Quaternary alluvial aquifers
situated along the Lockyer Creek drainage and its tributaries. Drilling by the
Queensland Department of Natural Resources, Mines and Energy
(NRM&E) has revealed the alluvium comprises a laterally continuous layer
of gravel overlain by mixed sands and clays. The underlying Mesozoic
sandstone bedrock aquifers are generally not used for irrigation as the
expected yield is generally much lower than the alluvium and the water
quality can be poor. The area under cultivation and the volume of
groundwater extracted from alluvium have increased substantially over the
past 60 years; of note, during drought conditions the demand for irrigation
water increases resulting in a reduction of yield from many bores and loss of
agricultural productivity.
Purpose and scope of the investigation
The focus of this study is two subcatchments in the south western Lockyer
Valley, those of Tenthill and Ma Ma. Although separate drainages for most
of their length, they converge and flow out onto the broad Lockyer alluvial
plain before discharging separately into Lockyer Creek. Both catchments
contain irrigated agriculture, however, the most intensive cultivation is on
the Lockyer plain below the convergence. Management of the valuable
groundwater resource requires an understanding of the hydrogeology of the
alluvial aquifers, the aim of this study. Hydrogeological techniques utilised
in this study include: bore hydrograph interpretation, pumping tests, and
hydrochemical and stable isotope analyses. The results of these
investigations are incorporated into a conceptual model, which is an
essential step before the development of a numerical groundwater flow
2
model. A calibrated groundwater flow model is a tool for predicting the
behaviour of this heavily exploited aquifer and can be used to test different
extraction scenarios, and provide the basis for decisions on future
groundwater management.
Aim
Establish the hydrogeology and a conceptual groundwater model of the
alluvial aquifers in the Tenthill and Ma Ma catchments and from this a
numerical groundwater flow model, as a tool for groundwater management.
Objectives
a) Define the types of aquifers and aquitards present within the Quaternary
alluvium;
b) Examine long term water level variations in the alluvial aquifer of the
Lockyer plain and their relationship to climatic conditions;
c) Determine estimates of the hydraulic properties of the alluvial aquifers by
the use of hydraulic (pump) testing;
d) Examine the hydrochemical and stable isotopic character of the alluvial
groundwater in Tenthill and Ma Ma catchments and the Lockyer plain, and
compare with bedrock groundwater;
e) Develop a conceptual hydrogeological model of the Lockyer alluvial
plain;
f) Develop a transient numerical groundwater flow model for the Lockyer
plain and determine the effects of different groundwater extraction rates on
the minimum saturated aquifer thickness.
3
2. PHYSICAL SETTING
Location
The study area comprises the Tenthill and Ma Ma catchments (TMMC),
situated in the western Lockyer Valley, south of the town of Gatton,
approximately 80 km west of Brisbane in southeast Queensland (Figure 1).
These two separate drainages rise in the Great Dividing Range to the south
and flow onto an alluvial plain before discharging separately into Lockyer
Creek. Elevations range from 400m at the headwaters of the creeks to
75masl at Gatton. The combined area of both drainages and the alluvial
plain is approximately 850 000 km2 (NRM&E GIS database).
Climate
Climatic conditions in the Lockyer Valley are subtropical and most
precipitation is received during the warmer months. The Great Dividing
Range to the south and west exerts a strong orographic effect on the local
climate, particularly during the summer when the dominant wind direction
is from the southeast. The resulting distribution of rainfall is of mean annual
precipitation of up to 1200 mm at the higher elevations compared to 720
mm at Gatton in the centre of the valley (Commonwealth Bureau of
Meteorology). The region has experienced numerous drought periods over
the last 40 years, notably during 1968-1970, 1979-1980, 1986-1987 and
1993-1995, with monthly rainfall events of 380 mm or greater occurring in
1968, 1974, 1988 and 1996 (Figure 2). Evaporation has been monitored at
the Queensland Department of Primary Industries (QDPI) Research station
at Gatton from 1992 onwards. Data for the period 1992 -2002 demonstrate
that evaporation is seasonal and may be more than twice as great in summer
than in winter (Figure 3).
5
Gatton monthly rainfall 1960-2003
0
50
100
150
200
250
300
350
400
450
500
Jan-60
Jan-62
Jan-64
Jan-66
Jan-68
Jan-70
Jan-72
Jan-74
Jan-76
Jan-78
Jan-80
Jan-82
Jan-84
Jan-86
Jan-88
Jan-90
Jan-92
Jan-94
Jan-96
Jan-98
Jan-00
Jan-02
Date
Mon
thly
rian
fall
(mm
)Jan 1968
Jan 1974
April 1988
May 1996
Figure 2. Monthly rainfall recorded at Gatton for the period 1960 – 2003,
demonstrating monthly rainfall events of 380 mm or greater occurred in
1968, 1974, 1988 and 1996.
Gatton monthly rainfall and evaporation 1992-2002
0
50
100
150
200
250
300
350
400
450
500
Jul-92
Jan-93
Jul-93
Jan-94
Jul-94
Jan-95
Jul-95
Jan-96
Jul-96
Jan-97
Jul-97
Jan-98
Jul-98
Jan-99
Jul-99
Jan-00
Jul-00
Jan-01
Jul-01
Jan-02
Jul-02
Date
Mon
thly
rain
fall
(mm
)
0
50
100
150
200
250
300
350
Mon
thly
eva
pora
tion
(mm
)
Monthly rainfallMonthly evaporation
Figure 3. Monthly rainfall compared to monthly evaporation recorded at
Gatton for period 1992 – 2002. Evaporation in summer (January) may be up
to two times the evaporation in winter (July).
6
Geomorphology
The TMMC are both major tributaries of Lockyer Creek, which is in turn a
tributary of the much larger Brisbane River drainage. The catchments are
bounded in the south by the Basaltic plateau of the Main Range Volcanics at
an elevation of approximately 400m, and to the north west and east by the
Jurassic Marburg Formation Sandstones. In the mid to upper reaches the
two drainages are separated by the quartzose sandstones of the upper
Marburg Formation which has been weathered to rounded hills with some
steep slopes. In the north the catchment is bounded by Lockyer Creek which
roughly follows the surface expression of the Triassic to Jurassic Gatton
Sandstone. This sandstone is finer grained and less resistant to erosion and
consequently forms gently rolling hills in the north. The TMMC drainage
systems evolve from a dendritic pattern at the basaltic headwaters to a trellis
pattern over the Marburg Sandstones. The numerous tributary streams
include Heifer, Lagoon, Dry Creeks in the Ma Ma drainage and Black Duck,
Blackfellow, Wonga and Deep Gully Creeks in the Tenthill drainage. These
systems display trellis style confluences with the main stream channels. In
the mid to upper reaches the creek channels are deeply incised with
extensive terrace deposits along their margins; while in the lower reaches
the channels become more meandering in nature and both drainages
converge to within 300 m of each other before flowing out onto the alluvial
plain of flat overbank deposits. Immediately before its confluence with
Lockyer Creek, Tenthill Creek follows the contact between the Quaternary
Alluvium and the Gatton Sandstone, which is exposed along the creek
channel.
Soils
Soils of the Lockyer Valley can be strongly correlated with the geological
units from which they are derived and in the study area seven different soil
types are recognised from the classification of Smith et al. (1990).
The Gatton Association as its name suggests occurs over the Gatton
Sandstone and is dominated by solodic soils of sandy loam and sand grading
7
down to heavy clay in the A horizons. The B horizon often contains calcium
carbonate and a greater proportion of exchangeable magnesium. Infiltration
of surface water is minimal and consequently runoff is large.
The Winwill Association is also named after the stratigraphic unit from
which it is derived, is characterised by soloths and solodized solonetz soils
with negligible amounts of exchangeable calcium but large amounts of
exchangeable sodium and magnesium. On the steeper slopes red podzolic
soils are more common. With all soils the A horizons are also hard setting
and impermeable resulting in high runoff.
The Ma Ma Association occurs over the Ma Ma Creek Sandstone and has a
varied composition ranging from sandy loam to sandy clay loam to sandy
clay with an abundance of exchangeable calcium throughout all the
horizons.
The Beins Mountain Association has formed on the steep slopes of the
Heifer Creek Sandstone Member. Resistant and non resistant beds of
sandstone have been weathered to produce red podzolic soils and clay soils
respectively. Red podzolic soils are characterised by fine sandy loam
grading down to silty clay loam and these upper horizons contain abundant
exchangeable calcium. The clay soils are typically dry cracking types with a
smooth ped fabric, containing abundant exchangeable calcium and
magnesium. Calcium carbonate is also present in the lower horizons.
A similar soil known as the Whitestone Association occurs on the upper
Heifer Creek Sandstone and the Walloon Coal Measures and comprises
grey, brown and red clays and red podzolic soils. Exchangeable cations
include calcium and magnesium.
Basalts typically weather to produce prairie soils of the Neumann
Association ranging from 30 to 80 cm thick, with abundant exchangeable
calcium and minor exchangeable magnesium.
The most productive soil in the Lockyer region is the Rosewood Association
of the Quaternary alluvium, comprised of prairie soils adjacent to the main
stream channels, ranging to black earths on the flat plains, with calcium the
dominant exchangeable cation.
8
Land Use
In the late 1800’s the Lockyer region supported dairy farming and extraction
of groundwater was minimal or non-existent. Clearing of the native eucalypt
forests exposed the agricultural potential of the rich soils and cultivation of
small crops began in the 1930’s and has continued with increasing intensity
to the present. Lucerne is widely cultivated in addition to numerous
vegetables including cauliflower, broccoli, cabbage, lettuce, onions and
potatoes. Cultivation is restricted to the alluvial soils along the major creek
channels and the broad alluvial plains in the central part of the valley and is
irrigation intensive. The surrounding bedrock slopes are used for stock
grazing, mainly beef cattle, or rejuvenation of native vegetation. Minor land
use includes a small vineyard at Mt Whitestone adjacent to Ma Ma Creek
and a fish farm in the upper Tenthill.
Water use
The use of groundwater for irrigation purposes began in the 1930’s, and
extraction had greatly increased in the 1950’s. Use of groundwater for
irrigation has continued to increase at a steady rate leading to shortages in
drought periods. Water is drawn primarily from the Quaternary alluvium
deposits throughout the valley. The underlying sandstone bedrock aquifers
are generally not used for irrigation as the expected yield is generally much
lower than the alluvium and the water quality can be poor in areas, up to
10000 µS/cm. In an attempt to quantify the volume of groundwater
withdrawn for irrigation NRM&E has established the central Lockyer region
as a proclaimed area and installed water meters on all irrigation bores. The
proclaimed area is defined as the broad alluvial plain extending from Gatton
east to Kentville and south along Laidley Creek almost to Mulgowie.
Beginning in the early 1990’s, automatic meters have been used to record
the volume of groundwater withdrawn and the data is read at approximately
3 monthly intervals and stored at the NRM&E Gatton office. Landholders
are charged for each ML of water used and the data obtained is utilised for
9
water resource management and planning. Stock watering and domestic
bores are not metered.
Three surface water storages have been constructed in the Lockyer Valley:
Lake Clarendon north of The University of Queensland Gatton Campus,
Lake Dyer (Bill Gunn Dam) at Laidley and Atkinson Dam at Lyons Bridge.
The purpose of the three dams is to catch and store runoff for later use as
irrigation water, at cost to landholders, or as is the case of Lake Dyer, the
dam acts as a source for releases into Laidley Creek to recharge the alluvial
aquifer. During the drought of 2001-2003 the only storage with useable
quantities of water remaining was Lake Clarendon. Numerous recharge
weirs have been constructed on many drainages in the Lockyer Valley,
including the TMMC, to retard the flow of surface water and increase
recharge through the creek channels to the alluvial aquifers.
5
3. GEOLOGICAL SETTING
Regional Geology
The Lockyer Valley is situated in the Laidley Sub-basin, which lies between
the Cecil Plains Sub-basin and the Logan Sub-basin in the broad
intracratonic Clarence Moreton Basin. The Laidley Sub-basin
unconformably overlies the Esk Trough and is separated from the Cecil
Plains Sub-basin in the west by the Gatton arch, a broad basement ridge, and
from the Logan Sub-basin in the east by the South Moreton Anticline. A
major structure, the West Ipswich Fault separates the Laidley Sub-basin and
the Esk Trough from the South D’Aguilar Block in the north east (Ingram
and Robinson 1996) (Figure 4).
Both the Permian Cressbrook Creek Group, comprising meta-sediments and
basic volcanics, and Permian to Triassic granites crop out in the north of the
valley. They are however overlain by younger units in other areas, primarily
the Jurassic Marburg sandstones. The definition of the Jurassic Marburg
Subgroup, has been the subject of many revisions (McTaggart 1963; Grimes
1968; Gray 1975; Wells et al. 1990; Wells and O’Brien 1994). Currently
this subgroup is divided into the Gatton Sandstone which outcrops both
north and south of Lockyer Creek, and the Koukandowie Formation (Wells
and O’Brien 1994), which only occurs south of Lockyer Creek, and includes
the Tenthill and Ma Ma catchments. The Marburg Subgroup is overlain by
the Jurassic Walloon Coal Measures which is in the upper part of the
stratigraphic profile of the Lockyer Valley, and has minor surface exposures
only. The ranges to the south and west of the valley are covered by Tertiary
basalt flows of the Main Range Volcanics. The incised channels in the
bedrock contain extensive deposits of Quaternary alluvial fill.
6
Geological units of the Tenthill and Ma Ma catchments
Four main geological units can be identified in the study area with the
following ages and stratigraphic positions:
Alluvium -Quaternary
Main Range Volcanics -Tertiary
Walloon Coal Measures -Jurassic
Marburg Subgroup -Jurassic
Marburg Subgroup
The units of the Marburg Subgroup, formally the Marburg Formation, have
been revised many times; a summary of the major revisions follows. The
group was first described in detail by McTaggart (1963), in a localised study
of the Mesozoic sequence of the Lockyer Marburg area. A type section was
presented in a south westerly direction from Gatton along Ma Ma Creek and
ending at Heifer Creek; this loosely followed the course of the Gatton-
Clifton Road. The formation conformably overlies the Helidon Sandstone in
the north and west and is conformably overlain by the Walloon Coal
Measures in the south. McTaggart (1963) described a lower caliche section
of the formation comprising three members: Gatton Sandstone, Tenthill
Conglomerate, Ma Ma Creek Sandstone and an upper siliceous portion
comprising a single member, the Heifer Creek Sandstone. All members dip
to the south and south-south west at an angle of 10o or less.
The Gatton Sandstone is a massive, caliche, lithic sandstone with minimal
cross bedding, rich in quartz and various lithic fragments set in argillaceous
matrix. Thickness ranges from 30 to 60 m.
The Tenthill Conglomerate, later renamed the Winwill Conglomerate to
avoid confusion with another unit in South Australia of the same name
(Gray 1975), is characterised by fossilwood clasts supported in a pale white
sandstone. Clasts are orientated horizontally suggesting torrential
7
accumulation from an outside source. The member generally outcrops on
the southern side of Lockyer Creek and is easily recognisable and mappable
due to the distinctive clasts. Thickness ranges from 30 to 45 m.
The Ma Ma Creek Sandstone Member is composed of micaceous, flaggy,
lithic sandstones, shales and siltstones. Minor fossilwood clasts are also
present however in much lower densities than the Tenthill Conglomerate,
supporting the definition of the Ma Ma Creek Sandstone as separate
member. Typical thickness is 75 m.
The coarse grained, ferruginous, siliceous Heifer Creek Sandstone Member
is easily recognisable as the steep resistant hills it forms in the Tenthill and
Ma Ma catchments. The member also includes minor shale and coal but its
high quartz content easily distinguishes it from the underlying Ma Ma Creek
Member and the overlying Walloon Coal Measures. Thickness ranges from
180 to 240 m.
This thesis will utilise the classification of McTaggart (1963) (Figure 5), as
each unit is treated as a lithologic and geomorphologic entity which
provides a level of detail suitable for identifying hydrological processes.
This approach has been utilised by previous groundwater investigations in
the Lockyer Valley (e.g. McMahon 1995; McMahon and Cox 1996).
Grimes (1968) noted that the conglomeritic bands and siliceous wood clasts
of the Winwill Conglomerate member were not continuous throughout the
Lower Marburg Formation. He suggested these bands were deposited in a
high energy environment, while the interbedded sandstones were deposited
in a much lower energy environment, adjacent to the stream channels. The
smooth upper boundary between the Winwill Conglomerate and the
overlying Ma Ma Creek Sandstone Member and the presence of some
fossilwood bands within the latter was argued as further justification for not
recognising the Winwill Conglomerate Member in that study.
10
The name Heifer Creek Sandstone Member of McTaggart (1963) was
dropped in favour of the name Upper Marburg Formation for the resistant
quartzose sandstones comprising up to 30% of the sequence interbedded
with non resistant friable sandstones, siltstones and shales (Grimes 1968).
The division of McTaggart (1963) into a lower caliche section and upper
siliceous section was rejected by Grimes (1968) on the basis of the
occurrence of calcite cement in both formations. Instead Grimes (1968)
placed emphasis on the lithic, non resistant Lower Marburg Formation
compared to the quartzose resistant Upper Marburg Formation.
Wells et al. (1990), and Wells and O’Brien (1994) presented a review of the
whole sedimentary sequence of the Clarence Moreton Basin, with a view
towards a standard lithological framework suitable for the entire basin in
both Queensland and New South Wales. Although the review comprises a
regional basin-wide study, as opposed to a localised classification of the
Lockyer Mesozoic sequence by McTaggart (1963) and Grimes (1968), it is
discussed here as it represents the most recent work on the sedimentary
units of the Lockyer Valley.
The Gatton Sandstone Member was elevated to Formation status, while the
Winwill Conglomerate Member was again omitted on the basis of it not
being a single discernable unit but rather numerous conglomeritic beds
within the Gatton Sandstone as detailed by Grimes (1968). The formation
was further subdivided into the shale and interbedded fine grained sandstone
of the Calamia Member, and the pebble to cobble sized Koreelah
Conglomerate, in the southern and western margins of the Clarence-
Moreton Basin, respectively. Neither of these two members outcrops in the
Lockyer Valley.
In place of the Upper Marburg Formation the Koukandowie Formation was
established. This new formation includes the lithic sandstones, shales and
siltstones of the Ma Ma Creek Sandstone Member, and quartzose sandstones
of the Heifer Creek Sandstone Member of McTaggart, which was also
reinstated. Due to the greater proportion of shales and siltstones it contains,
11
the Ma Ma Creek Sandstone Member was renamed the Ma Ma Creek
Member. Wells and O’Brien (1994), also identified an unnamed sandstone
member within the Ma Ma Creek Member, with a restricted exposure
between Ma Ma Creek and Murphy’s Creek in the Lockyer Valley. The
member is more quartz rich and less well sorted than the underlying
sandstones of the Ma Ma Creek member, although not as coarse grained as
the overlying Heifer Creek Sandstone Member. A low sinuosity river was
proposed as the environment of deposition with material sourced from the
New England Orogen, and cross bedding measurements were used to
suggest a direction of sediment transport to the north west. The shale and
thin sandstone beds of the Ma Ma Creek Member were proposed to be the
result of fluvial transgression into a lacustrine environment while the
additional description of elipson cross bedding in the Heifer Creek
Sandstone Member was used to support deposition within a highly sinuous
stream environment.
Walloon Coal Measures
A thin but continuous outcrop of the Mid Jurassic Walloon Coal Measures
occurs in the upper reaches of the Tenthill and Ma Ma catchments. The
lithology of the Walloon Coal Measures is varied and includes volcanolithic
sandstone, carbonaceous siltstone, shale and mudstone, bentonitic siltstone
and minor oil shale (McTaggart 1963). Economic coal occurs in the
Rosewood area near Ipswich with a thickness of up to 420 m; however in
the Lockyer Valley the maximum thickness is 60 m where the formation
outcrops from beneath the overlying basalts. The lower boundary is marked
by a change from quartzose sandstones of the Heifer Creek Sandstone
Member to volcanolithic sandstones and a generally higher proportion of
shale and siltstone. A lacustrine depositional environment with a volcanic
source area was suggested by Grimes (1968).
12
Main Range Volcanics
Tertiary age extrusives to the south and west of the Lockyer Valley can be
divided into two basaltic units, separated by a lateritic zone and are part of
the Main Range Volcanics. In the West Haldon area at the headwaters of
Ma Ma catchment, these flows consist of olivine basalts; the basalts also
contain plagioclase, clinopyroxene and up to 10% calcite at the base of the
sequence. Geochemical analyses have revealed the presence of normative
andesine, therefore the basalts have been classed as hawaiites (Dudgeon
1978). Cooling structures such as columnar jointing in basalt at Mt
Whitestone near Ma Ma village indicates an intrusive basaltic plug, with a
composition similar to the extrusives further south (Grimes 1968).
Quaternary Alluvium
The Tenthill and Ma Ma Creeks like all the other drainages in the Lockyer
Valley are flanked by Quaternary alluvium. NRM&E has drilled an
extensive network of alluvial monitoring boreholes throughout the Lockyer
Valley. Examination of borelogs reveals a typical fining upward sequence of
gravel, sandy gravel and sand, immediately overlying bedrock, proceeding
upwards to silt, sandy clay and clay towards the surface. The gravel, which
may approach cobble size, is well rounded and is sourced from the Main
Range Volcanics at the headwaters of the streams. In the central plains of
the lower Lockyer Valley sand is widespread and overlies the gravel,
however in the TMMC sand is minor and not laterally continuous; this sand
forms lenses above the gravel in the Lockyer plain. In the mid to upper
reaches of the catchments sand is typically absent. The gravel is an
extremely productive aquifer which supports the agricultural activities of the
region, while the overlying silt, sandy clay, and clay act as a semi-confining
layer. In the catchments being studied the alluvial sequence has an average
thickness of 27 m, of which the gravel has an average thickness of 4.5 m.
17
4. HYDROGEOLOGICAL BACKGROUND
Occurrence of Groundwater in the Lockyer Valley
The Lockyer Valley is a highly productive and economically important
agricultural region in southeast Queensland. The principal source of
irrigation water is groundwater drawn from the extensive Quaternary
alluvial deposits which infill the deeply incised channels in the sandstone
bedrock. Quaternary alluvium in the Lockyer Valley is typically up to 35 m
deep and is composed of gravel and minor sand with overbank deposits of
clay, sandy clay and silt. The alluvial aquifers produce the highest yields
and best quality water compared with the sandstone bedrock which is
typically too saline for irrigation purposes.
Types and Features of Alluvial Sequences
Alluvial channels may be divided into three main types: (a) bed load, (b)
mixed load and (c) suspended load (Galloway and Sharp 1998), which have
the following characteristics:
(a) bed load systems: contain both channel and channel flank deposits with
coarse sand common, and gravel common but not necessary. They are
characterized by a high width to depth ratio and low sinuosity with uniform
scour along the channel base. Within them longitudinal, traverse, lateral and
chaute bars may all occur.
(b) mixed load systems: have a much higher portion of sand, typically
between 30 and 60% sand with the channel fills flanked by crevasse splay
and levee sands. The width to depth ratio and the sinuosity are both lower
and higher respectively than bed load systems, which fosters the
development of lateral accretion structures such as point bars.
(c) suspended load systems: comprise of a fill of fine sand to silt to clay and
consequently levee and crevasse splay deposits are common. The width to
depth ratio is extremely low and the channels are highly sinuous to
anastomosing.
18
These different systems are closely related to topography and
geomorphology. In a downstream direction the channel slope, valley slope
and the channel width to depth ratio all decrease. This change is reflected by
the corresponding increase in sinuosity of a channel and decrease in grain
size of an alluvial sequence. Bed load systems therefore dominate the
steeper upper portions of a catchment, becoming mixed to suspended load
systems as the stream progresses down gradient (Galloway and Sharp 1998).
In an alluvial valley fill the deposits are bounded on two sides by bedrock
walls which typically are low permeability or impermeable. The channel is
only able to meander within the confines of the valley walls; coarse
sediment is deposited relatively quickly and dominates the fine overbank
deposits. This predominance of sand and gravel reflects a bed load system
and is of significance to groundwater as it forms the coarsest sediment
immediately above the valley floor which has the highest hydraulic
conductivity. In the deeper portions of the sequence this coarse sediment
may be locally confined by the upper stratum of floodplain deposits and
soil, while in shallower portions it may be hydraulically connected to the
stream channel (Galloway and Sharp 1998).
Groundwater flow within alluvial deposits may be parallel to the stream
channel as underflow or directly towards the stream channel as baseflow.
The criteria for distinguishing between these processes were investigated in
numerous alluvial basins by Larkin and Sharp (1992). The results
demonstrated that underflow was dominant when the channel gradient
exceeds 0.0008, the sinuosity is less than 1.3, the river penetration less than
20% of the alluvial sequence, and the width to depth ratio of the channel is
greater than 60. These criteria are most commonly met in valley fill and
mixed load to bed load systems, or in the upstream and tributary reaches of
a drainage.
Baseflow was found to dominate under the opposite conditions and is most
common in suspended load systems and in the lower reaches of a drainage.
Sinuosity of a fluvial channel acts as a hydraulic sink that fosters baseflow
19
and consequently baseflow is greatest where sinuosity is highest. Local
areas of baseflow may occur immediately adjacent to the stream channel in
otherwise underflow dominated systems. These areas can be recognized by
rapid fluctuations of groundwater level which correspond to the fluctuations
of the stream stage at the same location. Groundwater extraction through
pumping can also cause transient mixed flow conditions by inducing
localised underflow or baseflow and locally changing the dominant flow
process, however such effects are usually restricted to the area of pumping
influence.
Features of Bedrock Aquifers
Siliclastic sedimentary rocks including sandstone, siltstone and shale are
formed in all types of depositional environments such as marine, fluvial,
deltaic, lacustrine and eolian. The porosity and permeability of siliclastic
sedimentary rocks is a function of grain size and degree of sorting and is
lower than unconsolidated sediments due to cementation and compaction.
Cementation from clay minerals, carbonates, silica or iron oxides may
greatly reduce porosity by in-filling of spaces between grains. The effect of
cementation is greatest in sandstone; however a poorly sorted sandstone
may still have a porosity as high as 35%. In siltstones and shales the effect
of compaction on porosity is more apparent, with a decrease from 50-80% at
the time of deposition down to usually less than 3%. Therefore the primary
hydraulic conductivity of siliclastic rocks decreases with age.
Secondary porosity and permeability may be created by fracturing in
siliclastic rocks. When a rock at depth is uplifted to the surface it may
expand and subsequently fracture due to the decrease in pressure. This
process known as unloading produces fractures occurring within 100 m of
the surface. Tectonic activity may also create fractures however these
fractures can occur at any depth. Hydraulic conductivity along a fracture is
typically much greater than the surrounding rocks and vertical fractures
through impermeable strata may act as conduits for groundwater flow
(Fetter 1994; Singhal and Gupta 1999).
20
Previous groundwater investigations in the Lockyer Valley
A broad hydrogeological study presented by Zahawi (1975) provided a
useful overview of groundwater in the Lockyer Valley with discussion of
water chemistry variations. The dominance of sodium ions and lack of
calcium were suggested to originate from cation exchange in the clay
minerals in the sandstones. High magnesium concentrations were attributed
to the weathering of basalts in the south and west, some of which contain up
to 20% olivine. Zahawi also suggested magnesium may come from the
residue of marine transgressions during the Mesozoic. In the same report the
results of several pump tests conducted in the alluvial aquifers by the Water
Resources Commission were presented, with transmissivity varying from 75
to 1625 m2/day and storage coefficient ranging from 0.0001 to 0.074. From
over 500 boreholes drilled in the alluvium, an average aquifer thickness of
3.61 m was estimated.
Talbot and Dickson (1969) conducted a study of the salinity of surface
water and its suitability for irrigation purposes. Following this several
artificial recharge weirs were constructed throughout the Lockyer Valley in
the 1970’s to retard the flow of surface water and increase the amount of
recharge seeping through to the alluvial aquifers below the stream channels.
Lane and Zin (1980) presented an evaluation of the weir in the upper
reaches of Ma Ma Creek and estimated that, for the 3 year monitoring
period in the 1970’s, the weir contributed recharge of 195 000 ML per
annum to the Ma Ma creek alluvium.
Widespread sampling undertaken by Talbot et al. (1981) provided an
understanding of alluvial groundwater quality and the effects of the 1980
drought and significant deteoriation in water quality being observed.
Dixon (1988) examined the hydrochemistry of groundwater in the Tenthill
and Ma Ma catchments during wet and dry periods to establish the temporal
effects of rainfall. Following that study, Dixon and Chiswell (1992), used
hydrochemical sections to identify areas of saline intrusions from bedrock
21
into alluvial aquifers and also to identify areas of recharge from stream
waters. Dixon and Chiswell (1994) identified the enrichment in stable
isotopes δ2H and δ18O in samples from Ma Ma Creek alluvium as
evaporative concentration, and proposed re-circulation of irrigation water as
the cause of saline groundwater in this catchment.
For the Sandy Creek Catchment near Laidley McMahon (1995) and
McMahon and Cox (1996) examined the relationship between
hydrochemistry of saline groundwater in alluvial aquifers and that of the
underlying Jurassic sedimentary formations. Those studies demonstrated
that during periods of low stream flow, such as the 1993 – 1995 drought, the
chemistry of groundwater of the alluvial aquifers can be spatially grouped
and correlated to the underlying sandstone bedrock. The studies indicate
each bedrock unit has an influence on alluvial groundwater chemistry and
may discharge to the alluvium. Along the Sandy Creek drainage four
hydrochemical groups were identified, corresponding to the four members
of the underlying Marburg Formation. Two additional groups were
identified, one showing evidence of mixing between two of the Marburg
members, the other representing the influence of groundwater from the
adjacent Laidley Creek alluvium at the junction of the two drainages. It was
further suggested that the more resistant nature of the Winwill
Conglomerate Member may create a hydraulic barrier and reduce
groundwater flow. This hydrological barrier could result in longer residence
times and concentration of salts, which may account for the higher salinity
in waters observed immediately above the Winwill Conglomerate.
In a similar study in the Ma Ma Creek catchment (Macleod 1998), the
salinity of alluvial aquifers was attributed to contributions from the
underlying Gatton Sandstone and Ma Ma Creek Sandstone Members of the
Marburg Formation. From the identification of seven hydrochemical groups
it was determined that the lowest salinity waters were sourced from the
weathered basalts in the upper catchment. Higher salinity alluvial waters
22
were found to occur above the sandstones in the lower catchment, indicating
salinity increases down gradient.
A detailed assessment of existing water quality records for the whole
Lockyer Valley was conducted by McNeil et al. (1993), which demonstrated
that the existing monitoring network was inadequate. That study proposed
further monitoring bores and surface water stations, and stressed the
importance of a spatial distribution of sampling points. Wills and Raymount
(1996) compared the results of numerous groundwater chemical analyses
including the data of Talbot et al. (1981), with samples collected at different
times (a) 1984 following a flood, (b) 1994 during a drought, and (c) 1996
following a flood. Significant improvements in water quality were found to
occur following flood events or periods of regular rainfall.
An isotopic study of groundwater recharge to alluvial aquifers east of
Gatton was conducted using stable isotopes δ2H and δ18O and radiogenic
isotopes 3H and 14C (Dharmasiri and Morawska 1997). Emphasis was
placed on the importance of creek channels for the recharge of alluvial
aquifers, as evidenced by the similarity between the stable isotopic
composition of surface water and alluvial groundwater. Sandstone aquifers
were found to be isotopically distinct and not to contribute recharge to
alluvium; the exception is the Crowley Vale area, which received recharge
from the underlying Gatton Sandstone. The 14C ages of alluvial groundwater
from Crowley Vale ranged from modern up to 4810 years BP indicating
recharge from sandstone. In all other areas, 3H activities demonstrated that
the youngest alluvial groundwater occurred adjacent to the creek channels.
The 3H activity typically decreased with distance from the streams; these
variations suggest that infiltration from stream channels is the principal
recharge mechanism, as supported by stable isotope measurements.
The effects of irrigation on the water quality of alluvial aquifers were
investigated using the Lockyer Valley as a case study and presented by Ellis
and Dharmasiri (1998) and Ellis (1999). Investigation boreholes were
23
drilled at five sites throughout the valley and cores recovered for analyses of
pesticides, with 3H activities and stable isotope measurements also taken
from pore water from the cores. At all locations geological logs revealed a
fining upward alluvial sequence from gravel to sand to clay as described
previously. Results from 3H analyses indicate an average infiltration rate of
12 mm per year for the clay and silt layer, demonstrating the effects of
irrigation induced salinity have not yet reached the underlying gravel
aquifer. Pesticides were also absent below a certain depth further suggesting
slow infiltration.
A broad scale conceptualisation of the Upper Lockyer region including the
western and south western tributaries was undertaken by NRM&E for
estimating the storage potential and fluxes through the alluvium. The
thickness of the alluvium was calculated by subtracting the bedrock
elevations from the surface elevations obtained in NRM&E bore logs, and
the area of alluvium was divided into several large nodes with a
representative bore allocated for each node. Parameters used were hydraulic
conductivity of 20m/day, the measured hydraulic gradient between adjacent
nodes, and the cross sectional area of the alluvium at the boundary between
these nodes; these were substituted into Darcy’s Law to obtain an estimate
of the flow between different nodes. Landsat imagery was utilised to
determine the areas under irrigation including vegetables, lucerne, other
unspecified cultivation and soil ready for planting. An average value of
groundwater extraction was applied at 3.5 ML/ha for these areas; this is
based on average withdrawals in the NRM&E proclaimed area further east
and the storage curve for each node was calculated. The conceptualisation
did not consider the stratigraphy of the alluvium but rather the entire
sequence was treated as one aquifer. In addition the subdivision of the
alluvium into several large nodes each with a representative bore decreases
the accuracy of the determination of the hydraulic gradient and subsequently
the calculation of the flux down the valleys.
The first finite difference numerical groundwater flow model for the
Lockyer region was developed by Durick and Bleakley (2003).
Groundwater fluctuations in a drought and subsequent flood were simulated
24
for the proclaimed area using the software package MODFLOW (McDonald
and Harbaugh 1988). Geological logs were used to define the thickness of
the sand and gravel aquifer which occurs throughout the broad plain of the
proclaimed area. The overlying clay and sandy clay units were not included
as part of the aquifer. Water level measurements and extraction data from
the NRM&E database were input to estimate parameters including aquifer
hydraulic conductivity and specific yield, which were then used to estimate
recharge. The approach benefits from the abundance of groundwater
extraction measurements from meters installed on all irrigation bores in the
proclaimed area. As recharge was assumed to be zero during a drought
period, the drawdown around each pumping bore simulated by the model
was in effect a pump test. The numerous monitoring bores enabled the
spatial distribution of aquifer properties to be estimated. In all 53 zones of
different aquifer properties were identified with hydraulic conductivity
ranging from 1 to 250 m/day and specific yield ranging from 1 to 20%.
These aquifer properties were input to the model to estimate the magnitude
of recharge entering the aquifer from creeks during wet periods. The results
of the modelling have been used to test various scenarios for the application
rates of irrigation water.
NRM&E database
Queensland NRM&E has compiled an extensive groundwater database for
the entire state of Queensland. Records for monitoring bores typically
include, coordinates of the bore location and a strata log, as well as bore
completion details, bore elevations, water level measurements, water
chemical analyses and pump test data. Data are, however, variable and
continuous records are rare. In the case of the Lockyer Valley, extensive
water level measurements have been taken since the late 1950’s however
these are restricted to a few locations. In the TMMC the drilling of NRM&E
monitoring bores increased substantially in the early 1980’s and the area is
well represented by a network of bores with regular water level
measurements for the period 1988 to the present. In this network the longest
gap between water level measurements is 6 months, with measurements
25
typically being taken every 3 months. The network includes an auto
recorder bore where readings are taken and stored on a data logger;
measurements may be monthly or as regular as weekly for one period in the
mid 1990’s.
For manual readings the depth to water is measured with an electronic dip
meter comprising a tape with a probe at its end which emits a chime when
water is reached. All measurements are recorded relative to the top of the
steel well head, which for NRM&E monitoring bores has been surveyed to
Australian Height Datum (AHD); this is used as a reference for the depth to
water measurements. Bore completion details including length of slotted
casing and width of gravel pack are not always available; in these cases the
most common situation is assumed. Water chemical analyses have also been
conducted about every 5 years since 1985 and appear on the database.
Electrical conductivity and pH were not always measured in the field and
therefore may not be representative, particularly pH. Samples were taken in
plastic bottles and subsequently analysed in the laboratory for major cations
(sodium, potassium, magnesium and calcium) and major anions (chloride,
sulfate, bicarbonate and nitrate). As pumping test data is lacking for the
entire Lockyer region hydraulic testing was conducted during this study.
The NRM&E database uses a bore Registration Number (RN); the current
RN numbering system comprises 8 digits for NRM&E bores with the first 3
digits representing the basin number and the fourth digit representing the
sub basin number. The basin number for the Brisbane basin is 143 and the
sub basin number for the Lockyer basin is 2, therefore all government bores
in the Lockyer region start with 1432. The remaining 4 digits comprise the
bore’s identification number and in the Lockyer range from the oldest
0001to most recent 0865. For simplicity, in this thesis NRM&E bores will
be referred to by only the last 3 digits of their RN, for example, RN
14320865 will be 865.
Information from the database can be exported as either PDF file format to
be opened with Acrobat Reader, or dbf file format to be opened with
26
Microsoft Access. The PDF option allows the construction of a “bore card”
for a particular bore displaying all known information for that bore and
providing a useful overview of data, while the dbf format is fully compatible
with other data analysis software such as Microsoft Excel.
The NRM&E groundwater database was used as a partial data source for
this investigation as it offers several benefits in addition to historical
records. The database is useful for locating existing NRM&E monitoring
bores for current sampling and testing. Although the Lockyer Valley also
has hundreds of private irrigation bores which could be sampled, access
often presents a problem. NRM&E bores do not require landholder
cooperation for sampling, and as they are not equipped for irrigation
purposes, water level measurements are easy to take during pumping tests.
An additional benefit of NRM&E bores over private bores is they nearly
always contain a geological log on the database. An example of a bore
record from the NRM&E database is presented for bore 445 in Appendix 1.
27
5. HYDRAULIC INVESTIGATIONS
Background
The behaviour of the main aquifers in the catchments studied was also
investigated through hydrograph interpretation and the physical properties
were estimated through aquifer or pump testing. The Tenthill and Ma Ma
catchments contain NRM&E water level monitoring bores, the majority of
which are concentrated on the Lockyer plain where the two drainages
converge.
Methods
Hydrograph Interpretation
Precipitation data was obtained from the Commonwealth Bureau of
Meteorology for the synoptic station at the Gatton DPI. The NRM&E
database was searched for all available water level data for the study area
and exported to both pdf and MS Access files. This data was then imported
to MS Excel and used to create groundwater hydrographs for the 8
monitoring bores on the Lockyer plain with regular records, beginning in
January 1988 and continuing to January 2003, with rainfall data added for
comparison purposes.
The effects of rainfall on groundwater levels were examined by plotting
rainfall residual mass and groundwater levels against time. Rainfall residual
mass is the cumulative deviation from the mean as shown by the
relationship below:
( )MeanRainRain MOMORM −= ∑
where
RainMO = Monthly rainfall
MeanRainMO = Mean monthly rainfall
28
Pumping Tests
Pumping tests were conducted on two NRM&E monitoring bores in the
TMMC to obtain estimates of transmissivity which were then used to
estimate hydraulic conductivity. Test 1 comprised a single bore drawdown
test for a period of 90 minutes using a submersible Grundfos pump. The test
was stopped after 90 minutes as the water level had quickly reached
equilibrium under the pumping rate of 0.3 L/s, almost the Grundfos
maximum capacity. The drawdown was analysed with the Cooper Jacob
Time Drawdown Method by plotting drawdown vs log time; transmissivity
was estimated in accordance with the relationship shown below,
( )hhQT−Δ
=04
3.2π
where
T = transmissivity
Q = discharge
Δ (h0-h) = drawdown per log cycle of time
(Cooper and Jacob 1946)
The only requirements for the Cooper Jacob Time Drawdown method are
measurements of drawdown in a pumping bore and the pumping rate of the
pump. For this reason it is adaptable to NRM&E monitoring bores of 50
mm diameter which can be pumped with the Grundfos. This method was not
suitable for the numerous private bores in the study area as many are fully
enclosed and equipped for irrigation purposes.
Test 2 comprised drawdown in a private pumping bore with measurements
taken simultaneously in a NRM&E monitoring bore 13 m away over a
period of 22 hours. A pumping rate of 5 L/s was reported by the landholder;
however this rate could not be verified as all water was pumped directly to
an irrigation winch. After the pump was shut off the rise in water levels was
measured in the monitoring bore over a period of 5 hours. Data were
analysed with the Theis Recovery Method,
29
TQs
π43.2'=
'log
tt
where
s’ = residual drawdown
r = distance from pumping bore to observation bore
T = transmissivity
t and t’ = elapsed times from start and end of pumping
s’ is plotted on the logarithmic y axis and time is plotted on the x axis in the
form of (t/t’) and a line of best fit is drawn to produce a straight line from
which transmissivity can be estimated (Theis 1935).
For the Theis Recovery method the following conditions are assumed to be
valid:
1) The aquifer is confined and has an apparent infinite extent
2) The aquifer is homogeneous, isotropic and of uniform thickness over
the area influenced by pumping
3) The potentiometric surface was horizontal prior to the start of
pumping
4) All changes to the position of the potentiometric surface are due to
the effect of the pumping bore alone
5) The aquifer is compressible and water is released simultaneously
from the aquifer as the head is lowered
6) The pumping bore is fully penetrating
7) The pumping rate is constant for the duration of the test
8) The effects of water stored in the well is negligible
(Theis 1935; Fetter 1994)
The Theis Recovery method requires recovery versus time at a pumping or
observation bore, the distance from the pumping bore to the observation
bore and the pumping rate and duration. For this reason the method is
ideally suited for a test involving a private irrigation bore where drawdown
could not be measured, and a NRM&E monitoring bore where drawdown
30
could be measured, located 13 m away. Such a test is more desirable as the
drawdown in the observation bore is representative of the aquifer over the
distance between the pumping and observation bore. The distance of 13 m
between the private irrigation bore and the NRM&E monitoring bore was
considered close enough to observe drawdown and recovery at the
observation bore under the pumping rate specified by the landholder.
Test 3 comprised re-analysis of drawdown data collected at an observation
bore located 2 m from a pumping bore by McLeod (1998). A new aquifer
thickness of 4 m obtained by interpolation from nearby NRM&E geological
logs was utilised, as opposed to the aquifer thickness of 33 m used by
McLeod (1998). The data was re-analysed by plotting log drawdown versus
log time to produce an estimate of transmissivity using the Theis method
described below,
( )uWT
Qsπ4
=
where
s = drawdown
Q = discharge
W(u) = well function of u
Using the estimate of transmissivity produced, the Theis method was again
employed to determine an estimate of storativity from the observation bore
as shown below,
2
4rTutS =
where
S = storativity
T = transmissivity
u = dimensionless constant
31
t = elapsed times from start and end of pumping
r = distance from pumping bore to observation bore
(Theis 1935)
Each of the above tests produced an estimate of aquifer transmissivity which
was then combined with the aquifer thickness, obtained from geological
logs, to calculate an estimate of hydraulic conductivity as shown by the
following relationship,
bKT =
bTK =
where
T = transmissivity
b = aquifer thickness
K = hydraulic conductivity
The Cooper Jacob Time Drawdown, Theis Recovery and Theis methods
were selected as their requirements were consistent with the available
pumping test design.
32
Results
Hydrograph Interpretation
A continuous period of water level measurements exists for a network of 8
bores for a 15 year period from 1988 to 2003 (Figure 6). From Figure 7 it
can be seen that the highest water levels occurred in July 1990, while the
lowest occurred in October 1995. This trend is consistent for all monitoring
bores with regular measurements. Continued high levels during the period
1988 – 1991 coincides with a period of higher than average rainfall for these
years, and groundwater levels were maintained at a high level. From late
1992 and continuing through to late 1995 water levels in all bores declined.
The lowest point was reached in October 1995 and was alleviated by
frequent rains in the following summer.
A major flood event, 420 mm in one week, occurred in early May 1996 and
the responses of all monitoring bores to this event can be clearly seen on
Figure 7. To compare the response of bores adjacent to the creek channels
with that of bores far from the creek channels a plot of rainfall residual mass
and groundwater levels over the 15 year monitoring period was used. Figure
8 shows hydrographs of two bores adjacent to the creek channels, bore 446
and 516, and two bores some distance from the creeks, bores 490 and 462.
The bores adjacent to the creek display a good correlation between rainfall
residual mass and groundwater levels, while those far form the creeks
display a weaker correlation.
33
Figure 6. Locations of 8 bores with regular water level records for the15
year period 1988 – 2003.
34
Hydrographs of 8 bores with regular records 1988 - 2003
85
90
95
100
105
110
115
Date Dec-88 Dec-89 Dec-90 Dec-91 Dec-92 Dec-93 Dec-94 Dec-95 Dec-96 Dec-97 Dec-98 Dec-99 Dec-00 Dec-01 Dec-02
Date
Hea
d (m
asl)
446445502516490221442462
Figure 7. Hydrographs of 8 monitoring bores with regular records for 15
year period from 1988 – 2003.
35
446
-100
-50
0
50
100
150
200
250
300
350
400
450
Jan-88 Jan-89 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03
Date
Rai
nfal
l Res
idua
l Mas
s
85
86
87
88
89
90
91
92
93
94
95
Hea
d (m
asl)
RRMHead
516
-100
-50
0
50
100
150
200
250
300
350
400
450
Jan-88 Jan-89 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03
Date
Rai
nfal
l Res
idua
l Mas
s
82
84
86
88
90
92
94
96
98
100
102
104
Hea
d (m
asl)
RRMHead
Figure 8. Hydrographs of two bores adjacent to the creek channels, bore
446 and 516, and two bores some distance from the creeks, bores 490 and
462. The bores adjacent to the creek display a good correlation between
rainfall residual mass and groundwater levels, while those far form the
creeks display a weaker correlation.
36
490
-100
-50
0
50
100
150
200
250
300
350
400
450
Jan-88 Jan-89 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03
Date
Rai
nfal
l Res
idua
l Mas
s
88
90
92
94
96
98
100
102
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106
108
110
Hea
d (m
asl)
RRMHead
462
-100
-50
0
50
100
150
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250
300
350
400
450
Jan-88 Jan-89 Jan-90 Jan-91 Jan-92 Jan-93 Jan-94 Jan-95 Jan-96 Jan-97 Jan-98 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03
Date
Rai
nfal
l Res
idua
l Mas
s
98
100
102
104
106
108
110
112
114
116
Hea
d (m
asl)
RRMHead
Figure 8. Hydrographs of two bores adjacent to the creek channels, bore
446 and 516, and two bores some distance from the creeks, bores 490 and
462. The bores adjacent to the creek display a good correlation between
rainfall residual mass and groundwater levels, while those far form the
creeks display a weaker correlation.
37
Pumping Tests
In order to gain an estimate of aquifer hydraulic properties two pump tests
were conducted and data from a previous pump test was re-analysed using a
new aquifer thickness interpolated from nearby NRM&E geological logs.
The location of each of each pump test is shown in Figure 9. Test 1
consisted of drawdown data plotted against time in accordance with the
Cooper Jacob Time Drawdown method to produce an estimate of hydraulic
conductivity as shown by Figure 10. Test 2 involved pumping for 22 hours
from a private pumping bore with measurements taken in a NRM&E
monitoring bore located 13 m away. The recovery data was plotted by the
Theis Recovery method and manually fitted to the curve to produce an
estimate of hydraulic conductivity (Figure 11). Test 3 was conducted by
Macleod (1998) involving a pumping bore and an observation bore located
2 m away. The drawdown data was re-analysed with a new aquifer thickness
of 4m and plotted by the Theis method and manually fitted to the curve to
produce an estimate of hydraulic conductivity and storativity (Figure 12).
Data for each of the tests is presented in Appendix 2.
Discussion of Hydraulic Investigations
During the above average rainfall of the years 1988 – 1991 groundwater
was maintained at a high level in part due to regular recharge but also in part
due to the reduction in groundwater extracted for irrigation, as frequent
rainfall reduces the irrigation demand. Widespread declining water levels in
the drought years from 1993 – 1995 are a function of both the lack of
rainfall and recharge occurring at the time and also the higher demand
placed on groundwater for irrigation supplies in that period. The creeks in
the Lockyer Valley did not flow between April 1993 and September 1995
(Durick and Bleakley 2003), however hydrographs of bores 446 and 516,
both adjacent to Tenthill Creek, display a strong correlation with rainfall
residual mass during that period (Figure 8). By contrast, bores 490 and 462
both located away from any of the creeks display a weaker correlation with
rainfall residual mass (Figure 8). This response suggests that recharge does
occur through the creeks even when these channels are dry. It is therefore
38
Figure 9. Locations of 3 pumping tests conducted on alluvial bores.
39
Figure 10. Plot of drawdown versus log time from single bore drawdown
test with Grundfos pump.
K = 5.89E-04 m/s or 50.88 m/day.
Figure 11. Plot of residual drawdown versus, elapsed time form start of
pumping divided by elapsed time from end of pumping.
K = 9.20E-4 m/s or 79.5 m/day.
40
Figure 12. Plot of drawdown data from Macleod (1998) manually fitted to
Theis curve.
K = 7.28E-4 m/s or 62.9 m/day S = 1.66E-3
Bore 516 May 1996 flood
0
20
40
60
80
100
120
140
29-Apr 30-Apr 1-May 2-May 3-May 4-May 5-May 6-May 7-May 8-May 9-May 10-May 11-May
Date
Dai
ly ra
infa
ll (
mm
)
90
91
92
93
94
95
96
97
98
Hea
d (
mas
l)
Figure 13. Daily measurements recorded by bore 516 on bank of Tenthill
Creek during flood event of early May 1996.
41
likely that the creek channels are an important, if not the dominant pathway
for recharging water, irrespective of whether they contain flowing or
standing water, or are totally dry and only receive brief storm runoff. Daily
measurements were recorded for bore 516 during a May 1996 flood event,
in which the groundwater level rose 4 m in 4 days, further supporting a
strong hydrological connection to the creek at this location (Figure 13).
A summary of the three pumping tests and the estimates of aquifer
properties is presented in Table 1.
Test Type Distance Duration Pumping Analysis Estimated Between Rate method hydraulic pumping and conductivity
observation
bore 1 Drawdown - 1.5 hours 0.3 L/s Cooper Jacob 50 m/day single bore Time Drawdown
2 Recovery 13 m 22 hours
drawdown 5.1 L/s Theis Recovery 80 m/day
observation
bore 5 hours recovery
3 Drawdown 2 m 1.5 hours 8.6 L/s Theis 65 m/day
observation
bore
Literature 80 to Values 800 m/day For (Fetter 1994) Gravel
Table 1. Summary of the pumping test specifications, analysis methods and
estimated aquifer properties compared with literature values for gravel.
Analysis of the single bore drawdown test data produced an estimate of
hydraulic conductivity of 50 m/day, however, this value should be treated as
a lower end value due to the low pumping rate of the Grundfos pump and its
inability to draw the aquifer down more than 0.4 m within the pumping
bore.
By contrast the 22 hour pumping test drew down the aquifer 0.55 m;
although this is less than 1.5 times the single bore test, the drawdown was
observed at a distance of 13 m away and represents the cone of depression
42
formed by the pumping bore. During the first 30 minutes of the drawdown
test when frequent measurements were being recorded an irrigation pipe
was inadverdantly closed, reducing the pumping rate. As a consequence
water levels began to rise in the observation bore, with a resulting loss of the
initial drawdown data. The data was analysed without this initial drawdown,
however, the estimates of hydraulic conductivity and storativity produced
were not realistic for gravel and were therefore discarded. The recovery
data, however, were still useful as the standing water level was taken to be
the level at which the aquifer began to drawdown again at approximately 30
minutes into the test; the first 30 minutes were then subtracted from the
total pumping duration and used as the new pumping duration when
analysing the recovery data. The estimate of hydraulic conductivity of 79
m/day produced by this method is considered realistic for a semi confined
gravel aquifer.
The third phase of the pumping tests involved re-analysis of the drawdown
data recorded by Macleod (1998) using a new aquifer thickness of 4 m
obtained from interpolation of nearby NRM&E geological logs, as opposed
to the 33 m originally used by Macleod. The drawdown was recorded at an
observation well located 2 m from the pumping bore and produced an
estimate of hydraulic conductivity of 63 m/day. As the drawdown was
observed at an observation bore it was also possible to produce an estimate
of storativity of 0.00166. This value represents the confined storage
coefficient which is equal to the specific storage divided by the aquifer
thickness. Therefore the specific storage was calculated to be:
0.00166 / 4 = 0.000415
43
6. HYDROCHEMISTRY AND STABLE ISOTOPES
Background
The major cations (sodium, potassium, calcium, magnesium) and the major
anions (chloride, bicarbonate and sulfate) typically comprise approximately
98% of all salts dissolved in groundwater. The measurement of the
concentrations of these major constituents provides a method for
determination of the dissolved mineral species present or which reactions
may be occurring within a particular aquifer. Identification of these
components and processes can then be used to propose the history of water-
rock interaction within an aquifer (e.g. Appelo and Postma 1996).
Groundwater chemistry can also provide both an indication of variations in
aquifer properties, and a record of the behaviour of groundwater within
internally variable aquifers such as alluvium. In alluvial aquifers higher
dissolved ions can be an indicator of areas of lower permeability, reflecting
longer residence times of groundwater and the associated increased
weathering reactions of the aquifer materials (Garcia et al. 2001; Acworth
and Jankowski 1993).
Stable isotopes 2H and 18O are valuable as natural tracers as they do not
decay with time nor are they removed from water by exchange process
during movement though most low temperature materials (Acheampong and
Hess 2000). Concentrations of stable isotopes are measured as the difference
or ratio between the two most abundant isotopes of an element. In the case
of the water molecule which contains hydrogen and oxygen, the isotopic
ratios are expressed as 2H/1H and 18O/16O (Mazor 1997). The ratios of a
sample are expressed as the ‰ (per mille) difference relative to a reference,
which for oxygen is shown below:
δ18O sample ‰ = [(18O/16O)sample / (18O/16O)VSMOW – 1] x 1000
44
This reference is V-SMOW – Vienna Standard Mean Ocean Water. The
VSMOW standard is a distilled seawater sample defined by the
International Atomic Energy Agency (IAEA) (Clark and Fritz 1997).
Isotopes 2H and 18O are commonly involved in phase changes, therefore
their concentrations before and after such reactions are governed by kinetic
fractionation. The most common phase changes to affect stable isotopes are
evaporation and condensation. Evaporative enrichment occurs most
efficiently by wind agitation of an evaporating surface water body or the
spray action of some irrigation systems (Gat 1981). Enrichment of liquid
water can be identified by measuring the ratios of stable isotopes δ2H and
δ18O and comparing them to the meteoric relationship of global fresh
waters.
In a landmark paper Craig (1961) identified a straight line relationship
between δ2H and δ18O abundances in natural waters suggesting that the
isotopic composition of meteoric waters behaves in a predictable fashion.
The equation of the straight line was calculated as: δ2H = 818O + 10 and
provided a best fit relationship for the bulk of the samples. Samples
excluded were those from rivers and lakes (east Africa) which were heavily
influenced by evaporation, and plotted below the best fit line with a slope of
approximately 5. Laboratory studies of free evaporation at ordinary
temperatures confirmed a slope of 5 for 2H/18O ratios as being a signature of
evaporated waters (Craig 1961).
When conducting a groundwater investigation it is beneficial to obtain local
area precipitation data, so that the relative enrichment or depletion of
groundwater samples can be identified. This is done by constructing a δ2H
and δ18O plot of local precipitation, from which can be produced a local
meteoric water line. From such a graph the position of a sample relative to
the local meteoric water line can be seen. Calculation of the slope of the
trend line of groundwater samples will enable any effects of evaporation to
be identified (Clark and Fritz 1997).
45
Methods
Water chemistry
Data existed for samples collected by NRM&E from a selection of
groundwater bores in the area, as well as surface water samples in 1996
following a flood event and have been included for comparison. Sampling
for this study was during the winter of 2003 which coincides with a
prolonged drought in the Lockyer Valley and consequently water levels
were very low. A bailer was used to extract water from groundwater bores,
and the equivalent of three volumes of the casing were removed before
sampling took place. Physico-chemical parameters (temperature, pH,
electrical conductivity and Eh) were all measured in situ at the bore using a
TPS multimeter. For each bore two water samples were taken in plastic
bottles, one pre acidified with 1 mL nitric acid to be used for cation
analysis, and one non-acidified to be used for alkalinity and anion analysis.
Turbid samples were filtered in the laboratory using 0.45 µm filter paper in
a flask attached to a vacuum pump. Cations were determined using a Varian
Liberty Inductively Coupled Plasma Optical Emission Spectrometer (ICP-
OES). Where necessary, samples were diluted to 4000 µS/cm for the ICP-
OES. Anions were determined by a Dionex Ion Chromotograph and all
samples were required to be diluted to 200 µS/cm before analysis.
Alkalinity was determined by titration with 0.1 M HCl. As the pH of all
samples was less than 8.3, phenolphthalein alkalinity was 0 and therefore
total alkalinity was reported as HCO3. All procedures were conducted at the
QUT School of Natural Resource Sciences chemical laboratory. For a
detailed description of analytical methods refer to Appendix 3.
Stable Isotopes
Selected bores were sampled for analysis of stable isotopes δ2H and δ18O.
The same bore purging techniques for water chemistry outlined above were
followed and samples were taken in 30 mL glass screw top McCartney
bottles and sealed in accordance with the procedures outlined by Clark and
46
Fritz (1997). All samples were analysed by CSIRO Land and Water Isotope
Laboratory in Adelaide, South Australia.
Results
Water chemistry
Previous investigations reported water chemistry from bores screened
within various geological formations such as sandstone units in the Lockyer
Valley and basalt at the headwaters of the drainages (Dixon and Chiswell
1992 and 1994; Macleod 1998; Cox unpublished data). These results are
discussed here and compared to the alluvial samples colleted by NRM&E
and those collected as part of this study (Figures 14 and 15).
A piper diagram is useful for representing different water types based on the
position of the major cations and anions plotted on a ternary diagram
(Figure 16). Bores within the Ma Ma Creek Sandstone sampled in 1987
yielded Na,Mg-Cl type water and plot on the right side of the Piper diagram
(Figure 17); a sample from the same bedrock unit collected in 1998 was also
Na,Mg-Cl type. NRM&E data for two bores into the Gatton sandstone just
to the east of the study area on the north bank of Lockyer Creek (Figure 15)
yielded high conductivities of 10000 µS/cm and Na-Cl type water in 1996.
To date no reported samples have been collected from the Winwill
conglomerate which overlies the Gatton Sandstone. As the composition of
sandstone groundwater has been shown to be relatively stable over both wet
and dry periods (Dixon and Chiswell 1992), it is reasonable to compare
samples collected at different times with alluvial groundwater samples. A
bore sampled from the basalt near Pilton (Figure 15) on the headwaters of
Ma Ma catchment produced Mg,Ca-HCO3 type water with conductivity of
1100 µS/cm (Cox, unpublished data).
47
Figure 14. Locations of bores sampled for water chemistry only (open
symbols) and both water chemistry and stable isotopes (closed symbols);
and their relationship to the geological units of the study area. Bedrock
bores S1 and S2 (Dixon and Chiswell 1994), GW027 (Macleod 1998) and
822 (this study) shown for reference.
49
Figure 16. Piper diagram utilising the Davies and De Wiest (1966)
classification system for identifying groundwater types. Water types based
on the dominant cations (left ternary) and anions (right ternary).
50
Groundwater bores considered in this study were sampled in either 1996,
2003 or both; locations of bores sampled in this study and their relationship
to the underlying geology are shown in Figure 14. The 1996 data include
surface water samples taken during the May 1996 flood event, July 1996
and several groundwater samples taken in November 1996. Although
Tenthill Creek was sampled by NRM&E for major ion chemistry analysis
during the 1996 flood event, it was not sampled for stable isotope analysis.
However, both major ion chemical analyses (NRM&E), and stable isotope
analyses (Dharmasiri and Morawska 1997) have been carried out on
samples from the adjacent Laidley Creek at this time. Due to the similarity
in the major ion chemistry of flood samples from Tenthill Creek and
Laidley Creek it was considered acceptable to use the Laidley chemical and
isotopic results for comparative purposes in this study. The lowest
conductivity of 250 µS/cm was recorded from surface water during the May
1996 flood event, and is dominated by magnesium, calcium and bicarbonate
(Figure 17). In July 1996 surface water conductivity had increased to 490
µS/cm.
In November 1996 conductivity of alluvial groundwater in Ma Ma
catchment was typically 4700 µS/cm while conductivity of Tenthill
groundwater was less than 1600 µS/cm. On the Lockyer alluvial plain
conductivity ranged from 1200 to 6500 µS/cm. Bore 256 in Ma Ma
catchment, a Na,Mg-Cl type, plots on the right of the Piper diagram
indicating a significant contribution by the sandstone aquifer. Groundwater
from the Tenthill catchment and Lockyer plain samples contain a greater
proportion of calcium over sodium and plot to the left of the Piper diagram
(Figure 17). The concentrations of major ions are plotted on a Schoeller
diagram (Figure 18) to show relative proportions of major ions. The plot
shows lower concentrations in surface water from May 1996 than in July
1996, however, the relative proportions of these same ions are largely
unchanged. In addition the ionic proportions of alluvial groundwater from
Tenthill catchment in November 1996 are very similar to those of both
surface water samples (Figure 18). Chemical analyses for 1996 are
presented in Appendix 4.
51
80 60 40 20 20 40 60 80
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na HCO3 Cl
Mg SO4
Legend:
Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96
Figure 17. Piper diagram of surface and alluvial groundwater samples 1996,
compared with basalt and bedrock groundwater and surface water. Alluvial
groundwater from Tenthill catchment and the Lockyer plain is magnesium
dominated while the single sample from Ma Ma catchment is more strongly
associated with the sandstone bedrock aquifers.
52
Mg Ca Na+K Cl SO4 HCO30.01
0.1
1.
10.
100.
1000.Concentration (meq/l)
Legend:
Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96
Figure 18. Schoeller diagram showing relative proportions of major ions in
flooding surface water from May 1996, standing surface water from July
1996 and alluvial groundwater samples from November 1996. Higher
concentrations were observed in surface water from July 1996 than in May
1996, however, the relative proportions of major ions are unchanged and are
similar to the proportions of Tenthill alluvial groundwater. The single
sample of Ma Ma alluvial groundwater exhibits similar ionic proportions to
Ma Ma Creek Sandstone groundwater indicating some contribution from the
bedrock aquifer.
53
To augment existing water chemistry data and to provide a comparison,
twenty six bores were sampled in 2003 as part of the current study. The
sampling network comprises five from Ma Ma catchment, six from Tenthill
catchment and fifteen from the Lockyer plain. Results from each catchment
display a marked difference in salinity (as EC) and the proportions of major
cations and anions. Conductivity from Ma Ma catchment ranged from 8800
to 12900 µS/cm and water types were Na,Mg,Ca-Cl and Mg,Na,Ca-Cl
(Figure 19). In Tenthill catchment conductivity ranged from 1450 to 2640
µS/cm with Mg,Ca,Na-Cl,HCO3 water types dominating. The bore transect
B-B’ across the confluence of alluvium (Figure 14) provides a cross section
which enables comparison. The western (Ma Ma) portion of the transect
exhibits water of a similar chemical type to that found further upstream; and
the eastern (Tenthill) side of the transect is also similar to Tenthill
groundwaters further upstream, suggesting flow within incised channels.
Bores on the western side yielded conductivities ranging from 2500 to 9000
µS/cm and magnesium and sodium dominated waters; while on the eastern
side conductivities ranged from 3100 to 3750 µS/cm in magnesium and
calcium dominated waters.
All samples from the Lockyer plain display a conductivity ranging from
2300 to 6100 µS/cm with Mg>Na>Ca. The 5 bores of the Lockyer Creek
transect A-A’ (Figure 14), yield Mg,Na,Ca-Cl or Mg,Na,Ca-Cl,HCO3 type
water; the exception is bore 446 which is Mg,Ca,Na-HCO3,Cl with a lower
conductivity. Waters from the alluvial bore 447, and bore 822 in the Gatton
Sandstone, both located along Lockyer Creek are Na,Mg-HCO3 type and
plot well below all other samples on the Piper diagram (Figure 19). All
chemical analyses for 2003 are presented in Appendix 4.
Water chemical analyses of basalt groundwater were also conducted as part
of this study (Figure 15). Two groundwater samples both yielded Na-HCO3
type water. When compared with the sample from near Pilton, bicarbonate
is the dominant anion in each of these samples, however, there is some
variation in the proportions of major cations as is seen on the Piper diagram
(Figure 19).
54
80 60 40 20 20 40 60 80
20
40
60
80 80
60
40
20
20
40
60
80
20
40
60
80
Ca Na HCO3 Cl
Mg SO4
Legend:
Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96
Figure 19. Piper diagram of alluvial groundwater samples 2003, compared
with basalt and bedrock groundwater and surface water. Most alluvial
samples from the Lockyer plain display an increase in sodium from 1996. A
single alluvial sample from the Lockyer plain and a sample from the Gatton
Sandstone comprise an isolated group of Na-HCO3 type water. Two basalt
groundwater samples collected in 2003 also exhibit Na-HCO3 water types.
55
Stable Isotopes
Samples were collected from 18 of the bores sampled for water chemistry in
2003 (Figure 14). Results demonstrate a wide variation across the study area
and a general trend of enrichment. Values of δ2H range from -29.6 to -12.3
‰ relative to Vienna Standard Mean Ocean Water (VSMOW) while δ18O
ranges from -5.25 to -2.08 ‰ relative to VSMOW. Bore 502 and 822 are the
outliers being the most enriched and depleted waters respectively. The
majority of samples are within the ranges of δ2H: -24.9 ‰ and -21.7 ‰ and
δ18O: -4.28 ‰ and -3.77 ‰. Stable isotope data are presented with
conductivity, TDS and aquifer geology in Table 2.
Sample Date Aquifer EC TDS δ2Η δ18Ο Geology (µS/cm) (mg/L) VSMOW VSMOW
221 27/11/2003 Alluvium (Lockyer) 2600 1718 -24.5 -4.26 446 8/09/2003 Alluvium (Lockyer) 1443 824 -20.5 -3.95 447 20/11/2003 Alluvium (Lockyer) 4640 1421 -23.6 -4.15 490 6/09/2003 Alluvium (Lockyer) 3670 2086 -21.7 -3.77 491 8/09/2003 Alluvium (Lockyer) 6100 3404 -17.3 -3.05 502 8/09/2003 Alluvium (Lockyer) 3400 2002 -12.3 -2.08 516 8/09/2003 Alluvium (Lockyer) 5380 3688 -24.8 -4.51 P1 27/11/2003 Alluvium (Lockyer) 3040 1745 -23.1 -3.9 859 3/09/2003 Alluvium (Ma Ma) 9050 5444 -26.4 -4.49 861 10/09/2003 Alluvium (Ma Ma) 12160 7092 -21.2 -3.19 862 6/09/2003 Alluvium (Ma Ma) 12890 7673 -23.1 -3.83
55617 6/09/2003 Alluvium (Ma Ma) 8780 5416 -24.9 -4.28 477 25/08/2003 Alluvium (Tenthill) 2640 1518 -22.5 -4.11 783 3/09/2003 Alluvium (Tenthill) 3220 2350 -22.6 -3.81 784 3/09/2003 Alluvium (Tenthill) 3100 2488 -24.2 -4.08 864 6/09/2003 Alluvium (Tenthill) 1447 974 -23.3 -4.14 865 6/09/2003 Alluvium (Tenthill) 2340 1545 -23.5 -4.18 B1 20/11/2003 Basalt 720 223 -22.2 -4.49 B2 20/11/2003 Basalt 730 218 -23.4 -4.79 B3 30/03/1995 Basalt 1110 840 -21.7 -3.14 S1 1/01/1987 Ma Ma Ck Sandstone 4590 3016 -30.9 4.94 S2 1/01/1987 Ma Ma Ck Sandstone 6950 4865 -32.7 -5.06
GW027 1/07/1998 Ma Ma Ck Sandstone 14330 6767 -25.3 -4.1 822 10/09/2003 Gatton Sandstone 4930 2432 -29.6 -5.25
SW May 96 May-96 Surface water 255 164 -24 -4.4 SW July 96 Jul-96 Surface water 486 281 -20 -3.6
Table 2. Stable isotopes, EC, TDS and aquifer geology. S1 and S2 (Dixon
and Chiswell 1994), GW027 (Macleod 1998), B3 (Cox, unpublished data),
Surface water isotope measurements (Dharmasiri and Morawska 1997).
56
Discussion of Hydrochemistry and Stable Isotopes
The surface stream water for the valley may be represented by the Laidley
Creek sample collected in the May 1996 flood event. As demonstrated on
the Schoeller diagram (Figure 18) the concentrations of major ions are
higher in surface water from July 1996 than in May 1996, however the
relative proportions of these same ions are largely unchanged. The chemical
composition of the July surface water sample is also similar to the
compositions of groundwater samples collected several months later from
Tenthill catchment and the Lockyer plain. The sample from Ma Ma
catchment, however, is more associated with the sandstone waters identified
by Dixon and Chiswell (1992). These relationships suggest that the
chemical character of alluvial groundwater in Tenthill catchment and the
Lockyer plain is affected by surface water for a period of several months
after a major rainfall event. At the same time the effects of such an event are
not identifiable in Ma Ma catchment. A summary of aquifer geology and
water types is presented in Table 3.
Aquifer Location EC Chemical Geology (µS/cm) Type Alluvial Lockyer Plain 2300-6100 Mg,Na,Ca-Cl Alluvial Ma Ma catchment 5000-12000 Mg,Na,Ca-Cl Alluvial Tenthill catchment 1500-3500 Mg,Ca,Na-Cl,HCO3 Basalt Pilton 1100 Mg,Ca-HCO3 Basalt Mt Castle 700 Na-HCO3
Ma Ma Ck Sandstone Upper Tenthill, Mt Whitestone 4500-7000 Na,Mg-Cl
Gatton Sandstone UQ Gatton 10000 Na-Cl Stream (flooding) Laidley Ck 250 Ca,Mg,Na-HCO3 Stream (standing) Laidley Ck 490 Mg,Ca,Na-HCO3
Table 3. Summary of aquifer geology, electrical conductivity and water
chemical type.
The chemical composition of the alluvial groundwater has similarities to
stream flooding water of Ca,Mg,Na-HCO3,Cl type and basalt groundwater
of Mg,Ca-HCO3 type at the headwaters of Ma Ma catchment. The high
calcium in surface water from May 1996 may indicate the effects of runoff
57
from weathered basalt in the upper reaches. Basalt contains minerals with
available calcium including plagioclase and clinopyroxene. The basalts at
the headwaters of the Lockyer Valley have been shown to contain up to 10
% calcite (Dudgeon 1978), also a ready source of calcium. The total
dominance of magnesium in surface water and alluvial groundwater from
Tenthill catchment and the Lockyer plain may be from weathering and
runoff from these same basalts which contain up to 20% olivine (Zahawi
1975), or interactions between groundwater and basaltic gravel which
comprises the alluvial aquifer material. The two basalt groundwater samples
from Mt Castle contain sodium as the dominant cation and do not share the
same major cation chemistry with flooding water as does the Pilton sample
B3 (Figure 10); however their conductivity and TDS are similar to sample
B3. In addition bicarbonate is the dominant anion in all three samples.
For the 2003 samples the Ma Ma catchment alluvial groundwater was
sodium and magnesium dominated, consistent with the results of Dixon and
Chiswell (1992). In that study high conductivity, Na,Mg-Cl type water was
identified from private bores in the Ma Ma Creek Sandstone; the authors
proposed that bedrock groundwater mixes with the Ma Ma catchment
alluvial groundwater due to the small volume of this alluvial aquifer. A
comparison from the current sampling showed two alluvial bores overlying
(a) the Ma Ma Creek Sandstone had conductivities of 12000 µS/cm, and (b)
overlying the Winwill Conglomerate had conductivity 8000 and 9000
µS/cm. In the Sandy Creek catchment near Laidley, high salinity, sodium
dominated alluvial groundwater was identified directly overlying the
Winwill Conglomerate and attributed to upward flow from that unit into the
alluvium (McMahon 1995, McMahon and Cox 1996). A similar process
may be occurring in Ma Ma catchment due to the outcrop of Winwill
Conglomerate and Ma Ma Creek Sandstone which underlie the alluvium
using the classification of McTaggart (1963) (Figure 5). This could explain
the dominance of sodium and the high conductivity of many samples from
this catchment.
58
By contrast, alluvial groundwater samples from Tenthill catchment are
magnesium dominated with a conductivity less than 3500 µS/cm. The Ma
Ma Creek Sandstone bedrock unit does not appear to have a major influence
on the chemistry of alluvial groundwater in the Tenthill catchment. Samples
from the Lockyer plain are typically Mg,Na,Ca-Cl type water with
conductivity of 3000-6000 µS/cm; here the alluvium is underlain by the
Gatton Sandstone which yields Na-Cl type water with a conductivity of
10000 µS/cm. Like the Tenthill catchment the magnesium domination may
be due to the basaltic gravel of the aquifer material while the greater
proportion of sodium may be the result of upward discharge of Na-Cl type
water from the underlying Gatton Sandstone.
Relative variations of the major ions reflect the different aquifers. A
logarithmic plot of calcium vs TDS clearly separates these aquifers in the
study area by geographic location (Figure 20). Calcium is used on the y axis
as in all samples it is less abundant than sodium or magnesium and does not
create any bias when grouping the different aquifers. Chloride or
bicarbonate could be used on the x axis, however, TDS was used to
incorporate all water types regardless of their dominant anion. Ma Ma
catchment contains the highest calcium, while basalt waters contain the
least, with the Lockyer plain and Tenthill catchment of intermediate
character. A possible mixing relationship may exist between the bedrock
groundwater and Tenthill catchment alluvial water to produce the
groundwater of the Lockyer plain.
In Figure 21 a logarithmic plot of bicarbonate vs conductivity is used to
represent:
(a) recharge to alluvial and basalt aquifers,
(b) alluvial/bedrock groundwater mixing,
(c) variations in groundwater bicarbonate content.
Surface water during a flood is notably fresh and a starting point for
groundwater recharge. The fresh basalt groundwater with bicarbonate as the
dominant anion plots between flooding stream water and alluvial
groundwater; this indicates that rainfall may initially recharge the basalt first
59
100.0 1000.0 10000.010.0
100.0
1000.0Ca (mg/l)
TDS (mg/l)
Legend:
Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96
Ma Ma
Bedrock
Tenthill
Lockyer plain
Figure 20. Logarithmic plot of Ca (mg/L) vs TDS (mg/L) for groundwater
samples in 2003. A possible mixing relationship may exist between the
bedrock groundwater and Tenthill catchment alluvial water to produce the
groundwater of the Lockyer plain.
60
100.0 1000.0 10000.0 100000.0100.0
1000.0
10000.0HCO3 (mg/l)
Conductivity (µS/cm)
Legend:
Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96
Ma MaBasalt
822447
516
491
Bedrock
445
mixing
Flood water
rech
arge
to b
asal
t
recharg
e
direct
ly
to all
uvium
HCO type water3
Figure 21. Logarithmic plot of HCO3 (mg/L) vs conductivity (µS/cm) for
groundwater samples in 2003. Recharge may occur to basalt before
alluvium or directly to alluvium. The alluvial samples from Ma Ma
catchment and the most saline samples from the lower plain, bores 445, 491
and 516, may be mixing with bedrock groundwater. Bores 822 and 447
represent an isolated group of HCO3 type water. Broken line shows
chemical evolution of groundwater.
61
with subsequent discharge to the alluvium, plus direct recharge for the
alluvium. The similarity between the conductivity of bedrock groundwater
and Ma Ma catchment alluvial groundwater and the most saline alluvial
samples from the Lockyer plain, (bores 445, 491 and 516), indicates
possible mixing between alluvium and bedrock groundwater at these
locations. The HCO3 type water in the alluvial bore 447 and the Gatton
Sandstone bore 822 plot highest and isolated on Figure 21 and indicate an
external source of unidentified CO2.
Stable isotopes support the interpretation of water chemical evolution. A
plot of δ2H ‰ VSMOW versus δ18O ‰ VSMOW (Figure 22) indicates the
position of all samples relative to the Global Meteoric Water Line (Craig
1961) and the Brisbane Meteoric Water Line (GNIP 1998). Bedrock
groundwater is more depleted than both alluvial and basalt groundwater as
well as surface water; this water plots lower on Figure 22 indicating a
different recharge process and possibly a different climate at the time of
recharge. The alluvial and basalt and surface water have been plotted in
greater detail in Figure 23. It can be seen that surface water from the May
1996 flood plots to the left of the Global Meteoric Water Line and
represents “new water” and is as close to local rainfall composition as can
be determined for the study area. Samples collected following the May 1996
flood plot on an evaporation slope of 5 which is characteristic of
evaporation from standing surface water (Craig 1961, Gat 1981). Basalt
groundwater is slightly more enriched than the “new water” and may be
evaporated during recharge to the unconfined fractured basalt aquifer.
Tenthill catchment alluvial groundwater does not show any evaporation
which may be the result of regular recharge from the headwaters of this
large catchment. For Ma Ma catchment alluvial groundwater an evaporation
slope of 3.85 was calculated, while for the Lockyer plain alluvial
groundwater the slope calculated is 5.33 (Figure 23). These slopes are
similar to that calculated for standing surface water after the 1996 flood and
support recharge from evaporated surface water in creek channels as the
dominant recharge process to the alluvial aquifers. The samples of “new
62
-8 -6 -4 -2 0
-40
-30
-20
-10
0
-8 -6 -4 -2 0
-40
-30
-20
-10
0
-8 -6 -4 -2 0
-40
-30
-20
-10
0
-8 -6 -4 -2 0
-40
-30
-20
-10
0
-8 -6 -4 -2 0
-40
-30
-20
-10
0
-8 -6 -4 -2 0
-40
-30
-20
-10
0
-8 -6 -4 -2 0
-40
-30
-20
-10
0
-8 -6 -4 -2 0
-40
-30
-20
-10
0
-8 -6 -4 -2 0
-40
-30
-20
-10
0
Bedrock
Glo
bal M
eteor
ic W
ater
Lin
e y
= 8
x +
10 (C
raig
196
1)
Brisba
ne M
eteor
ic W
ater
Lin
e y
= 7
.7x
+ 12
.6 (G
NIP 1
996)
δ2H ‰ VSMOW
δ18O ‰ VSMOW
Figure 22. Stable isotope plot of surface water and alluvial, basalt and
bedrock groundwater with Brisbane Meteoric Water Line and Global
Meteoric Water Line shown for reference. Bedrock groundwater is more
depleted than all other samples indicating a different recharge process and
possibly a different climate at time of recharge.
63
-5 -4 -3 -2
-28
-24
-20
-16
-12
-5 -4 -3 -2
-28
-24
-20
-16
-12
-5 -4 -3 -2
-28
-24
-20
-16
-12Lockyer plain s = 5.33
Ma Ma s = 3.85
Surface water s = 5
Tenthill
δ2H ‰ VSMOW
δ18O ‰ VSMOW
-5 -4 -3 -2
-28
-24
-20
-16
-12
-5 -4 -3 -2
-28
-24
-20
-16
-12
-5 -4 -3 -2
-28
-24
-20
-16
-12
Brisba
ne M
eteor
ic W
ater
Lin
e y
= 7
.7x
+ 12
.6 (G
NIP 1
996)
"Loc
kyer
Mete
oric
Wat
er L
ine"
y
= 7.
7x +
9.9
4
Glo
bal M
eteor
ic W
ater
Lin
e y
= 8
x +
10 (C
raig
196
1)
516
"new water"
446
-5 -4 -3 -2
-28
-24
-20
-16
-12
-5 -4 -3 -2
-28
-24
-20
-16
-12
Figure 23. Detailed stable isotope plot of surface water and alluvial and
basalt groundwater with Global Meteoric Water Line and Brisbane Meteoric
Water Line shown for reference. Surface water from the May 1996 flood
plots to the left of the Global Meteoric Water Line and represents flowing
"new water". Tenthill alluvial groundwater shows no distinct trends
however alluvial groundwater from Ma Ma catchment and the Lockyer
plain plot on evaporation slopes of 3.85 and 5.33 respectively. The "new
water", bore 516 and bore 446 plot on a "Lockyer Meteoric Water Line"
which represents the initial composition of evaporated waters. Basalt
groundwater is slightly more enriched than "new water" indicating some
evaporation during recharge.
64
water”, bore 516 and bore 446 plot on a “Lockyer Meteoric Water Line”
(Figure 23) which represents the initial composition of evaporated waters.
When combined with groundwater salinity stable isotopes can be used to
further group different water types and identify hydrological processes. A
semi logarithmic plot of δ2H ‰ VSMOW versus conductivity (µS/cm) is
used to differentiate the alluvial groundwater samples into 4 groups (see
below); and confirm hydrological processes such as recharge, mixing and
evaporation (Figure 24).
Group 1: two samples from the upper reaches of Ma Ma atchment, both
being enriched with extremely high salinities of 12 000 µS/cm
Group 2: two samples from Ma Ma catchment and bore 516 from the
Lockyer plain, slightly more depleted but still with higher salinity
Group 3: all samples from Tenthill catchment and most samples from the
lower plain
Group 4: three samples from the Lockyer plain near which are the most
enriched of all samples
The May sample represents “new water” in the streams prior to evaporation,
while the July sample represents the effects of two months of evaporative
concentration of water in the creek channel. Before undergoing evaporation
the rainfall with a “new water” character is likely to recharge the basalt
aquifers of the surrounding ranges, which subsequently discharge to the
alluvium along the drainage systems. Basalt groundwater may also recharge
the sandstone aquifers.
The locations of the isotope samples relative to the underlying bedrock units
are shown in Figure 14. Samples from the upper reaches of Ma Ma
catchment which overlie the Ma Ma Creek Sandstone are both isotopically
enriched and strongly saline (Group 1, Figure 24). The locations of these
samples coincide with the areas where the alluvium is thinnest, with the
depth to bedrock ranging from 12 to 16 m, compared with a depth of 30 m
on the Lockyer plain. Despite the shallowness of the alluvial fill, these
highly saline samples do not represent bedrock mixing as they plot above
65
100 1000 10000 100000.0-35
-30
-25
-20
-15
-10
Conductivity (µS/cm)
Legend:
Alluvium (Lockyer)Alluvium (Ma Ma)Alluvium (Tenthill)BasaltSandstone (Ma Ma Ck)Sandstone (Gatton)Surface water May 96Surface water Jul 96
Bedrock
Group 1
Group 2
Group 3
Group 4
Basalt
“new water”
evap
orati
on
recharge
recharge
bedrock mixing
evaporation ofirrigation water
491
Figure 24. Semi logarithmic plot of δ2H ‰ VSMOW vs conductivity
(µS/cm) for groundwater samples in 2003 divided into 4 main groups;
enabling recharge, alluvial/bedrock mixing and evaporation of irrigation
water to be identified. Broken line indicates chemical evolution of
groundwater.
δ2H ‰ VSMOW
66
the “new water” on Figure 24; they also contain a greater portion of
evaporated recharge water.
Samples from bores further down Ma Ma catchment overlying the Winwill
Conglomerate, (bores 55617 and 859), and bore 516 from the Lockyer plain
are isotopically more depleted however their conductivity is high, 5500 –
9000 µS/cm (Group 2, Figure 24). It is possible that the Winwill
Conglomerate acts as a slow flow barrier as proposed by McMahon (1995)
and McMahon and Cox (1996); these samples have higher salinity, yet are
more isotopically depleted. The Winwill Conglomerate outcrops around the
alluvium for much of the Ma Ma catchment and may also underlie the
alluvium in the vicinity of bore 516 on the Lockyer plain; the conglomerate
does outcrop further east at UQ Gatton. Groundwater from the Winwill
conglomerate may be more isotopically depleted than that from the
alluvium, similar to the Ma Ma Creek Sandstone (Dixon and Chiswell 1994)
and the Gatton Sandstone (this study). As the clasts in the Winwill
Conglomerate have been suggested to lower its permeability and impede
flow (McMahon 1995), it is plausible that the longer residence times of
groundwater in this unit have led to more depletion of stable isotopes, while
maintaining a high salinity due to increased time for dissolution of minerals
in the conglomerate cement. The bores in Group 2 plot below “new water”
(Figure 24) and therefore contain a significant portion of bedrock water.
All samples from Tenthill catchment and the majority from the Lockyer
plain are less enriched and generally have conductivities lower than 3000
µS/cm (Group 3, Figure 24). In Tenthill catchment the portion of alluvium
sampled in this study is underlain by the Ma Ma Creek Sandstone and
groundwater was sampled from this unit during the 1987 drought (Dixon
and Chiswell 1994). The observed difference in both the isotopic character
and salinity between the alluvial and the more depleted bedrock
groundwater in that study suggests that any upward flow of groundwater
from the Ma Ma Creek Sandstone is likely to be minimal, even under
drought conditions. Therefore it is plausible that Tenthill alluvial samples in
the current study, also chemically and isotopically distinct from the
67
sandstone samples of Dixon and Chiswell (1994) and also sampled under
drought conditions reflect little if any contribution from the underlying Ma
Ma Creek Sandstone bedrock. With two exceptions all of these samples
plot above the “new water” indicating they were recharged by evaporated
surface water (Figure 24). The two samples which plot below “new water”
may represent some minor bedrock mixing but, unlike the mixed samples of
Group 2, their conductivity is much lower than the conductivity of bedrock
groundwater and they are not considered to be the result of mixing.
The three samples from the A – A’ transect near the confluence of Tenthill
and Lockyer Creeks, (bores 502, 491 and 446), have variable conductivity
but are the most isotopically enriched in the study (Group 4, Figure 24). At
this point the alluvial plain narrows into a thin channel between two bedrock
outcrops (Figure 14). All alluvial groundwater from the study area and the
entire western Lockyer Valley must flow through this narrow alluvial
channel which is located immediately north of the A – A’ transect and flow
around the town of Gatton before flowing down to the Central Lockyer. As
a comparison in the Juarez Valley of Mexico it was observed that stable
isotope enrichment increases down valley; this change suggested a
progressive re-cycling of irrigation water down the hydraulic gradient as the
dominant mechanism for increasing groundwater salinity (Fontes 1980).
The enriched waters of the A – A’ transect in the current study may
represent evaporative concentration of irrigation water from the entire
western Lockyer Valley accumulating in the lowest point and trapped in a
“bottle neck effect” before flowing down past Gatton. From the logarithmic
plot of bicarbonate vs conductivity (Figure 21) it could be speculated that
the high salinity of bore 491 was due to bedrock mixing. However Figure 24
demonstrates that bore 491 plots above July 1996 surface water and is
enriched relative to the evaporated water from the creek. On this basis the
bore water must have undergone an additional evaporative process,
probably evaporative enrichment of irrigation water. This evaporated
irrigation water subsequently remains in the upper soil layers until the next
flood flushes it into the creek channels where it enters the alluvial aquifer.
68
The semi logarithmic plot of δ2H ‰ V-SMOW vs conductivity (µS/cm)
(Figure 24) has been effective in identifying hydrological processes and
groundwater evolution typical of the Lockyer Valley. Samples from the
May 1996 flood represent “new water” with minimal modifications from the
composition of rainfall; a sample collected two months later is more
enriched in δ2H ‰ VSMOW with an increased conductivity indicating
evaporation of standing surface water has occurred in the creek channels.
Basalt groundwater exhibits an isotopic composition and salinity
intermediate to that of recharge water and alluvial groundwater, indicating
recharge to basalt and subsequent discharge to the alluvial aquifers, likely to
occur in the upper reaches of the catchments. The alluvial groundwaters also
show evidence of evaporation from standing surface water, indicating both
processes may contribute to alluvial aquifer recharge. Certain alluvial
samples from Ma Ma catchment have a salinity similar to that of bedrock
groundwater, and are more isotopically depleted than other alluvial waters;
this may be the result of mixing with depleted bedrock groundwater (Figure
24). The most enriched samples from the Lockyer plain have undergone an
additional evaporative process and represent the effects of evaporative
concentration of irrigation water which has returned to the creek channels
and re-entered the aquifer. A summary of hydrological processes occurring
within the Lockyer Valley is shown overleaf:
69
“New water” after a major rain event recharges the basalt aquifers and also
undergoes evaporation as standing water in the creek channels. Alluvial
aquifers subsequently receive recharge from both the basalt and evaporated
surface water. Basalt groundwater may also recharge the sandstone aquifers.
In Ma Ma catchment there is strong evidence of alluvial/bedrock
groundwater mixing, while on the Lockyer plain relatively more enriched
alluvial groundwater can be attributed to evaporative enrichment of
irrigation water.
New recharge from rain
Basalt groundwater
Alluvial groundwater
Sandstone groundwater
Evaporated surface water
Irrigation water
Mixed Alluvial- Sandstone
groundwater
70
7. DEVELOPMENT OF GROUNDWATER MODEL
Introduction
The purpose of the modelling effort is to develop a basic groundwater flow
model for the Lockyer alluvial plain and examine the effects of different
annual extraction rates on the minimum saturated aquifer thickness, as this
parameter is crucial to the yield of irrigation bores. Geological logs, water
level records and results of hydrochemical and stable isotope analyses have
been examined to produce a conceptual hydrogeological model, as the basis
to develop a groundwater flow model using PMWIN (Chiang and
Kinzelbach 2001) for the Lockyer plain. This region is the most intensively
cultivated portion of the study area and also contains abundant spatial data
including 32 regular bores (with geological logs), and 10 monitoring bores
with historical water level measurements. In addition water chemical
samples were collected from 15 bores and stable isotope samples from 10
bores. All of these data sources and the local terrain make it an interesting
and valuable area for groundwater modelling. The upper reaches of the two
catchments contain an uneven spread of bores separated by a distance of 2
km or greater from the bores of the Lockyer plain and were therefore not
included in the flow model. The model was calibrated to transient
conditions by head matching for the period March 1993 to November 1996,
representing a drought and subsequent flood and therefore two opposing
stresses on the aquifer. This period was also selected as it contains metered
groundwater extraction data. A sensitivity analysis indicates that the model
is insensitive to variations of aquifer properties within realistic bounds.
Predictive simulations have been performed using various annual extraction
rates for the model duration to establish the minimum saturated thickness in
the aquifer.
71
Background
A groundwater model is a physical or numerical representation of a real
world hydrogeological system. Models may be of 3 different types, (a)
Predictive: used for prediction of future conditions, (b) Interpretative: used
for studying system dynamics or organising data, and (c) Generic: used to
analyse hypothetical hydrogeological systems (Anderson and Woessner
1992). Although modelling is important for any of the above purposes, it is
only one component of a hydrogeological investigation requiring sound data
foundations and cannot stand alone. To ensure modelling consistency, best
practice guidelines for the development, revision and reporting of
groundwater flow models have been proposed (e.g. Murray-Darling Basin
Commission 2000; Middlemis et al. 2002; Merrick et al. 2002).
Groundwater modelling methodology can be divided into three components;
conceptualisation, calibration and prediction, which will be outlined below
with a focus towards the industry standard MODFLOW
Conceptualisation
A conceptual model is a pictorial representation of the groundwater flow
system incorporating all available geological and hydrogeological data into
a simplified block diagram or cross section (Anderson and Woessner 1992).
The first phase in producing a conceptual model is defining the geological
framework including the thickness, continuity, lithology and structure of
any aquifers and confining units. Data for the geological framework is
typically obtained from geological maps, bore logs, geophysics and
additional field mapping. Establishment of the geological framework then
permits the hydrological framework to be defined involving four important
steps; identifying the boundaries of the hydrological system, defining
hydrostratigraphic units, preparing a water budget and defining the flow
system.
The boundaries of a model must be identified first so that all the following
steps can proceed within their framework. Boundaries can be either natural
72
hydrogeological boundaries including the surface of the water table,
groundwater divides and impermeable contacts between different geological
units, or may need to be unnatural such as cadastral boundaries. The type of
boundary selected will depend on the modelling scope and requirements and
will affect how the boundaries are represented within MODFLOW, however
for simplicity, natural boundaries should be used wherever possible.
Defining hydrostratigraphic units is crucial in determining the number of
layers controlling groundwater flow within the system. A hydrostratigraphic
unit is comprised of geological units of similar hydrogeological properties.
Numerous geological units may be grouped together or a single formation
may be subdivided into different aquifers and aquitards. Estimates of
hydraulic conductivity and storativity from pump tests combined with water
chemical analyses are often used to identify and distinguish different
hydrostratigraphic units.
Preparation of a water budget involves the identification and quantification
of all flows in and out of the groundwater system. The mechanisms of
recharge are defined as areally distributed, preferential or seepage from
surface water bodies and their fluxes are estimated based on precipitation
data, the permeability of the aquifer or confining units or chemical and
isotopic techniques. Outflows from the system are defined as springflow,
baseflow, evapotranspiration or extraction and their fluxes are estimated by
chemical or isotopic techniques or metering in the case of extraction.
Definition of the flow system is essential to understanding groundwater
movement throughout the hydrogeological system. Water level
measurements are used to identify the dominant directions of groundwater
flow, the hydraulic gradient, locations of recharge areas, location of
discharge areas and connections between ground and surface water. As in
the water budget preparation, water chemical analyses are also employed to
qualitatively represent recharge and baseflow.
73
Calibration
The first phase involves model construction; the design and orientation of
the model grid. In the case of a finite difference grid, cells are rectangular
and may be all equally sized or some areas of the grid may be smaller or
larger. Finite difference grids may be divided into two different types: block
centred grids in which flux boundaries are always located at the margins of
the block; and mesh centred grids in which the boundary is centred on a
node. MODFLOW is a block centred grid. The size of each individual cell
should be as large as possible to minimise computational time and storage
space, yet small enough to reflect the curvature of the water table and the
hydraulic gradient, and also the effects of point stresses on the
hydrogeological system such as preferential recharge and pumping from
well nodes (Anderson and Woessner 1992). The spatial distribution and
heterogeneity of aquifer properties is also important when choosing an
appropriate grid size, with the more variable the aquifer properties, the finer
the model grid should be to express these variations. When aquifer
properties are not accurately defined or known a larger grid size should be
used. With lower resolution data on the distribution of aquifer properties a
larger grid size should be used. The orientation of the model grid is not
important in an isotropic aquifer as the hydraulic conductivity is constant in
all directions, however when an aquifer is anisotropic the model grid must
be orientated with the main axes of the hydraulic conductivity tensor and
these axes of maximum and minimum hydraulic conductivity are always
perpendicular to each other (Kresic 1997).
Four different layer types are recognised in MODFLOW as discussed
below:
Type 0: The layer is strictly confined and transmissivity of each cell remains
constant for the entire simulation.
Type 1: The layer is strictly unconfined and can only be applied for the
uppermost layer of a model.
Type 2: The layer is used when the aquifer alternates between confined and
unconfined as the simulation progresses.
74
Type 3: The layer is used when the aquifer alternates between confined and
unconfined as the simulation progresses resulting in variations in the
saturated thickness.
(Chiang and Kinzelbach 2001).
Three boundary conditions can be applied to cells in a finite difference grid
such as MODFLOW including (a) Dirichlet, (b) Neuman and (c) Cauchy.
(a) Dirichlet condition: the head at the boundary is known, examples are the
water table in an unconfined aquifer, or a river or lake in contact with an
unconfined aquifer, all under steady state conditions. Dirichlet conditions
are also used when simulating unnatural boundaries such as cadastral
boundaries of a hydrogeological system which are often defined for the
purposes of the modelling investigation. In a natural hydrogeological system
an aquifer may continue onwards past the boundary and therefore must be
accounted for by placing a fixed or specified head cell or cells, in which the
allocated head is known. All applications of Dirichlet boundaries require
some form of head measurement on or very near the boundary.
(b) Neuman condition: the flux across a boundary is known, examples
include no flow boundaries between geological units, interactions between
groundwater and surface water bodies, springflow, underflow, and seepage
from bedrock into alluvium. The simulation of Neuman Boundaries requires
the measurement or estimation of one of the above fluxes, which is often
inaccurate. The most commonly applied form of a Neuman Boundary is a
No-Flow or Impermeable Boundary, often occurring between a highly
permeable unit and a unit of much lower permeability. A difference in
hydraulic conductivity of two orders of magnitude or greater between two
adjacent units is sufficient to justify placement of a No-Flow Boundary, as
this contrast in permeability causes refraction of flow lines such that flow in
the higher conductivity layer is essentially horizontal and flow in the lower
conductivity unit is essentially vertical (Anderson and Woessner 1992;
Freeze and Witherspoon 1967; Neuman and Witherspoon 1969).
(c) Cauchy condition: the flux across the boundary is dependant on the
magnitude of the difference in head across the boundary, with the head on
one side of the boundary being input to the model and the head on the other
75
side being calculated by the model. Examples of a Cauchy Boundary
include leakage from a surface water body where the flux is dependant on
the difference in elevation between the surface water and groundwater level
and the vertical hydraulic conductivity of the boundary; and
evapotranspiration where the flux is proportional to the depth of the water
table in an unconfined aquifer. A Cauchy Boundary has the advantage over
a Neuman Boundary in that its flux can be calculated by the model if given
sufficient input data.
A groundwater model may represent either steady state or transient aquifer
conditions. In a steady state groundwater model all flows in and out of the
model are equal and there is no net change in storage, consequently no
storage terms are required in the input parameters. A steady state model may
be run for different times and the outcome will be the same as time is
irrelevant under steady state conditions. A transient groundwater model
simulates stresses on an aquifer over time and is therefore divided into stress
periods which are further divided into time steps. The number of stress
periods can be input by the user and should reflect any temporal stress on
the aquifer such as recharge or extraction.
Initial hydraulic heads must be input before running the simulation. In the
case of a steady state model the heads can be estimates or averages of all the
available data, however, for transient models the heads can be real values or
can be the result of a steady state simulation. Heads at fixed head cells must
be real values and therefore should be interpolated from the nearest
observation bore.
Aquifer parameters including hydraulic conductivity and storativity must be
input to the grid, with hydraulic conductivity required for all simulations
while storage terms are only required for transient simulations. Vertical
hydraulic conductivity is required for each layer of a multiple layer model
and in the absence of field data is typically taken to be 10% of the horizontal
hydraulic conductivity (Kresic 1997). Transmissivity may be input manually
or MODFLOW can be set to calculate the transmissivity for each iteration
76
in each cell by multiplying the hydraulic conductivity by the saturated
thickness of the cell. Specific storage must be input manually for a Type 0
(confined) or Type 2 or 3 (convertible) and MODFLOW can calculate the
confined storage coefficient for each cell by multiplying the specific storage
by the saturated thickness. For a Type 1 (unconfined) and Type 2 or 3
(convertible) layer the specific yield must be input manually.
Recharge can be simulated in MODFLOW as a flux of length per unit time
across the top of a cell which is then combined with the dimensions of the
cell to calculate a flow rate per unit time entering the cell. Recharge can be
areally distributed over the entire model grid as infiltration, or restricted to a
single cell or group of cells allowing recharge zones to be delineated. There
is also the option to allocate recharge to the top layer, as would be the case
with infiltration to an unconfined aquifer, or to any layer in a multi layer
model, regardless of its position in relation to the top layer.
Groundwater extraction is simulated by a pumping well using the well
package. A well is allocated to an individual cell where it occupies the
entire cell and draws water out of the model from that cell. A well can be
allocated in any model layer and it is assumed that the well penetrates the
entire thickness of that layer and consequently draws from the entire layer.
The pumping rate must be specified as the L3 per unit time for the pumping
well such as L3/s or L3/day (where L is the length term) and this is used by
MODFLOW to calculate the net extraction from that well.
The Time Variant Specified Head package is used at the model boundaries
or at any other place where a fixed head changes over time but the change in
head is known. For cells designated as Time Variant Specified Head, a
starting head and an end head can be allocated for a stress period, simulating
the head change in those cells during the course of that stress period.
Numerous stress periods with head changes can then be used to represent
the change in head at a fixed head cell during a transient simulation. This
feature is particularly useful for simulating unnatural boundaries such as
cadastral boundaries of a hydrogeological system which are often defined
77
for the purposes of the modelling investigation. In a natural hydrogeological
system an aquifer may continue onwards past the boundary and therefore
must be accounted for in the simulation by placing a fixed or specified head
boundary, which can be modified to a time variant specified head boundary
for transient conditions.
Model calibration is the process of modifying one or more model
parameters until the results of the simulation match the measured data.
Calibration of an inverse problem involves modifying the boundary
conditions, hydraulic properties and stresses of the model until the simulated
heads match the observed heads, typically the case with real world
hydrogeologic systems. Calibration of a forward problem involves working
from an existing set of boundary conditions, hydraulic properties and
stresses to estimate heads, which is usually the case with a theoretical
system (Anderson and Woessner 1992). In an inverse problem such as this
study, it is usual to match the head outputs of the model to the observed
heads as head measurements are likely to be the most accurate and most
readily available. A steady state calibration is performed to water levels that
represent steady state conditions such as long term mean water levels, mean
annual water levels, or mean seasonal water levels for a particular season. A
quasi steady state calibration is conducted to water levels that represent the
aquifer’s behaviour at a given point in time under certain stresses applicable
at that time. Transient calibration is performed to water levels that represent
the aquifer’s response to stresses such as recharge and extraction over time,
and consequently it is essential to have some handle on the magnitude of
these fluxes for the duration of the modelling period in order to achieve
accurate calibration.
Two methods may be employed to reduce the non uniqueness of the
calibrated solution. Firstly the model should be calibrated with parameters
that are consistent with field measured parameters, for example aquifer
properties determined from pumping tests. Secondly the model should be
calibrated to multiple distinct hydrological conditions, to demonstrate that
the parameters chosen are capable of reproducing the system behaviour
78
under different hydrological stresses. The different hydrological conditions
used can be natural such as a dry period and a wet period, or artificial such
as variable extraction (Murray Darling Basin Commission 2000).
The process whereby the user modifies one or more parameters to achieve
model calibration is commonly known as trial and error calibration and may
be extremely time consuming. Automated calibration is conducted by a
specialised code working in conjunction with MODFLOW to achieve a
solution to an inverse problem. In a direct solution unknown parameters are
treated as dependant variables and heads are treated as independent
variables. In an indirect solution the heads are used to adjust one or more of
the model parameters so that the objective function (phi) or sum of squared
residuals (difference between observed and calculated heads) is reduced as
low as is possible. When performing automated calibration it is usual to
input an initial guess for a parameter value and both an upper and lower
limit for the parameter in order to constrain the calibration process within
acceptable limits. The most common program for automated calibration
currently is PEST (Doherty et al. 1994) and has been added onto all major
MODFLOW graphical user interfaces such as PMWIN (Chiang and
Kinzelbach 2001).
Whether the calibration method is trial and error or automated, several
techniques are commonly employed to assess the calibration. To
qualitatively gauge the efficiency of the calibration, contour plots of heads
may be constructed. To quantitatively assess the calibration, the difference
between observed and calculated heads, otherwise known as residuals, may
be compared graphically and statistically. When the mean of the residuals is
reduced to as close to zero as possible and the standard deviation is reduced
as much as possible, the model is calibrated. Plots of observed and
calculated heads over time can be used to graphically compare the
differences between the two head datasets during the course of the model
simulation. The calibration should also be evaluated by a standard statistical
method such as the Root Mean Square (RMS) Error, which is the average of
79
the squared differences in measured and simulated heads, as shown by the
following formula:
( )5.0
1
21 ⎥⎦
⎤⎢⎣
⎡−= ∑
=
n
iiCO HHnRMS
where
n = number of model observations
HO = observed head for each observation
HC = calculated head for each observation
Running a calibrated model with changes to a parameter by predetermined
amounts within a realistic range can be utilised to establish the model’s
sensitivity to that parameter and is known as a sensitivity analysis. It is
essential that only one parameter is varied at a time in order to see the
effects of the changes on the solution, and that any effects be evaluated by
the same statistical methods used to evaluate the model calibration.
In order to compensate for the effects of any bias or uncertainty in the
system stresses and boundary conditions used in the model solution, the
calibrated model should be tested under a different set of stresses and
boundary conditions in order to verify the model. Such an experiment is
most easily facilitated by running the model with a different set of head,
rainfall and pumping measurements in order to determine if the same level
of calibration accuracy can be replicated with the different datasets. If
successful the model can be deemed to be verified.
Prediction
Predictions can be used to test various scenarios of how a calibrated model
will respond to different system stresses such as recharge and extraction.
Predictions are limited by the uncertainties in the calibrated solution and the
accuracy of the verification.
80
Conceptualisation
Geological Framework
The bedrock in the study area is the Triassic–Jurassic Marburg Formation,
within which incised channels contain Quaternary alluvial fill. The alluvium
/ bedrock contact was obtained from geological maps and the extent and
area of alluvium in the Lockyer plain was calculated. The examination of 32
drill logs revealed a laterally continuous layer of gravel at the base of the
sequence, overlain by clay, sandy clay and silt. The gravel is a productive
aquifer with a mean thickness of 4.47 m while the overlying deposits form a
semi confining layer. A summary of geological data is presented in Table 4
with the locations of bores displayed in Figure 25. Two cross sections, both
west-east, are displayed in Figures 26 and 27.
Based on the width of the alluvium at cross section A – A’ (Figure 26) of
3000 m and the average depth to bedrock of 28.2 m, the width to depth ratio
of the channel is 106. Similarly the width of the alluvium at cross section B
– B’ (Figure 27) is 3480 m and the average depth to bedrock is 28 m,
resulting in a width to depth ratio of the channel of 124. The average
bedrock elevation on cross section A – A’ is 82 m and cross section B – B’
is 99 m, with a difference in elevation of 17 m. The distance between two
bores in the middle of these cross sections bores 491 and 231 is 5950 m,
resulting in a channel gradient of 0.00285.
Due to the high width to depth ratios of 106 and 124 of the cross sections
and the channel gradient of 0.00285, the alluvial sequence in the study area
can be classed as underflow dominated using the classification of Larkin
and Sharpe (1992).
81
Figure 25. Location of model extent and the 32 bores used to define the
hydrogeological framework for the conceptual model of the Lockyer plain.
Bore RN Easting
(AGD 84) Northing (AGD 84)
Surface elevation (mAHD)
Depth to gravel (m)
Depth to bedrock (m)
Gravel elevation (mAHD)
Bedrock elevation (mAHD)
Gravel Thickness (m)
106054 425310 6948653 111 22.6 27.7 88.4 83.3 5.1 171 425416 6949969 111.25 19.8 27.7 91.45 83.55 7.9 173 425722 6949386 113.48 22 25 91.48 88.48 3 175 425859 6949202 114.23 25.9 32.6 88.33 81.63 6.7 176 426081 6948896 114.64 22 24.4 92.64 90.24 2.4 177 426219 6948712 113.92 19.2 24.4 94.72 89.52 5.2 220 423801 6947943 120.01 26.8 29.7 93.21 90.31 2.9 221 424271 6947886 119 24.5 31.1 94.5 87.9 6.6 222 424575 6947692 120.03 20.7 22.9 99.33 97.13 2.2 227 422068 6945886 128.5 28.3 30.8 100.2 97.7 2.5 228 422427 6945831 127.1 27.1 30.5 100 96.6 3.4 229 422899 6945759 129 22.9 28 106.1 101 5.1 231 423332 6945678 128.5 27.4 33.4 101.1 95.1 6 232 423661 6945619 126.8 19.8 25.3 107 101.5 5.5 233 424073 6945560 125.2 20.3 26.5 104.9 98.7 6.2 235 424402 6945500 124.7 18.3 23.8 106.4 100.9 5.5 426 422681 6948966 115.9 18.7 25 97.2 90.9 6.3 428 422759 6949490 116.67 17.5 21.8 99.17 94.87 4.3 440 423956 6947059 123.52 25.9 29.5 97.62 94.02 3.6 442 423403 6947209 124.54 24.3 28 100.24 96.54 3.7 445 427435 6950520 110.02 24.9 29.8 85.12 80.22 4.9 446 428044 6950846 107.68 25.6 28 82.08 79.68 2.4 462 423823 6945612 126.92 20.4 26.2 106.52 100.72 5.8 489 423888 6948882 117.01 25.5 28 91.51 89.01 2.5 490 423285 6948817 116.61 18 24.5 98.61 92.11 6.5 491 426619 6950622 110.94 21.4 27 89.54 83.94 5.6 502 425414 6950369 111.9 25.6 27.8 86.3 84.1 2.2 516 425748 6949632 113.42 25.1 27 88.32 86.42 1.9 557 426155 6950373 110 25.75 28.4 84.25 81.6 2.65 444 427221 6950995 105 15.2 19.5 89.8 85.5 4.3 447 427520 6951427 105.59 18.8 27.1 86.79 78.49 8.3 449 426341 6951297 106.04 16.1 17.9 89.94 88.14 1.8
Table 4. Summary of bore logs used to define the thickness of the gravel aquifer in the study area.
Figure 26. Cross section A-A’ showing alluvial infill into channels incised in sandstone bedrock. Bore screens shown where records exist.
Figure 27. Cross section B-B’ showing alluvial infill into channels incised in sandstone bedrock. Bore screens shown where records exist.
85
Hydrologic Framework
When the gravel is fully saturated the aquifer exhibits confined conditions
and its upper surface forms a no flow boundary with the overlying semi
confining layer. In drought conditions when the demand for irrigation water
is high the potentiometric surface of the aquifer falls below the top of the
gravel layer in some locations; the aquifer exhibits unconfined behaviour
with the water table as its upper boundary. At all times a no flow boundary
also exists between the gravel and the adjacent and underlying sandstone
bedrock.
Unnatural boundaries were allocated in three locations for the purposes of
the modelling study, in the south at the junction of the two catchments, in
the west at the confluence of Ma Ma and Lockyer Creeks, and in the north
immediately downstream of the confluence of Tenthill and Lockyer Creeks.
These boundaries were allocated in order to enclose the Lockyer plain. A
monitoring bore is situated at each of these locations and the head on the
boundary is known, enabling these boundaries to be designated as Dirichlet
(constant head) boundaries.
From the cross sections in Figure 26 and 27 two hydrostratigraphic units
were identified, the gravel aquifer and the mixed sands and clays of the semi
confining layer. All monitoring bores are screened in the gravel aquifer and
therefore water level measurements and water samples taken from these
bores are representative of the basal aquifer, not the semi confining unit and
as such represent a potentiometric surface. In addition the results of pump
tests conducted on these bores and the estimates of hydraulic properties are
also indicative of the gravel. Therefore the gravel aquifer was designated as
the single hydrostratigraphic unit. As presented in the results section, the
hydraulic conductivity values of the gravel were estimated at 63 and 79
m/day which were averaged for the conceptual model to 70 m/day; and
storativity (storage coefficient) was estimated at 0.0016 which was divided
by the aquifer thickness of 4 m to obtain the specific storage of 0.0004.
Specific yield was conceptualised as 0.24 which is suggested as the mean
value of specific yield for gravel by Morris and Johnson (1967).
86
Preparation of a water budget and definition of the flow system involves
identifying and quantifying all fluxes into and out of the hydrogeological
system. Areal recharge through the clay, sandy clay and silt was considered
unlikely due to the low permeability of these sediments and an average
infiltration rate of 12 mm/year for unsaturated sediments of the Lockyer
Valley was calculated using tritium methods (Ellis 1999). Preferential
recharge through the creek channels was considered the primary source of
recharge to the gravel aquifer. This interpretation is because bore 516
adjacent to Tenthill Creek displays a positive response to a monthly rainfall
of 100 mm or greater, indicating such a minimal amount of rainfall can have
an effect on measurements in a nearby bore (Figure 28). A flood event in
May 1996 when 400 mm of rain was received in 4 days had a dramatic
effect on this bore, with levels rising 4 m in 4 days, and continued flow in
creeks resulting from this event filled the aquifer to its pre 1993-1995
drought levels.
A surface water sample collected during the flood in May 1996 is extremely
fresh with a conductivity of 250 µS/cm, while the conductivity of a sample
collected later that year in July was 490 µS /cm. The ionic proportions of
surface water did not change from May to July, however the ionic
concentrations increased, with those of the July sample approaching the
concentrations of groundwater as indicated on the Schoeller diagram (Figure
18). The increase in salinity from May to July is likely due to evaporation,
with water standing in the creek channels after the flood event.
Ratios of stable isotopes δ2H and δ18O also support preferential recharge
through the creek channels as the dominant recharge mechanism. Infiltration
through the mixed sand and clay overlying the aquifer was quantified as 12
mm/year using tritium methods (Ellis and Dharmasiri 1998; Ellis 1999). In
the same studies, stable isotopes were also measured in pore water from drill
cores of the mixed sand and clay at 5 different sites throughout the Lockyer
Valley. The ratios of δ2H and δ18O for pore water from these cores plot on a
slope of 2.9. By contrast a plot of δ2H vs δ18O for water samples from the
87
0
50
100
150
200
250
300
350
400
450
500
Jan-93 Jan-94 Jan-95 Jan-96
Date
Mon
thly
rain
fall
(mm
)
82
84
86
88
90
92
94
96
98
100
Hea
d (m
asl)
Monthly RainfallHead
Figure 28. Hydrograph of bore 516 adjacent to Tenthill Creek for period
1993-1996, showing 100 mm is the minimum monthly rainfall needed for
positive response from groundwater.
88
gravel aquifer taken during the current study plot on a slope of 5.56 (Figure
23). A slope of between 2 and 3 is indicative of evaporation from the
unsaturated zone, while a slope of between 4 and 6 is indicative of
evaporation from a surface water body (Gat 1981).
These relationships suggest the following:
(a) Water from the unsaturated zone has undergone different evaporative
processes to that of groundwater.
(b) Infiltration through the semi confining layer is extremely low and has
minimal influence on the aquifer (Ellis and Dharmasiri 1998; Ellis 1999).
(c) Water from the gravel aquifer has undergone evaporation characteristic
of standing surface water at some stage (data from this study).
The effects of evaporative concentration from re-infiltration of spray
irrigation water can be discounted due to the extremely low infiltration rate
of the semi-confining layer. Therefore seepage of surface water from the
creek channels is the dominant recharge process.
A study of a similar alluvial system in the Logan Albert catchment (Please
et al. 1997), with a gravel and sandy gravel aquifer ranging from 1-10 m
thick overlain by a semi confining unit of mixed sands and clays ranging
from 10-20 m thick, proposed evaporation from surface water as the cause
of isotopic enrichment in groundwater. For the three sub-catchments, plots
of δ2H vs δ18O produced slopes of 6.61, 5.62 and 4.59. The most enriched
samples were found to occur in bores adjacent to the drainage channels,
suggesting that some recharge was received from evaporated surface water
bodies. In addition an increase in enrichment was observed down the flow
path providing further evidence of evaporated surface water contribution.
Like NRM&E monitoring bores, private irrigation bores are also screened in
the gravel aquifer for the best yields possible. Groundwater extraction of the
Lockyer plain has not been measured, however, in the NRM&E proclaimed
area to the east of Gatton all private irrigation bores have been installed with
automatic meters to measure the volumes of groundwater withdrawn in ML.
Data exists for this region for a 4 year period from 1993 – 1997, with meters
89
being read approximately every 3 months. The total extraction ranges from
18.9 – 70 ML/day over an area of 10800 ha (Durick and Bleakley 2003). By
contrast the Lockyer plain of this study covers an area of 1460 ha, which
can be rounded up to one eighth the size of the NRM&E proclaimed area.
Dividing the extraction rates of the NRM&E proclaimed area by eight
produces extraction rates ranging from 2.36 – 8.75 ML/day for the Lockyer
plain. As the landholders in the study area are practising the same forms of
agriculture as in the NRM&E proclaimed area, growing the same species of
crops using groundwater for irrigation, the rates from the proclaimed area
are applicable for this study on a volume per hectare basis and produce the
best estimation of data available.
Figure 29 (overleaf). Conceptual hydrogeological model for cross section
A-A’ on the Lockyer plain. Water levels are shown at the beginning of the
proposed simulation period in March 1993, at their lowest point in October
1995 and at the end of the simulation period in November 1996 following a
major flood event. Estimates of aquifer properties hydraulic conductivity
and specific storage determined from pump tests are shown for the gravel
aquifer with a literature value of 0.24 applied for specific yield. The
similarity between both the major ion chemical and stable isotopic
composition of surface water and groundwater indicates recharge from
creek channels is the dominant recharge process. This is supported by the
different stable isotopic composition of water from the mixed sand and clay
semi confining layer and the low infiltration rates for this layer presented by
Ellis and Dharmasiri (1998) and Ellis (1999). Groundwater extraction from
the gravel aquifer ranging from 2.4-8.75 ML/day was calculated for the
Lockyer plain based on data presented in Durick and Bleakley (2003).
Discharge of higher salinity groundwater may occur from the adjacent and
underlying sandstone bedrock aquifers. Arrows show fluxes.
91
Calibration
Spatial Discretisation
To represent the Lockyer plain a model grid of 50 columns x 50 rows was
selected. The grid size was selected as 200 x 200 m as this size had been
used successfully to model a similar alluvial system with a similar
resolution of geological and water level data in the NRM&E proclaimed
area. Utilising the same grid size as that study would enable useful
comparisons between these two areas for water resource planning. The grid
was angled at 62.68 deg from east so that the grid was orientated with the
main axes of the hydraulic conductivity tensor, thus all cells were
perpendicular to the flow direction (Figure 30).
Boundary Conditions
The IBOUND array in MODFLOW was used to designate the different
boundaries and their types in the model. A base map was positioned under
the model grid and used to distinguish the alluvium-bedrock contact. Grid
cells outside the alluvium coverage were all allocated a value of 0 in the
IBOUND array thus rendering these cells as inactive and creating a no flow
boundary between the alluvium and bedrock. Cells inside the area of
alluvium were all left with the default value of 1 and therefore they
remained active. The bounds of the Lockyer plain in the south, west and
north, created for the purposes of this modelling investigation, were all
allocated a value of -1, designating these cells as fixed head (Dirichlet
conditions) resulting in a total of 30 fixed head cells. This was necessary as
the aquifer continues onwards past the boundary and therefore must be
accounted for by placing fixed or specified head cells, in which the allocated
head is known (Figure 30).
Layer type
Although two hydrostratigraphic units were identified in the conceptual
model, only the gravel aquifer could be modelled, largely due to the total
absence of head data for the overlying semi confining unit, and therefore a
one layer model was chosen. As shown on previous hydrographs the
92
Figure 30. Model grid orientated at 62.68 degrees from east showing active
cells (white), inactive cells (grey) and fixed head cells (green).
93
potentiometric head of the aquifer varies over time and when the gravel is
fully saturated confined conditions prevail, while when the water level falls
below the top of the gravel unconfined conditions prevail. For this reason
alone, a type 3 layer was selected in PMWIN to represent the gravel aquifer.
A type 3 layer allows the layer to convert from confined to unconfined as
the head varies, and the transmissivity of each cell is recalculated for each
model iteration based on the hydraulic conductivity and the saturated
thickness of each cell.
Top and Bottom of Layer
The top of the aquifer, and therefore the top of the layer was taken as the top
of the gravel. The elevation of the gravel surface was obtained from 32 bore
logs and these data points were then interpolated by kriging into the model
grid (Figure 31). The bottom of the aquifer, and therefore the bottom of the
layer was taken as the contact between alluvium and the underlying
sandstone bedrock. The elevation of the bedrock was also obtained from 32
bore logs and interpolated by kriging into the model grid (Figure 32).
Time
The aquifer in the lower plain is under constant pressure from extraction,
and to truly reproduce its behaviour a transient model is required. The
period March 1993 – November 1996 was chosen for the simulation as it
represents the aquifer’s response to a 3 year drought and the associated
decline in water levels due to the increase in demand for irrigation water,
followed by a flood in May 1996 in which the aquifer was recharged
significantly. This period was also selected as it contains water level
measurements at approximately 3 monthly intervals or better, while prior to
March 1993 the preceding measurement was 6 months earlier and after
November 1996 the following measurement was 10 months later. Such long
hiatus in water level measurements greatly decrease the accuracy of the
model calibration in a hydrogeological system under constant stress. Finally
the governing variable for the selection of the period to be modelled was the
availability of extraction data for the same period from the NRM&E
proclaimed area which could be applied at the same rates per unit area for
94
Figure 31. Top of layer contours interpolated from bore logs with 1 m
interval.
Figure 32. Bottom of layer contours interpolated from bore logs with 1 m
interval.
95
this modelling study. The model period contained 16 water level
measurements and was subdivided into 15 stress periods with a
measurement at the start and end of each stress period. By trial and error a
timestep of 7 days was identified as the largest possible timestep that did not
affect the solution outcome and therefore was implemented as
recommended by Anderson and Woessner (1992). For a summary of
temporal data refer to Table 5.
Stress Period Start Finish WL Date
Length (Days) Timesteps
Cumulative (Days)
1 8/03/1993 11/05/1993 11/05/1993 64 9 64 2 12/05/1993 5/08/1993 5/08/1993 86 12 150 3 6/08/1993 24/11/1993 24/11/1993 111 16 261 4 25/11/1993 28/01/1994 28/01/1994 65 9 326 5 29/01/1994 29/03/1994 29/03/1994 60 9 386 6 30/03/1994 26/05/1994 26/05/1994 58 8 444 7 27/05/1994 21/09/1994 21/09/1994 118 17 562 8 22/09/1994 11/01/1995 11/01/1995 112 16 674 9 12/01/1995 11/04/1995 11/04/1995 90 13 763
10 12/04/1995 21/07/1995 21/07/1995 101 14 863 11 22/07/1995 17/10/1995 17/10/1995 88 12 950 12 18/10/1995 17/01/1996 17/01/1996 92 13 1042 13 18/01/1996 27/03/1996 27/03/1996 70 10 1112 14 28/03/1996 26/07/1996 26/07/1996 121 17 1233 15 27/07/1996 9/11/1996 9/11/1996 106 15 1339
Table 5. Summary of temporal data.
Initial Heads
The hydrogeological system in the study area is under constant stress from
extraction and has never been at a steady state during the period for which
water level measurements exist. Consequently a steady state calibration was
not possible and initial heads could not be sourced from the results of a
steady state simulation as is common in modelling practice. Instead the
heads measured at the beginning of the period to be modelled, 8 March
1993,were used as initial heads for the start of the simulation. The head
dataset was interpolated into the model grid using kriging (Figure 33).
96
Observation boreholes
Ten NRM&E monitoring boreholes exist in the Lockyer plain with 3
monthly or better water level measurements for the simulation period and
were utilised as data points for head matching during calibration. These 10
bores were also used in the interpolation of initial heads and time variant
specified head boundary conditions and their locations are shown in Figure
33.
Aquifer properties
Horizontal hydraulic conductivity was applied at a blanket value of 70
m/day. The specific storage was applied at a blanket value of 0.0004 to all
cells in the grid so that the confined storage coefficient was calculated by
PMWIN in each cell based on the thickness of the cell. The unconfined
storage term, specific yield was applied at a blanket value of 0.24 for the
entire grid.
Time Variant Specified Head
The cells defined as fixed head boundaries in the IBOUND array were
modified with the Time Variant Specified Head package to simulate the
change in head at these boundaries over time. The package allows the heads
at the boundary cells to be input for the start and end of each stress period.
For each stress period, the start and end set of head measurements were
interpolated using kriging from the set of 10 observation bores, and the
values at the boundary cells were allocated for the start and end of the stress
period using the Time Variant Specified Head Package.
97
Figure 33. Initial heads interpolated from 10 head measurements in March
1993 with 1 m contour interval.
Figure 34. Locations of Tenthill Creek (east) and Lockyer Creek (north)
and Ma Ma creek (west) in the model grid.
98
Recharge
Recharge was conceptualised as not areally distributed but as preferential
seepage through the creek channels. As no creeks in the study area were
gauged during the period of the model simulation the MODFLOW River
package could not be used to estimate the flux from the creeks to the
aquifer. Therefore the recharge flux was unknown and was estimated by
PEST during calibration. Hydrograph peaks and monthly rainfall indicate
recharge occurred in stress periods 2, 5, 9, 12, 13, 14 and 15; with the two
last stress periods corresponding to the May 1996 flood event and the
subsequent standing water in the creek channels for several months. Using a
base map of the drainages, Tenthill and Lockyer Creeks were digitised as
recharge cells in the model grid. Ma Ma Creek was not digitised as recharge
cells as it flows over bedrock for much of its length in the Lockyer plain
(Figure 34). The creek channels were divided into seven different recharge
zones, based on the locations of monitoring bores for increased accuracy in
estimating recharge during calibration. In total 73 cells were designated as
recharge cells (Figure 35).
Extraction
Pumping from the aquifer for irrigation was simulated by the well package.
The volumes of water extracted from the NRM&E proclaimed area have
been measured and expressed as volume per time as shown in the table
below. As the rate of groundwater extraction per unit time for the study area
is largely unknown, it was decided to apply the pumping rates of the Central
Lockyer on a volume per area basis. The Central Lockyer model constructed
by Durick and Bleakley (2003) contained 2700 active cells, excluding
boundary cells, covering an area of 10800 ha. By contrast the Lockyer plain
covers an area of 1800 ha and this model contained 478 active cells. Of
these 478 active cells 30 were time variant specified head cells, 73 were
recharge cells and 10 contained a water level observation bore, leaving 365
active cells for potential extraction. This represents an area of 1460 hectares,
which has been rounded up to one eighth the size of the proclaimed area. To
adapt the pumping rates of the NRM&E proclaimed area to the Lockyer
99
Figure 35. Locations of 7 recharge zones relative to observation bores.
Figure 36. Extraction cells applied to entire model grid excluding the 30
time variant specified head cells, the 73 recharge cells and each of the 10
cells containing an observation bore.
Table 6. Summary of extraction data.
Stress Start Finish No of Days Central Lockyer Extraction Rate m3/Day m3/Day
Period Extraction Rate divided by 8 divided by
(ML/Day) (ML/Day) 365 pumping
cells 1 8/03/1993 11/05/1993 64 70.00 8.75 8750.00 23.97 2 12/05/1993 5/08/1993 86 61.21 7.65 7651.74 20.96 3 6/08/1993 24/11/1993 111 60.29 7.54 7536.15 20.65 4 25/11/1993 28/01/1994 65 53.38 6.67 6673.08 18.28 5 29/01/1994 29/03/1994 60 46.04 5.76 5755.00 15.77 6 30/03/1994 26/05/1994 58 44.61 5.58 5576.29 15.28 7 27/05/1994 21/09/1994 118 63.62 7.95 7952.12 21.79 8 22/09/1994 11/01/1995 112 52.57 6.57 6570.76 18.00 9 12/01/1995 11/04/1995 90 30.61 3.83 3826.25 10.48
10 12/04/1995 21/07/1995 101 41.14 5.14 5142.08 14.09 11 22/07/1995 17/10/1995 88 39.30 4.91 4912.78 13.46 12 18/10/1995 17/01/1996 92 23.70 2.96 2963.04 8.12 13 18/01/1996 27/03/1996 70 18.90 2.36 2362.50 6.47 14 28/03/1996 26/07/1996 121 25.49 3.19 3186.36 8.73 15 27/07/1996 9/11/1996 106 30.31 3.79 3789.03 10.38
101
plain the extraction rates were divided by eight and converted to m3 per day
for each stress period for input to PMWIN as summarised in Table 6.
In the NRM&E proclaimed area the locations, pumping rates and pumping
durations of each irrigation bore were known with reasonable confidence,
however for the Lockyer plain this data was largely unknown. Therefore to
avoid any bias in the allocation of extraction rates to the model grid, a
blanket value of extraction was applied to all the 365 cells. The 30 time
variant specified head cells, 73 recharge cells and 10 observation bore cells
were not allocated a pumping rate as this would create errors in the
modelling calibration (Figure 36).
Calibration
The flow model was calibrated as an inverse problem with head values,
boundary conditions, aquifer properties, and extraction all input and the
model used to estimate recharge. PEST was used for calibration of recharge
fluxes in meters per day for each of the seven zones for each of the seven
stress periods when recharge occurred. PEST requires a Parval value or
initial starting value for the optimisation process and this was initially set at
10% of Gatton rainfall for each stress period designated to receive recharge.
The Parval was allowed to vary between a minimum of 1E-06 of the Parval
value and a maximum of 100% of the rainfall. The Parameter
transformation was set at log transformed which is suitable for values which
do not become negative during the optimisation process such as recharge.
Plots of observed and calculated heads for the entire model simulation
display an initial gap between the observed and model calculated heads
which may be due to numerical instability at the beginning of the
simulation, however after the first two stress periods the graphs display a
close fit and clearly correspond for the recharge event of May 1996 (Figure
37). The optimisation results from PEST produced a phi value of 4002 from
1900 observations and a correlation coefficient of 0.9650. The calibrated
recharge values were then input to the model and the model subsequently
run and using the residuals for all model observations the RMS error was
calculated as 1.61m. A water budget for each stress period in the model is
presented in Figure 38. A graph of the total rainfall for each stress period
102
446
8890929496
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
445
8890929496
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
502
85
90
95
100
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
516
85
90
95
100
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 37. Head time graphs of observed and calculated heads.
103
514
92949698
100102
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
220
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
221
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
442
95100105110115
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 37. Head time graphs of observed and calculated heads.
104
490
90
95
100
105
0 2 4 6 8 10 12 14 16
Stress period
Hea
d (m
asl)
CalculatedObserved
462
102104106108110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 37. Head time graphs of observed and calculated heads.
105
Period 1 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 23053.01 151.91 22901.10
CONSTANT 56309.62 460.89 55848.73 HEAD
WELLS 0 78750.15 -78750.15
RECHARGE 0 0 0
SUM 79362.63 79362.95 -0.32
Period 2 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 4203.53 2688.22 1515.32
CONSTANT 64886.35 2593.53 62292.83 HEAD
WELLS 0 91821.20 -91821.20
RECHARGE 28012.39 0 28012.39
SUM 97102.28 97102.94 -0.66
Period 3 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 22774.99 0.00 22774.99
CONSTANT 97863.61 59.87 97803.74 HEAD
WELLS 0 120578.33 -120578.33
RECHARGE 0 0 0
SUM 120638.60 120638.20 0.40
Period 4 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 12480.27 172.63 12307.64
CONSTANT 47954.20 205.61 47748.59 HEAD
WELLS 0 60057.51 -60057.51
RECHARGE 0 0 0
SUM 60434.47 60435.76 -1.28
Period 5 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 2713.64 8510.06 -5796.42
CONSTANT 35947.27 945.94 35001.33 HEAD
WELLS 0 51794.90 -51794.90
RECHARGE 22588.73 0 22588.73
SUM 61249.64 61250.90 -1.26
Figure 38. Water budget for each stress period of the model
106
Period 6 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 11818.84 129.41 11689.43
CONSTANT 33469.28 546.98 32922.31 HEAD
WELLS 0 44610.27 -44610.27
RECHARGE 0 0 0
SUM 45288.12 45286.65 1.47
Period 7 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 74342.06 0.00 74342.06
CONSTANT 63214.22 2367.97 60846.25 HEAD
WELLS 0 135185.99 -135185.99
RECHARGE 0 0 0
SUM 137556.27 137553.96 2.31
Period 8 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 72386.17 268.86 72117.31
CONSTANT 35737.71 2722.86 33014.85 HEAD
WELLS 0 105132.08 -105132.08
RECHARGE 0 0 0
SUM 108123.88 108123.80 0.08
Period 9 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 22188.45 8424.85 13763.60
CONSTANT 24225.26 1695.58 22529.69 HEAD
WELLS 0 49741.39 -49741.39
RECHARGE 13446.83 0 13446.83
SUM 59860.54 59861.81 -1.28
Period 10 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 45077.66 353.27 44724.40
CONSTANT 27814.11 549.76 27264.36 HEAD
WELLS 0 71989.11 -71989.11
RECHARGE 0 0 0
SUM 72891.78 72892.14 -0.36
Figure 38. Water budget for each stress period of the model
107
Period 11 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 42777.90 3.42 42774.48
CONSTANT 18565.88 2388.75 16177.13 HEAD
WELLS 0 58953.34 -58953.34
RECHARGE 0 0 0
SUM 61343.78 61345.51 -1.72
Period 12 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 6445.26 98307.66 -91862.40
CONSTANT 34387.35 3988.90 30398.45 HEAD
WELLS 0 38519.53 -38519.53
RECHARGE 99980.38 0 99980.38
SUM 140812.98 140816.09 -3.11
Period 13 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 4415.73 52430.46 -48014.73
CONSTANT 36113.69 3758.92 32354.77 HEAD
WELLS 0 23625.10 -23625.10
RECHARGE 39283.13 0 39283.13
SUM 79812.55 79814.48 -1.93
Period 14 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 167.39 125679.63 -125512.24
CONSTANT 72128.46 8764.07 63364.39 HEAD
WELLS 0 54168.05 -54168.05
RECHARGE 116311.75 0 116311.75
SUM 188607.60 188611.74 -4.14
Period 15 FLOW TERM IN (m3) OUT (m3)
IN-OUT (m3)
STORAGE 2033.31 49936.61 -47903.30
CONSTANT 71287.74 8474.76 62812.98 HEAD
WELLS 0 56835.29 -56835.29
RECHARGE 41924.95 0 41924.95
SUM 115246.00 115246.67 -0.67
Figure 38. Water budget for each stress period of the model
108
Correlation between rainfall (m) and calibrated recharge volume (m3) for each stress period
0
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Stress period
Rai
nfal
l (m
)
0
20000
40000
60000
80000
100000
120000
140000
Rec
harg
e vo
lum
e (m
3)
Rainfall (m)Recharge Volume (m3)
Figure 39. Graph of rainfall and derived recharge volumes for each stress
period of the model.
109
with the calibrated recharge volume (Figure 39) displays a strong
correlation between these two parameters.
Sensitivity Analysis
To determine the calibrated solution’s sensitivity to the aquifer properties
hydraulic conductivity and specific yield each was varied in turn by factors
of 0.5, 0.8, 1.2, 1.5 so that all values were within realistic bounds for each
parameter. These multipliers and the resultant values are shown in Table 7
below:
Multipliers 0.5 0.8 1.2 1.5
Parameter Calibrated Value Hydraulic
Conductivity 70 35 56 84 105 Specific Yield 0.24 0.12 0.192 0.288 0.36
Table 7. Parameter variations used in the sensitivity analysis.
Specific storage was varied by an order of magnitude each way from the
calibrated value of 0.0004 in order to see a significant change. Model
simulations were then run with each parameter being varied by the above
values while the other two parameters were kept constant, culminating in a
total of 10 model runs. Graphs of RMS error versus each varied parameter
value demonstrate the relative sensitivity of the model to each parameter
change. For hydraulic conductivity the value of 70 m/day and RMS error of
1.61m for the calibrated model is by far the lowest point on the graph, and
the model is relatively insensitive to the variables of 56, 84 and 105 m/day
compared with the outlier of 35 m/day (Figure 40). For specific yield the
variables of 0.12 and 0.192 both produced a higher RMS error than the
calibrated model value of 0.24, while for the other variables RMS error
decreases as specific yield increases (Figure 41). For specific storage the
variable of 0.00004 plots slightly below the value of 0.0004 for the
calibrated model, while the other variable of 0.004 produced a much higher
RMS error (Figure 42).
110
Hydraulic Conductivity Sensitivity
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110
Hydraulic conductivity (m/day)
RM
S er
ror
Figure 40. Graph of RMS error vs hydraulic conductivity, showing the
model is highly sensitive to a decrease in hydraulic conductivity and
relatively less sensitive to increases in hydraulic conductivity.
Specific Yield Sensitivity
0
1
2
3
4
5
6
7
0.1 0.15 0.2 0.25 0.3 0.35 0.4
Specific yield
RM
S er
ror
Figure 41. Graph of RMS error vs specific yield showing model is more
sensitive to decreases in specific yield compared to increases in this
parameter which produced lower RMS errors.
111
Specific Storage Sensitivity
0
1
2
3
4
5
6
7
8
9
10
11
0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032 0.0036 0.004 0.0044
Specific Storage
RM
S er
ror
Figure 42. Graph of RMS error vs specific storage showing model is
relatively insensitive to decreasing the specific storage by an order of
magnitude, yet highly sensitive to increasing the specific storage by an order
of magnitude.
112
The effects of no groundwater extraction were also tested as part of the
sensitivity analysis. Groundwater extraction from the WEL package was
turned off for the entire simulation and the model was run. All hydrographs
display higher calculated than observed heads (Figure 43) than in the
calibrated solution (Figure 37). The RMS error was 9165m, considerably
higher than in the calibrated solution.
The model’s sensitivity to the applied boundary conditions was tested in two
ways. Firstly all the time variant specified head boundary cells were
replaced by fixed head cells which remained constant for the entire model
simulation. The fixed head cells were set at the same values as those applied
for the initial hydraulic heads in those cells and the model was run.
Hydrographs of bores near the boundaries are highly influenced by the fixed
head boundaries, with higher calculated than observed heads (Figure 44),
and higher calculated heads than in the calibrated model (Figure 37). The
resulting RMS error of 6961m was also much higher. Secondly the time
variant specified head boundary cells were retained on the southern and
northern alluvial boundaries of the study area however the western
boundary was replaced with a no flow boundary. Head time graphs
demonstrate an improved correlation (Figure 45) when compared to the
previous simulation (Figure 44), and a lower RMS error of 966 m.
To investigate the influence of the semi-confining unit of mixed sands and
clays on the gravel aquifer a two layer model was constructed, covering an
area identical to that of the single layer model. Layer 1 represented the
mixed sands and clays and layer 2 the gravel aquifer. All existing
parameters were retained for layer 2, while for layer 1, the semi confining
unit, a number of assumptions were made: k = 1 m/day, Ss = 0.001, Sy =
0.01 all of which are within the range for sandy clay (Heath 1983;
Domenico 1972; Morris and Johnston 1967). Vertical hydraulic
conductivity is required for each layer of a multiple layer model. Vertical
hydraulic conductivity was taken to be 10% of the horizontal hydraulic
conductivity values listed above, in accordance with the relationship
outlined by Kresic (1997). The initial hydraulic heads were assumed to be
113
446
85
90
95
100
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
445
889092949698
0 5 10 15 20
Stress Period
Hea
d (m
asl)
CalculatedObserved
502
859095
100105
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
516
859095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 43. Head time graphs for simulation with no groundwater extraction.
114
514
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
220
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
221
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
442
95100105110115
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 43. Head time graphs for simulation with no groundwater extraction.
115
490
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
462
102104106108110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 43. Head time graphs for simulation with no groundwater extraction.
116
446
8890929496
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
445
8890929496
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
502
859095
100105
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
516
859095
100105
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 44. Head time graphs for simulation with all time variant specified
head boundaries replaced by constant head boundaries set at initial heads.
117
514
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
220
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
221
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
442
95100105110115
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 44. Head time graphs for simulation with all time variant specified
head boundaries replaced by constant head boundaries set at initial heads.
118
490
90
95
100
105
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
462
102104106108110112
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 44. Head time graphs for simulation with all time variant specified
head boundaries replaced by constant head boundaries set at initial heads.
119
446
88
90
92
94
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
445
8890929496
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
502
8890929496
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
516
85
90
95
100
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 45. Head time graphs for simulation with western time variant
specified head boundary only replaced by no flow boundary.
120
514
90
95
100
105
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
220
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
221
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
442
95100105110115
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 45. Head time graphs for simulation with western time variant
specified head boundary only replaced by no flow boundary.
121
490
90
95
100
105
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
462
102104106108110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 45. Head time graphs for simulation with western time variant
specified head boundary only replaced by no flow boundary.
122
446
88
90
92
94
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
445
8890929496
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
502
8890929496
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
516
85
90
95
100
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 46. Head time graphs for two layer model with derived recharge
rates applied to creek cells in layer 2 and recharge applied as 1% of rainfall
for layer 1.
123
514
92949698
100102
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
220
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
221
9095
100105110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
442
95100105110115
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 46. Head time graphs for two layer model with derived recharge
rates applied to creek cells in layer 2 and recharge applied as 1% of rainfall
for layer 1.
124
490
90
95
100
105
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
462
102104106108110
0 2 4 6 8 10 12 14 16
Stress Period
Hea
d (m
asl)
CalculatedObserved
Figure 46. Head time graphs for two layer model with derived recharge
rates applied to creek cells in layer 2 and recharge applied as 1% of rainfall
for layer 1.
125
potentiometric heads and set as the same for layer 2. Recharge was applied
as 1% of rainfall to layer 1 for each stress period when recharge was
received (Table 5), while for layer 2 the derived recharge rates from the
calibrated model were retained and applied to only layer 2 using the WEL
package. The model was run, producing higher calculated than observed
heads (Figure 46) and the resulting RMS error was 796m.
Prediction
In order to determine the safe annual extraction rate for the total model
duration of 44 months, the calibrated solution was run with 6 different
annual extraction scenarios to determine the minimum saturated thickness in
the aquifer at the end of stress period 11 in October 1995, when the water
levels were at their lowest point before the major recharge of stress periods
12, 13, 14 and 15 in 1996. The annual extraction rates were applied in ML
per ha, converted to m3 per day for input to PMWIN and applied for each
day of the 44 months of the model simulation. By trial and error it was
established that the maximum annual extraction rate before any cell goes
dry at the end of stress period 11 is 1.75 ML/ha and the minimum saturated
thickness of the aquifer is 0.029 m. The model was run with additional
annual extraction scenarios of 1.5, 1.25, 1, 0.75 and 0.5 ML/ha and the
corresponding minimum saturated thicknesses are summarised in Figure 47.
126
Minimum saturated thickness of aquifer vs annual extraction rate
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2
Annual extraction rate (ML/Ha)
Min
imum
sat
urat
ed th
ickn
ess
(m)
Figure 47. Graph of minimum saturated thickness of aquifer at end of stress
period 11 versus annual extraction rate applied for entire simulation.
Minimum saturated thickness decreases as pumping rate increases.
127
Discussion of Groundwater Modelling
In the model calibration all 10 observation bores display an initial gap
between the observed and calculated heads as shown in the head time
graphs of Figure 37. This deficit is possibly due to numerical instability at
the beginning of the simulation as the initial heads were not sourced from a
steady state simulation but rather from real head data recorded in March
1993 which is the beginning of the model period. The simulation period was
chosen to be from March 1993 to November 1996 as these years include the
aquifer’s response to a drought from 1993 to late 1995 followed by regular
rain in the summer of 1995-96, culminating in a flood event in May 1996.
The other crucial point in the nomination of the simulation period was the
availability of extraction data recorded by meters on all irrigation bores in
the NRM&E Proclaimed Area, as this data could be adapted for the Lockyer
plain. As metering of private irrigation bores does not occur in the study
area, the pumping rates utilised in the model were adapted on a volume per
unit area from the extraction records of the NRM&E proclaimed area. The
addition of meters on private irrigation bores in the study area would greatly
increase the accuracy of the extraction rates in the model. If the location and
pumping rates of all irrigation bores are known it would also permit better
determination of the spatial distribution of aquifer properties as done by
Durick and Bleakley (2003)
In the current modelling study the estimates of the aquifer properties
hydraulic conductivity and specific storage were based on two pumping
tests conducted with a pumping bore and a NRM&E monitoring bore close
enough to observe drawdown and recovery. Additional NRM&E monitoring
bores drilled close enough to private irrigation bores to be influenced by
pumping at distances of 15 m or less would enable better delineation of the
spatial distribution of aquifer properties which could be input to the model
grid as different zones.
128
Although the influence of the semi confining layer of clay, sandy clay and
silt has been shown to be minimal (Ellis and Dharmasiri 1998; Ellis 1999),
the provision of monitoring bores within this hydrostratographic unit would
allow leakage rates to the aquifer to be calculated in the long term, further
increasing the accuracy of any water resource studies. In addition, any
upward leakage from the adjacent and underlying sandstone aquifers, which
has been qualitatively shown to occur, cannot be quantified due to the total
absence of monitoring bores screened in the sandstones.
As streams in the study area were not gauged during the period of the model
simulation there is no stream stage data to compare with the calibrated
recharge volumes derived using PEST. Consequently the recharge volumes
have been compared with rainfall for each stress period of the model to find
a physical process for the varying recharge rates. A graph of rainfall (m) and
calibrated recharge volumes (m3) for each stress period in Figure 39
demonstrates a strong correlation between these two parameters and
indicates that temporal variations in rainfall throughout the model
simulation are the controlling variable on the calibrated recharge volumes.
To investigate the sensitivity of the calibrated model to variations in the
aquifer properties hydraulic conductivity and specific yield, these were both
increased and decreased by factors of 20% and 50% so that the variables
were still within realistic bounds for gravel. Specific storage was varied by
an order of magnitude each way in order to see a significant change. The
model has demonstrated relative insensitivity to increases in hydraulic
conductivity, however decreases in this parameter have resulted in a much
higher RMS error. The storage terms specific yield and specific storage
display an inverse and a direct relationship respectively with the RMS error
with the calibrated parameters sitting in the middle of the curve. It is
therefore plausible that the aquifer material has a higher specific yield of
0.36, and a lower specific storage of 0.00004 than the calibrated values.
The higher specific yield of 0.36 which produced a RMS error lower than
the calibrated value of 0.24 may suggest that the aquifer material is more
129
sandy than previously thought. A maximum of 0.46 and mean of 0.32 for
the specific yield of sand were presented by Morris and Johnson (1967).
NRM bore completion details indicate that monitoring bores are typically
screened in the gravel, irrespective of whether the gravel is overlain by a
sand lens or not at that point. For this modelling study the thickness of
gravel was taken as the thickness of the aquifer in order to produce a
conservative estimate of the water resource. If future monitoring bores are
screened in the sand, where it is present, it may be possible to model sand as
an additional hydrostratigraphic unit and to investigate the potential release
from storage of this unit.
A lower specific storage of 0.00004 is still within the bounds of specific
storage of gravel set out by Domenico (1972), however the calibrated value
of 0.0004 was obtained from a pumping test. A possible explanation may be
the short duration of the pumping test of 90 minutes in which the aquifer
was not stressed long enough which decreased the accuracy of the estimates
of the aquifer properties. However an increase in the specific storage of an
order of magnitude to 0.004 produced a much higher RMS error, indicating
this value is unrealistic for gravel.
Removing groundwater extraction from the model has produced poor
matches in the head time graphs (Figure 43) with the calculated heads much
higher than the observed heads indicting groundwater extraction is an
essential component of the water budget.
Changing the applied boundary conditions has revealed the model is highly
sensitive. All time variant specified head boundary cells were replaced with
fixed head cells set at the same values as those applied for the initial
hydraulic heads. Head time graphs, particularly of bores near the fixed head
boundaries eg. 446, 490 and 462 display higher calculated than observed
heads. This suggests these observation bores are highly influenced by the
fixed head boundaries. A much higher RMS error than that of the calibrated
solution was obtained. Similarly, retaining the time variant specified head
cells on the southern and northern alluvial boundaries yet designating the
130
western boundary as no flow has produced a worse correlation at bore 490
than in the calibrated solution, suggesting that the western time variant
specified head boundary was responsible for the near perfect head matches
at bore 490 in the calibrated solution.
The 2 layer model has produced higher calculated than observed heads at all
observation bores which is undoubtedly due to the effects of leakage from
the overlying mixed sands and clays of layer 1. It should be noted that these
results are highly influenced by the choice of parameters for layer 1 and as
there are no bores screened in this semi confining layer, no field data could
be obtained for the hydraulic properties of this layer and consequently all
values are based on mean values from literature eg Domenico (1972); Heath
(1983); Morris and Johnson (1967).
The predictive simulations were based on an annual extraction rate applied
for the entire model duration and used to demonstrate the minimum
saturated thickness of the aquifer at the end of stress period 11 in October
1995 before the recharge of stress periods 12, 13, 14 and 15 in the summer
of 1995-96. The extraction rates ranged from 1.75 ML/ha, the maximum
pumping rate before the aquifer goes dry resulting in a minimum saturated
thickness of 0.029 m, to 0.5 ML/ha resulting in a minimum saturated
thickness of 1.4 m. Scenario results were expressed as a minimum saturated
thickness as opposed to a volume of water as the saturated thickness is the
governing variable in the effectiveness of an irrigation bore and therefore
the pumping rate. Discussions with landholders indicate that yields are
severely reduced in periods of low water levels when pumps draw in air.
These minimum thicknesses are applicable only in one small area of the
model grid, yet represent the absolute worst case scenario with all other
regions of the model domain producing higher saturated thicknesses. This
conservative approach was adopted in order to produce an underestimation
as opposed to an overestimation of the groundwater resource. It must also be
noted that these predictions are only valid for the 44 month period from
March 1993 to November 1996 and that a longer pumping and head dataset
would greatly increase the accuracy of these predictions.
131
8. CONCLUSION
Hydrograph interpretation of bores screened in the gravel has demonstrated
that the alluvial aquifer in the Lockyer plain is subject to large variations in
groundwater levels, which can be directly correlated to recharge and
indirectly correlated to irrigation use. Water levels in bores adjacent to the
creek banks respond to small amounts of rainfall e.g. 100 mm/month; these
bores also display a rapid response to a flood event. Pumping tests or
aquifer tests on two boreholes screened in gravel has produced estimates of
hydraulic conductivity of 50 – 80 m/day. The higher value is considered to
be more realistic for both the duration and magnitude of the stress placed on
the aquifer and also the gravel-dominant character of the aquifer material.
Re-interpretation of a previous drawdown test (Macleod 1998) has produced
estimates of hydraulic conductivity of 63 m/day and of storativity of 0.0016,
which are considered realistic for a semi-confined gravel aquifer.
Hydrochemical analyses of samples collected under both wet and dry
conditions display little variation, however, the major ion chemistry of
surface water from the May 1996 flood is similar to alluvial groundwater
which suggests a strong connection. Ma Ma catchment alluvial groundwater
is magnesium and sodium dominated with conductivity range of 4500 to
12000 µS/cm. This groundwater is a water type very similar to bedrock
groundwater defined in previous studies (e.g. Dixon and Chiswell 1992;
Macleod 1998). Groundwater in the Tenthill catchment is magnesium
dominated with calcium as the secondary cation and typically less than 3500
µS/cm with a water type different to bedrock groundwater. Major ion
chemistry of the Lockyer alluvial plain is extremely variable, with the
magnesium domination observed in Tenthill catchment continuing down to
the plain with some areas more sodium rich. Conductivity may reach 6000
µS/cm.
Samples analysed for stable isotopes from throughout both catchments and
the Lockyer plain show a range of values depending on aquifer type and
other processes such as evaporation and mixing. Stream water from a flood
132
event (data from Dharmasiri and Morawska 1997) represents recharging
water and indicates a starting point for isotopic evolution of groundwater.
Basalt groundwater displays an isotopic composition and salinity between
new water and alluvial groundwater which indicates that precipitation may
recharge basalt first and subsequently discharge to the alluvium or may also
recharge the alluvium directly. Alluvial groundwater from Ma Ma
catchment and the Lockyer plain display slopes of sample distribution
characteristic of evaporation from standing surface water. This trend
suggests evaporated water in the creek channels is the principal source of
recharging water; however, leakage from bedrock units may account for the
relatively more depleted composition of Ma Ma catchment alluvial
groundwater.
A conceptual hydrogeological model was developed for the Lockyer plain
incorporating all the previously interpreted data. Geological logs from
NRM&E bores were examined to determine the thickness and extent of both
the gravel aquifer and the mixed sands and clays of the overlying semi-
confining unit. Bore hydrograph variations when combined with the
thickness of the gravel indicate that the aquifer changes from confined to
unconfined conditions in some locations as the water level drops. Previous
studies, for example Ellis and Dharmasiri (1998) and Ellis (1999) have
demonstrated that infiltration through the mixed sands and clays is
extremely slow; water chemical and stable isotopic investigations in this
current study suggest that recharge of evaporated surface water through the
creek channels is the dominant recharge process.
To simulate groundwater flow in the gravel aquifer a single layer model was
constructed using PMWIN and calibrated to water level fluctuations using
PEST to estimate recharge. The transient simulation period ranged from
March 1993 to November 1996 for a total of 44 months, incorporating a
drought and the associated decline in water levels followed by a wet period
and flood and the resulting rise in water levels. The sensitivity analysis
demonstrates the model is insensitive to variations in hydraulic
conductivity, specific yield and specific storage within realistic bounds for
133
the aquifer material, however, the model is highly sensitive to changes in
the chosen boundary conditions. Predictive simulations with different
annual extraction scenarios for the model duration produced a minimum
saturated aquifer thickness with a range of 0.03 m to 1.4 m.
The main findings of this study are summarised as follows:
• The Quaternary alluvium is comprised of a laterally continuous semi
confined gravel aquifer overlain by mixed sands and clays.
• Pumping tests of the gravel aquifer has produced estimates of
hydraulic conductivity of 50 – 80 m/day and storativity of 0.0016.
• Alluvial groundwater in Ma Ma catchment is Mg and Na dominated
with a conductivity ranging from 4500 – 6500 µS /cm. Alluvial
groundwater in Tenthill catchment and the Lockyer plain is Mg
dominated with Ca>Na in Tenthill catchment and Na>Ca on the
Lockyer plain. Conductivity of Tenthill alluvial groundwater ranges
from 1500 – 3500 µS/cm while the Lockyer plain ranges from 2000
– 6500 µS/cm.
• Major ion chemistry of surface water from the May 1996 flood is
similar to alluvial groundwater suggesting a strong connection.
• Stable isotope plots of alluvial groundwater from Ma Ma catchment
and the Lockyer plain display slopes characteristic of evaporation
from standing surface water, suggesting recharge from evaporated
water in creek channels is the dominant recharge process.
• Relatively more depletion in stable isotopes was observed in alluvial
groundwater from Ma Ma than in Tenthill catchment and the
Lockyer plain, indicating possible mixing with more depleted
sandstone bedrock groundwater.
134
• Transient simulations of groundwater flow using PMWIN with a
number of annual extraction scenarios have demonstrated the
resulting minimum saturated thickness of the aquifer ranges from
0.03 to 1.4 m.
135
9. REFERENCES
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groundwater system in the southern Voltaian Sedimentary Basin of
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Anderson, M. P. and Woessner, W. W. 1992. Applied Groundwater
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Appello, C. A. J. and Postma, D. 1996. Geochemistry, groundwater and
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Cooper, H. H., Jr. and Jacob, C. E. 1946. A generalized graphical method
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Chiang, W.-H. Kinzelbach, W. 2001. 3D-Groundwater Modelling with
PMWIN, A Simulation System for Modeling Groundwater Flow and
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Clark, I. D. and Fritz, P. 1997. Environmental Isotopes in Hydrogeology.
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Craig, H. 1961. Isotopic Variations in Meteoric Waters. Science 133, 1702-
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Davies, S. N. and De Wiest, R. J. M. 1966. Hydrogeology. John Wiley and
Sons, New York.
Dharmasiri, J. K. and Morawska, L. 1997. Isotope Studies on Groundwater
Recharge to Alluvial Aquifer in Gatton, Queensland. Centre for
Medical and Health Physics, Queensland University of Technology,
(Unpublished).
Dixon, W. 1988. Hydrochemistry of groundwater salinity in the S. W.
Lockyer Valley, Queensland. MSc Thesis, University of
Queensland, Brisbane (Unpublished).
Dixon, W. and Chiswell, B. 1992. The use of hydrochemical sections to
identify recharge and saline intrusions in alluvial aquifers, southeast
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Dixon, W. and Chiswell, B. 1994. Isotopic study of alluvial groundwaters,
south-west Lockyer Valley, Queensland, Australia. Hydrological
Processes. 8, 359-367.
Doherty, J., Brebber, L., and Whyte, P. 1994. PEST Model-independent
parameter estimation. Users Manual. Watermark Numerical
Computing, Brisbane.
Domenico, P. A. 1972. Concepts and Models in Groundwater Hydrology.
McGraw-Hill, New York.
Dudgeon, M. 1978. The geology of east and west Haldon, Main Range,
South- east Queensland. Hons thesis, University of Queensland,
Brisbane, (Unpublished).
Durick, A. and Bleakley, A. 2003. Central Lockyer Groundwater Model.
Queensland Government Natural Resources and Mines: 125,
Brisbane.
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Ellis, R. 1999. Water Quality Deterioration in Alluvial Aquifers. LWRRDC
Project QPI30 Final Report. Queensland Department of Natural
Resources, Brisbane.
Ellis, R. and Dharmasiri, J. K. 1998. Chemical and Stable Isotopic Methods
used in Investigating Groundwater Quality Deterioration in the
Lockyer Valley, IAH International groundwater conference ’98,
Groundwater Sustainable Solutions, Melbourne, Australia 8 -13
February 1998.
Fetter, C. W. 1994. Applied Hydrogeology. Prentice Hall, New Jersey.
Fontes, J. C. 1980.Environmental Isotopes in Groundwater Hydrology, in
Fritz P. and Fontes J. C. (eds), Handbook of Environmental Isotope
Geochemistry,Volume 1. Elsevier Scientific Publishing Company,
Amsterdam – Oxford – New York.
Freeze, R. A. and Witherspoon, P. A. (1967). Theoretical analysis of
regional groundwater flow: 2. Effect of water-table configuration
and subsurface permeabllity variation. Water Resources Research. 3,
623-624.
Freeze, R. A. 1969. The mechanism of natural groundwater recharge and
discharge. 1. One-dimensional, vertical, unsteady, unsaturated flow
above a recharging or discharging ground-water flow system. Water
Resources Research. 5, 1, 153-171.
Galloway, W. E. and Sharp, J. M Jr. 1998. Hydrogeology and
characterization of fluvial aquifer systems, in G. S. Fraser and J. M.
Davis (eds), Hydrogeologic Models of Sedimentary Aquifers. SEPM
(Society for Sedimentary Geology), 91-106.
138
Garcia, M. G., Hidalgo, M. D. V., and Blesa, M. A. 2001. Geochemistry of
groundwater in the alluvial plain of Tucuman province, Argentina.
Hydrogeology Journal. 9, 597-610.
Gat, J. R. 1981. Isotope Fractionation, in J. R. Gat and R. Gonfiantini (eds),
Stable Isotope Hydrology Deuterium and Oxygen-18 in the Water
Cycle. IAEA Technical Report Series No. 210, International Atomic
Energy Agency, Viena.
GNIP 1998. Global Network for isotopes in precipitation. International
Atomic Energy Agency.
Gray, A. R. G. 1975. Bundamba Group - stratigraphic relationships and
petroleum prospects. Queensland Government Mining Journal. 76,
310-324.
Grimes, K. G. 1968. The geology of the Lockyer Valley area, south-east
Queensland. Hons thesis, University of Queensland, Brisbane,
(Unpublished).
Heath, R. C. 1983. Basic ground-water hydrology. USGS, Water Supply
Paper 2220.
Ingram, F. T. and Robinson, V. A 1996. Petroleum Prospectivity of the
Clarence Moreton-Basin in New South Wales (R. A. Facer Editor).
Petroleum Bulletin 3, New South Wales Department of Mineral
Resources, Sydney.
Kresic, N. 1997. Quantitative Solutions in Hydrogeology and Groundwater
Modeling. Lewis Publishers, New York.
Lane, W. B. and Zinn, P. 1980. Recharge from weir storages. Groundwater
recharge conference, Canberra.
139
Larkin, R. G. and Sharpe, J. M. Jr. 1992. On the relationship between river
basin geomorphology, aquifer hydraulics and groundwater flow
direction in alluvial aquifers. Geological Society of America
Bulletin. 104, 1608-1620.
Macleod, K. 1998. The groundwater resource of the Ma Ma Creek
catchment. Hons thesis, Queensland University of Technology,
Brisbane, (Unpublished).
Mazor, E. 1991. Chemical and Isotopic Hydrology The Applied Approach.
Marcel Dekker Inc, New York.
McDonald, M. G. and Harbaugh, A. W. 1988. MODFLOW, A modular
three-dimensional finite difference ground-water flow model.
Open-file report 83-875, Chapter A1, U. S. Geological Survey.
McMahon, G. A. 1995. Hydrochemistry of saline groundwater in the Sandy
Creek catchment, Lockyer Valley, Southeast Queensland. Hons
thesis, Queensland University of Technology, Brisbane,
(Unpublished).
McMahon, G. A. and Cox M. E. 1996. The relationship between
groundwater chemical type and Jurassic sedimentary formations:
The example of the Sandy creek catchment, Lockyer, Southeast
Queensland. Mesozoic '96, Brisbane, Australia, Geological Society
of Australia (Queensland Division).
McNeil, V. H., McNeil, A. and Zannakis, G. 1993. The Lockyer Valley
water quality monitoring network, Volume 1: Summary report.
Queensland Department of Primary Industries, Water Resources
Division, Water Quality Group, 16.
140
McTaggart, N. R. 1963. The Mesozoic sequence in the Lockyer-Marburg
area, south-east Queensland. Preceedings of the Royal Society of
Queensland 73, 93-104.
Merrick, N. P., Middlemis, H., and Ross, J. B. 2002. Groundwater
Modelling Guidelines for Australia – The Review Process.
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Groundwater Budget, Darwin, Australia 12 - 17 May 2002.
Middlemis, H., Merrick, N. P., Ross, J. B., and Rozlapa, K. L. 2002.
Groundwater Modelling Guidelines for Australia – An overview of
the need for and use of the guidelines, International Groundwater
Conference, Balancing The Groundwater Budget, Darwin, Australia
12 - 17 May 2002.
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properties of rock and soil materials as analysed by the hydrologic
laboratory of the US Geological Survey 1948-1960, USGS, Water
Supply Paper 1839-D.
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Guidelines. Report to MDBC by Aquaterra project team, including
UTS and PPK.
Please, P. M., Watkins, K. L. and Bauld, J. 1997. A groundwater quality
assessment of the alluvial aquifers in the Logan-Albert catchment,
SE Queensland. Australian Geological Survey Organisation,
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Rocks. Kluwer Academic Publishers, Dordrecht.
141
Smith, K. J., Beckmann G. G., and Little, I. P. 1990. Soils of the southern
Lockyer Valley, Queensland. Soils and Land use series, no.62.
Gatton
Talbot, R. J., Roberts, M. H., McMahon, C. R. and Shaw, R. J. 1981.
Irrigation quality of Lockyer Valley alluvia bores during the 1980
drought. Technical Publication No. 5. Department of Biology,
Queensland Agricultural Collage, Gatton.
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discharge of a well using ground water storage. Transactions,
American Geophysical Union. 16, 519-535.
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lithostratigraphic framework for the Early Jurassic units in the
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South Wales. BMR Journal of Australian Geology and Geophysics.
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Clarence-Moreton Basin, in Wells A. T. and O'Brien P. E. (eds),
Geology and Petroleum Potential of the Clarence-Moreton Basin,
New South Wales and Queensland. Australian Government
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Hydrogeological report. Record 1975/36. Department of Mines
Geological Survey of Queensland, Brisbane.
APPENDIX 1 EXAMPLE OF NRM&E DATABASE RECORD
27Page
27/09/2002DATEGROUNDWATER DATABASE
BORE CARD REPORT
BASIN 27-34-07LATITUDE MAP-SCALE
OFFICE SUB-AREA 152-15-50LONGITUDE MAP-SERIES
UG 7/2D/O FILE NO. SHIRE 427328EASTING 9342-14MAP-NOR/O FILE NO. LOT 6950342NORTHING MAP NAMEH/O FILE NO. PLAN 56ZONE PROG SECTION
ORIGINAL DESCRIPTION ACCURACY
GPS ACC
NEPRES EQUIPMENT
NCHECKED
-27.5687400101GIS LAT
152.2638107809GIS LNG
4495-TENTHILLPARISH NAME
CHURCHILLCOUNTY
ORIGINAL BORE NO
PROPERTY NAME
-BORE LINE
FIELD LOCATION
01/06/1979DATE DRILLED
POLYGON
DRILLERS NAME
RN OF BORE REPLACED
DRILL COMPANYCABLE TOOL - V DOONAN JUNE 197METHOD OF CONST.
CONFIDENTIAL
SFFACILITY TYPE
EXSTATUS
ROLES
A
A
A
A
PIPE
01/06/1979
01/06/1979
01/06/1979
01/06/1979
DATE
1
2
3
4
RECORDNUMBER
Plastic Casing (unspecified)
Perforated or Slotted Casing
Open Hole
Gravel Pack
MATERIAL DESCRIPTION
3.350
MAT SIZE(mm)
WT
SIZE DESC
50
50
203
OUTSIDEDIAM
0.00
26.40
27.40
0.00
TOP(m)
27.40
27.40
30.40
30.40
BOTTOM(m)
1
2
3
RECORDNUMBER
0.00
0.60
1.20
STRATATOP (m)
0.60
1.20
7.30
STRATABOT (m)
TOPSOIL (FILE UG 7/2)
SANDY CLAY
LOAMY SOIL
STRATA DESCRIPTION
STRATA LOG DETAILS
CASING DETAILS
LICENSE DETAILS
M
253
Gatton
REGISTRATION DETAILS
1432
T01
P15
157-GATTON
14320445REG NUMBER
**** NO RECORDS FOUND ****
DATA OWNER
PDF processed with CutePDF evaluation edition www.CutePDF.com
28Page
27/09/2002DATEGROUNDWATER DATABASE
BORE CARD REPORT
DNR
SOURCE
1
RECORDNUMBER
0.00
STRATATOP (m)
29.80
STRATABOT (m)
TENTHILL CK ALLUV
STRATA DESCRIPTION
1
REC
20.70
TOPBED(M)
29.80
BOTTOMBED(M)
BEDLITHOLOGY
DATE SWL(m)
FLOW QUALITY
SAND
GRAV
CGRY
YIELD(l/s)
CTR
UC
CONDIT
TENTHILL CK ALLUV
FORMATION NAME
4
5
6
7
8
902
RECORDNUMBER
7.30
20.70
23.70
24.90
29.80
STRATATOP (m)
20.70
23.70
24.90
29.80
30.40
STRATABOT (m)
SANDY CLAY
SAND - WB
SAND AND GRAVEL - WB
CLAYBOUND GRAVEL - WB
SANDSTONE
SWL 15.6 METRES WHEN DRILLED
STRATA DESCRIPTION
A
PIPE
10/09/1979
DATE
110.31
ELEVATION
AHD
DATUM
SVY
PRECISION
R
MEASUREMENT POINT
ELEVATION DETAILS
AQUIFER DETAILS
STRATIGRAPHY DETAILS
PUMP TEST DETAILS PART 1
PUMP TEST DETAILS PART 2
BORE CONDITION
14320445REG NUMBER
**** NO RECORDS FOUND ****
**** NO RECORDS FOUND ****
**** NO RECORDS FOUND ****
SURVEY SOURCE
29Page
27/09/2002DATEGROUNDWATER DATABASE
BORE CARD REPORT
A
A
A
A
A
A
A
A
PIPE
18/10/1979
03/03/1981
12/05/1981
05/03/1984
23/04/1985
01/03/1991
14/03/1991
30/08/2001
DATE
1
1
1
1
1
1
1
1
RD
085437
088728
089083
104932
108468
138112
138075
211631
QAN
27.00
27.00
28.00
28.00
15.00
15.00
20.00
DEPTH(m)
PU
PU
AI
AI
AI
AI
PG
RMK
GB
GB
GB
GB
GB
GB
GB
GB
SRC
4000
4400
4600
4800
4950
3600
3550
4790
COND(uS/cm)
7.5
7.5
7.5
7.4
7.6
8.2
7.8
7.9
pH
34
36
32
32
32
29
30
30
Si(mg/L)
2224.30
2407.10
2549.10
2670.22
2886.40
2235.23
2156.82
2909.79
TOTALIONS
2122.08
2260.11
2389.47
2539.57
2727.79
2065.99
1983.50
2697.58
TOTALSOLIDS
1412
1511
1645
1658
1712
1095
1107
1622
HARD
220
295
309
264
310
329
332
397
ALK
2.6
2.7
2.8
2.4
2.2
1.5
1.5
1.9
FIG. OFMERIT
2.8
2.9
2.9
3.4
3.8
4.4
4.5
4.2
SAR
0.00
0.00
0.00
RAH
A
A
A
A
A
A
A
A
PIPE18/10/1979
03/03/1981
12/05/1981
05/03/1984
23/04/1985
01/03/1991
14/03/1991
30/08/2001
DATE1
1
1
1
1
1
1
1
RD 246.0
260.0
270.0
315.0
360.0
335.0
345.0
391.3
Na 4.0
4.0
5.0
4.1
4.0
4.4
5.0
4.9
K 196.0
226.0
250.0
260.0
265.0
150.0
155.0
260.5
Ca 224.0
230.0
248.0
245.0
255.0
175.0
175.0
236.5
Mg
0.00
0.35
0.01
0.01
2.27
Mn 268.0
360.0
377.0
320.0
375.0
390.0
400.0
476.9
HCO3
0.12
0.05
0.02
0.01
0.00
Fe 0.0
0.0
0.0
0.9
1.4
5.6
2.3
3.5
CO3 1190.0
1230.0
1300.0
1400.0
1500.0
1050.0
960.0
1421.0
Cl 0.10
0.10
0.10
0.10
0.10
0.20
0.10
0.12
F 0.2
2.0
0.0
0.0
0.5
10.0
9.4
33.1
NO3 96.0
95.0
99.0
125.0
125.0
115.0
105.0
82.0
SO4
0.02
Zn
0.00
Al
0.06
B
0.00
Cu
A A A
A A A
A A A
A A A
PIPE
10/09/1979 05/11/1979 14/01/1980
07/02/1980 08/02/1980 11/02/1980
15/02/1980 15/04/1980 06/08/1980
07/11/1980 02/01/1981 05/01/1981
DATE
-15.90 -16.14 -16.22
-16.42 -16.40 -16.30
-16.19 -16.93 -17.44
-17.94 -18.08 -17.83
MEASURE(m)
R R R
R R R
R R R
R R R
N/R RMK
X
PIPE
10/09/1979
DATE
110.02
ELEVATION
AHD
DATUM
SVY
PRECISION
N
MEASUREMENT POINT
WATER LEVEL DETAILS
WATER ANALYSIS PART 2
WATER ANALYSIS PART1
PIPE DATE MEASURE(m)
N/R RMK PIPE DATE MEASURE(m)
N/R RMK
GCL
GCL
GCL
GCL
GCL
GCL
GCL
GCL
ANALYST
14320445REG NUMBER
SURVEY SOURCE
30Page
27/09/2002DATEGROUNDWATER DATABASE
BORE CARD REPORT
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
PIPE
07/01/1981 22/01/1981 09/02/1981
10/02/1981 11/02/1981 13/02/1981
23/02/1981 25/02/1981 27/03/1981
06/04/1981 10/04/1981 14/04/1981
14/08/1981 15/12/1981 12/03/1982
18/06/1982 13/08/1982 22/02/1983
05/05/1983 12/05/1983 15/07/1983
14/10/1983 03/02/1984 04/05/1984
06/07/1984 09/11/1984 25/01/1985
12/04/1985 28/06/1985 30/09/1985
13/12/1985 21/03/1986 18/06/1986
05/11/1986 16/01/1987 30/03/1987
03/07/1987 23/10/1987 25/11/1987
09/12/1987 08/01/1988 03/05/1988
18/05/1988 12/08/1988 21/10/1988
10/02/1989 03/05/1989 07/07/1989
26/09/1989 20/11/1989 29/01/1990
19/03/1990 31/05/1990 26/07/1990
18/09/1990 22/11/1990 31/01/1991
14/03/1991 01/05/1991 11/06/1991
09/08/1991 01/10/1991 20/01/1992
03/06/1992 19/08/1992 19/10/1992
08/03/1993 11/05/1993 04/08/1993
24/11/1993 28/01/1994 31/03/1994
26/05/1994 23/09/1994 11/01/1995
11/04/1995 21/07/1995 17/10/1995
17/01/1996 27/03/1996 26/07/1996
09/11/1996 16/01/1997 18/09/1997
01/10/1997 13/03/1998 27/03/1998
14/05/1998 01/07/1998 29/07/1998
11/09/1998 22/09/1998 09/11/1998
DATE
-17.76 -17.53 -17.31
-17.18 -17.12 -16.98
-16.38 -16.31 -16.00
-15.94 -15.86 -15.83
-15.81 -15.64 -14.87
-15.35 -15.61 -16.30
-16.38 -15.98 -14.22
-15.10 -15.10 -15.33
-15.41 -15.40 -15.45
-15.57 -15.65 -15.87
-15.80 -16.86 -16.70
-17.56 -17.80 -17.42
-17.75 -18.09 -17.46
-17.17 -16.95 -14.92
-15.15 -15.09 -15.34
-15.42 -14.87 -14.94
-15.38 -15.28 -15.28
-15.42 -14.58 -15.04
-15.26 -15.54 -15.63
-15.44 -15.94 -16.11
-16.55 -17.35 -15.85
-15.54 -15.55 -15.90
-16.65 -17.75 -18.04
-18.69 -18.46 -18.28
-18.78 -19.49 -20.20
-18.70 -19.53 -20.20
-17.27 -16.88 -15.36
-15.58 -16.00 -17.33
-17.38 -16.00 -16.33
-16.53 -16.92 -17.00
-17.00 -17.00 -17.00
MEASURE(m)
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R R
N/R RMK PIPE DATE MEASURE(m)
N/R RMK PIPE DATE MEASURE(m)
N/R RMK
14320445REG NUMBER
31Page
27/09/2002DATEGROUNDWATER DATABASE
BORE CARD REPORT
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A
PIPE
06/12/1998 08/03/1999 23/03/1999
03/06/1999 25/08/1999 08/09/1999
22/11/1999 07/12/1999 28/02/2000
02/03/2000 29/05/2000 04/09/2000
17/10/2000 04/12/2000 27/02/2001
30/05/2001 04/06/2001 29/08/2001
03/09/2001 04/12/2001 07/03/2002
16/04/2002 10/07/2002
DATE
-16.50 -15.44 -15.60
-15.68 -15.90 -15.90
-15.71 -15.86 -15.75
-15.73 -16.55 -17.00
-17.27 -17.40 -15.75
-16.02 -16.20 -16.85
-16.96 -16.65 -17.04
-17.50 -18.10
MEASURE(m)
R R R
R R R
R R R
R R R
R R R
R R R
R R R
R R
N/R RMK
A
A
A
A
A
A
A
A
PIPE
18/10/1979
03/03/1981
12/05/1981
05/03/1984
23/04/1985
01/03/1991
14/03/1991
11/04/2002
DATE DEPTH(m)
4000
4400
4600
4800
4950
3600
3550
5000
COND(uS/cm)
pH TEMP(C)
NO3(mg/L)
DO(mg/L)
Eh(mV)
PU
PU
AI
AI
AI
AI
AI
METH
GB
GB
GB
GB
GB
GB
GB
GB
SOURCE
Y 30/06/1992
WLVDETREGDET
Y 30/06/1992
STRLOG
Y 30/06/1992
PUMTES
Y 27/07/1993
FIELDQ
Y 30/06/1992
ELVDETCASING
Y 30/06/1992 Y 30/06/1992
AQUIFR
FIELD MEASUREMENTS
WIRE LINE LOG DETAILS
VALIDATION LOG - PART 1
SPECIAL WATER ANALYSIS
PIPE DATE MEASURE(m)
N/R RMK PIPE DATE MEASURE(m)
N/R RMK
14320445REG NUMBER
**** NO RECORDS FOUND ****
**** NO RECORDS FOUND ****
32Page
27/09/2002DATEGROUNDWATER DATABASE
BORE CARD REPORT
APIPE
22/03/2001DATE
1REC
Bore shield and marker post replaced.NOTES
WIRLOGWATANL
Y 30/06/1992
STRTIG
Y 28/07/1993
SAMPLE MULCND
Y 28/07/1993
GNOTESFPREADBRCOND
GENERAL NOTES
METERED USE
VALIDATION LOG - PART 2
14320445REG NUMBER
**** NO RECORDS FOUND ****
APPENDIX 2 PUMPING TEST DATA
Pumping Test 1
Drawdown vs time dataAquifer thickness = 6.1 m
Time (s) Depth to Drawdown (m)water level (m)
30 20.425 0.39560 20.43 0.490 20.436 0.406120 20.439 0.409150 20.441 0.411180 20.442 0.412210 20.442 0.412240 20.442 0.412270 20.443 0.413300 20.444 0.414330 20.445 0.415360 20.446 0.416390 20.446 0.416420 20.446 0.416450 20.446 0.416480 20.446 0.416510 20.446 0.416540 20.447 0.417570 20.447 0.417600 20.447 0.417630 20.447 0.417660 20.447 0.417690 20.447 0.417720 20.447 0.417750 20.447 0.417780 20.447 0.417810 20.447 0.417840 20.447 0.417870 20.448 0.418900 20.448 0.418960 20.45 0.421020 20.45 0.421080 20.45 0.421140 20.45 0.421200 20.451 0.4211500 20.454 0.4241800 20.456 0.4262100 20.456 0.4262400 20.458 0.4282700 20.455 0.4253000 20.457 0.4273300 20.458 0.4283600 20.459 0.4294200 20.459 0.4294800 20.46 0.435400 20.46 0.43
Pumping Test 2
Recovery vs time dataAquifer thickness = 4.2 m
Time (s) Depth to Drawdown (m)water level (m)
81000 27.745 0.5481010 27.7 0.49581020 27.69 0.48581030 27.69 0.48581040 27.69 0.48581050 27.69 0.48581060 27.69 0.48581070 27.69 0.48581080 27.69 0.48581090 27.685 0.4881100 27.685 0.4881110 27.685 0.4881120 27.682 0.47781130 27.68 0.47581140 27.68 0.47581150 27.68 0.47581170 27.682 0.47781180 27.675 0.4781210 27.67 0.46581240 27.665 0.4681270 27.665 0.4681300 27.662 0.45781330 27.66 0.45581360 27.655 0.4581390 27.655 0.4581420 27.652 0.44781450 27.645 0.4481480 27.645 0.4481510 27.643 0.43881540 27.641 0.43681570 27.64 0.43581600 27.637 0.43281630 27.635 0.4381660 27.632 0.42781690 27.63 0.42581720 27.628 0.42381750 27.628 0.42381780 27.625 0.4281810 27.62 0.41581840 27.62 0.41581870 27.618 0.41381900 27.618 0.41381960 27.613 0.40882020 27.608 0.40382080 27.605 0.482140 27.602 0.39782200 27.602 0.39782260 27.595 0.3982320 27.593 0.388
82380 27.59 0.38582440 27.59 0.38582500 27.587 0.38282560 27.582 0.37782620 27.58 0.37582680 27.58 0.37582740 27.578 0.37382800 27.575 0.3783100 27.565 0.3683400 27.55 0.34583700 27.54 0.33584000 27.525 0.3284300 27.512 0.30784960 27.5 0.29585800 27.48 0.27586400 27.47 0.26586700 27.465 0.2687000 27.46 0.25587300 27.455 0.2587600 27.45 0.24588200 27.445 0.2488500 27.44 0.23588800 27.435 0.2389100 27.435 0.2389400 27.43 0.22589700 27.425 0.2290000 27.422 0.21791800 27.405 0.294200 27.39 0.18594800 27.385 0.1895400 27.38 0.17596000 27.375 0.17
Pumping Test 3
Drawdown vs time data (Macleod 1998)Aquifer thickness = 4 m (this study)
Time (s) Depth to Drawdown (m)water level (m)
0 22 030 22.8 0.860 22.82 0.8290 22.9 0.9120 22.99 0.99150 23.02 1.02180 23.09 1.09210 23.12 1.12240 23.15 1.15270 23.18 1.18300 23.21 1.21330 23.23 1.23360 23.26 1.26390 23.29 1.29420 23.32 1.32450 23.34 1.34480 23.36 1.36510 23.38 1.38540 23.41 1.41570 23.42 1.42600 23.43 1.43630 23.45 1.45660 23.47 1.47690 23.485 1.485720 23.5 1.5750 23.52 1.52780 23.54 1.54810 23.56 1.56840 23.58 1.58870 23.6 1.6900 23.615 1.615960 23.64 1.641020 23.655 1.6551080 23.685 1.6851140 23.71 1.711200 23.74 1.741260 23.77 1.771320 23.79 1.791380 23.815 1.8151440 23.835 1.8351500 23.865 1.8651800 23.955 1.9552100 24.035 2.0352400 24.105 2.1052700 24.17 2.17
APPENDIX 3 HYDROCHEMICAL METHODS
WATER ANALYSIS
OVERVIEW OF SAMPLE COLLECTION, PRESERVATION, ANALYSIS AND RESULTS
Essential analyses carried out in situ are pH, conductivity and temperature. Redox potential (Eh) may also be determined. Before going into field it is very important that all equipment is calibrated properly and in some cases recalibration will be required every few hours while in the field. See individual procedural notes for calibration of equipment. Samples will need to be collected for the determinations that will be carried out in the Geochemistry Laboratory. The following cation and anion, determinations are required for most projects. Cations: Na+, K+, Ca++ and Mg++ (Majors) Fe, Al, Si, Cu, Mn, Pb and Sr may also be included Anions: SO42-, Cl- and Alkalinity F-, Br-, PO4
3- and NO3- may also be included
· Cations are determined by ICP-OES, refer to ‘Cation in Water by ICP-OES’ procedural
notes for sample requirement and more information on this determination. · Alkalinity is determined using a titrimetric method, refer to ‘Alkalinity in Water’ procedural
notes for more information on this determination. · The rest of the anions listed above are determined by ion chromatography, refer to ‘Anions
in Water by Ion Chromatography’ procedural notes. It is important to note if chloride concentration is high, it must be determined by titration. Ion chromatography may give low results for high chloride.
PRESERVATION and STORAGE of SAMPLES: Use the following Table 1 to determine what bottle preparation, preservation and storage requirements is required for each sample. For some determinations more than one method is possible, methods other than the usual or preferred method are listed in italics.
TABLE 1: Sampling and preservation requirements.
Determination
Container
Minimum
Sample Size mL
Preservation
Maxim
um Storage
Analysis Method
Alkalinity P 200mL Refrigerate 14d Titration Bromide P 100mL None required Ion chromatography Chloride P 100mL Refrigerate 14d Titration
Fluoride P 300mL None required 28d Ion chromatography
or ion selective electrode
Nitrate P 100mL Refrigerate 48h Ion chromatography or ion selective electrode
pH P Analyse Immediately
nil pH electrode
Phosphate G(A) 100mL Refrigerate 48h Ion chromatography or colourimetry
Sulfate P 100mL Refrigerate 28d Ion chromatography or ICP-OES or nephelometry
Turbidity P 100mL Analyse same day or store in dark for up to 24h, refrigerate
48h Nephelometry
Metals (Most cations come under this category)
P(A) 250 mL For dissolved metals filter immediately, add HNO3 to pH<2
6mths ICP-OES
For determinations not listed refrigerate and analyse as soon as possible. P = Plastic (polyethylene or equivalent) P(A) = Plastic and rinsed with 1:1 HNO3 G(A) = Glass and rinsed with 1:1 HNO3 Refrigerate = Store at <4oC nil = No storage allowed If both anion and cation analyses are to be done, two samples bottles will be required for each site: one acidified sample for cation analysis (metals) of at least 250 mLs is required and one unacidified sample of at least 500 mLs for anion analysis is required. Sample bottles may need to be acid rinsed before use (Check table 1 to see if this is required). How to acid rinse Sample Bottles: Prepare 50 mLs of 1:1 nitric acid by diluting 25mL of conc nitric acid (HNO3) in a 100 mL beaker. Transfer approximately 20 mL of 1:1 nitric acid to a bottle, shake vigorously for about 30 seconds, and transfer to the next bottle. Rinse the bottle thoroughly at least 3 times with deionised water. This operation must be performed in a fume cupboard. Do not pour dilute acid or even the rinse water down stainless steel sinks.
How to Acidify Sample: (This can be done before going into field.) Add 2 mL of concentration nitric acid (HNO3) to each cation sample bottle (This should be half your sample bottles) to give a pH <2 in the final sample. SAFETY: Transporting concentration acid involves risks. Please read risks assessment for this application before acidifying bottles. RESULTS Once all determinations are done it is important to do a cation-anion balance to check the correctness of analyses. The cation-anion balance compares the total anions to the total cations on a molecular level. To do this the results must be converted to milliequivalents per litre (me/L) by multiplying each analyte concentration (mg/L) by the conversion factor given in Table 1. The factor is equal to the number of charges associated with the ion species divided by the weight of the ion. eg for Sodium, Na+, there is one positive charge associated and it has an atomic weight of 22.99 thus me/L = mg/L x 1/22.99 = mg/L x 0.043 Once the results are in the form of me/L the percentage difference between sums of anion and cation species is calculated as follows: % Difference = 100 x [(Σ Cations - Σ Anions)/(Σ Cations + Σ Anions)] An agreement of <10% is acceptable, greater than this may require further ion determinations or examination of procedural techniques. REPORTING OF RESULTS CHECKLIST Have you: • completed all determinations required (all those it the attached table)? • taken into account any dilutions made before analyses and recalculated results? • checked results are not below the detection limit of the method? If results are less than
the detection limit report as being less than detection limit as stated in Table 1. • calculated a cation/anion balance to check the correctness of your results and reported on
accuracy of determinations? • only included significant figures in final values?
CATIONS in WATER by INDUCTIVELY COUPLED PLASMA - OPTICAL EMISSION
SPECTROSCOPY (ICP-OES) Cations commonly analysed in water samples by ICP-OES are: Major Cations: Na, K, Mg and Ca Minor Cations: Al, Si, Sr, Mn, Fe, Zn and Cu DECTECTION LIMITS: Element
Working Detection Limits
Na 0.015 – 1500 mg/L
K 0.20 – 150 mg/L
Mg 0.001 – 150 mg/L
Ca 0.0003 – 250 mg/L
Al 0.015 – 75 mg/L
Si 0.011 – 75 mg/L
Sr 0.0006 – 75 mg/L
Mn 0.003 – 7.5 mg/L
Fe 0.015 – 7.5 mg/L
Zn 0.009 – 7.5 mg/L
Cu 0.02 – 0.75 mg/L
THEORY OF OPERATION: The cation and sulfur concentrations are measured using inductively coupled plasma - optical emission spectroscopy (ICP-OES). This technique involves the water sample being aspirated into a plasma. The intensity of characteristic wavelengths emitted by the excited analyte ions in the plasma are measured by a spectrophotometer. The measured intensity is proportional to concentration, thus concentration of ions in the sample can be determined. SAMPLE PREPARATION: Little or no sample preparation is required for analysis of aqueous samples by ICP-OES except for highly turbid samples which must be filtered and samples of high conductivity which must be diluted to <4000 µS before analysis. Also, concentration of elements
determined must be within the detection limits of the ICP-OES for the results to have analytical meaning. Filter turbid samples through a 0.45 or 0.8 µm membrane filter, collect and analyse the filtrate, diluting if necessary. It is possible for cations other than those listed above to be analysed, however it may not be feasible if the selected analyte ions are present only in trace amounts ie at levels below the limits of ICP-OES detection. RESULTS All data should be within detection limits set out above. Any results out of this range should be recorded as being out of detection limits. Data out of dectection limits has no real meaning, inclusion this data in a report or thesis is completely inaccurate. Interpreting ICP-OES results print-outs: Sample Name Program File Name Date Time Element Mean Units Standard Weight/Volume Analysed Intensity Deviation Recalculated concentration element Wavelength Concentration Percent in original sample at which of element in Relative adjusting for sample element is solution Standard weight and dilution. determined Deviation The above printout shows for Sample 1 the potassium (K) concentration was measured at a wavelenth of 769.896 nm and was found to be 3.101 ppm in the original sample.
ANIONS in WATER By ION CHROMATOGRAPHY (IC)
Anions determined by this method: Cl-, SO4
2-, Fl-, Br-, NO3- and PO4
3- (NO2
- and SO32- can also be analysed but are not included in the routine analysis.)
DECTECTION LIMITS: A working range has been given below. This range is based on a combination of standard concentration range and instrument working range. Fl- 0.05 to 12 ppm Cl- 0.5 to 150 ppm SO4
2- 0.5 to 100 ppm Br- 0.05 to 12 ppm NO3
- 0.05 to 12 ppm PO4
3- 0.05 to 12 ppm THEORY OF OPERATION: The Ion Chromatographic Process: The sample is introduced in the flowing stream and carried into the anion exchange column. Ions interact with the ion exchange sites on the stationary phase in the column. Mobile phase ions (or eluent ions) compete with the sample ions for ion exchange sites on the column. Separation depends upon the different ions having different affinities for both phases. In the case of anion separations the differing affinities for stationary and mobile phases are due to the ionic charge and ion size (ionic radius) of each anion species. Once anions are separated the concentration of each species present in the sample is measured using a conductivity detector. A chromatogram displays peaks in conductivity at various retention times. Each anionic species is identified by its retention time which remains constant throughout successive runs. Stationary Phase: the column packing material containing functionalised active sites. For anion determinations the Dionex AS14 anion exchange column is used. Mobile Phase (or Eluent): The liquid flowing though the column that contains competing ion for the active sites. SAMPLE PREPARATION: Little of no sample preparation is required of analysis of aqueous sample by ion chromatography. However highly turbid samples must be filtered before analysis and sample
of high conductivity require diluting before analysis. Samples analysed must have a conductivity of less than 700 μS, if not dilution is required. Filter turbid samples through a 0.45 of 0.8 um membrane filter, collect and analyse the filtrate, diluting if necessary. REAGENTS:
Eluent: 3.5mM Na2CO3/1.0 mM NaHCO3. Prepare diluting the 100x concentrate 100 fold. Ie pipette 10 mL of 100x concentrate into a 1000 mL volumetric flask and dilute to the mark with ultra pure water. (Obtain ultra pure water from the purification unit located on the back island bench located in the Geochem lab R431.) Fill eluent bottle with this solution and sparge with argon for at least ten minutes before starting eluent pump.
Regenerant solution: Add 2.4 mL of conc H2SO4 to 1000 mL of ultra pure water and dilute further to 2000mLs. Fill regen bottle with this solution recap and allow to pressurise. After several minutes ensure regen solution is flowing through suppressor.
RESULTS: Ion chromatography is a excellent method of anion species determination in water samples. It has a extremely good precision with a %RSD of <2%. However it is important that results obtained are not taken on face value but are checked to assure data is reasonable. This is particularly important as peaks can be misnamed due to small shifts in retention time. The retention time can change due to a variety of reasons most commonly due to problems with the eluent pump, blockages and inaccurate preparation of eluent. Always check with previous days data to determine if retention times have not changed (refer to daily log, located next to instrument for this information). Also data should be with the working range of each species listed above, if not an dilution may be require before reruning samples or an alternative method of analysis may be required. In particular, high chloride data should be checked by titration as concentrations over 150-200 ppm may not be linear, giving inaccurate results. An example of a chromatogram using
ALKALINITY ACID TITRATION METHOD
DETECTION LIMIT: 0.25 ppm CaCO3 (mg/L water) APPARATUS: 250 mL conical flask, calibrated pH meter and 25 mL burette SAFETY EQUIPMENT: Laboratory coat, safety glasses. Refer to Risk Assessment/s: Hydrochloric acid (32%) - Student usage REAGENTS: 0.1N Standard HCl: SAFETY: This dilution must be carried out in a fume cupboard.
Pipette 10 mLs of conc HCl (10 M) into a 1000 mL volumetric flask and dilute to mark.
Standardisation of 0.1 N HCl: Weigh 0.7 - 0.8 g of pure sodium tetraborate by difference into a 150 mL conical
flask, dissolve in about 50 mLs of distilled water and add a few drops of methyl red indicator. Titrate the sodium tetraborate solution with the 0.1N HCl as the titrant until the colour changes to pink. Record the volume of HCl used. Carry out this procedure in triplicate. Use the following equation to calculated the normality of the acid solution.
N HCl = Weight of Na2B4O7 mg / (190.72 x Vol of Titrant (HCl) ml ) 0.02 N Standard HCl: Pipette 200 mLs of standard 0.1N HCl into a 1000 mL
volumetric flask and dilute to the mark. PROCEDURE: The alkalinity of a sample is due to the presence of hydroxide, carbonate or
bicarbonate ions. The concentration of each of these ions in a sample can be calculated once the phenolphthalein and total alkalinity have been determined.
1) Determination of phenolphthalein alkalinity or P
a) Pipette 100 mLs of sample into a 250 mL beaker. Measure the pH of the sample. If pH is less than 8.3 go on to step 2) as P=0.
b) If pH is greater than 8.3 then titrate the sample with 0.1N HCl to pH 8.3. Use a magnetic stirrer and leave pH probe in sample while titrating. Record volume of
HCl used. Calculate alkalinity due to hydroxide, P, by using Calculation (a). Go on to step 2).
2) Determination of total alkalinity or T
a) Titrate the sample to the pH 4.7 if the sample alkalinity is unknown. If known choose the appropriate total alkalinity equivalence point from the following
table. These pH values are suggested equivalence points for the corresponding alkalinity concentrations.
Alkalinity (mg/L CaCO3)
End Point pH: Total
30 4.9 150 4.6 500 4.3 Silicates, phosphates known or
suspected 4.5
Industrial waste or complex system 4.5
b) Record total volume of HCl titrated ie. include volume of titrant used in step 1 if appropriate. Calculate the Total Alkalinity, T, using calculation (b). If Total
Alkalinity, T, is less than 20 mg/L CaCO3 go to step 3). If Total Alkalinity, T, is greater than 20 mg/L CaCO3 go to step 4. 3) Determination of Total Alkalinity less the 20mg/L CaCO3 a) Pipette 100 mLs of sample into a 250 mL beaker and titrate using 0.01M HCl to
an end point in the range of 4.3 to 4.7. Record the volume and the exact pH. b) Titrate the solution further to reduce the pH exactly 0.30 pH units and record
volume. Use Calculation (c) to determine Total Alkalinity, T. 4) Determine the relationship between Hydroxide, Carbonate and Bicarbonate Alkalinity
using Table 2. NOTE: As the end point is approached make smaller additions of acid and be sure that pH
equilibrium is reached before adding more titrant. CALCULATIONS: a) P (Phenolphthalein Alkalinity) P mg/L CaCO3 = A x N x 50 000 / volume of sample where A = mL standard acid used N = normality of standard acid b) T (Total Alkalinity) T mg/L CaCO3 = A x N x 50 000 / volume of sample where A = mL standard acid used N = normality of standard acid c) Potentiometric titration of low alkalinity (<20mg/L CaCO3):
T (Total alkalinity), T mg/L CaCO3 = (2B - C) x N 50 000 / volume of sample where B = mL of titrant to first recorded pH C = total mL of titrant of reach pH 0.3 unit lower N = normality of acid TABLE 2: Calculation of alkalinity relationships:
Result of titration Hydroxide Alkalinity as CaCO3
Carbonate Alkalinity as CaCO3
Bicarbonate Alkalinity as CaCO3
P = 0 0 0 T P < 1/2T 0 2P T - 2P P >=1/2T 0 2P 0 P > 1/2T 2P-T 2(T-P) 0
P=T T 0 0 Where P = phenolphthalein alkalinity T = total alkalinity Report total alkalinity as: "The alkalinity to pH ____ = ____ mg CaCO3/L" To convert hydroxide, carbonate and bicarbonate expressed as alkalinity to concentration of their own species to be used in a mass balance multiply by the following factors. Hydroxide mg/L OH- = mg/l CaCO3 x 0.34 Carbonate mg/L CO32- = mg/L CaCO3 x 0.60 Bicarbonate mg/L HCO3- = mg/L CaCO3 x 1.22 WORKED EXAMPLE: A 100mL sample of pH 9.0 was titrated with 0.09871 M HCl to the phenolphthalein end point, pH 8.3, and the titrant volume of 2.60 mL was recorded. The sample was then titrated further to and end point of pH 4.7 and the additional titrant volume of 7.35 mL was recorded. i) Calculation of Phenolphthalein Alkalinity P = A x N x 50 000 / volume of sample = 2.6 x 0.09871 x 50 000 / 100 = 128.32 mg/L CaCO3 ii) Calculation of Total Alkalinity T = A x N x 50 000 / volume of sample
= (2.60 + 7.35) x 0.09871 x 50 000 / 100 = 491.08 mg/L CaCO3 iii) Determination of alkalinity relationship using Table 2 Where P = 128.32 mg/L CaCO3 and T = 491.08 mg/L CaCO3 since 128.32 < 1/2 of 491.08 thus P < 1/2 T
According to Table 2 alkalinity is due to the following alkali concentrations Hydroxide = 0 mg/L CaCO3 Carbonate = 2P = 2 x 128.32 = 256.64 mg/L CaCO3 Bicarbonate = T - 2P = 491.08 - (2 x 128.32) = 234.44 mg/L CaCO3 iv) Alkali concentrations expressed as species concentrations Hydroxide mg/L OH- = mg/L CaCO3 x 0.34 = 0 x 0.34 = 0 mg/L OH- Carbonate mg/L CO32- = mg/L CaCO3 x 0.60 = 256.64 x 0.60 = 153.98 mg/L CO32- Bicarbonate mg/L HCO3- = mg/L CaCO3 x 1.22 = 234.44 x 1.22 = 284.80 mg/L HCO3
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v) Finally reporting Alkalinity = 491.08 mg/L CaCO3 to pH 4.7 Hydroxide = 0 mg/L Carbonate = 153.98 mg/L Bicarbonate = 284.80 mg/L
APPENDIX 4 HYDROCHEMICAL DATA
Bore RN Date pH EC (µS/cm) Na K Mg Ca Cl SO4 HCO3220 25/10/1996 7.8 1880 150 1.8 116.8 79 334 57 549221 25/10/1996 7.8 1255 76 1.0 73.0 77 226 49 350222 14/11/1996 7.8 1730 123 0.3 139.9 45 283 71 565256 12/11/1996 7.6 4710 757 8.8 173.0 93 1230 171 755462 14/11/1996 7.5 4090 144 2.2 304.0 289 1080 82 610476 1/11/1996 7.8 1550 90 1.5 85.9 100 288 52 391477 14/11/1996 7.5 1480 88 1.7 88.4 95 246 100 390 Table A1. Chemical analyses of 490 25/10/1996 7.6 4170 213 5.7 273.8 231 1093 59 680 major constituents 1996.491 25/10/1996 7.4 6580 490 4.2 365.1 387 2039 121 651 All concentrations in mg/L.777 13/11/1996 7.8 9500 2016 14.2 146.7 86 2862 129 1119 DL: detection limit778 12/11/1996 7.4 11420 2419 14.6 177.7 99 3894 14 916783 4/11/1996 7.5 2450 144 5.5 144.6 151 559 59 560784 4/11/1996 7.8 2540 94 2.6 182.5 162 603 71 546865 25/10/1996 7.6 1530 100 1.6 83.8 96 265 62 423
SW May 96 9/05/1996 7.57 507 29 2.7 27.3 35 54 12 197SW Nov 96 28/11/1996 8.3 1470 105 3.9 75.2 78 272 67 328
Bore RN Date Al Fe Mn Zn Cu F NO3 CO3 SiO2220 25/10/1996 0.01 <DL <DL <DL 0.01 0.2 32.3 2.6 36221 25/10/1996 0.01 <DL <DL <DL <DL 0.2 4.2 1.8 35222 14/11/1996 <DL <DL <DL <DL <DL 0.2 9.7 3.0 43256 12/11/1996 <DL <DL 0.06 0.23 0.01 0.4 18.4 2.9 27462 14/11/1996 <DL <DL <DL 0.01 <DL 0.2 78.8 2.0 34476 1/11/1996 <DL <DL <DL <DL <DL 0.2 30.8 1.9 36477 14/11/1996 <DL <DL <DL 0.01 0.01 0.2 14.2 0.9 33 Table A2. Chemical analyses of 490 25/10/1996 <DL <DL <DL <DL 0.01 0.1 91.3 2.4 35 minor constituents 1996.491 25/10/1996 <DL <DL <DL 0.01 0.01 0.2 35.6 1.8 36 All concentrations in mg/L.777 13/11/1996 <DL <DL 1.44 0.02 0.01 0.2 <DL 8.2 23 DL: detection limit778 12/11/1996 <DL <DL 0.48 <DL <DL 0.2 <DL 3.0 18783 4/11/1996 <DL <DL 0.01 <DL 0.02 0.2 9.1 1.4 30784 4/11/1996 <DL <DL <DL 0.01 0.01 0.1 5.9 2.8 29865 25/10/1996 0.01 <DL <DL 0.37 0.01 0.1 24.9 1.4 39
SW May 96 9/05/1996 <DL <DL <DL <DL <DL 0.1 11.2 0.4 33SW Nov 96 28/11/1996 <DL <DL <DL <DL <DL 0.2 8.2 5.0 27
Bore RN Date pH Eh T EC Na K Mg Ca Cl SO4 HCO3(mV) ( C ) (µS/cm)
220 3/09/2003 7.33 40 20.8 2110 118 10.0 172.2 110 297 58 423221 27/11/2003 7.17 116 23 2600 100 3.6 155.0 131 431 82 740445 8/09/2003 7.04 -15 21.8 5030 367 6.1 268.0 249 1276 227 415446 8/09/2003 7.3 -101 21.7 1443 87 3.8 77.3 86 191 27 345447 20/11/2003 6.37 -70 22.7 4640 609 7.2 134.3 85 102 10 2385462 3/09/2003 7.47 85 21.9 3750 152 4.1 340.4 319 768 58 516477 25/08/2003 7.2 72 18.6 2640 128 3.1 172.1 173 428 120 412489 6/09/2003 7.17 57 22.6 3800 205 4.7 218.5 178 833 79 536490 6/09/2003 6.91 76 22.9 3670 244 6.5 250.3 205 686 56 536491 8/09/2003 7.01 46 22.2 6100 478 4.6 343.0 306 1570 236 400502 8/09/2003 7.13 -140 21.3 3400 246 10.0 249.1 176 681 111 454514 8/09/2003 7.44 8 22.9 2045 132 5.1 151.3 76 228 150 603515 8/09/2003 7.48 -87 22.3 2330 104 2.9 199.4 99 305 38 680516 8/09/2003 6.87 -165 22.8 5380 205 6.2 432.5 407 1879 127 490
55617 6/09/2003 6.95 71 23.5 8780 847 6.8 462.4 413 2565 349 619557 8/09/2003 7.44 22 15.4 2320 160 4.4 134.4 126 368 71 365783 3/09/2003 7.87 81 22.3 3220 199 11.0 319.0 424 652 63 418784 3/09/2003 7.52 38 22.3 3100 120 6.5 455.9 499 619 81 526822 10/09/2003 6.97 -67 21.5 4930 915 14.9 186.0 147 440 105 2681858 3/09/2003 7.48 -69 21.9 2490 271 8.3 158.7 120 332 24 459859 3/09/2003 7.42 83 23.1 9050 475 7.9 735.8 822 2584 84 722861 10/09/2003 6.9 106 22.2 12160 776 13.3 1039.0 649 3706 392 397862 6/09/2003 7.01 63 23 12890 1536 31.5 715.2 586 3737 223 799864 6/09/2003 7.52 109 22.3 1447 80 2.6 126.8 156 177 56 356865 6/09/2003 7.23 76 21.7 2340 138 4.6 193.8 237 361 77 448P1 27/11/2003 7.47 32 24 3040 174 2.2 193.7 62 587 45 672B1 20/11/2003 7.2 22 720 95 2.0 14.5 19 22 3 490B2 20/11/2003 7.37 22 730 107 2.5 15.2 15 17 5 535
Table A3. Chemical analyses of major constituents 2003. All concentrations in mg/L. DL: detection limit
Bore RN Date Al Fe Mn Sr Zn Cu F Br NO3220 3/09/2003 6.20 8.82 3.97 1.20 1.30 0.12 1.50 1.0 50.8221 27/11/2003 1.70 4.57 0.63 0.90 0.17 0.00 0.13 0.9 66.4445 8/09/2003 0.73 1.86 2.09 1.67 0.64 0.04 0.40 <DL 14.8446 8/09/2003 0.60 2.84 0.42 0.73 0.24 0.02 0.30 <DL 1.7447 20/11/2003 1.18 18.37 0.26 1.19 0.51 0.04 <DL <DL <DL462 3/09/2003 11.14 17.83 6.28 1.56 0.35 0.17 0.40 <DL 30.0477 25/08/2003 2.74 31.13 19.33 0.87 0.50 0.08 <DL <DL 27.3489 6/09/2003 1.48 3.93 0.66 1.59 0.16 0.04 <DL 3.2 116.0490 6/09/2003 7.24 5.15 4.15 2.55 0.27 0.04 1.20 2.8 79.2491 8/09/2003 1.62 4.40 0.67 2.42 0.07 0.02 0.40 <DL 57.6502 8/09/2003 6.63 7.24 10.57 1.17 1.31 0.06 <DL 1.1 47.3514 8/09/2003 0.76 6.39 2.77 0.49 0.27 0.02 0.25 <DL <DL515 8/09/2003 1.80 12.34 1.40 0.49 0.12 0.03 <DL 0.5 <DL516 8/09/2003 5.83 100.88 26.12 2.87 0.70 0.08 0.40 4.0 <DL
55617 6/09/2003 0.17 0.08 0.03 4.28 0.00 0.04 50.40 27.2 72.0557 8/09/2003 3.82 6.06 7.90 0.87 0.42 0.05 0.25 <DL 16.5783 3/09/2003 9.55 204.70 18.84 2.66 0.62 0.06 6.65 2.8 19.3784 3/09/2003 11.41 105.80 12.60 2.76 0.48 0.07 <DL <DL 48.3822 10/09/2003 0.09 0.15 3.89 2.91 0.70 0.01 0.40 <DL 3.6858 3/09/2003 5.05 19.58 4.24 1.51 1.20 0.05 1.75 <DL <DL859 3/09/2003 0.39 4.55 1.57 5.39 0.06 0.03 1.60 <DL <DL861 10/09/2003 0.25 0.22 1.77 6.19 0.24 0.00 3.60 6.0 102.0862 6/09/2003 13.48 5.21 18.30 8.18 0.84 0.00 <DL <DL <DL864 6/09/2003 7.60 6.15 3.91 0.80 0.40 0.06 0.15 <DL 1.2865 6/09/2003 9.46 5.56 14.30 1.40 0.44 0.08 9.00 <DL 43.8P1 27/11/2003 0.04 0.03 0.09 0.44 0.00 0.01 0.30 2.9 5.4B1 20/11/2003 0.89 3.11 0.11 0.22 0.02 0.01 <DL <DL <DLB2 20/11/2003 0.05 0.17 0.01 0.16 0.02 0.01 <DL <DL <DL
Table A4. Chemical analyses of minor constituents 2003. All concentrations in mg/L. DL: detection limit
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