Integrated Approach to Characterisation of Coastal Plain Aquifers and Groundwater Flow Processes: Bells Creek Catchment, Southeast Queensland

Ezzy, Timothy Robert (2005) Integrated Approach to Characterisation of Coastal Plain Aquifers and Groundwater Flow Processes: Bells Creek Catchment, Southeast Queensland. PhD by Publication, Queensland University of Technology.


Low-lying coastal plains comprised of unconsolidated infill are internally complex

hydrogeological settings, due to the high level of heterogeneity in the infill material.

In order to resolve the hydrogeological processes active in these complex settings, an

integrated multi-disciplinary, geoscientific approach is required. This research

determines quantitatively, the effects of sedimentary aquifer heterogeneity on

groundwater flowpaths and groundwater processes within a heavily laterised, coastal

plain setting. The study site is the Bells Creek catchment in southeast Queensland,

Australia. The methodology developed in this study provides a new approach to

enable the determination of groundwater flowpaths and groundwater processes at

macroscale resolution within other shallow alluvial and coastal plain aquifers. The

multi-disciplinary approach utilises sedimentological, geophysical, chronological and

hydrogeological techniques (including hydrochemistry and groundwater flow

modelling) to develop a high-resolution aquifer framework, and to determine

accurately, both groundwater flowpaths and relative flow rates.

Sedimentary framework is confirmed to be the principal factor controlling the

distribution of aquifer permeability pathways in any given setting, and is therefore,

the dominant control over groundwater flow and processes. For the Bells Creek

catchment, interpretation of stratigraphic and sedimentary data allowed the

compilation of a detailed sedimentary framework. This interpretation demonstrated

that weathering of the low-lying arkose sandstone bedrock has developed thick

lateritic profiles. Within the weathering profiles, cemented, iron-rich horizons have

resisted erosion and developed raised and elongated ridges in the modern landscape,

while other clay-rich weathered layers have submitted to erosion and downgraded

around those iron-rich ridges. Consequently, alluvial deposition throughout the Late

Quaternary has been restricted to narrow, and relatively deep valleys containing sandrich

channels, and thin floodplains at shallow depth.

From a hydrogeological perspective, there is significant macroscopic aquifer

heterogeneity between fine-grained lateritic mixed clay layers, floodplain clays, ironcemented

ferricrete horizons, and permeable sand-rich alluvial aquifers. This

variability of aquifer material has created a complex subsurface arrangement of

permeability pathways. Application of Ground Penetrating Radar (GPR) in this setting enabled accurate definition of alluvial channel boundaries and the high degree

of connectedness within the channels themselves. Interpretation of a comprehensive

GPR dataset (that covered the entire catchment) allowed refinement of the

sedimentary framework previously established to develop a detailed threedimensional

aquifer framework.

Finite-difference groundwater modelling and particle tracking analysis (using

MODFLOW and MODPATH) has clearly demonstrated that the macroscopic

heterogeneity within the various aquifer materials of the plain has marked impacts on

groundwater pathways, and especially groundwater travel times. The variability

between a maximum residence time of 18 months for groundwater within the

alluvium, compared to hundreds of years for groundwater within the mixed clay

layers of the laterite, clearly demonstrates the importance of accurately defining the

spatial distribution of the various aquifer materials in a groundwater flow

investigation. In this setting, the interconnection of the narrow alluvial channels

feeding into a deeper alluvial delta has provided an effective conduit for shallow

groundwater flow. The role of the alluvial delta in discharging the bulk of fresh

groundwater from the central plain into the coastal and estuarine aquifers to the east,

is certainly critical in preventing saline intrusion from encroaching further west.

Hydrochemical and isotopic indicators have identified the dominant recharge

processes and groundwater flowpaths within the plain, and indicated that the

processes are strongly related to sub-surface permeability distributions determined in

the aquifer framework (and groundwater modelling), as well as seasonal fluctuations

in rainfall. In the northwest of the plain, sandstone hills provide a delayed and

slightly mineralized component of groundwater recharge into adjacent highly

permeable, unconfined alluvial aquifers; these aquifers also recharge directly via

precipitation. Aluminosilicate weathering in the bedrock hills and eastern peripheries

of the laterised bedrock are a source of excess Na, SiO2, and HCO3 to the alluvial

groundwater. As this groundwater flows down-gradient to the east, however, its

chemical composition evolves by sulfate reduction, silica equilibrium and ion

exchange processes into a more mature Na-Cl type.

Within the shallow coastal aquifers proximal to the eastern shoreline, sulfate

enrichment is occurring (associated with increases in Ca, HCO3, Fe and Al) resulting

in major deterioration in groundwater quality. The deterioration is produced by saline

intrusion from the adjacent estuary coupled with oxidation of sulfide materials in

shallow marine and estuarine clays. Reverses in salinity in those coastal aquifers have

been correlated with surges in fresh recharge waters from unconfined coastal dunes

and semi-confined landward alluvium, following significant rainfall events.

The multi-disciplinary methodology developed, provides an effective approach for

accurately defining the three-dimensional distribution of shallow aquifer material of

varying permeability via detailed stratigraphic interpretation and GPR analysis.

Utilising this aquifer framework, finite-difference groundwater modelling aided by

hydrogeological data and hydrochemical analysis, allows accurate determination of

groundwater flowpaths and groundwater processes. This research provides a new

hydrogeological analogue for alluvial channel aquifers within a laterised coastal plain


Key Words:

groundwater flow, aquifer heterogeneity, numerical modelling, hydrochemistry,

recharge, ground penetrating radar, coastal plain aquifers, weathering, alluvial


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ID Code: 16166
Item Type: QUT Thesis (PhD by Publication)
Supervisor: Cox, Malcolm, Huftile, Gary, & Turner, Ian
Keywords: groundwater flow, aquifer heterogeneity, numerical modelling, hydrochemistry, recharge, ground penetrating radar, coastal plain aquifers, weathering, alluvial channels
Divisions: Past > Schools > Biogeoscience
Past > QUT Faculties & Divisions > Faculty of Science and Technology
Department: Faculty of Science
Institution: Queensland University of Technology
Copyright Owner: Copyright Timothy Robert Ezzy
Deposited On: 03 Dec 2008 03:57
Last Modified: 28 Oct 2011 19:44

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