The Lake Connewarre Complex is an internationally protected wetland in southeast Australia, undergoing increasing environmental change due to urbanisation. Stable isotopes of water (δ¹⁸O and δ²H) and other geochemical indicators were used to assess sources of water and salinity in the shallow groundwater and surface-water systems, and to better understand groundwater/surface-water interactions. While much of the shallow groundwater is saline (from 1.27 to 50.3 g/L TDS) with overlapping salinities across water groups, stable isotopes allow clear delineation of two distinct sources of water and salinity: marine water with δ¹⁸O between −1.4 and +1.3 ‰ and ion ratios characteristic of seawater; and meteoric water with δ¹⁸O between −6.1 and −3.6 ‰ containing cyclic salts, probably concentrated by plant transpiration. Groundwater bodies in shallow sediments beneath the wetlands have salinities and stable isotopic compositions intermediate between fresh wetland surface water and a marine water end-member. This marine-type water is likely relict seawater emplaced when the wetlands were connected to the estuary, prior to modern river regulation. Freshwater input to underlying groundwater is a recent consequence of this regulation. Future predicted changes such as increased stormwater inflow, will increase rates of freshwater leakage to shallow groundwater, favouring the proliferation of exotic reed species.

This study investigated the use of three-dimensional (3D) geological methods to provide better groundwater resource estimates for the Spring Hill area in central Victoria, Australia. Geological data were gathered in 3D geological software, which was utilised to derive fundamental dimensional parameters of the groundwater system in the study area. Mining industry software and hydrogeological methods were combined to give volumetric determinations of the basalt aquifer that were used to improve estimates of the groundwater resource. The methods reduce uncertainty about the physical attributes of the aquifer systems and greatly improve conceptual understanding of their behaviour. A simple numerical water-balance model was developed to refine the estimates of aquifer volume and fluxes to approximate observed water-level behaviour in the area. This enabled a much better comparison of groundwater resource use to the natural inputs and outputs for the area. A key conclusion was that the main issues for sustainable development and use in the study area are more to do with the physical aspects of the aquifer system, rather than simply the volume of water pumped. Visualisations of the area’s hydrogeology also provide improved hydrogeological understanding and communication for groundwater users and administrators.

Groundwater time-series modeling has emerged as an efficient approach for simulating the impacts of multiple drivers of groundwater-head variation such as rainfall, evaporation and groundwater pumping. However, a bottom-up approach has generally been adopted whereby the input drivers have been assumed without statistical evidence for their inclusion. In this study, a parsimonious time-series model was adopted which accounts for various drivers and is able to simulate the overall groundwater-head variation. It can also separate the effects of pumping and climate drivers on multi-annual time series of groundwater-level variation. The time-series model consists of a soil-moisture layer to account for non-linearity between rainfall and recharge, as well as different pumping response functions to account for pumping from a single well, lake-induced recharge and the effects of multiple pumping bores. The method was applied to a groundwater-pumping region in south-eastern Australia. The results showed that the model is able to separate the effects of pumping from the effects of climate on groundwater-head variation. However, improved estimation of those influences requires a flexible model structure that can account for spatially varying physical processes within the study region such as the relative influence of single or multiple pumping bores and induced recharge from surface-water bodies.

Modelling cumulative impacts of basin-scale coal seam gas (CSG) extraction is challenging due to the long time frames and spatial extent over which impacts occur combined with the need to consider local-scale processes. The computational burden of such models limits the ability to undertake calibration and sensitivity and uncertainty analyses. A framework is presented that integrates recently developed methods and tools to address the computational burdens of an assessment of drawdown impacts associated with rapid CSG development in the Surat Basin, Australia. The null space Monte Carlo method combined with singular value decomposition (SVD)-assisted regularisation was used to analyse the uncertainty of simulated drawdown impacts. The study also describes how the computational burden of assessing local-scale impacts was mitigated by adopting a novel combination of a nested modelling framework which incorporated a model emulator of drawdown in dual-phase flow conditions, and a methodology for representing local faulting. This combination provides a mechanism to support more reliable estimates of regional CSG-related drawdown predictions. The study indicates that uncertainties associated with boundary conditions are reduced significantly when expressing differences between scenarios. The results are analysed and distilled to enable the easy identification of areas where the simulated maximum drawdown impacts could exceed trigger points associated with legislative ‘make good’ requirements; trigger points require that either an adjustment in the development scheme or other measures are implemented to remediate the impact. This report contributes to the currently small body of work that describes modelling and uncertainty analyses of CSG extraction impacts on groundwater.

Parameterisation of unsaturated flow models for estimating spatial-scale groundwater recharge is usually reliant on expert knowledge or best-estimated parameters rather than robust uncertainty analysis. This study chose the Campaspe catchment in southeastern Australia as a field example and examined the uncertainty of spatial groundwater recharge by performing uncertainty analysis. The study area was first divided into 13 zones according to different vegetation types, soil groups and precipitation. Individual models were then established for these zones using the biophysically based modelling code WAVES (Water Atmosphere Vegetation Energy and Solutes), which is capable of simulating unsaturated flow. The Monte Carlo method, together with the Latin-Hypercube sampling technique, was employed to perform uncertainty analysis by comparing modelled monthly evapotranspiration (ET) to MODIS ET. The results show that the common one-estimate-per-site approach can still identify the spatial pattern of groundwater recharge in the study area due to the presence of a precipitation pattern. In comparison, the uncertainty analysis not only identifies the spatial pattern, but also provides confidence levels in groundwater recharge that are critical for water resources management. The results also show that recharge absolute uncertainty is directly proportional to the amount of water input, but relative uncertainty in recharge is not. This study indicates that spatial recharge estimation without model calibration or knowledge of model uncertainty could be highly uncertain. MODIS ET can be used to reduce recharge uncertainty, but it is unlikely to lower the recharge uncertainty by a large extent because of the MODIS ET estimation error.

Hydraulic head measurements in the Great Artesian Basin (GAB), Australia, began in the early 20th century, and despite subsequent decades of data collection, a well-accepted smoothed potentiometric surface has continually assumed a contiguous aquifer system. Numerical modeling was used to produce alternative potentiometric surfaces for the Cadna-owie–Hooray aquifers with and without the effect of major faults. Where a fault created a vertical offset between the aquifers and was juxtaposed with an aquitard, it was assumed to act as a lateral barrier to flow. Results demonstrate notable differences in the central portion of the study area between potentiometric surfaces including faults and those without faults. Explicitly considering faults results in a 25–50 m difference where faults are perpendicular to the regional flow path, compared to disregarding faults. These potential barriers create semi-isolated compartments where lateral groundwater flow may be diminished or absent. Groundwater management in the GAB relies on maintaining certain hydraulic head conditions and, hence, a potentiometric surface. The presence of faulting has two implications for management: (1) a change in the inferred hydraulic heads (and associated fluxes) at the boundaries of regulatory jurisdictions; and (2) assessment of large-scale extractions occurring at different locations within the GAB.

Determining groundwater ages from environmental tracer concentrations measured on samples obtained from open bores or long-screened intervals is fraught with difficulty because the sampled water represents a variety of ages. A multi-tracer technique (Cl, ¹⁴C, ³H, CFC-11, CFC-12, CFC-113 and SF₆) was used to decipher the groundwater ages sampled from long-screened production bores in a regional aquifer around an open pit mine in the Pilbara region of northwest Australia. The changes in tracer concentrations due to continuous dewatering over 7 years (2008–2014) were examined, and the tracer methods were compared. Tracer concentrations suggest that groundwater samples are a mixture of young and old water; the former is inferred to represent localised recharge from an adjacent creek, and the latter to be diffuse recharge. An increase in ¹⁴C activity with time in wells closest to the creek suggests that dewatering of the open pit to achieve dry mining conditions has resulted in change in flow direction, so that localised recharge from the creek now forms a larger proportion of the pumped groundwater. The recharge rate prior to development, calculated from a steady-state Cl mass balance, is 6 mm/y, and is consistent with calculations based on the ¹⁴C activity. Changes in CFC-12 concentrations with time may be related to the change in water-table position relative to the depth of the well screen.

The western Great Artesian Basin (GAB) is an important water source for pastoral and town water supplies, as well as for springs containing endemic flora and fauna, within arid Australia. This study focuses on the hydrochemical variations of groundwater and spring discharge in order to determine the major geochemical processes responsible for water quality and evolution across the western GAB. Regional hydrochemical trends within groundwater generally support the modern groundwater potentiometric surface and interpreted flow paths, highlighting that these approximately represent the long-term flow paths. Additionally, the regional chemical variations along the flow paths in the western GAB are complex, with their composition being a function of several controlling processes, including location of recharge, evapo-concentration, mixing and various water–rock interactions. These processes cause groundwater east of Lake Eyre to be predominantly of Na-HCO₃ type, whereas groundwater originating from the western margin is of Na-Cl-(-SO₄) type. The GAB springs appear to be discharging water predominantly from the main GAB aquifer, the J Aquifer; however, a component of the discharging water from several springs is from a source other than the J Aquifer. Current understanding of the hydrochemical variations of groundwater and spring discharge of the western GAB can help provide constraints on groundwater flow, as well as provide an understanding of the geochemical and hydrological processes responsible for water quality evolution.

Vertical leakage (discharge to upper aquifers) is an important but poorly constrained component of water balance in the Great Artesian Basin (GAB), Australia. It ranges from negligible discharge where the GAB is overlain by aquitards, to high discharge where artesian water feeds the shallow unconfined aquifer (thereby raising the water table) causing elevated surface soil moisture and extensive surface salinisation. Adequately representing the temporal and spatial variability of vertical leakage is difficult due to the large scale over which the discharge occurs. An innovative method is presented that integrates a supervised classification of high-discharge zones using time-series Landsat data with landform mapping information to improve classification results. ‘Wetness persistence’ and ‘salt persistence’ classes, determined from the time series data, are related to groundwater discharge processes through a discharge framework that allows scaling up of field-based discharge estimates. The results show that using multi-image classification integrated with landform data will significantly reduce uncertainty by reducing false positives. No significant temporal trends were found in a time series assessment, with results featuring high variability, most likely due to image normalisation issues. The lack of a clear temporal signal suggests that an assumption of steady-state discharge is valid for estimating annual fluxes of vertical leakage. Supervised classification and landform outputs provide updated knowledge on GAB vertical leakage rates by providing useful lower and upper bounds of discharge rates respectively. Additionally, groundwater-dependent ecosystem classification, covering the full extent of the basin margins, is a new source of information resulting from the work.

The effective deep recharge to the Hutton Sandstone, a major confined aquifer of the Surat Basin, Australia, has been quantified for the first time with the aid of environmental tracers. A factor of ten discrepancy was found when deriving groundwater flow velocities from applying the environmental tracers ¹⁴C and ³⁶Cl. It was possible to reconcile these contradictory results describing the Hutton Sandstone as a dual porosity system, in which a significant part of the tracer is not only lost by radioactive decay, but also by diffusion into stagnant zones of the aquifer. The conceptual and mathematical description of this process allowed for quantification of the effective deep recharge into this aquifer. The resulting recharge value is only a small percentage (~3%) of earlier estimates using chloride mass balance. The chloride mass balance probably gives a correct shallow infiltration rate but most of that infiltration is diverted to springs and surface water nearby (“rejected recharge”). Only a small fraction of recharge finally reaches the deeper system. These results are significant for water resource quantification from groundwater in deep confined systems. The presented dual porosity reconceptualization is likely applicable to a significant number of earlier studies that apply environmental tracers to old groundwater, and indicates that those original results may actually give too small values for groundwater velocity and too large estimates of recharge. This reconceptualization may be particularly valid for systems that include old groundwater and that have limited spatial and temporal coverage of tracer data such as the Great Artesian Basin.