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Groundwater levels represent the aggregation of different hydrological processes acting at multiple spatial and temporal scales within aquifer systems. Analyzing trends in groundwater levels is therefore essential to quantify available groundwater resources for beneficial use, and to devise plans/policies to better manage these resources. In this work, three trend analysis methods are employed to detect long-term (1971–2021) trends in annual mean/minimum/maximum depth to water table (DTW) at 910 bores. This analysis is performed in eight main alluvial systems in the Murray–Darling Basin (MDB), Australia, which concentrate nearly 75% of groundwater use. The results show: (a) an overall increasing trend in DTW across alluvial aquifers attributable to changes in recharge from rainfall and groundwater extraction; (b) the analysis methods employed show similar statistical significances and magnitudes, but differences exist; (c) the annual minimum DTW has a smaller trend magnitude than annual mean DTW, and the annual maximum DTW has a larger trend magnitude than mean DTW; (d) trends in annual rainfall and potential evaporation, and cumulative number of production bores, are consistent with the groundwater trends; (e) irrigation is responsible for some of the decreasing trend in groundwater level. These results could be used to target further research and monitoring programs, and inform groundwater resource management decisions in the MDB.

Water quality is a key consideration for urban stormwater harvesting via aquifers. This study assessed catchment spill management options based on a calibrated dynamic wave routing model of stormwater flow in an urban catchment. The study used measured travel times, pluviometer and gauging station observations from 21 storms to calibrate a stormwater model to simulate transport of pollutants from spill locations to the point of harvest. The simulations considered the impact of spill locations, spill durations, storm intensities and storm durations on the pollutant concentration at the point of harvest and travel time of a pollutant spill to the harvesting point. During dry weather, spill events travelled slower than spills occurring during wet weather. For wet weather spills, the shortest travel times tended to occur in higher intensity storms with shorter duration, particularly when a spill occurred in the middle of the storm. Increasing the intensity of rainfall reduced the peak concentration of pollutant at the harvest point via dilution, but it also reduced the time of travel. On a practical level, due to the short response times in urban catchments, management of spills should be supported by automated detection/diversion systems to protect stormwater harvesting schemes.

The production of coalbed methane, or coal seam gas (CSG) in Australia increased 250-fold since the 1990s to around 1502 petajoules in 2019 and continues to expand. Groundwater flow in the aquifers intersected by gas wells could potentially facilitate a transport pathway for migration of contaminants or poorer quality water from deeper formations. While regulatory and mitigation mechanisms are put in place to minimize the risks, quantitative environmental impact assessments are also undertaken. When many gas wells are drilled in a wide area where many potential receptors are also spatially distributed, potential source-receptor combinations are too numerous to undertake detailed contamination risk assessment using contaminant transport modelling. However, valuable information can be gleaned from the analysis of groundwater flow directions and velocities to inform and prioritise contamination risk assessment and can precede computationally challenging stochastic contaminant transport modelling. A probabilistic particle tracking approach was developed as a computationally efficient screening analysis of contamination pathways for a planned CSG development near Narrabri in northern New South Wales, Australia. Particle tracking was run iteratively with a numerical groundwater flow model across a range of plausible parameter sets to generate an ensemble of estimated flow paths through the main Great Artesian Basin aquifer in the area. Spatial patterns of path lines and spatial relationships with potential receptors including neighbouring groundwater extraction wells and hydrologically connected ecological systems were analysed. Particle velocities ranged from 0.5 to 11 m/year and trajectories indicated dedicated contaminant transport modeling would be ideally focused at the local scale where wells are near potential receptors. The results of this type of analysis can inform the design of monitoring strategies and direct new data collection to reduce uncertainty and improve the effectiveness of adaptive management strategies and early detection of impacts.

Banking water in aquifers during wet years for long-term storage then recovering it in drought is an application of managed aquifer recharge (MAR) that minimises evaporation losses. This requires a suitable aquifer for long-term storage of banked water and occasional periods when entitlements to surface water are available and affordable. This has been widely practised in Arizona and California but thus far not in Australia, in spite of severe impacts on agriculture, society, and the environment during recent droughts in the Murray–Darling Basin. This preliminary study based on a simple area exclusion analysis using six variables, some on a 90 m grid, over the 1 million km2 basin produced a first estimate of the order of 2–4 × 109 m3 of additional aquifer storage potential in surficial aquifers close to rivers. For 6 of the 23 catchments evaluated, banking capacity exceeded an average water depth of 0.3 m for the irrigated area. At one prospective site in the Macquarie River catchment in New South Wales, water banking operations at various scales were simulated using 55 years of historical monthly hydrologic data, with recharge and recovery triggered by dam storage levels. This showed that the estimated 300 × 106 m3 additional local aquifer capacity could be fully utilised with a recharge and recovery capacity of 6 × 106 m3/month, and recharge occurred in 67% of months and recovery in 7% of months. A novel simulation of water banking with recharge and recovery triggered by water trading prices using 11 years of data gave a benefit cost ratio of ≈ 2. Data showed that water availability for recharge was a tighter constraint on water banking than aquifer storage capacity at this location. The analysis reveals that water banking merits further consideration in the Murray–Darling Basin. Firstly, management across hydrologically connected systems requires accounting for surface water and groundwater entitlements and allocations at the appropriate scale, as well as developing equitable economic and regulatory arrangements. Of course, site-specific assessment of water availability and hydrogeological suitability would be needed prior to construction of demonstration projects to support full-scale implementation.

Managed aquifer recharge (MAR) is the intentional recharge of water to suitable aquifers for subsequent beneficial use or to achieve environmental benefits. Well injection techniques for MAR, such as Aquifer Storage and Recovery (ASR), rely on implementing appropriate design and defining the operational parameters to minimise well clogging and maintain sustainable rates of recharge over the long term. The purpose of this study was to develop water quality targets and pre-treatment requirements for recycled water to allow sustained recharge and recovery in a medium-coarse siliceous aquifer. The recharge water is a blend of 40% Class A recycled water and 60% reverse osmosis (RO)-treated Class A recycled water. Four source waters for MAR were evaluated: (1) this blend with no further treatment, and this blend with additional treatment using: (2) a 20 µm sediment cartridge filter, (3) a 5 µm sediment cartridge filter, or (4) a 5 µm granular activated carbon (GAC) cartridge filter. All four treatment options were also further disinfected with chlorine. The four blended and treated recycled waters were used in laboratory columns packed with aquifer material under saturated conditions at constant temperature (20.7 °C) with light excluded for up to 42 days. Substantial differences in the changes in hydraulic conductivity of the columns were observed for the different treatments within 14 days of the experiment, despite low turbidity (

The authors wish to make the following correction to this paper [...]

In this study, we developed a workflow that applies a complex groundwater model for purpose-driven groundwater monitoring network design and uses linear uncertainty analysis to explore the predictive dependencies and provide insights into the veracity of the monitoring design. A numerical groundwater flow model was used in a probabilistic modelling framework for obtaining the spatial distribution of predicted drawdown for a wide range of plausible combination of uncertain parameters pertaining to the deep sedimentary basin and groundwater flow processes. Reduced rank spatial prediction was used to characterize dominant trends in these spatial drawdown patterns using empirical orthogonal functions (EOF). A differential evolution algorithm was used to identify optimal locations for multi-level piezometers for collecting groundwater pressure data to minimize predictive uncertainty in groundwater drawdown. Data-worth analysis helps to explore the veracity of the design by using only the sensitivities of the observations to predictions independent of the absolute values of predictions. A 10-bore monitoring network that collects drawdown data from multiple depths at each location was designed. The data-worth analysis revealed that the design honours sensitivities of the predictions of interest to parameters. The designed network provided relatively high data-worth for minimizing uncertainty in the drawdown prediction at locations of interest.

Population growth and increased irrigation demand have caused a decline in groundwater levels that limit water supply in the Darwin rural area. Managed Aquifer Recharge (MAR) is a practical solution that can be adopted to augment stressed groundwater systems and subsequently increase the security of water supply. Aquifer storage capacity is considered to be the primary constraint to MAR where unconfined dolostone aquifers rapidly recharge during the tropical, wet season and drain again in the dry season. As a result, there is a general understanding that aquifers of this nature recharge to full capacity each wet season. However, the aquifer storage capacity and the potential for niche opportunities for MAR to alleviate declining groundwater levels has not previously been examined. This paper uses the Darwin rural area’s Proterozoic Koolpinyah Dolostone aquifer and the existing Koolpinyah Groundwater System to evaluate the prospects of MAR using both infiltration and injection techniques. Direct injection wells in an aquifer storage transfer and recovery (ASTR) scheme were favoured in this area, as injection wells occupy a smaller surface footprint than infiltration basins. This assessment suggested MAR during the early to mid-dry season could alleviate the impact of the dry season decline in groundwater levels in the Darwin rural area. The use of a larger aquifer storage and recovery (ASR) system (5,000,000 m3/year) was also assessed as a potentially viable technical solution in the northern part of the aquifer where it is understood to be confined. The ASR scheme could potentially be scaleable to augment the urban water system and provide strategic long-term storage. Consideration must also be given not only to the strategic positioning of the ASR water bank, but also to the hydrogeology of the aquifers in which the systems would be developed. Not all locations or aquifer systems can successfully support a strategic storage ASR system. Scheme-scale feasibility assessment of an ASR water bank is required. The study reported here is an early phase of a series of investigations that would typically be required to demonstrate the viability of any proposal to apply MAR to increase the reliability of conjunctive groundwater and surface water supplies in stressed water resources systems. It focusses on assessing suitable storage areas in a lateritic aquifer.

Managed aquifer recharge (MAR) is used worldwide in urban environments to replenish groundwater to provide a secure and sustainable supply of potable and non-potable water. It relies on natural treatment processes within aquifers (i.e., filtration, sorption, and degradation), and in some cases involves infiltration through the unsaturated zone to polish the given source water, e.g., treated wastewater, stormwater, or rainwater, to the desired quality prior to reuse. Whilst MAR in its early forms has occurred for millennia, large-scale schemes to replenish groundwater with advanced treated reclaimed water have come to the fore in cities such as Perth, Western Australia, Monterey, California, and Changwon, South Korea, as water managers consider provision for projected population growth in a drying climate. An additional bonus for implementing MAR in coastal aquifers is assisting in the prevention of seawater intrusion. This review begins with the rationale for large-scale MAR schemes in an Australian urban context, reflecting on the current status; describes the unique benefits of several common MAR types; and provides examples from around the world. It then explores several scientific challenges, ranging from quantifying aquifer removal for various groundwater contaminants to assessing risks to human health and the environment, and avoiding adverse outcomes from biogeochemical changes induced by aquifer storage. Scientific developments in the areas of water quality assessments, which include molecular detection methods for microbial pathogens and high resolution analytical chemistry methods for detecting trace chemicals, give unprecedented insight into the “polishing” offered by natural treatment. This provides opportunities for setting of compliance targets for mitigating risks to human health and maintaining high performance MAR schemes.

When evaluating uncertainties in developing an aquifer storage and recovery (ASR) system, under normal budgetary constraints, a systematic approach is needed to prioritise investigations. Three case studies where field trials have been undertaken, and clogging evaluated, reveal the changing perceptions of viability of ASR from a clogging perspective as a result of the progress of investigations. Two stormwater and one recycled water ASR investigations in siliceous aquifers are described that involved different strategies to evaluate the potential for clogging. This paper reviews these sites, as well as earlier case studies and information relating water quality, to clogging in column studies. Two novel theoretical concepts are introduced in the paper. Bayesian analysis is applied to demonstrate the increase in expected net benefit in developing a new ASR operation by undertaking clogging experiments (that have an assumed known reliability for predicting viability) for the injectant treatment options and aquifer material from the site. Results for an example situation demonstrate benefit cost ratios of experiments ranging from 1.5 to 6 and apply if decisions are based on experimental results whether success or failure are predicted. Additionally, a theoretical assessment of clogging rates characterised as acute and chronic is given, to explore their combined impact, for two operating parameters that define the onset of purging for recovery of reversible clogging and the onset of occasional advanced bore rehabilitation to address recovery of chronic clogging. These allow the assessment of net recharge and the proportion of water purged or redeveloped. Both analyses could inform economic decisions and help motivate an improved investigation methodology. It is expected that aquifer heterogeneity will result in differing injection rates among wells, so operational experience will ultimately be valuable in differentiating clogging behaviour under different aquifer conditions for the same water type. This paper was originally presented at ISMAR9, Mexico City 20–24 June 2016.