<div>This report presents the findings of a study conducted in the upper Darling River floodplain, aimed at improving optical and interferometric synthetic aperture radar (InSAR) remote sensing products for groundwater dependant vegetation (GDV) characterisation. The research was part of the Upper Darling Floodplain (UDF) groundwater study, funded by the Exploring for the Future program.</div><div>This work tests the suitability of two novel remote sensing methods for characterising ecosystems with a range of likely groundwater dependence: combined wetness and greenness indices derived from Landsat products available through Geoscience Australia’s Digital Earth Australia platform, and an InSAR derived index of vegetation structure (known as SARGDE), which has been so far tested only in northern Australia. In addition, the relationship between the Normalised Difference Vegetation Index (NDVI), a remotely sensed proxy for vegetation condition, and water availability from surface water flows, rainfall, and groundwater was tested for sites with a range of low to high likely groundwater dependence.&nbsp;</div><div>The key findings of this work, and potential implications, are:</div><div>• A multiple lines of evidence approach, drawing on persistence of wetness/greenness and vegetation structure, and correlation between inferred vegetation condition and groundwater levels, gives high confidence in the groundwater dependence of parts of the floodplain, particularly within the riparian zone. These indices require calibration with ground condition data to be applied in different regions, but a combined index could provide a high confidence measure of groundwater dependence.</div><div>• Combined greenness and wetness, SARGDE, and the relationship between NDVI and groundwater levels all showed areas classified as ‘moderate’ likelihood of groundwater dependence having signatures comparable to areas classified as high likelihood. This could address a shortcoming of the groundwater dependence classification methodology, which, when groundwater level information is missing, classifies some vegetation types as moderate.</div><div>• A combined index taking into account both greenness and wetness was able to better delineate vegetation types with a range of groundwater dependence previously not achievable using remote sensing products.&nbsp;</div><div>This work has provided improved methodology for applying remote sensing products to groundwater dependent vegetation characterisation in the study area. The methods are likely to be applicable to other regions with groundwater dependent vegetation. The results add to the evidence that it is necessary to better integrate surface and groundwater resources in water sharing plans at a basin scale. Further work is required to quantify the frequency and magnitude of flow events required to replenish alluvial groundwater sufficiently to maintain existing groundwater dependent ecosystems.&nbsp;&nbsp;</div><div><br></div><div><br></div>

<div>This report presents key results from the Upper Darling River Floodplain groundwater study conducted as part of the Exploring for the Future (EFTF) program in north-western New South Wales. The Australian Government funded EFTF program aimed to improve understanding of potential mineral, energy, and groundwater resources in priority areas for each resource.</div><div><br></div><div>The Upper Darling River Floodplain study area is located in semi-arid zone northwest New South Wales is characterised by communities facing critical water shortages and water quality issues, along with ecosystem degradation. As such, there is an imperative to improve our understanding of groundwater systems including the processes of inter-aquifer and groundwater-surface water connectivity. The key interest is in the fresh and saline groundwater systems within alluvium deposited by the Darling River (the Darling alluvium - DA) which comprises sediment sequences from 30 m to 140 m thick beneath the present-day floodplain.</div><div><br></div><div>The study acquired airborne, surface and borehole geophysical data plus hydrochemical data, and compiled geological, hydrometric, and remote sensing datasets. The integration of airborne electromagnetic (AEM) data with supporting datasets including surface and borehole magnetic resonance, borehole induction conductivity and gamma, and hydrochemistry data has allowed unprecedented, high resolution delineation of interpreted low salinity groundwater resources within the alluvium and highly saline aquifers which pose salination risk to both the river and fresher groundwater. Improved delineation of the palaeovalley architecture using AEM, seismic, and borehole datasets has permitted interpretation of the bedrock topography forming the base of the palaeovalley, and which has influenced sediment deposition and the present-day groundwater system pathways and gradients.</div><div><br></div><div>The integrated assessment demonstrates that the alluvial groundwater systems within the study area can be sub-divided on the basis of groundwater system characteristics relevant to water resource availability and management. Broadly, the northern part of the study area has low permeability stratigraphy underlying the river and a generally upward groundwater gradient resulting in limited zone of freshwater ingress into the alluvium around the river. A bedrock high south of Bourke partially restricts groundwater flow and forces saline groundwater from deeper in the alluvium to the surface in the vicinity of the Upper Darling salt interception scheme. From approximately Tilpa to Wilcannia, sufficiently permeable stratigraphy in hydraulic connection with the river and a negligible upward groundwater gradient allows recharge from the river, creating significant freshwater zones around the river within the alluvium.</div><div><br></div><div>Hydrometric and hydrochemical tracer data demonstrate that the alluvial groundwater systems are highly coupled with the rivers. Results support the conceptual understanding that bank-exchange processes and overbank floods associated with higher river flows are the primary recharge mechanism for the lower salinity groundwater within the alluvium. When river levels drop, tracers indicative of groundwater discharge confirm that groundwater contributes significant baseflow to the river. Analysis of groundwater levels and surface water discharge indicates that the previously identified declining trends in river discharge are likely to produce the significant decline in groundwater pressure observed across the unconfined aquifer within the alluvium. Improved quantification and prediction of groundwater-surface water connectivity, water level and flux is considered a high priority for both the Darling River and the wider Murray–Darling Basin. This information will assist in understanding and managing water resource availability in these highly connected systems, and enhance knowledge regarding cultural values and groundwater dependent ecosystems (GDEs).</div><div><br></div><div>This study identifies several aquifers containing groundwater of potentially suitable quality for a range of applications in the south of the study area between Wilcannia and Tilpa and assessed the geological and hydrological processes controlling their distribution and occurrence. Potential risks associated with the use of this groundwater, such as unsustainable extraction, impacts on GDEs, and saline intrusion into aquifers or the river, are outside the scope of this work and have not been quantified.</div>

<div>This report provides an assessment of the viability of Managed Aquifer Recharge (MAR) as a potential supplementary water supply for the township of Wilcannia in the Upper Darling River Floodplain (UDRF) region of northwest New South Wales, Australia, in addition to existing emergency water supply bores and a proposed replacement weir across the Darling River. The Baaka is the traditional name for the Darling River by the Barkindji people. </div><div>This study was completed during the UDRF Project, as part of the Exploring for the Future (EFTF) program—an eight-year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential of mineral, energy and groundwater resources across Australia. </div><div>The UDRF region's heavy reliance on surface water results in inadequate water security during drought, affecting economic prospects, community welfare, and the environment. Geoscience Australia, in partnership with the New South Wales Department of Climate Change, Energy, the Environment and Water (DCCEEW), has undertaken the UDRF Project with the aim of improving groundwater system understanding, assessing groundwater-surface water connectivity, and investigating potential MAR options to enhance drought resilience. </div><div>A MAR scheme is a sustainable proposition in the area compared to groundwater extraction without replenishment, as the semi-confined aquifer doesn’t necessarily represent a viable water resource due to natural recharge of this aquifer taking hundreds of years. As part of the UDRF project, analyses of the hydrodynamic data show that the Darling River is strongly connected to the groundwater systems in the study area, specifically the shallow unconfined aquifers of the Menindee/Coonambidgal Formations and the semi-confined Calivil Formation. The permeable sand-rich unconfined aquifers facilitated groundwater recharge during high river flow periods. Groundwater quality assessments indicate fresh to moderately saline water in the shallower formations, with significantly higher salinity observed in the deeper Renmark Group.</div><div>Four areas potentially suitable for a MAR scheme were identified within the Darling River valley from 2 km to 30 km upstream of Wilcannia, and were delineated through the integrated interpretation of datasets including regional airborne electromagnetics (AEM), ground-based and borehole geophysics, hydrodynamics and hydrochemistry. The four MAR targets were identified based on AEM conductivity threshold of 0.06 S/m, and the borehole water chemistry supports a water quality of &lt;1,200 mg/L TDS (i.e. good to acceptable quality). For a MAR scheme, selecting an area with acceptable quality groundwater is important as the quality of the injected water can remain as acceptable following mixing with the in-situ groundwater. </div><div>Geophysical surveys, including surface magnetic resonance and downhole natural gamma and nuclear magnetic resonance logs, highlight the potential suitability of sand facies within the Calivil Formation as storage aquifer for MAR.&nbsp;Interpretation of AEM models across the four MAR targets suggests that the Calivil Formation aquifer extends beyond the target boundaries and could provide the storage capacity to hold injected water. Additional storage capacity from operating a MAR scheme can only be assessed by a local injection and extraction pilot study.</div><div>In a semi-confined aquifer such as the Calivil Formation, injection of water increases the hydraulic pressure and pushes the acceptable quality in-situ groundwater outwards from the injection sites, displacing the surrounding saline groundwater. The in-situ groundwater of acceptable quality then forms a buffer zone around the injected water, and this improves the recovery efficiency by minimising the flow of saline groundwater towards the extraction well. </div><div>MAR Target 1 is recommended as a potential pilot study area owing to its proximity to Wilcannia and the availability of existing utility infrastructure, such as electricity. Potential sites within the target area were identified for riverbank filtration and Aquifer Storage and Recovery (ASR) wells, considering proximity to the river, groundwater quality, and infrastructure requirements. Proposed ASR sites target the Calivil Formation aquifer, and two of these sites have Paleozoic bedrock directly underlying this storage aquifer. The bedrock acts as an aquitard and minimises the risk of saline groundwater ingress from the Renmark Group, which is present in a palaeovalley adjacent to the two proposed sites.&nbsp;</div><div>If MAR is to be further considered in the region the report offers recommendations for future studies, including the development of pilot ASR sites with drilling to more accurately characterise the sedimentary sequence and the aquifer lithology, and assess the viability of any proposed system.&nbsp;</div>

<div>This dataset comprises hydrochemistry results for groundwater, surface water, and rainwater samples collected as part of the Upper Darling Floodplain groundwater study. Associated methods, interpretation, and integration with other datasets are found in the Upper Darling Floodplain geological and hydrogeological assessment (Geoscience Australia Ecat ID:149689). This project is part of the Exploring for the Future (EFTF) program, an eight-year, $225 million Australian Government funded geoscience data and precompetitive information acquisition program. The dataset contains 68 groundwater samples, 17 surface water samples, and four rainwater samples. Groundwater samples are from the Cenozoic formations within the alluvium of the Darling River, the Great Artesian Basin, and the Murray geological basin. Surface water samples are from the Darling River, and rainwater samples were taken within the study area. Subsets of the samples were analysed for major ions and trace metals, stable isotopes of water (δ2H and δ18O), radiocarbon (14C), stable carbon isotopes (δ13C), strontium isotopes (87Sr/86Sr), sulfur hexafluoride (SF6), chlorofluorocarbon (CFC) isotopes, chlorine-36 (36Cl), noble gases, and Radon-222. The results were used to inform a range of hydrogeological questions including aquifer distribution and quality, inter-aquifer connectivity, and groundwater-surface water connectivity.&nbsp;</div><div><br></div>

<div>Defining and characterising groundwater aquifers usually depends on the availability of data necessary to represent its spatial extent and hydrogeological properties, such as lithological information and aquifer pump test data.&nbsp;In regions where such data is of limited availability and/or variable quality, the characterisation of aquifers for the purposes of water resource assessment and management can be problematic.&nbsp;The Upper Darling River Floodplain region of western New South Wales, Australia, is an area where communities, natural ecosystems and cultural values are dependent on both surface and groundwater resources.&nbsp;Owing to a relative paucity of detailed geological and hydrogeological data across the region we apply two non-invasive geophysical techniques—airborne electromagnetics and surface magnetic resonance—to assist in mapping and characterising the regional alluvial aquifer system.&nbsp;The combination of these techniques in conjunction with limited groundwater quality data helps define an approximate extent for the low salinity alluvial aquifer in a key part of the Darling River valley system and provides insights into the relative water content and its variation within the aquifer materials.&nbsp;This work demonstrates the utility of these key geophysical data in developing a preliminary understanding of aquifer geometry and heterogeneity, thereby helping to prioritise targets for follow-up hydrogeological investigation. Presented at the 2024 Australian Society of Exploration Geophysicists (ASEG) Discover Symposium