Poster prepared for International Association of Hydrogeologists Congress 2013 Surface-groundwater interactions are often poorly understood. This is particularly true of many floodplain landscapes in Australia, where there is limited mapping of recharge and discharge zones along the major river systems, and only generalised quantification of hydrological fluxes based on widely spaced surface gauging stations. This is compounded by a lack of temporal data, with poor understanding of how surface-groundwater interactions change under different rainfall, river flow and flood regimes. In this study, high resolution LiDAR, in-river sonar, and airborne electromagnetic (AEM) datasets (validated by drilling) have been integrated to produce detailed 3-dimensional mapping that combines surface geomorphology and hydrogeology. This mapping enables potential recharge zones in the river and adjacent landscape to be identified and assessed under different flow regimes. These potential recharge zones and groundwater flow pathways were then compared against the spatial distribution of discontinuities in near-surface and deeper aquitard layers derived from the AEM interpretation. These 3D mapping constructs provide a framework for considering groundwater processes. Hydrochemistry data, allied with hydraulic data from a bore monitoring network, demonstrate the importance of recharge during significant flood events. In many places, the AEM data also affirm the spatial association between fresher groundwater resources and sites of river and floodplain leakage. At a more localised scale, hydrogeochemical data allows discrimination of lateral and vertical fluxes. Overall, this integrated approach provides an important conceptual framework to constrain hydrogeological modelling, and assessments of sustainable yield. The constructs are also invaluable in targeting and assessing managed aquifer recharge (MAR) options.

The greater Eromanga Basin is an intracratonic Mesozoic basin covering an area of approximately 2,000,000 km2 in central and eastern Australia. The greater Eromanga Basin encompasses three correlated basins: the Eromanga Basin (central and western regions), Surat Basin (eastern region) and the Carpentaria Basin (northern region). The greater Eromanga Basin hosts Australia's largest known resources of groundwater as well as major onshore hydrocarbon resources, including significant coal bed methane (CBM) that has been discovered in recent years, and also contains extensive hot-sedimentary aquifer geothermal energy systems. Additionally, the basin has potential as a greenhouse gas sequestration site and will likely play a key role in securing Australia's energy future. Finally, although no major metallic mineral deposits are currently known in the greater Eromanga Basin, there is significant potential for undiscovered uranium mineralisation. A 3D geological map has been constructed for the greater Eromanga Basin using publicly available datasets. These are principally drilling datasets (i.e. water bores; mineral and petroleum exploration wells) and the 1:1,000,000 scale Surface Geology Map of Australia. Geophysical wireline logs, hydrochemistry, radiometrics, magnetic and gravity datasets were also integrated into the 3D geological map. This study has highlighted the potential of the southwest margin of the Eromanga Basin and the Euroka arch region to contain sandstone-hosted uranium mineral systems. The report demonstrates how incorporating disparate datasets in a 3D geological map can generate an integrated mapping solution with diverse applications: 1. Provide new insights into the geology and geodynamic evolution of the basin. 2. Identify hydrocarbon resource plays. 3. Assess the basin's mineral potential (e.g., sandstone-hosted uranium mineral systems). 4. Assess the basin's geothermal potential (e.g., hot-sedimentary aquifer geothermal systems). 5. Provide resource management information (e.g., groundwater). 6. Identify potential contaminants in groundwater.

This report presents key results from the Ti Tree Basin project completed as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. Hydrogeological data acquisition and interpretation in the Ti Tree Basin, Northern Territory, was undertaken by Geoscience Australia as part of the EFTF Program. Located ~150 km north of Alice Springs, the Cenozoic basin hosts regionally significant groundwater resources, relied upon by communities, irrigators and pastoralists. Although the basin has been extensively studied over several decades, critical information gaps still remain, particularly for the deep groundwater system (>80 m depth). Work combining new geophysical and hydrochemical data with pre-existing datasets has revealed a more complex basin hydrogeology. Mapping based on airborne electromagnetics (AEM) has identified complex structural controls on the distribution of the deep basin sequence, with consequences for aquifer compartmentalisation, regional groundwater flow and aquifer connectivity. The mapping also shows where the basin sediments are much thicker than previously drilled. The hydrochemical assessment highlighted the complexity in groundwater recharge mechanisms, showing that the rainfall threshold for effective recharge and the role of evaporation are not consistent across the floodout zones in the basin. The EFTF products provide guidance for future hydrogeological investigations. In particular, there is evidence from historic drilling for potentially useful groundwater resources in the underexplored deep basin sequence. The EFTF program has expanded the knowledge base and datasets for the Ti Tree Basin. Collectively, these are valuable assets not just for basin groundwater management but also for the broader understanding of groundwater resources and processes in central Australia.

This report presents key results of the Ti Tree Basin study completed as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. As part of EFTF, Geoscience Australia undertook an assessment of available and new hydrochemical data collected in the Ti Tree Basin, Northern Territory. The basin is one of the four water control districts within the Southern Stuart Corridor Project area. Communities, irrigation farms and pastoral stations in the basin rely on groundwater, and extensive groundwater sampling and hydrochemical investigations have been undertaken over the past 50 years. An opportunity was recognised to collate and interpret the existing data, supplemented by new EFTF data, not only to add value to the understanding of groundwater processes in the basin itself but also to provide a useful knowledge base for other groundwater resources in the region that are poorly understood. This study largely relied on the available groundwater analysis data from the Northern Territory Department of Environment and Natural Resources database, supplemented by publicly available analyses from other sampling campaigns, including the EFTF, totaling 1913 groundwater samples across the district. The key findings of the study are: • The hydrochemistry data, particularly on salinity (total dissolved solids (TDS)), ion ratios (e.g. HCO3/Cl, Cl/(Cl+HCO3), Cl/(Cl+HCO3+SO4), Na/Cl) and radiocarbon (14C) could be used to map the three major recharge areas for the basin—the floodout of the Woodforde River to the west, the floodout of Allungra Creek in the basin centre, and the eastern basin margin. This is consistent with the current accepted interpretation that recharge is dominated by episodic run-on and infiltration in drainage floodout areas, driven by intense rainfall events that generate runoff in upland basement headwaters and ephemeral flows in basin creeks. There are no hydrochemical indicators of recharge in the vicinity of the channelised reaches of the basin creeks (i.e. both Woodforde River and Allungra Creek), located upstream of the floodouts. • From a groundwater resource perspective, the Allungra Creek floodout has broadly the best combination of low-salinity groundwater (median TDS = 740 mg/L) and bore yield statistics (median = 10 L/s). The Woodforde River floodout also has areas with high-yielding bores (>10 L/s) of fresh groundwater (<1000 mg/L), with the borehole distribution suggesting that the fresh groundwater resource is significantly more extensive to the west of the river than that previously mapped. The eastern basin margin generally has low-salinity groundwater (median TDS = 775 mg/L) but lower bore yields (median = 4.4 L/s). • There are differences in the recharge characteristics of the three floodout areas, due to differences in drainage catchments and floodout hydrogeology. The Woodforde River floodout has the most depleted stable isotopes, interpreted to be due to a higher rainfall/runoff threshold for recharge (>150 mm/month). It also has the largest isotopic range and the best δ18O-δ2H linear regression, suggesting the most influence of evaporation, such as a longer period of surface water ponding. In comparison, the stable isotope signature for Allungra Creek groundwaters suggests a lower rainfall/runoff threshold for recharge (>100 mm/month) and low evaporative influence, hence relatively rapid infiltration. This is also inferred to be the case for the low-salinity eastern basin margin groundwaters. For both Woodforde River and Allungra Creek, modern recharge is indicated by groundwaters with high radiocarbon activity (14C percent modern carbon (pMC) >70). For the eastern basin margin, radiocarbon activity is low to moderate (14C pMC 20–50). This is interpreted to reflect a longer travel time in the unsaturated zone. • In the floodout areas, the dominant hydrogeochemical process relating to the fresh groundwater is water–rock interactions. Groundwater tends to be the least evolved Ca(Mg)-HCO3 or transitional Na(K)-HCO3 water type, according to Chadha plots. Zones of prevalence of carbonate-gypsum dissolution or Na-silicate weathering could be mapped using indicators such as cation chloride ratio. Ion exchange is also a likely process in these fresh groundwaters, as inferred from chloro-alkaline indices. • Groundwater salinity is higher away from the floodout areas. This increased salinity is due to evapotranspirative concentration in addition to water–rock interactions, as inferred from ion ratios, including Cl/Br. Stable isotopes indicate that transpiration of groundwater by vegetation accessing the watertable, rather than direct evaporation, is the dominant process in these areas. This process is particularly evident in the Wilora Palaeochannel, the northern extension of the basin, which generally has the highest groundwater salinities (median TDS = 1575 mg/L), the lowest bore yields (median = 1.9 L/s) and the greatest prevalence of shallow watertables (<15 m). With higher salinities, groundwaters tend to be the evolved Ca(Mg)-Cl(SO4) and Na(K)-Cl(SO4) water types and potentially influenced by reverse ion exchange processes. • Mountain-front recharge has previously been proposed as an additional recharge mechanism, notably near the southern basin margin. Although sampling is limited in this area, hydrochemical indicators such as low HCO3/Cl, high Na/Cl and evolved Na(K)-Cl(SO4) water type suggests that active recharge is not significant. The watertable is deep along the southern basin margin (>50 m), so groundwater chemistry can be strongly influenced by processes during downward infiltration through a thick unsaturated zone. • Limited sampling of deeper bores (>80 m), potentially in the Hale Formation, generally have the characteristics of being more saline and lower yielding compared to bores in the shallow groundwater resource (particularly from 40 m to 80 m). However, there are deep bores with good yields of fresh groundwater; of 57 bores in the basin with interval depths exceeding 80 m, eight (14%) have the combination of yield >5 L/s and salinity <1000 mg/L. The deeper groundwaters are typically Ca(Mg)-Cl(SO4) and Na(K)-Cl(SO4) water types, with the latter, more evolved, water type dominating at depths >120 m. There are very few stable isotope analyses for the deeper groundwaters, but these are within the isotopic range for the shallow groundwaters in the same area, suggesting similarity in recharge processes and a degree of aquifer connectivity. Likewise, there are very few radiocarbon analyses for deeper groundwaters (depth >60 m), but these consistently show low 14C activity (pMC <40). The higher salinities, evolved water types and low 14C activity reflect longer residence times in the deeper groundwater system. The study highlighted that floodout recharge, involving episodic flow of basin creeks from headwater catchments, is the most dominant mechanism, rather than direct infiltration from large rainfall events. The study also identified that recharge characteristics, particularly the rainfall threshold for effective recharge and the role of evaporation, are not consistent across the floodout zones in the basin. This likely reflects differences in upland catchment size and geology, as well as floodout landform and hydrogeology. The study also highlighted the importance of groundwater-dependent vegetation in the basin, with dominance of transpiration of groundwater rather than direct evaporation. The groundwater hydrochemistry datasets and interpretation maps can support informed water management decisions within the basin. For example, improved understanding of the spatial and temporal distribution of recharge is not only needed for defining groundwater extraction limits but also used in strategies such as managed aquifer recharge. The EFTF work adds to the knowledge base and datasets that have developed over decades for the Ti Tree Basin, which are also valuable assets for broader understanding of groundwater resources in central Australia.

This service provides access to hydrochemistry data (groundwater and surface water analyses) obtained from water samples collected from Australian water bores or field sites.

This report presents a summary of the groundwater hydrochemistry data release from the Ti Tree project conducted as part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. This data release records the groundwater sample collection methods and hydrochemistry and isotope data from monitoring bores in the Alice Springs project area, Northern Territory (NT). The Ti Tree project is a collaborative study between Geoscience Australia and the NT Government. Hydrochemistry and isotope data were collected from existing and newly drilled bores in the Ti Tree area

This report presents a summary of the groundwater hydrochemistry data release from the Western Davenport project conducted as part of Exploring for the Future (EFTF). This data release records the groundwater sample collection methods and hydrochemistry and isotope data from monitoring bores in the Western Davenport project area, Northern Territory (NT). The Western Davenport project is a collaborative study between Geoscience Australia and the NT Government. Hydrochemistry and isotope data were collected from existing and newly drilled bores in the Western Davenport area.

This report presents a summary of the groundwater hydrochemistry data release from the Alice Springs project conducted as part of Exploring for the Future (EFTF). This data release records the groundwater sample collection methods and hydrochemistry and isotope data from monitoring bores in the Alice Springs project area, Northern Territory (NT). The Alice Springs project is a collaborative study between Geoscience Australia and the NT Government. Hydrochemistry and isotope data were collected from existing and newly drilled bores in the Alice Springs area.

We present a multifaceted hydrogeological investigation of the McBride and Nulla basalt provinces in the Upper Burdekin region, north Queensland. The project aims to better understand their key groundwater system processes to inform future development and water management decisions. This work, carried out as part of the Exploring for the Future Upper Burdekin Groundwater Project, has shown that basalt aquifers in each province are typically unconfined where monitored. Groundwater recharge is widespread but highly variable, largely occurring within the boundaries of the basalt provinces. Groundwater salinity based on electrical conductivity is <1000 μS/cm in the McBride Basalt Province (MBP) and up to 2000 μS/cm in the Nulla Basalt Province (NBP). Groundwater levels have been declining since 2011 (following major flooding in Queensland), showing that the study period covers a small fraction of a longer-functioning dynamic groundwater system. The basalt provinces contain distinct lava flows, and the degree of hydraulic connectivity between them is unclear. Despite similarities in their rock properties, the geometry of lava emplacement leads to different groundwater flow regimes within the two basalt provinces. Radial flow away from the central high elevations towards the edges is characteristic of the MBP, while regional flow from west to east dominates the NBP. Basalt aquifers in both provinces support a range of groundwater-dependent ecosystems, such as springs, some of which sustain flow in tributaries of the Burdekin River. Where streams intersect basalt aquifers, this also results in direct groundwater discharge. Springs and perennial tributaries, particularly emanating from the MBP, provide important inflows to the Burdekin River, especially in the dry season. This work has highlighted that management of MBP and NBP groundwater sources is crucial for maintaining a range of environmental assets in the region and for ensuring access for existing and future users. <b>Citation:</b> Ransley, T.R., Dixon-Jain, P., Cook, S.B., Lai, E.C.S., Kilgour, P., Wallace, L., Dunn, B., Hansen, J.W.L. and Herbert, G., 2020. Hydrogeology of the McBride and Nulla basalt provinces in the Upper Burdekin region, north Queensland. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

This web service provides access to geological, hydrogeological and hydrochemical digital datasets that have been published by Geoscience Australia for the Great Artesian Basin (GAB).