<div>The Darling River is the primary water source for communities on the Upper Darling River Floodplain (UDF) in arid northwest New South Wales. A 70% reduction in mean annual flow down the Darling over the past 80 years, due to droughts and over-extraction, has resulted in critical water shortages and water quality issues for communities and ecosystems. Presently there is a limited understanding of the spatial extent and controls on the occurrence of lower salinity groundwater within the surrounding Darling Alluvium; a possible&nbsp;alternative water source that is also important to groundwater-dependent ecosystems.</div><div>&nbsp;</div><div>The UDF project, part of the Australian Government’s Exploring for the Future program is working in collaboration with State partners to collect and integrate new data with existing hydrogeological knowledge. The project aims to improve the hydrogeological understanding of the region to help inform water management decisions and increase water security. A key focus of the project is the Darling Alluvium (DA)—a closed regional groundwater system comprising unconsolidated Cenozoic sediments deposited primarily by the paleo and current Darling River systems and their tributaries. Connectivity with aquifers of varying quality, within the underlying Murray and Great Artesian Basins, is also being investigated. </div><div>&nbsp;</div><div>Integration of airborne electromagnetic (AEM), hydrometric and hydrochemical data with lithology logs and geological maps has revealed a broad trend in groundwater–surface water dynamics. In the upper reaches of the floodplain systems appear to be disconnected, while in the lower reaches losing stream conditions prevail. In the losing stream setting, resistive AEM signatures, at depths of up to 60 m below ground level and extending laterally for several hundred metres from the river, indicate a hydraulic gradient away from the river. Low salinity groundwater measured in shallow bores suggest the potential for a significant quality groundwater resource. Further investigations will improve confidence in the geometry of fresh water zones, recharge rates, connectivity with underlying saline aquifers and relationships with groundwater-dependent ecosystems.&nbsp;</div><div><br></div>This Abstract was submitted/presented to the 2022 Australasian Groundwater Conference 21-23 November (https://www.aig.org.au/events/australasian-groundwater-conference-2022/)

<div>Groundwater is critical to the survival of a range of ecosystems in Australia through provision of a direct source of water to plants with suitable root systems, and through discharge into surface water systems. Effectively managing groundwater dependent ecosystems (GDEs) alongside other water demands requires the ability to identify, characterise, and monitor vegetation condition.&nbsp;<em>&nbsp;</em><br> As part of the <a href="https://www.eftf.ga.gov.au/upper-darling-river-floodplain-groundwater-study">Exploring for the Future Upper Darling Floodplain</a> (UDF) groundwater project in western New South Wales, we present results from a study testing the suitability of two novel methods (a) recently available tasselled cap percentile products with national coverage through Digital Earth Australia, and (b) dry-conditions interferometric radar (InSAR) coherence images for mapping vegetation that is potentially groundwater dependent. <em>&nbsp;</em></div><div><em>&nbsp;</em></div><div>A combination of greenness and wetness 10th percentile tasselled cap products delineated terrestrial and aquatic GDEs with greater accuracy than existing regional ecosystem mapping, demonstrating the utility of these products for GDE identification. These results suggest the tasselled cap products can be used to support and refine the existing GDE mapping for this region, and further testing of their suitability and application for other regions is warranted.&nbsp;<em>&nbsp;</em></div><div><em>&nbsp;</em></div><div>The InSAR coherence images produced good agreement with the Bureau of Meteorology national GDE Atlas for areas of high probability of groundwater dependence. Although data availability and technical expertise currently lags behind optical imagery products, if research continues to show good performance in mapping potential GDEs and other applications, InSAR could become an important line of evidence within multi-dataset investigations.&nbsp;<em>&nbsp;</em></div><div><em>&nbsp;</em></div><div>Key next steps for improving the utility of these techniques &nbsp;are (a) comparison with vegetation condition data, and (b) further assessment of the likelihood of groundwater dependence through assessing relationships between vegetation condition and groundwater, surface water, and soil moisture availability.<em>&nbsp;</em></div><div>&nbsp;</div><div>This abstract was submitted/presented to the 2023 Australasian Groundwater / New Zealand Hydrological Society (AGC NZHS) Joint Conference (https://www.hydrologynz.org.nz/events-1/australasian-groundwater-nzhs-joint-conference)</div>

<div><strong>Output Type: </strong>Exploring for the Future Extended Abstract</div><div><br></div><div><strong>Short Abstract: </strong>Communities and ecosystems along the Darling-Baaka River have been impacted by critical water shortages and water quality issues including high salinity, algal blooms, and fish kills due to declining surface water flows. The river is characterised by naturally highly variable flows and is the primary water source for the region, but extraction and a meteorological drying trend associated with climate change have caused declines in discharge of 53–73% since the advent of post-settlement agriculture and industry. Understanding of the spatial extent, quality, and useability of lower salinity groundwater within the surrounding Darling Alluvium, which could provide an alternative and potentially more sustainable water source, was previously limited. Here we present the findings of an integrated study combining modelled ground and airborne geophysical data, groundwater and surface water levels, hydrochemistry, lithology, and remote sensing data to delineate groundwater systems and understand the geological and hydrological controls on their occurrence. The resolution and breadth of datasets acquired and collated permit mapping of the key factors controlling occurrence and quality of groundwater aquifers, namely basement topography and hydrostratigraphy, groundwater-surface water dynamics, and inter-aquifer connectivity. On this basis the study area can be sub-divided into regions with distinctive aquifer distribution and quality, recharge mechanisms, and pressure gradients between aquifers. We also showed that the groundwater levels in the unconfined aquifer have declined, an expected outcome of the decline in discharge in the Darling-Baaka River which forms the primary recharge mechanism for the alluvial aquifers. These outputs have direct implications for key management questions including location and quantity of potentially useable groundwater, risk of saline groundwater up-coning or discharging to the river, and likelihood of groundwater extraction impacting river flows and groundwater dependent ecosystems.&nbsp;</div><div><br></div><div><strong>Citation: </strong>Buckerfield, S., McPherson, A., Tan, K.P., Walsh, C., Buchanan, S., Kilgour, P., Suckow, A., Raiber, M., Symington, N. & Pincus, J., 2024. Groundwater systems of the Upper Darling-Baaka River Floodplain. In: Czarnota, K. (ed.) Exploring for the Future: Extended Abstracts. Geoscience Australia, Canberra. https://doi.org/10.26186/149718</div>