Integrated geoscience for improved groundwater management in the Upper Darling Floodplain, New South Wales

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 alternative water source that is also important to groundwater-dependent ecosystems.   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.   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. 

This Abstract was submitted/presented to the 2022 Australasian Groundwater Conference 21-23 November (https://www.aig.org.au/events/australasian-groundwater-conference-2022/)