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.
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.
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.
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.
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 <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.
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. 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.
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.
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.
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.
