A Trans-disciplinary Hydrogeological Systems Analysis Approach for Identifying and Assessing Managed Aquifer Recharge Options: Example from the Darling River Floodplain, N.S.W., Australia

Surface water availability and quality generally limits managed aquifer recharge (MAR) opportunities in inland Australia's highly salinized landscapes and groundwater systems. Economic factors also commonly limit MAR investigations to shallow freshwater groundwater systems near existing infrastructure. Aquifer opportunities lie mainly in zones of fresh groundwater in relatively thin fluvial sedimentary aquifer systems with highly variable hydraulic properties. As part of a broader strategy to identify water savings in the Murray-Darling Basin, the Broken Hill Managed Aquifer Recharge (BHMAR) project was tasked with identifying and assessing MAR and/or groundwater extraction options to reduce evaporative losses from existing surface water storages, secure Broken Hill's water supply, protect the local environment and heritage, and return water to the river system. A trans-disciplinary research approach was used to identify and assess MAR options across a broad area of the Darling River floodplain. This methodology enabled the team to recognise fundamental problems in discipline approaches, helped identify critical data gaps, led to significant innovation across discipline boundaries, was critical in the development of a new hydrogeological conceptual model, facilitated development of new models of landscape, geological and tectonic evolution of the study area, and enabled completion of pre-commissioning maximal and residual MAR risk assessments. An airborne electromagnetics (AEM) survey, acquired over a large (>7,500 sq km) area of the Darling Floodplain, enabled rapid identification of a multi-layer sequence of aquifers and aquitards, while a phased assessment methodology was developed to rapidly identify and assess over 30 potential MAR targets (largely in fresh groundwater zones within palaeochannels and at palaeochannel confluences). Hydraulic properties were confirmed by a 7.5 km drilling program (100 sonic and rotary mud holes), and complementary field (including limited pump tests) and laboratory measurements. Recognition of significant Neogene-to-Present faulting, warping and tilting of the unconsolidated sediments (using AEM, airborne magnetics, regional gravity, LiDAR and drilling data) was critical to understanding recharge, inter-aquifer leakage and potential environmental impacts of MAR options. A program of borehole Nuclear Magnetic Resonance (NMR) logging provided a record of near-continuous variations in K through the saturated sedimentary sequence, with the NMR data integrated with other borehole and AEM data to produce 3D maps of aquifer transmissivity. A priority site was identified where aquifer storage and recovery (ASR) options were assessed. Maximal and residual risk assessments of 12 hazard types included hydrogeological modelling, laboratory column clogging studies and geochemical assessment to identify source water treatment requirements. The study found that the residual scientific/technical risks for ASR at the priority site are low if the supplementary water treatment trains are included.