Experience over the past 15 years has demonstrated that the use of airborne electromagnetics (AEM) for near-surface hydrogeological investigations in the Australian landscape context often requires high resolution data to map key functional elements of the hydrogeological system. Optimisation of AEM data therefore requires careful consideration of AEM system suitability, calibration, validation and inversion methods. The choice of an appropriate AEM system for a given task should be based on a comparative analysis of candidate systems, consisting of both theoretical considerations and field studies including test lines over representative hydrostratigraphic targets. In the Broken Hill Managed Aquifer Recharge (BHMAR) project, the SkyTEM AEM system was chosen, after a rigorous selection process, to map a multi-layered stratigraphy in unconsolidated sediments in the top 100 m of the River Darling Floodplain. The AEM acquisition strategy was governed by the need to rapidly identify and assess potential managed aquifer recharge (MAR) and groundwater resource targets over a large area (>7,500 km2), with a high degree of confidence. A flight line spacing of 200-300 m successfully mapped the key elements of the hydrostratigraphy, important neotectonics features, and 14 potential MAR and groundwater targets. Subsequent to successful completion of the project, the AEM data were re-inverted to assess optimal line spacings for the different mapping objectives. Data for the central project area were re-inverted, corresponding to a line spacing of 200 m, 600 m, 1 km, 2 km and 5 km. Analysis of these data show that a number of key features of the hydrogeological system required for MAR target mapping and evaluation are only mapped with high resolution (200m) line spacings. In contrast, the larger groundwater resource targets can be identified at coarser line spacings (even at km spacings). For many groundwater mapping objectives, recconaisance surveys at wide line spacings can be used to identify broad-scale features, with higher resolution data acquired subsequently to address specific questions. This strategy is not always possible in project timelines, and, in the BHMAR project, it was fortunate that a large number of targets were mapped at high resolution simultaneously due to a high failure rate in MAR evaluations.

Abstract for oral presentation at the ASEG-PESA-AIG 2016 25th Geophysical Conference and Exhibition August 21-24, 2016

The keystone element of a system is one which is disproportionately important to the workings of that system relative to its size, abundance and/or distribution. In the Broken Hill Managed Aquifer Recharge (BHMAR) Project, previously unidentified faulting of the unconsolidated sediments beneath the Darling Floodplain, N.S.W., may be considered as such a keystone element, as it is a spatially discrete and subtle element of the regional hydrogeological system that is critical to the recharge of the underlying Pliocene aquifers, and consequentially vital to the viability of MAR and groundwater extraction options in the area. Initial inversions of a regional airborne electromagnetics (AEM) dataset revealed a multi-layered conductivity structure in the top 100m, broadly consistent with the hydrostratigraphy identified in a sonic drilling program. However, initial laterally and spatially constrained inversions showed only moderate correlations with ground data in the near-surface (~20m). As additional information from drilling and complementary hydrochemical and hydrodynamic studies became available, various horizontal and vertical constraints were trialled using a new Wave Number Domain Approximate Inversion procedure with a 1D multi-layer model and constraints in 3D. The resultant improved 3D conductivity model revealed that an important Pleistocene aquitard (Blanchetown Clay) confining the main target aquifer (Pliocene Calivil Formation), has an undulating top which is locally sharply offset. The interpreted top surface suggests that it has been affected by significant warping and faulting, as well as regional tilting due to basin subsidence or margin uplift. Overall, the aquitard top surface varies in elevation by 60m. Several of the sharp offsets in the conductivity layers are coincident with lineaments observed in LiDAR data, and with underlying basement faults mapped from airborne magnetic data. The recognition of neotectonics in this area was made possible through the acquisition of high resolution AEM data and the selection of appropriate horizontal and vertical constraints in inversion procedures. Prior to the structural features being mapped it had not been possible to explain apparently contradictory data, nor develop a plausible hydrogeological conceptual model.

Water security in extensive arid parts of Australia is reliant upon groundwater resources to meet the requirements of remote towns, isolated Aboriginal communities, the pastoral and mining industries and the environment. Greater understanding and predictability of groundwater resources in these regions is imperative for future sustainable water supplies, particularly where mining activities are increasing. Hydrogeological investigations in diverse geologic provinces in Western Australia, South Australia and the Northern Territory have been undertaken in frontier areas to assess palaeovalleys and associated groundwater systems. This work, funded by the Australian Federal Government, appraised various methodologies for regional reconnaissance of arid zone palaeovalley aquifers. Demonstration studies were conducted in large regions, spread across an area comparable in size to Europe. Permian glacial valleys, ancient fluvial valleys and Cenozoic basin-and-range lake settings were investigated. Mapping of buried palaeovalley networks beneath dunefields was a particular focus. Investigations in these little-known regions included integrated application of innovative landscape analysis, geophysics - including Airborne Electromagnetic and ground-based gravity surveys - drilling, bore installation and monitoring and hydrochemical analysis. The depths of the infilled valleys, their geographic extents and stratigraphy, and their groundwater resources were assessed. Substantial heterogeneity of palaeovalley aquifers was revealed. Neotectonism appears to have influenced palaeovalley evolution in some regions. Groundwater quality is variable and aquifer volumes and interconnectivity are yet to be established. A key finding has been the widespread presence of palaeowaters; 14C groundwater ages reveal residence times up to 30,000 years, with only limited, infrequent and localised recharge due to proximity to cyclonic trajectories and topographic position. This multidisciplinary approach to meet regional-scale groundwater resource challenges is applicable in desert lands in other Gondwanan sub-continents and arid to semi-arid zones elsewhere, particularly for reconnaissance investigations in 'greenfield' regions where major groundwater abstractions are required.

This study reports the findings of salt store and salinity hazard mapping for a 20-km wide swath of the Lindsay - Wallpolla reach of the River Murray floodplain in SE Australia. The study integrated remote sensing data, an airborne electromagnetics (AEM) survey (RESOLVE frequency domain system), and lithological and hydrogeochemical data obtained from a field mapping and drilling program. Maps of surface salinity, and surface salinity hazard identified Lindsay and Wallpolla Islands, and the lower Darling Floodplain as areas of high to extreme surface salinity hazard. In the sub-surface, salt stores were found in general to increase away from drainage lines in both the unsaturated and saturated zones. Beneath the Murray River floodplain, salt stores in both unsaturated and saturated zones are high to very high (100 to 300t/ha/m) across most of the floodplain. Sub-surface salinity hazard maps (incorporating mapped salt stores and lithologies, depth to water table and the hydraulic connectivity between the aquifers), identify Lindsay and Wallpolla Islands; the northern floodplain between Lock 8 and Lock 7; and northern bank of Frenchman's Creek as areas of greatest hazard. Overall, the new data and knowledge obtained in this study has filled important knowledge gaps particularly with respect to the distribution of key elements of the hydrostratigraphy and salinity extent across the Murray River and lower Darling floodplain. These data are being used to parameterise groundwater models for salinity risk predictions, to recalculate estimates of evapotranspiration for salt load predictions, address specific salinity management questions, and refine monitoring and management strategies.

Internationally, problems with Aquifer Storage and Recovery (ASR) schemes are commonly attributed to inadequate characterisation of the hydrogeological system and a failure to predict aquifer clogging potential. ASR success relies on defining appropriate design and operational parameters in order to maintain high injection and recovery rates over the long term. The objective of this study was to determine the potential for near-well clogging for a proposed ASR scheme in the Darling Floodplain near Menindee, N.S.W. A methodology was developed to define the water quality criteria and hence minimum pre-treatment requirements to allow long-term ASR operation. Laboratory column studies using four types of treated source water were performed at constant temperature (19C) with light excluded. The source water was turbid raw water from the Darling River and three treated waters including bank filtration, coagulation, and coagulation and granular activated carbon (GAC). Over the 37 days of the experiment, declines in hydraulic conductivity occurred in the columns packed with representative aquifer fluvial sands. The GAC treated town water gave an 8% decline in hydraulic conductivity, which was significantly different from the other three source waters with mean declines of 26-29%. Over the first 3 cm of column length, where most clogging occurred in each column, the mean hydraulic conductivity declined by 10% for GAC treated water compared with 40 to 50% for the other source waters. Polysaccharide concentrations and bacterial numbers in columns when they were dissected and analysed at the end of the experiment confirmed that biological growth was the dominant form of clogging in the treated waters. Further, chemical clogging through precipitation of minerals was found not to occur within the laboratory columns, and dispersion of clay was also found to be negligible. While the laboratory column studies provided useful indicative data on clogging potential, sample preparation required disaggregation and re-packing of aquifer materials. This creates additional uncertainty in the transferability/scaling of changes in hydraulic conductivities (and clogging potential) from the laboratory to the in situ aquifer scale. Future column experiments should be carried out on 'undisturbed' representative core materials.

National wealth generation in Australia is underpinned by the strategic development and security of our water, food and fibre, new energy, and mineral resources. These are all critically dependent on the sustainable management of our groundwater resources. Today, fresh groundwater, through direct extraction, and indirectly through replenishing our river systems, contributes over 50% of Australia's water supplies. Groundwater will also provide an increasingly important higher security store of water in a carbon economy, particularly in the face of increased evaporation and predicted climate drying in the southern half of the continent. In this scenario, the challenges will be even greater to balance productive water use with the environmental needs of our unique terrestrial and aquatic ecosystems. Brackish groundwater will also become increasingly important in new energy development. Despite its mighty contribution to national wellbeing, groundwater remains the 'poor cousin' in the national water debate - often overlooked, insufficiently measured and monitored, frequently misunderstood or taken for granted, and increasingly overexploited. Delegates from Australia's National Groundwater Conference (2010) contributed to a Strategic Paper 'Australia's Groundwater Future'. This paper recommends that groundwater should be elevated to a national priority because it is a critical component of Australia's future water, energy, minerals and food and fibre security, as well as environmental sustainability in a water-insecure world, in a growing nation. The paper recommended that a National Groundwater Priority Program be established, with six programs identified: i. 'Australian Groundwater Resources Inventory'. ii. 'New Energy and Mineral Developments: Regional Groundwater Frameworks and Cumulative Impact Assessments'. iii. 'Increased Water Security Options for Regional Australian Communities, Industries and Agriculture' iv. Assessing Risks to Groundwater Quality, Environmental Assets and Groundwater Dependent Ecosystems (GDEs) v. National Centre for Groundwater Research and Training (NCGRT) vi. 'Groundwater Knowledge Transfer, Capacity Building, and Communication: Bringing Groundwater to the Surface'.

Climate change is expected to increase severe wind hazard in many regions of the Australian continent with consequences for exposed infrastructure and human populations. The National Wind Risk Assessment (NWRA) aims to identify communities subject to high wind risk under present climate, and also those communities which will be most susceptible to any climate change related exacerbation of local wind hazard, requiring an adaptation response. Australia and New Zealand wind loading standards (AS/NZS 1170.2) have established estimates of wind speeds at open atmosphere level. The current study has developed a national methodology for assessing the hazard that peak wind gusts pose at surface level. The estimation of the local wind speeds was evaluated by combining the local wind multipliers (terrain/height, shielding and topographic) for eight cardinal directions with the return period regional wind speeds from AS/NZS 1170.2 on a 25 metre grid across the areas examined for each region using remote sensing techniques. Here we seek to use the 500 year return period wind gust hazard from AS/NZS 1170.2, which is a building design document that seeks to 'envelope' possible wind effects, as a proxy for the regional hazard. These regional wind hazard estimates are envisaged to assist AS/NZS 1170.2 and wind loads for housing AS4055 in reviewing the current building standards for wind loading. The influence of all wind multipliers was aggregated to 1388 statistical local areas (SLA's) over the Australian region using a cumulative probability approach developed utilising the results from all major cities and some towns. Only wind multipliers relevant to current urban and peri-urban regions were evaluated (i.e. only regions containing residential housing were assessed). The cumulative probability approach was used to estimate and aggregate the influence of the wind multipliers for ABS mesh-block regions within SLA areas containing residential structures, for a sample of over 100 SLA's, (capital cities and major towns). This approach was generalised to the entire Australian region by matching non-sampled SLA's with sampled SLA's considering the percent slope, aspect (direction of slope), building density, vegetation cover and the wind loading region. Results in the form of mapped return period gust wind hazard at the SLA level will be presented for both current climate and a range of climate change scenarios, and uncertainties with the present methodology discussed.

2D seismic vibroseis reflection data were acquired in the South Gippsland region of Victoria in June-July 2015 as part of a collaborative project between the Geological Survey of Victoria and Geoscience Australia. The purpose of the survey was to gain an understanding of the geometry and internal structure of the Cretaceous Strzelecki Group that includes up to 100m of volcanics (Older Volcanics) and the underlying Palaeozoic basement of the Melbourne Zone. The depth to the basement varies across the four transects from 400 m to 7 km maximum. The survey was designed to image shallow near surface groundwater targets and basin down to 7 km depth as well as deeper crustal structures. The potential deterioration of seismic data quality due to the presence of the shallow volcanics also required investigation. The Fairfield Zland cableless Nodal system was used with 15 m spacing of point receiver nodes rather than the cable acquisition system previously used by Geoscience Australia with an array of 6-geophone strings with 20m spacing. The advantages of using the nodal system are (a) more flexibility in design of the survey, especially in rugged terrains, or urban areas, and (b) significantly easier deployment of the equipment with much less downtime. A number of tests were carried out prior to the acquisition program to compare various sweep parameters and to optimise the acquisition parameters for a range of targets, both shallow and deep. These tests included linear sweeps with expanded bandwidth and non-linear customised high-dwell sweeps. High fold seismic reflection data (nominal fold 600) were collected to improve signal to noise ratio using two 50,000 lb vibroseis units for the source array. In an attempt to overcome the shallow volcanic layer issue data were recorded to long offsets up to 10 km, and not less than 4.5 km where the roads in the area were crooked. Despite the effort of collecting the high fold data and long offsets, the quality of seismic data was significantly degraded due to several reasons including acquisition issues, and, more likely, geology of the region that is not easy to image using conventional seismic techniques. Attenuation appears to have had a substantial effect on seismic data quality, resulting in a loss of energy. The most significant issue seems to be a high level of noise observed in the data, especially at far offsets. This noise is more likely related to environmental noise in the region and due to nodes not being fully buried. However, the seismic data previously acquired in the same area using a cable system also exhibits poor data quality. This suggests a `geological factor as a major issue for good quality imaging of the crust in this area. During the acquisition stage some general issues with the current nodal system were experienced, such as delays and problems of data harvesting and re-construction of shot gathers. This created a problem with real time monitoring of the data quality and resulted in difficulties in modifying acquisition parameters or calling shutdowns due to poor weather conditions. One example of lack of real time monitoring was a leap second event that caused timing errors that was identified only a few days after the event. The data processing is currently being undertaken and is expected to be completed in June 2016. The advanced processing stream includes Pre-Stack Time and Depth Migration, DMO, Common Reflection Surface and Post-Stack Migration processing. The preliminary results show good images of the basin in the shallower section but little reflectivity observed in middle and low crust.

Short abstract for SCAR 2016 conference.