U-PB-HF-O CHARACTER OF NEOARCHAEAN BASEMENT TO THE PINE CREEK OROGEN, NORTH AUSTRALIAN CRATON

Evidence based disaster management enables decision makers to manage more effectively because it yields a better informed understanding of the situation. When based on evidence, the decision making process delivers more rational, credible and objective disaster management decisions, rather than those influenced by panic. The translation of fundamental data into information and knowledge is critical for decision makers to act and implement the decisions. The evidence from appropriate information helps both tactical and strategic responses to minimise impacts on community and promote recovery. The information requirements of such a system are quite comprehensive in order to estimate the direct and indirect losses; the short and long term social and economic resilience. Disasters may be of rapid onset in nature like earthquakes, tsunamis and blast. Others are slow onset such those associated with gradual climate change. Climate change has become a real challenge for all nations and the early adaptors will reduce risk from threats such as increased strength of tropical cyclones, storm surge inundations, floods and the spread of disease vectors. The Australian Government has recognised the threats and prioritised adaptation as an opportunity to enhance the nation's existing infrastructure and thereby reduce risk. A thorough understanding of the exposure under current and future climate projections is fundamental to this process of future capacity building. The nation's exposure to these increased natural hazards includes all sectors from communities to businesses, services, lifeline utilities and infrastructure. The development of a National Exposure Information System (NEXIS) is a significant national capacity building task being undertaken by Geoscience Australia (GA). NEXIS is collecting, collating, managing and providing the exposure information required to assess multi-hazard impacts.

In this study, airborne electromagnetics (AEM), high resolution LiDAR, and drilling (100 bores) were acquired to map and assess groundwater resources and managed aquifer recharge options in the River Darling Floodplain. Neotectonic faulting and uplift has previously been described along the north-western margin of the Murray Basin along the adjacent Darling Lineament, however no evidence of neotectonics had previously been identified in the study area. Initial inversions of the AEM data revealed a multi-layered conductivity structure broadly consistent with the hydrostratigraphy identified in drilling. 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 ground and borehole geophysical surveys 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 3D conductivity model revealed that an important Pleistocene aquitard (Blanchetown Clay) confining the main aquifer of interest (Calivil Formation), has an undulating surface, which is locally sharply offset. An 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 top surface of the Blanchetown Clay varies in elevation by 60m. Many of the sharp offsets in the conductivity layers are coincident with lineaments observed in the LiDAR data, and with underlying basement faults mapped from airborne magnetic data. The identification 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. Recognition of faulting in the unconsolidated sedimentary sequence helps explain the rapid recharge of underlying Pliocene aquifers, with neotectonics recognised as a key component of the hydrogeological conceptual model.

Abstract for indonesian Geophysics Conference (HAGI)

A multi-disciplinary, hydrogeological systems mapping approach has been developed to guide development of new geological and hydrogeological conceptual models, and provide a framework for understanding complex hydrogeological and hydrogeochemical processes. Integration of the 3D mapping with hydrochemical and hydrodynamic data provides critical new insights into surface-groundwater interactions and groundwater flow. Using this approach, it has been possible to develop a new understanding of recharge processes, and identify potential recharge and groundwater flow pathways. The new datasets, knowledge and hydrogeological conceptual models provide a reliable basis for the identification, characterisation and initial assessment of groundwater resources and MAR options. To meet the challenge of rapid identification and assessment of potential MAR targets and groundwater resources over the relatively large study area (7,541.5 sq km) within relatively short timeframes (18 months), the only cost-effective method with the ability to resolve key features of the hydrogeological system in the 0-150m depth range was airborne electromagnetics (AEM). The SkyTEM system is a high-resolution helicopter-borne time-domain electromagnetic system, and was developed specifically for high-resolution groundwater and environmental investigations. The SkyTEM survey, validated by borehole and ground geophysics and drilling, successfully delineated the key functional elements of the Darling Floodplain hydrogeological system, and identified potential groundwater resources, zones of river leakage, and a large number of potential MAR targets. The survey revealed significant heterogeneity in the sub-surface electrical conductivity structure, reflecting a complex geology. The survey mapped heterogeneity (and 'holes') within the near-surface aquifers and confining aquitards, while conductivity variations validated by drilling enabled five hydraulic classes (based on grain size) to be mapped within the main aquifers, as well as groundwater salinities. Locally, pump and slug tests, and NMR data were integrated with the AEM data to produce maps of interpreted hydraulic conductivity and aquifer transmissivity. Previously unrecognised faults, and landscape warping and tilting are observed to disrupt hydrostratigraphic units. These data necessitated development of a completely new hydrogeological conceptual model for the study area. This model shows the importance of faulting and erosional 'holes' in aquitards for recharge models. Discrete vertical fault offsets up to 20m produce localised inter-aquifer leakage. Sampling of rainfall, river, lake, groundwater and pore fluids has provided a comprehensive hydrochemical dataset for the alluvial aquifers of the Darling River floodplain. Major ion chemistry highlighted a mixing signature between river waters, the shallow unconfined aquifer and the underlying semi-confined target Calivil aquifer. Hydrochemical analysis including fuzzy-k means (FCM) cluster analysis, integrated with conventional hydrochemical and hydrodynamic analysis also provides invaluable new insights into groundwater processes. Recharge is dominated by river leakage during high flows, when scouring of riverbank mud veneers allows infiltration. In summary, the new hydrogeological conceptual model of the study area has enabled a number of MAR options to be identified and assessed. The integrated, multi-disciplinary approach provides critical insights for developing appropriate conceptual models for groundwater processes and dynamics. This approach provides an invaluable tool for the rapid identification and assessment of MAR options, particularly in shallow sedimentary systems. *Note: corresponding author is Ken Lawrie, as Ross S. Brodie is currently on leave until February.

The discovery of significant volumes of good-quality groundwater resources in the BHMAR project study area, near Menindee, NSW, highlights the likelihood of similar opportunities further upstream in the Darling-Barwon system, and in other data-poor river systems within the Murray-Darling Basin (MDB) and elsewhere. The project identified the importance in the Darling floodplain of river leakage for recharge, especially during high-flow events. Similarities in geomorphology, stratigraphy and tectonics between the study area and the Upper Darling indicate that groundwater resources could occur where recharge pathways through the upper confining aquitard connect scroll-plain tracts to suitable (Calivil Formation equivalent) aquifer cells. Based on project findings, groundwater investigations in the Darling upstream of Menindee along coincident, separate and particularly intersecting scroll-plain tracts should acquire fundamental data to characterise confining aquitards, semi-confined and surficial unconfined aquifers and zones of preferential river leakage. In the Upper Darling, hydrogeological similarities with the BHMAR study area are likely to also provide opportunities for managed aquifer recharge (MAR). The new understanding of recharge mechanisms during flood events has broader implications for the modelling and assessment of surface-groundwater interaction in many Basin rivers. This includes the need to vary stream bed conductance under different stream flow regimes. It is also recommended that estimates of groundwater extraction limits for relevant aquifers should focus on recharge from flood-based episodic river leakage. In the BHMAR study, the integrated use of airborne electromagnetics (AEM), ground electrical methods, sonic drilling and borehole nuclear magnetic resonance (NMR), enabled the rapid characterisation of complex hydrogeological systems, including key groundwater parameters necessary for assessing groundwater resources and MAR options. This methodology has the potential for application in many Australian landscapes (and more broadly). The new geological, geophysical, geochemical and hydrogeological datasets and understanding acquired in this project also have broader implications for fundamental geological studies and mineral exploration.

International efforts to protect the Vulnerable Marine Ecosystems (VMEs) that live on cold seeps and hydrothermal vents requires methods to predict where these features might be in advance of human activity. We suggest an approach to identifying seeps and vents in the CCAMLR region that uses existing data to highlight areas of possible seep and vent communities. These hierarchical criteria can be used to reduce the accidental disturbance of seep communities. We propose a 4 level classification of indicators: Class 1 Areas: VME confirmed by recovery of organisms or observation (video, stills). This level would qualify for VME status and high levels of protection. Class 2 Areas: Seepage/venting present but VME not confirmed. These locations would have a number of indicators of active seepage but VMEs have not been identified. Class 3 Areas: Seepage suspected from geophysical, geochemical or oceanographic observations. These areas have seismic indications of shallow gas or clathrates , structures suggesting fluid escape but where bubble flares or water column plumes have not been detected or where plume has been detected but not tied to an area of sea floor. Class 4 Areas: Area or geomorphic features associated with seepage and vents. These areas are large-scale geomorphic features such as Mid-Ocean Ridge rift valleys or volcanoes where vents are likely but not yet detected. Class 3 and Class 4 areas have been mapped from 45oE to 160oE using global bathymetry grids and seismic data from the SCAR Seismic Data Library.

Integrating surface water and groundwater sampling with pore fluid analysis of cored sediments, combined with fuzzy-k means (FCM) cluster analysis, provides a novel, relatively simple but powerful tool to interpret groundwater processes. This methodology has been applied to a study of shallow (<120m) alluvial aquifers in the Darling River floodplain, Pore fluids were extracted from sediments from 100 sonic-cored bores, and together with surface and groundwater samples, provided a hydrochemical dataset with over 1600 samples and 25 analytes. The FCM cluster analysis used analytes that were present in at least 60% of samples and resulted in samples being classified into eight classes (or hydrochemical facies). Pore fluids and groundwaters with the greatest affinity to the surface water samples were easily identified. In this way, sites with significant active recharge, principally by river leakage, were mapped. Downhole plots of the pore fluid FCM classes provided additional insights into groundwater processes. Comparing the FCM classification of pore fluids within the target (semi)confined aquifer with those from the overlying clay aquitard and shallow aquifer allowed the assessment of vertical inter-aquifer leakage. The FCM cluster analysis also assigns indices to each sample as indicators of how well it relates to each of the eight classes. A simple recharge index was calculated from these FCM indices. This novel approach has provided invaluable new insights into groundwater processes and has assisted greatly with assessing groundwater resources and managed aquifer recharge options.

This collaborative project between Geoscience Australia (GA) and CSIRO aims to use physicochemical measurements, collected from surface overbank sediments as part of the National Geochemical Survey of Australia (NGSA) project, to help validate the ASTER multispectral geoscience maps of Australia. Both data sets have common information including that related to the surface abundance of silica, aluminium, iron, clay, sand and volatiles (including carbonate). The ASTER geoscience maps also provide spatial information about trends of mineral composition, which are potentially related to pH and oxidation state.

Floods are Australia's most expensive natural hazard with the average annual cost of floods estimated at AUD$377 million (BITRE 2008). This figure is likely to have risen following the widespread and devastating floods across eastern Australia that occurred over the summer of 2010-11. The development of tools to support the identification and analysis of flood risk is an important first step in reducing the cost of floods in the community. The Australian Government through Geoscience Australia (GA) has been leading the development of tools which assist in flood intelligence, modelling and damage assessment. An overview of three of these tools will be provided in this presentation. Note: Rest of abstract is too long for space provided.