Salinity in the River Murray and in adjacent floodplains of south‐central Australia, has important environmental, economic and social consequences. Methods to monitor the temporal state of river and particularly river‐groundwater interactions, have been in place for many years now. However, few have the capacity to define variability at a resolution appropriate for developing effective salinity management strategies, such as salt interception schemes. The use of geophysical methods for rapid high resolution mapping of river sediments has been successfully trialed in Australia, particularly using the "in stream" NanoTEM, a time domain ground EM system, deployed in a boat with the transmitter and receiver towed behind on a rigid floating boom. More recently, tests have been conducted using two different helicopter EM systems; a frequency domain EM system (FDHEM) and a time‐domain EM system (TDHEM). Comparisons between conductivity‐depth sections derived from the "in stream" NanoTEM and the airborne datasets suggest that the different approaches are comparable. This paper examines the potential of using the FDHEM RESOLVE system as basis for mapping reaches of the river that contribute to elevated salt loads in the Murray River to the south east of Mildura in Victoria. The advantages of the airborne systems become more apparent when data coverage and acquisition costs are considered, particularly in a situation where a parallel swath approached is employed. This entails the acquisition of adjacent lines of EM data along the centre and along the margins of the river. We suggest this approach provides for a better understanding of recharge and discharge processes and links between the floodplain and the main‐river channel. Compared with data acquired along the river alone, this study demonstrated our ability to use Helicopter EM data to map losing and gaining (from a salt load perspective) stretches of the river and to provide insight into which parts of the groundwater‐floodplain system were significant contributors to river salt loads. The rapid acquisition of airborne EM data makes these systems more suited to providing temporal snapshots of a river‐floodplain environment during dramatic climatic events, such as flooding. In the Murray basin this may assist our understanding of how salt stores are mobilised during such occasions.
Increasing salinity in the River Murray is well documented and is of concern environmentally, economically and socially. The Murray Darling Basin Commission and the Mallee Catchment Management Authority engaged the authors to collect base-line in-stream NanoTEM data within the River Murray from Lock 1 to Mallee Cliffs (675 km). This is a new application of a high resolution fast sampling Transient Electro-Magnetic (TEM) system, towed behind a boat, taking soundings every seven to ten metres along the river. The observed NanoTEM response was interpreted against the current understanding of the regional hydrogeology and groundwater processes in and around the river. This paper summarises some of the results from this investigation. The observed response correlates strongly with previously mapped major changes in underlying lithostratigraphy along the Murray River, and with gaining and losing reaches of the river. The extensive length of the survey provides an insight into potential interactions between the river, floodplain and groundwater, but does not replace the need for focussed ground-truthing programs to examine specific correlations. This rapid, portable technique should be applicable outside the Murray-Darling Basin as well as at additional locations within the Basin.
This paper examines the potential of using the FDHEM RESOLVE system as basis for mapping reaches of the river that contribute to elevated salt loads in the Murray River to the south east of Mildura in Victoria. The advantages of the airborne systems become more apparent when data coverage and acquisition costs are considered, particularly in a situation where a parallel swath approached is employed. This entails the acquisition of adjacent lines of EM data along the centre and along the margins of the river. We suggest this approach provides for a better understanding of recharge and discharge processes and links between the floodplain and the main-river channel. Compared with data acquired along the river alone, this study demonstrated our ability to use Helicopter EM data to map losing and gaining (from a salt load perspective) stretches of the river and to provide insight into which parts of the groundwater-floodplain system were significant contributors to river salt loads. The rapid acquisition of airborne EM data makes these systems more suited to providing temporal snapshots of a river-floodplain environment during dramatic climatic events, such as flooding.
In the lower Murray-Darling Basin, most groundwater discharges to the floodplain of the River Murray. Most of the groundwater is of high salinity and therefore can transfer significant salt loads into the river. To mitigate saline groundwater intrusion into the river, salt interception schemes (SIS) have been commissioned since the early 1990s. The SIS intercept high-salinity groundwater flow adjacent to the river floodplain and the intercepted water is pumped to distant evaporation basins. The in-river transient electromagnetic (RTEM) geophysics technique can be used to infer saline groundwater discharge areas and to inform SIS locations. RTEM results have also been used, albeit qualitatively, in the monitoring and evaluation of the performance of SIS. A methodology for evaluating SIS performance has been developed based on the area above the cumulative frequency distribution (ACFD) of RTEM riverbed-only resistivities. In addition to RTEM maps and cross-sections, the ACFD characterises a river reach with a single number. Increases in ACFD, from pre-to post-SIS RTEM surveys, indicate the changing groundwater flow regime and the building of freshwater lenses.
AbstractSalt interception schemes (SIS) have been developed to manage high salt loads and to improve the health of the River Murray, both in the Riverland (South Australia) and Sunraysia (Victoria/NSW) areas. Currently SIS at Loxton and Bookpurnong, in the South Australian Riverland are being developed, both incorporating borefields in the Loxton-Parilla Sands aquifer to intercept saline groundwater flux from groundwater mounds that have formed beneath irrigated areas. A detailed interpretation of borehole geology, ground and airborne geophysics, combined with the analysis of sediments for the Loxton Sands and underlying Bookpurnong Beds has resulted in an improved hydrogeological model for the area. Lateral and vertical changes in sedimentary facies associated with the main aquifer systems relevant to the SIS are now better understood. This is an important precursor in the development of a predictive model for aquifer hydraulic properties using hydrogeological and geophysical data. Relatively thin zones of high hydraulic conductivity, associated with the lower Loxton sands sedimentary package, are characterized by slightly reduced electrical conductivity response at the watertable, and represent a target for ground and airborne EM systems. These zones have been identified as elements of a basin-wide beach-barrier strandline sequence that developed in the Pliocene. Results from the constrained inversion of helicopter EM data have helped to better define the geometry of this sedimentary system, the location of these zones and have provided elements of a predictive framework for a more informed approach to the design, development and potential performance of the Loxton Sands SIS borefields.Keywords: Salt interception schemegeophysicsloxton Parilla Sandsaquifersgroundwater Additional informationNotes on contributorsT J MundayEmployed with CSIRO Exploration and Mining, and working in the CRC for Landscapes, Environment and Mineral Exploration, Tim Munday has over 20 years research experience in the application of remote sensing and geophysical technologies to exploration and the environment. His current research interests concern the role and application of geophysical data in providing an improved biophysical foundation for natural resource management. He has also been working on the use of geophysics in the exploration of concealed ore deposits in regolith dominated terrains.
New Miocene and Quaterna1y foraminiferid faunas have been recovered from previously unrecorded localities onshore near Penguin and Strahan, and at nine offshore localities off northwestern, northeastern and southeastern Tasmania.Most Miocene benthic forms found in these samples are well known from other Tasmanian Tertiary sections but a few previously unreported taxa are recorded in Tasmania for the first time.Two samples from off northeastern Tasmania are Miocene.The sample from southeastern Tasmania is Early Miocene with Quaternary overlying it.Pebbles from Ocean Beach, north of Strahan, contain earliest Middle Miocene faunas.Other samples from off northeastern and northwestern Tasmania contain Quaternary faunas which probably reflect both periods oflower sea level and cool water and also periods of higher sea level and warmer water.These samples extend the range of Miocene calcareous sediments much farther south on both west and east coasts of Tasmania.They also reinforce the pattern of Tasmanian Neogene sedimentation cycles (earliest Early Miocene, latest Early-earliest Middle Miocene, mid Late Pliocene) identified previously.
Successful implementation of a salt interception schemes (SIS) requires monitoring to determine locations where the scheme needs revision. Current monitoring methods involve near-surface water-salinity measurements, which are affected by water-flow displacement. A survey method that can determine the salinity of water contained in the top few metres of alluvial sediments immediately beneath the river would be a more accurate tool for SIS monitoring.A fast sampling Transient EM technique is investigated as a potential tool for imaging the conductivity of the top 5m of sediment, and thus monitoring the Waikerie SIS in South Australia’s Riverland. A towed TEM array was used to collect 9km of data that shows resistive anomalies correlating with SIS production bores. The system has the advantage of being a small, manageable array and the short inversion time allows same-day interpretation.
Salinity in the River Murray and in adjacent floodplains of south-central Australia, has important environmental, economic and social consequences. Methods to monitor the temporal state of river and particularly river-groundwater interactions, have been in place for many years now. However, few have the capacity to define variability at a resolution appropriate for developing effective salinity management strategies, such as salt interception schemes. The use of geophysical methods for rapid high resolution mapping of river sediments has been successfully trialed in Australia, particularly using the “in stream” NanoTEM, a time domain ground EM system, deployed in a boat with the transmitter and receiver towed behind on a rigid floating boom. More recently, tests have been conducted using two different helicopter EM systems; a frequency domain EM system (FDHEM) and a time-domain EM system (TDHEM). Comparisons between conductivity-depth sections derived from the “in stream” NanoTEM and the airborne datasets suggest that the different approaches are comparable. This paper examines the potential of using the FDHEM RESOLVE system as basis for mapping reaches of the river that contribute to elevated salt loads in the Murray River to the south east of Mildura in Victoria. The advantages of the airborne systems become more apparent when data coverage and acquisition costs are considered, particularly in a situation where a parallel swath approached is<br>employed. This entails the acquisition of adjacent lines of EM data along the centre and along the margins of the river. We suggest this approach provides for a better understanding of recharge and discharge processes and links between the floodplain and the main-river channel. Compared with data acquired along the river alone, this study demonstrated our ability to use Helicopter EM data to map losing and gaining (from a salt load perspective) stretches of the river and to provide insight into which parts of the groundwater-floodplain system were significant contributors to river salt loads. The rapid acquisition of airborne EM data makes these systems more suited to providing temporal snapshots of a river-floodplain environment during dramatic climatic events, such as flooding. In the Murray basin this may assist our understanding of how salt stores are mobilised during such occasions.
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