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Bekesi G.,Australian Water Environments | Telfer A.,Australian Water Environments | Woods J.,Flinders University | Forward P.,SA Water | And 2 more authors.
Australian Journal of Water Resources | Year: 2014

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 highsalinity 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. © Institution of Engineers Australia, 2014.

Burnell R.,Australian Water Environments | Bekesi G.,Australian Water Environments | Telfer A.,Australian Water Environments | Forward P.,SA Water | Porter B.,Water and Natural Resources
Australian Journal of Water Resources | Year: 2013

In addition to the threat posed by high salinity to drinking water, increased salinity in the River Murray also represents a threat to the health of floodplains, wetlands and may increase the costs of infrastructure maintenance. In the Lower Murray Basin most of the salts in the river originate from groundwater. Run of river salinity surveys are used to measure salt inflow. They measure electrical conductivity every kilometre over five consecutive days, at low and steady river flows. For a robust interpretation of salt inflow, the background electrical conductivity has to be removed from the measurements. The existing methodology is robust for analysing cumulative salt inflows over river reaches but assigns salt inflows up to several kilometres downstream from where they actually occur. A new method has therefore been developed to assign the salt inflow more closely to the location where it actually occurs and at the correct rate. The new methodology is based on the assumptions that salt inflow is the function of space only (during the survey) and the background conductivity can be described by the temporal variations observed at a fixed location. These in turn allow better targeting of the high salt inflow zones for salt interception. © Institution of Engineers Australia, 2013.

Bekesi G.,Australian Water Environments | Tyler M.,BHP Billiton | Waterhouse J.,Golder Associates
Quarterly Journal of Engineering Geology and Hydrogeology | Year: 2013

In the Great Artesian Basin (GAB) of Australia the combination of high temperatures and deep wells makes the calculation of groundwater heads challenging. Regulatory requirements set small drawdown conditions that require improved accuracy in the determination of head. The objectives of this study are to calculate temperature-inclusive groundwater heads to a sub-metre precision and analyse the implications of including temperatures in head calculations on groundwater management in the GAB. If groundwater is discharged from an ordinary well containing cold and fresh water, both the wellhead pressure and head decline; once the well is shut-in both the wellhead pressure and head recover. Observations in several deep and hot wells in the GAB confirm that if a well is allowed to flow, the wellhead pressure measured at the surface increases. Wellhead pressure has also been observed to decrease in several wells in the GAB after shut-in with corresponding cooling of the wellhead. A method has been developed to calculate temperature-inclusive head. The head may be calculated from well depth, elevation, wellhead pressure and near-surface and bottom-hole temperatures. Hydraulic gradients and therefore groundwater inflow to South Australia, calculated using current practices of temperature-exclusive heads or assuming constant temperatures in wells, may be incorrect. © 2013 Geological Society of London.

Wellfield B, in the Great Artesian Basin (GAB), supplies 30 ML/day of fresh groundwater to BHP Billiton's Olympic Dam mine and the town of Roxby Downs in South Australia. Groundwater use from Wellfield B is regulated according to the regional effects on pressures in the aquifer. Drawdown assessment criteria (allowing a maximum of 5 m as pressure drawdown measured in piezometers) were set at five sites, including two active pastoral production wells that existed prior to the commissioning of Wellfield B. Aquifer pressure in these production wells was measured after a predetermined recovery time. Pastoral flow was eliminated in 2009/10 in one of the wells, providing an opportunity to assess whether antecedent flow had affected the measured pressures and therefore the reported apparent drawdown. In the GAB, the combination of deep wells, high pressures, and hot water make flow and pressure measurements and the calculation of head more challenging than in cold aquifers. Pressures measured at the well head often decrease during recovery, and the influence of temperature has to be incorporated in head calculations. Based on one example, Jackboot Bore, it is clear that recovery times in the order of months are required, which is impractical. Hence, the use of an active production well for assessing compliance with drawdown criteria is not recommended in the GAB. © 2012 Springer-Verlag.

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