Combining geology and geophysics to develop a hydrogeologic framework for salt interception in the Loxton Sands aquifer, central Murray Basin, Australia

Abstract

Salt 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.