Instream NanoTEM: providing increased resolution to stream salinisation and floodplain processes along the river Murray, southeast Australia

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.