River sediment salt-load detection using a water-borne transient electromagnetic system

The technique has been extensively trialed around the River Murray town of Waikerie in South Australia. An initial series of surveys along a 40 km section of river showed a range of sub-riverbed resistivities between 1 and 20 Ωm, with a top layer of about 10-15 Ωm closely following the water depth. Regions of high-resistivity in the riverbed sediments correlated well with saline-aquifer borehole pumping locations, indicating a localized drawdown of fresher river water. Low-resistivity anomalies have been interpreted as regions of saline water influx into the river. The technique is now used for routine mapping in Australia, with over 800 km of the Murray surveyed, and has potential application to other major world river systems.