MAPPING SALT-LOADS OF THE MURRAY RIVER, AUSTRALIA, USING AIRBORNE AND IN-RIVER ELECTROMAGNETIC METHODS.

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 an