Utilizing airborne electromagnetic (EM) data, high resolution DEM and hydrogeological information to derive customised products for natural resource management along the River Murray corridor

Abstract

To improve on earlier hydrogeological models and to better manage the River Murray floodplain environment and water resources from salinity and irrigation impacts, stakeholders in the New South Wales and Victorian Mallee worked with project scientists to identify hydrogeological parameters that might be collected from existing data sets to help resolve land and water management issues (Lawrie at al., 2008). Several areas where improved information were identified, including the extent and thickness of the river flush zone, salt stores in both the unsaturated and saturated zones, and the thickness, extent and depth to the top of the Blanchetown Clay and other clay units across the floodplain and its adjacent uplands. Previous AEM-based studies have demonstrated the potential for these data to provide high geospatial resolution of key elements of the hydrogeological system (Walker et al., 2004). An airborne electromagnetic (AEM) survey was flown in early 2007 along a 450 km stretch of the Murray River and its floodplains in Victoria from the South Australian-Victorian border to Gunbower. The data were acquired under the auspices of the Australian Government?s Community Stream Sampling and Salinity Mapping Project, and were managed by the Bureau of Rural Sciences. This survey utilised a Fugro RESOLVE frequency domain system, with flight lines at 200m line spacing, and oriented at a high angle to the river corridor. RESOLVE is a six frequency EM system mounted in a bird towed beneath a helicopter at a nominal altitude of 30 m. The bird contains horizontal coplanar coils and measure EM responses at 390 Hz, 1798 Hz, 8177 Hz, 39470 Hz and 132700 Hz. It also has one coaxial coil pair which measured a response at 3242 Hz. This paper presents methods for mapping the thickness of Blanchetown Clay in the highlands of the areas surveyed during the course of this work, and the distribution of near surface clay across the floodplains, specifically at Lindsay-Wallpolla, Lake Victoria, Darling River and its anabranch.