An Airborne Electro-Magnetic (AEM) survey used as a precision investigation tool to address salinity and land managment issues in a sem-arid floodplain environment
Lawrie, K, Brodie, R, Clarke, J, Tan, KP, Wong, VNL, Edwards, D, Apps, H, Halas, L & Cullen, K 2008, 'An Airborne Electro-Magnetic (AEM) survey used as a precision investigation tool to address salinity and land managment issues in a sem-arid floodplain environment', paper presented to the 33rd International Geological Congress, Oslo, Norway, 6-14 August.
In Australia, airborne electromagnetic (AEM) surveys have now been used successfully to address a wide range of land and groundwater management issues. The approach has relied upon high resolution geophysical imaging to map and characterize key elements of the biophysical knowledge framework in the shallow (<120m) sub-surface. These data provide a basis for dynamic modelling and the targeted management of salinity and groundwater issues. The need for high precision geospatial investigation tools has required development of geologically constrained AEM datasets, and an increasing sophistication in the development of information products that incorporate other biophysical data. Recently, a new approach to the interpretation of AEM data has been developed using a 4-D landscape analysis approach to complement more traditional hydrogeological analytical techniques. This approach incorporates an understanding of landscape evolution and scale, utilises modern investigative approaches to the conceptualisation of aquifer systems, and incorporates data on water, salinity and vegetation dynamics to provide key constraints on interpretation of both near-surface AEM responses and floodplain hydrostratigraphy. This approach has been greatly facilitated by development of a holistic inversion method that inverts all of the airborne samples in one large inversion, allowing it to capitalise upon the spatial coherency in the data. The superior spatial continuity of the holistic model allows us to interpret more subtle features in the data than we could from the conventional sample by sample stitched inversions. This method also obviates the need for iterative, time-consuming calibration-processing-recalibration paradigm, and allows for more rapid-turn around in developing interpretation products. These new inversion and interpretation methods were applied to an airborne electromagnetic (AEM) survey acquired in 2007 along a 450 km reach of the River Murray Corridor (RMC) in SE Australia. The survey was acquired under the auspices of the Australian Government's Community Stream Sampling and Salinity Mapping Project managed by the Bureau of Rural Sciences. This survey involved acquisition of a total of 24,000 line km of AEM data, and was designed to address specific land management questions, in an area that encompasses iconic wetland areas, national and state forest parks, and irrigation and dryland farming. Integration of the AEM data with new surface geomorphic and surface salt mapping, new borehole hydrogeological data, and spatio-temporal analysis of vegetation health, has facilitated development of a broader range of interpretation products. Preliminary analysis of these high resolution products has revealed important new findings on the nature of salinity impacts and distribution of fresh groundwater in the Murray River Corridor.