APPLICATION OF AIRBORNE ELECTROMAGNETICS TO SALT MAPPING – 3 AUSTRALIAN CASE STUDIES

This paper will discuss a number of airborne electromagnetic salt-mapping projects undertaken by the Australian Government in the last five years. These surveys were flown primarily to provide information to inform land management decisions in areas of high value agricultural land. These techniques are also being applied in the management of water quality and to inform decision making in high conservation value wetlands. In 2001 an airborne electromagnetic (AEM) survey was flown across an area of 870,000 hectares in the Lower Balonne river catchment of eastern Australia. This area is a major centre of cotton production, and the survey was flown as part of a project to identify where salt was stored in the landscape and to test how land management options influenced potential salt mobilization. Also in 2001 a combined AEM and airborne magnetics survey was flown over approximately 120,000 hectares in an area of the Honeysuckle Creek catchment of southern Australia. The airborne magnetics survey mapped magnetic gravels infilling a series of major subterranean paleochannels, and showed that these channels intersected buried landscape salt stores of approximately 16 million tonnes. These paleochannels were identified by the study as the primary mechanism of salt export from the Honeysuckle Creek catchment. In 2002 an AEM survey was flown over the Jamestown area of South Australia, a major agricultural district. The AEM data was acquired to provide information for the development of salinity management plans for the district, which are now being used to protect high value cropping land. The study identified bottlenecks in groundwater flow caused by the subsurface geology, and showed that these groundwater bottlenecks are areas of rapid groundwater rise during high rainfallyears, causing salinity and waterlogging at the surface. This work has contributed to a significant change in the understanding of salt in the Australian landscape. The traditional view that salt is relatively widespread has been confirmed, but it is now understood that much of this salt is stable and locked up in the landscape, and therefore unlikely to become a salinity problem.