Defining spatial patterns of inter-aquifer leakage through the application of a-priori constraints when inverting airborne EM data

Abstract

Key to the effective management of natural ecosystems that characterise the floodplains of the Murray Basin in south eastern Australia, and maintenance of river health (a critical water resource) in a setting where severe salinisation is an ever-present threat, is the need for a sound understanding of surface water-groundwater processes. The importance of this has been emphasised in the recent, prolonged drought throughout the Basin with riparian communities on the floodplains in severe decline reflecting the lack of water in the system. Protecting the natural floodplain environment and limiting the flow of saline groundwater into the river system presents particular management challenges requiring that our conceptual hydrogeological knowledge is soundly based. In the eastern margins of the Basin, the drying climate, causing permanent or temporary restrictions to existing surface water entitlements has led to increased demand for groundwater. Its sustainable extraction requires an understanding of aquifer integrity, geometry and quality, particularly where it is extracted from confined or multi-layered systems, and where shallow, unconfined aquifers are too saline for use either as a source of potable water or for irrigated agriculture or stock. In such situations, a major threat to the long-term sustainability of groundwater resources is leakage of saline water from formations that overlie and/or underlie the target aquifers. Interestingly, these issues have a wider relevance, particularly given the growing interest in managing groundwater resources through managed aquifer recharge (MAR) in rural areas, and from the growing interest in coal seam gas, where an understanding of aquifer integrity and variability is critical. From a hydrogeological perspective these various situations demand information on the spatial variations in groundwater quality, aquifer integrity and information on surface water-groundwater interactions.