Resilience of inland freshwater lenses along the regulated Murray River at the Mallee Cliffs Salt Interception Scheme, NSW

Abstract

This research aims to demonstrate that inland freshwater lenses along regulated rivers are more resilient to changes in nearby groundwater pumping than anticipated. The study site at the Mallee Cliffs Salt Interception Scheme (SIS) in NSW extracts saline groundwater that naturally enters the Murray River due to the shape of the Murray Basin. With the implementation of salinity management strategies and drier weather conditions since the 1990s, it is no longer necessary to continuously operate the SIS. It was anticipated that a temporary shutdown of the SIS would deteriorate the freshwater lens. However, the freshwater lens was found be resilient to change with the high degree of regulation in the Murray River at the study site. The buoyancy allows the lens to maintain integrity with the rising pressure in the underlying aquifer. Defining the freshwater lens as resilient contradicts existing literature that describes inland freshwater lenses as vulnerable. From this research, a conceptual model was created that can be applied to other SIS in semi-confined aquifers adjacent to the highly regulated Murray River The intensive monitoring program for this research into freshwater lens can be adapted for long-term monitoring applied to all 14 SIS operated by the Murray Darling Basin