Monitoring Changes to Freshwaters Lens Systems in a “Sea” of Saline Groundwater across the Murray River Floodplain in SE Australia using Multi-date Airborne EM
We examine the role of airborne EM systems in defining the geometry of these lens systems in 3D. An assessment of their value for monitoring variations associated with these ecosystems, including spatio-temporal processes connected with surface water and groundwater interactions, formed part of the study. The advent of “calibrated” AEM systems and robust inversion tools have given added impetus to their use for monitoring. The focus was over the Katfish Reach of the Murray River in South Australia. Spatio-temporal variations are observed in the near surface (top 20m) from a multi-temporal assessment of Clark’s Floodplain, adjacent to the Bookpurnong Irrigation area in co-incident airborne EM surveys acquired between 2008 and 2015. Spatial changes in ground conductivity, attributed to changing groundwater quality have been observed. The freshwater lens systems appear to have contracted significantly over the last decade. This is attributed, in part, to land use patterns and the development of an irrigation-related groundwater mound on the highlands adjacent to the floodplain, and an increased hydraulic gradient towards the river. The results indicate the geometry of the hyporheic zone may have also changed along the river.