Hydrogeochemical evidence for surface water recharge to a shallow regional aquifer in northern Victoria, Australia

The Third, Middle and Reedy Lakes system in northern Victoria is a series of interconnected lakes in which groundwater discharge and recharge occur under seasonal climatic and artificial influences. At high lake levels there is a pronounced mounding effect which tends to cause localised perturbation of flow systems and recharge into the uppermost aquifer. Three hydrostratigraphic units (referred to as 'Lower', 'Middle' and 'Upper') are identified beneath the lakes. An upward hydraulic gradient exists in the region under the present hydrologic regime. Despite this, hydrochemical and isotopic evidence has demonstrated a fresh water lens beneath Reedy Lake in the Middle and Lower aquifers. These waters have similar characteristics to the present-day water table which is being recharged from the lakes, suggesting that the lens represents lake-water recharge under a prior hydrologic regime when regional water tables were lower. The recognition of this lens has important implications for future management strategies in that it may be possible to implement a more natural wetting-drying cycle without the intrusion of saline water into this ecologically sensitive area.