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Injection of fresh river water into a saline floodplain aquifer in an attempt to improve the condition of river red gum (Eucalyptus camaldulensis Dehnh.)

The delivery of environmental flows to riverine floodplains is often constrained by water scarcity and infrastructure. This means that areas of floodplain are unable to receive environmental water through mechanisms like dam release, weir pool surcharge and artificial flooding of low lying areas. This study trials aquifer injection as a method of providing environmental flows to areas of stressed river red gum (Eucalyptus camaldulensis) on the floodplain of the lower River Murray. The objective was to inject fresh river water at the top of the saline alluvial aquifer to reduce root zone salinity and improve the condition of E. camaldulensis. Localized radial freshening of ∼10 m was observed at each of the five injection wells when 4·9 Ml (megalitres) of river water was injected into the aquifer over 45 days. Injection was abandoned after 45 days due to aquifer and well clogging, and increases in groundwater head, which caused four of the five wells to breach the confining clay layer. The trial resulted in localized and short‐lived freshening of the groundwater, which reduced salinity in the associated capillary fringe. This did not result in an improvement in the tree condition as they lay beyond the lateral extent of the freshening and were unable to access the water. Solutions to technical issues such as aquifer clogging and well breaching, as well as a need to increase the lateral extent of freshening, are required before shallow aquifer injection can be recommended as a method of delivering environmental flows. Copyright © 2009 John Wiley & Sons, Ltd.