Ecological response of Eucalyptus camaldulensis (river red gum) to extended drought and flooding along the River Murray, South Australia (1997–2011) and implications for environmental flow management

Abstract

Riparian forest and woodlands of the lower River Murray floodplain are exhibiting deteriorating health as a result of anthropogenic alterations to flow regimes and south-eastern Australia’s long-term ‘Millennium Drought’ from 1997 to 2009. Extensive flooding in 2010/2011 brought the drought to an end, providing an opportunity to monitor ecological floodplain recovery. The relationship between flooding and lateral recharge and condition of the dominant riparian tree species, Eucalyptus camaldulensis, was determined between 2007 and 2011 using the Landsat (LTM5) Normalised Difference Vegetation Index (NDVI). Linking the river hydrograph with the River Murray Floodplain Inundation Model (RiM-FIM) allowed exploration of the relationship between inundation duration and E. camaldulensis water requirements. Results indicate lateral bank recharge is an important mechanism in the maintenance of vegetation condition along the River Murray channel. Higher in-channel irrigation water delivery during summer months was identified as critical to survival of trees adjacent to the channel during the drought. The research suggests that weir pool manipulation to create in-channel flood pulses will aid E. camaldulensis maintenance. Furthermore, release of environmental flows once every 3 to 5 years to create bank-full flow or preferably overbank flows, will increase hydrological connectivity between river banks, wetlands and riparian zones, providing positive ecological benefits to E. camaldulensis and other floodplain and aquatic ecological assets.