Drought and flood are a natural phenomenon in the Murray–Darling Basin. This is one of the main differences between the rivers of the Murray–Darling Basin and most European rivers. During wet years, the rivers of the Basin will overflow into floodplains. These floodplains may be thousands of hectares in size, such as the Macquarie Marshes in central New South Wales. However during times of drought the rivers become strings of disconnected waterholes along the course of the drying riverbed.
Caterpillars on a flooded tree in the Macquarie
Marshes NSW 2012 Photo: Janna Randell
On average, the natural flow into the Basin is around 33,000 GL per year, although this is highly variable from year to year. Under natural conditions, flows would produce regular floods, which would flush the system and provide water to floodplains.
The system is now highly regulated with many structures such as dams, locks and weirs that have altered the natural pattern of flows.
After almost a decade of drought, a return to wetter conditions throughout the Basin in 2010 led to widespread flooding. This resulted in inundation of many floodplains and refilling of the Basin's water storages, with the total Basin water storage increasing from 32% to 81% during 2010-11.
This widespread flooding was good news for the environment and enabled many species to recover from the effects of a long drought. Despite its many benefits, the flooding caused widespread damage to property and also delayed new and ongoing work scheduled to be carried out at significant ecological sites along the River Murray.
Dry river bank, Billa Downs Station, near Euston
NSW 2007 Photo by Irene Dowdy
Climate change studies (e.g. SEACI, 2010) predict that the climate of the Murray–Darling Basin is likely to become drier in the future, due to the rising concentrations of greenhouse gases in the atmosphere. The studies indicate that the Basin climate is likely to become even more variable, as well as drier. So, in addition to more extreme droughts, there may also be more extreme floods.
There is a projected impact of a 10% reduction on average surface water availability across the entire Basin for 2030. The impact is expected to be greater in the southern the Basin, and these predictions are also more reliable in the south.
Visit the SEACI website and learn more about climate change predictions in South Eastern Australia.
Lack of water and a decrease in the frequency of natural flooding events are having an impact on many wetlands and other important environmental sites, including the Murray Mouth and river floodplains. The long-term health of the whole system is now at risk.