Risks to Shared Water Resources
The Murray-Darling Basin Commission (the Commission) has identified six risks to the shared water resources of the Murray-Darling Basin (the risks). These include climate change, increased groundwater use, increased number of farms dams, bushfires, afforestation and reduced flow from irrigation.
The identified risks have the potential to change flow patterns and water quality in the Murray-Darling Basin (the basin) and thus undermine the Commission objective to manage the shared water resources in an efficient, equitable and sustainable manner. Addressing the risks will help the continued success of Commission initiatives such as the Living Murray Initiative, The Basin Salinity Management Strategy and the Cap on Water Diversions as well as the future trade in water entitlements.
As part of the development of a strategy to address the risks, the Commission has released a suite of reports intended to inform decisions by the Murray-Darling Basin Ministerial Council (the Council), Commission and partner governments.
The Commission released two CSIRO reports in 2006 that summarised the current understanding of the individual and cumulative impacts of the risks upon the shared water resources of the Murray-Darling Basin:
These reports do not necessarily represent the position of the Commission. They are intended to inform discussion for improvement of the management of the natural resources of the basin.
The figures provided are based on results of scientific research and data available at the time of publication. The Commission acknowledges that ongoing research is required to continue improving our understanding of the impacts associated with risks to the shared water resources requires and their cumulative impact.
The Commission are now releasing an additional four reports on 7 February 2007 that either informed the CSIRO reports or provide more specific information regarding the risks. These were:
Review of selected factors that may change future flow patterns in the River Murray System , Murray-Darling Basin Commission (Earth Tech Engineering (Pty Ltd, August 2003)
Summary of Estimated Impact of Groundwater Use on Streamflow in the Murray-Darling Basin (the Overview report) (Resource & Environmental Management, December 2004);
Overview of Statutory Frameworks – Risks to Shared Water Resources (M. Dyson, October 2005); and
Evaluation of the Connectivity Between Surface Water and Groundwater in the Murray-Darling Basin (Resource & Environmental Management, July 2006).
These reports were prepared in consultation the Commission’s jurisdictional partners and organisations such as the National Water Commission (NWC) and in the light of the National Water Initiative.
The information contained in these reports do not necessarily represent the position of the Commission. The figures provided in these reports reflect scientific analysis based on the best available data at the time of their production. Estimates may vary due to assumptions about human activities which may or may not eventuate.
The Commission acknowledges that some of the information in the reports may not accurately reflect the true impacts of the risks and is continuing to undertaking further research to improve our understanding of the risks and their cumulative impact.
The identified risks include:
Climate change is estimated to cause the largest and most likely reduction in flow, accounting for almost half of the estimated reduction in water volumes. A number of studies claim that the future climate of the Basin will be characterised by higher temperatures and reduced rainfall, resulting in reduced inflows to reservoirs and increased evaporation.
Groundwater stores are being depleted in certain parts of the Basin due to growth in agricultural development resulting in increased groundwater extraction. A depletion of the groundwater resources is likely to impact on surface water flows depending on the level of connectedness between aquifers and the river system.
There is strong evidence to suggest the number and size of farm dams have increased significantly in the last ten years. Farm dams capture surface flows resulting in reduced flow to streams. The estimated impact of farm dams on water volume is second only to climate change; however the future impact will depend on the potential for future agricultural development and the effectiveness of legislation or policies to restrict further establishment of farm dams.
It is recognised that farm dams often provide economic, social and environmental benefits.
In the short term, bushfire events can significantly affect water quality and reduce surface and groundwater levels in the longer term as vegetation regenerates. It is expected that climate change will lead to more frequent and intense bushfire events.
Increased areas of plantation forestry may reduce the mean annual water yield in a catchment, due to trees requiring more water than other vegetation types.
It is recognised that plantations have social, economic and environmental benefits. Strategically placed plantation forests may reduce groundwater recharge and address salinity.
Reduced flows from irrigation
It is estimated that improvements in the water use efficiencies in irrigation may result in reduced flows back to the stream. It is possible that this may result in increased salinity levels in rivers as salt is concentrated in the reduced return volume of water flowing back to the stream. There may also be water quality benefits as the return flow from irrigation may carry large amounts of pollutants.