Sustainable diversion limit adjustment mechanism
As part of the Murray-Darling Basin Plan, our department is developing supply and efficiency measure projects to help recover water for the environment and productive use.
The Murray-Darling Basin Plan sets sustainable diversion limits (SDL), which states how much water can be used in the Murray-Darling Basin, while leaving enough water for the environment.
The limits aim to ensure that there is sufficient water to maintain the environmental health of the Murray-Darling Basin, by limiting the amount of water that can be extracted from the Basin, while considering the social and economic impacts of water recovery.
The Sustainable Diversion Limit (SDL)
The MDBA has determined that the average baseline diversion level (the BDL), or the existing level of water extraction, for the Basin in 2009 was 13,623 GL. The MDBA also determined that the long term sustainable diversion limit (the SDL) was approximately 10,873 GL per year or 2,750 GL lower than the 2009 BDL.
The Australian Government has committed to recovering the additional 2,750 GL of water for the environment through a combination of licence buybacks and water recovery and efficiency projects. Any project needs to ensure that environmental, social, and economic outcomes are properly balanced.
Mechanism to adjust the SDL
To provide flexibility, the Basin Plan also includes a mechanism to adjust SDLs. If the environmental outcomes targeted in the Basin Plan can be achieved with less water, more water can remain in the system for other users, including irrigated agriculture. Similarly, if farming practices can be made more efficient, more water can be made available for the environment. Refer to the graph below to see how SDL adjustments are able to alter the water recovery balance.
An SDL adjustment can be achieved through either supply measures or efficiency measures. A supply measure is a project that allows equivalent environmental outcomes to be achieved with less water. Project examples include environmental works, changes in river operations, and evaporation savings. By allowing equivalent outcomes to be achieved with a lower amount of water, supply measures effectively reduce the amount of water that needs to be recovered from productive use to meet the SDL.
An efficiency measure is a project that recovers additional water for the environment through improving the efficiency of irrigation or water delivery. Project examples include replacing or upgrading less efficient methods of on farm irrigation, and lining channels to reduce water losses within an irrigation network. Efficiency measures work by decreasing the amount of water required for consumptive use, with the water savings made available for environmental use. Efficiency measures aim to recover up to 450 GL of water across the entire Basin in addition to the 2,750 GL recovery target, and can only be undertaken if done in a way that is socioeconomically neutral or positive.
How SDL adjustments can change the water recovery balance
The graph below compares the use of water under three conditions:
- In the first, the Baseline Diversion Limit as of 2009, a total of 13,623 GL per year is taken for consumptive use
- In the second, under the Sustainable Diversion Limit, a total of 10,873 GL of water is available for consumptive use, with the remaining 2,750 GL per year required to be recovered
- In the third, under the Sustainable Diversion Limit with full implementation of both supply and efficiency measures, the total water available for consumptive use and the water required to be recovered are both offset by the adjustment measures. The water to be recovered has been offset by the supply measures, while the consumptive water pool has been decreased by the efficiency measures. Note that in reality, these two mechanisms will offset each other to some extent.
The graph below shows the BDL, SDL, and water required to be recovered in the Murray-Darling Basin. All volumes are measured in Gigalitres per year.
For more information regarding the SDL adjustment mechanism, visit the MDBA website.