Australia has a variable climate – it is a country of droughts and flooding rain. This means that water management needs to be adaptable.
Each region in the Murray–Darling Basin has its own sustainable diversion limit and water resource plan – these plans set out the local rules and arrangements for how water is used in every region.
Sustainable diversion limits are how much water, on average, can be used in the Basin by towns and communities, farmers and industries.
Each area also has a baseline diversion limit, which is an estimate of how much water could be used in the Basin, prior to the Basin Plan (June 2009). The best information available at the time was used as the basis of the baseline diversion limit estimates noted in the Basin Plan.
Accounting for water use is complex – some aspects of water movement in the Basin remain difficult to account for. As Basin governments implement the Basin Plan and other water management policies, they are gaining new and better information about historic water use.
To incorporate this new information into new water management policies, governments can adjust the estimate of the surface water baseline diversion limit, through a water resource plan. The surface water sustainable diversion limit and the baseline diversion limit are linked – changes to the baseline diversion limit will change the sustainable diversion limit.
The groundwater sustainable diversion limit and baseline diversion limit are independent and listed as fixed volumes in the Basin Plan. When groundwater knowledge is improved and there are better estimates of the groundwater baseline diversion limit and sustainable diversion limit, these may be updated through an amendment to the Basin Plan.
Changes to the limits do not mean more water is available for use, this water is being used already – it is just bringing this use into the new system, ensuring it can be monitored, and water use does not grow over time. Importantly, changes to the limits do not change the volume of water recovered for the environment.
Reasons for changing surface water limits
Under the Basin Plan, as with the Cap system, some diversions are not well understood, and the limit currently used is considered the best available information. Governments are committed to obtaining more information about these diversions, and continuously improving measurement and monitoring – this means the baseline diversion limit estimates will be improved in the future through the accreditation of water resource plans.
As part of water resource plan development, Basin state governments may choose to conduct improved modelling, consultation, analysis and measurement to review the baseline diversion limit estimates established in 2012 and, if necessary, update these for each surface water resource plan.
Further work is being conducted to improve accounting of water used through floodplain harvesting, farm dams and commercial plantations. These activities are represented in the baseline diversion limit and there may be improvements in the volumes of the limits, but we know this will take some time and may need further adjustments in the future.
Since 2012, Basin governments have an improved understanding of how state policies work in conjunction with the Basin Plan 2012 and the Water Act 2007. For instance, at the time of Basin Plan development, South Australia’s water allocation plans were being drafted and these have since been finalised. The improved understanding of state limits obtained since that time has been included in their water resource plans, which improves the baseline diversion limit estimate.
When the Basin Plan was developed there were some instances where there was no estimate on how much water was being used. Basin governments now have a better understanding of water use for these forms of take and an estimate has been determined, using relevant data and best available methods.
An evidence base for this new information must be presented to the Murray–Darling Basin Authority (MDBA) for assessment for inclusion in water resource plans. The MDBA then assesses the information and determines if that information means the limit should change. This new limit is then included in the relevant water resource plan and results in a new baseline diversion limit and sustainable diversion limit, through the accreditation of water resource plan.
Process for updating the baseline diversion limit estimate
