Sustainable diversion limits
Ensuring a balance between the water needs of communities, industries and the environment is key to achieving a healthy working Basin. The Basin Plan sets new long-term average sustainable diversion limits (SDLs) that reflect an environmentally sustainable level of water use (or 'take').
See the progress on water recovery for recovery target figures, progress against recovery targets and the balance of recovery effort required at both a Basin scale and at specific locations.
An environmentally sustainable level of take (ESLT) is the amount of water that can be taken for town water supplies, industry, agriculture and other human or consumptive uses, while ensuring there is enough water to achieve healthy river and groundwater systems.
The Basin Plan sets a sustainable diversion limit (SDL) for each catchment and aquifer in the Basin, as well as an overall limit for the Basin as a whole. The SDLs are like a new 'cap' on water use. They regulate the amount of water that can be used for consumptive purposes in the Basin. The SDLs in the Basin Plan also apply to groundwater and mean that for the first time there are comprehensive limits on groundwater take across the Basin.
The new SDLs mean that more water will be available for the environment. Water returned to the environment will be used to improve and maintain the health of rivers, lakes, major wetlands and floodplains as well as important habitats for animals and plants that rely on the Basin's rivers. Good environmental health means Basin communities can rely on good quality water.
The SDLs will commence in 2019, by which point they will be incorporated in state water resource plans. We will work with Basin states to develop smooth transition arrangements from existing state water resource plans.
How are SDLs determined?
Surface water SDLs
The Basin receives about 32,500 gigalitres per year (GL/y) of surface water inflows. This includes about 950 GL/y of surface water transferred into the Basin from other valleys mainly through the Snowy Mountains Hydro-electric Scheme.
To determine what changes were required to reach a sustainable level of water use, we had to determine how much of this water was currently used — this is the 'baseline diversion' limit. The baseline diversions include all water pumped, diverted or intercepted for consumptive purposes as at 2009. The MDBA estimated that baseline diversions for surface water systems in the Basin total 13,623 GL/y. This baseline takes account of 873 GL/y of water that was recovered for environmental purposes before 2009, through The Living Murray program, Water for Rivers program and state water sharing plans.
We then had to determine the ESLT. This required a balanced judgement to optimise social, economic and environmental outcomes, taking into account current environmental and hydrological science, socio-economic knowledge and any system constraints that may limit the flows along river channels.
To determine the environmental water requirements for surface water, the MDBA chose a number of locations within rivers, floodplains and wetlands across the Basin. At these locations, known as hydrologic indicator sites, the environmental water requirements were determined by assessing the needs of the local ecology, as well as the water needed to provide the many functions necessary for healthy ecosystems downstream.
In working out these environmental water requirements and establishing a long-term average SDL across the Basin, we took into account infrastructure in the rivers, such as dams and weirs, as well as the risk of flooding to towns and properties along rivers.
Through this process, the MDBA determined that the Basin-wide long-term average SDL for surface water is 10,873 GL/y. This comprises 3,468 GL/y in the northern Basin and 7,405 GL/y in the southern Basin. Basin-wide this represents a reduction of 2,750 GL/y of water from the 2009 baseline diversion level of 13,623 GL/y.
The Basin also has substantial groundwater resources. However, a large proportion of these resources are not accessible or suitable for consumptive use. We have estimated the volume of recharge to groundwater across the Basin to be 23,450 GL/y and the level of baseline diversions to be 2,386 GL/y.
Determining the SDLs for groundwater was based on an assessment of the ESLT, in terms of the risks of groundwater extraction to:
- the ability of aquifers to continue to be productive over time
- groundwater-dependent ecosystems
- surface water resources that are fed from groundwater
- the water quality (salinity) of groundwater.
We used groundwater models where available to inform this risk assessment, along with other factors such as existing planning arrangements, current programs to reduce groundwater use, the depth of the groundwater resource and whether the groundwater resource receives recharge.
Following this process, the MDBA determined that the Basin-wide long-term average total SDLs for groundwater is 3,334 GL/y. This represents an increase of 949 GL/y of water from baseline diversion level of 2,386 GL.
SDLs and water recovery
The new SDLs mean that at a Basin-wide scale, as well as in some particular catchments, the volume of water taken for consumptive purposes must reduce.
The Australian Government has committed to recovering the 2,750 GL through a combination of investment in infrastructure efficiency and water buybacks, with at least 600 GL to be recovered through infrastructure efficiency improvements.
Across the Basin there are 66 groundwater SDL resource units (the large number of resource units reflects the complex nature of the groundwater systems). Of these, there is one SDL resource unit (Upper Condamine Alluvium in Queensland) where water needs to be recovered; 34 where the SDL equals the baseline and no change is required; and 31 where the SDL provides for an increase in extraction above the current baseline.
The Australian Government's commitment to recover the water needed to meet SDLs will apply to the Upper Condamine Alluvium. Entitlements will be purchased to provide for the transition to the SDL. The amount and location of the entitlements that need to be purchased in the Upper Condamine Alluvium will be the subject of further investigation and consultation.
The transition from Cap to SDL
With the adoption of the Basin Plan in 2012, the monitoring and reporting obligations under the Water Act first came into effect for the 2012–13 water year. SDLs willl be introduced in 2019. This gives us a 7 year transition period (from Cap to SDLs) for reporting water use in the Murray-Darling Basin. More information on Cap reporting is available here.