The Victorian Government has recently released the Groundwater Management 2030 (GM2030) Sustainable Yield Assessment. It is a strong piece of work and a credit to the team within DEECA who put it together. We also acknowledge their preparedness to engage with the CWA over that journey.
Now for the first time, groundwater systems across the state have been assessed using a consistent methodology. Relationships between extraction and groundwater levels have been examined, and an attempt has been made to zero in on just how much water can actually be taken from our aquifers before systems are deemed to be failing?
Why that matters for our rivers is that the base flows from ground water are why they continue to flow when there isn’t any rain. Examples of groundwater dependent ecosystems (GDE’s) include:
- Rivers and creeks sustained by baseflow
- Wetlands that are groundwater-fed or groundwater-influenced
- Springs and soaks
- Riparian and terrestrial vegetation dependent on shallow water tables
In these systems, groundwater discharge maintains flows during dry periods. However when groundwater levels decline, the first observable impact is often reduced baseflow, followed by ecological stress. This is why the CWA has taken a long term and active interest in the issue of groundwater management. These include:
Concerned Waterways Alliance comments on GM2030
CWA Submission to Latrobe Valley licence applications
Concerned Waterways Alliance Feedback on Groundwater Monitoring Strategy
It is fair to say that for many years, groundwater management in Victoria has relied on a mix of legacy caps, incomplete data, and regionally inconsistent approaches. The result has been a system where confidence in the numbers has not always matched the significance of the decisions being made from them. This Sustainable Yield Assessment begins to change that. It provides a clearer line of sight between use and impact, and it does so in a way that can be applied consistently across the state.
The three most relevant terms are Permissible Consumptive Volume (PCV), licensed volume, and sustainable yield (SY):
A useful way to think about them is:
- Sustainable yield is what the system can likely sustain
- PCV (cap) is what the system’s managers are allowed to allocate (note this has been historically well above sustainable yield in some significant catchments)
- Licensed volume or entitlement is what has actually been allocated to users (again in some catchments well above sustainable yields)
Then there is the historical use which may not reach the full entitlement volumes.
The following example is drawn from the DEECA online dashboard that uses the data derived from the Assessment.
The Bungaree Groundwater Management Unit sits to the east of Ballarat. A Sinclair Knight Mertz report from 2003 explains that for every megalitre of water taken from this groundwater aquifer 0.7ML is effectively kept from the river.
While the historical take has been at or below the Sustainable Yield figure, due to the PCV and entitlement values being much higher this system is at real risk as water becomes more scarce due to a drying climate and allocations are more fully realised.
As illustrated in many parts of Victoria, the connection between groundwater and surface water is direct. When groundwater levels fall, rivers lose water. When extraction increases, baseflows decline.
The Assessment recognises this relationship. It applies a more conservative drawdown threshold of 2 metres in surface, or so-called unconfined systems, to reflect their closer connection to surface water environments and GDEs. But it also acknowledges that these thresholds are generic, and not tailored to the ecological requirements of individual systems.
While a consistent threshold is useful for comparison, it is not the same as an ecological limit. It does not tell us when a wetland begins to fail, or when a river system loses the flows required to sustain habitat. It tells us when a line has been crossed in a model. What is up for scrutiny is whether the 2 mt limit which sits near the high risk category is the right figure to protect ecosystems.
Similarly, while climate change is recognised within the Assessment, the underlying methodology still draws heavily on historical conditions. Systems that appear stable under past conditions may not remain so under future ones.
There are also areas that sit outside the scope of the Assessment altogether. Water quality impacts, including salinity, are not incorporated. Nor are some forms of extractive pressure, such as dewatering. In certain catchments, these factors are central to long-term system condition.
The Assessment is described as a foundation for improved management over time, not as a trigger for immediate change. Monitoring is emphasised, and the importance of adaptive management is acknowledged. But in many areas, the mechanisms that would translate monitoring into action such as defined triggers, mandated responses, enforceable limits are not yet in place.
From a waterways perspective enforceable limits are vital, and if risk can now be identified with greater confidence, at what point does or should that risk begin to constrain use?
Because ultimately, water systems are not governed by assessments. They are governed by decisions. And those decisions are shaped not just by what is known, but by how that knowledge is applied.
The GM2030 Sustainable Yield Assessment represents a significant step in improving what is known. It brings a level of consistency and transparency that has been lacking, and it creates a platform from which more informed decisions can be made.
But it does not, on its own, ensure that those decisions will protect the systems that depend on groundwater.
That next step will be translating understanding into enforceable limits, integrating groundwater and surface water management, embedding ecological thresholds, and responding to climate risk with precaution rather than retrospect.
The Assessment provides the map for action but it will be up to water managers including the State government to use it to inform future allocations and deliver protections for our waterways.