Chapter 3
Ground water
3.1
Like its approach to surface water, the Murray-Darling Basin Authority (MDBA)
has developed Sustainable Diversion Limits (SDLs) and Baseline Diversion Limits
(BDLs) for ground water as part of the Basin Plan. The MDBA has determined
ground water SDLs and BDLs for different resource units and aggregated these to
provide a total for the basin system.
3.2
The proposed total SDL can be compared to a basin-wide (BDL) which
represents the MDBA's determination of the limits on ground water use under state-based
water management arrangements in 2009.
3.3
However, these numbers have changed dramatically across the various
iterations of the Basin Plan. The total ground water SDL went from 1601 gigalitres
per year (GL/y) in the Guide (October 2010), to 4340 GL/y in the Basin Plan (November
2011), to 3184 GL/y in the Basin Plan (May 2012), and finally to 3324 GL/y
in the Basin Plan (August 2012). The BDL on the other hand has changed from
1786 GL/y in the Guide, to 2352 GL/y in the Basin Plan (November 2011) and 2373
GL/y in the Basin Plan (May 2012).[1],[2]
There were also significant changes for the SDLs in a number of different resource
units and the changes were not uniform across the Basin.[3]
Surface and ground water connectivity
3.4
The committee heard evidence that surface water and ground water are
strongly connected water resources and therefore they should be jointly managed.
For example, the Conservation Council of South Australia stated 'by default,
these systems should be treated as connected'.[4]
3.5
This supports information from bodies such as National Water Commission
(NWC) which has stated that surface and ground water resources are 'intimately
linked' and should be managed together.[5]
The committee has also previously addressed this connectivity concern in its
earlier interim report for this inquiry regarding coal seam gas.[6]
3.6
That said, the committee notes that connectivity between ground water
and surface water is not uniform. Some aquifers in deep ground water systems
have little or no connection with surface water. The CSIRO has estimated that
around one quarter of current ground water extraction is believed to be
reducing surface water availability, amounting to just four per cent of the
Basin’s surface water use.[7]
3.7
The committee also notes that this figure doesn't include the Basin
Plan's proposed additional extraction and the associated potential impact on
surface water.
Ground water extraction and limited
information
3.8
Stakeholders in the Basin are well aware of the connectivity between
water systems and they voiced concerns regarding the limited knowledge and
scientific understanding of the impact of ground water extractions. As Ms
Smiles from the Inland Rivers Network explained:
Those of us who have been following water for a long time
know that the knowledge and science around groundwater is relatively new
compared to what we know about what is in front of our faces on a regular basis
with surface flow.[8]
3.9
The NWC identified the Murray-Darling Basin as an area of 'particular
concern' in managing the interconnectedness of the resources because of the
increases in ground water extraction following the surface water diversion cap
introduced in 1997.[9]
The MDBA initially estimated that, across the entire basin, the annual
extraction level of ground water was approximately 1795 GL.[10]
3.10
This concern was echoed by the Wentworth Group of Concerned Scientists (Wentworth
Group) that stated that the MDBA's failure to include the impact of increasing
ground water extractions in the surface water modelling means the surface water
SDLs are unlikely to deliver the claimed outcomes. The Wentworth Group analysis
of the Basin Plan (November 2011) stated:
The failure to adequately analyse the impacts of increasing
ground water extractions on surface water means the draft basin Plan will not
adequately protect environmental assets, particularly those dependent on low
flows.[11]
3.11
There is very little scientific understanding of the impacts (especially
on surface water) of increasing ground water extraction. As the CSIRO told the
committee:
The surface water impacts from the ground water take...will
take a long time to emerge. There is a review process that has been put in
place. There may be no demand for that increase in groundwater use to happen in
a hurry, but that does not necessarily mean it is scientifically defensible.[12]
3.12
The MDBA increased ground water extraction limits from the Guide to
Basin Plan November 2011–based on incorporating the work that state governments
had done in establishing sustainable groundwater limits, including through the
Australian Capital Territory Plan limit, the Achieving Sustainable Groundwater
Entitlements program in New South Wales, South Australian natural resource
management regulations, and local groundwater management rules in Victoria and
Queensland.[13]
Some stakeholders have suggested that any increases to ground water extraction from
those that were presented in the Guide should be delayed until thorough
assessments are completed.[14]
The proposed increase in ground water extraction also led to committee concerns
about the approach the MDBA is taking to ground and surface water connectivity.
The MDBA's modelling and
assumptions
3.13
Despite the apparent need to consider the connectivity of the two
resources, the MDBA's treatment of connectivity is limited. Although MDBA
documentation released in July 2012 did reflect some consideration of ground
water and surface water connectivity in its revision to the ground water SDLs
and BDLs, this connectivity is only considered in the ground water modelling,
not for surface water modelling.[15]
3.14
The committee is not surprised, therefore, that the CSIRO called for
more science to be undertaken on ground water extraction and the impact on
surface water:
Dr Young: There are a number of areas around the
ground water parts of the proposed plan where we believe that there is a more
robust evidence base that could be assembled to try and support the proposed
position.
CHAIR: Is that code for, 'We need a little more time
to sort this out to make sure the science is right?'
Dr Young: No. We have undertaken a lot of the science,
as you referred to, and I think not all of that science has necessarily been
taken into full account.[16]
3.15
The CSIRO went on to say that:
...the evidence base that has been presented by the authority
to date to support the plan has not demonstrated that it has undertaken a
rigorous assessment of the surface water impacts of the proposed levels of
ground water take. The only caveat I would put on that is that on the last day
of the consultation period they released another 100-page report supporting the
ground water information. I have not had the opportunity yet to review that
information.[17]
3.16
In contrast the NSW Office of Water argued that the MDBA was still being
too conservative in its setting of ground water limits:
The most recent altered plan sets out sustainable diversion
limits for four New South Wales aquifers. These are deep aquifer that contain
water that is brackish or saline at best. We believe that the sustainable
diversion limits established by the Murray-Darling Basin are overly
conservative and not based on the best available science. The four aquifers in
particular have no or minimal connectivity to surface water and the sustainable
diversion limits developed in New South Wales are already extremely
conservative without another layer of conservation put over the top of them.[18]
3.17
Even though the MDBA has made several adjustments to the ground water
SDLs from the Guide and through the various iterations of the Basin Plan, the
Wentworth Group claimed there was no new modelling undertaken which would
explain these changes:
In the 12 months since [the release of the Guide in October 2010],
there has not been any new science done—let us make that clear—but there has
been a change of 2,600 gigalitres. We have increased the amount of ground water
we can take by 2,600 gigalitres. I am a little bit shocked at that without new
science to back that up.[19]
3.18
Furthermore, the Wentworth Group has strongly criticised the assumptions
used to calculate the diversion limits and stated that the assumptions used
'ignore the long-term connectivity of surface and ground water' resources.[20]
It explained how connectivity may operate in this situation:
...documentation supporting the draft Basin Plan [Basin Plan
(November 2011] the Authority states that for the purpose of determining
Sustainable Diversion Limits, rivers that are classified as losing streams...can
be treated as unconnected systems. This is then used to justify the assumption
that drawing these aquifers down further will not increase the loss of water
from the overlying rivers.
However, this assumption is incorrect. The aquifers that
receive water from losing river reaches will provide water to these rivers
further upstream or downstream; i.e. there are gaining reaches elsewhere.
Allowing additional extractions from these aquifers simply means that the level
of the watertable will drop, and the extent of the losing stream will increase
into areas that are currently gaining streams. Reducing the length of these
gaining streams will affect river flows, including important base flows.[21]
3.19
The committee considers that in the absence of firm science and research
as outlined above, the MDBA should provide more information in regard to its
assumptions on surface and ground water connectivity.
Ground water advisory group
3.20
The committee welcomes the consideration by the MDBA to establish a ground
water advisory group.[22]
3.21
Given the significant gaps in scientific information that exist, the
committee considers this to be positive step (provided it is implemented
properly) towards addressing some of the committee's concerns regarding the
state of knowledge about ground water extractions in the Basin. However, it is
essential that such a move be combined with significant changes to the MDBA's
approach to ground water and the open and transparent provision of information
to stakeholders and Parliament to ensure that informed decisions can be made about
the Basin Plan.
Navigation: Previous Page | Contents | Next Page