The management of surface water resources in the Murray-Darling Basin is
a key aspect of the Basin Plan. The central feature of surface water management
was the development of the Basin's surface water and the associated quantities
of sustainable diversion limits (SDLs) and baseline diversion limits (BDLs).
The setting of the SDLs and BDLs will be discussed in turn.
The quantity of water set for the SDLs and BDLs has a major impact on
the way in which water in the Basin will be managed under the Basin Plan. As a
result, these items have been a major focus of the public debate regarding the
Basin Plan. This chapter examines the modelling and key assumptions that informed
Murray-Darling Basin Authority's (MDBA) setting of the SDLs and BDLs for surface
water in the Basin Plan. The chapter also identifies some key areas of concern
regarding the MDBA's modelling including:
- the MDBA's lack of clarity in presenting information about the
modelling to stakeholders and the public;
- the lack of information available about the alternative scenarios
for a reduction in take other than the 2750 GL/y figure proposed by the MDBA;
- reliance on historical data for the modelling;
inadequate treatment of predicted impacts of climate change in
the modelling; and
inadequate treatment of water interception in the modelling.
The SDLs and BDLs for groundwater resources and the issue of surface
water and groundwater connectivity are discussed in the following chapter.
Although modelling of scenarios for 3200 GL/y return of take is
discussed in this chapter, the additional return of 450 GL/y to the Murray
River that was proposed by the Government in October 2012 is dealt with in
Surface water resources
SDLs and BDLs
The MDBA established a baseline from which to measure diversion reductions,
known as BDLs. In general, a specific BDL is:
...a combination of limits established by state law (e.g.
existing water resource plan limits), defined levels of take where there are no
established limits, and in some cases, the limits established by the
Murray–Darling Basin cap arrangements where these establish the lowest limit.
Schedule 3 of the Basin Plan determines the BDL for the various
individual resource units in the Basin. The
MDBA determined the total, Basin-wide BDL to be 13 623 GL in the baseline year
The Basin Plan also establishes SDLs. The Basin Plan's explanatory
statement notes that an SDL:
...is defined in section 1.07 [of the Basin Plan] to mean the
long-term average sustainable diversion limit. 'Long-term average sustainable
diversion limit' means the maximum long-term annual average quantities of water
that can be taken, on a sustainable basis, from the Basin water resources as a
whole, and the water resources, or particular parts of the water resources of
each water resource plan area (item 6 of subsection 22(1) of the Act [Water
Act 2007]). Each long-term average sustainable diversion limit must reflect
an environmentally sustainable level of take (subsection 23(1) of the Act). An
environmentally sustainable level of take (ESLT) is the level of take at which
water can from be taken from a water resource without compromising key
environmental assets, key ecosystem functions, the productive base or key
environmental outcomes for the water resource (subsection 4(1) of the Act).
The long-term average SDLs across all the Basin's catchments will come
into effect in 2019.
This is currently estimated as 10 873 GL/y.
The difference between the Basin wide BDL and the Basin wide SDL is
2750 GL/y. This is the total return of water to the Basin system for
environmental purposes. The northern basin is to contribute 390 GL/y, the
southern basin 2289 GL/y and the disconnected tributaries contribute the
remaining 71 GL/y to the total 2750 GL/y.
In addition, the final Basin Plan contains a mechanism to adjust the
reduction amounts, therefore the 2750 GL/y figure becomes a range of total
reduction of 2750 GL/y plus or minus 5 per cent of the long-term Basin
This adjustment mechanism is discussed further below.
SDL adjustment mechanism
In November 2012, the Water Act 2007 (Water Act) was amended to
allow the final Basin Plan to include an adjustment mechanism to change SDLs
'based on new initiatives which achieve better environmental outcomes, or
reduced social and economic impacts, relative to those considered in setting initial
Although the surface water recovery figure in the Basin Plan remains at 2750
GL/y, the SDL adjustment mechanism allows for changes to this figure of plus or
minus 5 per cent of the Basin‑wide SDL. As noted in the explanatory
statement to the Basin Plan:
SDL adjustments resulting from application of the SDL
adjustment mechanism must operate in the net range of plus or minus 5% of the
surface water SDL for the Basin. Adjustments resulting from supply and
efficiency measures will be netted against one another to provide the total
adjustment amount while maintaining the plus or minus 5% limit.
As a result, with 'an initial surface water SDL of 10 873 GL this limits
the net adjustment to 544 GL.'
Importantly, the primary way of achieving changes from the 2750 GL/y
figure are through either efficiency measures or supply measures. An efficiency
measure is a measure that 'makes savings in the amount of water required for
consumptive purposes. Examples include investment in more efficient irrigation
A supply measure is:
...a measure that increases the quantity of water available
before consumptive take. The measure may do this either by making water
available for environmental use without reducing the volume of water available
for consumptive take (e.g. through reducing evaporation losses at suitable
storages) or by allowing environmental managers to achieve the same
environmental outcomes more efficiently, thus reducing the volume of water
needing to be recovered for the environment. Supply measures allow equivalent
environmental outcomes to be achieved without needing to reduce consumptive
take as much as originally anticipated in the Basin Plan.
The amendment to the Water Act that provided for the adjustment
mechanism was inquired into by the Senate Environment and Communications
That committee's report stated that '[m]any
submitters were generally supportive of an adjustment mechanism'.
However, the report also identified three concerns with the amendment as
it was initially proposed in Parliament:
lack of opportunity for public participation in and consultation
on the adjustment mechanism;
- lack of ministerial discretion as to whether to adopt an
adjustment amendment to the Basin Plan; and
whether such an amendment to the Basin Plan is a disallowable
On 30 October 2012, the House of Representatives made amendments to the
bill and the Environment and Communications Committee was of the view that the
amendments addressed the above concerns.
The bill with amendments was enacted on 21 November 2012.
As noted above, the Senate Environment and Communications Committee's
report stated that many stakeholders supported the enabling legislation for the
This is reflective of the views raised by witnesses in this committee's inquiry
that the 2750 GL/y should be considered as a 'starting point' for reduction in
take and that future flexibility was required.
This was also the view of the MDBA at the time of Basin Plan (November
2011 and May 2012), that the 2750 GL/y figure should be viewed as a 'starting
point for an adaptive process' and it could shift following future reviews,
proposals to address constraints, efficiencies gained through environmental
works and measures and as new science or other knowledge is gathered.
More detail on the adjustment mechanism (specifically in terms of supply
measures and efficiency measures) is included in chapter four.
Modelling of surface water
sustainable division limits and the 2750 GL/y
To determine the Basin SDLs and as a consequence arrive at the 2750 GL/y
reduction in take, the MDBA undertook significant modelling of surface water in
the Basin. Initial work undertaken by the MDBA included assessing the water
needs of species, communities and areas of diversity, in particular 'those
recognised under international agreements such as the Ramsar Convention' and
the Environment Protection and Biodiversity Conservation Act 1999
throughout the Basin.
However, the modelling techniques for surface water SDLs have also
shifted over time. The modelling of surface water in the Guide involved an 'end-of-system
flow model'. For the development of the various iterations of the Basin Plan, the
MDBA moved to a 'hydrological indicator flow model' which 'targets a range of
sites up and down the basin' to capture flow issues across the basin.
The MDBA argued that the hydrological modelling approach for surface
water SDLs was the best available approach to test a range of scenarios and
Hydrological models have been used to represent and test
environmental water requirements and flow regimes. They are the best available
tools for representation of long term flow regimes in the Basin under current
water sharing arrangements (baseline conditions) and without development
The MDBA further explained that the surface water resources of the Basin
were represented by linking 24 individual river system models developed by the MDBA,
CSIRO and Snowy Mountains Hydro into an Integrated River Systems Modelling
Framework (IRSMF). The IRSMF allowed the MDBA to assess responses across the
Basin, to changes in flow regime, over time and with different
scenarios of water recovery.
The MDBA noted:
The Basin Plan scenario modelling was carried out by
simulating a reduction in consumptive water use, and making an equivalent
volume of water available for environmental use within the water sharing and
water management rules and constraints as prescribed under baseline conditions.
The environmental water requirements were assessed at 122 hydrologic indicator
sites across the Basin.
The MDBA summarised the 'basic approach' to determining the SDLs in the
following four step process:
Basin-wide environmental objectives that reflect the requirements of the
environmental flows required to achieve these objectives, using a group of
hydrological indicator sites at key locations across the Basin;
options for water recovery and environmental water use targeted at delivering
these flow requirements; and
the model results to determine the effectiveness of the options in achieving
objectives, and iterate as required until an option is found that achieves an
appropriate balance in environmental, social and economic outcomes.
Therefore, to determine the 2750 GL/y for surface water, the MDBA
modelled key reduction scenarios ranging from 2400, 2800 and 3200 GL/y.
Modelling documentation released by the MDBA explains the 2750 GL/y figure:
Key scenarios modelled are ‘without development’ (a
near-natural condition scenario); ‘baseline’ (reflecting water sharing
arrangements and levels of infrastructure as per June 2009); and a reduction of
2800 GL across the Basin. Sensitivity analysis was carried out for the Southern
Connected System (Murray, Murrumbidgee and Goulburn-Broken catchments), where
two further diversion reduction scenarios were modelled to represent a
Basin-wide reduction of 2400 GL, and 3200 GL to gauge the sensitivity of the
proposed scale of change. Some initial sensitivity testing has also been
undertaken for the Condamine-Balonne, exploring alternative water recovery
volumes and strategies. The results of this sensitivity analysis led to a
further increase of 50 GL in SDL for the Condamine-Balonne system and
consequently a total proposed reduction of 2750 GL across the Basin has been
proposed in the draft Basin Plan.
The MDBA further explained the results of the modelling of 2400 GL/y and
3200 GL/y reduction scenarios and why this directed it towards the 2750 GL/y
MDBA also conducted sensitivity testing of 2400GL and 3200GL
reduction scenarios. The analysis showed a number of key ecological targets and
objectives of the proposed Basin Plan might not be achievable with the 2400
GL/y scenario, whereas the 3200 GL/y achieved some marginal improvements over
the 2800 GL/y scenario, but not sufficient to justify the potential additional
socioeconomic impacts. In addition, flow delivery constraints such as roads,
bridges, or rules to avoid flooding private property, limit the capacity to
actively use extra environmental water available under the 3200 GL/y scenario.
Despite criticisms about the MDBA's modelling discussed below, the MDBA
defended the scientific basis for development of the Basin Plan. As Dr Rhondda Dickson,
Chief Executive, MDBA stated:
We challenge any assertion that the plan is not based on firm
science. The modelling that we have done is far more detailed and more robust
than any previous scientific work carried out, either by the authority or by
any other independent groups.
Additional modelling scenarios
In October 2012, the MDBA released the details of further modelling
which considered the possibility of 'relaxing' a number of constraints in the
southern part of the Basin system. In this modelling, eight river operating
constraints were relaxed 'to increase the peak rate at which environmental
flows can be delivered'. In addition, an 'altered environment watering strategy
was adopted, necessitated by and taking advantage of the relaxation of
Of the eight constraints relaxed:
Seven of these represent an increase in the allowable
discharge to pass key river reaches in the southern Basin. The eighth
represents the inclusion of a new regulator on the Darling Anabranch to
accommodate efficient delivery of Menindee releases made to contribute to environmental
flows to the Murray.
The new modelling predicted results for achieving environmental outcomes
for scenarios of 2800 GL/y and 3200 GL/y reduction in take with relaxed
constraints. The results for 2800 GL/y relaxed constraints were summarised as:
Overall, the model results indicate that combining 2800 GL/y
of recovered water with constraint relaxation would have a positive effect on
the ability to deliver high-flow events; enabling greater areas of mid- to
high-elevation parts of the River Murray floodplain to be inundated for longer
periods and at a greater frequency. However, in order to detect changes using
the flow indicators developed by MDBA to assess modelling scenarios, the
improvements in flow have to meet specified flow rate and durations before
environmental outcomes can be inferred. The BP-2800-RC [the Basin Plan 2800
GL/y relaxed constraints reduction in take] modelling showed that while, in
general, the duration and peak of existing events could be extended (providing
environmental benefits), the events were not enhanced sufficiently to achieve
additional flow indicator targets for mid- to high-level floodplains.
The results for the relaxed constraints model of 3200 GL/y return of
take were noted as:
The BP-3200-RC [the Basin Plan 3200 GL/y relaxed constraints
reduction in take] scenario indicates that the combination of constraint
relaxation and an additional average of 400 GL/y of available environmental
- can substantially increase environmental benefits, with many more flow
indicators being met for the River Murray... [and]
- could provide the capacity to water mid- to high-level parts of the
floodplain in the Lower Murray (with the potential to benefit large areas of
natural wetlands and floodplains).
In order to demonstrate the improved environmental outcomes, the MDBA
produced the following table for key environmental targets for the Murray
River. It shows 'achievement of 'actively managed' river channel and floodplain
environmental flow indicators achieved on the River Murray for the baseline and
Basin Plan scenarios.'
Outcomes (River Murray) for Modelled Scenarios of Reduction in ESLT
Number of flow indicators achieved – River Murray
Criticisms of the modelling for the Basin Plan
Many stakeholders criticised the modelling process undertaken by the
MDBA, first for the iterations prior to the final Basin Plan and even after additional
modelling for the 2800 GL/y and 3200 GL/y relaxed constraint scenarios was
complete. At a general level, some of these criticisms questioned the
fundamentals (or assumptions) of the MDBA's approach to the modelling and why
other modelling scenarios (such as 4000 GL/y return of take) had not been
undertaken. These general criticisms will be discussed in turn.
The concerns about the limited modelling of alternative scenarios were expressed
to the committee. Conservations Councils across Australia called for further
modelling and specified 4000 GL/y should be modelled to demonstrate that this
would 'meet the ecological objectives set by the MDBA.'
The Wentworth Group supported this and advised the committee:
The science seems to indicate that you need to be up around 4
000 gigalitres if you want to just achieve the minimum targets to have a
functioning system. Obviously that is going to have social and economic
The Commonwealth Science and Industrial Research Organisation (CSIRO),
in its science review of the MDBA modelling, stated that the 2800 GL/y
reduction scenario was 'not consistent with the stated environmental targets'
and recommended that scenarios above this figure be modelled.
When questioned (regarding Basin Plan (November 2011)) about what scenarios
greater than the 2750 GL/y figure the MDBA had modelled, CSIRO representatives
[The MDBA] have published, as you are probably aware, some
limited information around a 3200 gigalitre scenario, and that shows some
incremental improvements. I guess it comes back to whether people think those
incremental improvements are worth the incremental costs and what the value
proposition is for the different scenario. The modelling [the MDBA] have done
for the 3200 gigalitre scenario, as I understand it, is only for the Murray
system. [The MDBA] have not run the connected models for the entire basin in
assessing that; [the MDBA] have just made some additional modifications and
water recovery in the Murray system and looked at the consequences of those for
the environmental outcomes at the bottom end of the system.
The Wentworth Group advised the committee that the MDBA could model
other scenarios with the current tools available:
Dr Williams: Scientifically and technically it is
possible to do. I think the guide had set in place the range of requirements to
give you levels of confidence in returning the river to sustainability. I think
that is still a very valid means of saying it because the science can give you
some indication. If you use this amount of [water], what level of confidence
can you have as a taxpayer that you will get a sustainable functioning river?
To do that with 4000 gigalitres, we did some preliminary work that suggests it
is entirely feasible. I think the modelling capacity is there, from my
background in CSIRO and also my background in the CRCs [Cooperative Research
Mr Stubbs: ...The [MDBA] has the tools and has some very
good people doing a very good job at the level of modelling. It would take them
approximately two months to run the model for a different scenario. If we were
not on this deadline of getting everything wrapped up by the end of , we
could do a range of scenarios and get a very full understanding of the
different outcomes—environmental, social and economic—and also of the
constraints in a relatively short time so that parliament could make a very
well informed decision on the future of the basin.
Concerns about the modelling
The committee heard evidence of a number of other concerns about the
assumptions used in the MDBA's modelling. This included, general concerns about
the lack of scientific justification for the final 2750 GL/y
or that the MDBA's approach would simply embed existing management practices in
the Basin. As Ms Beverly Smiles, President, Inland Rivers Network, explained:
The MDBA changed the hydrological-modelling approach adopted
in the [Guide] to one that is more closely aligned with current river
operations and management. This approach has effectively locked in the poor
management and ecological outcomes currently entrenched in state water planning
and implementation processes.
More specifically, the committee identified several themes that emerged in
evidence about the assumptions used in the MDBA's modelling which will be
discussed in turn and included:
(and its assumptions) is reflected in complex and technical reports;
is based on historical data, and does not include recent wet years;
impacts of climate change are not captured in the modelling; and
activity has not been adequately reflected in the modelling.
Modelling reflected in highly complex
and technical reports
The committee heard evidence that the technical nature of the material that
supports the modelling remains unclear and difficult to understand, for both
technical experts and the public alike. Mr Stubbs from the Wentworth Group
reflected on the complexity of the modelling and explained that the science had
not been clearly explained when it could have been:
[W]e cannot understand the outcomes of the modelling run they
[the MBDA] have done. It is very opaque. It does not clearly state what the
outcomes are for Ramsar [wetlands] or for [other environmental] assets. It
could have been clearly and easily stated [this information]. Even with just
one scenario [2750 GL/y], we cannot understand the costs and the benefits of
other scenarios, what we could actually achieve and why we are locked at this
one scenario. So we really have a complete dearth of information not just for
the scenario that has been looked at but even for other scenarios to understand
what could be achieved.
Notwithstanding this Plain English Summary, the modelling and
assumptions behind the plan have never been set out concisely, in an easy to
understand format. Despite many calls by the committee to have the methodology clearly
articulated, the MDBA have failed to do so. This remains a key concern for the
committee. Although the following recommendation applies to the MDBA's
modelling of surface water, they align with the concerns noted in chapter seven
about the MDBA's consultation process and stakeholder engagement.
The committee recommends that the Murray-Darling Basin Authority develop
a concise and non-technical explanation of the hydrological modelling and
assumptions used to develop the 2750 GL/y return of surface water to the
environment, to be made publicly available.
Modelling based on historical data
The modelling that informed the Basin Plan is based on 114 years of
historical data, which the MDBA has argued captures climate variability over an
extensive period. As the Chair of the Authority, Mr Knowles explained:
For the Basin Plan, the proposed new arrangements have been
applied to the historical climate period of July 1895 to June 2009, which
covers periods of drought as well as floods.
However, this historical data does not take capture the significant
rainfall experienced in the years beyond 2009. This approach has been heavily criticised
and some have argued that the long-term SDLs may have been different if the
modelling captured the recent wet years:
Senator JOYCE: But what your data set does not include
is the La Nina substantial wet period that basically started in 2010—or 2009,
to be precise. If you amended you data set you would get a substantial change
in the assessment of the water profile, would you not? In fact, we have done
it—about 500 gigs.
Dr Dickson: I cannot comment on that. We have not done
that assessment. I would just repeat that the amount of variability in the
historic record is sufficient to be able to estimate the scale of change that
we use for the Basin Plan modelling.
The MDBA did subsequently review the impact of the recent flood years
and maintains that including two additional years in this data would have no
impact on the SDLs and that the 2009 baseline would not change:
Estimating SDLs is not a simple averaging and subtraction
exercise... If we changed the climate baseline to include 2010 and 2011 data, the
relativities between the SDL scenarios would not change. The last two years
have been very wet but no wetter than the very wet periods already included in
114 year period we have used to test the scenarios.
The MDBA reiterated that, although it has not used future projections in
its modelling, it is confident that the historical record generates appropriate
estimates for future management of the Basin. As Dr Rhondda Dickson from the
...what we have done in the plan is, as the chairman said, used
as the starting point the best available information where we do have
confidence, which is the historical record. Because it is a 10-year planning
framework that gives us the opportunity to get a lot more certainty about some
of those estimates.
CHAIR: So is it fair to say you have not used the
future at this point?
Dr Dickson: We have not used the future as far as our
modelling, given the range of uncertainty.
Due to the reliance on historical data in the MDBA hydrological
modelling, the committee questions the claim by the MDBA that the Basin Plan
was developed on the basis of the best available scientific knowledge. The
committee considers that the MDBA's claim is undermined by excluding recent
flooding in the development of the Basin Plan and, as discussed in the remainder
of the chapter, by not appropriately addressing the predicted impacts of
climate change and water interception.
Climate change projections not
captured in modelling
The treatment of the predicted impacts of climate change in developing
the Basin Plan was another key concern identified in the inquiry. Previous
reports have indicated that climate change will have a significant impact on
water runoff in the Basin. For example, the CSIRO also conducted extensive
analysis on this issue in 2008, including modelling rainfall run-off to the
year 2030. According to the report, the likely impact would be significant:
The best estimate or median indicates that the future mean
annual runoff in the MDB in ~2030 relative to ~1990 will be lower, by 5 to 10
percent in the north-east and southern half [of the Basin], and by about 15
percent in the southernmost parts. Averaged across the entire MDB, the best
estimate or median is a 9 percent decrease in mean annual runoff.
In addition, the Garnaut Review on climate change stated that 'a
decrease in rainfall can result in a two- to three-fold
decrease in streamflow.'
Therefore, the impact for water run-off is far more significant than the change
in rainfall due to a multiplier effect.
Prior to the release of the Basin Plan, climate change was identified by
the MDBA as a significant issue and stated in the Guide that it was 'essential
that the proposed Basin Plan appropriately addresses the impacts of climate
Furthermore, the Guide details the predicted impact of climate change as
In light of the various issues associated with climate change,
the Authority has determined that 3% is an appropriate allowance to account for
the effect of climate change in the proposed Basin Plan. That is, the reduction
being considered as necessary to achieve an environmentally sustainable level
of take is inclusive of a 3% reduction in the current surface-water diversion
limit in the Basin.
Despite allowances being made in the Guide for projected climate change impacts,
the MDBA advised the committee that projected climate change impacts are not in
the modelling that informed the Basin Plan:
[Future climate change] was never in the modelling. In the
guide it was not in the modelling, and we have not included it in our
modelling. We have modelled the historical sequence, as we have said before.
The approach to climate change is one of adaptive management as well as putting
various requirements in state water resource planning as part of the basin plan
and investing in information that is going to improve our understanding of
climate change in the future and how we might model those futures for climate
However, the MDBA have also argued that under an adaptive management
framework, the Basin Plan will account for future climate change as new
information emerges. This approach is reflected in the MDBA's factsheet about
managing climate change under the Basin Plan:
The Basin Plan lays the foundation for future adaptation to
climate change as we learn more about its impact on environmental water needs,
other water requirements, water availability and communities.
The future impact of climate change has also been acknowledged in the final
Basin Plan by being identified as a risk to be managed. These risks are
outlined in Chapter 4 of the Basin Plan and, as described in the Explanatory
Statement, the MDBA must have regard to certain strategies when carrying out
its functions. In the case of climate change, such strategies are to 'improve
knowledge of water requirements within the Murray-Darling Basin, including...the
impact of climate change on environmental water requirements' and also to
'improve knowledge of the impact on Basin water resources from...climate change'.
The MDBA's general approach to climate change in the various iterations
of the Basin Plan was criticised by some witnesses before the committee. For
example, the Wentworth Group claimed the Basin Plan (November 2011) set SDLs on
an 'assumption that there was no risk to river health from climate change'
and that it ignores climate change:
We know that the CSIRO modelling suggests that climate change
is likely to result in significant reductions in rainfall and runoff in
south-eastern Australia over the next 20 years. Yet the draft plan ignores
these effects even though it is intended to guide water use in the basin over
much of the same time period.
The committee also heard evidence that predicted climate change is
likely to have significant impacts on the outcomes to be expected from
returning water to the basin through setting the SDLs.
Ms Juliet Le Feuvre, Healthy Rivers Campaigner, Environment Victoria also
summarised the concerns about relying on historical climate conditions to the
The MDBA makes a risky assumption that future climate will
fall within the range of past climate variability, flying in the face of the
huge body of climate change research and projections for a dryer future,
particularly in the southern basin and here in Victoria.
The Wentworth Group has consistently criticised the lack of
consideration of climate change projections in later versions of the Basin Plan
and have stated that this position actually 'conflicts with Government Policy
on climate change.'
A similar criticism was noted following the modelling of the relaxed
constraint scenarios just prior to the release of the final Basin Plan. The response
from the Australian Conservation Foundation to a question about the improved
environmental outcomes achieved through this modelling states:
Senator RUSTON: ...What is the increase from that 57
per cent [of the MDBA's environmental targets achieved] once you add the 450
[GL/y additional reduction in take] onto it?
Mr La Nauze: According to the authority's modelling,
it goes up to
67 per cent [of the MDBA's environmental targets achieved]. But that excludes
any undermining by excessive groundwater extraction or diminished inflows due
to climate change. That is [the MDBA's] modelling based on historical climate
The call, noted above, for incorporating predicted climate change impacts
into the SDLs is not new. Following the release of the Guide, the House of
Representatives Standing Committee on Regional Australia's report Of drought
and flooding rains: Inquiry into the impact of the Guide to the Murray-Darling
Basin Plan (Windsor Report) emphasised the importance of considering the forecast
impacts of climate change in developing the SDLs for the Basin Plan:
Recommendation 2: The Committee recommends that the Murray-Darling
Basin Authority apply greater rigour to the assumptions made to develop the
proposed sustainable diversion limits, including the forecast impact of climate
change, taking into account regional variability.
The committee is of the view that the Windsor report's recommendation
regarding the forecast impact of climate change has not been adequately
addressed in the Basin Plan. This is consistent with the number of criticisms
noted above that the Basin Plan does not appropriately address predicted
impacts of climate change in its modelling of reduction of take scenarios.
The committee acknowledges that incorporating the predicted impacts of
climate change into the relevant risk management strategies (as per chapter 4
of the Basin Plan) is the most realistic option for managing the predicted impacts
of climate change given the Basin Plan has now come into effect. As a result,
the committee urges that the MDBA specifically include the predicted impacts of
climate change when implementing these strategies. The committee also considers
that further research into the predicted impacts of climate change on water
runoff in the Basin is necessary to properly implement the Basin Plan.
The committee recommends that the MDBA specifically include the predicted
range of impacts of climate change on water runoff when implementing the
relevant risk management strategies under chapter 4 of the Basin Plan.
Consistent with Recommendation 20, the committee recommends that the
government develop a clear research strategy on the future impacts of climate
change on water runoff in the Basin. The strategy should also include a process
for integrating the results of the research into the adaptive management process
under the Basin Plan.
Interceptions have not been
adequately reflected in modelling
Related to the issue of predicted climate change and the reliance on the
historical data, the committee heard evidence that the treatment of water
interception in the Basin Plan could be improved. Commenting on the Basin Plan
(November 2011) Dr Rhondda Dickson, Chief Executive, stated:
...the plan itself was based on...the best available estimate
of interceptions that we have at the moment. We would be the first to
acknowledge that the estimate of interceptions can be improved, and there are large
areas of uncertainty about future interceptions, about the interplay of climate
change and losses to the ground, between temperature as well as the
interception changes. However, what we have done in the plan is...used as the
starting point the best available information where we do have confidence,
which is the historical record.
The MDBA noted further that interception activity has only been captured
in the modelling in a 'point in time' approach. As Dr Dickson explained:
There are a whole range of projections out there—what future
irrigation use might be and future interceptions from farm dams and from a
whole range of things. That is the future. All we have done is set a limit
which is the best idea of what we have now and any future changes will need to
be within that limit. If there is going to be a huge expansion of plantation
forestry that is going to [increase] interceptions further that would have to
be traded off against an irrigation entitlement in a water resource sharing
Despite this, the MDBA advised the committee that interception activity
by commercial plantations and runoff dams have been 'taken into account' in the
modelling through 'developing the baseline diversion limits for the proposed
The Plain English Summary of the proposed Basin Plan also outlined
that interception activity needs to be captured in the water resource plans which
will be managed by Basin states:
The water resource plan must list the classes of interception
activity that have been identified. When deciding whether an activity needs to
be listed, consideration must be given to the location of the activity, its
likely impact and likely growth over time. If there is interception by a runoff
dam, a commercial plantation, mining activity (including coal seam gas mining)
or floodplain harvesting, in the water resource plan area, those activities
must be included on the list.
Where such a list is included, the water resource plan must
set out how the impacts of each class of interception activity will be
monitored. The plan must also state what action will be taken if monitoring
shows that the impacts of the activities have a significant impact on an
environmental watering requirement, or there is an increase in the quantity of
water being intercepted by an activity.
The committee heard evidence that the Basin Plan also appears to fail to
account for interceptions from biodiversity planting projects. Professor Mike
Young provided information to the committee that stated:
Under the [Basin Plan (November 2011)], States will be
required to adjust for the adverse effects on water availability of increased
forestry, increases in farm-dam interception and increases in the capture of
Missing from the [Basin Plan (November 2011)] is a
requirement for the adverse interception effects of biodiversity plantings to
be fully accounted for.
The MDBA's response to this issue was that although the Basin Plan
(November 2011) listed some types of interception activities, like commercial
plantations or runoff dams, this was not intended to be an 'exclusive list'.
The MDBA explained that the Basin Plan had an 'assessment of how much
interception is going on at the moment'
and that if the level of interception increases in the future, that it must be
monitored by states and that this process was contained in the Basin Plan.
Specifically, Mr Russell James, Executive Director, Policy and Planning,
MDBA advised the committee:
[I]n the future there needs to be monitoring arrangements put
in place and in future the interception increases regardless of what is causing
that—whether it is biodiversity plantings or other things. Those are things
that will have to be taken into account in the way in which water is kept
within the diversion limit.
In the final Basin Plan, there is the obligation for water resource
specify whether there are any types of interception activity
in the water resource plan area which have the potential to have a significant
(a) the water resources of the water resource plan area; or
(b) water resources which are hydrologically connected to the
water resources of the water resource plan area...
However, the following note for guidance is also added to the relevant
section, with biodiversity planting not specifically listed:
The following are types of interception activity which may
have the potential to have a significant impact on the water resources of a
water resource plan area:
(a) interception by runoff dams;
(b) interception by commercial plantations;
(c) interception by mining activities, including coal seam
(d) interception by floodplain harvesting.
The committee understands and accepts that future intercepts will need
to fall within each state's water resource plan. In the committee's view this
must include all forms of interceptions (such as runoff dams, commercial
plantations and biodiversity planting, mining activities (including coal seam
gas mining) and floodplain harvesting) so that the overall water diversion cap
is not compromised. The committee notes that although biodiversity planting has
not been specifically listed, the final Basin Plan refers to 'any types of
interception activity...which have the potential to have a significant impact'
which appears sufficiently broad to capture biodiversity plantings.
Nevertheless, the committee has concerns regarding the modelling of
historical change in rain water run-off and the lack of appropriate modelling
of interceptions. In taking this approach, the MDBA continues to ignore calls
from stakeholders, including from parliamentary committees, to consider all
factors in its modelling, particularly the interception activities.
The committee recommends that the MDBA model a range of possible future
intercept scenarios and publish the results so that each state can better plan
for the impacts of the interception on its overall consumptive water
The committee recommends that, in undertaking its adaptive management
approach to the Basin Plan, the Murray Darling Basin Authority clearly
considers, assesses and incorporates all elements that could impact environmental
watering requirements. This includes climate change, interception activities,
coal seam gas mining, surface-groundwater connectivity and possible negative
effects such as over watering caused by increased river flows. This information
should be clearly set out in non-technical language and be made publicly
available in a timely manner.
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