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Draft Basin Plan and Environmental water


The Murray Darling Basin Authority (MDBA) released the long-awaited Draft Basin Plan on 28 November 2011. The plan will be available for public comment until 16 April 2012. The MDBA also released a Socio-economic analysis of the plan, and a plain English summary, Delivering a healthy working basin, that is intended to put the ideas into a broader context. Criticism began almost as soon as the document went out.

But first, what is the purpose of the plan, and what does it propose?

The draft Basin Plan outlines the amount by which Australia needs to reduce its consumption of water from the Murray-Darling Basin. Water consumption needs to be reduced in order to preserve the river system into the future. The reduction in the amount of water allowed to be taken under the proposed Plan is the difference between what is referred to as surface water baseline diversion limits (BDLs), as at 2009, and long-term average sustainable diversion limits (SDLs). Note that surface water BDLs include not just diversions from water courses and floodplain harvesting but also interceptions by runoff dams and by commercial forest plantations. SDLs are not currently in effect across the Basin, but it is proposed that they will become so in 2019.

The reduction in BDLs in the draft Basin Plan is 2,750 Giglalitres/y (GL) and is in addition to the 823 GL/y of environmental water that was recovered for the use in the MDB before 2009. This will mean that by 2019, when the surface water SDLs will be included in all the Water Plans in the MDB, a total of 3,578 GL/y of water will have been returned to the environment. The seven year transition period for the SDLs to be finally enforced is to reduce the socio-economic impacts of the reduction in diversions.

The 2010 Guide to the Basin Plan proposed that 3,000–4,000 GL/y be considered as the additional water required by the environment. It is not clear whether the 2,750 GL/y figure should be considered as a reduction in environmental water compared to the 3,000 GL/y figure or whether the 3,578 GL/y figure should be used instead.

According to the plain English summary, setting the SDLs requires a balance of environmental, socio-economic and operational factors and must be based on future rather than historic sustainability. The MDBA media release stated why the reduction in water diversions was less than the 3,000-4,000 GL/y proposed in the 2010 Guide to the proposed Basin Plan. “More recent and robust modelling has shown that key environmental objectives can be met with a lower volume than the range suggested in the Guide. The lower volume, based on the modelling, will achieve the objectives of keeping the Murray flowing to the sea nine years out of ten, to flush salt from the system and water important sites in the Basin.”

The MDBA aimed to strike a balance and originally adopted the lower 3,000 GL/y figure from the Guide to minimise social costs. This was further reduced to 2,800 GL/y when further studies showed that lower levels of reductions in the northern Basin were needed. Their studies of a 3,200 GL/y scenario indicated this would give minor environmental improvements but at much higher socio-economic costs.

The reduction of 2,750 GL/y is not all in the future. 1,068 GL/y of this water has already been recovered over the period 2009 through September 2011. It is expected that Stage 2 of the Northern Victorian Irrigation Renewal Project will contribute a further 214 GL/y in the future. This leaves reductions of 1,468 GL/y still to be found. Future reductions will be achieved by investment in water-saving infrastructure and water purchases from voluntary sellers

Environmental water will need to be found both to meet the needs of the Murray River and to meet the local environmental water needs of individual river catchments. The shared reductions to meet the needs of the Murray River total 971 GL/y from the southern Basin and 143 GL/y from the northern Basin. No details of the precise quantities of these reductions per catchment will be known until the total shared reductions are achieved across the MDB.

In many cases local reductions for individual river catchments have already been achieved, and as a result there is no further reduction required in these catchments. Note that the BDL in the ACT (Murrumbidgee) is the same as the SDL so no reduction is required. The four catchments in the northern Basin that still need to find local reductions are the: Condamine-Balonne (95 GL), Queensland Border Rivers (1 GL), Barwon-Darling Watercourse (6.9 GL) and Namoi (5 GL). Those nine catchments in the southern Basin are: Murrumbidgee (183 GL), NSW Murray (68 GL) Lower Darling (7.6 GL), Victorian Murray (63 GL), Goulburn (99 GL), Campaspe (12 GL), Loddon (10 GL), Wimmera-Mallee (23 GL) and South Australian Murray (22 GL). Note that 26 GL/y in savings has already exceeded the environmental needs of some river catchments in the northern Basin and it will contribute to the Murray River shared reduction total.

In the case of groundwater BDLs and SDLs, the only groundwater resource units where a reduction in the BDL to meet the SDL is required are in the Victorian Riverine Sedimentary Plain, the Upper Condamine Alluvium (Central Condamine Alluvium) and the Upper Condamine Alluvium (Tributaries). The Lower Lachlan Alluvium is expected to be reduced to the SDL by 2018.

In calculating the SDLs, the MDBA used the period 1895-2009 as the climate baseline because the median predicted climate change impacts on 2030 streamflow were within natural variability. It did note, however, that the surface water availability in the MDB in the decades to come is much more likely to decline than to increase.

CSIRO prepared a “Science review of the estimation of the environmentally sustainable level of take for the Murray-Darling Basin.” The review examined the 2,800 GL/y reduction scenario proposed by the MDBA and concluded that such reductions would not meet some specified hydrological and ecological targets. This is due to the fact that in some cases operational constraints prevent the delivery of environmental water and in others shortfalls against targets may be the result of insufficient environmental water.

The Greens Spokeswoman on Water, Senator Hansen-Young, is quoted as saying that she would recommend that the Greens should vote for a disallowance of the Basin Plan if the reduction in diversions was not raised to 4,000 GL/y. South Australian Premier, Jay Wetherill, is reported to have indicated that at least 3,500 GL/y needed to be returned to the Murray and his government may consider launching a High Court challenge to the Basin Plan if this does not occur.

One of the objects of the Water Act 2007 is to “promote the use and management of the Basin water resources in a way that optimises economic, social and environmental outcomes.” Of course, it can be argued that the environment should take precedence, because if environmental services are permanently damaged, the economic and social structures that rely on the Basin will also fail. Although the MDBA has tried to balance the environment with social and economic imperatives, it has not proved possible to please all parties and so there may yet be legal challenges to the Basin Plan. The 2010 advice from the Australian Government Solicitor discusses this matter and has been used by both sides of this argument to support their case.

Authored by Bill McCormick