Melbourne
Future outlook

Future prospects

Table 1 shows that there is a surplus of available water assets over water liabilities and future water commitments that are expected to be settled within 12 months of the reporting date.

Table 1 Future prospects for the Melbourne region

 

Volume (ML)



Total water assets as at 30 June 2013

1,445,709

Less water assets not available to be accessed, taken or delivered within 12 months of the reoprting date


Dead storage1

21,534


1,467,243

Less total water liabilities as at 30 June 2013

0


1,420,245

Less future commitments expected to be settled within 12 months of the reporting date


Expected diversion of allocated surface water to users (irrigation scheme)2

7,568

Expected surface water transfer under inter-region agreement3

3,133

Expected extraction of allocated groundwater to users4

14,278

Expected delivery to urban water system users5

351,589

Surplus / (deficit) of available water assets over water liabilities and future commitments expected to be settled within 12 months of the reporting date

1,090,675



add Future rights expected to be realised within 12 months of the reporting date


Expected delivery of water under inter-region agreement6

33,334

Surplus / (deficit) of available water assets, expected future inflows and future water rights over water liabilities and future water commitments within 12 months of the reporting date

1,124,009

1Dead storage for surface water–refer to line item 1.1 Storages

2Average of 2009–10, 2010–11, 2011–12, and 2012–13 surface water diversions reported at line item 17.11 Entitled diversion of allocated surface water to users

3Average of 2009–10, 2010–11, 2011–12, and 2012–13 surface water diversions reported at line item 17.14 Surface water transfer under inter-region commitment

4Average of 2009–10, 2010–11, 2011–12, and 2012–13 groundwater extractions reported at line item 18.11 Entitled extraction of allocated groundwater to users

5Average of 2009–10, 2010–11, 2011–12, and 2012–13 urban water use reported at line item 19.4 Delivery to urban water system users

6Average of 2009–10, 2010–11, 2011–12, and 2012–13 water delivered from outside the region reported at line item 9.11 Delivery of water under inter-region agreement to surface water

The volumes reported for future water rights and future water commitments are indicative only. The volumes presented in Table 1 were estimated from the average diversions and extractions in the previous four years. The actual volume of water delivered under these future water rights and future water commitments will depend on climatic conditions and demand.

Above average rainfall was experienced in the Melbourne region in both 2010–11 and 2011–12, increasing water availability and corresponding to a reduction in demand on water resources. These wetter conditions also enabled surface water storage levels to recover considerably. Consideration of diversions and extractions from these two years is likely to result in an underestimate of expected diversions and extractions for an average rainfall year.

Rainfall for the 2012–13 period was below average and the region was much drier than the previous two years. Therefore the commitments stated in Table 1 are likely to be slightly underestimated and the surplus after the commitments is likely to be a slight overestimate of available water assets. 

Although it was not possible to quantify future inflows, it is expected that with current storage levels even below average inflows will meet the demands of future water commitments. The Victorian desalination plant at Wonhaggi was commissioned in December 2012 and is now another source for future urban water supply when required.

Contingent water assets and contingent water liabilities

Contingent water assets

The non-extractable portion of groundwater in the region (volume unknown)

Sustainable yields have been estimated for all ground water resources within Victoria, in the context of the permissible consumptive volumes (PCV). These were determined by the Victorian Department of Environment and Primary Industries and represent the long-term average annual volume permitted to be extracted from aquifers within the Melbourne region. The limits are set to ensure groundwater is maintained at a sustainable level, and is sufficient to maintain groundwater dependent ecosystems within the region.

The methods used to determine sustainable yields varied across the State according to the characteristics of the aquifers being investigated, and in many cases the full volume of the aquifer cannot be accurately quantified.

Water resource managers within the Melbourne region must adhere to the PCV extraction limitations for groundwater resources in the Melbourne region. The combined volume of the PCV has been recognised as a water asset in the water account. The volume of water that is beyond this extraction limit is considered a contingent water asset in the Melbourne region; however, there is currently not enough information available regarding the aquifers in the region to allow for a volumetric estimate.

Contingent water liabilities

Potable and non-potable water for urban use (367,000 ML)

Urban water retail authorities within the Melbourne region supply potable and non-potable water to customers throughout the region. Water providers maintain water within distribution pipes for the delivery of water to the city but the actual delivery of water is determined by the customers when they turn on the tap. During the 2012–13 year, 381,256 ML of potable and non-potable water was supplied to residential customers within the region. Notwithstanding any major changes, it is expected that a similar volume of water (367,000 ML; the average of the previous two water years) will need to be delivered in the 2013–14 year.

Water for irrigation use (10,000 ML)

Southern Rural Water provides water to the Bacchus Marsh and Werribee irrigation districts in the Melbourne region; however, the actual delivery of the water is contingent on the irrigators of the Melbourne region drawing water from the system. It is estimated that 10,000 ML will need to be delivered in the 2013–14 year.