Melbourne
Future outlook

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.

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.

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.

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.

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.