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.
|Total water assets as at 30 June 2012
|Less water assets not available to be accessed, taken or delivered within 12 months of the reoprting date|
|Less total water liabilities as at 30 June 2012
|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
|Expected surface water transfer under inter–region agreement3||3,100
|Expected extraction of allocated groundwater to users4||13,900
|Expected delivery to urban water system users5||341,700
|Surplus / (deficit) of available water assets over water liabilities and future commitments expected to be settled within 12 months of the reporting date||1,056,848|
|add future rights expected to be realised within 12 months of the reporting date|
|Expected delivery of water under inter–region agreement6||35,700
|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||1,092,548
1Dead storage for surface water – refer to line item 1.1 Storages
2Average of 2009–10, 2010–11 and 2011–12 surface water diversions reported at 17.11 Entitled diversion of allocated surface water to users
3Average of 2009–10, 2010–11 and 2011–12 surface water diversions reported at 17.14 Surface water transfer under inter–region commitment
4Average of 2009–10, 2010–11 and 2011–12 groundwater extractions reported at 18.11 Entitled extraction of allocated groundwater to users
5Average of 2009–10, 2010–11 and 2011–12 urban water use reported at 19.4 Delivery to urban water system users
6Average of 2009–10, 2010–11 and 2011–12 water delivered from outside the region reported at 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 three 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. These conditions suggest that diversions and extractions during these two years are likely to underestimate expected diversions and extractions in an average rainfall year.
Preliminary climate data suggest that 2012–13 will be drier than the previous two years. Therefore the future prospects suggested in Table 1 are likely to overestimate the surplus 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 commissioning of the Wonthaggi desalination plant will probably lessen dependence on surface water as a source for urban water supply. However, the timing of the delivery of the first desalinated water will probably be such that this lessening dependence on surface water is realised in future years, rather than the 2012–13 year.
Contingent water assets and water liabilities
Contingent water assets
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 Sustainability and Environment 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
Urban water retail authorities within the Melbourne 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 2011–12 year, 353,309 ML of potable and non-potable water was supplied to residential customers within the Melbourne region. Notwithstanding any major changes, it is expected that a similar volume of water (350,000 ML; the average of the previous two water years) will be required to be delivered in the 2012–13 year.
Southern Rural Water provide 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 2011–12 year.