The following table shows that there is a surplus of 786,838 ML 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 2011||1,188,822|
|Less water assets not available to be accessed, taken or delivered:|
|Less total water liabilities as at 30 June 2011:||13,946|
|Less future water commitments expected to be settled within 12 months of the reporting date|
|Expected diversion of surface water allocation||6,512|
|Expected non-allocated diversions to users (surface water)||16,883|
|Expected diversion of ground water allocations (urban water system)||10,196|
|Expected delivery of urban water to system users (individual users)||332,913|
|Surplus / (deficit) of available water assets over water liabilities and future water commitments expected to be settled within 12 months of the reporting date||786,838
The expected diversions and extractions are based on abstractions made during the 2010–11 year. Record high rainfall during the 2010–11 year has resulted in higher storage levels across the region compared to previous years. As a consequence, more surface water is available in the region and, therefore, it is likely that surface water allocation will remain high in the 2011–12 year.
Runoff to surface water increased in the 2010–11 year by over 200% compared to the 2009–10 year, meaning that the full volume of allocations can be met in the year.
During the 2010–11 year, 30,626 ML of groundwater allocations were forfeited, indicating that entitlement holders had sufficient surface water available for irrigation and water supply.
The expected volume for delivery of urban water to the region was estimated from the average of the 2009–10 year and the 2010–11 year urban water use, reported at 19.4 Delivery to urban water system users.
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 PCV's were determined by the Victorian Department of Sustainability and Environment. They 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 dependant 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 providers within the Melbourne region are required to supply potable water to residential 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 2010–11 year, 343,000 ML of potable water was supplied to residential customers within the Melbourne region. Notwithstanding any major changes, it is expected that a similar volume of water (333,000 ML; the average of the previous two water years) will be required to be delivered in the 2011–12 year.
It is estimated that 13,946 ML will need to be delivered in the 2011–12 year. The amount of water delivered is contingent on the irrigators of the Melbourne region drawing water from the system.