National Water Account 2018

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Key findings

Climate and water

Water Accounting Statements

Supporting information

Region description

Reference information

Melbourne: Statement details

Water assets

Surface water assets

• More than half of the surface water assets are inter-region claims, which are the portion of water in the Thomson Reservoir and Lake Eildon set aside for water supply to the Melbourne region.
• Most of the remaining surface water asset volume is water held in storages.

Storages

Figure S1 Total storage volume in the region at 30 June 2018 compared with the previous eight years

• Storage volumes decreased from 64% full at 30 June 2017 to 59% full at 30 June 2018.
• The end of year storage volume of 59% was the lowest since 2010.

Figure S2 Percentage-full volume on 30 June 2018 for each storage

• Storage volumes peaked in late-September 2017 following rainfall during the winter months, and then declined for the remainder of the year. 
• Storage in the Pykes Creek and Melton reservoirs, which are used primarily for irrigation supply, dropped by more than 20% from last year due to the relatively dry conditions.
• More detailed information on the individual storages within the region is available on the Bureau of Meteorology's Water Storage website.

Inter-region claims

• Inter-region claims refer to the volume of allocation remaining on licence entitlements from inter-region sources at the end of the 2017–18 year.

• Water supply from the Thomson Reservoir is classified as an inter-region transfer and is the primary source of water supply outside the region boundary.
• Over 90% of the total claim at 30 June 2018 is related to water delivery from the Thomson Reservoir.
• A more detailed description of inter-region water sources for the Melbourne region is given in the Region Description.

Figure S3 Inter-region claim from Thomson Reservoir at 30 June 2018 compared with the previous eight years

• The inter-region claim from the Thomson Reservoir at 30 June 2018 was 6% less than that at 30 June 2017 because water transfers from the reservoir into the Melbourne region during the year were relatively higher than the reservoir inflows.

Groundwater assets

Figure S4 Permissible consumptive volumes: water table and underlying aquifers in the Melbourne region

• The groundwater asset volume for the region represents permissible consumptive volumes for water table aquifers and underlying aquifers in groundwater management and water supply protection areas.
• The groundwater asset volume remained constant during the year as there was no change in licences or the permissible consumptive volume.

Urban water system assets

• The urban water system asset volume at 30 June 2018 was 510,500 ML, most of which is the claim on surface water.
• The remaining urban water asset volume is water held in lagoons at wastewater treatment plants, which changes little from year to year.

Water liabilities

• Water liabilities in the Melbourne region refer to the volume of allocation remaining on licence entitlements at the end of the 2017–18 year. 

• As there are no carryover provisions for groundwater supply licences in the region, the portion of water allocation that has not been abstracted at the end of a water year is forfeited and the allocation remaining at the end of the year was 0 ML.
• A more detailed description of water allocations and associated water rights in the Melbourne region is given in the Water access and use note.

Water asset increases

• Total water asset increases for the year was 2,167,005 ML.
• The key item contributing to water asset increases for the region was runoff, which made up approximately 40% of the total water asset increases. Runoff was less than average, and much less than last year, due to the below-average rainfall conditions across the region for most of the year (see Climate and water).
• Recharge: landscape represented more than 50% of the total groundwater increases and was also less than the previous year.

Water asset decreases

• Total water asset decreases for the year was 1,869,892 ML.
• The key item contributing to water asset decreases for the region was outflow, which made up approximately 35% of the total water asset decreases. Outflow was more than 30% below average due to the relatively poor rainfall conditions during the year, particularly during winter–spring 2017 (see Climate and water).
• Supply system delivery: urban users, which changes little from year to year, made up around 45% of the total urban water system decreases.

Water flows

• Total water inflows to the region was 2,115,984 ML, which differs from the volume of Water asset increases (2,167,005 ML). Total water inflows include the volume of water delivered under inter-region claims; total water asset increases include the annual allocation for inter-region claims.
• Total water outflows from the region was 2,230,104 ML, which differs from the volume of Water asset decreases (1,869,892 ML). Total water outflows include the flows corresponding to the accrual transactions—allocated diversions and allocated extractions. Total water asset decreases include the forfeiture of inter-region claims.
• A detailed description of all the water flows associated with the surface water and groundwater stores, as well as the urban system, is provided in the Water stores note.

Unaccounted-for difference

• The unaccounted–for difference is the volume necessary to reconcile the opening water storage and closing water storage with the total water inflows and total water outflows reported in the water accounting statements.

• The unaccounted-for difference value is primarily attributed to uncertainties associated with the runoff and river outflow estimates, as well as unaccounted groundwater information including discharge to landscape and rivers.