National Water Account 2016

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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

Surface water asset volume for the Melbourne region at 30 June 2016 was 1,107,787 ML, which comprised water held in storages (511,129 ML), regulated and unregulated rivers (4,553 ML) and inter-region claims  (592,105 ML).

Storages

The location of each storage within the Melbourne region and the volume of water in each storage (including dead storage) as a percentage of total storage capacity at the end of the 2015–16 year are shown in Figure S1.

Figure S1 Percentage-full volume on 30 June 2016 for each storage

Total surface water storage and inter-region claim volume for Thomson Reservoir at 30 June 2016 compared with the previous six years are given in Figure S2.

Thomson Reservoir is the largest storage supplying water to the Melbourne metropolitan area located outside the Melbourne region boundary. Therefore, it is not shown in Figure S1. Water sourced from Thomson Reservoir to the region is treated as an inter-region transfer.

The total storage volume within the Melbourne region at 30 June 2016 was at 60% capacity. All four storages located in the western part of the region supplying water for irrigation activities experienced a major decrease in storage volume. The remaining eight storages supplying water for urban consumption were relatively unchanged collectively. The majority of these storages are connected through supply networks.

Figure S2 Total surface water storage volume and inter-region claim from Thomson Reservoir at 30 June 2016 compared with the previous 6 years

Rivers

The estimated volume of water in rivers (regulated and unregulated) was 4,553 ML at 30 June 2016.

Inter-region claims

Surface water claims (592,105 ML) in the Melbourne region refer to the remaining volume of surface water that Melbourne retail water authorities were entitled to under bulk entitlements from inter-region sources at the end of the 2015–16 year. There were claims associated with:

• bulk entitlements for Thomson Reservoir and Silver and Wallaby creeks
• rights to water from Goulburn and Murray systems (water held in Lake Eildon)
• bulk entitlements to desalinated water from the Victorian Desalination Plant.

Inter-region water claims on Thomson Reservoir and Silver and Wallaby creeks were major contributors to urban water supply. If the volume of water transferred from the Thomson Reservoir had not been increased by 66%, total volume of the storages within the region would have been below 50% at the end of the 2015–16 year.

Inter-region claims for water from all the sources at the beginning and end of the 2015–16 year are summarised in Table S1.

Inter-region claim for water in the Thomson Reservoir

The inter-region claim for water in the Thomson Reservoir was 556,617 ML for Melbourne region's urban water supply at the end of the 2015–16 year. This represents 94% of the closing balance stated in Table S1. The inter-region claim at end of the year is the volume allowed to be carried over to the following year for the entitlement holders from their unused water. The claim for water in the Thomson Reservoir decreased from 68% of the capacity to 52% between 2014–15 and 2015–16 reporting years (Figure S2).

Inter-region claim for water from the Silver and Wallaby creeks

Unused water allocated under the Silver and Wallaby creeks bulk entitlement is not carried over to the following year. As a result, the opening and closing balance of the claim remained zero for this source.

Inter-region claim on rights to water from Goulburn and Murray systems

The inter-region claim to water from the Goulburn and Murray systems (held in Lake Eildon) was 35,488 ML at the end of the 2015–16 year, which is a 3% increase from that of the previous year. This is due to an increase in allocated volume from the Goulburn and Murray systems during the 2015–16 year from that recorded for the previous year.

Claim for desalinated water from the Victorian Desalination Plant

The Victorian Government did not order any water from the desalination plant for the region during the 2015-16 year, hence the volume is zero ML.

Groundwater assets

The aquifers in the Melbourne region are described in the Water resources section of the 'Region description'. The groundwater asset volume for the Melbourne region represents permissible consumptive volumes for water table aquifer (22,054 ML) and underlying aquifers (16,565 ML) in groundwater management areas (GMAs) and water supply protection areas (WSPAs) (Figure S3).

Figure S3 Permissible consumptive volumes: water table and underlying aquifers in the Melbourne region

The groundwater asset volume remained constant during the 2015–16 year as there was no change in licences or the permissible consumptive volume.

The volume presented does not include groundwater in unincorporated areas outside of groundwater management units. Unincorporated areas have not been evaluated from a groundwater resource perspective and do not have established permissible consumptive volumes. The allocation limit for these unincorporated areas in the southern half of Victoria including the Melbourne region was 71,542 ML.

Urban system assets

Assets at 30 June 2016 were 29,828 ML and included water held in treatment plant lagoons in the wastewater system. The volume comprised water in:

• the Western Treatment Plant lagoons—27,725 ML
• storages and holding basins in the Eastern Treatment Plant—2,103 ML.

These volumes change little from year to year. The volume of water within the urban water supply system (distribution pipe network and service reservoirs), the recycled water system, and some of the lagoons receiving wastewater could not be quantified due to a lack of available data.

Water liabilities

Surface water

Surface water liabilities in the Melbourne region refer to the volume of allocation remaining on licensed entitlements at the end of the 2015–16 year.

The allocation (water liability increases), allocated diversion (water outflow), and the adjustment and forfeiture (water liability decreases) for entitlements is provided in the tables S2 to S6.

A more detailed description of surface water allocations and associated water rights in the Melbourne region is given in the Water rights note.

Carryover of unused water allocated for high-reliability and low-reliability water shares in the Werribee and Bacchus Marsh irrigation districts was not permitted in the previous years. The Victorian Minister for Water approved carryover provisions for the two irrigation districts on 22 June 2014. As a result, unused water in an allocation account at the end of the water year could be carried over to a limit of 100% of the entitlement volume subject to a 15% evaporation loss.

Within the Melbourne region, several bulk entitlements are in place that govern the source, volume, and arrangements under which the retail water authorities can divert surface water for urban water supply. Carryover of unused allocations from the reservoirs within Yarra, Tarago, and Bunyip has been made possible under the Bulk Entitlement Order 2014 for the Greater Yarra System–Thomson River Pool.

Bulk entitlements for the regional water sources other than the Greater Yarra System–Thomson River Pool specify an annual volumetric upper limit; but formal annual allocations are not made. As allocations are not made, carryover of allocations is not possible. Water authorities are, however, entitled to a share of the storage volume. This fluctuates annually depending on inflows into storages (rainfall, runoff) and outflows from storages (evaporation, other losses). This share of storage, at the start and end of the year, is recognised as carryover and included in Table S3.

Gippsland Water has a right to access water from the Tarago River under Bulk Entitlement (Tarago River–Gippsland Water) Conversion Order 2009. As the bulk entitlement does not provide for a share of storage, carryover of unused water is not permitted. Therefore, the volumes reported for the opening and closing balance of the inter-region commitment on surface water were zero (see Table S4).

Groundwater liabilities

Groundwater liabilities in the Melbourne region for the 2015–16 year (0 ML). They refer to the volume of groundwater allocation remaining on licence entitlements at the end of the year for individual users and the urban water system.

Carryover rules for groundwater entitlements throughout the Melbourne region do not allow unused water to be carried over at the end of the year. Therefore, any unused water is forfeited, resulting in a zero carryover volume. Details of the reconciliation of groundwater carryover, allocations, extraction, and forfeiture are provided in tables S5–6.

A more detailed description of groundwater allocations and associated water rights in the Melbourne region is given in the Groundwater rights note.

Urban water liabilities

There are no urban water liabilities recognised for the Melbourne region; however, there is between-store commitment within the region to supply water from surface water sources (Table S3) and groundwater sources (Table S6) to the urban water supply system.

Water assets increases

Total water asset increases for the region (1,663,747 ML) comprised:

• surface water increases—1,091,830 ML
• groundwater increases—  220,851 ML
• urban water system increases—351,066 ML.

The key water asset increases for the region were runoff and inter-region claims. These make up more than 63% of the total water asset increases. Runoff is climate-dependent and was less than for the previous year, reflecting the lower rainfall experienced across the region (see Climate and water). The inter-region claims were for Thomson Reservoir, Silver and Wallaby creeks and the Goulburn and Murray rivers systems which decreased mainly due to the reduced share of gross inflow.

Urban water system increases primarily represents wastewater collection. The volume of wastewater collected has changed little from year to year over the last 5 years (see Urban water store note).

Water assets decreases

Total water asset decreases for the region (1,704,380 ML) comprised:

• surface water decreases—827,955 ML
• groundwater decreases—136,831 ML
• urban water system decreases—739,594 ML.

The key water asset decreases for the region were river outflow from the region (surface water decrease) and inter-region coastal outflow (groundwater decrease). These two decreases were around 48% of the total water asset decreases. These flows is very climate-dependent and were lower than for the previous year, reflecting the lower rainfall experienced across the region (see Climate and water).

Urban water system decreases primarily relate to the delivery of water to the customers from the supply system. The delivery of water from this system is less climate-dependent than surface water and groundwater decreases and generally changes little from year to year.

Water flows

Total water inflows to the region (1,778,911 ML) are higher than the volume of Water asset increases (1,663,747 ML) because the region received more water than the entitled share of inflows (mainly from Thompson Reservoir) under inter-region claim.

Total water outflows from the region (1,679,173 ML) are lower than the volume of Water asset decreases (1,704,380 ML) because the volume of water outflows includes the flows corresponding to the accrual transactions, i.e. the allocated water abstractions (see the Water liabilities section above).

A detailed description of all the water inflows and outflows including between-store flows associated with the surface water store, groundwater store and urban water system is provided in the Water stores note. Between store flows are not included in the inflow and outflow volumes shown above (more details in water accounting policies note).

Unaccounted-for difference

The volume recognised in the water accounting statements (104,973 ML) represents the total unaccounted-for difference for the Melbourne region for the 2015–16 year.

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 (Table S7).

The unaccounted–for difference can also be calculated by adding the volumes necessary to reconcile (balance) the opening and closing storage with the water inflows and outflows of each of the separate water stores of the region, as shown in Table S8.

Table S8 shows that the unaccounted-for difference volume is largely explained by the surface water and groundwater store balancing item volumes. The surface water balancing item is attributed to uncertainty associated with runoff and river outflow (see Surface water store note). The groundwater balancing item is due to several unaccounted items e.g., discharge to surface water and discharge to landscape (not quantified this year) and overestimation of recharge from landscape (see Groundwater store note).