Melbourne
11.12 Entitled diversion of allocated surface water to urban water system

Supporting information

a. Surface water diverted to the urban water system in the 2012–13 year

The line item value for the 2012-13 year is (408,812 ML). The value represents the volume of water diverted from surface water for distribution via the urban water supply system under the various bulk entitlements held by Melbourne's retail water authorities, including Western Water. The volume reported includes:

  • Bulk water supplied by Melbourne Water to the City West Water, South East Water, and Yarra Valley Water  from the Yarra, Tarago and Bunyip rivers and to Western Water from the Melbourne Headworks system.
  • Surface water diverted from the Maribyrnong and Werribee river basins by Western Water under various bulk entitlements. Surface water is primarily diverted from storages managed by Southern Rural Water, but also includes diversions from smaller storages operated by Western Water.

Refer to line item 3.7 Urban claim on surface water for more information on these bulk entitlements.

The following table shows the volumes of surface water diverted for urban water supply by Melbourne Water and Western Water during the 2012–13 year. 

Surface water diversions to the urban water system
Authority Volume (ML)
Melbourne Water—bulk water supplied to retail water authorities
406,268
Western Water—surface water diverted from the Maribyrnong and Werribee rivers
2,544
Total 408,812


The volume of surface water diverted for bulk water supply by Melbourne Water is derived from the volume of water supplied to the retail authorities accounting for losses between the point of diversion and the point of supply to the authorities. This is explained in more detail in the quantification approach.

The volume of surface water diverted by Western Water is the metered volume at various offtake points. This is explained in more detail in the quantification approach.

The volume reported does not include water delivered by Melbourne Water to Gippsland Water (see 17.14 Surface water transfer under inter-region commitment).

Melbourne Water reports estimated proportions of water released from each of the reservoirs as an indication of the proportion of water intake from each reservoir to supply the total volume of bulk water (see following table).

Estimated proportions of water released from surface water storages
Release location Percentage of total released
Cardinia 26%
Silvan 41%
Winneke 22%
Tarago <1% 
Yan Yean <1%
Greenvale 9%
Yarra Valley (small treatment plants) <1%
Total 100 %

b. Urban water supply system overview

The urban water supply system is one of three sub-components of Melbourne's urban water system. The three sub-components are the:

  • urban water supply system
  • wastewater system
  • recycled water system.

During the 2012–13 year Melbourne's urban water was sourced mostly from surface water (line item 11.12), with a very small proportion sourced from groundwater (line item 11.13). While a desalination plant has been built at Wonthaggi to supplement Melbourne's urban water supply, this was not required to supply any water during the 2012–13 year.

Urban water consumption (line item 19.4) of potable and non-potable water was 361,339 ML during the 2012–13 year, comprising of 360,931 ML of potable water and 408 ML of non-potable water, representing almost 90% of all urban water supply system outflows. A very small volume of water was transferred out of the region via normal operations in Western Water's service area (line item 19.11). Non-revenue water, including pipes bursting (line item 19.2), background leakage (line item 19.3) and other losses (line item 19.20), made up the remaining urban water supply system outflows.

The following figure shows all the inflows and outflows for the urban water supply system. For more detail on a particular flow associated with the urban water supply system, refer to the line item notes.

Schematic diagram of water inflows and outflows for Melbourne's urban water supply system during the 2012–13 year; line item numbers are provided in brackets
Schematic diagram of water inflows and outflows for Melbourne's urban water supply system during the 2012–13 year; line item numbers are provided in brackets

A small misbalance 127 ML from the previous figure can be attributed to possible differences in metering accuracies and unaccounted losses associated with water intake and supply.

Quantification approach

Melbourne Water

Data source

Waterworks database.

Provided by

Melbourne Water.

Method

The total volume of surface water diverted for bulk water supply was calculated from the following two components:

  • volume of potable and non-potable water supplied to the retail water authorities
  • volume of losses from the potable water system. 
The breakdown of these volumes is shown in the following table.

Melbourne Water – Surface water diverted for bulk water supply
Component Individual items Volume (ML)
Total volume of water provided to the urban retail water authorities by Melbourne Water  potable water provided to City West Water 103,231
potable water provided to South East Water 140,539
potable water provided to Yarra Valley Water 149,306
potable water provided to Western Water 10,433
non-potable water provided to Yarra Valley Water - water taken from Maroondah aqueduct as direct supply to customers 329
non-potable water provided to South East Water - water taken from Bunyip River as direct supply to customers 77
subtotal: volume provided to urban retail water authorities 403,915
Total volume of losses and leakage  loss of potable water from major pipes - line item 19.2 38
loss of potable water due to minor leaks - line item 19.3 21
loss of potable water through service reservoir and tank dewatering - line item 19.20 163
loss of potable water through operational activities - line item 19.20 2,131
subtotal: losses from the potable water system 2,353
Total 406,268

Bulk water supplied to retailers

Volumes were calculated using the weekly metered volume of bulk water supplied by Melbourne Water to urban retail water authorities. Metered volumes are based on Melbourne Water bulk meters located at the interface between Melbourne Water and each of the retail water authorities. 

Losses from the potable water system
Refer to the individual line item quantification approaches (as shown in the table) for the methods used to estimate losses from the potable water system.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

Volumes shown in the above table are based on flow meter measurements. The flow meters are generally ultrasonic flow meters for larger pipes (greater than 600 mm diameter) and magnetic flow meters for smaller pipes (less than 600 mm diameter). Both types of meters have an accuracy of +/– 1% as reported by the manufacturers.

Western Water

Data source

Western Water metering database and Southern Rural Water database.

Provided by

Western Water.

Method

The volume of surface water diverted for urban supply was calculated using the weekly metered volume of surface water diverted from the Merrimu, Rosslynne, Pykes Creek, Kerrie, Djerriwarrah, Garden Hut, and Wright reservoirs and treated at the Myrniong, Merrimu, Rosslyne, Romsey and Lancefield water filtration plants (WFP). It also includes water diverted from Macedon and Mt Macedon storages to supplement surface water storages in Woodend. Meters are located on outlet pipes from reservoirs.

Western Water–surface water taken for bulk water supply
Surface water intake point Water filtration plant
Volume (ML)
Forster and Wright reservoirs Romsey 32
Garden Hut Creek Reservoir Lancefield1 95
Kerrie Reservoir Romsey 371
Macedon and Mt Macedon storages Reservoir C
250
Merrimu and Djerriwarrh reservoirs Merrimu2 1,707
Pykes Creek Reservoir Myrniong 39
Rosslynne Reservoir Rosslynne 50
Total     2,544

1–2 This volume included non-potable and potable water supplied to users.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

Uncertainty is +/– 5% in accordance with the manufacturer's annual bulk meter test.