Melbourne
5.2 Surface water allocation remaining – urban water system

Supporting information

The line item value for the 2012-13 year is (495,189 ML). The value represents the total volume of water that Melbourne's retail and regional water authorities are entitled to within the Melbourne region.

Quantification approach

Data source

Melbourne Water Annual Report (2013); Western Water Annual Report (2013)

Provided by

Melbourne Water; Western Water

Method

Within the Melbourne region several bulk entitlements are in place which govern the source, volume, and arrangements under which the retail water authorities can divert surface water for urban water supply. Each bulk entitlement specifies an annual (or rolling annual average) volumetric upper limit; however, formal annual allocations are not made. As allocations are not made, carry-over of allocations is not possible.

Under the majority of the bulk entitlements, however, the retail and regional water authorities are entitled to a share of storage. This fluctuates annually depending on inflows to (rainfall, runoff) and outflows (evaporation, other losses) from the storages. This share of storage, at the start and end of the year, is recognised at this line item, as shown in the following table.

Melbourne retail and regional water authorities' share of storage at the start and end of the 2012–13 year

Entitlement holder

Source–bulk entitlement

30 June 2013 (ML)

30 June 2012 (ML)

City West Water

Yarra River1

428,906

535,307

South East Water

Yarra Valley Water

City West Water

Tarago and Bunyip rivers2

29,547

19,434

South East Water

Yarra Valley Water

Western Water

Melbourne Headworks system3

0

0

Western Water

Maribyrnong catchment

Gisborne—Baringo Creek

15

20

Lancefield

9

46

Macedon and Mount Macedon

360

461

Maribyrnong

18,596

15,739

Riddells Creek

43

71

Romsey

72

297

Subtotal Maribyrnong catchment

19,095

16,634

Western Water

Werribee catchment

Myrniong4

0

0

Werribee system

17,641

17,243

Subtotal Werribee catchment

17,641

17,243

Total

495,189

588,618

1–2 The storage volume data does not include dead storage and was provided by Melbourne Water. It refers to a share of storage capacity only, and therefore does not correspond to the storage data reported at line item 1.1 Storages.

3–4 These entitlements do not include a share of storage capacity; therefore the volume reported as claim remaining is zero.

Detailed information on the bulk entitlements used for urban water supply in the Melbourne region, including annual volumetric entitlement limits and share of storage, is provided in line item 32.3.

The Melbourne retail and regional water authorities' share of storage at the end of the 2012–13 year was derived from the opening storage volumes, inflows, diversions, and outflows or losses from the storages. These calculations are presented in the following tables for those entitlements which include a share of storage.

Calculation of the Melbourne retail water authorities' share of storage in the Melbourne region for the 2012–13 year
Account
Volume (ML)
Opening balance at 1 July 2012 588,618
11.18 Increase of urban claim on surface water 368,435
11.12 Entitled diversion of allocated surface water to urban water system (408,812)
19.17 Adjustment and forfeiture of urban claim on surface water (53,052)
Closing balance at 30 June 2013 495,189

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

The uncertainty estimate was not quantified.