9.15 Increase of inter-region claim on water

Supporting Information

The volume presented in the water accounting statements (262,417 ML) represents the increase in the claim that Melbourne retail authorities City West Water, South East Water and Yarra Valley Water are entitled to under:                                                                                                                                                        

  • bulk entitlements for Thomson Reservoir, and Silver and Wallaby creeks
  • agreement for water held in Lake Eildon.

The following table presents the breakdown of increases to inter-region claims for the Melbourne region during the 2010–11 year.

Increases to inter-region claims
Component Volume (ML)
Share of inflows to Thomson Reservoir 203,636
Inflows from Silver and Wallaby creeks1 11,300
Allocation announcements: Goulburn River2 46,310
Allocation announcements: Murray River2 1,171
Total 262,417

1 Increase in the claims on the Silver and Wallaby creeks were recognised as equal to the volume delivered during 2010–11 (see 9.11 Delivery of water under inter-region agreement). There was no allocation announcement on the volume that can be taken from the resource, although an upper limit is specified in the bulk entitlements held by the Melbourne retail authorities.

2 Allocation announcements are made once a year around November, and are based on audited water savings achieved from modernisation projects in northern Victoria in the previous year (e.g. the 2009–10 year). The volume of water allocated is stored in Lake Eildon.

During 2010–11 inflows to the Thomson Reservoir almost doubled its storage volume, significantly increasing the inter-region claim for the Melbourne region. Allocation announcements for the region's entitlement to water from the Goulburn River was almost five times greater in the 2010–11 year compared to the 2009–10 year. This was attributable to completion of additional modernisation projects in northern Victoria and higher water use in northern Victoria's irrigation districts.

Quantification Approach

Data Source

Melbourne Water: Waterworks database.

Provided by

Melbourne Water.


Increases to inter-region claims held by the Melbourne Region were calculated using the following methods.

Thomson Reservoir
Inflow into Thomson Reservoir is not directly measured/gauged. Net inflow is determined using a mass–balance approach that considers the reservoir's measured daily outflows and changes in storage level. Inflow is the net of evaporation and referred to as net inflow.
Silver and Wallaby creeks

The volume of inflows from Silver and Wallaby creeks to the Toorourrong and Yan Yean Reservoirs occurs via Clearwater Channel. Clearwater Channel also diverts water from the Plenty River (in the Melbourne region) to Yan Yean Reservoir. The total volume of water transferred along the Clearwater Channel was metered after the point where water enters from Plenty River.

Based on historical records of catchment runoff, the flow along Clearwater Channel was estimated to comprise 64% of the water delivered from the Silver and Wallaby catchments, and 36% of water diverted from the Plenty River.

The volume of water transferred-in from the Silver and Wallaby catchments was derived by multiplying the Clearwater Channel meter reading by a factor of 0.64.

Lake Eildon

Allocation announcements made once a year around November, are based on audited water savings achieved from modernisation projects in Northern Victoria in the previous year (e.g. the 2009–10 year).

Assumptions, Limitations, Caveats and Approximations

·         The factor applied to derive the flow from water delivered from Silver and Wallaby creeks is an assumption based on historical data. 

Uncertainty Information

The uncertainty estimate was not quantified.

Comparative year

This line item corresponds to line item 23.4 Other lumped non-physical surface water asset increases reported in the 2010 Account. The comparative year volume is 151,809 ML.