17.17 Decrease of inter-region surface water claim on water

Supporting information

The volume presented in the water accounting statements (60,064 ML) represents the decrease to the claim that Melbourne retail authorities City West Water, South East Water and Yarra Valley Water are entitled to under:

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

The following table presents the breakdown of decreases to inter-region claims for the Melbourne region during the 2012–13 year.

Decrease of inter-region surface water claim on water
Component Volume (ML)
Thomson Reservoir evaporation 18,958
adjustment for environmental flow 187
adjustment to opening store volume 1
Silver and Wallaby creeks n/a 0
Lake Eildon evaporation 2,716
spills 16,682
trade 21,520
Total 60,064

Quantification approach

Data source

Waterworks database.

Provided by

Melbourne Water.


Decreases to inter-region claims held by the Melbourne region were calculated using the following methods:

Thomson Reservoir

Evaporation of the Melbourne retailer's share of storage in Thomson Reservoir is determined using the Pan evaporation method.

As the Environmental Water Account in the Thomson Reservoir has been overdrawn by 187 ML, this volume came temporarily from the retailer's account until the payback from the environmental account was done on 1 July, 2013.

An adjustment of 1 ML has been made to the opening store volume as at 30 June 2012 as reported by Melbourne Water.

Silver and Wallaby creeks

There were no decreases to the inter-region claim on water from Silver and Wallaby creeks during the 2012–13 year.

Lake Eildon

Evaporation: 5 % of the water held in Lake Eildon for the Melbourne region is subtracted on 01 July each year to account for annual evaporation, as per the water allocation under bulk entitlement for the Goulburn system.

Assumptions, limitations, caveats and approximations


Uncertainty information

The uncertainty estimate was not quantified.