Melbourne
9.11 Delivery of water under inter-region agreement to surface water

Supporting information

The volume presented in the water accounting statements (26,237 ML) represents the volume of water delivered to Melbourne's retail water authorities City West Water, South East Water, and Yarra Valley Water under bulk entitlements to Thomson Reservoir and Silver and Wallaby creeks (refer to line item 1.5 Inter-region claim on water for further information).

The following table presents the breakdown of the delivery of water to the Melbourne Region during the 2012–13 year.

Delivery of water under inter-region agreement
Source Volume (ML)
Thomson Reservoir 25,148
Silver and Wallaby creeks 1,071
Lake Eildon 18
Total 26,237

The volume of water delivered to the Melbourne region during the 2012–13 year was substantially higher than in previous years. This is largely due to:

  • below-average rainfall across the Melbourne region in the reporting year, increasing reliance on sources of water from outside the region
  • storage volumes in the Thomson Reservoir had recovered in the past two years.
Delivery from Thomson Reservoir

Water stored in Thomson Reservoir is delivered to Upper Yarra Reservoir for distribution to Melbourne's water supply system.

Delivery from Silver and Wallaby creeks

Water is diverted from Silver and Wallaby creeks, and delivered to Tooroorung Reservoir and Yan Yean Reservoir for distribution to Melbourne's water supply system.

Delivery from Lake Eildon

There was also 18 ML diverted from Lake Eildon during 2012–13 year. This water was used to maintain the operational capacity of the North-South pipeline and keep the pipeling charged for fire fighting purposes.

In late 2010, the Victorian Government introduced its policy to phase out Melbourne's reliance on the north–south pipeline. In future years, the pipeline will only be used for critical human needs and only when there is sufficient water in the Goulburn system. On 2 July 2012, the Victorian Minister for Water gazetted new bulk entitlements for the three retail water corporations (South East Water, Yarra Valley Water and City West Water) in the River Murray and Goulburn system of up to 75,000 ML annually, as a result of the water retail corporation's (Melbourne Water Corporation and three urban water retailers) investment in the Goulburn-Murray Water Connections Project.

Quantification approach

Data source

Waterworks database.

Provided by

Melbourne Water.

Method

The total volume of water delivered to the Melbourne region under an inter-region claims is the sum of the following components.

Thomson Reservoir

The volume of water delivered from Thomson Reservoir was measured by the depth of water flowing over the spillway chute at the inflow point to Upper Yarra Reservoir (which behaves as an ogee weir) using a Mindata 2100P level sensor. The water depth was converted to flow using a stage–discharge relationship.

Silver and Wallaby creeks

The volume of water delivered from the 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

The volume of water delivered from Lake Eildon was measured at the north–south pipeline pump station. There are six pumps at the pump station, which are divided evenly into two pump-well groups. The total volume of water diverted from the Goulburn River was calculated as the sum of the volume pumped from the two wells, measured using a Siemens Sitrans SONOKIT dual-beam ultrasonic flow meter.

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 relates to the accuracy of the measurement device used to measure the volume of water transferred-in. The uncertainty for each delivery is shown below:

  • Thomson Reservoir: estimated uncertainty is +/– 2%
  • Silver and Wallaby creeks: estimated uncertainty is +/– 1%
  • Lake Eildon: estimated uncertainty is +/– 1%.