Perth
18.8 Non-allocated extractions to users

Supporting Information

This line item refers to groundwater extraction from domestic non-licensed bores within the Perth region.

Quantification Approach

Data Source

Department of Waters: Water Resource Licensing database, Australian Bureau of Statistics (ABS): domestic bore survey database.

Provided by

Department of Water.

Method

The Department of Water does not have sufficient metering information relating to actual extraction from domestic non-licensed bores to determine the total volume of water extracted. Consequently, the extraction was estimated based on ABS (2009) survey results for the Perth metropolitan area. These usage figures in the Perth metropolitan area were then extrapolated to also include the southwest area (around Mandurah). The estimated annual extraction per bore is 0.405 ML per year, which is based on the initial results of the Department of Water's domestic bore metering project for several dozen domestic bores across Perth.

Assumptions, Limitations, Caveats and Approximations

The estimate for domestic non-licensed extraction is based on a number of assumptions, including:

  • The ABS domestic bore survey is relevant for the southwest area, for which there is no alternative, independent research or evidence available.
  • The usage based on the Department of Water's research for several dozen bores was used to estimate the usage of all non-licensed bores in the region.

Uncertainty Information

The uncertainty estimate was not quantified.

Comparative year

The following table presents substantive changes in the line item reported in this 2011 Account with the corresponding line item in the 2010 Account.

 

Comparative year information for line item 18.8

2011 Account line item

2010 Account line item

2011 Account volume for the 2009–10 year (ML)

2010 Account volume for the 2009–10 year (ML)

Change from the 2010 Account to the 2011 Account

18.8 Non-allocated extractions to users

16.4.2 Groundwater extraction–other lumped basic rights

69,492

76,721

Methodology change: revised estimated extraction

Change in line item name and number


The Department of Water used a change in methodology to recalculate non-allocated groundwater extraction for the 2009–10 year, which resulted in a 10% decrease in the line item volume from that reported in the 2010 Account. Although this change had a relatively minor impact on the water balance for the groundwater store, this line item is important for the management of the water store by the Department of Water. Therefore the comparative year value was restated in the water accounting statements.