Perth
18.11 Groundwater allocation extraction
Supporting Information
This line item refers to all groundwater extracted from licensed bores in the Perth region not related to urban water systems or irrigation schemes. It includes groundwater extracted by individual users in the agricultural and industrial sectors.
The groundwater supply licences are divided into licence entitlement purposes. Total groundwater extracted for each licence purpose during the 2010–11 year is given in the following table. The following figure shows the percentage of the total volume of water extracted for each licence category.
Graph of the percentage of the total volume of groundwater extracted for each licence category
Licence category – groundwater |
Allocation extraction (ML) |
Agriculture |
139,269 |
Commercial and institutional |
12,179 |
Environment and conservation |
6,086 |
Industry and power generation |
33,286 |
Mining |
2,363 |
Parks, gardens and recreation |
75,159 |
Stock and domestic |
18,241 |
Other |
461 |
Total |
287,044 |
Quantification Approach
Data Source
Provided by
Method
The Department does not have sufficient metering information relating to actual extraction from licensed bores to determine the total volume of water extracted. Consequently, the allocation extraction during the 2010–11 year is estimated based on the licensed allocation.
The volume of extraction is estimated to be the full allocation, divided by the number of days that each licence was active during the 2010–11 year. The number of days the licences were active is calculated using the issue date of each individual licence.
- For licences that expired during the 2010–11 year (and were not renewed), the volume of extraction is estimated to be the full allocation, divided by the number of days from 1 July 2010 until its expiry date.
- For new licences that were created during the 2010–11 year, the volume of extraction is estimated to be the full allocation, divided by the number of days from the licence issue date until 30 June 2011.
Some licences are issued in perpetuity and do not have a finalisation date. In these cases, the volume of extraction is estimated as the amount of one full year's allocation for licences in force during the 2010–11 year.
Assumptions, Limitations, Caveats and Approximations
There is not sufficient information relating to actual extraction to provide more accurate estimates of extraction for all licences. The pro-rata estimates of extraction assume that the full annual allocation is extracted each year, and that the rate of extraction is uniform throughout the year. It is unlikely on both counts that this will be the case for all licences.
Uncertainty Information
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.
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 |
18.11 Groundwater allocation extraction |
16.5.3.7 Groundwater allocation extraction–other lumped holders |
273,321 |
294,482 |
Prior period error: incorrect dates used when calculating the allocation extraction Change in line item name and number |