18.11 Entitled extraction of allocated groundwater to users
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 volume recognised in the water accounting statements (289,305 ML) represents the total volume of groundwater extracted for these licence entitlements during the 2011–12 year.
The Department of Water 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 2011–12 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 2011–12 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 2011–12 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 2011 until its expiry date.
- For new licences that were created during the 2011–12 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 2012.
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 2011–12 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.
This line item corresponds to line item '18.11 Groundwater allocation extraction' reported in the 2011 Account.