18.11 Entitled extraction of allocated groundwater to users
The volume recognised in the water accounting statements (11,266 ML) represents the total volume of groundwater extracted for individual user licence entitlements in the Ord region during the 2011–12 year.
The Department of Water administers 38 separate licences in this category held by individual licensees. Licences primarily relate to water sourced from the Canning–Kimberley groundwater area for the mining and commercial sectors.
The volume presented for this line item is a combination of metered data and estimates.
Where metered data are available, the abstraction is calculated as the actual groundwater extracted during the 2011–12 year. Where metered data are not available, the volume of extraction is estimated to be the full annual 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 start date until 30 June 2012.
Some licences are issued in perpetuity and do not have an annual renewal date. In these cases, the volume of extraction is estimated to be 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 abstraction to provide more accurate estimates of abstraction for all licences. The pro-rata estimates of abstraction assume that the full annual entitlement is abstracted each year and that the rate of abstraction is uniform throughout the year. It is unlikely on both counts that this will be the case for all licences.
For measured data, the expected error for water meters is +/– 5%.
The Department of Water requires that all water meters, when tested under in situ conditions, must be within 5% accuracy across the full flow rate range (Guidelines for water meter installation 2009).
For estimated data, the uncertainty is not quantified.
This line item corresponds to line item '18.11 Groundwater allocation extraction' reported in the 2011 Account.