Perth
17.11 Entitled diversion of allocated surface water to users

The volume recognised in the water accounting statements (30,817 ML) represents the total volume of surface water diverted for individual user licence entitlements during the 2012–13 year.

This line item refers to all surface water supply in the Perth region not related to urban water system or irrigation schemes. It includes water diverted by individual users in the mining, industrial and agricultural sectors.

The Department of Water does not have sufficient metering information relating to actual licensed diversion to determine the total volume of water diverted. Consequently, the allocation diversion during the year was estimated based on the total licensed allocation.

The volume of abstraction is estimated to be the full allocation, multiplied by the proportion of days that each licence was active during the 2012–13 year. The number of days the licences were active is calculated using the issue date of each individual licence.

• For licences that expired and were renewed during the 2012–13 year, the volume of abstraction is estimated to be the full licensed allocation.
• For licences that expired during the 2012–13 year (and were not renewed), the volume of abstraction is estimated to be the full allocation, divided by the number of days from 1 July 2012 until its expiry date.
• For new licences that were created during the 2012–13 year, the volume of abstraction is estimated to be the full allocation, divided by the number of days from the licence issue date until 30 June 2013.

Some licences are issued in perpetuity and do not have a finalisation date. In these cases, the volume of abstraction is estimated as the amount of one full year's allocation for licences in force during the 2012–13 year.

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 allocation 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.