Perth

This line item refers to the total water abstracted for all other surface water supply in the Perth region not related to public water or irrigation schemes.

The water supply licences are divided into licence entitlement purposes. The total allocation diversions for each licence purpose during 2009-10 are given in the table below. The figure below shows the percentage of the total volume of water abstracted for each licence category.

Graph of the percentage of the total volume of surface water abstracted for each licence category

Data source

Western Australian Department of Water: Water Resource Licensing database.

Data provider

Western Australian Department of Water.

Method

The Department of Water does not have sufficient metering information relating to actual licensed abstraction to determine the total volume of water abstracted. Consequently, the allocation diversion during the reporting period 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 reporting period. The number of days the licences were active is calculated using the annual renewal date of each individual licence.

• For licences that expired and were renewed during the reporting year, the volume of abstraction is estimated to be the full licensed allocation.
• For licences that expired during the reporting year (and were not renewed), the volume of abstraction is estimated to be the full entitlement, divided by the number of days from 1 July 2009 until its expiry date.
• For new licences that were created during the reporting year, the volume of abstraction is estimated to be the full entitlement, divided by the number of days from the licence start date until 30 June 2010.

Some licences are issued in perpetuity and do not have an annual renewal 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 reporting year.

Uncertainty

Ungraded.

Approximations, assumptions, caveats/limitations

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.