Perth
17.11 Surface water allocation diversion

Supporting Information

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

The water supply licences are divided into licence entitlement purposes. The total allocation diversions for each licence purpose during the 2010–11 year are given in the following table. The following figure 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
Graph of the percentage of the total volume of surface water abstracted for each licence category



Total allocation diversion for each licence purpose during the 2010–11 year

Licence category

Allocation diversion

(ML)

Agriculture

4,684

Commercial and institutional

 127

Industry and power generation

 18,091

Mining

 18,918

Parks, gardens and recreation

 195

Stock and domestic

 252

Other

 373

Total

42,640

Quantification Approach

Data Source

Department of Water: Water Resource Licensing database.

Provided by

Department of Water.

Method

The Department 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 2010–11 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 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 and were renewed during the 2010–11 year, the volume of abstraction is estimated to be the full licensed allocation.
  • For licences that expired during the 2010–11 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 2010 until its expiry date.
  • For new licences that were created during the 2010–11 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 2011.

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 2010–11 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 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.

Uncertainty Information

The uncertainty estimate was not quantified.

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.

 

Comparative year information for line item 17.11

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

17.11 Surface water allocation diversion

14.7.9.7 Allocation diversion of regulated flows–other lumped holders

37,917

42,325

Prior period error: incorrect dates used when calculating the allocation diversion

Change in line item name and number