South East Queensland
42.3 Leakage from storages

Supporting Information

This line item represents the leakage from Lake Samsonvale (North Pine Dam), Lake Somerset and Lake Wivenhoe to landscape.

As there was more precipitation than evaporation in the 2010–11 year, net evaporation was not removed from the leakage figures. This may have resulted in an over estimate of the leakage from the storages.

The quantification approach listed below shows the method used to calculate the leakage for all storages. Only the component for Lake Samsonvale (North Pine Dam), Lake Somerset and Lake Wivenhoe is relevant to this line item.

Quantification Approach

Data Source

Queensland Department of Environment and Resource Management (DERM), storage loss factors from Moreton and Logan Basin ROPs, Water Management System database and DERM staff calculations. Seqwater monthly storage height or volume data.

Provided by

DERM and Bureau of Meteorology.

Method

Storage loss is the loss in the water supply scheme (WSS) storages. Where storage-loss was not specifically evaluated as part of ROP reporting requirements, the storage loss allowance detailed in the ROPs was used as an estimate. This was done by adding the storage loss allowances calculated for each month, based on the storage surface area at the start of month and the application of the difference between monthly storage-loss factors in the applicable ROP tables. The Moreton and Logan Basin ROPs provide storage loss tables for Lake Wivenhoe, Lake Somerset and Lake Maroon, Cedar Grove Weir and Bromelton Off–Stream Storage.

ROP storage loss factors include a component for net evaporative losses from the storages. Evaporation from storages was included in line item 17.1 Evaporation from surface water, and precipitation on storages was included in line item 9.1 Precipitation on surface water. To prevent double counting of the net evaporative loss from storages, the net evaporative loss calculated by the Bureau of Meteorology was subtracted from the storage loss volumes provided by DERM. Where the net evaporation for an individual storage was calculated to be greater than the ROP storage loss, a storage loss was not recognised for the individual storage. Where precipitation was greater than evaporation, no net evaporation was calculated and the total storage loss was considered in this line item.

Assumptions, Limitations, Caveats and Approximations

As precipitation was greater than evaporation on all storages during the 2010–11 year, ROP storage losses were not adjusted down to account for net evaporative loss. This has resulted in all storage loss from the ROP considered as leakage to landscape. This may have resulted in an overestimate of the leakage to landscape.

It has been assumed that the WMS database data were current, accurate and correct.

The Moreton and Logan Basin ROPs list loss factors to apply when estimating losses from storages where the storages are part of the WSS. Where the storages are not part of a WSS, losses were not available and could not be quantified accurately.

Losses from the storages that form part a WSS have been estimated and reported where information was available to allow accurate quantification. Therefore:
  • transmission losses were not reported in the Moreton or Gold Coast water resource plan (WRP) areas
  • storage losses were not reported in the Gold Coast WRP area.

Uncertainty Information

Derived from storage loss estimates. DERM reliability and accuracy rating is B4.

Comparative year

This line item was not reported in the 2010 Account.