18.11 Entitled extraction of allocated groundwater to users
The volume presented in the water accounting statements (13,173 ML) represents metered extraction and estimated stock and domestic extraction under groundwater entitlements in groundwater management units in the Melbourne region.
The following table shows the breakdown of groundwater volumes extracted from groundwater management units in the Melbourne region during the 2011–12 year.
|Groundwater management unit||Metered extraction (ML)||Estimated S&D extraction (ML)||Usage of allocation %|
|Cut Paw Paw Groundwater Management Area (GMA)
|Deutgam Water Supply Protection Area (WSPA)—groundwater||979||294||23%|
|Koo Wee Rup WSPA—groundwater||1,921||1,877||26%|
|Wandin Yallock WSPA—groundwater||285||126||13%|
The volume presented for this item is a combination of metered extraction data and estimates of non-metered extractions.
Southern Rural Water meter groundwater extractions and submit this data to the Victorian Water Register. Metered extraction volumes were obtained from the Victorian Water Register for all groundwater management units for the 2011–12 year.
Stock and domestic entitlements are not currently metered in Victoria. Extraction was estimated by multiplying a usage factor between 0 and 2 ML by the number of stock and domestic bores in the region:
- A factor of zero estimates that no extraction occurred
- A factor of two estimates that the full entitlement was extracted.
During the 2011–12 year, a usage factor of 1.5 was applied to all stock and domestic entitlements, with the exception of Nepean GMA where a usage factor of 1 was applied.
Assumptions, limitations, caveats and approximations
- Not all groundwater bores are metered. Bores that were not metered were not used or did not fall within the threshold of Southern Rural Water's metering program. The number of non-metered bores is estimated to be 10-20% of the total bores in the area. The volume of extraction from bores that are not metered is not considered to have a material impact on this water accounting report.
- A broad assumption is made to estimate stock and domestic extraction. It is unlikely that all extraction matches the assumption. In a wet year, the estimate is likely to overestimate the volume of stock and domestic extraction.
- Metered data has an uncertainty of +/–5% based on meter specifications.
- Estimated data has an uncertainty of +/–100% based on the broad assumptions applied.
In the 2011 Account, it was not possible to separate urban and non-urban entitlements to groundwater. Therefore, the volume of groundwater extracted for all groundwater entitlements was reported at line item 18.11 'Groundwater allocation extraction'.
In the 2012 Account, data provided to the Bureau has enabled non-urban entitlements to groundwater to be reported separately in the Melbourne Account.
Consequently, the volume has been restated from 10,196 ML (as published in the 2011 Account) to 10,184 ML.
|Groundwater management unit||2012 Account volume for the 2010–11 year (ML)
||2011 Account volume for the 2010–11 year (ML)
|Cut Paw Paw GMA
|Koo Wee Rup WSPA— groundwater||3,884||3,888|
|Wandin Yallock WSPA— groundwater||321||321|