Melbourne
18.11 Groundwater allocation extraction

The volume presented in the water accounting statements (10,196 ML) represents metered extraction and estimated stock and domestic (S&D) extraction under groundwater entitlements in groundwater management units in the Melbourne region.

The table below shows the breakdown of groundwater volumes extracted from groundwater management units in the Melbourne region during the 2010–11 year.

Groundwater allocation extraction in the Melbourne region during the 2010–11 year

Groundwater Management Unit	Permissible Consumptive Volume (ML)	2010-11 allocation (ML)	Metered extraction (ML)	Estimated S&D extraction (ML)	Usage of allocation %
Deutgam Water Supply Protection Area - Groundwater	5,100	5,100	244	18	5.1%
Koo Wee Rup Water Supply Protection Area – Groundwater	12,915	12,018	1,939	1,949	15%
Wandin Yallock Water Supply Protection Area – Groundwater	2,924	2,933	198	123	11%
Cut Paw Paw Groundwater Management Area	3,650	515	30	0	6%
Frankston Groundwater Management Area	3,200	1,069	72	207	26%
Lancefield Groundwater Management Area	1,485	1,390	51	114	12%
Merrimu Groundwater Management Area	451	440	177	21	45%
Moorabbin Groundwater Management Area	2,700	2,614	545	555	42%
Nepean Groundwater Management Area	6,013	6,115	1,798	2,155	65%
Total	38,438	32,194	5,054	5,142	32%
Total extraction			10,196

 

The volume of groundwater allocation extraction includes extractions by retail water authorities in the Melbourne region, according to the table below.

Groundwater allocations and extractions by urban retail authorities during the 2010–11 year

Authority	Location	Volume allocated (ML)	Volume extracted (ML)
South East Water	Lang Lang	119	4
Western Water	Lancefield	294	8
	Romsey	600	0
Total		1,013	12

Southern Rural Water: Irrigation Planning Module Generation 2database.

Southern Rural Water.

Groundwater extraction in the Melbourne Region was calculated using the following methods:
Groundwater entitlements over 10 ML were metered in Groundwater Management Units. Meters are installed at each bore, and must comply with Southern Rural Water's metering standards.

Stock & 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 S&D 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 2010–11 year, a usage factor of 1.5 was applied to S&D entitlements as it was a wet year and usage was expected to be lower than the full entitlement. The exception to this was Nepean Groundwater Management Area which is known to have less S&D extraction compared to other areas. Deutgam Water Supply Protection Area calculations used a factor of 0.1 due to allocation restrictions in the area. The factors applied to each Groundwater Management Unit are presented in the table below:

Usage factors applied to estimate S&D extraction in the Melbourne Region during the  2010–11 year

Groundwater Management Unit	No. of S&D bores	S&D usage (ML)	Usage factor
Deutgam Water Supply Protection Area - Groundwater	180	18	0.1
Koo Wee Rup Water Supply Protection Area – Groundwater	1,299	1,949	1.5
Wandin Yallock Water Supply Protection Area – Groundwater	82	123	1.5
Cut Paw Paw Groundwater Management Area	0	0	1.5
Frankston Groundwater Management Area	138	207	1.5
Lancefield Groundwater Management Area	76	114	1.5
Merrimu Groundwater Management Area	14	21	1.5
Moorabbin Groundwater Management Area	370	555	1.5
Nepean Groundwater Management Area	2,155	2,155	1
Total	4,314	5,142

• 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 & Domestic extraction. It is unlikely that all extraction matches the assumption. Given that it was a wet year, the estimate is likely to overestimate the volume of S&D 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.

This item corresponds to the subcategories of line item 16.5 Groundwater allocation extraction reported in the 2010 Account. In the 2011 Account, the presentation of the line items has changed since the 2010 Account: line items 16.5.1 Groundwater allocation extraction – S&D water access entitlement and 16.5.3.7 Groundwater allocation extraction – other lumped holders were merged into a single line item: 18.11 Groundwater allocation extraction.

The comparative year volume is 18,643 ML and is the sum of volumes reported at line items 16.5.1 (9,384 ML) and 16.5.3.7 (9,079 ML).