Melbourne
18.11 Groundwater allocation extraction

Supporting Information

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

Quantification Approach

Data Source

Southern Rural Water: Irrigation Planning Module Generation 2database.

Provided by

Southern Rural Water.

Method

Groundwater extraction in the Melbourne Region was calculated using the following methods:
Metered groundwater extraction
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.

Estimated Stock & Domestic extraction
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

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 & 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.

Uncertainty Information

  • Metered data has an uncertainty of +/–5% based on meter specifications.
  • Estimated data has an uncertainty of +/–100% based on the broad assumptions applied.

Comparative year

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).