Adelaide
2.5 Other groundwater assets

Supporting Information

The groundwater asset in the Adelaide region included the managed groundwater volume and the balance of recharged water credits. The opening (87,833 ML) and closing (88,252 ML) balance for the groundwater asset in the 2011 Account are itemised by management area and provided in the following table. The groundwater asset could not be separated into water table aquifers and underlying aquifers, due to the complex hydrostratigraphy.

Groundwater asset opening and closing balances for the 2010–11 year
Groundwater management area Managed groundwater volume* (ML) Recharged water credit balance (ML) Total groundwater asset (ML)
Allocation/ extraction limit Non-licensed extraction volume (ML) Volume at 30 June 2010 (ML) Volume at 30 June 2011 (ML) Volume at 30 June 2010 (ML) Volume at 30 June 2011 (ML)
Barossa Prescribed Water Resources Area (PWRA) 7,147
0 0 7,147 7,147
McLaren Vale Prescribed Wells Area (PWA) 6,560 500 14 10 7,074 7,070
Northern Adelaide Plains Prescribed Wells Area (PWA)
1,463 1,886 1,463 1,886
Western Mount Lofty Prescribed Water Resources Area (PWRA) 70,325 1,824 0
0
72,149 72,149
Total 87,833 88,252
* The managed groundwater volume is constant across years, therefore the opening and closing balance does not change.
Managed groundwater volume

The National Water Account recognises the managed groundwater volume as the groundwater asset, provided there is evidence that the volume results from an assessment of the resources available to be extracted. In the Adelaide region the managed groundwater volume is the sum of groundwater extraction or allocation limits described by the relevant water allocation plan. The following prescribed groundwater resources are included in the groundwater asset for the Adelaide region:

The volume reported for the groundwater asset did not include the following prescribed groundwater resources:

  • Northern Adelaide Plains PWA: although the Northern Adelaide Plains has an operational water allocation plan, there is no evidence that this volume is the result of an assessment of the resources available to be extracted.
  • Central Adelaide Plains PWA and Dry Creek PWA do not currently have operational water allocation plans and therefore a managed groundwater volume has not been determined for these resources.

The volume of the Northern and Central Adelaide Plains and Dry Creek groundwater asset is considered to be significant in proportion to the total Adelaide groundwater asset. The Northern Adelaide Plains PWA Water Allocation Plan has identified that the current water allocation on water licenses is 26,500 ML, however the capacity of the resource is insufficient to meet the water use demands (i.e. currently the resource is over-allocated).  Omission of these groundwater resources will have a material impact on the volume reported for the groundwater store and is highly relevant to users of the 2011 Account.

Resource assessments are in progress for the Adelaide Plains Water Allocation Plan which will include Northern Adelaide Plains PWA, Central Adelaide Plains PWA and Dry Creek PWA. Further information on the status of the resource assessment can be found in the South Australian Department for Water's Groundwater status reports.

Recharged water credit balance

Recharged water credits accrue from water drained or discharged into a well within the prescribed groundwater resource. The recharged water credit balance is a portion of the recharge credit that may be carried forward (according to the rules detailed in the relevant water allocation plan). For more information about recharged water credits, refer to the Water allocations section of the Contextual information. 

Further information on the groundwater resources for the individual prescribed areas is provided below.

Barossa PWRA

The following table indicates the level of development of the groundwater resource in the Barossa PWRA. The proportion of the total extraction for the Barossa PWRA is shown for each aquifer type.

Groundwater development in the Barossa PWRA

Groundwater management area

Aquifer type

Aquifer

Percentage of extraction

Barossa PWRA

Generally unconfined or semi-confined

Upper aquifer

9%

Confined

Lower aquifer

16%

Confined and unconfined

Fractured rock

55%

Unknown

Unknown

20%

McLaren Vale PWA

The following table indicates the level of development of the groundwater resource in the McLaren Vale PWA. The proportion of the total extraction for the McLaren Vale PWA is shown for each aquifer type.

Groundwater development in the McLaren Vale PWA

Groundwater management area

Aquifer type

Aquifer

Percentage of extraction

McLaren Vale PWA

Generally unconfined or semi-confined

Quaternary sediments

<1%

Generally unconfined or semi-confined

Port Willunga Formation

66%

Confined

Maslin Sands

14%

Generally confined

Fractured rock

13%

Not specified

Unknown

8%

Quantification Approach

Data Source

South Australian Department for Water: Water Information and Licensing Management Application (WILMA) database; McLaren Vale Prescribed Wells Area Water Allocation Plan (2007); Western Mount Lofty Ranges Prescribed Water Resources Area draft Water Allocation Plan (2010); Barossa Prescribed Water Resources Area Water Allocation Plan (2009).

Provided by

South Australian Department for Water.

Method

Barossa Prescribed Water Resource Area (PWRA) – Managed groundwater volume

The sum of estimated underground water allocation volumes, detailed in the current Barossa PWRA Water Allocation Plan, was reported as the managed groundwater volume.

McLaren Vale Prescribed Wells Area (PWA) – Managed groundwater volume

The estimated sustainable yield and estimated stock and domestic extraction, detailed in the current McLaren Vale Water Allocation Plan, was reported as the managed groundwater volume.

Western Mount Lofty Ranges Prescribed Water Resource Area (PWRA) – Managed groundwater volume

The sum of groundwater extraction limits, including existing non-licensed extraction volumes, detailed in the Draft Water Allocation Plan for the Western Mount Lofty Ranges PWRA, was reported as the managed groundwater volume. The results of a comprehensive resource assessment including groundwater resource capacity, baseflow and extraction limits are summarised in the following table.

Western Mount Lofty Ranges PWRA managed groundwater volume

Catchment

Groundwater resource capacity (ML)

Baseflow (ML)

Existing non-licensed extractions (ML)

Extraction limit (ML)

South Para River

17,004

7,333

156

9,517

Little Para River

5,366

2,163

33

3,171

River Torrens

28,540

11,668

271

16,600

Onkaparinga River

38,932

18,084

413

20,435

Fleurieu Peninsula

52,960

31,407

951

20,602

 Total

142,802

70,655

1,824

70,325


Recharged water credit balance – All management areas in the Adelaide region

The opening and closing recharged water credit balance for the 2010–11 year was extracted from the WILMA licensing database.

Assumptions, Limitations, Caveats and Approximations

Managed groundwater volume

The availability of information to complete a groundwater assessment, the method of assessing the groundwater resource and the date of the groundwater assessment differs significantly between the management areas. The outcome of the groundwater assessment may produce an extraction limit or an allocation limit. These outcomes are treated the same for the purposes of defining the groundwater asset.   

Recharged water credit balance

The recharged water credit balance was reported as the groundwater asset, rather than the volume injected. The recharged water credit balance is influenced by the conditions for allocating recharge water stated in the relevant water allocation plan. For more information, refer to the Water allocations section of the Contextual information.

Uncertainty Information

The uncertainty estimate was not quantified. Completing a volumetric groundwater resource assessment is extremely difficult and relies on incomplete knowledge of the physical processes involved and less than comprehensive monitoring information. Groundwater resource assessments involve making numerous assumptions, some with very high uncertainty.

Comparative year

This line item corresponds to 2.3 Aquifers - other lumped reported in the 2010 Account. In the 2011 Account, there were a number of changes to the scope of the groundwater asset. The following changes were made that caused the 2009–10 year value to be restated:

  • In the 2011 Account, the Bureau of Meteorology recognised the managed groundwater volume as the groundwater asset. This volume included the allocation/extraction limit and unlicensed extraction volumes (where detailed in the relevant water allocation plan). In the 2010 Account, only the allocation/extraction limit was reported.
  • In the 2011 Account, the managed groundwater volume was only recognised as the groundwater asset when there was evidence of a resource assessment. For the Northern Adelaide Plains PWA no such resource assessment exists, therefore this groundwater resource was no longer recognised as part of the groundwater asset.
  • In the 2011 Account, the Western Mount Lofty Ranges managed groundwater volume was reported whereas this volume was omitted from the 2010 Account. This is because the water allocation plan was (and still is) in draft form. However, there is evidence of a resource assessment to determine a managed groundwater volume, therefore this is reported as part of the groundwater asset in the 2011 Account.
  • In the 2011 Account, the groundwater asset included the recharged water allocation balance. This was not included as part of the reported asset in the 2010 Account.

Restatement of the volume published in the 2010 Account was made as the difference from these changes was material and increased the accuracy of the information provided to the users of the National Water Account. The changes and their respective volumes are detailed in the following table. The restated comparative year opening balance is 86,356 ML and closing balance is 87,833 ML.

Restatement of comparative year information for line item 2.5 Other groundwater assets
2010 Account line item name Groundwater management area Volume at 30 June 2010 reported in 2010 Account (ML) Value difference to volume reported due to  inclusion of recharged water allocation balance (ML) Value difference to volume reported due to managed groundwater volume (ML) Volume at 30 June 2010 reported in 2011 Account (ML)
Opening balance Closing balance Opening balance Closing balance Opening balance Closing balance Opening balance Closing balance
Line item 2.3 Aquifers - other lumped Barossa PWRA 7,580 7,580     (433) (433) 7,147 7,147
McLaren Vale PWA 6,506 6,506   14 554 554 7,060 7,074
Northern Adelaide Plains PWA 25,182 25,182   1,463 (25,182) (25,182) 1,463
Western Mount Lofty Ranges PWRA
    72,149 72,149 72,149 72,149
Total

39,268 39,268 0 1,477 47,088 48,565 86,356 87,833