Murray–Darling Basin
Water resources and systems

Introduction

The following set of notes provides consolidated reports for each of the water stores and systems within the Murray–Darling Basin (MDB) region during the 2011–12 year. The water stores included in the region are shown in Figure 1.

 


Figure 1  Schematic diagram of the water stores within the MDB region
Figure 1  Schematic diagram of the water stores within the MDB region

 

For more information about the region, please refer to the General description section of the Contextual information.

Information on all water flows to and from each water store and system is presented in this note, including between-store flows and transfers that are not presented in the water accounting statements. The between-store flows and transfers that occur in the region are presented in Figure 2.

The numbers on the diagram refer to the line item numbers in the water store notes. For each between-store flow, there are two line item numbers: one refers to flow out of a water store and the other refers to flow into a water store.

 


Figure 2  Schematic diagram of between-store flows that occur within the MDB region: line item numbers are provided next to the flows
Figure 2  Schematic diagram of between-store flows that occur within the MDB region: line item numbers are provided next to the flows

 

The between-store flows and transfers (Figure 2), which are eliminated from the region's water accounting statements, are shown in italics throughout the following set of notes.

Surface water

Background

A description of the Murray–Darling Basin (MDB) region's surface water resources is provided in the Surface water section of the Contextual information.

Water in store

Table 1 shows that the total surface water store increased during the 2011–12 year in the MDB region.

 

Table 1  Statement of Water Assets and Water Liabilities for the surface water store for the MDB region as at 30 June 2012
Water assets

Northern Basin

Southern Basin

Whole region

Volume at 30 June 2012 (ML)

Volume at 30 June 2011 (ML)

Volume at 30 June 2012 (ML)

Volume at 30 June 2011 (ML)

Volume at 30 June 2012 (ML)

Volume at 30 June 2011 (ML)

1 Surface water            
1.1 Storages

4,314,709

3,333,324

16,872,487

15,798,138

21,187,196

19,131,462

1.2 Unregulated river

 –

 –

 –

 –

 –

 –

1.3 Regulated river

16,249

19,234

1,309,763

1,287,103

1,326,012

1,306,337

1.4 Lakes and wetlands

0

0

1,811,372

1,925,145

1,811,372

1,925,145

1.5 Inter-region claim on water

0

0

913,776

470,066

913,776

470,066

1.10 Other surface water assets

0

0

19,952

18,131

19,952

18,131

Total surface water assets

4,330,958

3,352,558

20,927,350

19,498,583

25,258,308

22,851,141

             
5 Water liabilities            
5.1 Surface water allocation remaining

2,090,549

1,341,685

4,909,329

5,438,652

6,999,878

6,780,337

5.2 Surface water allocation remaining – urban water system

0

0

0

25

0

25

Total surface water liabilities

2,090,549

1,341,685

4,909,329

5,438,677

6,999,878

6,780,362

             
Opening net water assets

2,010,873

672,772

14,059,906

6,952,943

16,070,779

7,625,715

Change in net water assets

229,536

1,338,101

1,958,115

7,106,963

2,187,651

8,445,064

Closing net water assets

2,240,409

2,010,873

16,018,021

14,059,906

18,258,430

16,070,779

 

Table 1 includes information only for eight lakes: Dock Lake, Pine Lake, Lake Batyo Catyo, Green Lake, Lake Albert, Lake Alexandrina, Lake Burley Griffin, Lake Ginninderra and Lake Tuggeranong. Volume of water stored in other lakes and wetlands could not be quantified accurately due to a lack of available data.

The location of major storages within the MDB region, and the volume of water, including dead storage, in each storage as a percentage of total storage capacity (% full) at the end of the 2011–12 year, is shown in Figure 3.


Figure 3  Location map of major storages within the MDB region: the % full volume on 30 June 2012 for major storages is also shown
Figure 3  Location map of major storages within the MDB region: the % full volume on 30 June 2012 for major storages is also shown


 
The water volume in majority of the storages within the MDB region at the end of the 2011–12 year was more than that at the start (see line item 1.1 Storages). The large increase in surface water storage during the year is primarily attributed to high inflows into the storages during the 2011–12 year. This situation reflects the well above average rainfall conditions observed in the region in the 2011–12 year. Some areas, within the region, recorded their highest annual rainfall on record (see Rainfall in 'Climate overview').

Changes in water store

The Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows for the surface water store are provided in Tables 2 and 3, respectively. In addition to flows reported in the water accounting statements, the tables also show flows between the surface water and groundwater stores within the region.

 

Table 2  Statement of Changes in Water Assets and Water Liabilities for the surface water store for the year ended 30 June 2012
Description

Northern Basin

Southern Basin

Whole region

2011–12 volume (ML)

2010–11 volume (ML)

2011–12 volume (ML)

2010–11 volume (ML)

2011–12 volume (ML)

2010–11 volume (ML)

Water asset increases
 
9 Surface water increases
9.1 Precipitation on surface water 247,093 226,027 1,401,857 1,899,698 1,648,950 2,125,725
9.2 River inflow to region 0 0 4,547,315 1,840,333 01 01
9.3 Groundwater discharge 35,207 7,058 7,159 8,670 42,366 15,728
9.4 Runoff to surface water 32,492,437 33,913,170 31,090,750 49,069,283 63,583,187 82,982,453
9.5 Point return from irrigation scheme 0 0 198,314 216,917 198,314 216,917
9.6 Overbank flood return to river channel

 –

 –

 –

 –

 –

 –

9.9 Discharge from urban water system 0 0 34,325 34,897 34,325 34,897
9.10 Direct discharge by user

 –

 –

 –

 –

 –

 –

9.15 Increase of inter-region surface water claim on water 0 0 2,560,022 3,137,374 2,560,022 3,137,374
9 Total surface water increases 32,774,737 34,146,255 39,839,742 56,207,172 68,067,1641 88,513,0941
 
13 Surface water liability decreases
13.1 Adjustment and forfeiture of surface water allocation 165,143 187,573 2,010,884 1,136,827 2,176,027 1,324,400
13.2 Adjustment and forfeiture of surface water allocation – urban water system 30,021 26,606 255,722 262,492 285,743 289,098
13 Total surface water liability decreases 195,164 214,179 2,266,606 1,399,319 2,461,770 1,613,498
 
Water asset decreases
 
17 Surface water asset decreases
17.1 Evaporation from surface water 366,255 320,996 2,892,164 2,692,725 3,258,419 3,013,721
17.2 River outflow from the region 4,547,315 1,840,333 9,565,600 12,839,048 9,565,6002 12,839,0482
17.3 Leakage to groundwater 104,977 122,295 244,817 268,210 349,794 390,505
17.4 Leakage to landscape

 –

 –

 –

 –

 –

 –

17.5 Overbank flood spilling 299,151 652,699 0 0 299,151 652,699
17.6 Surface water diversions – other statutory rights 38,066 28,516 30,523 19,135 68,589 47,651
17.7 Entitled diversion on non-allocated surface water to users 1,090,894 1,451,542 523,155 565,240 1,614,049 2,016,782
17.8 Entitled diversion of non-allocated surface water to urban water system 3,567 3,167 6,294 17,421 9,861 20,588
17.10 River and floodplain leakage, evaporation and errors 24,648,167 26,656,458 18,308,972 24,978,289 42,957,139 51,634,747
17.17 Decrease of inter-region surface water claim on water 0 0 625,000 765,817 625,000 765,817
17 Total surface water asset decreases 31,098,392 31,076,006 32,196,525 42,145,885 58,747,6022 71,381,5582
 
Water liability increases
 
21 Surface water liability increases
21.1 Surface water allocation announcements 1,599,474 1,904,177 7,412,187 7,839,249 9,011,661 9,743,426
21.2 Surface water allocation announcements – urban system 42,499 42,150 539,521 514,394 582,020 556,544
21 Total surface water liability increases 1,641,973 1,946,327 7,951,708 8,353,643 9,593,681 10,299,970
             
Balancing item – surface water  0 0 0 0 0 0
             
Change in net water assets 229,536 1,338,101 1,934,252 7,106,963 2,163,788 8,445,064
  1. Please note the volume for the Southern Basin for line item 9.2 'River inflow to region' was eliminated in the whole region.
  2. Please note the volume for the NorthernBasin for line item 17.2 'River outflow from the region' was eliminated in the whole region.

 

Table 3  Statement of Water Flows for the surface water store for the year ended 30 June 2012
Description

Northern Basin

Southern Basin

Whole region

2011–12 volume (ML)

2010–11 volume (ML)

2011–12 volume (ML)

2010–11 volume (ML)

2011–12 volume (ML)

2010–11 volume (ML)

Water inflows
 
9 Surface water increases
9.1 Precipitation on surface water 247,093 226,027 1,401,857 1,899,698 1,648,950 2,125,725
9.2 River inflow to region 0 0 4,547,315 1,840,333 01 01
9.3 Groundwater discharge 35,207 7,058 7,159 8,670 42,366 15,728
9.4 Runoff to surface water 32,492,437 33,913,170 31,090,750 49,069,283 63,583,187 82,982,453
9.5 Point return from irrigation scheme 0 0 198,314 216,917 198,314 216,917
9.6 Overbank flood return to river channel

 –

 –

 –

 –

 –

 –

9.9 Discharge from urban water system 0 0 34,325 34,897 34,325 34,897
9.10 Direct discharge by user

 –

 –

 –

 –

 –

 –

9.11 Delivery of water under inter-region agreement to surface water 0 0 1,491,312 2,310,491 1,491,312 2,310,491
9 Total surface water increases 32,774,737 34,146,255 38,771,032 55,380,289 66,998,4541 87,686,2111
 
Water outflows
 
17 Surface water asset decreases
17.1 Evaporation from surface water 366,255 320,996 2,892,164 2,692,725 3,258,419 3,013,721
17.2 River outflow from the region 4,547,315 1,840,333 9,565,600 12,839,048 9,565,6002 12,839,0482
17.3 Leakage to groundwater 104,977 122,295 244,817 268,210 349,794 390,505
17.4 Leakage to landscape

 –

 –

 –

 –

 –

 –

17.5 Overbank flood spilling 299,151 652,699 0 0 299,151 652,699
17.6 Surface water diversions – other statutory rights 38,066 28,516 30,523 19,135 68,589 47,651
17.7 Entitled diversion on non-allocated surface water to users 1,090,894 1,451,542 523,155 565,240 1,614,049 2,016,782
17.8 Entitled diversion of non-allocated surface water to urban water system 3,567 3,167 6,294 17,421 9,861 20,588
17.10 River and floodplain leakage, evaporation and errors 24,648,167 26,656,458 18,308,972 24,978,289 42,957,139 51,634,747
17.11 Entitled diversion of allocated surface water to users 685,467 507,631 5,930,626 3,513,176 6,616,093 4,020,807
17.12 Entitled diversion of allocated surface water to urban water system 12,478 15,509 283,824 251,875 296,302 267,384
17 Total surface water asset decreases 31,796,337 31,599,146 37,785,975 45,145,119 65,034,9972 74,903,9322
 
Balancing item – surface water  0 0 0 0 0 0
 
Opening water storage 3,352,558 805,449 19,028,517 8,793,347 22,381,075 9,598,796
Add/(Less): Change in water storage 978,400 2,547,109 985,057 10,235,170 1,963,457 12,782,279
Closing water storage 4,330,958 3,352,558 20,013,574 19,028,517 24,344,532 22,381,075
  1. Please note the volume for the Southern Basin for line item 9.2 'River inflow to region' was eliminated in the whole region.
  2. Please note the volume for the NorthernBasin for line item 17.2 'River outflow from the region' was eliminated in the whole region.

 

A schematic diagram representing all the inflows and outflows associated with the surface water store in the MDB region is provided in Figure 4. The numbers in brackets on the diagram refer to the line item numbers in Table 3.


 

Figure 4  Schematic diagram of water inflows and outflows for the surface water store within the MDB region during the 2011–12 year: line item numbers are provided in brackets. Irrigation diversions are included in line items 17.7 and 17.11
Figure 4  Schematic diagram of water inflows and outflows for the surface water store within the MDB region during the 2011–12 year: line item numbers are provided in brackets. Irrigation diversions are included in line items 17.7 and 17.11


 

Surface water diversions

Allocation diversions, non-allocated diversions, and water abstraction under other statutory rights are the main forms of surface water diversions within the MDB region.

The allocation diversions are associated with a water access entitlement. When an allocation is announced, an obligation (water liability) is created on the surface water to deliver water to the user. The entitlement holder (an individual or water supply organisation, where necessary) then orders the release or delivery of the allocated water and diverts it, which reduces the water liability. Allocation diversions, 6,912,395 ML, account for 80% of all diversions within the region for the 2011–12 year.

Non-allocated diversions are also associated with a water access entitlement, but are primarily unregulated diversions. Other statutory rights for surface water diversions are non-entitled water rights. They may be conferred by jurisdictional water acts or be written in water management plans and include land owner basic rights, riparian rights, Indigenous rights and stock and domestic rights.

The entitlement, allocation announcement and forfeiture for water rights associated with surface water diversion during the 2011–12 year are provided in the Water rights, entitlements, allocations and restrictions note.

Figure 5 compares surface water diversions within the MDB region for the 2010–11 year and the 2011–12 year. Non-allocated diversions have decreased but increased for all other categories compare to diversions made during the 2010–11 year.


 

Figure 5  Graph of surface water diversions from storages within the MDB region during the 2011–12 year and the 2010–11 year comparison
Figure 5  Graph of surface water diversions from storages within the MDB region during the 2011–12 year and the 2010–11 year comparison

 

Balancing item – surface water store

The volume of the balancing item represents the volume necessary to reconcile the opening and closing balances of the surface water store with the physical water inflows and outflows (Table 4). Inter-store flows between groundwater and surface water stores were included in calculating balancing volume for the surface water store (these flows were excluded in calculating unaccounted-for difference for the water accounting statements because water accounting statements were prepared considering all stores together on an elimination approach, eliminating inter-store flows).

 

Table 4  Balancing item for the surface water store for the 2011–12 year
 Description

Volume (ML)

Northern Basin

Southern Basin

Whole region

  Opening balance (30 June 2011)

3,352,558

19,028,517

22,381,075

add

Total 9 Surface water inflows

32,774,737

38,771,032

66,998,454

minus

Total 17 Surface water outflows

31,796,337

37,785,975

65,034,997

minus

Closing balance (30 June 2012)

4,330,958

20,013,574

24,344,532

 

 Balancing item – surface water store

0

0

0

 

The volume of the balancing item for the MDB region should be zero. This is because line item  17.10 River and floodplain leakage, evaporation and errors was calculated applying a water balance approach. Therefore, any balancing volume for the region is included in that line item.

Groundwater

Background

A description of the Murray–Darling Basin (MDB) region's groundwater resources are provided under Groundwater in the 'Physical information' section in the 'Contextual information'.

Water in store and groundwater asset

Information on groundwater assets in the region is shown in Table 5. Long term estimates of volumes for extraction (include volume of supplementary access licence that was available for use in New South Wales in the 2011–12 year) and basic landholder rights are defined as the groundwater assets considered for the region. These assets do not reflect temporal fluctuation of groundwater levels. Therefore, groundwater assets for the region are not responsive to groundwater storage changes resulting from water table fluctuations. As a result, groundwater assets are constant except for administrative changes to long-term estimates of volumes for extraction and landholder rights. Increases to administrative groundwater asset volumes may be the result of the commencement of a water resource plan for a groundwater source area within the basin. Decreases in administrative groundwater asset volume in New South Wales may be a result of the reduction of supplementary access licence volumes as outlined in the relevant water resource plans. Information for asset volumes separated into water table aquifers and underlying aquifers are not available for the region.

 

Table 5  Statement of Water Assets and Water Liabilities for the groundwater store for the MDB region as at 30 June 2012
Water assets

Northern Basin

Southern Basin

Whole region

Volume at 30 June 2012 (ML)

Volume at 30 June 2011 (ML)

Volume at 30 June 2012 (ML)

Volume at 30 June 2011 (ML)

Volume at 30 June 2012 (ML)

Volume at 30 June 2011 (ML)

2 Groundwater
2.1 Water Table aquifer

 –

 –

 –

 –

 –

 –

2.2 Underlying aquifers

 –

 –

 –

 –

 –

 –

2.5 Other groundwater assets 1,548,941 440,728 2,464,674 913,498 4,013,615 1,354,226
Total surface water assets 1,548,941 440,728 2,464,674 913,498 4,013,615 1,354,226
 
6 Water liabilities
6.1 Groundwater allocation remaining 0 0 2,498 2,139 2,498 2,139
6.2 Groundwater allocation remaining – urban water system 0 0 0 0 0 0
Total surface water liabilities 0 0 2,498 2,139 2,498 2,139
 
Opening net water assets

440,728

368,741

911,359

826,159

1,352,087

1,194,900

Change in net water assets

1,108,213

71,987

1,550,817

85,200

2,659,030

157,187

Closing net water assets

1,548,941

440,728

2,462,176

911,359

4,011,117

1,352,087

– = Data not available

 

Changes in water store

The Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows for the groundwater store are provided in Table 6 and Table 7, respectively. In addition to flows reported in the water accounting statements, the tables also show flows between the surface water and groundwater stores within the region.

 

Table 6  Statement of Changes in Water Assets and Water Liabilities for the groundwater store for the year ended 30 June 2012
Description

Northern Basin

Southern Basin

Whole region

2011–12 volume (ML)

2010–11 volume (ML)

2011–12 volume (ML)

2010–11 volume (ML)

2011–12 volume (ML)

2010–11 volume (ML)

Water asset increases
 
10 Groundwater increases
10.1 Groundwater inflow from outside region 0 0 2,797 2,941 2,797 2,941
10.2 Groundwater inflow from outside region at coast 0 0 53 76 53 76
10.3 Recharge from landscape 254,547 260,133 2,878,644 10,012,996 3,133,191 10,273,129
10.4 Recharge from surface water 104,977 122,295 244,817 268,210 349,794 390,505
10.5 Leakage from off-channel water storage

 –

 –

 –

 –

 –

 –

10.6 Leakage from urban water system

 –

 –

 –

 –

 –

 –

10.7 Leakage from irrigation scheme

 –

 –

 –

 –

 –

 –

10.8 Managed aquifer recharge – private user 0 0 2,340 4,158 2,340 4,158
10.13 Other groundwater increases 1,116,554 80,562 1,567,106 91,927 2,683,660 172,489
10 Total groundwater increases 1,476,078 462,990 4,695,757 10,380,308 6,171,835 10,843,298
 
14 Groundwater liability decreases
14.1 Adjustment and forfeiture of groundwater allocation 385,945 271,847 692,254 608,017 1,078,199 879,864
14.2 Adjustment and forfeiture of groundwater allocation – urban water system 11,874 9,128 5,205 3,292 17,079 12,420
14 Total groundwater liability decreases 397,819 280,975 697,459 611,309 1,095,278 892,284
 
Water asset decreases
 
18 Groundwater asset decreases
18.1 Groundwater outflow to outside region 0 0 19 14 19 14
18.2 Groundwater outflow to outside region at coast 0 0 1,551 1,625 1,551 1,625
18.3 Discharge to landscape 7,104 36,992 610,649 200,575 617,753 237,567
18.4 Discharge to surface water

35,207

7,058

7,159

8,670

42,366

15,728

18.7 Groundwater extractions – other statutory rights 48,948 12,858 145,228 36,437 194,176 49,295
18.18 Other groundwater decreases 8,341 8,575 15,930 6,254 24,271 14,829
18 Total groundwater asset decreases 99,600 65,483 780,536 253,575 880,136 319,058
 
Water liability increases
 
22 Groundwater liability increases
22.1 Groundwater allocation announcements 634,486 396,879 1,051,042 817,370 1,685,528 1,214,249
22.2 Groundwater allocation announcements – urban system 19,107 18,175 6,886 4,631 25,993 22,806
22 Total groundwater liability increases 653,593 415,054 1,057,928 822,001 1,711,521 1,237,055
 
Balancing item – groundwater 12,491 191,441 2,003,935 9,830,841 2,016,426 10,022,282
 
Change in net water assets 1,108,213 71,987 1,550,817 85,200 2,659,030 157,187

 1 See Supporting information of line item 25.1 Unaccounted-for difference for details.

 

Table 7  Statement of Water Flows for the groundwater store for the year ended 30 June 2012
Description

Northern Basin

Southern Basin

Whole region

2011–12 volume (ML)

2010–11 volume (ML)

2011–12 volume (ML)

2010–11 volume (ML)

2011–12 volume (ML)

2010–11 volume (ML)

Water inflows
 
10 Groundwater increases
10.1 Groundwater inflow from outside region 0 0 2,797 2,941 2,797 2,941
10.2 Groundwater inflow from outside region at coast 0 0 53 76 53 76
10.3 Recharge from landscape 254,547 260,133 2,878,644 10,012,996 3,133,191 10,273,129
10.4 Recharge from surface water 104,977 122,295 244,817 268,210 349,794 390,505
10.5 Leakage from off-channel water storage

 –

 –

 –

 –

 –

 –

10.6 Leakage from urban water system

 –

 –

 –

 –

 –

 –

10.7 Leakage from irrigation scheme

 –

 –

 –

 –

 –

 –

10.8 Managed aquifer recharge – private user 0 0 2,340 4,158 2,340 4,158
10.13 Other groundwater increases 1,116,554 80,562 1,567,106 91,927 2,683,660 172,489
10 Total groundwater increases 1,476,078 462,990 4,695,757 10,380,308 6,171,835 10,843,298
 
Water outflows
 
18 Groundwater asset decreases
18.1 Groundwater outflow to outside region 0 0 19 14 19 14
18.2 Groundwater outflow to outside region at coast 0 0 1,551 1,625 1,551 1,625
18.3 Discharge to landscape 7,104 36,992 610,649 200,575 617,753 237,567
18.4 Discharge to surface water

35,207

7,058

7,159

8,670

42,366

15,728

18.7 Groundwater extractions – other statutory rights 48,948 12,858 145,228 36,437 194,176 49,295
18.11 Entitled extraction of allocated groundwater to users 248,541 125,032 358,429 208,880 606,970 333,912
18.12 Entitled extraction of allocated groundwater to urban water system 7,233 9,047 1,681 1,339 8,914 10,386
18.18 Other groundwater decreases 8,341 8,575 15,930 6,254 24,271 14,829
17 Total surface water asset decreases 355,374 199,562 1,140,646 463,794 1,496,020 663,356
 
Balancing item – groundwater 12,491 191,441 2,003,935 9,830,841 2,016,426 10,022,282
 
Opening water storage 440,728 368,741 913,498 827,825 1,354,226 1,196,566
Add/(Less): Change in water storage 1,108,213 71,987 1,551,176 85,673 2,659,389 157,660
Closing water storage 1,548,941 440,728 2,464,674 913,498 4,013,615 1,354,226

 1 See Supporting information of line item 25.1 Unaccounted-for difference for details.

Allocations and extractions

 Allocation extraction and water abstraction under other statutory rights are the main forms of groundwater extractions within the MDB region. The allocation extractions are associated with a water access entitlement.

Allocation extractions reported in line item 18.11 (primarily for non-urban purposes), 606,970 ML, account for 75% of all extractions within the region for the 2011–12 year. Extractions for all three entitlement / right categories showed increase in water extractions compare to 2010–11 extractions.  Increased volume for other statutory rights were primarily due to availability of data from the water sharing plans implemented during the 2011–12 year.

The entitlement, allocation announcement and forfeiture for water rights associated with groundwater extraction during the 2011–12 year are provided in the Water rights, entitlements, allocations and restrictions note.

Balancing item – groundwater store

Table 8  Balancing item for the groundwater store for the 2011–12 year
 Description

Volume (ML)

Northern Basin

Southern Basin

Whole region

  Opening balance (30 June 2011)

440,728

913,498

1,354,226

add Total 10 Groundwater inflows

1,476,078

4,695,757

6,171,835

minus Total 18 Groundwater outflows

355,374

1,140,646

1,496,020

minus Closing balance (30 June 2012)

1,548,941

2,464,674

4,013,615

   Balancing item – groundwater store

12,491

2,003,935

2,016,426

 

Information on balancing item – groundwater store is available under Supporting information of line item 25.1 Unaccounted–for difference.

Changes in groundwater stored in aquifers

Changes in the groundwater store volume of the water table aquifers for which data are available during the 2011–12 year were evaluated using aquifer characteristics and groundwater level measurements (see quantification methods given below). Table 9 reports on changes in the groundwater store volume of the watertable aquifers for the sustainable diversion limit (SDL) areas within region for which data were available.

Table 9  Volumetric values of changes in groundwater storage in the MDB region for the 2011–12 year
Groundwater resource plan area

Groundwater SDL area  

State

Change in groundwater storage in the 2011–12 year (ML)1

Method used to quantify change in groundwater storage2

Groundwater asset volume (ML)3

Change in groundwater storage relative to groundwater asset (%)

Code

Name

Gwydir Alluvium GS24 Lower Gwydir Alluvium  NSW

550,721

The Bureau method

40,954

1345%

Namoi Alluvium GS29 Lower Namoi Alluvium  NSW

83,370

NSW model

97,654

85%

GS47 Upper Namoi Alluvium  NSW

68,353

NSW model zone 2–12  

141,236

48%

Macquarie–Castlereagh Alluvium GS26 Lower Macquarie Alluvium  NSW

47,055

NSW model zone 1 to 6

71,981

65%

Sub-total Northern Basin

749,499

 

 –

Lachlan Alluvium GS25 Lower Lachlan Alluvium  NSW

62,100

NSW model

124,743

50%

Murrumbidgee Alluvium GS28 Lower Murrumbidgee Alluvium, shallow; Shepparton formation  NSW

308,751

NSW model

287,478

107%

GS31 Mid-Murrumbidgee Alluvium, shallow; Shepparton formation  NSW

14,840

NSW Model

Murray Alluvium GS27 Lower Murray Alluvium, shallow; Shepparton formation  NSW

163,477

The Bureau method

205,344

80%

GS46 Upper Murray Alluvium, Shallow Shepparton formation

 NSW

4,387

The Bureau method

14,109

31%

Goulburn–Murray GS8 Goulburn-Murray: Ovens–Kiewa sedimentary plain  Vic.

33,339

The Bureau method

254,372

102%

GS8 Goulburn–Murray: Victorian Riverine sedimentary plain, shallow; Shepparton formation Vic.

226,670

The Bureau method 
Wimmera–Mallee (groundwater)  GS09 Wimmera Mallee sedimentary plains Vic.

-656,891

The Bureau method 18,477

-3,555%

Eastern Mount Lofty Ranges GS01 Angas Bremer (Quaternary sediments and Murray Group limestone) SA 5,831 The Bureau method 6,500

90%

South Australian Murray GS03 Mallee (Murray Group limestone) SA 50,715 The Bureau method 5,138

987%

GS05 Peake–Roby–Sherlock (unconfined) SA 3,417 5,983

57%

Sub-total Southern Basin

216,636

 

Total for the region

966,135

 

 

1Change in groundwater storage is the estimated difference between all inflows to the store and outflows from the store for the 2011–12 year (see 'Method' in 'Quantification approaches' for more details). Changes in store volumes (based on aquifer characteristics) shown in the table for selected SDL areas are not reflected in the water accounting statements for the MDB region. Therefore, there is no relation between the changes in storage volumes shown in the table, and included in Table 7 and the water accounting statements.

2 See 'Method' in quantification approaches for more details.

3 Groundwater asset volumes shown in the table are long-term estimates of volumes for extraction plus landholder rights (see line item 2.5 Other groundwater assets). The table does not include all the aquifers considered in the water accounting statements. Therefore, the total for the asset volumes shown in the table is less than the total asset volume shown in the water accounting statements and the line item 2.5 Other groundwater assets.

NSW = New South Wales, Vic. = Victoria, SA = South Australia, The Bureau = Bureau of Meteorology

 

Table 9 also indicates what method was used to quantify the change in groundwater storage in each SDL area: either the Bureau method based on measured groundwater levels or the New South Wales groundwater model results (New South Wales models).

With time, trends in the yearly changes in groundwater storages will provide more useful information about the adequacy of the extraction limits set in the groundwater management plans. For instance, a long-term trend of negative changes in groundwater storage may indicate that groundwater in an area may be over allocated. This year most of the changes indicate an increase in groundwater storage which is consistent with the above average rainfall observed during the reporting year and the year before.

Quantification approaches for the estimation of changes in groundwater stored in aquifers

Data source: The Bureau method

Bore locations and groundwater level data in South Australia were sourced from the Drillhole Enquiry System (Department of Environment, Water and Natural Resources 2012).

Bore locations and groundwater level data in Victoria were sourced from the Department of Sustainability and Environment (DSE) and Victorian Department of Primary Industries (DPI) through a database developed by the University of Melbourne.

Bore locations and groundwater level data in New South Wales were sourced from New South Wales Office of Water.

The geographic information system (GIS) data relating to the boundaries of the aquifers and SDL regions were received from the Murray–Darling Basin Authority.

Data source: NSW Office of Water method

The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Data provider

The Bureau and New South Wales Office of Water.

Method: The Bureau method

Change in extractable storage is estimated using a simple geographic information system (GIS) approach based on measured groundwater levels and aquifer properties. Firstly, groundwater levels at the start (1 July 2011) and the end (30 June 2012) of the 2011–12 year were estimated. This was achieved by considering all groundwater level measurements between March 2011 – October 2011 and March 2012 – October 2011, respectively, and using the measurements closest in time to interpolate the start and end levels. The estimated groundwater levels on the start and end dates were then spatially interpolated to grids using kriging with external drift and the 9" Digital Elevation Model as an external driver following the methodology presented in Peterson et al. (2011). The change in volume within the sedimentary area was calculated using these interpolated groundwater level surfaces.

These volumes were multiplied by appropriate specific yield values (Commonwealth Scientific and Industrial Research Organisation and Sinclair Knight Merz 2010a and 2010b) to convert the volume to a change in groundwater storage. Finally, change in storage was only considered within a 10 km mask of each groundwater observation bore to ensure an appropriate influence from the change in each bore and the volume was reported for the water table aquifer only. Groundwater storage outside these buffer areas was assumed constant throughout the year given that there is no data available.
 

Method: New South Wales Office of Water method

New South Wales groundwater (see list of applicable SDL areas in Table 9) model outputs were used to evaluate the changes in groundwater storage. The change in groundwater storage derived from the groundwater models in New South Wales included all the groundwater model layers (not just the water table aquifer layer).

Uncertainty: The Bureau method

Uncertainty estimate was not quantified.

The uncertainty in the field-measured data (e. g. groundwater levels, specific yield) was not specified and hence the impacts of such uncertainty on the change in storage were not estimated.

The change in storage estimations were calculated from the interpolated groundwater level grids produced using kriging with external drift and the 9" Digital Elevation Model as an external driver. Use of other interpolation methods may impact the values of the groundwater level grids and hence the estimated values for change in groundwater storage.

Uncertainty: New South Wales Office of Water method

The uncertainty estimate was not quantified.

It is currently not feasible to estimate the uncertainty of modelled change in extractable storage from outputs of a MODFLOW groundwater model.

Approximations, assumptions, caveats and limitations

The Bureau method:

  • Change in groundwater storage outside the buffer areas is assumed zero given that no data is available for calculation.

  • Change in groundwater storage was not calculated for confined aquifers. Under normal circumstance, the annual change in storage is considered to be negligible for confined aquifers due to their very low storage coefficient, which is much lower than the specific yield of water table aquifers (Freeze and Cherry 1979, Johnson 1967). As long as confined aquifers remain saturated, changes in piezometric levels (i. e. aquifer pressure) usually cause small changes in water volumes stored in the aquifers; the changes are equivalent to the volumetric expansion/contraction of the water and the pore space.

  • The specific yield values used in each water table aquifer are presented in Table below.

New South Wales groundwater models (see list of applicable SDL areas concerned in Table 9):

  • Details on the limitations of groundwater models used by New South Wales Office of Water can be accessed through its webpage on Water accounting.

 

 

Table 10  Specific yield values used in calculating the change in groundwater storage with the Bureau method. The specific yield values was sourced from CSIRO and SKM 2010a and b)
SDL area

Specific Yield

Northern Basin  
Lower Gwydir Alluvium 

0.200

Southern Basin  
Lower Murray Alluvium, shallow; Shepparton formation 

0.100

Upper Murray Alluvium, shallow, Shepparton formation

0.100

Goulburn–Murray: Ovens–Kiewa sedimentary plain 

0.150

Goulburn–Murray: Victorian Riverine sedimentary plain, shallow; Shepparton formation

0.100

Wimmera–Mallee sedimentary plains

0.115

Angas Bremer (Quaternary sediments and Murray Group limestone)

0.100

Groundwater inflow to a SDL area from other SDL areas within a segment

Groundwater inflow from other SDL areas within a segment has been calculated for selected SDL areas. Table 11 and Table 12 provide details for the Northern Basin and the Southern Basin.

 

Table 11  Details of groundwater inflow to a SDL area from other SDL areas within the Northern Basin
SDL area

Volume (ML) for the 2011–12 year for the 2012 Account

Volume (ML) for the 2010–11 year for the 2012 Account

Volume (ML) for the 2010–11 year reported in the 2011 Account

Lower Gwydir Alluvium – unconfined

380

122

279

Lower Gwydir Alluvium – confined

1

0

Lower Namoi – unconfined

10

16

667

Lower Namoi – confined

8,480

8,620

Not reported

 

Table 12  Details of groundwater inflow to a SDL area from other SDL areas within the Southern Basin
SDL area

Volume (ML) for the 2011–12 year for the 2012 Account

Volume (ML) for the 2010–11 year for the 2012 Account

Volume (ML) for the 2010–11 year reported in the 2011 Account

Lower Lachlan (unconfined and confined)

370

2,550

370

Lower Murrumbidgee Alluvium (unconfined)

1,030

16

1,030

Lower Murrumbidgee Alluvium (confined)

9,330

9,600

9,330

Mid-Murrumbidgee Alluvium (unconfined)

6,982

3,909

Mid-Murrumbidgee Alluvium (confined)

2,671

1,319

Lower Murray Alluvium (shallow; Shepparton formation)

41,056

39,674

17,034

Lower Murray Alluvium (deep; Renmark Group and Calivil formation)

871,425

851,486

276,448

Goulburn–Murray (unconfined: Ovens–Kiewa sedimentary plains including Upper Murray)

978

1,041

 4

Goulburn–Murray (confined: Ovens–Kiewa including Upper Murray)

423

388

212

Goulburn–Murray: Victorian Riverine sedimentary plain (shallow; Shepparton formation) 

30,609

28,980

6,280

Goulburn–Murray: Victorian Riverine sedimentary plain (deep; Calivil and Renmark formations) 

44,717

47,732

61,413

Wimmera–Mallee sedimentary area (unconfined)

152,472

156,235

Wimmera–Mallee sedimentary area (confined)

168,524

168,070

Angas Bremer (Quaternary sediments and Murray Group limestone)

7,239

7,121

Angas Bremer (confined)

Mallee (Murray Group limestone) and Peake–Roby–Sherlock (unconfined)

77,784

77,616

Mallee (Murray Group limestone) and Peake–Roby–Sherlock (confined)

1,526

1,618



Quantification approaches for the estimation of inflow to a SDL area from other SDL areas within a segment – Northern Basin

Two estimation methods, the Bureau method and New South Wales Office of Water method were applied in calculations (see line Item 10.1 Groundwater inflow from outside region for more details on the methods).

Data source

The Bureau method:

  • Bore locations and groundwater level data in New South Wales were sourced from New South Wales Office of Water.

  • Bore locations and groundwater level data in Queensland were sourced from Department of Environment and Resource Management.

  • The GIS data relating to the boundaries of the SDL regions were provided by the Murray–Darling Basin Authority.

New South Wales Office of Water method:

  • The outputs of the New South Wales groundwater models available within selected SDL areas were used.

 Data Provider

The Bureau and New South Wales Office of Water.

 Method: The Bureau method

The regional groundwater flow across selected SDL areas within the Northern Basin was considered. The selected SDL areas represent major groundwater resources for the Northern Basin. Groundwater flow was estimated for the unconfined and selected confined aquifers that underlie these boundaries.

Groundwater flow was calculated using a simple GIS approach based on Darcy's Law. Groundwater levels were interpolated for seasons using kriging with an external drift from 9" Digital Elevation Model following the methodology presented in Peterson et al. (2011) and simple GIS analysis for the watertable and confined aquifers, respectively. The seasonal values were aggregated to the 2011–12 year.

Seasonal groundwater flow-grids were derived from groundwater level grids, aquifer thickness and hydraulic conductivity using a modification of the ArcGIS Darcy Velocity tool. Groundwater flow across selected flow boundaries was then calculated using a simple GIS analysis and seasonal values were aggregated to the 2011–12 year.

Method: New South Wales Office of Water method

The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Uncertainty information: The Bureau method

The uncertainty estimate was not quantified.

The uncertainty in the field-measured data (e.g. groundwater levels, hydraulic conductivity) was not specified and unknown and hence the impacts of such uncertainty on the calculated groundwater flow were not estimated.

The regional flow estimations were based on the interpolated groundwater level grids produced using kriging with an external drift from 9" Digital Elevation Model and simple GIS analysis for the water table and confined aquifers, respectively. Use of different interpolation methods may impact on the values of the groundwater level grids and hence the estimated regional flow; however, the regional flow estimated with interpolated groundwater levels using GIS analysis was compared with a simple groundwater flow model developed on MODFLOW model (United States Geological Survey 2013). The results from the two methodologies indicated a 6 7% difference.

Groundwater flow was estimated for a simplified boundary constructed from a series of line segments. Groundwater flow across this boundary was calculated using the method described above. The uncertainty surrounding this simplification was not analysed.

Uncertainty Information: New South Wales Office of Water method

The uncertainty estimate was not quantified.

It is currently not feasible to estimate the uncertainty of modelled regional flow from outputs of a MODFLOW groundwater model.

Assumptions, limitations, caveats and approximations

The Bureau method:

  • Regional flow estimations are provided for the SDL areas indicated in Table 11 only. Due to the fact that not all the hydrological processes within the Northern Basin have been taken into consideration, the total regional inflows to the Northern Basin are not comparable with that provided in Table 11.

  • Constant aquifer thicknesses were assumed for the Lower Gwydir SDL region. The thicknesses were consistent with those reported in the RAAM report (Commonwealth Scientific and Industrial Research Organisation and Sinclair Knight Merz 2010a and 2010b) and Lower Gwydir Valley groundwater model (Huseyin 2002). Aquifer conductivity values were also used from the Lower Gwydir Valley Groundwater Model (Huseyin 2002). Transmissivity values are calculated by multiplying the aquifer thickness with the relevant hydraulic conductivity.

New South Wales Office of Water method:

Quantification approaches for the estimation of inflow to a SDL area from other SDL areas within a segment – Southern Basin

Two estimation methods, the Bureau method and New South Wales Office of Water method, were applied in calculations (see line Item 10.1 Groundwater inflow from outside region for more details on the methods).

Data source

The Bureau method:

  • Bore locations and groundwater level data in South Australia were sourced from the Drillhole Enquiry System (Department of Environment, Water and Natural Resources, 2012).

  • Bore locations and groundwater level data in Victoria were sourced from the Department of Sustainability and Environment (DSE) and Victorian Department of Primary Industries (DPI) through a database developed by the University of Melbourne

  • Bore locations and groundwater level data in New South Wales were sourced from New South Wales Office of Water.

New South Wales Office of Water method:

  • The New South Wales Office of Water has developed a series of groundwater models for selected areas using the groundwater flow simulation computer program MODFLOW. The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Data Provider

The Bureau and New South Wales Office of Water.

Method: The Bureau method

The regional groundwater flow across selected SDL areas within the Southern Basin was considered. 

Groundwater flow was calculated using a simple GIS approach based on Darcy's Law. Groundwater levels were interpolated for seasons using kriging with an external drift from 9" Digital Elevation Model following the methodology presented in Peterson et al. (2011), and simple GIS analysis for the water table and confined aquifers, respectively. The seasonal values were aggregated to the 2011–12 year.

Seasonal groundwater flow-grids were derived from groundwater level grids, aquifer thickness and hydraulic conductivity using a modification of the ArcGIS Darcy Velocity tool. Groundwater flow across selected flow boundaries was then calculated using a simple GIS analysis and seasonal values were aggregated to the 2011–12 year.

Method: New South Wales Office of Water method

The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Uncertainty information: The Bureau method

The uncertainty estimate was not quantified.

The uncertainty in the field-measured data (e.g. groundwater levels, hydraulic conductivity) was not specified and unknown and hence the impacts of such uncertainty on the calculated groundwater flow were not estimated.

The regional flow estimations were based on the interpolated groundwater level grids produced using kriging with an external drift from 9" Digital Elevation Model and simple GIS analysis for the water table and confined aquifers, respectively. Use of different interpolation methods may impact on the values of the groundwater level grids and hence the estimated regional flow; however, the regional flow estimated with interpolated groundwater levels using GIS analysis was compared with a simple groundwater flow model developed on MODFLOWmodel (United States Geological Survey 2013). The results from the two methodologies indicated a 6 – 7% difference.

Uncertainty information: New South Wales Office of Water method

The uncertainty estimate was not quantified.

It is currently not feasible to estimate the uncertainty of modelled regional flow from outputs of a MODFLOW groundwater model.

Assumptions, limitations, caveats and approximations

The Bureau method:

  • Regional flow estimations were provided for the aquifers indicated in Table 12 only and also due to the fact that not all the hydrological processes within the Southern Basin have been taken into consideration, the total regional inflows to the Southern Basin are not comparable with that provided in Table 12.

  • The Geofabric version 2 (Bureau of Meteorology 2011a), and Southern Riverine Plains groundwater model (Goode and Barnett 2008) were used to estimate aquifer thicknesses. The hydraulic conductivity values were sourced from Mallee Prescribed Wells Area – Murrayville Water Supply Protection Area groundwater model (Barnett and Osei-bonsu 2006), Southern Riverine Plains groundwater model (Goode and Barnett 2008) and the report on sustainable extraction limits derived from the recharge risk assessment method – New South Wales (Commonwealth Scientific and Industrial Research Organisation and Sinclair Knight Merz 2010a and 2010b). The transmissivity values were calculated by multiplying the aquifer thickness with the relevant hydraulic conductivity.

  •  It is possible that small differences occur between the University of Melbourne database and the DSE groundwater database (from which bore locations and groundwater level data in Victoria were sourced).

Groundwater outflow from a SDL area to other SDL areas within a segment

Groundwater outflow to other SDL areas within a segment has been calculated for selected SDL areas. Tables 13 and 14 provide details for the Northern Basin and the Southern Basin.

  

Table 13  Details of groundwater outflow from a SDL area to other SDL areas within the Northern Basin
SDL area

Volume (ML) for the 2011–12 year for the 2012 Account

Volume (ML) for the 2010–11 year for the 2012 Account

Volume (ML) for the 2010–11 year reported in the 2011 Account

Lower Gwydir Alluvium (unconfined)

4,998

5,269

1,109

Lower Gwydir Alluvium (confined)

623

619

Lower Namoi (unconfined)

997

1,020

260

Lower Namoi (confined)

5,416

5,470

 

Table 14  Details of groundwater outflow from a SDL area to other SDL areas within the Southern Basin
SDL area

Volume (ML) for the 2011–12 year for the 2012 Account

Volume (ML) for the 2010–11 year for the 2012 Account

Volume (ML) for the 2010–11 year reported in the 2011 Account

Lower Lachlan (unconfined and confined)

24,750

26,850

24,750

Lower Murrumbidgee Alluvium (unconfined)

4,260

973

4,260

Lower Murrumbidgee Alluvium (confined)

118,190

5,080

118,190

Mid-Murrumbidgee Alluvium (unconfined)

1,109

137

Mid-Murrumbidgee Alluvium (confined)

2,157

2,380

Lower Murray Alluvium (shallow; Shepparton formation)

43,484

43,484

8,720

Lower Murray Alluvium (deep; Renmark Group and Calivil formation)

567,854

567,854

184,377

Goulburn–Murray (unconfined: Ovens–Kiewa sedimentary plains including Upper Murray)

12,159

11,286

1,729

Goulburn–Murray (confined: Ovens–Kiewa including Upper Murray)

13,209

12,891

7,751

Goulburn–Murray: Victorian Riverine sedimentary plain (shallow; Shepparton Formation) 

28,722

29,270

10,133

Goulburn–Murray: Victorian Riverine sedimentary plain (deep; Calivil and Renmark formations) 

157,100

152,157

117,410

Wimmera– Mallee sedimentary area (unconfined)

146,369

147,977

Wimmera– Mallee sedimentary area (confined)

516,309

514,454

Angas Bremer (Quaternary sediments and Murray Group limestone)

2,210

1,958

Angas Bremer (confined)

Mallee (Murray Group limestone) and Peake–Roby– Sherlock (unconfined)

73,181

72,299

Mallee (Murray Group limestone) and Peake–Roby– Sherlock (confined)

1,538

1,501

 

Quantification approaches for the estimation of outflow from a SDL area to other SDL areas within a segment

Two estimation methods, the Bureau method and New South Wales Office of Water method, were applied in calculations (see line Item 10.1 Groundwater inflow from outside region for more details on the methods).

Data source

The Bureau method:

  • Bore locations and groundwater level data in New South Wales were sourced from New South Wales Office of Water.

New South Wales Office of Water method:

  •  The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Data provider

The Bureau and New South Wales Office of Water.

Method: The Bureau method

The regional groundwater flow across selected SDL areas within a segment was considered. The selected SDL areas represent major groundwater resources for the segment.

Groundwater flow was calculated using a simple GIS approach based on Darcy's Law.


Method: New South Wales Office of Water method

The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Uncertainty information: The Bureau method

The uncertainty estimate was not quantified.

The uncertainty in the field-measured data (e.g. groundwater levels, hydraulic conductivity) was not specified and unknown and hence the impacts of such uncertainty on the calculated groundwater flow were not estimated.

The regional flow estimations were based on the interpolated groundwater level grids. Use of different interpolation methods may impact on the values of the groundwater level grids and hence the estimated regional flow;  however, a comparison of the methodology was carried out using a simple groundwater flow model developed on MODFLOW model (United States Geological Survey 2013). The results from the two methodologies indicated a 6 – 7% difference.

Groundwater flow was estimated for a simplified boundary constructed from a series of line segments. Groundwater flow across this boundary was calculated using the method described above. The uncertainty surrounding this simplification was not analysed.

Uncertainty information: New South Wales Office of Water method

The uncertainty estimate was not quantified.

It is currently not feasible to estimate the uncertainty of modelled regional flow from outputs of a MODFLOW groundwater model.

Assumptions, limitations, caveats and approximations

The Bureau of Meteorology method:

  • Regional flow estimations were provided for the SDL areas shown in tables 14 and 15 only. Due to the fact that not all the hydrological processes within the segments have been taken into consideration, the total regional outflow are not comparable with that provided in tables 14 and 15.

New South Wales Office of Water method:

Details on the limitations of groundwater models used by the New South Wales Office of Water are available in General Purpose Water Accounting Reports - Groundwater methodologies.

Off-channel storages

Purpose of note

The purpose of this note is to provide a consolidated report on the off-channel water storages within the Murray–Darling Basin (MDB) region during the 2011–12 year. Information on storage volumes, inflows and outflows for the off-channel water storages is provided in this note.

Background

The off-channel water storages consists of all private reservoirs that are used to harvest runoff before reaching the surface water store or that are filled by pumping from a watercourse or groundwater.

The store includes constructed storages that are not connected either seasonally or perennially to rivers, filled predominantly by local catchment runoff. They include off-channel farm dams, run-off dams, hill-side dams, industrial, commercial and mining water storages. They exclude on-channel farm dams and other storages.

The off-channel water storages for the 2012 Account were determined from waterbody mapping conducted by Geoscience Australia as those that are:

  • not named storages (assuming that any storage with a name is unlikely to be a off-channel storage)

  • above 600 m in elevation or are in areas that receive greater than 400 mm per annum in precipitation and are not within 50 m of a major or perennial stream.

The above rules attempt to divide storages into those that are likely to be filled primarily by local catchment runoff and those which are filled by abstraction from surface water, groundwater or floodplain harvesting.

As discussed in General description in 'Physical information' in the 'Contextual information', the off-channel water store has been excluded from the scope of the MDB region for the purposes of the 2012 Account, because it is constituted of water already abstracted from the shared pool of water resources. Therefore off-channel water store reporting line items do not appear in the water accounting statements. Off-channel water storages influence water assets and water liabilities recognised in the water accounting statements though, as they harvest water from the landscape and thus reduce groundwater recharge and runoff into surface water.

Water in store

Table 15 shows that the total off-channel water store increased during the 2011–12 year in the MDB region.

 

Table 15  Off-channel water storage volume at the start and end of the 2011–12 year for the MDB region
Description

30 June 2012 (ML)

30 June 2011 (ML)

Northern Basin

Southern Basin

Whole region

Northern Basin

Southern Basin

Whole region

27.1 Off-channel water storages

534,236

618,502

1,152,737

513,351

618,587

1,131,938

27.2 Rainwater tanks

Total

534,236

618,502

1,152,737

513,351

618,587

1,131,938

 –  = Data not available

 

The water volume held in off-channel water storages within the MDB region at the end of the 2011–12 year was more than that at the start (1 July 2011). This was primarily attributed to the high rainfalls and inflows recorded in the Northern Basin of the region during the 2011–12 year. Some areas in the Northern Basin recorded their highest annual rainfall on record (see Rainfall in 'Climate overview' in the 'Contextual information').

Off-channel water inflows and outflows

The inflow and outflow volumes for the off-channel water store during the 2011–12 year are given in Table 16.

 

Table 16  Volume of inflows and outflows for the off-channel water store during the 2011–12 year
 Description

Volume (ML)

Northern Basin

Southern Basin

Whole region

Off-channel water inflows      
30.1 Precipitation on off-channel water store

849,216

435,568

1,284,785

30.2 Groundwater discharge into off-channel water store

­–

30.3 Runoff harvesting into off-channel water store

742,969

577,978

1,320,947

30.4 Surface water diversion into off-channel water store

­–

30.5 Groundwater extraction into off-channel water store

­–

Total Off-channel water inflows

1,592,185

1,013,546

2,605,732

       
Off-channel water outflows      
31.1 Evaporation from off-channel water storages

1,039,856

571,476

1,611,332

31.2 Leakages from off-channel water storages

­–

31.3 Off-channel water abstraction

531,432

442,169

973,602

Total Off-channel water outflows

1,571,288

1,013,645

2,584,934

       
Balancing item – off-channel water

12

(14)

(1)

       
Change in off-channel water storage

20,885

(85)

20,799

       
Opening off-channel water storage 

513,351

618,587

1,131,938

Closing off-channel water storage

534,236

618,502

1,152,737

– = data not available

 

Precipitation on to off-channel water store and runoff harvesting into them decreased by 10% and 13% respectively for the 2011–12 year compared to the 2010–11 year. Most likely due to that reason, water use from off-channel storages decreased by 12% in the 2011–12 year compared to the previous years' use.

Balancing item – off-channel water

This volume represents the volume necessary to reconcile the opening and closing balances of the off-channel water storage with the physical water inflows and outflows. The difference was calculated according to Table 17.

 

Table 17  Balancing item – off-channel water 2011–12 year
Description

Account

Volume (ML)

  Opening balance (30 June 2011)

1,131,938

add Total 30 Off-channel water inflows

2,605,732

minus Total 31 Off-channel water outflows

2,584,934

minus Closing balance (30 June 2012)

1,152,737

  Balancing item – off-channel water store

(1)

 

The calculation of the water balance on the off-channel water store yielded a balance of -1 ML. This is negligible compared to the opening and closing balances. Despite this, one should note that the values presented for off-channel storages remain broad estimates based on numerous assumptions and simplifications (see quantification approaches of the various line items linked from the tables).