Ord
Water resources and systems

Introduction

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

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


Figure 1  Schematic diagram of the water stores and systems within the Ord region
Figure 1  Schematic diagram of the water stores and systems within the Ord region


Information on all water flows to and from each water store and system are 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 Ord region. Line item numbers are provided next to the flows.
Figure 2  Schematic diagram of between-store flows that occur within the Ord 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 Ord region's surface water resources is provided in the Surface water section of the 'Contextual information'.

Water in store

The Statement of Water Assets and Water Liabilities for the surface water store (Table 1) shows that total surface water assets and net water assets decreased during the 2011–12 year in the Ord region.


Table 1  Statement of Water Assets and Water Liabilities for the surface water store
Water assets Volume at 30 June 2012
(ML)
Volume at 30 June 2011
(ML)
1 Surface water    
1.1 Storages 10,759,396 15,078,047
1.2 Unregulated river
1.3 Regulated river 16,385 70,444
1.4 Lakes and wetlands
Total surface water assets 10,775,781 15,148,491
     
Water liabilities    
5 Surface water liability    
5.1 Surface water allocation remaining 23,801 21,294
5.2 Surface water allocation remaining – urban water system 670 735
5.3 Surface water allocation remaining – irrigation scheme 282,202 282,202
Total surface water liabilities 306,673 304,231
     
Opening net water assets 14,844,260 8,517,669
Change in net water assets (4,375,152) 6,326,591
Closing net water assets 10,469,108 14,844,260


The volume of water in unregulated rivers (line item 1.2) and lakes and wetlands (line item 1.4) could not be quantified due to a lack of available data; however, the volume of water held in channels and lakes is considered to be relatively small compared to the volume held in storages.

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


Figure 3  Location map of the storages within the Ord region. The percentage-full volume on 30 June 2012 for each storage is also shown.
Figure 3  Location map of the storages within the Ord region. The percentage-full volume on 30 June 2012 for each storage is also shown.


The water volume in Lake Argyle decreased during the 2011–12 year from 139% full at the start to 99% full at 30 June 2012 (see 1.1 Storages). The above capacity volume at the start of the 2011–12 year was due to the record rainfall conditions observed the previous year (see the 2011 Account). Note that percentage full may exceed 100% during periods of high flow (see the Water storage glossary).

All storages within the Ord region were more than 90% of capacity on 30 June 2012 (Figure 3). 


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.


Table 2  Statement of Changes in Water Assets and Water Liabilities for the surface water store
Water asset increases 2011–12 volume
(ML)
2010–11 volume
(ML)
9 Surface water increases    
9.1 Precipitation on surface water 756,582 1,485,020
9.3 Groundwater discharge
9.4 Runoff to surface water 6,794,954 37,140,631
9.5 Point return from irrigation scheme
9.6 Overbank flood return to river channel
9.9 Discharge from urban water system 686 591
Total surface water increases 7,552,222 38,626,242
     
Water liability decreases    
13 Surface water liability decreases    
13.1 Adjustment and forfeiture of surface water allocation 14,266 23,664
13.2 Adjustment and forfeiture of surface water allocation – urban water system 418 333
13.3 Adjustment and forfeiture of surface water allocation – irrigation scheme 182,738 178,586
Total surface water liability decreases 197,422 202,583
     
Water asset decreases    
17  Surface water decreases    
17.1 Evaporation from surface water 1,663,087 2,080,765
17.2 River outflow from the region 7,286,990 18,104,939
17.3 Leakage to groundwater
17.4 Leakage to landscape 19 0
17.5 Overbank flood spilling
Total surface water decreases 8,950,096 20,185,704
     
Water liability increases    
21 Surface water liability increases    
21.1 Surface water allocation announcements 36,802 34,570
21.2 Surface water allocation announcements – urban water system 775 775
21.3 Surface water allocation announcements – irrigation scheme 338,100 338,100
Total surface water liability increases 375,677 373,445
     
Balancing item—surface water 2,799,023 11,943,085
     
Change in net water assets (4,375,152) 6,326,591


Table 3  Statement of Water Flows for the surface water store
Water inflows 2011–12 volume
(ML)
2010–11 volume
(ML)
9 Surface water inflows    
9.1 Precipitation on surface water 756,582 1,485,020
9.3 Groundwater discharge
9.4 Runoff to surface water 6,794,954 37,140,631
9.5 Point return from irrigation scheme
9.6 Overbank flood return to river channel
9.9 Discharge from urban water system 686 591
Total surface water inflows 7,552,222 38,626,242
     
Water outflows    
17 Surface water outflows    
17.1 Evaporation from surface water 1,663,087 2,080,765
17.2 River outflow from the region 7,286,990 18,104,939
17.3 Leakage to groundwater
17.4 Leakage to landscape 19 0
17.5 Overbank flood spilling
17.11 Entitled diversion of allocated surface water to users 20,029 12,339
17.12 Entitled diversion of allocated surface water to urban water system 422 430
17.13 Entitled diversion of allocated surface water to irrigation scheme 155,362 161,155
Total surface water outflows 9,125,909 20,359,628
     
Balancing item—surface water 2,799,023 11,943,085
     
Opening water storage 15,148,491 8,824,962
Add/(Less): Change in water storage (4,372,710) 6,323,529
Closing water storage 10,775,781 15,148,491


A schematic diagram representing all the inflows and outflows associated with the surface water store in the Ord 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 Ord region during the 2011–12 year. Line item numbers are provided in brackets.
Figure 4  Schematic diagram of water inflows and outflows for the surface water store within the Ord region during the 2011–12 year. Line item numbers are provided in brackets.


Table 3 shows that surface water storage decreased during the 2011–12 year by 4,372,710 ML (approximately 30%). This is a substantial change from the previous year, where water storage increased by 6,323,529 ML (approximately 70%). The primary reason for the decrease in water storage during the 2011–12 year is that runoff to surface water (line item 9.4) was more than five times less than the comparison year (Table 3).

Despite the decrease in water storage during the 2011–12 year, the closing net water assets and water storage remain above the 2010–11 year opening balance volumes (Tables 1 and 3 respectively). 


Allocation diversions

Figure 5 shows that most of the allocation diversion from surface water is for irrigation scheme water supply (line item 17.13). During the 2011–12 year, irrigation scheme water supply made up approximately 88% of the total allocation diversion, a marginal decrease from the previous year (which was 93% of the total allocation diversion).

Figure 5 shows that allocation diversions from surface water during the 2011–12 year to individual users (line item 17.11) have increased by approximately 62% from last year.


Figure 5  Graph of allocation diversions from surface water within the Ord region during the 2011–12 year and the 2010–11 comparison year. Line item numbers are given in brackets.
Figure 5  Graph of allocation diversions from surface water within the Ord region during the 2011–12 year and the 2010–11 comparison year. Line item numbers are given in brackets.


These allocation diversions are all associated with a water access entitlement. When an allocation is announced, a present obligation (water liability) is created on the surface water to deliver water to the users. As there is no carryover provision in the region, the portion of the announced allocations that were not diverted by the end of the year was forfeited.

The entitlement, allocation announcement and forfeiture for each of these water rights during the 2011–12 year are provided in the Surface water rights section of the 'Water access and use' note.


Balancing item

The balancing item volume represents the difference between the measured opening and closing balances of the surface water store, after physical inflows and outflows have been applied. This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete surface water store balance.

The balancing item is calculated according to Table 4.


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

 

Account

Volume (ML)

 

Opening balance (30 June 2011)

15,148,491

add

Total surface water inflows (see Table 3)

7,552,222

less

Total surface water outflows (see Table 3)

9,125,909

less

Closing balance (30 June 2012)

10,775,781

 

Balancing item—surface water store

2,799,023


The calculation of the water balance on the surface water store yielded a balancing item of 2,799,023 ML. This is approximately 26% of the total surface water store volume at the end of the 2011–12 year and approximately 37% of the total surface water inflows during the 2011–12 year.

It is likely that the balancing item is primarily attributed to uncertainties associated with the runoff (a large source of surface water increase, line item 9.4), river outflow from the region (a large source of surface water decrease, line item 17.2) and the lack of an estimate of surface water discharge to groundwater.

The runoff volume is derived from a rainfall–runoff model and it is reasonable to expect a 10–20% uncertainty around the estimated runoff volume (+/– 1,360,000 ML). The river outflow to sea is based on measured flow data collected at the most downstream station along a river. There is no adjustment made for the contributing area below the gauging station. As such, outflow to sea is likely to be underestimated by 10–20% (1,460,000 ML).

Groundwater

Background

A description of the Ord region's groundwater resources is provided in the Groundwater section of the 'Contextual information'.

Water in store

The aquifers in the Ord region are described in the Groundwater section of the 'Contextual information'. While some information exists on water movement to and from the aquifers (see following section on 'Changes in water store'), no value is available for the volume of water stored in the aquifers. No value could be estimated for the volume of the groundwater asset either, indicated by dashes ('–') in Table 5. Further information is provided in line item notes 2.1 Water table aquifer and 2.2 Underlying aquifers.

The Statement of Water Assets and Water Liabilities for the groundwater store is shown in Table 5.


Table 5  Statement of Water Assets and Water Liabilities for the groundwater store
Water assets Volume at 30 June 2012
(ML)
Volume at 30 June 2011
(ML)
2 Groundwater    
2.1 Water table aquifer
2.2 Underlying aquifers
Total groundwater assets
     
Water liabilities    
6 Groundwater liability    
6.1 Groundwater allocation remaining 1,320 1,246
6.2 Groundwater allocation remaining – urban water system 2,252 2,292
Total groundwater liabilities 3,572 3,538
     
Opening net water assets (3,538) (2,897)
Change in net water assets (34) (641)
Closing net water assets (3,572) (3,538)


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 Tables 6 and 7 respectively.


Table 6  Statement of Changes in Water Assets and Water Liabilities for the groundwater store
Water asset increases 2011–12 volume
(ML)
2010–11 volume
(ML)
10 Groundwater increases    
10.1 Groundwater inflow from outside region
10.3 Recharge from landscape 13,108 9,686
10.4 Recharge from surface water
Total groundwater increases 13,108 9,686
     
Water liability decreases    
14 Groundwater liability decreases    
14.1 Adjustment and forfeiture of groundwater allocation 85 4,136
14.2 Adjustment and forfeiture of groundwater allocation – urban water system 898 989
Total groundwater liability decreases 983 5,125
     
Water asset decreases    
18 Groundwater decreases    
18.1 Groundwater outflow to outside region
18.3 Discharge to landscape
18.4 Discharge to surface water
Total groundwater decreases
     
Water liability increases    
22 Groundwater liability increases    
22.1 Groundwater allocation announcements 11,425 12,752
22.2 Groundwater allocation announcements – urban water system 2,700 2,700
Total groundwater liability increases 14,125 15,452
     
Balancing item—groundwater 0 0
     
Change in net water assets (34) (641)


Table 7  Statement of Water Flows for the groundwater store
Water inflows 2011–12 volume
(ML)
2010–11 volume
(ML)
10 Groundwater inflows    
10.1 Groundwater inflow from outside region
10.3 Recharge from landscape 13,108 9,686
10.4 Recharge from surface water
Total groundwater inflows 13,108 9,686
     
Water outflows    
18 Groundwater outflows    
18.1 Groundwater outflow to outside region
18.3 Discharge to landscape
18.4 Discharge to surface water
18.11 Entitled extraction of allocated groundwater to users 11,266 7,912
18.12 Entitled extraction of allocated groundwater to urban water system 1,842 1,774
Total groundwater outflows 13,108 9,686
     
Balancing item—groundwater 0 0
     
Opening water storage
Add/(Less): Change in water storage 0 0
Closing water storage


A schematic diagram representing all the inflows and outflows associated with the groundwater store in the Ord region is provided in Figure 6. The numbers in brackets on the diagram refer to the line item numbers in Table 7.


Figure 6  Schematic diagram of water inflows and outflows for the groundwater store within the Ord region during the 2011–12 year. Line item numbers are provided in brackets.
Figure 6  Schematic diagram of water inflows and outflows for the groundwater store within the Ord region during the 2011–12 year. Line item numbers are provided in brackets.


Allocations and extractions

Most of the extractions from the groundwater store are for licensed private use (line item 18.11), which accounts for approximately 86% of the total groundwater extraction. The majority of the allocated private water extractions are for mining use (see line item 22.1).

Figure 7 shows that allocation extractions from aquifers during the 2011–12 year for private use have increased by approximately 42% from last year. Extractions for urban water supply are similar to the 2010–11 year. 


Figure 7  Graph of extractions from aquifers within the Ord region during the 2011–12 year and the 2010–11 comparison year. Line item numbers are given in brackets.
Figure 7  Graph of extractions from aquifers within the Ord region during the 2011–12 year and the 2010–11 comparison year. Line item numbers are given in brackets.


The allocation extractions are all associated with a water access entitlement. When an allocation is announced, an obligation (water liability) is created on the groundwater to deliver water to the users. As there is no carryover provision in the region, the portion of the announced allocations that were not diverted by the end of the year was forfeited.

The entitlement, allocation announcement and forfeiture for each of these water rights during the 2011–12 year are provided in the Groundwater rights section of the 'Water access and use' note.

 

Balancing item

This volume represents the difference between the measured opening and closing balances of the groundwater store, after physical inflows and outflows have been applied.

The balancing item of zero is calculated according to Table 8.

 

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

 

Account

Volume (ML)

 

Opening balance (30 June 2011)

add

Total groundwater inflows (see Table 7)

13,108

minus

Total groundwater outflows (see Table 7)

13,108

minus

Closing balance (30 June 2012)

 

Balancing item—groundwater store

0