Ord
Water resources and systems

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

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.

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.

A description of the Ord region's surface water resources is provided in the Surface water section of the 'Contextual information'.

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.

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). 

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.

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.

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).

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

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)

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.

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.

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