South East Queensland
Water resources and systems

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




Figure 1 Schematic diagram of the water stores and systems within the South East Queensland region




For a more detailed description of the region, please refer to the General description.

Background

A description of the South East Queensland region's surface water resources is provided in 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 increased during the 2011–12 year in the South East Queensland 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	2,479,671	2,219,099
1.2 Unregulated river	–	–
1.3 Regulated river	–	–
1.4 Lakes and wetlands	–	–
Total surface water assets	2,479,671	2,219,099
Water liabilities
5 Surface water liability
5.1 Surface water allocation remaining	11,578	12,234
Total surface water liabilities	11,578	12,234
Opening net water assets	2,206,865	2,085,120
Change in net water assets	261,228	121,745
Closing net water assets	2,468,093	2,206,865

The surface water storage volume includes water that was held in reservoirs, weirs, lakes and major dams, where these data are available. For the purposes of the water accounting statements, all of these surface water storages are reported at line item 1.1 Storages as the volumes of water held in these storages are used to administer entitlements. The volume of water in rivers and natural lakes and wetlands could not be quantified in a way that is complete, neutral and free from material error due to a lack of available data.

The location of surface water storages in the South East Queensland region and the volume of water including dead storage held in each of these storages (as a percentage of total storage capacity) at the end of the 2011–12 year is shown in Figure 2.

Figure 2 Location map of surface water storages within the South East Queensland region; the % full volume on 30 June 2012 for each water storage is also shown

The volume of water held in all storages within the South East Queensland region increased by approximately 12% during 2011–12 (Table 1). At the end of the 2011–12 year storage volume, as a percentage of the total storage capacity (% full), was very high in the region, at almost 95%. The majority of surface water storages in South East Queensland were more than 90% full (Figure 1). The increase in overall surface water storage may be attributed to the accumulation of water received from 2010–11 flood. In particular, the region experienced above-average rainfall (see Climate overview). Of the five storages that recorded decreases in volume stored, only the decrease in the volume of water stored in Bromelton Off-Stream Storage was material (7%). Following significant flooding in January 2011 and pursuant to the 13 February 2011 announcement by the Queensland State Government (Flood Commission), the operating level of the Wivenhoe dam was reduced until 31 March 2011 from elevation 67 to 64 metres to temporarily increase the flood mitigation capacity of the Wivenhoe dam.

It should be noted that the Hinze Dam Stage 3 Project increased the storage capacity of the dam during the 2010–11 year. The project raised the dam wall by approximately 15 metres and increased storage capacity from 161,073 ML – 310,730 ML.

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 Table 2 and Table 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	239,397	417,313
9.4 Runoff to surface water	5,673,771	12,286,627
9.9 Discharge from urban water system	62,517	57,333
9.10 Direct discharge by user	6,964	1,846
Total surface water increases	5,982,649	12,763,119
Water liability decreases
13 Surface water liability decreases
13.1 Adjustment and forfeiture of surface water allocation	68,055	66,841
13.2 Adjustment and forfeiture of surface water allocation – urban water system	230,474	245,498
Total surface water liability decreases	298,529	312,339
Water asset decreases
17 Surface water asset decreases
17.1 Evaporation from surface water	259,859	270,156
17.2 River outflow from the region	3,631,308	12,043,399
17.4 Leakage to landscape	232,271	256,778
17.6 Surface water diversions– other statutory rights	3,628	3,628
17.7 Entitled diversion on non–allocated surface water to users	2,049	2,016
17.8 Entitled diversion of non–allocated surface water to urban water system	4,383	7,458
17.21 Other surface water decreases	6,165	5,706
Total surface water asset decreases	4,139,663	12,589,141
Water liability increases
21 Surface water liability increases
21.1 Surface water allocation announcements	73,304	73,304
21.2 Surface water allocation announcements – urban system	442,826	442,826
Total surface water liability increases	516,130	516,130
Balancing item – surface water	1,364,157	(151,558)
Change in net water assets	261,228	121,745

 

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	239,397	417,313
9.4 Runoff to surface water	5,673,771	12,286,627
9.9 Discharge from urban water system	62,517	57,333
9.10 Direct discharge by user	6,964	1,846
Total surface water inflows	5,982,649	12,763,119
Water outflows
17 Surface water outflows
17.1 Evaporation from surface water	259,859	270,156
17.2 River outflow from the region	3,631,308	12,043,399
17.4 Leakage to landscape	232,271	256,778
17.6 Surface water diversions– other statutory rights	3,628	3,628
17.7 Entitled diversion on non–allocated surface water to users	2,049	2,016
17.8 Entitled diversion of non–allocated surface water to urban water system	4,383	7,458
17.11 Entitled diversion of allocated surface water to users	5,905	5,905
17.12 Entitled diversion of allocated surface water to urban water system	212,352	197,328
17.21 Other surface water decreases	6,165	5,706
Total surface water outflows	4,357,920	12,792,374
Balancing item – surface water	1,364,157	(151,558)
Opening water storage	2,219,099	2,096,796
Add: Change in water storage	260,572	122,303
Closing water storage	2,479,671	2,219,099

Inflows to the surface water store were higher (>37%) than outflows from the surface water store during the 2011–12 year. A schematic diagram representing all the inflows and outflows associated with the surface water store in the South East Queensland region is provided in Figure 3. The inflow and outflow volumes for the surface water store during the 2011–12 year are given in Table 2.

Figure 3 Schematic diagram of water inflows and outflows for the surface water store within the South East Queensland region during the 2011–12 year; line item numbers are provided in brackets

 

The most significant contribution to surface water inflows was runoff to surface water that was a direct result of above-average rainfall experienced by the South East Queensland region during the 2011–12 year. There were some flash flooding at places in the South East Queensland region in late January and early February 2012. By comparison, all other surface water inflows were minor. Decreases to the surface water store were mainly due to river outflow to sea and, combined with evaporation and leakage, far exceeded decreases to the surface water store due to diversions.

Allocation diversions

Figure 4 shows that the majority (92%) of surface water diversions in the South East Queensland region during 2011–12 were for urban water supply within the region (line item 17.8 Entitled diversion of non–allocated surface water to urban water system and line item 17.12 Entitled diversion of allocated surface water to urban water system). The volume of water diverted to the urban water supply system from surface water increased by 6% compared to the volume diverted in 2010–11. This can be attributed to an increased reliance on surface water due to an increase in availability of the resource and a decline in the reliance on groundwater and desalinated water resources.

In contrast, non–urban surface water diversions (line item 17.11 Entitled diversion of allocated surface water to users, 17.6 Surface water diversions – other statutory rights and 17.7 Entitled diversion of non–allocated surface water to users), which accounted for only a very small portion (8%) of surface water diversions in the region, did not change significantly in 2011–12 compared to 2010–11. Diversions of this nature are typically for riparian entitlement diversions, stock and domestic and irrigation purposes (see individual line items for more detail).

Decreases to the volume of water diverted from the region's surface waters for non-urban purposes are associated with above-average rainfall experienced during 2011–12. Increased precipitation is likely to have contributed significantly to the decrease in irrigation demand. Similarly, increased precipitation and subsequently runoff may have satisfied demand for stock and domestic purposes, whereas during drought years this was not the case.

Figure 4 Graph of diversions from surface water within the South East Queensland region during the 2011–12 year and 2010–11 comparison year; line item numbers are given in brackets

These diversions are all 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 users. Where the water year matches the 2012 Account year (July 2011–June 2012) 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 Water rights, entitlements, allocations and trade notes.

Balancing item – surface water store

This volume represents the volume necessary to reconcile the opening and closing balances of the surface water store with the physical water inflows and outflows. The balancing item – surface water store 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)	2,219,099
add	Total 9 Surface water inflows	5,982,649
less	Total 17 Surface water outflows	4,357,920
less	Closing balance (30 June 2012)	2,479,671
	Balancing item – surface water store	1,364,157

It is likely the balancing item is primarily attributed to uncertainty associated with the estimate of rainfall-runoff (a large source of surface water increase, line item 9.4 Runoff to surface water) and also outflow to outside region (a large source of surface water decrease, line item 17.2 River outflow from the region). The rainfall-runoff volume is derived from a rainfall-runoff model and it is reasonable to expect an uncertainty around the estimated runoff volume that could account for the balancing item. The surface water outflow to sea was based on flow gauge data and regression analysis.

Background

A description of the South East Queensland region's groundwater resources are provided in the Groundwater section of the 'Contextual information'.

Nominal volume (line item 33.2 Groundwater access entitlement for non–allocated extractions) of water in the Benefitted Area of the Lockyer Valley Groundwater Management Area (GMA) in the Central Lockyer Water Supply Scheme (WSS) was included as the groundwater asset in the 2012 Account. Progressive assessment of volumetric extractions in additional implementation areas of the Lockyer Valley GMA will occur in the future so that groundwater extraction can be managed within sustainable limits. Until this time, only the Benefitted Area part of the alluvial aquifer has been included as a groundwater asset.

Groundwater aquifers do occur elsewhere within the South East Queensland region; however, there are currently no models for these, and their storage volume could not be quantified in order to determine sustainable extraction limits.

A more detailed explanation is provided in line item 2.1 Water table aquifer and 2.2 Underlying aquifer.

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	9,340	9,340
2.2 Underlying aquifers	–	–
Total groundwater assets	9,340	9,340
Water liabilities
6 Groundwater liability
6.1 Groundwater allocation remaining	0	0
Total groundwater liabilities	0	0
Opening net water assets	9,340	9,340
Change in net water assets	0	0
Closing net water assets	9,340	9,340

 – = 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.

 

Table 6 Statement of Changes in Water Assets and Water Liabilities for the groundwater store

Water asset increases	Volume at 30 June 2012 ML	Volume at 30 June 2011 ML
10 Groundwater increases
10.6 Leakage from urban water system	28,662	25,534
Total groundwater increases	28,662	25,534
Water liability decreases
14 Groundwater liability decreases
14.1 Adjustment and fortfeiture of groundwater allocation	7,567	8,227
Total groundwater liability decreases	7,567	8,227
Water asset decreases
18 Groundwater decreases
18.8 Entitled extraction of non–allocated groundwater to users	2,003	258
18.9 Entitled extraction of non–allocated groundwater to urban water system	149	213
Total groundwater decreases	2,152	471
Water liability increases
22 Groundwater liability increases
22.1 Groundwater allocation announcements	9,340	9,340
Total groundwater liability increases	9,340	9,340
Balancing item – groundwater	24,737	23,950
Change in net water assets	0	0

 

 

Table 7 Statement of Water Flows for the groundwater store

Water inflows	Volume at 30 June 2012 ML	Volume at 30 June 2011 ML
10 Groundwater inflows
10.6 Leakage from urban water system	28,662	25,534
Total groundwater inflows	28,662	25,534
Water outflows
18 Groundwater outflows
18.8 Entitled extraction of non–allocated groundwater to users	2,003	258
18.9 Entitled extraction of non–allocated groundwater to urban water system	149	213
18.11 Entitled extraction of allocated groundwater to users	1,773	1,113
Total groundwater outflows	3,925	1,584
Balancing item – groundwater	24,737	23,950
Opening water storage	9,340	9,340
Add/(Less): Change in water storage	–	–
Closing water storage	9,340	9,340

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the South East Queensland region is provided in Figure 5. The inflow and outflow volumes for the groundwater store during the 2011–12 year are given in Table 7.

Figure 5 Schematic diagram of water inflows and outflows for the groundwater store within the South East Queensland region during the 2011–12 year; line item numbers are provided in brackets

Allocations and extractions

Most of the extractions from the groundwater store were Benefitted Area extractions within the Central Lockyer Valley WSS in the Lockyer Valley GMA (line item 18.11 Entitled extraction of allocated groundwater to users), which accounts for approximately 85% of the total groundwater extraction. Extraction data were not available for a number of other GMAs or for the Non–Benefitted Area of Implementation Area 1 of the Lockyer Valley GMA.

Figure 6 shows that allocation extractions from aquifers during the 2011–12 year have increased from last year. This can be attributed to a relatively dry year  requiring higher irrigation demand than last year (see Climate overview). Urban extractions decreased from last year. This can be attributed to a greater availability of surface water to meet the demand from the urban water system.

Figure 6 Graph of groundwater extractions from aquifers within the South East Queensland region during the 2011–12 year and 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 carry-over 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 Water rights, entitlements, allocations and trade note, in the 'Groundwater rights'.

Balancing item  groundwater store

This volume represents the volume necessary to reconcile the opening and closing balances of the groundwater store with the physical water inflows and outflows.

The balancing item was calculated across the whole South East Queensland region, not just the individual aquifers included as the groundwater asset.

The balancing item – groundwater store was 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)	9,340
add	Total 10 Groundwater inflows	28,662
less	Total 18 Groundwater outflows	3,925
less	Closing balance (30 June 2012)	9,340
	Balancing item – groundwater store	24,737

 

The calculation of the water balance on the groundwater store yielded a balancing item of 24,737 ML, approximately 86% of the total groundwater inflows during the 2011–12 year.

This large balancing item value is primarily due to the fact that groundwater asset and flows are calculated in ways that do not allow them to reconcile on an annual basis:

• The groundwater asset is quantified as the average long-term groundwater volume available for extraction without adversely impacting the system. This value is constant during the year, unless its scope (number of groundwater areas included) or quantification approach has changed.

• In contrast, inflows and outflows represent measured, estimated or modelled yearly values that vary depending on climatic conditions, extractions and so on.

For the 2011–12 year, the groundwater asset value was estimated as the nominal volume (entitled volumetric limit) of water in the Benefitted Area part of the alluvial aquifer in the Central Lockyer WSS only, whereas the inflows and outflows associated with groundwater were for the entire South East Queensland region.

Other factors that explain the large balancing item are inaccuracies made in the calculations of the groundwater terms are presented in Table 5.

• the most significant inflows and outflows, such as groundwater recharge and discharge, were not quantified.

This value of balancing item is 787 ML larger in magnitude than that reported in the 2011 Account (Table 7). This can be attributed due to higher groundwater inflows.

Background information on the urban water system within the South East Queensland region is available in the 'Contextual information' under Other water resources and distribution systems.

Water in store

The Statement of Water Assets and Water Liabilities for the urban water system (Table 9) shows that the volume of water in the urban water system changed marginally during the 2011–12 year in the South East Queensland region.  

Table 9 Statement of Water Assets and Water Liabilities for the urban water system

Water assets	Volume at 30 June 2012 ML	Volume at 30 June 2011 ML
3 Urban water system
3.1 Urban water supply system	2,842	2,094
Total urban water system assets	2,842	2,094
Opening net water assets	2,094	2,054
Change in net water assets	748	40
Closing net water assets	2,842	2,094

Table 9 shows that for the urban system in the South East Queensland region, only the volume of water contained in the urban water supply system could be quantified. The volume only includes bulk mains and does not include balancing tanks (locally called reservoirs) or distribution pipe networks. It is expected that the volume shown would be a significant underestimate of the total asset, which may be two to three times this volume. As balancing tanks have not been included, the volume in the urban system remains relatively constant over time as all pressurised pipes are required to remain completely full for the supply system to operate. A slight increase was expected due to upgrades to the network and the addition of new pipes to service new areas.

Volumes associated with other supply and collection systems could not be quantified in the South East Queensland due to lack of data. The recycled water supply system volume, being much smaller in extent than the urban water supply system, would have a much smaller volume. The wastewater collection system may cover a similar extent to the urban water supply system and have a similar capacity, although the volume would be smaller due to gravity sewers operating as part pipe flow rather than full pipe flow as occurs in the urban water supply system.

The extent of the urban water supply and collection systems within the South East Queensland region can be seen in the Seqwater infrastructure map. 

Changes in water store

The Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows for the urban water system are provided in Table 10 and Table 11, respectively.  

 

Table 10 Statement of Changes in Water Assets and Water Liabilities for the urban water system

Water asset increases	Volume at 30 June 2012	Volume at 30 June 2011
11 Urban water system increases
11.2 Entitled diversion of non–allocated surface water to urban water system	4,383	7,458
11.3 Entitled extraction of non–allocated groundwater to urban water system	149	213
11.4 Wastewater collected	246,055	269,214
11.5 Delivery of water from outside region to urban water system	22,902	24,636
11.6 Delivery of desalinated water to urban water system	3,427	13,495
11.18 Increase of urban claim on surface water	442,826	442,826
Total urban water system increases	719,742	757,842
Water asset decreases
19 Urban water system decreases
19.2 Leakage to landscape	_	747
19.3 Leakage to groundwater	28,662	25,534
19.4 Delivery to urban water system users	259,039	216,376
19.5 Discharge from urban water system to surface water	62,517	57,333
19.7 Wastewater discharge outside of region	203,228	180,867
19.8 Other wastewater discharge	645	363
19.11 Transfer of water outside of region	3,012	2,453
19.17 Adjustment and forfeiture of urban claim on surface water	230,474	245,498
Total urban water system decreases	787,577	729,171
Balancing item – urban water system	(68,583)	28,631
Change in net water assets	748	40

  

Table 11 Statement of Water Flows for the urban water system

Water inflows	Volume at 30 June 2012 ML	Volume at 30 June 2011 ML
11 Urban water system inflows
11.2 Entitled diversion of non–allocated surface water to urban water system	4,383	7,458
11.3 Entitled extraction of non–allocated groundwater to urban water system	149	213
11.4 Wastewater collected	246,055	269,214
11.5 Delivery of water from outside region to urban water system	22,902	24,636
11.6 Delivery of desalinated water to urban water system	3,427	13,495
11.12 Entitled diversion of allocated surface water to urban water system	212,352	197,328
Total urban water system increaseas	489,268	512,344
Water outflows
19 Urban water system outflows
19.2 Leakage to landscape	_	747
19.3 leakage to groundwater	28,662	25,534
19.4 Delivery to urban water system users	259,039	216,376
19.5 Discharge from urban water system to surface water	62,517	57,333
19.7 Wastewater discharge outside of region	203,228	180,867
19.8 Other wastewater discharge	645	363
19.11 Transfer of water outside of region	3,012	2,453
Total urban water system outflows	557,103	483,673
Balancing item – urban water system	(68,583)	28,631
Opening water storage	2,094	2,054
Add/(Less): Change in water storage	748	40
Closing water storage	2,842	2,094

 

A schematic diagram representing all the inflows and outflows associated with the urban water system in the South East Queensland region is provided in Figure 7.

Figure 7 Schematic diagram of water inflows and outflows for the urban water store within the South East Queensland region during the 2011-12 year; line item numbers are provided in brackets

Water sources, allocations and diversions

There are three main sources of water for the urban water supply system:

• surface water
• groundwater
• desalinated water

In the South East Queensland region the urban water rights for the South East Queensland Water Grid are owned and managed by South East Queensland Water Grid Manager. The Grid Manager holds both supplemented high-security surface water entitlements (see line item 32.2 Surface water access entitlement for non–allocated diversions) and unsupplemented surface water licences (see line item 32.3 Surface water access entitlement for allocated diversion).

Additional information on the types of surface water and groundwater entitlements used to provide the urban water supply system with water can be found in the Water rights, entitlements, allocations and restrictions note.

Regulated (supplemented) entitlements divert water from various water supply schemes managed by Seqwater (as the resource operations licence holder). The diversions of allocations based on regulated entitlements are reported under line item 11.12 Entitled diversion of allocated surface water to urban water system. Information on allocation announcement (made under line item 32.3 Surface water access entitlement for allocated diversions) for this line item are available in line item 11.18 Increase of urban claim on surface water.

Unregulated (unsupplemented) licences allow the South East Queensland Water Grid Manager to divert water from various weirs, rivers, channels and surface water storages subject to various rules relating to river/storage heights, flows or water qualities. Rules are stipulated on individual licences, which can be found in the Gold Coast, Logan Basin or Moreton resource operations plans. Diversions based on these licences are reported under line item 11.2 Entitled diversion of non–allocated surface water to urban water system (made under line item 32.2 Surface water access entitlement for non–allocated diversions).

In addition to these two sources, the South East Queensland Grid Manager also extracts groundwater under basic rights from various bore fields in the South East Queensland region that were developed to supplement supplies during the drought that occurred up until 2009. Extraction from these borefields has declined since high rainfalls resulted in traditional surface water sources become more reliable. The volume extracted from borefields in the South East Queensland region is reported under line item 11.3 Non–allocated diversion of groundwater (made under line item 33.2 Groundwater access entitlement for non–allocated extractions).

Desalination has been developed in the South East Queensland region as a new water source to supplement surface water supplies. This was developed as part of the South East Queensland Regional Drought Strategy, with the Gold Coast Desalination Plant having a capacity of 133 ML/day. Due to the increased yield from surface water storages during the 2011–12 year there has been a decrease in the volume sourced from the plant in 2011–12 compared to previous years.

The South East Queensland Water Grid extends to the north and east of the National Water Account's South East Queensland region. Various Water Grid sources outside of the region supply water into the region. Groundwater water treatment plants (WTPs) on Stradbroke Island and various surface water WTPs in the Sunshine Coast (via the Northern Pipeline Interconnector) supply water into the South East Queensland region. Such volumes received from outside sources are reported under line item 11.5 Delivery of water from outside region.

Figure 8 shows that the South East Queensland region relied heavily on regulated surface water entitlements to meet urban demand (87% of source water). Desalination constituted around 2% and transfers into the region around 9%, while unregulated surface water supplies accounted for around 2% of the total urban demand.

Figure 8 Sources of water for South East Queensland's urban water supply system; line item numbers are given in brackets

From Figure 8 it can be clearly seen that the South East Queensland region relied heavily on regulated surface water entitlements to meet urban demand (87% of source water). Desalination constituted around 2% and transfers into the region around 9%, while unregulated surface water supplies accounted for around 2% of the total urban demand.


Urban water restrictions

The South East Queensland region was on permanent water conservation measures (PWCM) from 1 December 2009. On April 2012, the PWCM were amended to remove a number of mainly non-residential restrictions which already existed elsewhere in the legislation or were shown to have been put in place. The residential restrictions only had minor changes which would not have significantly impacted on the overall consumption. The PWCM were then lifted on 1 January 2013 as a result of the abolition of the Queensland Water Commission (QWC).

Discharge from the urban wastewater collection system

Wastewater collected in the South East Queensland region was either exported from the region as raw wastewater, treated and discharged to receiving environments either inside or outside the region, or treated and provided to recycled water customers either inside or outside the region (see Figure 9).

Figure 9 Wastewater discharge, export and recycled water use in the South East Queensland region; line item numbers are given in brackets

From Figure 9 it can be clearly seen that the majority of wastewater is discharged out of the region, with surface water being the second most common receiving medium. It is expected that recycled water use was underestimated, as only the Western Corridor Recycled Water Scheme was included in the 2012 Account because other recycled water use information was not available from the retailers at the time of publication.

Balancing item – urban water system store

This volume represents the volume necessary to reconcile the opening and closing balances of the urban water system store with the physical water inflows and outflows. The balancing item – urban water system store was calculated according to Table 12.

Table 12. Balancing item for the urban water system store for the 2011–12 year

	Account	Volume
		(ML)
	Opening balance (30 June 2011)	2,094
add	Total 11 Urban water system inflows	489,268
less	Total 19 Urban water system outflows	557,103
less	Closing balance (30 June 2012)	2,842
	Balancing item – urban water system store	(68,583)

The calculation of the water balance on the urban water system store yielded a balancing item of (68,583) ML. Urban water systems typically have a small storage volume but high throughput and, as such, a comparison of the balancing item with the opening or closing balance is not appropriate.

It is likely that the balancing item can be attributed to uncertainty associated with consumer meter readings, lack of leakage data for off-grid water supply systems and uncertainty in estimating leakage.

The purpose of this note is to report on water held in off–channel water storages within the South East Queensland region during the 2011–12 year. Where available, water flows to and from off–channel water storages are reported here. Water held in off–channel water storages is not reported in the water accounting statements because the statements report only on water resources yet to be shared. Water held in off–channel water storages is considered to be abstracted from the shared pool of water resources and, as such, is not included as part of the region's water assets (see Scope of the South East Queensland region water account in the 'Contextual information').

Off–channel storages influence water assets and water liabilities recognised in the water accounting statements as they harvest water from the landscape and thus reduce groundwater recharge and runoff into surface water.

A description of South East Queensland's off–channel storages is provided in the Other water resources and distribution systems section of the Contextual information.

The number of off–channel storages was estimated by Queensland Department of Natural Resources and Mines (DNRM) using the following criteria:

• water storage must have a surface area greater than 0.25 ha
• water storage must be human-made.

The data is not intended as a complete count of off–channel storages, but is an indication of the number of larger storages within each water resource plan area. A reliable complete count of all off–channel storages was not readily available at the time of publication.

Off–channel storages were identified using remote sensing with 30 m pixels, and therefore some storages may have been omitted during the identification process. All off–channel storages identified have been sighted and their existence confirmed.

A water depth of 2 m was used to estimate the off–channel storage volume (Table 13). Although this was an arbitrary volume recommended by DNRM, it would be expected that most off–channel storages would have been relatively full at the start and end of the 2011–12 year as well above-average rainfall was experienced prior to and during the 2011–12 year (see Climate overview).

Table 13 Estimated storage volume and number of off–channel storages in the South East Queensland region.

Water resource plan (WRP) area	River system	Count		Total surface area	Volume
		Quantity	Percentage of total	(m2)	(ML)
Gold Coast	Coomera River	93	5	3,389,647	6,779
	Total Gold Coast WRP area	93	5	3,389,647	6,779
Logan Basin	Albert River	102	6	1,671,718	3,343
	Logan River	371	22	4,167,129	8,334
	Total Logan Basin WRP area	473	28	5,838,847	11,678
Moreton	Bremer River	302	18	4,808,992	9,618
	Brisbane River	156	9	2,770,688	5,541
	Caboolture River	87	5	788,129	1,576
	Lockyer River	320	19	7,101,810	14,204
	Maroochy River	116	7	1,884,659	3,769
	North Pine	53	3	1,611,937	3,224
	South Pine	19	1	544,028	1,088
	Stanley River	77	5	801,017	1,603
	Total Moreton WRP area	1,130	67	20,311,260	40,623
Total South East Queensland region		1,696	100	29,539,754	59,080

 

Off-channel storage inflows and outflows

The volume of inflows and outflows from off–channel storages could not be quantified in a way that is complete, neutral and free from material error due to the lack of both data and a suitable quantification approach.