South East Queensland
Resources and Systems

Surface water

Purpose of note

The purpose of this note is to provide a consolidated report on the surface water store within the region during the 2010–11 year. Information on all water flows to and from the surface water store are presented here, including between store flows and transfers that are not presented in the water accounting statements.

Background

A description of the South East Queensland (SEQ) region's surface water resources is provided in the Surface water section of the Contextual information.

Water in store

The surface water storage volume included water held in reservoirs, weirs, lakes and major dams, where this data were available. For the purposes of the water accounting statements all of these surface water storages were 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 SEQ region, and the volume of water held in each of these storages (as a percentage of total storage capacity) at the end of the 2010–11 year, is shown in Figure 1.

The volume of water held in all storages within the SEQ region increased by approximately 6% during 2010–11 (Table 1). At the end of the 2010–11 year storage volume, as a percentage of the total storage capacity (% full), was very high in the region, at almost 86%.This is reflected by the fact that the majority of surface water storages in South East Queensland were more than 80% full (Figure 1). The increase in overall surface water storage may be attributed to the accumulation of water since 2009 when the drought broke. In particular the region experienced above-average rainfall and significant flooding throughout the 2010–11 year (see Climate overview). If wet conditions such as those experienced in the 2010–11 year were to follow a dry period, it would be expected that the increase in storage would be greater than 6%. As many water storages were at or close to capacity at the start of the 2010–11 year, there was not the additional capacity within the storages to capture all of the inflow and as a consequence, controlled releases from storages occurred.

Of the three storages that recorded decreases in volume stored, only the decrease in the volume of water stored in Lake Wivenhoe was material (11%). Following significant flooding in January 2011 and pursuant to the Queensland State Government's 13 February 2011 announcement, the operating level of Lake Wivenhoe was reduced until 31 March 2011 from EL 67 to EL 64 to temporarily increase the flood mitigation capacity of Lake Wivenhoe. Without this reduction, Lake Wivenhoe may have had a greater volume of water stored at the end of the 2010–2011 year.

Table 1. Surface water store volume at the start and end of the 2010–11 year
  30 June 2011
(ML)
30 June 2010
(ML)
1 Surface water    

1.1 Storages

2,220,401 2,096,796

1.2 Unregulated river

1.3 Regulated river

1.4 Lakes and wetlands

Total
2,220,401 2,096,796


Figure 1. Location map of surface water storages within the South East Queensland region. The percent full volume on 30 June 2011 for each water storage is also shown.
Figure 1. Location map of surface water storages within the South East Queensland region. The percent full volume on 30 June 2011 for each water storage is also shown.


It should be noted that the Hinze Dam Stage 3 Project increased the storage capacity of Advancetown Lake (Hinze Dam) during the 2010–11 year. The project raised the dam wall by approximately 15 metres and increased storage capacity from 161,073 to 310,730 ML. This increase in capacity resulted in lowering the percentage full volume for the store.

Water flows

Surface water inflows and outflows

Inflows to the surface water store were only slightly (< 5%) more than outflows from the surface water store during the 2010–11 year. A schematic diagram representing all the inflows and outflows associated with the surface water store in the SEQ region is provided in Figure 2. The inflow and outflow volumes for the surface water store during the 2010–11 year are given in Table 2.

The most significant contribution to surface water inflows was runoff to surface water which was a direct result of above-average rainfall experienced by southeastern Australia during the 2010–11 year. High rainfall resulted in a large number of floods during the year. Widespread major flooding occurred throughout the region in January 2011. 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.

Figure 2. Schematic diagram of water inflows (blue arrows) and outflows (red arrows) for the surface water store within the South East Queensland region during the 2010–11 year. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.
Figure 2. Schematic diagram of water inflows (blue arrows) and outflows (red arrows) for the surface water store within the South East Queensland region during the 2010–11 year. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.


Table 2. Volume of inflows and outflows for the surface water store during the 2010–11 year. Line items in italics indicate between–store flows, which are not present in the water accounting statements as they occur within the region.
9 Surface water inflows
Volume
(ML)

9.1 Precipitation on surface water

410,129

9.3 Groundwater discharge

9.4 Runoff to surface water

12,694,060

9.6 Overbank flood return to river channel

9.9 Discharge from urban water system

57,333

9.10 Direct discharge by user

1,846
Total 9 Surface water inflows 13,163,368
   
17 Surface water outflows  

17.1 Evaporation from surface water

291,322

17.2 River outflow from region

12,043,399

17.3 Leakage to groundwater

17.4 Leakage to landscape

256,778

17.5 Overbank flood spilling

17.6 Diversions: other statutory rights

3,628

17.7 Non-allocated diversions to users

2,050

17.8 Non-allocated diversions - urban water system

7,458

17.11 Surface water allocation diversion

5,905

17.12 Surface water allocation diversion - urban system

197,328

17.21 Other surface water decreases

5,706
Total 17 Surface water outflows 12,813,574
   
Balancing item – surface water storage 226,189
   
Change in surface water storage 123,605
   
Opening surface water storage  2,096,796
Closing surface water storage 2,220,401

Allocation diversions

Figure 3 shows that the majority (97%) of surface water diversions in the SEQ region during 2010–11 were for urban water supply within the region (line item 17.8 Non-allocated diversions – urban water systemand line item 17.12 Surface water allocation diversion – urban system). The volume of water diverted to the urban water supply system from surface water increased by 7% compared to the volume diverted in 2009–10. 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 Surface water allocation diversions, 17.6 Diversions – other statutory rights and 17.7 Non-allocated diversions to users), which accounted for only a very small portion (3%) of surface water diversions in the region, decreased substantially (57%) in 2010–11 compared to 2009–10. 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 2010–11. 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 3. Graph of diversions from surface water within the South East Queensland region during the 2010–11 year and 2009–10 comparison year. Line item numbers are given in brackets.
Figure 3. Graph of diversions from surface water within the South East Queensland region during the 2010–11 year and 2009–10 comparison year. Line item numbers are given in brackets.


These diversions are all associated with a water access entitlement. In the case 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 2011 Account year (July 2010 – June 2011), 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 2010–11 year are provided in the Water rights, entitlements, allocations and trade note.

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 3.

Table 3. Balancing item for the surface water store for the 2010–11 year
  Account Volume
(ML)
  Opening balance (30 June 2010)         2,096,796
add Total 9 Surface water inflows       13,163,368
less Total 17 Surface water outflows       12,813,574
less Closing balance (30 June 2011)         2,220,401
  Balancing item – surface water store          226,189

The calculation of the water balance on the surface water store yielded a balancing item of 226,189 ML. This is approximately 10% of the total surface water store volume at the end of the 2010–11 year and 2% of the total surface water inflows during 2010–11.

It is likely that the balancing item is primarily attributed to errors associated with the rainfall-runoff (a large source of surface water increase, line item 9.4 Runoff to surface water) and outflow to outside region (a large source of surface water decrease, line item 17.2 Outflow to outside 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. The significant floods that occurred in December 2010 and January 2011 may have resulted in inaccurate gauge data as the river levels may have resulted in backwater effects, unmeasured overbank flows and breakouts previously unrecorded.

Storage inflows and outflows

Inflows to outflows from Lake Samsonvale (North Pine Dam), Lake Somerset and Lake Wivenhoe are shown in Table 4. These three water storages are the main water storages within the region and make up around 70% of the total storage capacity within the region. Only flows to and from these storages are shown because data for other storages were not readily available. These flows may be different from the flows reported in the Statement of physical water flows and Table 2, which refer to flows affecting the surface water store as a whole.


Table 4. Volume of inflows and outflows for Lake Samsonvale (North Pine Dam), Lake Somerset and Lake Wivenhoe during the 2010–11 year
  Volume
(ML)
Opening storage       1,681,378
41 Storage inflows  

41.1 Precipitation on storages

        322,513

41.2 Groundwater discharge into storages

                –

41.3 Runoff into storages

      5,246,416

41.4 Transfer of water into storages

      1,703,542
Total 41 Storage inflows       7,272,472
   
42 Storage outflows  

42.1 Evaporation from storages

        226,424

42.2 Groundwater recharge from storages

                 –

42.3 Leakage from storages

        248,711

42.4 Spillage from storages

      4,851,192

42.5 Releases from storages

      2,003,826

42.6 Diversions from storages

          30,053
Total 42 Storage outflows       7,360,206
   
Balancing item – storages 27,803
   
Closing storage       1,565,841
   
Net change in volume –115,537

The balancing item on these three storages was around 2% of the closing storage volume and may be due to an underestimation of diversions and lack of leakage to landscape data for Lake Samsonvale (North Pine Dam).

Groundwater

Purpose of note

The purpose of this note is to provide a consolidated report on the groundwater store within the region during the 2010–11 year. Information on all water flows to and from the groundwater store are presented here, including between store flows and transfers that are not presented in the water accounting statements.

Background

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

Water in store and groundwater asset

Only information on the nominal volume (entitled volumetric limit, described in line item 33.2 Groundwater access entitlements for direct diversion) of water in the Benefitted Area of Implementation Area 1 of the Lockyer Valley Groundwater Management Area (GMA) in the Central Lockyer Water Supply Scheme (WSS) was included as the groundwater asset in the 2011 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 SEQ region; however, there are currently no models for these, and their storage volume could not be quantified to determine sustainable extraction limits. The estimated volume of the groundwater asset in Table 5 is therefore only a small portion of the actual groundwater asset within the SEQ region.

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

Table 5. Groundwater asset volume at the start and end of the 2010–11 year
 2 Groundwater 30 June 2011
(ML)
30 June 2010
(ML)

2.1 Water table aquifer

9,340 9,340

2.2 Underlying aquifers



Total
9,340 9,340
Water flows

Groundwater inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the SEQ region is provided in Figure 4. The inflow and outflow volumes for the groundwater store during the 2010–11 year are given in Table 6.


Figure 4. Schematic diagram of water inflows (blue arrows and outflows (red arrows) for the groundwater store within the South East Queensland region during the 2010–11 year. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.
Figure 4. Schematic diagram of water inflows (blue arrows and outflows (red arrows) for the groundwater store within the South East Queensland region during the 2010–11 year. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.


Table 6. Volume of inflows and outflows from the groundwater store during the 2010–11 year. Line items in italics indicate between-store flows. These flows are not presented in the water accounting statements as they occur within the region.
  Volume
(ML)
10 Groundwater inflows  

10.1 Groundwater inflow from outside region

10.3 Recharge from landscape

10.4 Recharge from surface water

10.5 Leakage from off-channel water storage

10.6 Leakage from urban water system

25,534
Total 10 Groundwater inflows 25,534
   
18 Groundwater outflows  

18.1 Groundwater outflow to outside region

18.2 Groundwater outflow to outside region at coast

18.3 Discharge to landscape

18.4 Discharge to surface water

18.6 Infiltration to urban water system

18.7 Extraction - other statutory rights

18.8 Non-allocated extractions to users

258

18.9 Non-allocated extractions - urban water system

213

18.11 Groundwater allocation extraction

1,113
Total 18 Groundwater outflows 1,584
   
Balancing item – groundwater storage 23,950
   
Change in groundwater storage 0
   
Opening groundwater storage  9,340
Closing groundwater storage 9,340

It can be seen in Table 6 that there are a significant number of flows for which a volume could not be quantified. The only increase reported was the leakage from the urban water system and the only decreases were extractions.

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 Groundwater allocation extraction), 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 5 shows that allocation extractions from aquifers during the 2010–11 year have decreased from last year. This can be attributed to a wetter year resulting in less irrigation demand (see Climate overview). Similarly, urban extractions also 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 5. Graph of groundwater extractions from aquifers within the South East Queensland region during the 2010–11 year and 2009–10 comparison year. Line item numbers are given in brackets.
Figure 5. Graph of groundwater extractions from aquifers within the South East Queensland region during the 2010–11 year and 2009–10 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 2010–11 year are provided in the Water rights, entitlements, allocations and tradenote, in the 'Groundwater rights' table.

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 SEQ region, not just the individual aquifers included as the groundwater asset.

The balancing item – groundwater store was calculated according to Table 7.

Table 7. Balancing item for the groundwater store for the 2010–11 year
  Account Volume
(ML)
  Opening balance (30 June 2010)          9,340
add Total 10 Groundwater inflows        25,534
less Total 18 Groundwater outflows          1,584
less Closing balance (30 June 2011)          9,340
  Balancing item – groundwater store        23,950

The calculation of the water balance on the groundwater store yielded a balancing item of 23,950 ML, approximately 93% of the total groundwater inflows during the 2010–11 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 2010–11 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 SEQ region.

Other factors that explain the large balancing item are errors and gaps made in the calculations of the groundwater terms presented in Table 5 and 6:

  • only urban water system leakage and extractions could be quantified from the groundwater inflows and outflows
  • the most significant inflows and outflows, such as groundwater recharge and discharge, were not quantified.

This value of balancing item is considerably larger in magnitude than that reported in the 2010 Account (–5,556 ML). This can be attributed to the leakage from urban water system being reported as a groundwater increase in the 2011 Account, where as in the 2010 Account it was only reported as an urban water system decrease.

Urban system

a. System's interaction with the region

Purpose of the note

The purpose of this note is to provide a consolidated report on the urban water system within the region during the 2010–11 year. Information on all water flows to and from the urban water system are presented here, including between-store flows and transfers that are not presented in the water accounting statements.

The Sub-systems analysis note analyses the urban water system at a finer level, splitting it in sub–systems (supply, wastewater and recycled water).

Background

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

Water in store

Table 8 shows that for the urban system in the SEQ 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.

Table 8. Urban water system store volume at the start and end of the 2010–11 year
3 Urban water system 30 June 2011
(ML)
30 June 2010
(ML)

3.1 Urban water supply system

2,056 2,054

3.2 Wastewater collection system


3.3 Recycled water supply system

Total
2,056 2,054

Volumes associated with other supply and collection systems could not be quantified in SEQ 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 SEQ region can be seen in the Seqwater infrastructure map.

Water flows

A schematic diagram representing all the inflows and outflows associated with the urban water system in the SEQ region is provided in Figure 6. The inflow and outflow volumes for the urban water system during the 2010–11 year are given in Table 9.


Figure 6. Schematic diagram of water inflows (blue arrows) and outflows (red arrows) for the urban water system within the South East Queensland region. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.
Figure 6. Schematic diagram of water inflows (blue arrows) and outflows (red arrows) for the urban water system within the South East Queensland region. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.


Table 9. Volume of inflows and outflows for the urban water system store during the 2010–11 year. Line items in italics indicate between–store flows. These flows are not presented in the water accounting statements as they occur within the region.
11 Urban water system inflows
Volume
(ML)

11.1 Precipitation on urban water system

11.2 Non-allocated diversion of surface water

7,458

11.3 Non-allocated extraction of groundwater

213

11.4 Wastewater collected

269,214

11.5 Delivery of water from outside region to urban water system

24,636

11.6 Delivery of desalinated water to urban water system

13,495

11.7 Stormwater ingress

11.8 Infiltration from groundwater

11.12 Allocation diversion of surface water to urban water system

197,328
Total 11 Urban water system inflows 512,344
   
19 Urban water system outflows  

19.1 Evaporation from urban water

19.2 Leakage to landscape

747

19.3 Leakage to groundwater

25,534

19.4 Delivery to urban water system users

216,376

19.5 Urban water discharge to surface water

57,333

19.7 Wastewater discharge outside of region

180,867

19.8 Other wastewater discharge

363

19.11 Transfer of water outside of region

2,453
Total 19 Urban water system outflows 483,673
   
Balancing item – urban water system store 28,669
   
Change in urban water system storage 2
   
Opening urban water system storage  2,054
Closing urban water system storage 2,056

Water sources, allocations and diversions

In the SEQ region the urban water rights for the SEQ Water Grid are owned and managed by SEQ Water Grid Manager. The Grid Manager holds both supplemented high-security surface water entitlements (see line item 32.2 Surface water access entitlement for direct diversion) and unsupplemented surface water licences (see line item 32.3 Surface water access entitlement for allocation 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 Allocation diversion of surface water to urban water system. Information on allocation announcement (made under line item 32.3 Surface water access entitlement - regulated flow) for this line item are available in line item 11.18 Increase of urban claim on surface water.

Unregulated (unsupplemented) licences allow the SEQ 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 operation plans. Diversions based on these licences are reported under line item 11.2 Non-allocated diversion of surface water (made under line item 32.2 Surface water access entitlement - unregulated flow).

In addition to these two sources, the SEQ Grid Manager also extracts groundwater under basic rights from various bore fields in the SEQ 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 becoming more reliable. The volume extracted from borefields in the SEQ region is reported under line item 11.3 Non-allocated diversion of groundwater (made under line item 33.2 Groundwater access entitlement for direct extraction).

Desalination has been developed in the SEQ region as a new water source to supplement surface water supplies. This was developed as part of the SEQ Regional Drought Strategy, with the Gold Coast Desalination Plant having a capacity of 133 ML/d. Due to the increased yield from surface water storages during the 2010–11 year, the Gold Coast Desalination Plant has been operating in 'hot standby' mode (25 ML/d two days a week) to minimise operating costs since December 2010. This has resulted in a decrease in the volume sourced from the plant in 2010–11 compared to previous years.

The SEQ Water Grid extends to the north and east of the National Water Account's SEQ 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 SEQ region. Such volumes received from outside sources are reported under line item 11.5 Delivery of water from outside region.

Figure 7 summarises the volumes received by the urban water supply system from various sources.


Figure 7. Sources of water for South East Queensland's urban water supply system. Line item numbers are given in brackets.
Figure 7. Sources of water for South East Queensland's urban water supply system. Line item numbers are given in brackets.


From Figure 7 it can be clearly seen that the SEQ region relied heavily on regulated surface water entitlements to meet urban demand (81% of source water). Desalination constituted around 5% and transfers into the region around 10%, while unregulated surface water supplies accounted for around 3% of the total urban demand.

Urban water restrictions


During the 2010–11 year permanent water conservation measures were in place in South East Queensland.

Discharge from the urban wastewater collection system


Wastewater collected in the SEQ 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 8).


Figure 8. Wastewater discharge, export and recycled water use in the South East Queensland region. Line item numbers are given in brackets.
Figure 8. Wastewater discharge, export and recycled water use in the South East Queensland region. Line item numbers are given in brackets.


From Figure 8 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 2011 Account as 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 10.

Table 10. Balancing item for the urban water system store for the 2010–11 year.
  Account Volume
(ML)
  Opening balance (30 June 2010)          2,054
add Total 11 Urban water system inflows
      512,344
less Total 19 Urban water system outflows
      483,673
less Closing balance (30 June 2011)          2,056
  Balancing item – urban water system store       28,669

The calculation of the water balance on the urban water system store yielded a balancing item of 28,669 ML. This is approximately 6% of the total urban water system inflows during the 2010–11 year. 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.

b. Sub–systems analysis

Purpose of the note

This note complements the System's interactions with the region note. It gives the following additional information:

  • split of the urban water flows according to the sub-systems they affect by water type, source and quality
  • flows between sub-systems, which are not reported in the System's interactions with the region note as they occur within the urban water system itself
  • split of the total urban water use into several components.
Urban water system

The urban water system is made up of three sub–systems which serve the urban water users:

  • the urban water supply system
  • the wastewater collection system
  • the recycled water system.

The main urban water users are residential, commercial, industrial and municipal consumers.

The urban water supply system collects water from various sources including surface water, groundwater, marine desalinated water and transfers–in across the region's geographical boundaries. It treats and distributes water to urban water users. Part of the water is used outdoor (e.g. garden use) while the rest is collected into the wastewater collection system. Wastewater is treated and then discharged to surface water, the sea or the landscape, or delivered into the recycled water system. The recycled water system, in turn, distributes treated water to users.

Tables 11 to 13 show the balance of each sub–system including, including its inflows, outflows, balancing item and percentage error of the balancing item compared to the total of the inflows. The balancing items are calculated as the difference between the inflows less the outflows, considering that the changes in storage are not material. The values of the balancing items reflect measurement and data handling errors and/or missing data.

Table 14 shows a breakdown of the total urban water use per use sectors and type of water (potable, non–potable and recycled).

For each row in the tables 11 to 14, correspondence is given to the line items that are reported in the water accounting statements and the System's interactions with the region note. The correspondence can either be:

  • 'Line item A': meaning a one-to-one correspondence of the volume in the table with the line item A
  •  'Part of: line item A': meaning that the volume in the table is a part of the line item A
  • 'Line item A + line item B': meaning that the volume in the table is the sum of line items A and B
  •  'Part of: line item A + line item B': meaning that the volume in the table is the sum of a part of line items A and a part of line item B
  • 'Not applicable': in the case when there is no correspondence to a line item.

When a volume in a table is given as '0' it means that the value has been evaluated as nil for the 2010–11 year. When the volume in a table is given as dash (–), it means that the volumes could not be quantified for the 2010–11 year.

Supporting information and quantifications approaches for each volume shown in the tables 11 to 14 can be accessed via links on the line item numbers. In the cases when there is no corresponding line item, the supporting information and quantification approaches are given at the end of the note.

 

Table 11. Balance of the urban water supply system for the 2010–11 year
Flow component

Volume(ML)

Line item

Inflow component:    
Surface water diverted 

204,786

11.2 + 11.12

Groundwater extracted

213

11.3

Desalinated water produced

13,495

11.6

Total water produced or sourced by agency

218,494

 
Potable water imported

24,636

11.5

Potable water received

0

 
Total potable water transferred

24,636

 
Non–potable water imported

0

 
Non–potable water received

0

 
Total non–potable water transferred

0

 
Total inflow

243,130

 
     
Outflow component:    
Potable water flow back to storage

0

 
Non–potable water flow back to storage

0

 
Potable water supplied to water users

194,797

Part of 19.4

Potable water exported

0

 
Non–potable water exported

0

 
Water lost due to leakage

25,534

19.3

Total outflow

220,331

 
     
Balance (inflows less outflows)

22,799

 
Error

10%

 
  Notes:
  1. Misbalance was due to meter errors, data handling errors, estimation errors from databases and missing terms or temporal values.

Table 12. Balance of the wastewater collection system for the 2010–11 year
Flow component

Volume (ML)

LineiItem

Inflow component:    
Wastewater collected within the region

269,214

11.4

Ingress of stormwater and groundwater

11.7 + 11.8

Total inflow

269,214

 
     
In-process volumes:    
Wastewater used on-site

4,208

 
Total in-process volume

4,208

 
     
Outflow component:    
Wastewater (treated) discharged to rivers

57,333

19.5

Wastewater (treated) discharged to landscape 363

19.8

Wastewater (treated) discharged to sea 180,867

19.7

Total wastewater (treated) discharged 238,563  
Wastewater (treated) supplied to recycled water system 22,958

Part of
(19.4 + 19.11)

Wastewater delivered to external entity 1,074

Part of 19.11

Overflow to stormwater and groundwater 747

19.2

Total outflow

263,342

 
     
Balancing item (inflows less outflows)

1,664

 
Error

1%

 

Notes:

  1. Misbalance was due to meter errors, data handling errors, estimation errors from databases and missing terms or temporal values.

Table 13. Balance of the recycled water system for the 2010–11 year
Flow component

Volume (ML)

Line Item

Inflow component:    
Inflow from wastewater collection system

22,958

Part of
(19.4 + 19.11)

Total inflow

22,958

 
     
Outflow component:    
Recycled water exported

1,379

Part of 19.11

Recycled water supplied to users

21,579

 
Total outflow

22,958

 
     
Balancing item (inflows less outflows)

0

 
Error

0%




Table 14. Urban water consumption for the 2010–11 year
 

Potable

Non-potable

Recycled

Total

Volume
(ML)

Line item

Volume
(ML)

Line item

Volume
(ML)

Line item

Volume
(ML)

Residential 136,337

Part of 19.4

0

 

233

Part of 19.4

136,570

Commercial, industrial and municipal uses 55,348

Part of 19.4

0

 

20,673

Part of 19.4

76,021

Other than residential, commercial, municipal and industrial              
Agricultural/individual irrigation

0

 

0

 

673

Part of 19.4

673

Irrigation water supply systems/schemes 0  

0

 

0

 

0

Managed aquifer recharge 

0

 

0

 

0

 

0

Environment 0  

0

 

0

 

0

To infiltration basin to supplement groundwater 0   0  

0

 

0

Other uses 3,112

Part of 19.4

0

 

0

 

0

Total supplied to uses other than residential, commercial, municipal and industrial 3,112   0   673   673
Total volume supplied  194,797   0   21,579   213,264


Figure 9 represents graphically the inflows and outflows of tables 11 to 14 that affect the urban sub-system and the urban users. Corresponding line items are given in brackets in the figure.



Figure 9. Inflows and outflows affecting the urban sub-systems and the urban users for the 2010–11 year
Figure 9. Inflows and outflows affecting the urban sub-systems and the urban users for the 2010–11 year


Notes on volumes that have no corresponding line items

The following notes are provided for the volumes in the tables 11 to 14 and Figure 9 that do not correspond to any line item in the water accounting statements or the System's interactions with the region note.


Volume of recycled water produced

Supporting information

This line item represents the volume of recycled water produced at treatment plants in the region in the 2010–11 reporting period (38,668 ML) as summarised in Table 15.

Table 15. Recycled water produced by utility for the 2010–11 year
Allconnex Water Allconnex provided the data extracted from National Performance Review (NPR) submission 9,564
Queensland Urban Utilities NPR (W4) 27,438
Unitywater (only for SEQ portion) Estimated from the individual plant data provided by Unitywater 1,666
Total 38,668

Quantification approach

Data source

Allconnex Water; Queensland Urban Utilities; Unitywater.

Data provider

The National Performance Report (NPR), 2010–11 (the National Water Commission) and data received from Unitywater. 

Method

Data of volume of recycled water produced under each water utility were obtained from the NPR report for Queensland Urban Utilities and the compiled data provided by Allconnex Water. For the SEQ portion of Unitywater operational area, the volume was estimated from the individual plant data provided by Unitywater. The corresponding volumes under three water utilities were summed.

Uncertainty

Derived from measured data.

Approximations, assumptions, caveats and limitations

Water balance for some plants was not perfect.


Volume of recycled water used on-site or on-site in-process

Supporting information

This line item represents the volume of recycled water used in on-site in the 2010–11 year (4,207 ML).

Quantification approach

Data source

Allconnex Water; Queensland Urban Utilities; Unitywater.

Data provider

The National Performance Report (NPR), 2010–11 (the National Water Commission) and these data matched with the data received from Qldwater statewide water information managment (SWIM).

Method

Data of recycled water used on-site wastewater under each water utility (W24) were obtained from the NPR report. Only the area under Queensland Urban utilities contributed to this line item.

Uncertainty

Derived from measured data.

Approximations, assumptions, caveats and limitations

None.

 

Off-channel storages

Purpose

The purpose of this note is to report on water held in off-channel water storages within the SEQ region during the 2010–11 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.

Background

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.

Water in Store

The number of off-channel storages was estimated by Queensland Department of Environment and Resource Management (DERM) using the following criteria:

  • the water storage must have a surface area greater than 0.25 ha
  • the 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 dams 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. Although this was an arbitrary volume recommended by DERM, it would be expected that most off-channel storages would have been relatively full at the start and end of the 2010–11 year as well above-average rainfall was experienced prior to and during the 2010–11 year (see Climate overview).

Table 16. 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 1,602
Total Moreton WRP area 1,130 67 20,311,260 40,623
Total SEQ region 1,696 100 29,539,754 59,080
Water flows

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.