Canberra
Water resources and systems
Introduction
The following set of notes provides consolidated reports for each of the water stores and systems within the Canberra region during the 2012–13 year. The water stores and systems included in the region are shown in Figure 1.
For a more detailed description of 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 Canberra 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 Canberra 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. The allocation announcement, forfeiture and allocation remaining line items associated with each between-store abstraction (brown arrows in Figure 2) are also shown in italics in the following notes.
Surface water
A description of the Canberra region's surface water resources is provided in the Contextual information.
The Statement of Water Assets and Water Liabilities for the surface water store (Table 1) shows that total surface water decreased during the 2012–13 year in the Canberra region.
| Water assets | Volume at 30 June 2013 (ML) | Volume at 30 June 2012 (ML) |
| Water assets | ||
| 1 Surface water | ||
| 1.1 Storages | 181,290 | 206,139 |
| 1.2 Unregulated river | – | – |
| 1.3 Regulated river | – | – |
| 1.4 Lakes and wetlands | 34,631 | 34,622 |
| Total surface water assets | 215,921 | 240,761 |
| Water liabilities | ||
| 5 Surface water liability | ||
| 5.1 Surface water allocation remaining | 0 |
0 |
| 5.2 Surface water allocation remaining – urban water system | 0 | 0 |
| Total surface water liabilities | 0 | 0 |
| Opening net water assets | 240,761 | 239,752 |
| add/(less): Change in net water assets | (24,840) | 1,009 |
| Closing net water assets | 215,921 | 240,761 |
The volume of the surface water asset included water held in surface water storages and some lakes within the Canberra region. The surface water asset excluded the water in river channels and some lakes and wetlands in the region due to the lack of both data and a suitable quantification approach.
The location of each storage within the Canberra region, and the volume of water, including dead storage, in each storage as a percentage of total storage capacity (per cent full) at the end of the 2012–13 year, is shown in Figure 3.
Figure 3 Location map of the storages within the Canberra region; the capacity and the % full volume on 30 June 2013 for each storage is also shown.
There are four urban water supply storages within the Canberra region: Bendora Reservoir, Corin Reservoir, Cotter Reservoir and the Googong Reservoir. At the end of the 2012–13 year the volumes of water at some of these storages were low due to the lower rainfall experienced in the region (see line item 1.1 Storages).
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.
| Water asset increases | 2012–13 volume (ML) | 2011–12 volume (ML) |
| 9 Surface water increases | ||
| 9.1 Precipitation on surface water | 11,604 | 21,110 |
| 9.2 River inflow to region | 200,283 | 582,184 |
| 9.3 Groundwater discharge | – | – |
| 9.4 Runoff to surface water | 463,836 | 1,075,728 |
| 9.6 Overbank flood return to river channel | – | – |
| 9.9 Discharge from urban water system | 31,702 | 34,325 |
| Total surface water asset increases | 707,425 | 1,713,347 |
| Water liability decreases | ||
| 13 Surface water liability decreases | ||
| 13.1 Adjustment and forfeiture of surface water allocation | 1,832 | 0 |
| 13.2 Adjustment and forfeiture of surface water allocation – urban water system | 23,162 | 29,210 |
| Total surface water decreases | 24,994 | 29,210 |
| Water Asset Decreases | ||
| 17 Surface water decreases | ||
| 17.1 Evaporation from surface water | 20,516 | 20,097 |
| 17.2 River outflow from the region | 508,738 | 1,596,539 |
| 17.3 Discharge from surface water to groundwater | – | – |
| 17.4 Surface water leakage to landscape | – | – |
| 17.5 Overbank flood spilling | – | – |
| 17.6 Surface water diversions – other statutory rights | – | – |
| 17.7 Entitled diversion of non-allocated surface water to users | 1,648 | 1,415 |
| 17.8 Entitled diversion of non-allocated surface water to urban water system | 66 | 0 |
| Total surface water asset decreases | 530,968 | 1,618,051 |
| Water liability increases | ||
| 21 Surface water liability increases | ||
| 21.1 Surface water allocation announcements | 1,832 | 0 |
| 21.2 Surface water allocation announcements – urban water system | 71,000 | 71,000 |
| Total surface water liability increases | 72,832 | 71,000 |
| Balancing item—surface water | 153,459 | 52,497 |
| Change in net water assets | (24,840) | 1,009 |
A schematic diagram representing all the inflows and outflows associated with the surface water store in the Canberra region is provided in Figure 4. The numbers 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 Canberra region during the 2012–13 year; line item numbers are provided in brackets
Table 3 shows that surface water storage decreased during the 2012–13 year by 24,840 ML. This is a substantial change from the previous year, where water storage increased by 1,009 ML. The primary reason for the decrease in water storage is that runoff to surface water (line item 9.4) was less than half the comparison year (Table 3). The decrease in runoff reflects the below average rainfall observed throughout the region during the 2012–13 year (see Climate overview) relative to the average rainfall conditions experienced during the comparison year (see the 2012 Account ).
Allocation diversions
In the 2012–13 year the largest diversion made from the surface water system was for the public water supply (17.12 Entitled diversion of allocated surface water to urban water system).
Figure 5 Graph of allocation diversions from surface water within the Canberra region during the 2012–13 year and the 2011–12 comparison year. Line item numbers are given in brackets.
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.
Account |
Volume (ML) |
Opening balance at 1 July 2012 |
240,761 |
Total surface water inflows (see Table 3) |
707,425 |
Total surface water outflows (see Table 3) |
(578,806) |
Closing balance at 30 June 2013 |
(215,921) |
Balancing item—surface water store |
153,459 |
The calculation of the water balance on the surface water store yielded a balance difference of 153,459 ML. This is approximately 22% of the total surface water inflows during the 2012–13 year.
The balancing item is primarily attributed to the fact that river and floodplain losses cannot be quantified in the account. It is likely that these losses are a relatively large source of surface water decrease throughout the region.
The balancing item is also attributed to uncertainty associated with the runoff (a large source of surface water increase, line item 9.4) and river outflow from the region (a large source of surface water decrease, line item 17.2). 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 (+/– 90,000 ML).
Groundwater
The aquifers in the Canberra region are described in 'Physical information' in Groundwater. Given the majority of groundwater within the region is stored in fractured rock aquifers that are difficult to measure and monitor, no value was available for the volume of water stored in the aquifers. As a result, volumes in the Statement of Water Assets and Water Liabilities for the groundwater store shown in Table 5 are unquantified.
A more detailed explanation is provided in line item notes 2.1 and 2.2.
| Water Assets | Volume at 30 June 2013 (ML) | Volume at 30 June 2012 (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 | – | – |
| Total Groundwater Liabilities | – | – |
| Opening net water assets | – | – |
| Add/(Less): Change in net water assets | – | – |
| Closing net water assets | – | – |
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.
| Water asset increases | 2012–13 volume (ML) | 2011–12 volume (ML) |
| 10 Groundwater increases | ||
| 10.1 Groundwater inflow from outside region | – | – |
| 10.3 Recharge from landscape | – | – |
| 10.4 Recharge from surface water to groundwater | – | – |
| 10.5 Leakage from off-channel water storage | – | – |
| 10.6 Leakage from urban water system | 2,803 | 2,906 |
| Total Groundwater Assets Increases | 2,803 | 2,906 |
| Water Liability decreases | ||
| 14 Groundwater liability decreases | ||
| 14.1 Adjustment and forfeiture of groundwater allocation | 851 | 0 |
| Total Groundwater Liability decreases | 851 | 0 |
| Water Asset Decreases | ||
| 18 Groundwater decreases | ||
| 18.1 Groundwater outflow to outside region | – | – |
| 18.3 Discharge to landscape | – | – |
| 18.4 Discharge to surface water | – | – |
| 18.5 Discharge to off-channel water storage | – | – |
| 18.7 Groundwater extractions – other statutory rights | 435 | 435 |
| 18.8 Entitled extraction of non-allocated groundwater to users | 585 | 335 |
| Total Groundwater decreases | 1,020 | 770 |
| Water Liability Increases | ||
| 22 Groundwater liability increases | ||
| 22.1 Groundwater allocation announcements | 851 | – |
| Total Groundwater Liability Increases | 851 | – |
| Unaccounted for difference – groundwater | 1,783 | 2,136 |
| Change in Net Water Assets | 0 | 0 |
A schematic diagram representing all the inflows and outflows associated with the groundwater store in the Canberra region is provided in Figure 6. The inflow and outflow volumes for the groundwater store during the 2012–13 year are given in Table 7. The numbers 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 Canberra region during the 2012–13 year; line item numbers are provided in brackets
Allocations and extractions
The groundwater extractions–other statutory rights (
line item 18.7) and entitled extraction of non-allocated
groundwater (
line item 18.8) to users are shown in Figure 7.
Figure 7 Graph of extractions from aquifers within the Canberra region during the 2012–13 year and the 2011–12 comparison year. Line item numbers are given in brackets.
Balancing item
The balancing item volume represents the difference between the measured opening and closing balances of the groundwater store, after physical inflows and outflows have been applied.
Account |
Volume (ML) |
Opening balance at 1 July 2012 |
– |
Total groundwater increases (see Table 7) |
2,803 |
Total groundwater decreases (see Table 7) |
(1,020) |
Closing balance at 30 June 2013 |
– |
Balancing item—groundwater store |
1,783 |
The calculation of the water balance on the groundwater store yielded a balance of 1,783 ML during the 2012–13 year.
Because the volume of water in the groundwater stores within the Canberra region could not be quantified, the volume disclosed in the balancing item of 1,783 ML represents the net change in groundwater store throughout the 2012–13 year.
Urban water system
The urban water system within the Canberra region is discussed in the Other water resources and systems section of the 'Contextual information'. It consists of three sub-components:
- Urban water supply system
- Wastewater system
- Recycled water system.
Surface water (11.12) is the main source of water for the Canberra's urban water supply system.
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 little during the 2012–13 year in the Canberra region.
| Water assets | Volume at 30 June 2013 (ML) | Volume at 30 June 2012 (ML) |
| 3 Urban water system | ||
| 3.1 Urban water supply system | 953 | 904 |
| 3.2 Wastewater system | – | – |
| 3.3 Recycled water system | 2 | 2 |
| 3.7 Urban claim on surface water | 0 | 0 |
| Total Urban water system assets | 955 | 906 |
| Opening net water assets | 906 | 855 |
| add/(less): Change in net water assets | 49 | 51 |
| Closing net water assets | 955 | 906 |
The information in Table 9 includes service water storages or the pipe network managed and owned by ACTEW Water and Queanbeyan City Council (QCC) for the year 2013. The data for QCC were not available for the year 2012.
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.
| Water asset increases | 2012–13 volume (ML) | 2011–12 volume (ML) |
| 11 Urban water system increases | ||
| 11.2 Entitled diversion of non-allocated surface water to urban water system | 66 | 0 |
| 11.4 Wastewater collected | 35,708 | 38,429 |
| 11.18 Increase of urban claim on surface water | 71,000 | 71,000 |
| Total Urban water system asset increases | 106,774 | 109,429 |
| Water liability decreases | ||
| 19 Urban water system decreases | ||
| 19.1 Evaporation from urban water system | 3,877 | 3,838 |
| 19.2 Urban water system leakage to landscape | – | – |
| 19.3 Urban water system leakage to groundwater | 2,803 | 2,906 |
| 19.4 Delivery to urban water system users | 43,949 | 39,117 |
| 19.5 Discharge from urban water system to surface water | 31,702 | 34,325 |
| 19.17 Adjustment and forfeiture of urban claim on surface water | 23,162 | 29,210 |
| 19.20 Other urban water system decreases | 1,270 | 780 |
| Total Urban water system asset decreases | 106,763 | 110,176 |
| Unaccounted for difference—urban water system | (38) | (798) |
| Change in net water assets | 49 | 51 |
| Water inflows | 2012–13 volume (ML) | 2011–12 volume (ML) |
| 11 Urban water system inflows | ||
| 11.2 Entitled diversion of non-allocated surface water to urban water system | 66 | 0 |
| 11.4 Wastewater collected | 35,708 | 38,429 |
| 11.12 Entitled diversion of allocated surface water to urban water system | 47,838 | 41,790 |
| Total Urban water system inflows | 83,612 | 80,219 |
| Water outflows | ||
| 19 Urban water system outflows | ||
| 19.1 Evaporation from urban water system | 3,877 | 3,838 |
| 19.2 Urban water system leakage to landscape | – | – |
| 19.3 Urban water system leakage to groundwater | 2,803 | 2,906 |
| 19.4 Delivery to urban water system users | 43,949 | 39,117 |
| 19.5 Discharge from urban water system to surface water | 31,702 | 34,325 |
| 19.20 Other urban water system decreases | 1,270 | 780 |
| Total Urban water system outflows | 83,601 | 80,966 |
| Unaccounted-for difference – urban water system | (38) | (798) |
| Change in net water storage | 49 | 51 |
| Opening water storage | 906 | 855 |
| add/(less): Change in water storage | 49 | 51 |
| Closing water storage | 955 | 906 |
A schematic diagram representing all the inflows and outflows associated with the urban water system in the Canberra region is provided in Figure 8. The inflow and outflow volumes for the urban water system during the 2012–13 year are given in Table 11. The numbers on the diagram refer to the line item numbers in Table 11.
Figure 8 Schematic diagram of water inflows and outflows for the urban water system within the Canberrs region during the 2012–13 year; line item numbers are provided in brackets
Table 11 shows that urban water system inflows increased due to the higher usage of entitled diversion of allocated surface water to urban water system during the 2012–13 year. The usage was 47,838 ML about 14% increase compared to the previous year. During the year contribution to urban water inflows from the waste water collection has decreased by 2,721 ML. Delivery to urban water system users has increased to 43,949 ML, that is about 12% increase compared to 2011–12 year.
Water sources, allocations and diversions
ACTEW Water holds a licence to deliver urban water to the Canberra region. The total annual urban water access entitlement to ACTEW Water is 71,000 ML. More information on this entitlement is available in line item 21.2 Surface water allocation announcements-urban system.
Figure 9 Sources of water for the Canberra region's urban water supply system during the 2012–13 year and the 2011–12 comparison year. Line item numbers are given in brackets.
Balancing item
The balancing item volume represents the difference between the measured opening and closing balances of the urban water system, 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 urban water system store balance.
The balancing item is calculated according to Table 12.
Account |
Volume (ML) |
Opening balance at 1 July 2012 |
906 |
Total urban water system inflows (see Table 11) |
83,612 |
Total urban water system outflows (see Table 11) |
(83,601) |
Closing balance at 30 June 2013 |
(955) |
Balancing item—urban water system |
(38) |
The calculation of the water balance on the urban water system yielded a balance difference of -38 ML. This is less than 0.05% of the total urban water system inflows during the 2012–13 year.
Off-channel storages
Water held in off-channel water storages is considered to be taken from the shared pool of water resources and, as such, is not included as part of the region's water assets (see General description in 'Physical information' section of 'Contextual information').
This note provides additional information about the water assets and water liabilities recognised in the water accounting statements, and reports on water that has been harvested from the landscape into off-channel water storages and thus did not contribute to groundwater recharge or runoff into surface water.
The volume of water held in off-channel water storages decreased from 8,534 ML at the beginning of the 2012–13 year by approximately 15% to 7,214 ML at the end of the 2012–13 year. This decrease in off-channel water storage is attributed to the decreased inflows into the storages during 2012–13, driven by below average rainfall experienced throughout the year (see Rainfall in the 'Climate overview' section of 'Contextual information').
The volume of water held in off-channel water storages included only off-channel water storages filled primarily by rainfall-runoff capture. Volumes of water held in off-channel water storages filled by groundwater extractions, surface water diversions, or recycled water were excluded as these volumes could not be quantified due to a lack of available data; however, it is expected that this volume is not material as these types of off-channel water storages only make up a small proportion of off-channel water storage capacity within the Canberra region.
Off-channel water storage inflows and outflows are given in Table 13.
| 2012–13 volume (ML) | 2011–12 volume (ML) | |
| 30 Off-channel water inflows | ||
| 30.1 Precipitation on off-channel water store | 3,848 | 6,387 |
| 30.2 Groundwater discharge into off-channel water store | – | – |
| 30.3 Runoff harvesting into off-channel water store | 5,505 | 4,475 |
| Total 30 Off-channel water inflows | 9,353 | 10,862 |
| 31 Off-channel water outflows | ||
| 31.1 Evaporation from off-channel water storages | 6,229 | 5,701 |
| 31.2 Leakages from off-channel water storages | – | – |
| 31.3 Off-channel water abstraction | 4,552 | 4,715 |
| Total 31 Off-channel water outflows | 10,781 | 10,416 |
| Balancing item–off-channel water store | (108) | 22 |
| Change in off-channel water storage | (1,320) | 424 |
| Opening off-channel water storage | 8,534 | 8,110 |
| Closing off-channel water storage | 7,214 | 8,534 |
The majority of volumes reported for inflows and outflows to off-channel water storages were modelled (see individual item quantification approaches). Data was unavailable for inflows to off-channel water storages via surface water diversions and groundwater extractions. Therefore, the only volumes reported for inflows to off-channel water storages were runoff harvesting and precipitation, both of which made a significant contribution to the overall inflow to off-channel water storages in 2012–13.
Evaporation from off-channel water storages was the most significant outflow from off-channel water storages and was substantially higher than the volume reported for water use.
Balancing item
This volume represents the volume necessary to reconcile the opening and closing balances of the off-channel water storage with the physical water inflows and outflows. The difference was calculated according to Table 14.
| Account | Volume (ML) |
| Opening balance at1 July 2012 | 8,534 |
| Total off-channel water inflows (see Table 13) | 9,353 |
| Total off-channel water outflows (see Table 13) | (10,781) |
| Closing balance at 30 June 2013 | (7,214) |
| Balancing item—off-channel water store | (108) |
The calculation of the water balance on the off-channel water storages yielded a balance of -108 ML. This is about 1.5% of the total off-channel water storage volume at the end of the 2012–13 year and about 1.2% of the total off-channel water storage inflows during the 2012–13 year.
Although a large balancing item was not observed for the off-channel water store, it should be noted that volumes reported were mainly derived from modelled data.