Canberra
Water resources and systems

The following set of notes provides consolidated reports for each of the water stores and systems within the Canberra region during the 2011–12 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/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.

Figure 2  Schematic diagram of between-store flows that occur within the Canberra region; line item numbers are provided next to the flows

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.

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 increased during the 2011–12 year in the Canberra 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	206,139	201,252
1.2 Unregulated river	–	–
1.3 Regulated river	–	–
1.4 Lakes and wetlands	34,622	38,500
Total surface water assets	240,761	239,752
Water liabilities
5 Surface water liability
5.2 Surface water allocation remaining – urban water system	0	0
Total surface water liabilities	0	0
Opening net water assets	239,752	153,148
Change in net water assets	1,009	86,604
Closing net water assets	240,761	239,752

The volume of the surface water asset included water held in surface water storages 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.

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 2011–12 year the volume of water in these storages was high (see line item 1.1 Storages).The water levels at Corin Reservoir and Googong Reservoir were slightly above their total capacity level and Cotter Reservoir was almost full. The higher surface water storage during the 2011–12 year is attributed to the increased inflows into the storages, primarily driven by higher than average rainfall experienced throughout the period (see Climate statement).

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 2011–12 year, is shown in Figure 3.

Figure 3  Location map of the storages within the Canberra region; the % full volume on 30 June 2012 for each storage is also shown

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	21,110	19,713
9.2 River inflow to region	582,184	287,899
9.3 Groundwater discharge	–	–
9.4 Runoff to surface water	1,075,728	1,240,466
9.6 Overbank flood return to river channel	–	–
9.9 Discharge from urban water system	34,325	39,262
Total surface water increases	1,713,347	1,587,340
Water liability decreases
13 Surface water liability decreases
13.2 Adjustment and forfeiture of surface water allocation–urban water system	29,210	30,056
Total surface water liability decreases	29,210	30,056
Water asset decreases
17  Surface water decreases
17.1 Evaporation from surface water	20,097	18,982
17.2 River outflow from the region	1,596,539	1,144,888
17.3 Leakage to groundwater	–	–
17.4 Leakage to landscape	–	–
17.5 Overbank flood spilling	–	–
17.6 Surface water diversions–other statutory rights	–	–
17.7 Entitled diversion on non-allocated surface water to users	1,415	1,188
17.8 Entitled diversion of non-allocated surface water to urban water system	0	4,365
Total surface water decreases	1,618,051	1,169,423
Water liability increases
21 Surface water liability increases
21.2 Surface water allocation announcements–urban water system	71,000	71,000
Total surface water liability increases	71,000	71,000
Balancing item–surface water	52,497	290,369
Change in net water assets	1,009	86,604

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	21,110	19,713
9.2 River inflow to region	582,184	287,899
9.3 Groundwater discharge	–	–
9.4 Runoff to surface water	1,075,728	1,240,466
9.6 Overbank flood return to river channel	–	–
9.9 Discharge from urban water system	34,325	39,262
Total surface water inflows	1,713,347	1,587,340
Water outflows
17 Surface water outflows
17.1 Evaporation from surface water	20,097	18,982
17.2 River outflow from the region	1,596,539	1,144,888
17.3 Leakage to groundwater	–	–
17.4 Leakage to landscape	–	–
17.5 Overbank flood spilling	–	–
17.6 Surface water diversions–other statutory rights	–	–
17.7 Entitled diversion on non-allocated surface water to users	1,415	1,188
17.8 Entitled diversion of non-allocated surface water to urban water system	0	4,365
17.12 Entitled diversion of allocated surface water to urban water system	41,790	40,944
Total surface water outflows	1,659,841	1,210,367
Balancing item – surface water	52,497	290,369
Opening water storage	239,752	153,148
add/(less): Change in water storage	1,009	86,604
Closing water storage	240,761	239,752

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 2011–12 year; line item numbers are provided in brackets

Allocation diversions

In the 2011–12 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).

Balancing item

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

The balancing item is calculated according to Table 4.

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

	Account	Volume (ML)
	Opening balance (30 June 2011)	239,752
add	Total surface water inflows (see Table 3)	1,713,347
minus	Total surface water outflows (see Table 3)	1,659,841
minus	Closing balance (30 June 2012)	240,761
	Balancing item–surface water store	52,497

The calculation of the water balance on the surface water store yielded a balance difference of 52,497 ML. This is approximately 3% of the total surface water inflows during the 2011–12 year.

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

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.

A more detailed explanation is provided in line item notes 2.1 and 2.2.

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

Table 5  Statement of Water Assests and Water Liabilities for the groundwater store

Water assets	Volume at 30 June 2012 (ML)	Volume at 30 June 2011 (ML)
2 Groundwater
2.1 Water table aquifer	–	–
2.2 Underlying aquifers	–	–
Total groundwater assets	–	–
Opening net water assets	–	–
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.

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

Water asset increases	2011–12 volume (ML)	2010–11 volume (ML)
10 Groundwater increases
10.1 Groundwater inflow from outside region	–	–
10.3 Recharge from landscape	–	–
10.4 Recharge from surface water	–	–
10.5 Leakage from off–channel water storage	–	–
10.6 Leakage from urban water system	2,906	3,099
Total groundwater increases	2,906	3,099
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	335	335
Total groundwater decreases	770	770
Balancing item–groundwater	2,136	2,329
Change in net water assets	0	0

Table 7  Statement of Water Flows for the groundwater store

Water inflows	2011–12 volume (ML)	2010–11 volume (ML)
10 Groundwater inflows
10.1 Groundwater inflow from outside region	–	–
10.3 Recharge from landscape	–	–
10.4 Recharge from surface water	–	–
10.5 Leakage from off–channel water storage	–	–
10.6 Leakage from urban water system	2,906	3,099
Total groundwater inflows	2,906	3,099
Water outflows
18 Groundwater outflows
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	335	335
Total groundwater outflows	770	770
Balancing item–groundwater	2,136	2,329
Opening water storage	0	0
add/(less): Change in water storage	0	0
Closing water storage	0	0

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the Canberra 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. The numbers on the diagram refer to the line item numbers in Table 7.

Figure 5  Schematic diagram of water inflows and outflows for the groundwater store within the Canberra region during the 2011–12 year; line item numbers are provided 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.

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

	Account	Volume (ML)
	Opening balance (30 June 2011)	–
add	Total groundwater increases (see Table 7)	2,906
minus	Total groundwater decreases (see Table 7)	770
minus	Closing balance (30 June 2012)	–
	Balancing item–groundwater store	2,136

 

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 2011–12 year in the Canberra region.

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

Water assets	Volume at 30 June 2012 (ML)	Volume at 30 June 2011 (ML)
3 Urban water system
3.1 Urban water supply system	904	853
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	906	855
Opening net water assets	855	887
Change in net water assets	51	(32)
Closing net water assets	906	855

The information in Table 9 does not include service water storages or the pipe network managed and owned by Queanbeyan City Council (QCC). The QCC water supply system is much smaller in size than the ACTEW Water system and it is expected that the volume stored within the QCC tanks and pipes would be much less than that reported for ACTEW Water's system.

Table 9 shows that for the urban system in the Canberra region, only the volume of water contained in the urban water supply system could be quantified. The volume only includes 47 tanks and the pipe network owned by ACTEW Water. This volume does not include any data from the Queanbeyan area as this was unavailable.

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 store

Water asset increases	2011–12 volume (ML)	2010–11 volume (ML)
11 Urban water system increases
11.1 Precipitation on urban water system	–	–
11.2 Entitled diversion of non–allocated surface water to urban water system	0	4,365
11.4 Wastewater collected	38,429	39,457
11.18 Increase of urban claim on surface water	71,000	71,000
Total urban water system increases	109,429	114,822
Water asset decreases
19 Urban water system decreases
19.1 Evaporation from urban water system	3,838	4,353
19.2 Leakage to landscape	–	–
19.3 Leakage to groundwater	2,906	3,099
19.4 Delivery to urban water system users	39,117	37,015
19.5 Discharge from urban water system to surface water	34,325	39,262
19.17 Adjustment and forfeiture of urban claim on surface water	29,210	30,056
19.20 Other urban water system decreases	780	0
Total urban water system decreases	110,176	113,785
Balancing item–urban water system	(798)	1,069
Change in net water assets	51	(32)

Table 11  Statement of Water Flows for the urban water store

Water inflows	2011–12 volume (ML)	2010–11 volume (ML)
11 Urban water system inflows
11.1 Precipitation on urban water system	–	–
11.2 Entitled diversion of non–allocated surface water to urban water system	0	4,365
11.4 Wastewater collected	38,429	39,457
11.12 Entitled diversion of allocated surface water to urban water system	41,790	40,944
Total urban water system inflows	80,219	84,766
Water outflows
19 Urban water system outflows
19.1 Evaporation from urban water system	3,838	4,353
19.2 Leakage to landscape	0	0
19.3 Leakage to groundwater	2,906	3,099
19.4 Delivery to urban water system users	39,117	37,015
19.5 Discharge from urban water system to surface water	34,325	39,262
19.20 Other urban water system decreases	780	0
Total urban water system outflows	80,966	83,729
Balancing item–urban water system	(798)	1,069
Opening water storage	855	887
add/(less): Change in water storage	51	(32)
Closing water storage	906	855

A schematic diagram representing all the inflows and outflows associated with the urban water system in the Canberra region is provided in Figure 6. The inflow and outflow volumes for the urban water system during the 2011–12 year are given in Table 11. The numbers on the diagram refer to the line item numbers in Table 11.

Figure 6  Schematic diagram of water inflows and outflows for the urban water system within the Canberrs region during the 2011–12 year; line item numbers are provided in brackets

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.

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.

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

	Account	Volume (ML)
	Opening balance (30 June 2011)	855
add	Total urban water system inflows (see Table 11)	80,219
minus	Total urban water system outflows (see Table 11)	80,966
minus	Closing balance (30 June 2012)	906
	Balancing item–urban water system	(798)

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 increased from 8,110 ML at the beginning of the 2011–12 year by approximately 5% to 8,534 ML at the end of the 2011–12 year. This increase in off–channel water storage is attributed to the increased inflows into the storages during 2011–12, driven by above 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.

Table 13  Inflows and outflows for the off–channel water store in the Canberra region during the 2011–12 year

	Volume (ML)
30 Off–channel water inflows
30.1 Precipitation on off–channel water store	6,387
30.2 Groundwater discharge into off–channel water store	-
30.3 Runoff harvesting into of–channel water store	4,475
Total 30 Off–channel water inflows	10,862
31 Off–channel water outflows
31.1 Evaporation from off–channel water storages	5,701
31.2 Leakages from off–channel water storages	-
31.3 Water use	4,715
Total 31 Off–channel water outflows	10,416
Balancing item–off–channel water store	22
Change in off–channel water storage	424
Opening off–channel water storage	8,110
Closing off–channel water storage	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 2011–12.

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.

Table 14  Balancing item for Off–channel water store for the 2011–12 year

	Account	Volume (ML)
	Opening balance (30 June 2011)	8,110
add	Total off–channel water inflows (see Table 13)	10,862
minus	Total off–channel water outflows (see Table 13)	10,416
minus	Closing balance (30 June 2012)	8,534
	Balancing item – off–channel water store	22

The calculation of the water balance on the off–channel water storages yielded a balance of 22 ML. This is less than 1% of the total off–channel water storage volume at the end of the 2011–12 year and less than 1% of the total off–channel water storage inflows during the 2011–12 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. The modelling process essentially constrains the data to achieve a water balance, hence removing any potential balancing difference.