Supplementary information for statements/asset accounts
- Above-average rainfall in 2015–16 led to increased storage volumes for that year.
- Although rainfall was below average for most of the 2016–17 year, heavy rainfall in September contributed to high runoff volumes and helped maintain storage levels.
- The majority of water stocks in the region are held in surface water storages, though most of the changes in water stocks occur in rivers.
This section provides further supporting information and analysis relating to the three preceding sections - the Statement of Water Assets and Water Liabilities, the Statement of Changes in Water Assets and Liabilities and the Water Asset Accounts.
This information is organised in the following categories:
Water assets / stocks
- In 2016-17 the total closing water asset/stocks volumes in the Canberra region were 279,968 ML, equivalent to approximately 55% of the volume of water held in Sydney Harbour. Most of the stored water was from surface water (99.7%), with the remaining water from the urban water system.
- The amount of water stocks in the Canberra region increased by 27% between the beginning of the 2013-14 and the end of the 2016-17 reference periods, from 220,546 ML to 279,968 ML. There was a positive net change in water stocks every year from 2013-14 to 2015-16, before a slight decrease (0.6%) in 2016-17.
Figure S1 Total closing water asset volumes / stocks by year
Storages
- Major reservoirs account for 86% of the 279,002 ML of total surface water stored.
- Storage volumes increased to 84% full (238,900 ML) at 30 June 2017, the fourth consecutive increase in end of year storage volume.
- The increases in storage volume are due to inflows exceeding outflows for all four years.
Figure S2 Total storage volume in the region at 30 June 2017 compared with the previous 3 years
- During the 2016–17 period, above-average rainfall during winter and spring contributed to storage volumes reaching 100% full in mid-October 2016. Storage volumes steadily decreased for the remainder of the 2016–17 year.
- The region's smallest surface water storages—Corin and Bendora reservoirs—held 18% and 3% of the water held in storages at 30 June 2017. The storage levels of these two dams fluctuated the most between 2013-14 and 2016-17 as these are the primary source of the region’s water supply.
- The largest storage in the Canberra region is Googong Reservoir which, at 30 June 2017, held 46% of the total amount of water held in storages in the region. Googong Reservoir is the region's secondary source of water and has remained full, or near full, since the end of the millennium drought in 2010. This trend continued for the first half of the 2016–17 year before decreasing steadily, closing at 90% of capacity.
- Cotter Reservoir is the second largest storage in the region and held 32% of water held in storage in the region at 30 June 2017. In 2013 the Cotter Reservoir was enlarged, increasing the region's total storage capacity. Since then, storage levels have fluctuated very little, due to the preferential use of water from Corin and Bendora reservoirs.
Figure S3 Percentage-full volume over 2013–17 period for each storage
Lakes and wetlands
- Lake Burley Griffin, the largest lake in the region, had a closing volume of 33,670 ML at 30 June 2017. The closing volumes of Lake Ginninderra and Lake Tuggeranong were 3,700 ML and 1,800 ML, respectively.
- The volume of water held in Canberra’s lakes remained steady from 1 July 2014 to 30 June 2017, however during the 2013-14 period a 12% increase was recorded. This increase was mostly due to restoring normal water levels to Lake Burley Griffin following repair work undertaken on Scrivener Dam.
- More detailed information on the individual storages within the region is available on the Bureau of Meteorology's Water Storage website.
Figure S4 Volume of lakes in Canberra region by year over the 2012–17 period
Other water assets/stocks
- River storage closing water asset (stocks) volume was 932 ML for 2016–17, representing less than 0.3% of the total water assets (stocks) in the Canberra region.
- The volume of groundwater in aquifers cannot be quantified, and is assumed to remain unchanged throughout the year.
- The urban water system closing water asset (stock) volume was 966 ML for 2016–17, representing the volume of water held in the distribution pipe network. This represents only 0.3% of the total closing water assets (stocks) in the Canberra region.
Water liabilities
- Water liabilities in the Canberra region refer to the volume of allocation remaining on licence entitlements at the end of the water management year.
Description | Volume ML | |
Opening balance at 1 July 2016 | 0 | |
Allocation | 1,832 | |
Allocated diversion | – | |
Adjustment and forfeiture | (1,832) | |
Closing balance at 30 June 2017 | 0 |
Description | Volume ML | |
Opening balance at 1 July 2016 | 0 | |
Allocated | 851 | |
Allocation extraction | – | |
Adjustment and forfeiture | (851) | |
Closing balance at 30 June 2017 | 0 |
- The water supply licences for the region have a water management year that ends on 30 June. The portion of water allocation that has not been abstracted at the end of the water year is either forfeited or is carried over into the next water year.
- As the carryover cannot be quantified, the unused portion of the allocation is assumed to be forfeited and the allocation remaining at the end of the year was 0 ML.
- A more detailed description of water allocations and associated water rights in the Canberra region is given in the Water rights note.
Water flows
- Total water inflow to the region for 2016–17 was 1,100,266 ML and total water outflow from the region was 1,045,059 ML.
Surface water flows
- Total inflows to surface water for the region were 1,005,408 ML in 2016–17, primarily made up of runoff and river inflow.
- Total outflows from surface water asset for the region were 956,074 ML in 2016–17, primarily made up of outflow from the region.
Figure S5 Water inflows and outflows for the Canberra region's surface water store during the 2016–17 year
Runoff
- Runoff in the Canberra region increased by 41% between 2013-14 and 2016-17, from 486,042 ML to 682,897 ML. The largest increase (21%) occurred between the 2015-16 and 2016-17 period and can be attributed to heavy rainfall in September 2016.
- Most of the runoff in the Canberra region flows into rivers (83% in 2016-17), with the remaining flowing into major reservoirs and lakes, which account for 14% and 3% of total runoff flow respectively.
Figure S6 Proportion of runoff apportioned to reservoirs, lakes, and rivers for the 2016–17 year
Rivers
- River inflows to the Canberra region increased every year from 2013–14 to 2015–16, with a 106% increase over the period. This was followed by a 36% decrease from 2015-16 to 2016-17.
- A large proportion of the surface water that flows into the Canberra region eventually flows out of the region, via the Murrumbidgee River. Outflows from the region increased every year from 2013-14 (468,908 ML) to 2016-17 (818,608 ML), an increase of 75% over the period.
- In 2016-17, 262,309 ML of water flowed into the Canberra region via the Murrumbidgee River, while 818,608 ML flowed out of the region, a difference of 556,300 ML.
Abstractions / diversions
- During the 2016-17 year total surface water diverted in the region was 52,766 ML with 95% (49,958 ML) diverted for the urban system and the remaining 5% (2,808 ML) for licenced individual users.
- Between 2013-14 and 2016-17, abstractions/diversions from major reservoirs remained relatively consistent, varying between a low of 47,115 ML in 2014-15 and a high of 50,403 ML in 2015-16. This was an increase of 7% between these two years, before a slight decrease in 2016-17 of just less than 1%, to 49,958 ML.
- For a more detailed description of the water usage in the region, and the associated entitlements, see the Water rights note.
Groundwater flows
- Total inflow to groundwater for the region was 4,079 ML, which is all leakage from the urban water system. This volume has remained steady from 2013–14 to 2016–17.
- Total groundwater extracted in the region was 1,254 ML, similar to previous years. 65% of total extraction was for non-allocated extractions: individual users; 35% for extraction: statutory rights.
- Groundwater movement across the region boundary as well as surface water–groundwater interactions are considered to occur within the region; however, these flows could not be quantified due to a lack of available data.
Figure S7 Water inflows and outflows for the Canberra region's groundwater store during the 2016–17 year
Urban water system flows
- The increases to the urban water system were 90,779 ML in 2016-17. The increases included water diverted from storages to the urban supply system and wastewater supplied to the sewerage system.
- The total decreases from the urban water system was 87,731 ML, which included water delivered to urban users, treated wastewater discharged from the wastewater system to rivers, and leakage to the groundwater.
Figure S8 Water inflows and outflows for the Canberra region's urban water system during the 2016–17 year
- Between 2013-14 and 2016-17, diversions from storages remained relatively consistent, varying between a low of 47,115 ML in 2014-15 and a high of 50,403 ML in 2015-16.
- During the period 2013-14 to 2016-17, most of the water abstracted/diverted was from Bendora Dam (88% in 2016-17) located on the Cotter River. The remaining 12% of water abstractions/diversions in 2016-17 was from Googong Dam.
- The majority (90%) of water diverted from surface water for use by the urban system is supplied to users. Losses account for 10% of the total urban supply system outflows.
- The majority of treated wastewater is discharged to surface water. A small portion is recycled for other uses.