Canberra: Water stores
These notes provide a water balance for each of the region's water stores for the 2015–16 year. High rainfall associated with an east coast low event in early June resulted in an increase in annual runoff from the previous year, and storage volume increased to 83% full at 30 June 2016 compared with 80% at the start of the year. Yet prior to this event, relatively poor rainfall for the majority of the year contributed to an increase in water use.
Surface water store
The water balance for the Canberra region's surface water store is provided in Table S5. The volume of surface water in the region increased marginally during the 2015–16 year from 265,119 ML at 1 July 2015 to 273,135 ML at 30 June 2016 (Table S5).
| 2016 ML | 2015 ML | |
| Opening surface water store | 265,119 | 258,190 |
| Inflows | 957,231 | 815,068 |
| Outflows | (805,417) | (695,899) |
| Balancing item | (143,798) | (112,240) |
| Closing surface water store | 273,135 | 265,119 |
A schematic diagram representing all surface water inflows and outflows during the 2015–16 year is provided in Figure S5.
Figure S5 Water inflows and outflows for the surface water store during the 2015–16 year
Surface water inflows
The main natural water inflows in the region were runoff and river inflow into the region. Combined, these flows make up more than 98% of the total surface water inflow. This combined volume was approximately 18% more than the previous year, which is primarily attributed to the very high rainfall over the region associated with the east coast low event in early June (see Climate and water). Precipitation was similar to the previous year. The remaining natural surface water inflow (discharge: groundwater) could not be quantified due to a lack of available data.
The only water transfer in the region (discharge: wastewater) increased by approximately 3% from the previous year.
Surface water outflows
The largest natural water outflow was river outflow, which was approximately 18% more than the previous year. Most of the outflow occurred in June as a result of heavy rainfall associated with the east coast low event during 5–6 June (see Climate and water).
Evaporation was similar to the previous year. The remaining two natural surface water outflows (leakage: landscape and river and floodplain losses) could not be quantified due to a lack of available data.
The total surface water diversion in the region (52,994 ML) increased by more than 8% from the previous year. Allocated diversion: urban system (50,403 ML) accounted for approximately 95% of the total diversion in the region. The volume of water diverted from each storage to the urban system is shown in Figure S6. Non-allocated diversion: individual users (2,591 ML) accounted for approximately 5% of the total diversion. Diversion: statutory rights could not be quantified due to a lack of available data.
Figure S6 Surface water diversions to the urban system during the 2015–16 year; percentage of allocation diverted is also shown
For a more detailed description of the water usage in the region and the associated entitlements, see the Surface water rights note.
Surface water balancing item
The surface water balance (Table S5) yielded a balance of –143,798 ML, which is approximately 16% of the total surface water inflows during the year. The negative balancing item indicates that either the inflows are too high or the outflows are too low.
It is likely a portion of the balancing item is attributed to uncertainties associated with the runoff estimation (a large source of surface water increase). Runoff is estimated from a rainfall–runoff model (see Methods) and it is reasonable to expect a relatively high uncertainty around this volume.
Groundwater store
The water balance for the Canberra region's groundwater store is provided in Table S6. The volume of groundwater in the region is assumed to remain unchanged throughout the 2015–16 year (Table S6).
| 2016 ML | 2015 ML | |
| Opening groundwater store | – | – |
| Inflows | 4,454 | 2,920 |
| Outflows | (1,276) | (1,061) |
| Balancing item | (3,178) | (1,859) |
| Closing groundwater store | – | – |
A schematic diagram representing all groundwater inflows and outflows during the 2015–16 year is provided in Figure S7.
Figure S7 Water inflows and outflows for the groundwater store during the 2015–16 year
Groundwater flows
The only inflow to the groundwater store in the Canberra region that can be quantified is leakage: urban system, which increased marginally from the previous year. The only groundwater outflows that can be quantified are the groundwater extractions.
Natural 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.
Total groundwater extracted in the region (1,276 ML) increased by more than 20% from the previous year. Non-allocated extractions: individual users (841 ML) and extraction: statutory rights (435 ML) accounted for approximately 65% and 35% of the total extraction, respectively. For a more detailed description of the water usage in the region, and the associated entitlements, see the Groundwater rights note.
Groundwater balancing item
The groundwater balance (Table S6) yielded a balance of –3,178 ML. Given that the volume of water in aquifers and the natural groundwater movement in the region cannot be quantified, the balancing item is simply the difference between the leakage from the urban water system and the total volume of groundwater extraction.
Urban water system
The water balance for the Canberra region's urban water system is provided in Table S7. The volume of water in the region's urban water system is assumed to remain unchanged throughout the year (Table S7).
| 2016 ML | 2015 ML | |
| Opening urban water system | – | – |
| Inflows | 89,049 | 84,400 |
| Outflows | (85,518) | (84,305) |
| Balancing item | (3,531) | (95) |
| Closing urban water system | – | – |
A schematic diagram representing all urban inflows and outflows during the 2015–16 year is provided in Figure S8.
Figure S8 Water inflows and outflows for the urban water system during the 2015–16 year
A more detailed breakdown of the inflows and outflows of the urban water system components is provided in the urban water balance diagram. See downloadable table for a tabulated, utility-based version of the diagram.
Water supply inflows
Total inflow to the urban water supply system was 50,403 ML, an increase of approximately 7% from the previous year (Figure S9).
Figure S9 Water sources used in Canberra's urban supply system during the 2015–16 year compared with the previous 5 years
Surface water diversion from the region's storages makes up 100% of the urban water supply. The volume of surface water diverted from each storage to the urban water system during the 2015–16 year is given in Figure S6.
More details on water allocations and diversions associated with the urban water system are provided in the Water rights note.
Wastewater and recycled water inflows
Wastewater collected was 38,646 ML during the 2015–16 year.
Water supply outflows
Total outflows from the water supply system (50,882 ML) comprised the following (Figure S10):
Figure S10 Outflows from the water supply system
The majority of water supply outflow is supply system delivery: urban users. During the 2015–16 year, the delivery was marginally higher than the previous year, which aligned with the increased inflows to the water supply system during the year (see Water supply inflows above).
Approximately 11% of the total outflow from the urban supply system was related to losses (Figure S10). The losses, which comprised leakage: groundwater and other supply system decreases, were similar to the previous year.
Wastewater and recycled water outflows
Total outflows from the wastewater and recycled water systems (34,636 ML) comprised the following (Figure S11):
Figure S11 Outflows from the wastewater and recycled water systems
Approximately 98% of the treated wastewater was discharge: surface water. Recycled water delivery: urban users was around 1% (Figure S11). The remaining treated wastewater comprises other wastewater and recycled water system decreases.
Recirculation of treated wastewater and recycled water that occurs in the system may be subjected to additional treatment and/or re-use on site. The reported urban system outflows exclude any such recirculated volumes in the system.
Urban water balancing item
The urban water balance (Table S7) yielded a balance item of –3,531 ML. This is approximately 4% of the total urban water system inflows during the year 2015–16 year. The misbalance may be due to a number of factors, such as metering inaccuracies, unaccounted losses, and inaccuracies in the estimation of certain volumes.