South East Queensland: Water stores
This note provides a water balance for each of the region's water stores in the 2015–16 reporting year. Relatively poor rainfall conditions for most of the year contributed to low runoff across the region and a drop in storage volumes. Water supply to the urban system was similar to the previous year, but groundwater extraction increased.
Surface water store
The volume of water in the South East Queensland region's surface water store decreased by 14% during the 2015–16 year from 2,564,345 ML at 1 July 2015 to 2,213,337 ML at 30 June 2016 (Table S6).
| 2016 ML | 2015 ML | |
| Opening surface water store | 2,564,345 | 2,320939 |
| Inflows | 1,889,976 | 5,950,183 |
| Outflows | (2,226,819) | (5,331,609) |
| Balancing item | (14,165) | (375,168) |
| Closing surface water store | 2,213,337 | 2,564,345 |
A schematic diagram representing all surface water inflows and outflows during the 2015–16 year is provided in Figure S3.
Figure S3 Water inflows and outflows for South East Queensland's surface water store during the 2015–16 year
Surface water inflows
The largest natural water inflow in the region was runoff. Runoff was approximately 70% less than the 2014–15 year, which reflects the poor rainfall experienced across the region over most of the year (see Climate and water). Similarly, precipitation also decreased compared with the previous year.
There were two relatively small transfers of water to surface water (discharge: wastewater and discharge: user), the sum of which changes little from year to year.
Surface water outflows
The largest natural outflow in the region was river outflow, which was approximately 70% less than the previous year. This primarily reflects the poor rainfall experienced across the region over most of the year (see Climate and water).
Evaporation was marginally less than the previous year, which may be attributed to the decreased storage volumes and hence surface area of the storages during the year (see Statement details). The remaining natural surface water outflow was leakage: landscape, which generally varies little annually.
Total surface water diverted in the region (323,455 ML) decreased by approximately 8% from the previous year. Allocated diversion: urban system (287,410 ML) made up approximately 89% of the total diversion in the region. The volume of water diverted from each water resource plan area to the urban system is shown in Figure S4.
Figure S4 Surface water allocated diversion for urban supply within the South East Queensland region during the 2015–16 year
Allocated diversion: individual users accounted for approximately 8% of the total diversion. The remaining 3% of the total diversion comprised non-allocated diversion: individual users, non-allocated diversion: urban system and other statutory rights.
Surface water balancing item
The surface water balance (Table S6) yielded a balance of –14,165 ML. This is less than 1% of the total surface water inflows during the 2015–16 year. The negative balancing item indicates that either the inflows are too high or the outflows are too low.
It is likely that the balancing item volume 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 volume of water in the South East Queensland region's groundwater store is assumed to remain unchanged throughout the 2015–16 year (Table S7).
| 2016 ML | 2015 ML | |
| Opening groundwater store | 11,115 | 9,340 |
| Inflows | 25,513 | 22,256 |
| Outflows | (17,770) | (14,191) |
| Balancing item | (7,743) | (6,290) |
| Closing groundwater store | 11,115 | 11,115 |
A schematic diagram representing all groundwater inflows and outflows during the 2015–16 year is provided in Figure S5.
Figure S5 Water inflows and outflows for the groundwater store within the South East Queensland region during the 2015–16 year
Groundwater flows
The only inflow to the groundwater store in the South East Queensland region that could be quantified was leakage: urban system, which increased marginally from the previous year. The only groundwater outflows that could be quantified were 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 and are not presented in Figure S5.
Total groundwater extracted in the region (17,770 ML) increased by almost 70% from the previous year. Non-allocated extractions: urban system made up approximately 47% of the total extraction. Allocated extraction: individual users and non-allocated extraction: individual users accounted for approximately 25% and 28% 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 S7) yielded a balance of –7,743 ML. Given that the volume of water in aquifers remained unchanged and the natural groundwater movement in the region could not 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 volume of water in the South East Queensland region's urban water system is assumed to have remained unchanged throughout the year (Table S8).
| 2016 ML | 2015 ML | |
| Opening urban water store | 0 | 0 |
| Inflows | 545,851 | 537,557 |
| Outflows | (544,880) | (549,739) |
| Balancing item | (971) | 12,182 |
| Closing urban water store | 0 | 0 |
A schematic diagram representing all urban inflows and outflows during the 2015–16 year is provided in Figure S6.
Figure S6 Water inflows and outflows for the South East Queensland's urban water system during the 2015–16 year
A detailed breakdown of the inflows and outflows of the urban water system components are provided in the Urban water balance diagram.
Water supply inflows
Total inflow to the urban water supply system was 300,766 ML, similar to the previous year (Figure S7).
Figure S7 Water sources used in South East Queensland's urban water system during the 2015–16 year compared with the previous year
Total surface water diversion from the region’s storages made up almost 97% of the urban water supply during the 2015–16 year (Figure S6). The surface water supply comprised 287,410 ML for allocated diversion: urban system and 3,531 ML for non-allocated diversion: urban system. The volume of allocated surface water diverted from each water resource plan area to the urban system is shown in Figure S4.
The remaining sources of urban water supply were non-allocated extraction: urban system and delivery: desalinated water, which made up approximately 3% and 0.5% of inflows, respectively.
More details on water allocations and abstractions associated with the urban water system are provided in the Water rights note.
Wastewater and recycled water inflows
Wastewater collected was 245,085 ML during the 2015–16 year.
Water supply outflows
Total outflows from the water supply system (298,751 ML) comprised the following (Figure S8):
Figure S8 Outflows from the water supply system
Most of the water supply outflow is attributed to supply system delivery: urban users. During the 2015–16 year, the delivery was similar to the previous year, which aligned with the relatively unchanged inflows to the water supply system during the year (see Water supply inflows).
Approximately 12% of the total outflow from the urban supply system was related to losses (Figure S8). The losses, which comprised leakage: groundwater and other supply system decreases, were similar to the previous year.
Wastewater and recycled water system outflows
Total outflows from the wastewater and recycled water system (246,129 ML) comprised the following (Figure S9):
Figure S9 Outflows from the wastewater and recycled water systems
Approximately 9% of the treated wastewater was recycled water delivery: urban users, which was almost double that from the previous year. Less than 1% of the total outflow from the wastewater and recycled water system was related to losses (Figure S9).
Most of the remaining treated wastewater comprises discharge: sea and, to a much lesser extent, discharge: surface water and discharge: landscape.
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 system balancing item
The urban water balance (Table S3) yielded a balance item of –971 ML. This is less than 0.1% of the total urban water system inflows during the 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.