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National Water Account 2016

Sydney: 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 several east coast low events resulted in storage volume increasing to 98% full at 30 June 2016 compared with 93% at the start of the year. Yet for the majority of the year, relatively poor rainfall contributed to a decrease in runoff across the region, and water use was similar to the previous year.

 

 

 

Surface water store

Cordeaux Dam, New South Wales. Source: WaterNSW © A. Hollingworth

The water balance for the Sydney region's surface water store is provided in Table S5. The volume of water in the region's surface water store increased by 6% during the 2015–16 year from 2,664,966 ML at 1 July 2015 to 2,821,555 ML at 30 June 2016 (Table S5).

 

Table S5 Water balance for the surface water store
 2016
ML
2015
ML
Opening surface water store2,664,9662,388,070
Inflows5,125,0535,481,488
Outflows(4,794,630)(5,171,009)
Balancing item(173,834)(33,583)
Closing surface water store2,821,5552,664,966

 

A schematic diagram representing all surface water inflows and outflows during the 2015–16 year is provided in Figure S3.

 

Figure S3  Schematic diagram of water inflows and outflows for the surface water store during the 2015–16 year
Figure S3 Water inflows and outflows for the surface water store during the 2015–16 year

 

Surface water inflows

The largest natural water inflow in the region was runoff. Runoff was approximately 6% less than the previous year, reflecting the relatively poor rainfall experienced across the region for the majority of the year (see Climate and water). The remaining natural surface water inflow, precipitation, also decreased by more than 10% compared with the previous year.

Discharge: wastewater decreased by approximately 14% from the previous year. The remaining transfer of water to the surface water store was delivery: inter-region. No direct discharge to surface water was reported as the Wallerawang Power Station ceased operations before the start of the year.

 

Surface water outflows

The largest natural water outflow in the region was river outflow. Outflow was 8% less than the previous year, which reflects the relatively poor rainfall experienced across the region for the majority of the year (see Climate and water).

Evaporation decreased by 10% from the previous year. The remaining natural surface water outflow (river and floodplain losses) could not be quantified accurately due to a lack of available data.

Total surface water diversion in the region (608,140 ML) increased marginally from the previous year. Allocated diversion: urban system (555,109 ML) accounted for approximately 91% of the total diversion in the region. The volume of water diverted to the urban system by bulk supplier WaterNSW is shown in Figure S4. Allocated diversion: individual users (20,501ML) and diversion: statutory rights (32,530 ML) accounted for approximately 3% and 6% of the total diversion respectively.

 

Figure S4 Surface water diversions to the urban system by WaterNSW during the 2014–15 year
Figure S4 Surface water diversions to the urban system by WaterNSW during the 2014–15 year

 

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 –173,834 ML. This is approximately 3% of 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 a portion of the balancing item is attributed to uncertainties associated with the runoff estimation (a large source of surface water increase), river outflow from the region (a large source of surface water decrease) and the lack of an estimate of surface water discharge to groundwater.

WaterNSW used mass balance calculations to estimate the runoff volume to its storages and the Bureau of Meteorology (the Bureau) estimated runoff volumes from a rainfall–runoff model for storages not managed by WaterNSW. The Bureau calculated the runoff at several gauging stations and also estimated the runoff for ungauged areas from the rainfall–runoff model. It is reasonable to expect a relatively high uncertainty around this volume (see Methods).

The volume for river outflow to sea is mainly based on measured flow data collected at the most downstream gauging stations along rivers, environmental flow releases, and modelled data for ungauged river reaches and tidal streams. There are uncertainties associated with the model calculations and the gauged flows used (see Methods).



Groundwater store

The groundwater store is not discussed for the Sydney region as volumes related to groundwater store could not be quantified in a way that was complete, neutral, and free from material error. Also, it is not recognised in the water accounting statements as its contribution is very minimal.

 

Urban water system

Wollongong Water Recycling Plant, New South Wales. Source: Sydney Water Corporation © Sydney Water Corporation

The water balance for the Sydney region's urban water system is provided in Table S6. The volume of water in the region's urban water system is assumed to remain unchanged throughout the year (Table S6).

 

Table S6 Water balance for the urban water system
 2016
ML
2015
ML
Opening urban water store00
Inflows1,102,8921,091,984
Outflows(1,087,676)(1,082,771)
Balancing item(15,216)(9,213)
Closing urban water store00

 

A schematic diagram representing all urban inflows and outflows during the 2015–16 year is provided in Figure S5.

 

Figure S5  Schematic diagram of water inflows and outflows for the urban water system during the 2015–16 year
Figure S5 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.

 

Water supply inflows

Total inflow to the urban water supply system was 555,109 ML, similar to the previous year (Figure S6).

 

Figure S6  Graph of water sources used in Sydney's urban supply system during the 2015–16 year compared with the previous 5 years
Figure S6 Water sources used in Sydney's urban supply system during the 2015–16 year compared with the previous 5 years

 

Surface water diversion from the region's storages made up 100% of the urban water supply during the 2015–16 year. The volume of surface water transferred by WaterNSW to each water utility in the region is shown in Figure S4. More than 95% of the surface water is supplied to the Sydney Water Corporation.

There was no desalinated water supplied to the region's urban water supply system during the 201516 year.

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

More than 97% of the region's wastewater is collected by the Sydney Water Corporation. Wastewater collected by the Sydney Water Corporation was 547,783 ML during the 2015–16 year.

 

Water supply outflows

Total outflows from the water supply system (539,059 ML) comprised the following (Figure S7):

 

Figure S7  Graph of outflows from the water supply system
Figure S7 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 similar to the previous year, which aligned with the relatively unchanged inflows to the water supply system during the year (see Water supply inflows above). 

Approximately 9% of the total outflow from the urban supply system was related to losses (Figure S7). 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 (548,617 ML) comprised the following (Figure S8):

 

Figure S8  Graph of outflows from the wastewater and recycled water systems
Figure S8 Outflows from the wastewater and recycled water systems

 

Approximately 3% of the treated wastewater was recycled water delivery: urban users, which was similar to the previous year. Approximately 5% of the total outflow from the wastewater and recycled water system was related to other wastewater and recycled water system decreases (Figure S8).

Most of the remaining treated wastewater comprised discharge: sea and, to a much lesser extent, discharge: surface water. A portion of the discharge to surface water (10,837 ML) includes specific releases of highly treated recycled water to the Hawkesbury-Nepean River for environmental benefit. 

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 S6) yielded a balance item of –15,216 ML. This is approximately 1% 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.