Melbourne
Resources and Systems

The purpose of this note is to provide a consolidated report on the surface water store within the region during the 2010–11 year. Information on all water flows to and from the surface water store are presented here, including between store flows and transfers within the region that are not presented in the Water accounting statements.

A description of the Melbourne region's surface water resources is provided in the Surface water section of the Contextual information.

The volume of water held in water storages increased significantly during the 2010–11 year (Table 1). Very high rainfall, generated by one of the strongest La Niña events on record, resulted in water storages recording their highest inflows since the drought commenced in 1997. More information on the climatic conditions during the 2010–11 year can be found in Contextual information under the Climate overview. 

The volume of water in rivers and lakes and wetlands could not be quantified accurately due to a lack of available data.

Table 1. Surface water store volumes at the start and end of the 2010–11 year

	30 June 2011 (ML)	30 June 2010 (ML)
9 Surface water
1.1 Storages	669,642	400,646
1.2 Unregulated river	–	–
1.3 Regulated river	–	–
Total	669,642	400,646

Figure 1 shows the location of storages within the Melbourne region and the volume of water in each storage, including dead storage, as a percentage of total storage capacity (percent full) at the end of the 2010–11 year. At the end of the 2010–11 year, the average storage volume was 85%, up from 47% at the end of the 2009–10 year. All storages were above 60% full, with most between 85% and 100% full.

Figure 1. Location map of the storages within the Melbourne region. The percentage full volume on 30 June 2011 for each storage is also shown

Surface water inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the surface water store in the Melbourne region during the 2010–11 year is provided in Figure 2. In addition to flows reported in the water accounting statements, Figure 2 and Table 2 also show flows between water stores that are part of the region.

Figure 2. Schematic diagram of water inflows (blue arrows) and outflows (red arrows) for the surface water store during the 2010–11 year. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.

Table 2. Volumes of inflows and outflows for the surface water store during the 2010–11 year

	Volume (ML)
9 Surface water inflows
9.1 Precipitation on surface water	35,115
9.3 Groundwater discharge	–
9.4 Runoff to surface water	3,222,163
9.5 Point return from irrigation scheme	51
9.9 Discharge from urban water system	15,390
9.10 Direct discharge by user	–
9.11 Delivery of water under inter-region agreement	20,376
9.13 Delivery of claimed desalinated water	0
Total 9 Surface water inflows	3,293,095
17 Surface water outflows
17.1 Evaporation from surface water	35,365
17.2 River outflow from the region	2,502,127
17.3 Leakage to groundwater	–
17.4 Leakage to landscape	–
17.6 Diversions – other statutory rights	–
17.7 Non-allocated diversions to users	16,883
17.11 Surface water allocation diversion	6,512
17.12 Surface water allocation diversion – urban water system	353,431
17.14 Surface water transfer under inter-region commitment	235
Total 17 Surface water outflows	2,914,553
Balancing item – surface water store	109,546
Change in surface water storage	(268,996)
Opening surface water storage	400,646
Closing surface water storage	669,642

Line items in italics indicate between-store flows, which are not presented in the water accounting statements as they occur within the region.

The majority of diversions from surface water are for the urban water system (17.11 Surface water allocation diversion - urban water system), which accounts for 94% of the total diversion. Water is diverted from storages to the urban water system under bulk entitlements held by Melbourne retail authorities.

Figure 3 presents a comparison of surface water diversions during the 2010–11 and 2009–10 years.  Diversions for the urban water system decreased slightly. Non–allocated diversions to other users decreased by almost half in the 2010–11 year, due to less demand for water during that wet year. Allocation diversions (used for irrigation) increased in the 2010–11 year due to an increase in the volume of allocation announcements made due to the wet conditions.

Figure 3. Graph of diversions from storages within the Melbourne region during the 2010–11 and 2009–10 years. Line items numbers are given in brackets

Allocation diversions are associated with a water access entitlement. When an allocation is announced, a present obligation (water liability) is created on the surface water to deliver water to the users. As there is no carry-over provision in the region, the portion of the announced allocations that were not diverted by the end of the year was forfeited.

The entitlement, allocation announcement and forfeiture for each of these water rights during the 2010–11 year are provided in Table 1 of the Water rights, entitlements, allocations and restrictions note.

This volume represents the volume necessary to reconcile the opening and closing balances of the surface water store with the physical water inflows and outflows.

The Balancing item – surface water store is calculated according to Table 3.

Table 3. Balancing item for the surface water store for the 2010–11 year

	Account	Volume (ML)
	Opening balance (30 June 2010)	400,646
add	Total 9 Surface water inflows	3,293,095
less	Total 17 Surface water outflows	2,914,553
less	Closing balance (30 June 2011)	669,642
	Balancing item – surface water store	109,546

The calculation of the water balance on the surface water store yielded a balance difference of 109,546 ML. This is approximately 51% of the total surface water store volume at the end of the 2010–11 year and around 14% of the total surface water inflows during the 2010–11 year.

It is likely that the balancing item is primarily attributed to errors associated with the rainfall runoff, a large source of surface water increase (line item 9.4).

The rainfall runoff volume is derived from a rainfall-runoff model and it is reasonable to expect a 10–20% uncertainty around the modelled runoff volume (+/– 640,000 ML). As a consequence the modeled runoff is likely to be an overestimate of the volume that actually entered the surface water store.

The purpose of this note is to provide a consolidated report on the groundwater store within the region during the 2010–11 year. Information on all water flows to and from the groundwater store are presented here, including between store flows and transfers that are not presented in the water accounting statements.

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

The volume of groundwater assets remained constant during the 2010–11 year (Table 4). This was due to the quantification approach of the groundwater assets (refer to line items 2.1 Water table aquifer and 2.2 Underlying aquifers). 

Table 4. Groundwater store volume at the start and end of the 2010–11 year 

	30 June 2011 (ML)	30 June 2010 (ML)
2 Groundwater
2.1 Water table aquifer	21,873	21,873
2.2 Underlying aquifers	16,565	16,565
Total	38,438	38,438

Groundwater inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the Melbourne region is provided in Figure 4. The inflow and outflow volumes for the groundwater store during the 2010–11 year are given in Table 5. In addition to flows reported in the water accounting statements, Figure 4 and Table 5 also show flows between water stores that are part of the region.

Figure 4. Schematic diagram of water inflows (blue arrows) and outflows (red arrows) for the surface water store during the 2010–11 year. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line items numbers are provided next to the flows.

Table 5. Volume of inflows and outflows for the groundwater store during the 2010–11 year

	Volume (ML)
10 Groundwater inflows
10.1 Groundwater inflow from outside region	0
10.2 Groundwater inflow from outside region at coast	1,113
10.3 Recharge from landscape	877,331
10.4 Recharge from surface water	–
10.6 Leakage from urban water system	18,636
Total 10 Groundwater inflows	897,080
18 Groundwater outflows
18.1 Groundwater outflow to outside region	0
18.2 Groundwater outflow to outside region at coast	129,345
18.3 Discharge to landscape	16,516
18.4 Discharge to surface water	–
18.7 Extraction – other statutory rights	–
18.8 Non-allocated extractions to users	–
18.11 Groundwater allocation extraction	10,196
Total 18 Groundwater outflows	156,057
Balancing item – groundwater store	741,023
Change in groundwater storage	0
Opening groundwater storage	38,438
Closing groundwater storage	38,438

Line items in italics indicate between-store flows. These flows are not presented in the statements as they occur within the region.

Allocations and extractions

Most of the extractions from the groundwater store were for licensed private use (18.11 Groundwater allocation extraction). In general, extractions from groundwater were very low during the 2010–11 year, due to the wet year.

This volume represents the volume necessary to reconcile the opening and closing balances of the groundwater store with the physical water inflows and outflows.

The Balancing item – groundwater store is calculated according to Table 6.

Table 6. Balancing item for the groundwater store in the 2010–11 year

	Account	Volume (ML)
	Opening balance (30 June 2010)	38,438
add	Total 10 Groundwater inflows	897,080
less	Total 18 Groundwater outflows	156,057
less	Closing balance (30 June 2011)	38,438
	Balancing item – groundwater store	741,023

The calculation of the water balance on the groundwater store yielded a balance difference of 741,023 ML, approximately 82% of the total groundwater inflows during the 2010–11 year. 

The groundwater asset in the Melbourne region is equivalent to the legal extractable limit and does not reflect fluctuation of groundwater levels over time. Therefore, groundwater assets for the region are not responsive to groundwater storage changes resulting from water table fluctuations. As a result, estimated inflows and outflows are more sensibly compared to the change of water stored in the aquifers than to the opening and closing balance of the groundwater asset.

The volume reported as the balancing item for the groundwater asset is considerably larger than that reported for the 2009–10 comparative year (–12,397 ML). During the 2010–11 year, total groundwater outflows were less than the previous year while inflows were much greater than the previous year. This large increase in recharge reflects the well above average rainfall conditions observed throughout the region in 2010–11 (see Climate overview).

The change in aquifer storage was calculated using groundwater levels for the water table aquifer within the sedimentary area identified in Figure 5. The groundwater levels were estimated using all bores within the region, assuming that all hydrogeological layers are hydraulically inter-connected.

Figure 5. Map of water table aquifer within the sedimentary area used to calculate aquifer storage

The change in storage for water table aquifer in the Melbourne region during the 2010–11 year was estimated at 219,588 ML. This increase in storage was greater than that of the 2009–10 year (Table 7).

Table 7. Changes in aquifer storages estimated for the 2010–11 and 2009–10 years

Management area	Change in storage 2010–11 (ML)	Change in storage 2009–10 (ML)
Clipped sedimentary areas	208,284	33,1351

¹ The value reported in Table 7 for the 2009–10 year has been estimated using the same quantification approach that was used to calculate the 2010–11 value. In the 2010 Account, a value of 46,230 ML was reported as aquifer storage increase for the 2009–10 year, using a different quantification approach.

The large increase in aquifer storage during the 2010–11 year (208,284 ML reported in Table 7) is due to increased recharge and decreased extractions during that wet year. Because the aquifers included in the calculation of the change in aquifer storage represent only a fraction of the groundwater resources in the Melbourne region, the value in Table 7 only partially reflects the difference between inflows and outflows shown in Table 5 and 6.

Data source

Bore locations, groundwater level data and aquifer attribution: Melbourne University Groundwater Database. The database is populated using data from both the Victorian Department of Sustainability and Environment and Department of Primary Industries. Hydraulic conductivity and aquifer thickness are estimated using data from the Port Phillip Catchment Management Authority groundwater model (Department of Sustainability and Environment 2010b).

Data provider

Bureau of Meteorology.

Method

Change in extractable storage is estimated using a simple geographic information system (GIS) approach based on measured groundwater levels and aquifer properties. Firstly, groundwater levels are estimated at the start (1 July 2010) and the end (30 June 2011) of the 2010–11 year. This is achieved by considering all groundwater level measurements between March 2010 to October 2010 and March 2011 to October 2011, respectively, and using the measurements closest in time to interpolate the start and end levels.

The estimated groundwater levels on the start and end dates are then spatially interpolated to grids using the ArcGIS Topo-to-Raster tool. The interpolated groundwater level surfaces at the start and the end of financial year and the interpolated change in groundwater level at each bore were then used to calculate the change in volume between them within the sedimentary area. Finally, these volumes were multiplied by appropriate specific yield values to convert to a change in groundwater storage and masked for areas within 10 km of a groundwater observation bore. The average of these volumes is reported.

Uncertainty

The uncertainty estimate was not quantified.

The uncertainty in the field-measured data (example: groundwater levels, specific yield) was not specified and hence the impacts of such uncertainty on the change in storage is not estimated.

The change in storage estimations were based on interpolated groundwater level grids produced using the ArcGIS Topo-to-Raster tool. Use of other interpolation methods may impact the values of the groundwater level grids and hence the estimated values for change in groundwater storage.

Approximation, assumptions, caveats and limitations

The groundwater levels were estimated by assuming that all the hydrogeological layers (excluding basement) within the Port Phillip and Western Port groundwater model region are hydraulically inter-connected. This assumption facilitates the interpolation of a groundwater potential surface from groundwater level measurements as these measurements were limited in number.

Groundwater levels are assumed equal to 0 metres Australian Height Datum (mAHD) at the coastline.

Change in groundwater storage was not calculated for confined aquifers. The annual change in storage was considered to be negligible for confined aquifers due to their very low store activity, which is much lower than the specific yield of unconfined aquifers (Freeze and Cherry 1979). Upon lowering of water levels in such aquifers, they remain fully saturated so that no dewatering occurs. The water diverted is volumetrically equivalent to the volumetric expansion of the water and contraction of the pore space.

Annual change in storage in fractured bedrock was considered negligible as the fractures are the only water-holding structures and these systems typically have a low specific yield. Furthermore, groundwater extraction in fractured rock areas is limited in volume. 

The spatially-varying specific yield values considered in the Port Phillip and Western Port groundwater model are used in these estimations.

A 10 km buffer around bores was used to acknowledge the spatial variability of groundwater levels and the density of  the data available.

The purpose of this note is to provide a consolidated report on the urban water system within the region during the 2010–11 year. Information on all water flows to and from the urban water system are presented here, including between store flows and transfers that are not presented in the water accounting statements.

The urban water system within the Melbourne region primarily supplies the Melbourne metropolitan area. Public water system-related line item values in the water accounting statements represents the volume of water held in pipes and tanks that make up part of the Melbourne area's potable water supply system as shown in Table 8.

Volumetric information relating to the urban system is provided by the operators listed below. More information on the urban water system in the Melbourne region is available from the following websites:

• Melbourne Water
• City West Water
• South East Water
• Yarra Valley Water
• Western Water.

Table 8 shows that the volume of water in the urban water system changed little during the 2010–11 year in the Melbourne region.

Table 8. Urban water system store volume at the start and end of the 2010–11 year

	30 June 2011 (ML)	30 June 2010 (ML)
3 Urban water system
3.1 Urban water supply system	–	–
3.2 Wastewater collection system	24,219	24,737
3.3 Recycled water supply system	–	735
Total	24,219	25,472

A volume was not presented in the water accounting statements for urban water supply systems. Water used to supply the urban system is stored in surface water storages and presented as 1.1 Storages.

The recycled water supply system could not be quantified accurately due to a lack of available data for the 2010–11 year. Given that this system is smaller than the wastewater supply system, the volume of water within the recycled water supply would have been relatively small and its exclusion from the water accounting statements is not considered to be material.

A schematic diagram representing all the inflows and outflows associated with the urban water system in the Melbourne region is provided in Figure 6. The inflow and outflow volumes for the urban water system during the 2010–11 year are given in Table 9. In addition to flows reported in the water accounting statements, Figure 6 and Table 9 also show flows between water stores that are part of the region.

Figure 6. Schematic diagram of water inflows (blue arrows) and outflows (red arrows) for the urban water system during the 2010–11 year. Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.

 

Table 9. Volumes of inlfows and outflows for the urban water system during 2010–11 year.

	Volume (ML)
11 Urban water system inflows
11.1 Precipitation on urban water system	–
11.4 Wastewater collected	362,668
11.12 Allocation diversion of surface water to urban water system	353,431
Total 11 Urban water system inflows	716,099
19 Urban water system outflows
19.2 Leakage to landscape	10,779
19.3 Leakage to groundwater	18,636
19.4 Delivery to urban water system users	343,166
19.5 Urban water discharge to surface water	15,390
19.7 Wastewater discharge outside of region	304,745
19.8 Other wastewater discharge	46
19.11 Transfer of water outside of region	53
19.20 Other urban water decreases	9,318
Total 19 Urban water system outflows	702,133
Balancing item – urban water system	15,219
Change in urban water system storage	(1,253)
Opening urban water system storage	25,472
Closing urban water system storage	24,21

Line items in italic represent between-store flows, which are not presented in the water accounting statements as they occur within the region.

The urban system receives most of its water from diversion of surface water (11.12 Allocated diversion of surface water to urban water system) and collection of wastewater (11.4 Wastewater collected). Information about the water access entitlements and water allocations under which surface water and groundwater are abstracted for the urban water system is given in the Water rights, entitlements, allocations and restrictions note.

Most of the treated wastewater from the urban water system is discharged into the sea (19.7 Wastewater discharge outside of region). The volume reported in the water accounting statements is the volume of wastewater discharged from the Melbourne region to Port Phillip Bay and Bass Strait.

This volume represents the volume necessary to reconcile the opening and closing balances of the urban water system store with the physical water inflows and outflows. The Balancing item – urban water system store is calculated according to Table 10.

Table 10. Balancing item for the urban water system for the 2010–11 year

	Account	Volume (ML)
	Opening balance (30 June 2010)	25,472
add	Total 11 Urban water system inflows	716,099
less	Total 19 Urban water system outflows	702,133
less	Closing balance (30 June 2011)	24,219
	Balancing item – urban water system store	15,219

The calculation of the water balance on the urban water system yielded a balance of 15,219 ML.

This note complements the System's interactions with the region note. It gives the following additional information:

• split of the urban water flows according to the sub-systems they affect by water type, source and quality
• flows between sub-systems, which are not reported in the System's interactions with the region note as they occur within the urban water system itself
• split of the total urban water use into several components.

The urban water system is made up of three sub-systems which serve the urban water users:

• the urban water supply system
• the wastewater collection system
• the recycled water system.

The main urban water users are residential, commercial, industrial and municipal consumers.

The urban water supply system collects water from various sources including surface water, groundwater, marine desalinated water and transfers-in across the region's geographical boundaries. It treats and distributes water to urban water users. Part of the water is used outdoor (e.g. garden use) while the rest is collected into the wastewater collection system. Wastewater is treated and then discharged to surface water, the sea or the landscape, or delivered into the recycled water system. The recycled water system, in turn, distributes treated water to users.

Tables 11 to 13 show the balance of each sub-system, including its inflows, outflows, balancing item and percentage error of the balancing item compared to the total of the inflows. The balancing items are calculated as the difference between the inflows less the outflows, considering that the changes in storage are not material. The values of the balancing items reflect measurement and data handling errors and/or missing data.

Table 14 shows a breakdown of the total urban water use per use sectors and type of water (potable, non-potable and recycled).

For each row in the Tables 11 to 14, correspondence is given to the line items that are reported in the Water accounting statements and the System's interactions with the region note. The correspondence can either be:

• line item A – meaning a one to one correspondence of the volume in the table with the line item A
• part of line item A – meaning that the volume in the table is a part of the line item A
• line item A + line item B – meaning that the volume in the table is the sum of line items A and B
• part of line item A + line item B – meaning that the volume in the table is the sum of a part of line items A and a part of line item B
• not applicable – in the case when there is no correspondence to a line item.

When a volume in a table is given as '0' it means that the value has been evaluated as nil for the 2010–11 year. When the volume in a table is given as dash (–), it means that the volumes could not be quantified for the 2010–11 year.

Supporting information and quantifications approaches for each volume shown in the tables 11 to 14 can be accessed via links on the line item numbers. In the cases when there is no corresponding line item, the supporting information and quantification approaches are given at the end of the note.

Table 11. Balance of the regional urban water supply for the 2010–11 year

	Volume (ML)	Line item
Inflow component
Precipitation on urban water system	–
Surface water diverted	355,609	11.12, 17.14, part of 19.4A, part of 19.2 & 19.3B, & additional urban note 1
Groundwater abstracted	12	Part of 18.11
Desalinated water produced	–
Total potable water imported	0
Total non-potable water imported	0
Total inflow	355,621
Outflow component
Evaporation	–
Potable water flow back to storage	–
Non-potable water exported	288	19.11 & 17.14
Potable water supplied to water users	45	Part of potable component of 19.4A
Potable water supplied to water users	315,769	Part of potable component of 19.4C
Non-potable water supplied to water users	364	Non-potable component of 19.4
Sub-total water supplied to water users/consumption	316,466
Water lost due to pipe bursts and losses to landscape	10,779	19.2
Water lost due to leakage	18,636	19.3
Other non-revenue water losses	9,318	19.20
Sub-total losses (including pipe bursts, leakage and other )	38,733
Total outflow	355,199
Balance (inflows less outflows)	422
Error	0.12%

^A –  The 45 ML of potable water supplied from Southern Rural Water via Western Water to the Bacchus Marsh irrigation district 

^B – The Melbourne Water losses/leakages to landscape (19.2) and groundwater (19.3)

^C – The volume of potable water supplied to users reported at line item 19.4, except the 45 ML of potable water from Southern Rural Water to the Bacchus Marsh irrigation district

The misbalance in Table 11 is the difference between total inflow and outflow and can be attributed to possible differences in metering accuracies and unaccounted losses associated with water intake and supply.

Table 12. Balance of the regional wastewater collection system for the 2010–11 year

	Volume (ML)	Line item
Inflow component
Wastewater treated  by Melbourne Water	335,764	Additional urban note 2
Wastewater treated by retail water authorities	37,210	Additional urban note 3
Total inflow	372,974
Outflow component
Wastewater (treated) discharged to surface water	15,390	19.5
Wastewater (treated) discharged to landscape	46	19.8
Wastewater (treated) discharged to sea	304,745	19.7
Sub-total treated wastewater discharged	320,181
Recycled water used on-site in-process	18,182	Additional urban note 4
Recycled water used on-site for outdoor irrigation	9,328	Additional urban note 5
Sub-total recycled water used on-site	27,510
Wastewater treatment process losses	–
Treated wastewater supplied as recycled water	26,872	Part of 19.4A
Total outflow	374,563
Balance (inflows less outflows)	–1,589
Error	0.42%

^A – This volume approximates the volume of recycled water supplied to users, reported at line item 19.4. The volume of 26,872 ML is the actual volume of water supplied from the wastewater collection system to the recycled water system. The flow from wastewater collection to recycled water system is not reported in the water accounting statements because this is considered to be a flow within the urban water store.

The misbalance in Table 12 is due to meter errors, errors due to metering locations, errors in estimating recirculated volumes, data handling errors, estimation errors from databases and missing items from temporal values.

Table 13. Balance of the regional recycled water system for the 2010–11 year

	Volume (ML)	Line item
Inflow component
Recycled water from wastewater system	26,872	Part of 19.4A
Recycled water received from TopAq Water and from Inkerman Greywater Treatment Plant	140	Additional urban note 6
Total inflow	27,012
Outflow component:
Recycled water supply to irrigation/outdoor	3,737	Part of 19.4
Recycled water supplied to irrigation schemes (Western Treatment Plant to Southern Rural Water – Werribee Irrigation District; Eastern Treatment Plant to Eastern Irrigation Scheme)	3,412	Part of 19.4
Sub-total recycled water supplied for outdoor/irrigation use	7,149
Western Treatment Plant to Southern Rural Water – Werribee Tourist Precinct use	43	Part of 19.4
Supply to urban water use	1,072	Part of 19.4
Recycled water supplied to environment	18,723	Part of 19.4
Recycled water exported	–
Total outflow	26,987
Balance (inflows less outflows)	24
Error	0.09%

^A – This volume approximates the volume of recycled water supplied to users, reported at line item 19.4. The volume of 26,872 ML is the actual volume of water supplied from the wastewater collection system to the recycled water system. The flow from wastewater collection to recycled water system is not reported in the water accounting statements because this is considered to be a flow within the urban water store.

The imbalance in Table 13 is the difference between the volume of recycled water available for supply and the volume of recycled water supplied for use, and can be attributed to metering inaccuracies and unaccounted losses.

Table 14. Regional Urban water consumption for the 2010–11 year

	Potable		Non-potable		Recycled		Total (ML)
	Volume (ML)	Line item	Volume (ML)	Line item	Volume (ML)	Line item
Residential	225,223	Part of 19.4	48	Part of 19.4	168	Part of 19.4	225,439
Commercial, industrial and municipal uses	90,546	Part of 19.4	312	Part of 19.4	905	Part of 19.4	91,763
Other uses:
Agricultural/individual irrigation					3,737	Part of 19.4	3,737
Irrigation water supply systems/schemes	45	Part of 19.4	–		3,412	Part of 19.4	3,457
Environment	–		–		18,723	Part of 19.4	18,723
Other uses			4	Part of 19.4	43	Part of 19.4	47
Total supplied to uses other than residential, commercial, municipal  and industrial	45		4		25,915		25,964
Total volume supplied (excluding non-revenue water and on-site use of recycled water)	315,814		364		26,988		343,166

Figure 7 represents the inflows and outflows reported in tables 11 to 14 that occur between and within urban sub-systems and between urban systems and urban users. Flows that occur in the urban water system but could not be quantified are faded out.

Figure 7. Schematic diagram of water inflows and outflows for the urban sub-systems. Flow volumes and the corresponding line item number are provided next to the arrows and are shown in [] or with reference to the appropriate table number. Faded out arrows indicate flows that could not be quantified.

There are four unquantified inflow and outflow components in Figure 7. Insufficient data were available to quantify these volumes; however, they are important components of the urban water balance.

Individually abstracted water includes water abstracted from surface water, groundwater or rainwater by individual users. That is, water diverted from a stream, pumped from a domestic garden bore or sourced from a rainwater harvesting system.

The unquantified stormwater component represents stormwater that is claimed and then used by urban water consumers such as that which is collected, treated and used in municipal stormwater schemes or projects.

The outflow of water to landscape/outdoor represents the unquantified volume of water that urban users apply or discharge to the landscape. This includes garden, park and sports field watering, car washing and paved surface cleaning.

The unquantified line item [11.7] indicates groundwater or stormwater ingress into the stormwater system.

Volume: 830 ML

The volume of 830 ML was diverted from surface water by Western Water during the 2010–11 year and is shown in the following table.

Volumes per surface water intake point

Surface water intake point	Volume (ML)
Mariages Water Treatment Plant	348
Romsey Water Treatment Plant	284
Lancefield Water Treatment Plant	145
Macedon storage	53
Total	830

Data source

Western Water: metering database.

Data provider

Western Water.

Method

This item represents the total weekly metered volume of surface water taken from Kerrie, Djerriwarrah, Garden Hut and Wright reservoirs, and treated at the Mariages, Romsey and Lancefield water treatment plants. It also represents water taken from Macedon storage for non-potable water provided to Woodend. Meters are located on outlet pipes from reservoirs.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty

The uncertainty estimate was +/– 5% in accordance with the manufacturer's annual bulk meter test.

Volume: 335,764 ML

The Western Treatment Plant defines the volume of wastewater treated, 176,604 ML, as the volume of wastewater collected being 180,745 ML, less evaporative losses of 4,141 ML.

The Eastern Treatment Plant defines the volume of wastewater treated, 159,160 ML, as the volume of wastewater collected being 144,563 ML plus the amount of recycled water that is recirculated back into the treatment plant for on-site in-process use, 14,597 ML.

Volume of wastewater treated at Eastern and Western Treatment Plants in the 2010–11 year

Volume of wastewater treated	Volume (ML)
Volume of wastewater treated at the Western Treatment Plant	176,604
Volume of wastewater treated at the Eastern Treatment Plant (including 14,597 ML of wastewater treated and recirculated back into the treatment plant for on-site in-process use)	159,160
Total	335,764

Data source

Melbourne Water: ASPEN and supervisory control and data acquisition (SCADA) databases.

Data provider

Melbourne Water.

Method

This item represents the total metered volume of wastewater treated by Melbourne Water. Wastewater is metered at the influent pump stations of both the Eastern Treatment Plant and Western Treatment Plant. The treatment plants have primary inflow metering, as well as additional metering to record the inflows should the primary metering be offline.

Assumptions, limitations, caveats and approximations

The Western Treatment Plant logs data daily and reports quarterly. The Eastern Treatment Plant logs data daily and reports monthly. Thus, metering periods align with the reporting period.

Uncertainty

Wastewater inflows are measured using magnetic flow meters, which are assumed to be accurate to within +/– 5%.

Volume of wastewater inflow for treatment and volume of wastewater treated are expected to be the same.

Volume: 37,210 ML

Volume of wastewater treated by water authorities

Water authority	Volume (ML)
City West Water	5,773
South East Water	13,289
Yarra Valley Water	10,698
Western Water	7,450
Total	37,210

City West Water

Wastewater treated – City West Water

Wastewater treated	Volume (ML)
Altona Wastewater Treatment Plant	5,773
Sunshine Golf Club sewer mining plant	0
Total	5,773

Data source

City West Water: supervisory control and data acquisition (SCADA) database.

Data provider

City West Water.

Method

This item represents the metered volume of wastewater treated at City West Water wastewater treatment plants and sewer mining plants. Meters are located at both these plants and are read on a daily basis.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty

The uncertainty estimate was in the range of +/– 5%.

South East Water

Data source

South East Water's database.

Data provider

South East Water.

Method

This item represents the daily metered volume of wastewater treated at South East Water sewage treatment plants.

Daily metered volume of wastewater treated at South East Water

Sewage treatment plant	Volume (ML)
Blind Bight	182
Hastings (Somers)	1,781
Koo Wee Rup	187
Lang Lang	78
Longwarry	282
Mornington (Mount Martha)	4,860
Pakenham (Deep Creek)	2,349
Rosebud (Boneo)	3,570
Total	13,289

Assumptions, limitations, caveats and approximations

Assumes meters and readings are accurate.

Uncertainty

Estimated to be +/– 5% in accordance with the Water Industry Regulatory Audits 2011 independent annual audit report (South East Water 2011).

 

Western Water

Volumes of wastewater treated at Western Water

Wastewater treatment plant	Volume (ML)
Bacchus Marsh	576
Melton	3,343
Riddells Creek	263
Romsey	525
Sunbury	2,192
Gisborne	551
Total	7,450

Data source

Western Water: plant data.

Data provider

Western Water.

Method

This item represents the total volume of wastewater entering wastewater treatment plants within the Melbourne region (excluding Woodend). Meters are at the entrance to the plant and record all incoming water. Meters are read daily by the treatment plant operators.

Assumptions, limitations, caveats and approximations

Wastewater collected and treated assumed to be the same.

Uncertainty

Estimated to be +/– 5% in accordance with Summary Audit Report – October 2010 (Essential Services Commission 2010).

 

Yarra Valley Water

Volumes of wastewater treated by Yarra Valley Water

Wastewater treatment plant	Volume (ML)
Brushy Creek	4,328
Craigieburn	792
Healesville	550
Upper Yarra	934
Lilydale	2,646
Monbulk	21
Whittlesea	290
Aurora	532
Wallan	605
Total	10,698

Data source

Yarra Valley Water local treatment plants flow database.

Data provider

Yarra Valley Water.

Method

This item represents the metered volume of wastewater treated at Yarra Valley Water local treatment plants. Meters at the plants are read daily.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty

Estimated to be +/– 10%.

Volume: 18,182 ML

The volume of 18,182 ML of recycled water was used on-site in process at wastewater treatment plants during the 2010–11 year and is shown in the following table, itemised by water authority. Quantification approaches for each water authority are also detailed below.

Volume of recycled water used on site for each water authority

Water authority	Volume (ML)
City West Water	98
Yarra Valley Water	1,854
South East Water	889
Western Water	744
Melbourne Water	14,597
Total	18,182

City West Water

Data source

City West Water: supervisory control and data acquisition (SCADA) system.

Data provider

City West Water.

Method

This item represents the metered volume of recycled water used in-process at the Altona Wastewater Treatment Plant. Meters are read on a daily basis.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty

The uncertainty estimate was not quantified.

 

Western Water

Location of wastewater treatment plant where recycled water was used on-site in process

Wastewater treatment plant	Volume (ML)
Bacchus Marsh	0
Melton	168
Riddells Creek	1
Romsey	0
Sunbury	247
Gisborne	328
Total	744

Data source

Western Water: water usage spreadsheet.

Data provider

Western Water.

Method

This item represents the total metered volume of recycled water used on-site for wastewater treatment processes at Western Water's recycled water plants. Meters are read monthly.

Assumptions, limitations, caveats and approximations

Part of the volume used on-site for wastewater treatment processes re-enters the system. Therefore, the volumes may not be accurate at some plants.

Uncertainty

Estimated to be +/– 5% in accordance with Summary Audit Report – Regulatory Audit of AGL Energy Limited, October 2010 (Essential Services Commission 2010).

South East Water

Volumes of water used on-site in-process for each sewage treatment plant

Sewage treatment plant	Volume (ML)
Blind Bight	47
Hastings (Somers)	18
Koo Wee Rup	0
Lang Lang	0
Longwarry	0
Mornington (Mount Martha)	744
Pakenham (Deep Creek)	39
Rosebud (Boneo)	41
Total	889

Data source

South East Water: database.

Data provider

South East Water.

Method

This item represents the daily metered volume of recycled water used for in-process and on-site outdoor water at South East Water's sewage treatment plants. 

Assumptions, limitations, caveats and approximations

Assumes meters and readings are accurate.

Uncertainty

Estimated to be +/– 5% in accordance with the Water Industry Regulatory Audits 2011 independent annual audit report (South East Water 2011).

Yarra Valley Water

Volumes of recycled water used on-site in-process, per wastewater treatment plant

Wastewater treatment plant	Volume (ML)
Brushy Creek	802
Craigieburn	143
Healesville	130
Upper Yarra	202
Lilydale	389
Wallan	0
Monbulk	0
Aurora	162
Whittlesea	25
Total recycling water used in-process	1,854

Data source

Water Balance Audit report.

Data provider

Yarra Valley Water.

Method

This item represents the metered volume of recycled water used for in-process water at Yarra Valley Water's local treatment plants.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty

Estimated to be +/– 5%.

 

Melbourne Water

The volume of recycled water used on-site in-process at Melbourne Water's Eastern Treatment Plant during the 2010–11 year was 14,597 ML.

Data source

Melbourne Water: ASPEN and supervisory control and data acquisition (SCADA) databases.

Data provider

Melbourne Water.

Method

This item represents the total metered volume of recycled water used on-site at Melbourne Water's wastewater treatment plants. On-site recycled water is measured by Melbourne Water at the Eastern and Western treatment plants, using ultrasonic level transmitters.

Assumptions, limitations, caveats and approximations

The Eastern Treatment Plant logs data daily and reports monthly. Thus, metering periods align with the reporting period.

Uncertainty

Ultrasonic level transmitters are used to measure flows and are assumed to have an accuracy of +/– 5 to +/– 10%.

The volume of recycled water used on-site for outdoor/irrigation use at Melbourne Water's Western Treatmtent Plant during the 2010–11 year was 9,328 ML.

Data source

Melbourne Water: ASPEN and supervisory control and data acquisition (SCADA) databases.

Data provider

Melbourne Water.

Method

This item represents the total metered volume of recycled water used on-site at Melbourne Water's wastewater treatment plants. On-site recycled water is measured by Melbourne Water at the Eastern and Western treatment plants, using ultrasonic level transmitters.

Assumptions, limitations, caveats and approximations

The Western Treatment Plant logs data daily and reports quarterly.

Uncertainty

Ultrasonic level transmitters are used to measure flows and are assumed to have an accuracy of +/– 10%.

Volume: 140 ML

Recycled water received from external organisations within the region

Recycled water received from other organisations within the region	Volume (ML)
Recycled water purchased from TopAq Eastern Irrigation Scheme	139
Recycled water received from Inkerman Greywater Treatment Plant	1
Total	140

Data source

South East Water database.

Data provider

South East Water.

Method

This item represents the quarterly metered volume of recycled water purchased and received from TopAq Eastern Irrigation Scheme, and received from Inkerman Greywater Treatment Plant.

Assumptions, limitations, caveats and approximations

• Assumes meters and readings are accurate.
• The TopAq Eastern Irrigation Scheme meter-reading cycle does not align with the 1 July 2010 – 30 June 2011 reporting year; however, it does cover a 12-month period that is consistently applied each year.

Uncertainty

Estimated to be +/– 5% in accordance with the Water Industry Regulatory Audits 2011 independent annual audit report (South East Water 2011).