Melbourne
Supporting information
Introduction
The following set of notes provides consolidated reports for each of the water stores and systems within the Melbourne region during the 2013–14 year. The water stores and systems included in the region are shown in Figure 1.
For more information about the region, please refer to the General description section of the 'Contextual information'.
Figure 1 Water stores and systems within the Melbourne region
Information on all water flows to and from each water store and system are presented in the following set of notes, including between-store flows and transfers that are not presented in the water accounting statements. The between-store flows and transfers that occur in the region are presented in Figure 2.
Figure 2 Between-store flows that occur within the Melbourne region
The between-store flows and transfers (Figure 2), which are eliminated from the region's water accounting statements, are shown in italics throughout the following set of notes. The allocation announcement, forfeiture, and allocation remaining line items associated with each between-store abstraction (brown arrows in Figure 2) are also shown in italics in the following notes.
Surface water store
Surface water assets
The volume of the surface water assets comprised of water held in storages, regulated and unregulated rivers, and surface water claims.
Storages
The volume of water held in storages was 581,952 ML at end of the 2013–14 year. The location of each storage within the Melbourne region and the volume of water in each storage (including dead storage) as a percentage of total storage capacity at the end of the 2013–14 year is shown in Figure 3.
Figure 3 Percentage-full volume on 30 June 2014 for each storage
Thomson Reservoir, which is the largest storage supplying water to Melbourne metropolitan area, is beyond the Melbourne region boundary. Therefore, it is not shown in Figure 3. Water sourced from Thomson Reservoir to the region is treated as an inter-region transfer.
The overall storage volume within the Melbourne region during the 2013–14 year was slightly less than that during the previous year at 68% capacity. Five storages showed a decrease in volume while others showed increases. The majority of the storages are connected through supply networks; therefore, volume fluctuations during the 2013–14 year in individual storages are not a major concern.
Catchment runoff was the main contributor to storage volumes. During the 2013–14 year, 412,400 ML of surface water runoff reached the storages within the region. This volume is just 23% of the total runoff that reached rivers, storages, and wetlands within the region. The runoff volume to storages was 6% less than that observed for the previous year.
Storage volumes also include inter-region water transferred from Thomson Reservoir and Silver and Wallaby creeks (see Surface water claims and Water received under inter-region agreements).
Total volume of water within each storage at 30 June 2014 and at the end of the previous three years (2012, 2011, and 2010) is given in Figure 4.
Figure 4 Total volume of water in each storage at 30 June 2011, 2012, 2013 and 2014
Regulated and unregulated rivers
The volume of water in regulated and unregulated rivers could not be quantified due to a lack of available data. Regulated and unregulated rivers within the Melbourne region that could not be quantified are as follows (Figure 5):
- Yarra and Bunyip are unregulated rivers.
- The Maribyrnong River is regulated along Jacksons Creek downstream of Rosslynne Reservoir. Deep Creek is unregulated upstream of its confluence with the Maribyrnong River.
- The Werribee River is regulated downstream of the point where releases from Pykes Creek Reservoir enters the river. Tributaries of the Werribee River, the Lerderderg River, Pyrites Creek, and Djerriwarrh Creek are all unregulated upstream of the storages.
Figure 5 Regulated and unregulated river channels in the Melbourne region
Surface water claims
Surface water claims in the Melbourne region refer to the remaining volume of surface water that Melbourne retail water authorities were entitled to under bulk entitlements and agreements at the end of the 2013–14 year. There were claims associated with:
- bulk entitlements for Thomson Reservoir and Silver and Wallaby creeks
- rights to water from Goulburn and Murray systems (water held in Lake Eildon)
- bulk entitlements to desalinated water from the Wonthaggi desalination plant.
Inter-region claims for water from all the sources at the beginning and end of the 2013–14 year are summarised in Table 1.
| Account: inter-region claims | Volume (ML) |
| Opening balance at 1 July 2013 | 794,979 |
| Increase of inter–region surface water claim on water | 217,587 |
| Delivery of water under inter–region agreement to surface water | (134,084) |
| Decrease of inter–region surface water claim on water | (62,565) |
| Closing balance at 30 June 2014 | 815,917 |
Inter-region claim for water in the Thomson Reservoir
The inter-region claim for water in the Thomson Reservoir was 777,516 ML at the end of the 2013–14 year. This volume represents a 3% increase compared to the previous year. This reflects the delivery of less water than entitled, a trend observed in the recent past (Figure 6).
Figure 6 Inter-region claim for water in the Thomson Reservoir
Inter-region claim for water from the Silver and Wallaby creeks
Unused water allocated under the Silver and Wallaby creeks bulk entitlement is not carried over to the following year. As a result, the opening and closing balance of the claim remains zero for this source.
Inter-region claim on rights to water from Goulburn and Murray systems
The inter-region claim to water from Goulburn and Murray systems (held in Lake Eildon) was 38,401 ML at end of the 2013–14 year, which is a slight decrease than the previous year.
Claim for desalinated water from the Wonthaggi desalination plant
Melbourne's retail water authorities, City West Water, South East Water, and Yarra Valley Water hold bulk entitlements to desalinated water from the Wonthaggi desalination plant. The bulk entitlements allow them to take a combined volume up to 150,000 ML each year on an annual basis during any period of five consecutive years (subject to rules specified in the bulk entitlements). The Victorian Government has placed zero water order from the desalinated plant for 2013–14 and 2014–15 years. As a result, the desalinated claim at end of the 2013–14 year was considered as zero for the National Water Account 2014 (2014 Account).
Surface water liabilities
Surface water liabilities in the Melbourne region refer to the volume of surface water allocation remaining on licensed entitlements at the end of the 2013–14 year for:
- individual users (4,834 ML)
- urban water system (495,189 ML)
- inter-region commitment (0 ML).
Individual users
The allocation remaining for individual users is provided in Table 2.
| Account: individual users | Volume (ML) |
| Opening balance at 1 July 2013 | 0 |
| Surface water allocation announcements | 16,545 |
| Entitled diversion of allocated surface water to individual users | (9,844) |
| Adjustment and forfeiture of surface water allocation | (1,867) |
| Closing balance at 30 June 2014 | 4,834 |
Carry-over of unused water allocated for high-reliability and low-reliability water shares in the Werribee and Bacchus Marsh irrigation districts was not permitted in the previous years. The Victorian Minister for Water approved carry-over provisions for the two irrigation districts on 22 June 2014. As a result, unused water in an allocation account at the end of the water year could be carried over to a limit of 100% of the entitlement volume subject to a 15% evaporation loss.
Urban water system
The allocation remaining for the urban water system is provided in Table 3.
| Account: urban water system | Volume (ML) |
| Opening balance at 1 July 2013 | 495,189 |
| Surface water allocation announcements | 499,506 |
| Entitled diversion of allocated surface water to urban water system | (415,334) |
| Adjustment and forfeiture of surface water allocation | (84,172) |
| Closing balance at 30 June 2014 | 495,189 |
Within the Melbourne region, several bulk entitlements are in place that govern the source, volume, and arrangements under which the retail water authorities can divert surface water for urban water supply. Each bulk entitlement specifies an annual (or rolling annual average) volumetric upper limit; however, formal annual allocations are not made. As allocations are not made, carry-over of allocations is not possible.
Under the majority of the bulk entitlements, however, the retail and regional water authorities are entitled to a share of storage. This fluctuates annually depending on inflows to (rainfall, runoff) and outflows (evaporation, other losses) from the storages. This share of storage, at the start and end of the year, is recognised as carry-over as shown in Table 3.
Inter-region commitment
Gippsland Water has a right to water from the Tarago River under Bulk Entitlement (Tarago River–Gippsland Water) Conversion Order 2009. As the bulk entitlement has not made provision for a share of storage, carry-over of unused water is not permitted. Therefore, the volume reported as the opening and closing balance of the inter-region commitment on surface water was zero.
Surface water inflows and outflows
A schematic diagram representing all the inflows and outflows associated with the surface water store in the Melbourne region is provided in Figure 7.
Figure 7 Water inflows and outflows for Melbourne's surface water store during the 2013–14 year
Surface water inflows
Runoff to surface water
The largest water inflow was runoff to surface water (1,768,154 ML) during the 2013–14 year. This volume is about 93% of that during the previous year, which reflects the below average rainfall experienced across the region for the second year in a row (see Climate overview). The volume comprised of inflow to rivers and surface water storages. Inflow to surface water storages was 412,400 ML which is 23% of total runoff volume (see Surface water assets).
The other natural surface water inflows
The remaining natural surface water inflow is precipitation on surface water (39,796 ML). The volume of precipitation represents rainfall that fell on the major storages within the region. The other notable natural surface water inflow, the groundwater discharge to surface water, could not be quantified due to lack of data. The Port Phillip and Western Port Catchment Management Authority reports that the main watercourses in the Melbourne region gain flow from groundwater discharge along the majority of their length (Department of Sustainability and Environment 2010a).
Water received under inter-region agreements
The largest surface water source after runoff to surface water was water received under inter-region agreements comprised of:
- Thomson Reservoir (132,197 ML)
- Silver and Wallaby creeks (1,880 ML)
- Goulburn and Murray systems (7 ML)
Melbourne's retail water authorities, City West Water, South East Water, and Yarra Valley Water receive water from Thomson Reservoir and Silver and Wallaby creeks under their bulk entitlements.
Water stored in Thomson Reservoir is delivered to Upper Yarra Reservoir for distribution to Melbourne's water supply system. The volume of water received from the Thomson Reservoir during the 2013–14 year was over five times the volume delivered during the previous year (25,148 ML). The increase is largely due to below-average inflows to the surface water storages within the Melbourne region in the reporting year and increased water availability in the Thomson Reservoir.
Water is diverted from Silver and Wallaby creeks and delivered to Tooroorung Reservoir and Yan Yean Reservoir for distribution to Melbourne's water supply system. The volume received during the 2013–14 year represented a 75% increase on that of the previous year volume (1,071 ML).
Water stored in Lake Eildon (rights to water from Goulburn and Murray systems) is delivered to Sugarloaf Reservoir via the North–South pipeline for distribution to Melbourne's water supply system. The volume diverted (7 ML) during the 2013–14 year was for maintenance purposes. This water was not used in the Melbourne region.
The other surface water inflows
The remaining two transfers of water to the surface water store during the 2013–14 year were, discharge from the urban water system (29,318 ML), and return flow from irrigation systems (61 ML). Discharge from the urban water system comprised of:
- treated wastewater discharged to surface water from South East Water's wastewater treatment plants (WWTP), Western Water's recycled water plants (RWPs), and Yarra Valley Water's local treatment plants (LTPs)
- excess nonpotable water released to Glenfern service basin and Rosslynne Reservoir by Western Water
- recycled water provided from the Melbourne Water Western Treatment Plant as environmental flows to the Lake Borrie wetlands (Ramsar-listed).
Return flow from irrigation systems represents return flows from Bacchus Marsh Irrigation District into the Lerderderg River, which then flows into Melton Reservoir on the Werribee River. The volume for the 2013–14 year was a slight decrease compared to the previous year.
Although the Wonthaggi desalination plant was operational during the reporting year, water was not delivered to the region during the 2013–14 year. This was because The Victorian Government had placed an order not to deliver desalinated water during the 2013–14 year. Consequently, desalinated water is yet to be delivered under bulk entitlements after commissioning the plant.
Surface water outflows
The largest natural water outflow is river outflow from the region (1,274,041 ML), which refers to the annual volume of flow to the sea from the Bunyip, Yarra, Maribyrnong, and Werribee rivers during the 2013–14 year. This outflow is approximately 93% of river outflow during the previous year, reflecting lower flows and water availability during the 2013–14 year compared to the 2012–13 year (see Water overview).
Evaporation from surface water during the 2013–14 year was 44,132 ML, which represents evaporation from the major storages within the region. Total evaporation during the 2013–14 year is approximately 94% of that during the previous year, which may be attributed to declining rainfall observed for two years in a row and hence water availability (see Climate overview).
The volume of water diverted under the Tarago River–Gippsland Water bulk entitlement by Gippsland Water (3,526 ML) comprised of:
- Labertouche Creek at Labertouche Weir (0 ML)
- Pederson Weir / Westernport Pipeline (3,252 ML)
- Tarago Reservoir (Neerim South) (239 ML)
- Diversion made under drought contingency allocation for Gippsland Water from Tarago Reservoir (35 ML).
Entitled water diversions from the surface water store are described in Entitled water diversions below.
The volume of surface water leakage to landscape and groundwater and diversions made under other statutory rights (private right to abstract and use water for domestic and stock use without an entitlement) could not be quantified accurately due to a lack of available data.
Entitled surface water diversions
Non-allocated surface water diversions
Figure 8 presents entitled diversion of non-allocated surface water within the Melbourne region for most recent four years. Non-allocated water diversions for the 2013–14 year (13,682 ML) were almost same as the volume diverted during the previous year.
Figure 8 Non-allocated water diversions within the Melbourne region
Non-allocated surface water diversions represent the volume of water diverted under take and use licences issued for irrigation, stock and domestic, commercial and industrial, and other purposes. Take-and-use licences specify a maximum entitlement volume but this does not represent a surface water liability. Take-and-use licences exist for unregulated sections of the Bunyip, Maribyrnong, Werribee, and Yarra rivers as well as regulated sections of the Maribyrnong and Werribee rivers.
Allocated surface water diversions
Entitled diversion of allocated surface water within the Melbourne region occur for the following two purposes:
- entitled diversion of allocated surface water to the urban water supply system under the various bulk entitlements held by Melbourne's retail water authorities
- entitled diversion of allocated surface water for individual users.
Most of the entitled diversion of allocated surface water in the Melbourne region is to the urban water system. During the 2013–14 year, 415,334 ML of surface water was diverted from storages to Melbourne's urban water supply system, which accounts for about 98% of the total allocation diversion (Figure 9).
Figure 9 Volumes received by water authorities under surface water allocation diversion to the urban water systems during the 2013–14 year
The volume reported includes:
- bulk water supplied by Melbourne Water to City West Water, South East Water, and Yarra Valley Water from the Yarra, Tarago, and Bunyip rivers, and water received under inter-region agreements
- bulk water supplied by Melbourne Water to Western Water from the Melbourne Headworks system
- surface water diverted from the Maribyrnong and Werribee river basins by Western Water under various bulk entitlements.
Surface water from the Maribyrnong and Werribee river basins is primarily diverted from storages managed by Southern Rural Water. There are also diversions made from smaller storages operated by Western Water.
The Water access and use note provides more information on relevant bulk entitlements.
Entitled diversion of allocated surface water for individual users during the 2013–14 year was 9,844 ML, which accounts for about 2% of the total allocation diversion. These diversions mainly relate to irrigation water use by high and low reliability entitlement holders in Bacchus Marsh and Werribee irrigation districts (see Surface water allocation announcements below).
Surface water forfeitures
Surface water forfeitures in the Melbourne region during the 2013–14 year relate to forfeiture of claims, allocations, and inter-region commitments.
Forfeiture of surface water claims
Forfeiture of surface water claims in the Melbourne region during the 2013–14 year was 62,565 ML. This volume represents the decrease to the claim that Melbourne retail authorities City West Water, South East Water, and Yarra Valley Water are entitled to under:
- bulk entitlements for Thomson Reservoir and Silver and Wallaby creeks
- agreement for water held in Lake Eildon
- bulk entitlements to desalinated water from the Wonthaggi desalination plant.
The forfeiture volume from the Thomson Reservoir (21,028 ML) was due to a decrease in the retailers' share of storage associated with evaporation, adjustments for environmental flows, and Southern Rural water orders. Evaporation and trades were the reasons for forfeiture (41,537 ML) of entitled water from Lake Eildon. Carry-over provisions are not available, and diversion volume is treated as the claimed volume; therefore, there is no forfeiture of claims for entitled water from Silver and Wallaby creeks.
As desalinated water was not ordered from the Wonthaggi desalination plant, the forfeiture volume was zero.
Forfeiture of surface water allocations
Forfeiture of allocations relates to licence entitlements for:
- individual users (1,867 ML)
- urban water system (84,172 ML).
As per carry-over provisions recently made, carry-over of unused water allocated for high-reliability and low-reliability water shares in the Werribee and Bacchus Marsh irrigation districts has been permitted from 22 June 2014. As a result, a portion of surface water allocation that has not been diverted at the end of the water year is carried-over to the following year, and the remainder is forfeited.
As formal allocations are not made for bulk entitlements held by urban water system, carry-over of allocations is not possible; however, the retail and regional water authorities are entitled to a share of storage. This share of storage, at the start and end of the year, is recognised as carry-over. Decrease in share of storage through evaporation, spills, unaccounted differences from operational management, and other losses is recognised as forfeiture.
Forfeiture of inter-region commitments
The volume presented (365 ML) represents the remaining volume of water at the end of the 2013–14 year (which was not carried-over to the following year) under drought contingency allocation for Gippsland Water from Tarago Reservoir.
The forfeiture volume was zero for water allocated under the Tarago River–Gippsland Water bulk entitlement because formal annual allocations are not made for this bulk entitlement; the volume of water allocated was equivalent to the volume of surface water actually diverted.
Surface water: increase of claims, allocation announcements, and increase of inter-region commitments
Increase of surface water claims
Figure 10 presents increase of surface water claims (217,587 ML) for the Melbourne region as distributed on sources for the 2013–14 year.
Figure 10 Increase of surface water claims for the Melbourne region during the 2013–14 year
The increase of inter-region claims represents the increase in the water available to the Melbourne retail water authorities: City West Water, South East Water, and Yarra Valley Water.
The Thomson volume represents the Melbourne retail water authorities' share of gross inflow and rainfall on the reservoir during the year. The diversion volume (1,880 ML) was the increase of surface water claims for entitled water from Silver and Wallaby creeks. For the agreement to water held in Lake Eildon, allocation announcements (increase of claims) for the Goulburn (25,213 ML) and Murray (14,313) rivers are made once a year around November and are based on audited water savings achieved from modernisation projects in northern Victoria in the previous year (e.g., the 2012–13 year). The volume of water allocated is stored in Lake Eildon.
Surface water allocation announcements
Surface water allocation announcements in the Melbourne region during the 2013–14 year refer to surface water supply to:
- individual users (16,545 ML)
- urban water system (499,506 ML).
Allocation announcements for individual users represent the volume of water allocated in the Bacchus Marsh Irrigation District, Werribee River, and Werribee Irrigation District during the 2013–14 year. Allocations are made according to Southern Rural Water's Werribee and Bacchus Marsh Allocation Method. Allocations are reviewed fortnightly and low reliability water shares do not receive an allocation announcement until high reliability shares reach 100%.
Allocations are made for high reliability and low reliability water shares. In addition, there are a small number of entitlements that are in the process of being converted to water shares. For these entitlements, a supply by agreement arrangement is in place.
Figure 11 shows the details of annual allocation announcement for each user category for all entitlement classes together in the 2013–14 year.
Figure 11 Surface water allocation announcements to individual users for each licence purpose for the 2013–14 year
The surface water allocation announcements for the urban water system represent the increase in the volume of water available to the retail water authorities. This includes increases in the retailer's share of storage and increases in the entitlement equivalent to the delivery volume where a share of storage is not applicable. A more detailed description of surface water allocations and associated water rights in the Melbourne region is given in the Surface water rights note.
Increase of inter-region commitments
The volume presented (3,891 ML) represents the following water allocations for Gippsland Water:
- the volume of water allocated under the Tarago River–Gippsland Water bulk entitlement (3,491 ML)
- drought contingency allocation from Tarago Reservoir (400 ML).
Although a volumetric limit was specified for the Tarago River–Gippsland Water bulk entitlement, formal annual allocations are not made. Therefore, the volume of water allocated is equivalent to the volume of water diverted from the Tarago–Westernport Pipeline, Tarago Reservoir, Labertouche Creek, and Pederson Weir (see Surface water outflows for more details).
Surface water balancing item
The balancing item volume represents the difference between the measured opening and closing balances of the surface water store, after physical inflows and outflows have been applied (Table 4). This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete surface water store balance.
Account: surface water store | Volume (ML) |
Opening balance (at 1 July 2013) | 582,979 |
Total surface water inflows | 1,971,413 |
Total surface water outflows | (1,760,559) |
Closing balance (at 30 June 2014) | (581,952) |
Balancing item | 211,881 |
The calculation of the water balance on the surface water store yielded a balancing item of 211,881 ML. This is approximately 37% of the total surface water store volume at the end of the 2013–14 year and around 11% of the total surface water inflows during the 2013–14 year. The positive balancing item indicates that either inflows have been overestimated or outflows have been underestimated.
It is likely that the balancing item is primarily attributed to errors associated with the rainfall runoff volumes (Runoff to surface water), a large source of surface water increase. 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. As a consequence, the modelled runoff is likely to be an overestimate of the volume that actually entered the surface water store.
The portion of the catchment that is ungauged is 38%. River outflow from this ungauged catchment was calculated using the ratio of the mean average flows and included in the 2014 Account (see River outflow from the region). There are uncertainties associated with the calculation method and the gauged flows used in the calculation. Underestimated river outflow from the region resulting from these uncertainties could be another contributing factor to the balancing item.
Groundwater store
Groundwater assets
The aquifers in the Melbourne region are described in the Water resources section of the 'Contextual information'. The groundwater asset volume for the Melbourne region represents permissible consumptive volumes for water table aquifers (22,054 ML) and underlying aquifers (16,565 ML) in groundwater management areas (GMA) and water supply protection areas (WSPA) (Figure 12).
Figure 12 Permissible consumptive volumes: water table and underlying aquifers in the Melbourne region
The groundwater asset volume remained constant during the 2013–14 year as there was no change in licences or the permissible consumptive volume.
The groundwater asset volume does not include the permissible consumptive volume (2,015 ML) for Kinglake GMA as the majority of this GMA (which is included in Upper Goulburn GMA from July 2013) lies outside the boundary of the Melbourne region.
The volume presented does not include groundwater in unincorporated areas outside of groundwater management units. Unincorporated areas have not been evaluated from a groundwater resource perspective and do not have established permissible consumptive volumes. The allocation limit for unincorporated areas in the southern half of Victoria was 71,542 ML.
Groundwater liabilities
Groundwater liabilities in the Melbourne region for the 2013–14 year (0 ML) refer to the volume of groundwater allocation remaining on licence entitlements at the end of the year for individual users and the urban water system.
Carry-over rules for groundwater entitlements throughout the Melbourne region do not allow unused water to be carried over at the end of the year. Therefore, any unused water is forfeited, resulting in a zero carry-over volume.
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 13.
Figure 13 Water inflows and outflows for Melbourne's groundwater store during the 2013–14 year
Groundwater inflows
The largest groundwater inflow is recharge from landscape (338,319 ML), which accounts for approximately 85% of the total groundwater inflow. The volume of recharge during the 2013–14 year was about 88% of that during the previous year, which reflects the below average rainfall experienced across the region for the second year in a row (see Rainfall in 'Climate overview'). Total volume of rainfall over the entire landscape of the Melbourne region was 9,905,900 ML during the 2013–14 year (derived by multiplying the area-averaged rainfall of 845 mm by the area of the region [11,723 km2]), which means that 3% of the total annual rainfall over the Melbourne region contributed to groundwater recharge.
Groundwater inflow from outside the region at the coast (30,504 ML) during the 2013–14 year was relatively similar to the previous year's volume. The volume represents regional groundwater flow at the coastline through major sedimentary and basalt aquifers. The flow includes fresh and saline groundwater. In general, the dominant direction of groundwater flow in the Melbourne region is from the recharge area in the fractured rock aquifers in the north, northwest, and northeast towards Port Phillip Bay, and Western Port in the south. The volume for the 2013–14 year reflects that there was seawater movement towards the coastal aquifers. It should be noted that the interface between the aquifer and the ocean moves throughout the year. During the summer months, when levels in the water table aquifers are relatively low, the saltwater interface moves towards the coastline; however, net flow occurs from the aquifers into the ocean.
Groundwater inflow from outside the region (other than at coast) during the 2013–14 year was 0 ML. The volume represents groundwater flow across the Melbourne region boundary for the following processes:
- through fractured rock along the northern and north eastern boundary
- through major sedimentary and basalt aquifers at the western and eastern boundary.
Leakage from the urban water system (32,262 ML) during the 2013–14 year (Figure 14) is relatively similar to the previous year volume.
Figure 14 Leakage from the urban water system during the 2013–14 year
Recharge from surface water to groundwater could not be quantified for the region due to lack of relevant information.
Groundwater outflows
The largest water outflow from Melbourne's aquifers was outflow at the coastline through major sedimentary and basalt aquifers to outside the region during the 2013–14 year. The volume, 137,638 ML, was marginally increased from the previous year. This outflow may or may not specifically represent groundwater discharge to the sea.
Groundwater discharge to landscape (10,074 ML) during the 2013–14 year decreased by more than 50% from the previous year. The volume represents groundwater discharge via evapotranspiration from shallow water tables. Most of the groundwater discharge occurs from areas with shallow water tables in the south, southeast, and southwest of the region.
Details of other groundwater outflows are as follows:
- Groundwater outflow to outside the region (other than at coast) during the 2013–14 year was 0 ML.
- Entitled water extractions from the groundwater store are described in Groundwater allocation extractions below.
- Discharge to surface water, non-allocated entitled extractions, and extractions made under other statutory rights could not be quantified for the region.
Groundwater allocation extractions
Most of the entitled extraction of allocated groundwater in the Melbourne region is for individual use. During the 2013–14 year, 14,312 ML of groundwater was taken by individual users, which accounts for almost 99% of the total allocated groundwater extraction. The volume represents metered extraction and estimated stock and domestic extraction under groundwater entitlements in groundwater management units. The volume of water extracted from each groundwater management unit is shown in Figure 15.
Figure 15 Groundwater allocations and extractions for the Melbourne region during the 2013–14 year
The total volume of entitled extraction of allocated groundwater to the urban water system (102 ML) was made from Lancefield GMA during the 2013–14 year.
Groundwater forfeitures
Carry-over rules for groundwater entitlements throughout the Melbourne region do not allow unused water to be carried over at the end of the year. Therefore, any unused water is forfeited. Water forfeitures in the Melbourne region during the 2013–14 year relate to groundwater licence entitlements were as follows:
- individual users (26,156 ML)
- urban water system (311 ML).
Groundwater allocation announcements
Groundwater allocation announcements in the Melbourne region during the 2013–14 year refer to groundwater supply to:
- individual users (40,468 ML)
- urban water system (413 ML).
Allocation announcements for individual users represent allocations for licensed entitlements and stock and domestic entitlements in groundwater management units in the Melbourne region during the 2013–14 year. Figure 15 shows allocations for each groundwater management unit within the region. As a result of a 13% decrease in stock and domestic bores, there was a marginal decrease in groundwater allocations during the 2013–14 year from the previous year.
Allocation announcements for the urban water system represent the volume of water allocated from following groundwater sources:
- Koo Wee Rup WSPA for South East Water (119 ML)
- Lancefield GMA for Western Water (294 ML).
A more detailed description of groundwater allocations and associated water rights in the Melbourne region is given in the Groundwater rights note.
Groundwater balancing item
The balancing item volume represents the difference between the measured opening and closing balances of the groundwater store, after physical inflows and outflows have been applied (Table 5).
| Account: groundwater store | Volume (ML) |
| Opening balance (at 1 July 2013) | 38,619 |
| Total groundwater inflows | 401,085 |
| Total groundwater outflows | (162,126) |
| Closing balance (at 30 June 2014) | (38,619) |
| Balancing item | 238,959 |
The calculation of the water balance on the groundwater store yielded a balance difference of 238,959 ML, approximately 60% of the total groundwater inflows during the 2013–14 year. The volume reported as the balancing item for the groundwater asset is less than the reported volume (275,219 ML) for the 2012–13 year.
The volume reported as the balancing item is the difference between total inflows and total outflows because 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 do not reflect groundwater storage changes resulting from water table fluctuations. As a result, estimated inflows and outflows are more appropriately compared to the change of water stored in the aquifers, and the balancing item reflects these changes. The change in aquifer storage was calculated using groundwater levels for the water table aquifer within the sedimentary area identified in Figure 16. The groundwater levels were estimated using all bores within the region, assuming that all hydrogeological layers are hydraulically inter-connected.
Figure 16 Water table aquifer areas used to calculate aquifer storage
The change in storage for water table aquifer volume in the Melbourne region during the 2013–14 year was estimated as 37,593 ML, which is an increase in storage. This volume is a portion of estimated volume for the balancing item. 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 estimated change in storage volume only partially reflects the difference between inflows and outflows (and the volume reported as the balancing item).
Urban water system
Urban water assets
Melbourne’s urban water system comprises three subcomponents:
- urban water supply system (– ML)
- wastewater system (29,715 ML)
- recycled water system (– ML).
The volume of water in the wastewater system changes little from year to year and comprises water in the Western Treatment Plant lagoons (27,725 ML) and storages and holding basins in the Eastern Treatment Plant (1,990 ML). The volume of water within the urban water supply system, the recycled water system, and some of lagoons receiving wastewater could not be quantified due to a lack of available data. In addition, there are a number of smaller wastewater treatment plants operated by urban water authorities in the region; however, their volumes could not be quantified due to a lack of data and are not considered material to the 2014 Account.
Urban water claims
There are two urban water claims in the Melbourne region:
- urban claim on surface water (495,189 ML)
- urban claim on groundwater (0 ML).
These claims are equivalent to the volume of surface water and groundwater allocation remaining for urban water supply licence entitlements at the end of the 2013–14 year.
As carry-over rules for groundwater entitlements throughout the Melbourne region do not allow unused water to be carried over at the end of the year, any unused water is forfeited resulting zero carry-over volume.
The allocation remaining for surface water entitlement is provided in Tables 6. As remaining volumes in the Thomson Reservoir and Lake Eildon have been treated as inter-region claims to surface water store (see surface water claims), they are not included in Table 6.
| Account: surface water | Volume (ML) |
| Opening balance at 1 July 2013 | 495,189 |
| Surface water allocation announcements | 499,506 |
| Entitled diversion of allocated surface water to urban water system | (415,334) |
| Adjustment and forfeiture of surface water allocation | (84,172) |
| Closing balance at 30 June 2014 | 495,189 |
Urban water system inflows and outflows
A schematic diagram representing all the inflows and outflows associated with the urban water system in the Melbourne region is provided in Figure 17.
Figure 17 Water inflows and outflows for Melbourne's urban water system during the 2013–14 year
Urban water supply system inflows
There are three sources of water for the urban water supply system:
- allocated surface water (415,334 ML)
- allocated groundwater (102 ML)
- desalinated water (0 ML).
Entitled diversion of allocated surface water to the urban water supply system (415,334 ML) includes water received under inter-region agreements (134,077 ML) to the surface water store for the urban water system from the Thomson Reservoir, and Silver and Wallaby creeks. Therefore, net surface water diversion to the urban water supply system from the sources within the Melbourne region was 281,257 ML assuming that all water received under inter-region agreements was used. Figure 18 compares volumes received from different sources for the most recent four years.
Figure 18 Water sources used in Melbourne's urban water system and total volume for the years ending 30 June 2011, 2012, 2013, and 2014
Water diversions from surface water sources within the region show a 26% decrease during the 2013–14 year compared with the diverted volume during the 2012–13 year.
The volume of water received under inter-region agreements for the year 2011 in Figure 18 includes 7,476 ML received from Lake Eildon. The volume received under inter-region agreements (mainly from the Thomson Reservoir) increased remarkably in the 2013–14 year compared with the volumes received during preceding three years.
Entitled extraction of allocated groundwater to urban water system (102 ML) represents Western Water's extractions from Lancefield Bore 3 and Glenfern Road bore.
Desalinated water was not provided to the Melbourne region's urban water supply system during the 2013–14 year.
Wastewater system inflows
Total wastewater collected during the 2013–14 year was 350,537 ML, a 3% increase from the previous year. The volume of wastewater collected by each water authority is given in Figure 19.
Figure 19 Wastewater collected by each water authority during the 2013–14 year
Urban water supply system outflows
The largest water outflow from Melbourne's urban water supply system was the delivery to urban water users. During the 2013–14 year, the total delivery of potable water (362,835 ML), and nonpotable water (322 ML) from the urban water supply system to urban water users was 363,157 ML. This is approximately 95% of the total delivered volume (385,229 ML) to urban water users.
During the 2013–14 year, 112 ML of nonpotable water was provided by Melbourne Water to Southern Rural Water (water taken from Tarago River for Southern Rural Water to supply to farmers). During the same year, there was 351 ML of water transferred outside the region from the urban water supply system:
- Melbourne Water provided 111 ML of potable water to Barwon Water from Cowies Hill Reservoir.
- Western Water provided 240 ML of non-potable water from Mount Macedon to Woodend via Western Water's water supply infrastructure.
During the 2013–14 year, there was 362 ML discharged from the urban water supply system to surface water. This volume comprised of excess non-potable water released to Glenfern Service Basin (57 ML) and Rosslynne Reservoir (305 ML) by Western Water.
The loss from the urban water supply system was 50,970 ML for the 2013–14 year. The loss was approximately 12% of inflows to the supply system for both the 2013–14 and 2012–13 years. The 2013–14 year loss volume comprised of leakage to landscape from non-revenue potable water: pipe bursts (4,311 ML), background leakage to groundwater (32,262 ML) and other non-revenue water losses (14,397 ML). In addition to the other non-revenue water losses, other urban water system decreases (14,452 ML) reported in the 2014 Account includes 55 ML wastewater losses.
Wastewater and recycled water system outflows
The major outflows from the wastewater and recycled water systems during the 2013–14 year were (see also Figure 20):
- treated wastewater discharged to sea (275,538 ML)
- treated wastewater discharged to rivers and creeks (9,121 ML)
- recycled water delivered to the environment (19,835 ML)
- recycled water delivered to urban users for residential, commercial, industrial, municipal and on site (water and wastewater treatment plant) uses (22,072 ML)
- recycled water provided to irrigation schemes (5,769 ML)
- evaporation from wastewater lagoons (15,657 ML)
- other losses (55 ML).
Figure 20 Wastewater outflows from Melbourne's wastewater and recycled water systems during the 2013–14 year
Recirculation of treated wastewater and recycled water occurs in the system for additional treatment and/or re-use on site. The outflows in Figure 20 exclude any recirculated volumes.
The largest outflow from the wastewater system is wastewater discharge outside of region which is wastewater treated and discharged into the sea (275,538 ML) by following water authorities:
- City West Water (4,866 ML)
- Melbourne Water (261,983 ML)
- South East Water (8,689 ML).
In addition to this volume, the water authorities as shown below discharged 9,121 ML treated wastewater to the streams (see Figure 20) during the 2013–14 year:
- South East Water (282 ML)
- Western Water (1,743 ML)
- Yarra Valley Water (7,096 ML).
A portion of the collected wastewater volume was further treated in the recycled water plants to produce 62,054 ML of recycled water. Melbourne Water delivered 19,835 ML of recycled water produced at the Western Treatment Plant to Lake Borrie wetlands as an environmental flow (see Figure 20). This volume is the largest portion of treated wastewater and recycled water discharged to streams and wetlands.
A substantial portion of produced recycled water was supplied to urban users (22,072 ML as shown in 'Delivered to urban users' in Figure 20). Figure 21 provides a distribution of the recycled volume supplied to urban users during the 2013–14 year. The figure excludes recycled water volumes supplied to irrigation schemes and the environment (shown in Figure 20).
Figure 21 Recycled water use during the 2013–14 year
The volume provided to irrigation schemes (5,769 ML, see Figure 20) from the recycled water system during the 2013–14 year represents Class A recycled water delivered by:
- Melbourne Water from its Western Treatment Plant to Werribee irrigation district (2,132 ML)
- Water Infrastructure Group from the Eastern Irrigation Scheme to its customers (3,637 ML).
The volume is just over 70% of the volume provided in the previous year.
Over 90% of evaporation from wastewater system (15,657 ML) shown in Figure 20 is for Melbourne Water's Western Treatment Plant. Information for some of the small wastewater treatment plants could not be quantified due to a lack of data. These losses are considered to be relatively small and their omission will not have a material impact on the water balance of the urban water system.
Decrease of urban water claims
The portion of urban water claim that has not been abstracted at the end of the water year is forfeited. There is carry-over provision for unused water into the next water year from majority of surface water entitlements (see Urban water claims); however, such provisions are not available for groundwater entitlements. Water forfeitures in the Melbourne region during the 2013–14 year relate to licence entitlements for:
- surface water supply (84,172 ML)
- groundwater supply (311 ML).
Increase of urban water claims
Increase of water claims for the urban water system refers to allocation announcements during the 2013–14 year for:
- surface water supply (499,506 ML)
- groundwater supply (413 ML).
Details of increase of water claims for the urban water system are available in Surface water allocation announcements and Groundwater allocation announcements.
Urban water balancing item
The urban water system balancing item volume represents the difference between the measured opening and closing balances of the urban water system, after physical inflows and outflows have been applied (Table 7). This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete urban water system balance.
| Account: urban water system | Volume (ML) |
| Opening balance (at 1 July 2013) | 29,132 |
| Total urban water system inflows | 765,973 |
| Total urban water system outflows | (762,999) |
| Closing balance (at 30 June 2014) | (29,715) |
| Balancing item | 2,391 |
The calculation of the water balance on the urban water system yielded a balancing item of 2,391 ML. This is approximately 8% of the total urban water system store volume at the end of the 2013–14 year and 0.3% of the total urban water system inflows during the year.
Unaccounted-for difference
The volume recognised in the water accounting statements (453,234 ML) represents the total unaccounted-for difference for the Melbourne region for the 2013–14 year.
The unaccounted–for difference is the volume necessary to reconcile the opening water storage and closing water storage with the total water inflows and total water outflows reported in the water accounting statements (Table 8).
| Account: water storage | Volume (ML) |
| Opening balance (at 1 July 2013) | 650,730 |
| Total water inflows | 2,661,455 |
| Total water outflows | (2,208,668) |
| Closing balance (at 30 June 2014) | (650,286) |
| Unaccounted-for difference | 453,231 |
The unaccounted–for difference can also be calculated by summing the volumes necessary to reconcile (balance) the opening and closing storage with the water inflows and outflows of each of the separate water stores of the region, as shown in Table 9.
| Balancing item | Volume (ML) |
| surface water store | 211,881 |
| groundwater store | 238,959 |
| urban water system store | 2,391 |
| Unaccounted-for difference | 453,231 |
Table 9 shows that the unaccounted-for difference volume is largely explained by the surface water and groundwater store balancing item volumes. Details of the balancing items of these two stores are available in Surface water balancing item and Groundwater balancing item.