National Water Account 2017

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Key findings

Climate and water

Water Accounting Statements

Supporting information

Region description

Reference information

Melbourne: Geographic information

General description

Area: 11,723 km²
Population: 4.53 million (Australian Bureau of Statistics [ABS] 2016a)

The Melbourne region is located in the southeast of mainland Australia (Figure R1). It is home to 76% of Victoria's population as at June 2015 (ABS 2016a).

The Melbourne region extends from the coastlines of Port Phillip Bay, Western Port Bay, and Bass Strait to the south; the Yarra Ranges in the east; and the Great Dividing Range to the north and west (Figure R1).

Figure R1 Contextual map of the Melbourne region

Region definition

The Melbourne region is physically defined by the hydrological boundaries of the Bunyip, Yarra, Maribyrnong, and Werribee river catchments, as well as the 105 km² area beyond the Werribee River catchment serviced by the Melbourne Water Western Treatment Plant (Figure R1).

• Bunyip river catchment area: 4,078 km². The catchment lies to the east and south of Port Phillip Bay, and takes in the southeastern suburbs of Melbourne as well as the Mornington Peninsula. It extends from Western Port Bay in the south to the eastern highlands in the north. It contains Dandenong, Cardinia, Toomuc, and Yallock creeks and the Bunyip, Tarago, and Lang Lang rivers.
• Yarra river catchment area: 4,110 km². The catchment begins on the southern slopes of the Great Dividing Range. It extends through the Yarra Valley and metropolitan Melbourne to Port Phillip Bay. The upstream catchment area is forested and is the source of much of the region's urban water supply.
• Maribyrnong river catchment area: 1,452 km². The headwaters are located approximately 70 km north of central Melbourne, near the towns of Lancefield and Macedon. The upstream catchment area is primarily rural, while the downstream reaches extend through suburban Melbourne before joining the Yarra River estuary just upstream of Port Phillip Bay.
• Werribee river catchment area: 1,978 km². This catchment is located to the west of Melbourne. After its confluence with the Lerderderg River upstream of Melton Reservoir, the Werribee River flows through Werribee before entering Port Phillip Bay.

For the purpose of this report, the Melbourne region includes water stored in and transactions related to:

• surface water storages in the region
• rivers within the region
• groundwater aquifers beneath the region
• pipes and infrastructure as part of the urban water supply, wastewater collection, recycled water and storm water
• water in the Thomson Reservoir (to the region's east) and water in Lake Eildon (to the region's north). Any transfers of water from these reservoirs into the region are treated as inter-region claims.

The Melbourne region excludes water stored in and transactions related to:

• water held in farm dams used to harvest runoff, private and commercial water storages. Farm dams are excluded because these constitute water that is already abstracted and is no longer available for sharing
• rainwater tanks
• water held in wetlands that are not connected to rivers and estuaries
• water stored in the landscape, such as soil moisture

 For more information regarding items in this water accounting report, please refer to Water accounting policies note.

Land use

The Melbourne region contains major urban centres:

• Melbourne: population 4,323,100
• Melton: population 59,900
• Bacchus Marsh: population 20,300.

Population data for significant urban areas were sourced from 2016 Census QuickStats information (ABS 2016b).

Population for other urban centres: Sunbury, Pakenham, Healesville, Gisborne, Emerald and Wallan are included in the population provided for Melbourne significant urban area. A number of other smaller towns are interspersed throughout the region, including Ballan and Drouin (Figure R1).

Figure R2 shows the distribution of land use in the Melbourne region. Land use classifications were derived from Australian Government Department of Agriculture and Water Resources (2016)

The major land uses within the region are:

• grazing
• urban
• conservation and natural environment
• forestry
• other intensive uses.

Figure R2 Land use in the Melbourne region

Grazing is dominant in the west (Werribee catchment), north (Maribyrnong catchment), and southeast (Bunyip catchment) of the region. Urban use is the primary land use in Melbourne city and suburbs. Conservation and natural environment, and forestry uses are mostly confined to the upper Werribee and Yarra catchments. Other intensive uses are scattered across the region.

The Melbourne region also includes two irrigation districts, Werribee and Bacchus Marsh, which are both in the Werribee catchment. Market gardening and horticulture are the dominant irrigation activities in these districts (see Irrigation districts).

Significant aquatic ecosystems

Wetland systems of international and national importance are located in the Melbourne region as shown in Figure R3. The region contains all or part of three wetlands that are Ramsar listed:

• Edithvale–Seaford wetlands
• Western Port Bay wetlands
• Western shoreline of Port Phillip Bay wetlands.

It also contains five other wetlands of national importance:

• Lerderderg River
• Point Cook and Laverton Saltworks
• Werribee–Avalon area
• Yarra River wetlands
• Mud Islands wetlands (these occur within Port Phillip Bay).

Figure R3 Significant wetlands within the Melbourne region

Further information can be found in the Directory of important wetlands in Australia.

Water resources

Surface water is the main source of water for urban water supply in the Melbourne region. More than 1,570 km² of native forest catchment has been protected for the primary purpose of harvesting water. Most of the surface water comes from the mountain ash forest catchments in the Yarra Ranges in the region's east. Surface water is also transferred from outside the region. Refer to Inter-region transfers in the 'Water systems' section below.

Groundwater is a secondary source of water, to support agriculture in the region. Most groundwater comes from declared groundwater management areas that have prescribed permissible consumptive volumes.

Recycled water is a minor source of water in the region and is produced from wastewater collected at treatment plants.

Desalinated water is another source available to the region to provide a climate-independent alternative water source.

Surface water

The main source of surface water in the region is storages on or linked to rivers. Several storages also receive water from inter-region sources (refer to Inter-region transfers). In addition, there is little water sourced directly from rivers.

Storages

Surface water storages are an important water source for both urban water and irrigation scheme supply. The storages, which are managed by Melbourne Water and Southern Rural Water, are shown in Figure R4. The largest storages in the Melbourne region are Cardinia (288,964 ML), Upper Yarra (204,985 ML), and Sugarloaf (99,222 ML). Together these three storages represent 69% of the storage capacity of the Melbourne region's surface water storages.

Figure R4 Surface water storages in the Melbourne region; capacity of each storage is also shown

Thomson Reservoir is a notable exclusion in Figure R4 for the Melbourne region. It is not included because it is located outside the region boundary; however, it is considered under Inter-region transfer as shown in Figure R11.

Further information on the water storages within the region, including current levels and volumes, is given on the Bureau of Meteorology's Water storage website. Note that the volumes reported on the Water storage website exclude the dead storage volumes.

Rivers

There are four main rivers within the Melbourne region:

• Yarra
• Bunyip
• Maribyrnong
• Werribee.

Regulated and unregulated rivers within the Melbourne region are as follows (Figure R5):

• Yarra and Bunyip are unregulated rivers noting that the Upper Yarra Reservoir is not considered to be a regulating structure.
• 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 enter the river. Tributaries of the Werribee River (the Lerderderg River, Pyrites Creek, and Djerriwarrh Creek) are all unregulated upstream of the storages.

Figure R5 Regulated and unregulated river sections in the Melbourne region

Figure R6 shows the mean monthly flows for the region's four main rivers. Seasonal flow characteristics of these rivers reflect the local rainfall pattern, which is relatively constant throughout the year but with a slight increase in winter and early spring. Flows in each of these rivers are affected by storages or flow diversion structures. As such, streamflow is influenced by contributing catchment rainfall patterns, catchment geomorphology, land use, water supply needs, irrigation, and environmental flow obligations.

Figure R6 Mean monthly flows along the Werribee, Maribyrnong, Yarra, and Bunyip rivers, and mean monthly rainfall for the Melbourne region

The locations of the four gauging stations used to represent the general seasonal flow patterns of the Melbourne region in Figure R6 are shown in Figure R7.

Figure R7 Key flow gauging stations along the Bunyip, Yarra, Maribyrnong, and Werribee rivers within the Melbourne region

Groundwater

Geology of the Melbourne region can be broadly split into two zones: the northern zone and the southern zone. The northern zone comprises about two thirds of the total region. Geology of the northern zone is typically fractured bedrock and basalt. Smaller, local groundwater systems occur here. Geology of the coastal southern zone is unconsolidated sediments and basalts. Larger regional groundwater systems occur in this zone.

In Victoria, groundwater management units are classified as either Groundwater Management Areas (GMA), Water Supply Protection Areas (WSPA), or unincorporated areas.

A GMA is an area where groundwater has been or has the potential to be intensively developed. GMAs have boundaries defined for the purposes of setting a permissible consumptive volume (PCV), which is the maximum extraction limit for the groundwater management unit, for ongoing management.

A WSPA is an area declared under the Victorian Water Act 1989 to protect the groundwater or surface water resources through the development of a management plan. Such protection is required where there is a risk to the water resource or stricter management of use is required. Permissible consumptive volumes have been defined for each of WSPA.

Figure R8 provides information on aquifer geology for both the northern and southern zones, covering Merrimu GMA and Deutgam WSPA in the western part of the region.  More information on aquifer geology in the region can be found in the Port Phillip and Western Port groundwater atlas.

Figure R8 Groundwater system within the northern and southern zones of the western part of the Melbourne region

On average, groundwater provides less than 5% of the total water supplied to the Melbourne region. It is used mainly to supplement surface water sources for high-value agriculture, including production of vegetables, fruits, wine grapes, flowers, and turf. It is also used for commercial, stock, and domestic purposes. In the metropolitan area there is limited groundwater use, with extraction generally limited to the southeastern sandbelt.

There are six GMAs and three WSPAs in the region which are shown in Figure R9.

Throughout the rest of the Melbourne region, groundwater is considered to be in an unincorporated area. WSPAs or GMAs have not yet been defined for groundwater sources in unincorporated areas.

Further information about each GMA and WSPA can be found in the groundwater section of the website for the Victorian Department of Environment, Land, Water and Planning. The permissible consumptive volumes for each GMA and WSPA are provided under groundwater assets in the Statement details note.

Figure R9 Groundwater management areas within the Melbourne region

Desalinated water

The Victorian Desalination Plant (Figure R11) at Wonthaggi was completed and declared operational in December 2012. Melbourne's three retail water authorities have been granted bulk entitlements to desalinated water produced at this plant. The bulk entitlements allow the three water authorities to take a total average annual volume of up to 150,000 ML of desalinated water over any period of five consecutive years, as measured by the sum of the volume of desalinated water that is delivered to the delivery points (subject to other rules specified in the bulk entitlements).

The water authorities request a desalinated water allocation from the minister administering the Victoria's Water Act 1989. Taking these requests into consideration, the Victorian Government makes the order to provide desalinated water. The Victorian Government ordered 50,000 ML of desalinated water for the 2016–17 year (Melbourne Water 2017). The government announced that it would introduce a minimum annual order of 15,000 ML for the next three years. For further information on the Victorian Desalination Plant, refer to the Aquasure website.

Water systems

Urban water system

Urban water supply in the Melbourne region is sourced primarily from surface water, including Inter-region transfers. Melbourne Water manages and operates the majority of surface water storages throughout the region and is responsible for supplying bulk water to the retail water authorities.

Three urban retail water authorities operate exclusively in the Melbourne region, and they source all bulk water from Melbourne Water (Figure R10):

• South East Water 
• Yarra Valley Water
• City West Water

Two Regional water authorities also operate in the Melbourne region:

• Western Water
• Central Highlands Water

however, their service areas extend beyond the Melbourne region boundary. Western Water receives some bulk water from Melbourne Water, but also sources water for urban supply from storages managed by Southern Rural Water. A small portion of Central Highlands Water's service area is within the Melbourne region. Central Highlands Water imports water into the Melbourne region and also abstracts a small volume of water from within-region sources.

Figure R10 Urban retail and regional water authority service areas within the Melbourne region

Inter-region transfers

The Melbourne region's urban water supply is supplemented by water transferred from catchments outside of the region. Melbourne's water authorities hold bulk entitlements for water from the:

• Thomson Reservoir
• Silver and Wallaby creeks
• Goulburn system
• Murray system.

Further information regarding the water authorities' entitlements to transfer water can be found in the Water rights section of the 'Region description' and under Inter-region claims in 'Statement details' notes.

Figure R11 shows the location of the Thomson Reservoir, Silver and Wallaby creeks, and Lake Eildon as part of the Goulburn and Murray systems in relation to the Melbourne region.

 
Figure R11 Melbourne's inter-regional water sources; wastewater treatment and desalination plant locations

Thomson Reservoir

Bulk entitlements allow the Melbourne region's urban water authorities to hold a share of the Thomson Reservoir up to 1,060,100 ML. Storage volume is shared with other users in adjacent regions, including a bulk entitlement held by Southern Rural Water and an environmental entitlement for the Thomson River. Water stored in the Thomson Reservoir is delivered to the Upper Yarra Reservoir for distribution through the Thomson–Yarra pipeline to the Melbourne region's water supply system (Figure R11).

Silver and Wallaby Creeks

Melbourne water authorities hold bulk entitlements to water from the Silver and Wallaby creeks. These entitlements specify that a maximum volume of 66,000 ML may be diverted from Silver and Wallaby creeks over a three-year period (subject to rules specified in the bulk entitlements). Water is diverted from Silver and Wallaby creeks and delivered to Toorourrong Reservoir (a small upstream reservoir) and Yan Yean Reservoir for distribution to Melbourne region's water supply system (Figure R11).

Since 1 July 2014, the bulk entitlements held by the retail water authorities to water resources from the Thomson River, the Yarra River, Silver and Wallaby creeks, and the Tarago and Bunyip rivers have been replaced with a single delivery entitlement for the Greater Yarra–Thomson system.

Goulburn and Murray systems

Melbourne metropolitan retail water authorities hold bulk entitlements up to 75,000 ML of water annually from water savings from Stage 1 of the Goulburn Murray Connections project (previously the Northern Victoria Irrigation Renewal project). The entitlements are held within the Goulburn system (trading zone 1a) and the Murray system (trading zones 6 and 7). Each year, an allocation is made against the bulk entitlements that can either be held in Lake Eildon for future needs in the Melbourne region or traded in the water market. Water stored in Lake Eildon can be delivered to Sugarloaf Reservoir via the North–South pipeline for distribution to Melbourne’s water supply system (Figure R11). As directed by the Victorian Government, this water can only be delivered in times of critical human need or when needed for local fire-fighting (Melbourne Water 2014).

Irrigation districts

Southern Rural Water operates two irrigation districts in the Melbourne region: the Werribee Irrigation District and the Bacchus Marsh Irrigation District (see Figure R12). Both irrigation districts are important vegetable-growing areas for the Melbourne region. Water is sourced from Pykes Creek, Merrimu Reservoir, and Melton Reservoir. In both irrigation districts, water users hold water shares that enable them to order up to an allocated volume of water from Southern Rural Water. The water supply for these irrigation districts is further supplemented by Class A recycled water provided by Melbourne Water's Western Treatment Plant (Figure R11).

Figure R12 The Werribee and Bacchus Marsh irrigation districts within the Melbourne region

Recycled water

Recycled water is used for a range of activities such as the irrigation of agriculture, vineyards, market gardens, conservation areas, dual–pipe (or third–pipe) schemes, and golf courses. There are two large wastewater treatment plants in the region that are the main source of recycled water (Figure R11), the Western Treatment Plant and Eastern Treatment Plant. Melbourne Water operates these two plants.

Melbourne Water Western Treatment Plant

The major source of recycled water is the Melbourne Water Western Treatment Plant. About one third of the recycled water from this plant is supplied to Lake Borrie Wetlands. The remainder is mainly used for:

• pasture irrigation
• horticulture irrigation
• land and salinity management
• the Werribee tourist precinct, including golf club, equestrian centre, open range zoo, and the Werribee Park and Mansion.

The Werribee Irrigation District Recycled Water Scheme delivers recycled water from the Melbourne Water Western Treatment Plant to the Werribee irrigation supply system. The recycled water is mixed with water sourced from Pykes Creek, and Merrimu and Melton reservoirs.

Melbourne Water Eastern Treatment Plant

Recycled water from the Melbourne Water Eastern Treatment Plant is made available to South East Water via the Eastern Irrigation Scheme to supply customers in the area. The main uses include:

• horticulture irrigation
• sportsfield irrigation
• domestic dual-pipe schemes.

Retail and regional urban water authorities also operate wastewater treatment plants, and some are used to supply small volumes of recycled water locally.

Stormwater

There are a number of stormwater harvesting schemes in operation throughout the Melbourne region. In comparison to recycled wastewater, the volumes of water involved are small, but it is envisaged that this volume will increase in the future (Melbourne Water 2015).