Melbourne
Physical information

General description

Area: 11,723 km².
Population: Approximately 4.1 million (Australian Bureau of Statistics [ABS] 2013)

The Melbourne region is located in the southeast of mainland Australia (Figure P1). It is home to over 74% of Victoria's population (ABS 2013).


Figure P1 Location map of the Melbourne region
Figure P1 Location map of the Melbourne region


The Melbourne region, shown in Figure P2, extends from the coastlines of Port Phillip Bay, Westernport Bay, and Bass Strait to the south, the Yarra Ranges in the east; and the Great Dividing Range to the north and west.


Figure P2 Contextual and catchment boundary map of the Melbourne region
Figure P2 Contextual and catchment boundary map of the Melbourne region


Figure P2 shows the following surface water catchments that make up the Melbourne region:


Bunyip River catchment

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 several river systems: Dandenong Creek; Cardinia and Toomuc creeks; Bunyip and Tarago rivers; Yallock Creek; and Lang Lang River.

Yarra River catchment

Catchment area: 4,110 km2. The Yarra catchment begins on the southern slopes of the Great Dividing Range. It flows through the Yarra Valley and metropolitan Melbourne into Port Phillip Bay. The upstream catchment is forested and is the source of much of the region's urban water supply.

Maribyrnong River catchment

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 is primarily rural, while the downstream reaches flow through suburban Melbourne before joining the Yarra River estuary just upstream of Port Phillip Bay.

Werribee River catchment

Catchment area: 1,978 km2. It is located to the west of Melbourne. The Werribee and Lerderderg rivers meet upstream of Melton Reservoir and the rivers flow through Werribee before entering Port Phillip Bay.

Description of region

The Melbourne region is physically defined above and includes the Yarra River, Bunyip River, Maribyrnong River and Werribee River catchments and the 105 km² area serviced by the Western Treatment Plant beyond the Werribee River catchment, as shown in Figure P2.

The region includes all water within and beneath the land described above excluding:

  • water in off-channel water storages, such as catchment storages used to harvest water (also known as farm dams), as this water is already abstracted and no longer available for sharing;
  • rainwater tanks;
  • water stored in the landscape, such as soil moisture; and
  • water in the Thomson Reservoir (to the east) and water in Lake Eildon (to the north).
Any transfers of water from these stores into the region are treated as transfers, imports, or inter-region claims.

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

Land use


Major cities within the region

The major urban centres and their populations within the Melbourne region are:

  • Melbourne—3,999,982
  • Melton—45,624
  • Sunbury—33,062
  • Pakenham—32,911
  • Bacchus Marsh—14,913.

Population data was sourced from the Census QuickStats website for urban centres/localities (Australian Bureau of Statistics 2013).

A number of smaller towns are interspersed throughout the region, including Healesville, Drouin, Gisborne, Emerald and Wallan.

Land use activities

Figure P3 shows the distribution of land use in the Melbourne region. Land use classifications were derived from the Land Use Mapping Technical Specifications (ABARES 2010).

The major water users in the region are:

  • residential
  • manufacturing and industry
  • dairy
  • horticulture
  • viticulture.
Less than 3% of land use in the Melbourne region is used for irrigated agriculture.


Figure P3 Map of land use in the Melbourne region
Figure P3 Map of land use in the Melbourne region

Major land use activities in the Melbourne region are summarised in Table P1 (Department of Agriculture 2010).

Table P1  Land use in the Melbourne region
Land use Area (km2) Area (% of total)
grazing
4,196
36
urban
2,801
24
conservation and natural environments 1,941 17
forestry 1,302 11
dryland agriculture 513 4
other intensive uses
362
3
irrigated agriculture 350 3
water
187
1
mining 71 1
Total 11,723 100

Significant aquatic ecosystems

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

  • Edithvale–Seaford wetlands
  • Westernport Bay wetlands
  • the 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).

Further information can be found at the Directory of Important Wetlands in Australia.

Water resources

Surface water is the main source of water in the Melbourne region. More than 1,570 km2 of native forest has been protected for the primary purpose of harvesting water. Most of the surface water comes from mountain ash forest catchments in the Yarra Ranges in the east of the region. Surface water is also imported from outside the region. Refer to 'Imported water' in the Other water resources and systems note.

Groundwater is a secondary source of water. Most groundwater comes from declared groundwater management areas for which permissible consumptive volumes have been prescribed.

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

Surface water

The two main sources of surface water in the region are storages and river channels.

Storages

Table P2 presents storages in the Melbourne region. The largest storages in the Melbourne region are Cardinia (288,964 ML), Upper Yarra (204,985 ML), and Sugarloaf (99,222 ML). Together they represent 69% of the storage capacity of Melbourne's surface water storages.

Table P2  Surface water storages
Storage operator Storage Total storage
capacity (ML)
Dead
storage (ML)
Purpose
Melbourne Water Cardinia Reservoir 288,964 2,053 urban supply
Greenvale Reservoir 27,501 662 urban supply
Maroondah Reservoir 28,233 6,054 urban supply
O'Shannassy Reservoir1 3,123 not available
urban supply
Silvan Reservoir 40,581 136 urban supply
Sugarloaf Reservoir 99,222 2,969 urban supply
Tarago Reservoir2 37,580 not available
urban supply
Upper Yarra Reservoir 204,985 4,406 urban supply
Yan Yean Reservoir 33,125 2,859 urban supply
Southern Rural Water Melton Reservoir 14,360 140 irrigation supply
Merrimu Reservoir 32,215 335 urban supply and irrigation
Pykes Creek Reservoir 22,119 1,770 urban supply and irrigation
Rosslynne Reservoir 25,400 150 urban supply and irrigation
Total 857,408 21,534

1-2 As dead storage is unknown, it is not possible to calculate the total storage capacity. The volume should be considered as the accessible storage capacity excluding dead storage.

The location of the surface water storages in the region are provided in Figure P4.

Figure P4  Map of the water storages in the region
Figure P4  Map of the water storages in the region

Thomson Reservoir is a notable exclusion from the list of water storages in the Melbourne region. It is not included because it is located outside of the region boundary; however, it is considered under Other water resources.

Rivers

There are four main rivers within the Melbourne region:

  • Yarra
  • Bunyip
  • Maribyrnong
  • Werribee.

Figure P5 shows the mean monthly flows for the four main rivers in the region. 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 from each of these rivers are affected by a storage or flow diversion structure. As such, streamflow is influenced by contributing catchment rainfall patterns, catchment geomorphology, land use, water supply needs, irrigation, and environmental flow obligations. The Yarra and Bunyip river catchment sizes are similar, but the mean monthly stream flow volume patterns are different. This reflects variations in rainfall and catchment terrain characteristics.


Figure P5 Graph of mean monthly flows along the Werribee, Maribyrnong, Yarra and Bunyip rivers, and the mean monthly rainfall for the Melbourne region
Figure P5 Graph of mean monthly flows along the Werribee, Maribyrnong, Yarra and Bunyip rivers, and the mean monthly rainfall for the Melbourne region


Figure P6 shows the location of flow gauging stations along these main rivers used in Figure P5.

Figure P6  Location map of selected key flow gauging stations along the main rivers within the Melbourne region
Figure P6  Location map of selected key flow gauging stations along the main 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 is 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. More information on aquifer geology in the area can be found in the Port Phillip and Western Port Groundwater Atlas.

On average, groundwater provides less than 10% of the total water supply 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 the extraction generally limited to the southeastern sandbelt.

In Victoria, groundwater management units are classified as either groundwater management areas, water supply protection areas, or unincorporated areas. A Water Supply Protection Area (WSPA) is an area declared under the Water Act 1989  to protect the groundwater or surface water resources through the development of a management plan. A Groundwater Management Area (GMA) is an area where groundwater has been intensively developed or has the potential to be. GMAs have boundaries defined for the purposes of setting a Permissible Consumptive Volume (PCV) for ongoing management. Further information about each of these can be found in the groundwater section of the website for the Victorian Department of Environment and Primary Industries.

There are ten groundwater management units in the region (Figure P7); three are water supply protection areas and seven are groundwater management areas (GMAs). Approximately 19% of the Kinglake GMA is located within the Melbourne region, but values for the Kinglake GMA are not included in this report because most of the groundwater extraction from licensed bores occurs north of the region and is managed by Goulburn–Murray Water.

Throughout the rest of Melbourne region, the remaining groundwater is considered to be in an unincoporated area.


Figure P7 Map of groundwater management units
Figure P7 Map of groundwater management units


The permissible consumptive volumes, which are the maximum extraction limit for each GMA, are provided in line items 2.1 Water table aquifer and 2.2 Underlying aquifers.

Desalinated water

The Victorian desalination plant (Figure P9) at Wonthaggi was completed and declared operational in December 2012. The plant is able to augment Melbourne's urban water supply with up to 150,000 ML/year of desalinated water. Melbourne's three retail water authorities have been granted bulk entitlements to desalinated water (Order 2010) produced at the Victorian desalination plant. The bulk entitlements allow the three water authorities to take an 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).

On 1 April 2012, the Minister for Water made a zero desalinated water order for the 2012–13 financial year. Although operational during the 2012–13 year, the Victorian desalination plant has not produced any water since 18 December 2012. For further information on the Victorian desalination plant, refer to the Aquasure website.

Other water resources and systems

Urban water system

Melbourne's urban water supply is sourced primarily from surface water, including imported surface water (see below). 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 retail water authorities and one regional water authority operate in the Melbourne region (Figure P8). City West Water, South East Water, and Yarra Valley Water (retail water authorities) operate exclusively in the Melbourne region and all water is sourced from bulk water provided by Melbourne Water. Western Water is a regional water authority and also operates in the Melbourne region; however, its service area crosses 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, as described in Table P2.


Figure P8  Melbourne's urban retail water authorities and regional water authority service areas
Figure P8  Melbourne's urban retail water authorities and regional water authority service areas

Imported water

Melbourne's urban water supply is supplemented by water imported from catchments outside the Melbourne region. Melbourne's retail water authorities hold bulk entitlements to water from the:

  • Thomson Reservoir
  • Silver and Wallaby creeks
  • Goulburn System
  • Murray System

Further information regarding Melbourne's retail water authorities' entitlements to imported water can be found in the Water rights section of the 'Contextual information' and line item 1.5 Inter-region claim on water.

Figure P9 shows the location of the Thomson Reservoir, Silver and Wallaby creeks and Lake Eildon as part of Goulburn and Murray System in relation to the Melbourne region.

Figure P9 Location map illustrating the inter-region water sources
Figure P9 Location map illustrating the inter-region water sources


Thomson Reservoir

Bulk entitlements allow Melbourne's three retail water authorities to hold a share of the Thomson Reservoir up to its capacity 1,068,100 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 Melbourne's water supply system (Figure P9).

Silver and Wallaby creeks

Melbourne retail 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 Tooroorung Reservoir and Yan Yean Reservoir for distribution to Melbourne's water supply system (Figure P9).

Goulburn System

On 2 July 2012, the Victorian Minister for Water gazetted new bulk entitlements in the Goulburn River System of up to 75,000 megalitres annually, for the three retail water corporations as a result of the water retail corporation's investment in the Goulburn–Murray Water Connections Project. Melbourne retail water authorities have claim to water from the Goulburn system, under a water savings supply and transfer agreement entered into by the Goulburn–Murray Rural Water Corporation, Melbourne Water Corporation and the three urban retail water authorities. Under this agreement, water savings from Stage 1 of the Northern Victoria Irrigation Renewal Project (NVIRP) were allocated to Melbourne retail water authorities and stored in Lake Eildon. Water stored in Lake Eildon is delivered to Sugarloaf Reservoir via the north–south pipeline for distribution to Melbourne's water supply system (Figure P9).

Murray System

On 2 July 2012, the Victorian Minister for Water gazetted new bulk entitlements for the three retail water corporations in the Murray River System of up to 75,000 megalitres annually, as a result of the water retail corporation's investment in the Goulburn-Murray Water Connections Project. The holders of the bulk entitlements are entitled to a water entitlment volume in trading zone 6 and 7 of the Murray River System from the total Phase 4 water savings achieved in these parts of the Goulburn Murray Irrigation District (GMID) from Northern Victoria Irrigation Renewal Project (NVIRP) Stage 1, as verfied in the latest audit.

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 P10). Both irrigation districts are important vegetable-growing areas for the Melbourne region. Water is sourced from the Pykes Creek, and the Merrimu and Melton reservoirs. 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. For more information on this water entitlement arrangements, refer to line item 5.1. The water supply for these irrigation districts is further supplemented by Class A recycled water provided by Melbourne's Western Treatment Plant.

Figure P10  Location map of the Werribee and Bacchus Marsh irrigation districts in the Melbourne region
Figure P10  Location map of the Werribee and Bacchus Marsh irrigation districts in 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 P9).

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 rest 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 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 the 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 to supply customers in the area. The main uses include:

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

Retail water corporations 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 at present small, but it is envisaged that in future this volume will increase.