Melbourne
Physical information

Area: 11,723 km².
Population: Approximately 4 million in 2011 (based on the Greater Capital Statistical Area for Greater Melbourne)[Australian Bureau of Statistics 2013].

The Melbourne region is located in the southeast of mainland Australia (Figure P1). It is home to over 73% of Victoria's population (Australian Bureau of Statistics 2013).

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 map of the Melbourne region

Figure P3 shows the following surface water catchments that make up the Melbourne region:

• Yarra River catchment
• Bunyip River catchment
• Maribyrnong River catchment
• Werribee River catchment.

Figure P3  Map of surface water catchments in the Melbourne region

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.

Bunyip River catchment

Catchment area: 4,078 km². The catchment lies to the east and south of Port Phillip Bay, and takes in the south-eastern suburbs of Melbourne and the Mornington Peninsula. It extends from Western Port Bay in the south to the eastern highlands in the north. It contains several river systems: Patterson River; Cardinia and Toomuc Creeks; Bunyip and Tarago Rivers; and Yallock Creek and Lang Lang River.

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.

The Melbourne region is physically defined in the 'General description'. The region includes the Yarra River, Bunyip River, Maribyrnong River and Werribee River catchments and the 105 km² area serviced by Western Wastewater Treatment Plant.

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

• water in off-channel water storages, such as catchment storages (also known as farm dams) used to harvest floodwater, 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.

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

• Melbourne—3,707,530
• 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.

Major land use activities in the Melbourne region are summarised in Table P1.

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

Figure P4 shows the distribution of land use in the Melbourne region. Land use activities that are major water users in the region are:

• residential
• manufacturing and industry
• dairy
• horticulture
• viticulture.

Less than 1% of land use in the Melbourne region is for irrigated agriculture ( Southern Rural Water 2009).


Figure P4  Map of land use in the Melbourne region

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.

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 storages outside of the region. 

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.

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

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.

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.

There are four main rivers within the Melbourne region:

• Yarra
• Bunyip
• Maribyrnong
• Werribee.
  

Figure P5 shows the mean monthly flows for the main rivers in the region. Seasonal flow characteristics of these rivers reflect the local rainfall pattern, which is relatively constant throughout the year, with a slight maximum in early spring. Flows from each of these rivers are affected by a storage or flow diversion structure. As such, streamflow is influenced by rainfall patterns, water supply needs, irrigation and environmental flow obligations.

Figure P5  Graph of mean monthly flows along the Werribee, Maribyrnong, Yarra and Bunyip rivers and 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 key flow gauging stations along the main rivers within the Melbourne region

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. 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.

On average, groundwater provides less than 10% of total water supply to the Melbourne region. It is mainly used 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. Further information about each of these can be found at the Victorian Department of Environment and Primary industries website.

There are ten groundwater management units in the region (Figure P7); three are water supply protection areas and seven are groundwater management areas (GMAs). The Kinglake GMA is partially located within the Melbourne region: approximately 19% of the Kinglake GMA lies within the Melbourne region. Values for Kinglake GMA are not included in this report as the majority of the groundwater extraction from licensed bores is north of the region and 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

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

Melbourne's urban water supply is sourced primarily from surface water, including imported surface water (see below). Melbourne Water manage and operate 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 receive some bulk water from Melbourne Water, but also sources water for urban supply from Southern Rural Water managed storages, as well as several smaller storages that they manage.

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

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
• agreement to water in Lake Eildon.
  

Further information regarding Melbourne's retail water authorities' entitlement 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 in relation to the Melbourne region.

Figure P9  Location map illustrating the inter–region water sources: Thomson Reservoir, Silver and Wallaby creeks and Lake Eildon

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 to Melbourne's water supply system.

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.

Lake Eildon

Melbourne retail water authorities have claim to water from Lake Eildon under a Water Savings Supply and Transfer Agreement (an unpublished document). Under this agreement, water savings from Stage 1 of the Northern Victoria Irrigation Renewal Project were allocated to Melbourne retail water authorities and stored in Lake Eildon. In the 2010–11 year, as a one off arrangement, some unallocated water savings achieved from the CG1234 Modernisation Project and Shepparton Modernisation Project were also allocated to Melbourne. Water stored in Lake Eildon is delivered to Sugarloaf Reservoir via the North–South Pipeline for distribution to Melbourne's water supply system.

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 which enable them to order up to an allocated volume of water from Southern Rural Water. For more information on this water entitlement arrangement, 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 (see below).

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

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.

Western Treatment Plant
The major source of recycled water is the Western Treatment Plant. About one-third of the recycled water from the Western Treatment 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 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.

Eastern Treatment Plant
Recycled water from the 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.

The Wonthaggi desalination plant is under construction and, when completed, will augment Melbourne's urban water supply with up to 150,000 ML/year of desalinated water. Although not operational during the 2011–12 year, Melbourne's three retail water authorities have been granted bulk entitlements to desalinated water produced at the Wonthaggi desalination plant. The bulk entitlements allow the authorities to take a combined volume up to 150,000 ML each year on an annual basis over any period of five consecutive years (subject to rules specified in the bulk entitlements).

For further information on the Wonthaggi desalination plant refer to the Aquasure website.

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.