Melbourne
Physical information

Area: 11,723 km².
Population: Approximately 4 million in June 2009 (Australian Bureau of Statistics 2010).

The Melbourne region is located in the southeast of mainland Australia (Figure P1). It is the second-largest metropolitan area in Australia and is home to over 73% of Victoria's population (Australian Bureau of Statistics 2010).

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 and Dandenong 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 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 River and Lerderderg River 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
• 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-basin claims.

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

The major cities and their populations within the Melbourne region  are:

• Melbourne – 3,371,888
• Melton – 35,490
• Sunbury – 29,566
• Pakenham – 18,808
• Bacchus Marsh – 13,261.

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.

Figure P4. Map of land use in the Melbourne region

Figure P5 shows the irrigation areas in the Melbourne region. The major irrigation districts are Bacchus Marsh and Werribee, both to the west of the city of Melbourne. Irrigated agriculture occupies less than 1% of land use in the region (Southern Rural Water 2009).

Figure P5. Map of irrigation districts in the Melbourne region

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

1. Edithvale–Seaford wetlands
2. Westernport Bay wetlands
3. the western shoreline of Port Phillip Bay wetlands.

It also contains five other wetlands of national importance;

1. Lerderderg River
2. Point Cook and Laverton Saltworks
3. Werribee–Avalon area
4. Yarra River wetlands
5. 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 name	Storage operator	Total storage capacity (ML)	Dead storage (ML)	Purpose
Cardinia	Melbourne Water	288,964	2,053	Urban supply
Upper Yarra		204,985	4,406	Urban supply
Sugarloaf		99,222	2,969	Urban supply
Silvan		40,581	135	Urban supply
Yan Yean		33,125	2,859	Urban supply
Tarago1		37,580	Unknown	Urban supply
Maroondah		28,233	6,054	Urban supply
Greenvale		27,501	662	Urban supply
O'Shannassy1		3,123	Unknown	Urban supply
Merrimu	Southern Rural Water	32,215	335	Urban supply irrigation
Rosslynne		25,400	150	Urban supply irrigation
Pykes Creek		22,119	1,770	Urban supply irrigation
Melton		14,360	140	Urban supply irrigation
Total		857,408	21,534

¹ 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, and Werribee. Figure P6 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 P6. Chart of mean monthly river flows

Figure P7 shows the location of flow gauging stations along these main rivers used in Figure P6.



Figure P7. Map of flow gauging stations

The Werribee and Bacchus Marsh irrigation supply systems are located in the west of the 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 Sustainability and Environment website.

There are nine groundwater management units in the region (Figure P8); three are water supply protection areas and six are groundwater management areas. The rest of Melbourne region is considered to be unincoporated area.

P8. Map of groundwater management units

The permissible consumptive volumes, which are the maximum extraction limit for each groundwater management area, are listed in Table P3.

Table P3. Permissible consumptive volumes

River catchment	Groundwater management unit	Permissible consumptive volume (ML/y)
Bunyip	Koo Wee Rup WSPA	12,915
	Nepean GMA	6,013
	Moorabbin GMA	2,700
	Frankston GMA	3,200
Maribyrnong	Lancefield GMA	1,485 ML/y
Werribee	Deutgam WSPA	5,100 ML/y
	Cut Paw Paw GMA	3,650 ML/y
	Merrimu GMA	451 ML/y
Yarra	Wandin Yallock WSPA	2,924 ML/y
	Kinglake GMA1	n/a

GMA = Groundwater Management Area, WSPA = Water Supply Protection Area

¹Approximately 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.

Melbourne's urban water supply is supplemented by water imported from catchments outside the Melbourne region. Melbourne's retail water authorities have bulk entitlements to water from the Thomson Reservoir and Silver and Wallaby creeks. Melbourne's retail water authorities also have a claim to water from 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 (refer toEnvironmental benefit note for more information). 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 once 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.

For more information regarding these claims to imported water refer to line item 1.5 Inter-region claim on 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.

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
• a secure water supply to 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, Merrimu and Melton surface water storages.

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
• sports-field 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 GL/year of desalinated water. Although not operational during the 2010–11 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.