Melbourne
Physical information
General description
Area: 11,723 km²
Population: Approximately 4.35 million (Australian Bureau of Statistics [ABS] 2011a)
The Melbourne region is located in the southeast of mainland Australia (Figure P1). It is home to 76% of Victoria's population (ABS 2011a).
Figure P1 The Melbourne region within Australia
The Melbourne region, shown in Figure P2, 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 P2 Contextual 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 Dandenong, Cardinia, Toomuc and Yallock creeks, and the Bunyip, Tarago and Lang Lang rivers.
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. After its confluence with the Lerderderg River upstream of Melton Reservoir, the Werribee River flows through Werribee before entering Port Phillip Bay.
Region definition
The Melbourne region is physically defined (Figure P2), and includes the Yarra, Bunyip, Maribyrnong 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
- 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
The major urban centres and their populations within the Melbourne region are:
- Melbourne: population 4,181,000
- Melton: population 54,500
- Bacchus Marsh: population 18,900.
Population data for significant urban areas were sourced from the Census QuickStats website (Australian Bureau of Statistics 2011b).
Population for urban centres: Sunbury, Pakenham, Healesville, Gisborne, Emerald and Wallan are included in population provided for Melbourne significant urban area. A number of other smaller towns are interspersed throughout the region, including Ballan and Drouin.
Figure P3 shows the distribution of land use in the Melbourne region. Land use classifications were derived from Department of Agriculture sources.
The major land uses within the region are:
- grazing
- urban
- conservation and natural environment
- forestry
- other intensive uses.
Figure P3 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, both in the Werribee catchment. Market gardening and horticulture are the dominant irrigation activities in the districts (see Irrigation districts).
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
- Western Port 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 the 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 'Water systems' section below.
Groundwater is a secondary source of water. 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.
Surface water
The two main sources of surface water in the region are rivers and storages.
Rivers
There are four main rivers within the Melbourne region:
- Yarra
- Bunyip
- Maribyrnong
- Werribee.
Figure P4 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 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 P4 Mean monthly flows along the Werribee, Maribyrnong, Yarra, and Bunyip rivers, and the mean monthly rainfall for the Melbourne region
Figure P5 shows the location of flow gauging stations in the main rivers used in Figure P4.
Figure P5 Key flow gauging stations along the Bunyip, Yarra, Maribyrnong and Werribee rivers within the Melbourne region
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 P6. The capacity of each storage and its main purpose are shown in Table P1. 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.
Figure P6 Surface water storages in the Melbourne region
| 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, provided volume is accessible storage capacity which excludes dead storage.
Thomson Reservoir is a notable exclusion from the list of water storages in the Melbourne region. It is not included in Figure P6 and Table P1 because it is located outside the region boundary; however, it is considered under Imported water.
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.
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. Figure P7 provides information on aquifer geology for both the northern and southern zones, covering Merrimu Groundwater Management Area (GMA) and Deutgam Water Supply Protection Area (WSPA) in the western part of the region. More information on aquifer geology in the area can be found in the Port Phillip and Western Port groundwater atlas.
Figure P7 Groundwater system within the northern and southern zones of the western part of the Melbourne region
On average, groundwater provides less than 10% 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.
In Victoria, groundwater management units are classified as either GMAs, WSPAs, or unincorporated areas. A 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 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. 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. The permissible consumptive volumes for each GMA and WSPA are provided under groundwater assets in the Groundwater store notes.
There are ten groundwater management units in the region (Figure P8); three are WSPAs and seven are 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 the Melbourne region, groundwater is considered to be in an unincorporated area.
Figure P8 Groundwater management areas within the Melbourne region
Desalinated water
The Victorian desalination plant (Figure P10) 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 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).
The Victorian Government did not order desalinated water for the 2013–14 financial year (Melbourne Water 2014a). For further information on the Victorian desalination plant, refer to the Aquasure website.
Water systems
Urban water system
Melbourne's urban water supply is sourced primarily from surface water, including Imported surface water. 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 P9). 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 P1.
Figure P9 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 for 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 under inter-region claims in Surface water store notes.
Figure P10 shows the location of the Thomson Reservoir, Silver and Wallaby creeks, and Lake Eildon as part of Goulburn and Murray systems in relation to the Melbourne region.
Figure P10 Melbourne's inter-regional 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 P10).
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 P10).
Goulburn and Murray systems
Melbourne 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 P10). As directed by the Victorian Government, this water will only be delivered in times of critical human need or when needed for local fire-fighting (Melbourne Water 2014c).
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 P11). Both irrigation districts are important vegetable-growing areas for the Melbourne region. Water is sourced from the Pykes Creek, 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. More information on these water entitlement arrangements is provided in the Surface water store notes. The water supply for these irrigation districts is further supplemented by Class A recycled water provided by Melbourne's Western Treatment Plant.
Figure P11 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 P10).
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, 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 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 small, but it is envisaged that in future this volume will increase.