Perth: Physical information
General description
Area: 21,156 km2
Population: 1.9 million (Australian Bureau of Statistics [ABS] 2011)
The Perth region is located on the west coast of Western Australia (Figure C1). The region's boundary is mostly defined by three surface water catchments (Figure C2):
- Swan Coastal
- Murray River
- Harvey River.
The Perth region also includes a small part of the Moore–Hill Rivers and Collie River catchment areas (Figure C2). These areas were included to capture the groundwater management areas and two irrigation districts within the Harvey Water Irrigation Area.
Figure C1 The Perth region within Australia
Figure C2 Contextual map of the Perth region
The Darling escarpment is a geographic feature that splits the Perth region in half. The escarpment runs in a north–south direction and rises to more than 200 metres above sea level. To the east is the Darling Range (indicated by the lighter coloured shading in Figure C2), which extends to the eastern boundary of the region, and to the west is the coastal plain.
The region is home to waterways and wetlands of national significance. The Swan and Canning rivers and the Peel–Harvey estuarine system (Figure C2) have strong environmental, cultural, and recreational significance. There are also important groundwater resources in the region, such as the Gnangara and Jandakot groundwater systems. These aquifers are a source of public and self-supply and support numerous groundwater-dependant wetland ecosystems.
Other significant water features within the region include:
- the Integrated Water Supply Scheme, operated by the Water Corporation of Western Australia, which supplies potable water to the Perth metropolitan area (as well as areas outside the Perth region boundary)
- two irrigation districts, Waroona and Harvey, located in the southern area of the Perth region within the Harvey Water Irrigation Area
- the Perth Seawater Desalination Plant near Kwinana and the Southern Seawater Desalination Plant near Binningup that supply water to the Integrated Water Supply Scheme.
The Integrated Water Supply Scheme and the Harvey Water Irrigation Area are shown in Figure C3.
Figure C3 The integrated Water Supply Scheme and the Harvey Water Irrigation Area within the Perth region
Region definition
The Perth region is physically defined (Figure C2), and includes the Swan Coastal, Murray River, and Harvey River catchments, two groundwater management areas, and two irrigation districts within the Harvey Water Irrigation Area.
For the purposes of this report, the region includes water stored in:
- surface water storages
- pipes and infrastructure as part of the urban water supply, wastewater collection, and irrigation water supply systems
- groundwater aquifers.
The region excludes water stored in:
- off-channel water storages and rainwater tanks, such as farm dams and private commercial water storages used to harvest runoff or collect rainwater
- the landscape, such as soil moisture.
For more information regarding items in this water accounting report, please refer to the Water accounting policies.
Land use
The major population centres in the region are:
- Perth metropolitan area (including Rockingham and Kwinana): population 1,806,000
- Mandurah: population 91,300 (ABS 2011).
A number of smaller towns are interspersed throughout the rest of the region, including Harvey, Pinjarra, and Gingin.
The urban land use is primarily within the Perth metropolitan area (including Rockingham and Mandurah) along the Swan Coastal Plain, as shown in Figure C4 (Australian Bureau of Agricultural and Resource Economics and Sciences 2014).
Figure C4 Land use in the Perth region
The region also includes two irrigation districts, Harvey and Waroona, identified as 'Irrigated agriculture' in Figure C4. These districts are part of the Harvey Water Irrigation Area, which is located on the Swan Coastal Plain near the town of Harvey. The total operating area of these districts is approximately 170 km2 and 55 km2 at Harvey and Waroona respectively. Within these areas, there is currently around 55 km2 and 15 km2 of land in the Harvey and Waroona districts respectively under permanent irrigation for dairy farming, beef grazing, and horticulture.
Other major land uses in the Perth region include:
- conservation and natural environments
- dryland agriculture
- grazing.
There are extensive areas of conservation and natural environments within the Perth region, particularly throughout the Darling Range (to the east of the Darling escarpment). Dryland agriculture occurs across much of the region and grazing is dominant to the east of the Peel–Harvey Estuary south of Mandurah (Figure C4).
Significant aquatic ecosystems
There is a series of significant aquatic ecosystems within the Perth region, primarily located on the Swan Coastal Plain (Figure C5). Many of these systems are part of the groundwater system within the region.
Figure C5 Significant wetlands in the Perth region
The sites in Figure C5 are listed in the Directory of important wetlands in Australia. There are also three designated Ramsar wetlands within the Perth region:
- Forrestdale and Thomsons lakes
- Peel–Yalgorup wetland system
- Becher Point wetlands.
The Forrestdale and Thomsons lakes are located in the southern suburbs of Perth. The Peel–Yalgorup wetlands are located around Mandurah and include the Peel–Harvey Estuary and Yalgorup Lake. Both of these systems are major stop-overs for migratory wading birds and important drought refuge areas for waterbirds. The Peel–Yalgorup wetlands also support the largest professional and recreational estuarine fishery in Western Australia.
The Becher Point wetlands, located near Rockingham in the southern suburbs of Perth, is one of the youngest wetland systems on the Swan Coastal Plain. The sedgelands that occur within the chain of wetland depressions of the site are listed as a threatened ecological community under the Australian Government Environment Protection and Biodiversity Conservation Act (1999).
Water resources
Water supply in the Perth region is primarily sourced from groundwater aquifers, desalinated water, and storages.
Most of the region's water supply comes from groundwater. The groundwater is used for urban water supply as well as individual supply, including use in agriculture and parks and gardens. There are also an estimated 170,000 residential bores in the Perth metropolitan area (Department of Water 2009a). The important groundwater resources in the region include:
- Gnangara and Jandakot superficial aquifers
- Leederville and Yarragadee confined aquifers.
The scope for increased extraction, particularly in the Gnangara system, Perth's largest source of groundwater, is limited; however, a groundwater replenishment scheme is currently under construction, extending the scope for extraction of recycled water. Further information is available in the Major water reforms section of the 'Climate and water overview'.
There are three major surface water resources in the Perth region:
- Swan–Canning river system
- Murray River catchment
- Harvey River catchment.
These surface water resources have been developed to meet the region's water needs. Storages were constructed along tributaries in the upper reaches of these river systems for urban water and irrigation scheme supply. Land-clearing for urban and agricultural development has also been extensive throughout these catchment areas. The potential to develop additional storages in the region is limited.
Given the limited scope for increased abstraction from the region's surface water and groundwater resources, alternative water resources, such as seawater desalination and water recycling, are increasingly being used for public water supply. There are two desalination plants in the region that, in combination, are now capable of supplying almost half of Perth's urban water requirements.
Groundwater
The groundwater system within the Perth region comprises water table aquifers (superficial aquifers) and confined aquifers (e.g., Leederville and Yarragadee aquifers). An example subsection of the system taken from the Gnangara mound is shown in Figure C6.
Figure C6 Subsection of the groundwater system within the Perth region
Water table aquifer
Water table aquifers in the Perth region are also referred to as 'superficial aquifers'. Most groundwater extraction in the Perth region occurs from the Gnangara (see Figure C6) and Jandakot superficial aquifers. These aquifers are major sources of water for urban supply as well as individual supply, including for use in agriculture and public parks and gardens.
The Gnangara and Jandakot superficial aquifers are unconfined, multi-layered, complex aquifers that lie west of the Darling escarpment on the Swan Coastal Plain. The sediments of the aquifers range from mostly clay and sand in the east to sand in the centre, and sand and limestone in the west along the coast.
Underlying aquifers
The primary underlying aquifers in the Perth region are the Leederville and Yarragadee aquifers. The Leederville aquifer is a multi-layered, confined aquifer that underlies the majority of the Swan Coastal Plain within the region. The only areas of this aquifer that are unconfined are where it immediately underlies the superficial aquifer.
The Leederville aquifer ranges in thickness from 50 metres deep to more than 600 metres deep in the north of the region below the Gnangara superficial aquifer, and from 50–300 metres deep in the middle part of the region below the Jandakot superficial aquifer. It consists of around 50% sandstone and 50% a mix of siltstone and shale. The aquifer is a major source of water for urban water use as well as individual supply.
The Yarragadee aquifer is a multi-layered, confined aquifer that underlies the Leederville aquifer. The base of the aquifer is more than 2,000 metres deep and consists of around 50% sandstone and 50% a mix of siltstone and shale. The aquifer is a major source of water for urban use.
Surface water
Rivers
The seasonal flow characteristics of the main rivers within the Perth region reflect its annual rainfall pattern. Most of the rainfall occurs during a 5-month period between May and September. Although these rivers generally flow throughout the year, most of the streamflow within the region usually occurs during a 4-month period between June and September (Figure C7).
There are three primary river systems within the Perth region: Swan–Canning, Murray, and Harvey. The gauging stations used to represent the general seasonal flow patterns of these primary rivers shown in Figure C7 are located at Walyunga (Station 616011), Baden Powell Water Spout (Station 614006), and Clifton Park (Station 613052), and are shown in Figure C8. There are other gauging stations along these rivers although they are not shown on this map.
Figure C7 Mean monthly flows along the Swan, Murray, and Harvey rivers and mean monthly rainfall for the Perth region
Figure C8 Key flow gauging stations along the main rivers within the Perth region
Storages
Surface water storages are primarily located on various rivers in the Darling Range and are an important water source for irrigation scheme supply and, to a lesser extent, urban water supply. The storages and capacity, which are managed by the Water Corporation, are shown in Figure C9.
Most of the storages within the Perth region are used for urban water supply to the Integrated Water Supply Scheme. Further information on the urban supply storages, including current levels and volumes, is given on the Bureau of Meteorology's Water storage website.
Figure C9 Surface water storages in the Perth region; capacity of each storage is also shown
The six surface water storages located in the southern part of the region (Figure C9) are used for irrigation water supply to two Harvey Water irrigation districts: Harvey and Waroona. Harvey Water is a private irrigators' cooperative that delivers water from these storages to irrigators via a network of pipes and channels. Harvey Water has a bulk water licence to access a portion of the total capacity.
It should also be noted that Mundaring Reservoir, located in the northern part of the region (Figure C9), supplies water to the Goldfields and Agricultural region outside the Perth region boundary; therefore, this storage is not considered a surface water asset in the Perth region account.
Desalinated water
Desalinated water for the Perth region comes from two desalination plants (see Figure C3):
- Perth Seawater Desalination Plant, located near Kwinana
- Southern Seawater Desalination Plant, located near Binningup in the southern part of the region.
The combined desalinated water volume supplied by the two plants to the Integrated Water Supply Scheme can now meet approximately 50% of the region's annual urban water requirements.
For more details on desalinated water in the Perth region, see the Water Corporation website.
Wastewater recycling
Treated wastewater from several wastewater treatment plants throughout the Perth region is recycled. The primary uses of treated wastewater are:
- industrial use, particularly in the Kwinana Industrial Area
- local irrigation (i.e., parks and recreation grounds) near the treatment plants
- on-site use
- managed aquifer recharge (groundwater replenishment).
A groundwater replenishment scheme is currently under constuction and will treat wastewater to drinking water standards and recharge back into the groundwater store for future use. For more information on groundwater replenishment, see the Water Corporation website.
Water systems
Urban water system
The urban water system within the Perth region, also referred to as the Integrated Water Supply Scheme, is operated by the Water Corporation. The system primarily supplies water to the Perth metropolitan area and towns in the southwest area, including Mandurah and Harvey (see Figure C3 above). It also supplies water to areas outside the Perth region boundary, including the Goldfields and Agricultural region and Western Australia's southwest region.
Water into the system is sourced from surface water storages and bore fields within the region as well as the desalination plants near Kwinana and Binningup.
For more information on the urban water system in the Perth region, refer to the Water Corporation website.
Irrigation scheme
Harvey Water operates two irrigation districts, Waroona and Harvey, delivering water to irrigators in these districts via a network of pipes and channels from several storages in the region (see Figure C3 above).
For more information on the irrigation scheme, refer to the Harvey Water website.