Perth
Physical information

Area: 21,156 km²
Population: 1.8 million (Australian Bureau of Statistics, 2011)

The Perth region is located on the west coast of Western Australia (Figure P1). The boundary of the region is mostly defined by three surface water catchments (Figure P2):

1. Swan Coastal
2. Murray River
3. Harvey River.

The Perth region boundary only differs from that defined by these three surface water catchments in two areas – the northern and southern coastal areas of the region. The boundary in these areas was extended to incorporate the groundwater management areas and two irrigation districts within the Harvey Water Irrigation Area.

Figure P1. Location map of the Perth region within Australia

Figure P2. Contextual map of the Perth region

The Darling Escarpment is a geographic feature that splits the 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 dark brown shading in Figure P2), 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 P2) have strong environmental, cultural and recreational significance. There are also important groundwater resources in the region, such as the aquifers in the Gnangara and Jandakot Mounds. Not only are these aquifers a source of public and self-supply, they support numerous wetland ecosystems.

Other significant water features within the region include:

• the Integrated Water Supply System, operated by the Water Corporation, which supplies potable water to the Perth metropolitan area
• 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, which supplies almost 20% of Perth's potable water.

The Integrated Water Supply System and the Harvey Water Irrigation Districts are shown in Figure P3.

Figure P3. Map of the Integrated Water Supply System and the Harvey Water Irrigation Districts within the Perth region

The Perth region is physically defined in the General description, 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
• water held in 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 rain water
• water held in the landscape, such as soil moisture, and water held in wetlands that are not connected to rivers.

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

The major population centres in the region are:

• Perth metropolitan area (including Rockingham and Kwinana) – population 1,696,000
• Mandurah – population 85,800 (Australian Bureau of Statistics, 2011)

A number of smaller towns are interspersed throughout the rest of the region, including Harvey, Pinjarra and Gingin.

Figure P4 shows that urban land use is primarily within the Perth metropolitan area (including Rockingham and Mandurah) along the Swan Coastal Plain.

Figure P4. Map of land use in the Perth region

The region also includes two irrigation districts – Harvey and Waroona. These districts are part of the  Harvey Water Irrigation Area, which is located on the Swan Coastal Plain near the town of Harvey. There is currently around 55 km ² and 15 km ² of land in the Harvey and Waroona districts, respectively, under permanent irrigation for dairy farming, beef grazing and horticulture. The total irrigable area is approximately 170 km ² and 55 km ² at Harvey and Waroona, respectively.

The irrigation districts are located in the southern area of the region around the town of Harvey and are identified as other intensive uses in Figure P4.

Other major land uses in the Perth region include:

• conservation areas and natural environment
• dryland agriculture
• grazing.

Conservation areas and natural environment are extensive throughout the Perth region and are particularly dominant 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 inlet below Mandurah (Figure P4).

Table P1 shows the percentage areas of each major land use within the Perth region (Australian Bureau of Agricultural and Resource Economics and Sciences, 2010).

There are two significant aquatic ecosystems within the Perth region:

1. Forrestdale and Thomsons Lakes
2. Peel–Yalgorup wetland system.

Both systems are designated Ramsar 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 Inlet, Harvey Estuary and Yalgorup Lake. Both of these systems are major stopovers for migratory wading birds and important drought refuge areas for waterbirds. The Peel-Yalgorup wetland also supports the largest professional and recreational estuarine fishery in Western Australia.

There are also a series of significant wetlands and lakes on the Gnangara and Jandakot water table aquifers that are part of the groundwater system within the Perth region. These include Lake Monger, Herdsman Lake and Bibra Lake. Herdsman Lake is listed in the Directory of Important Wetlands in Australia.

There are three major surface water resources in the Perth region:

1. Swan–Canning river system
2. Murray River catchment
3. 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.

The important groundwater resources in the Perth region include:

• Gnangara Mound (water table aquifer)
• other unconfined aquifers, including the Jandakot Mound, Rockingham and Stakehill water table aquifers
• Leederville and Yarragadee confined aquifers.

The Gnangara Mound is Perth's largest source of groundwater.

These groundwater resources are used for public water supply as well as for private use by industry, agriculture and urban populations. There are an estimated 170,000 residential bores in the Perth metropolitan area. The scope for increased extraction, particularly in the Gnangara Mound, is limited.

Given that these surface water and groundwater resources are already well developed in the region, alternative water resources, such as seawater desalination and water recycling, are increasingly being used for public water supply.

Surface water storages are primarily located on various rivers in the Darling Range and are an important water source for both urban water and irrigation scheme supply. The storages, which are managed by the Water Corporation, are shown in Figure P5. The capacity of each storage is shown in Table P2.

Most of the storages within the Perth region are used for urban water supply to the Perth metropolitan area and Mandurah. Further information on the urban supply storages, including current levels and volumes, is given on the Bureau of Meteorology's Water storage website.

Figure P5. Location map of the surface water storages within the Perth region

The other surface water storages in the region 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 to irrigators via a network of pipes and channels from several storages in the region. Harvey Water has a bulk water licence to access a portion of the total capacity.

(a) Also supplies water to small towns outside of the Perth metropolitan area.

Mundaring primarily supplies water to the Kalgoorlie goldfields and agricultural region. This is the only storage within the region that transfers water outside of the region boundary.

There are three primary river systems within the Perth region: Swan–Canning, Murray and Harvey. These rivers generally flow throughout the year; however, most of the flow within these catchments usually occurs during a 3-month period (July to September).

The seasonal flow characteristics of the main rivers reflect the rainfall pattern of the region, where most of the rainfall occurs during a 4-month period between May and August (Figure P6).

Figure P7 shows the locations of the most downstream flow gauging stations (and their station number) along these main rivers. Flow data collected at these stations were used to represent the seasonal flow patterns along these rivers in Figure P6.

Figure P6. Graph of mean monthly flows along the Swan, Murray and Harvey Rivers and mean monthly rainfall for the Perth region

Figure P7. Location map of key flow gauging stations along the main rivers within the Perth region

Most groundwater extraction in the Perth region occurs from the Jandakot and Gnangara water table aquifers. These aquifers are major sources of water for residential, agricultural and commercial use.

The Jandakot and Gnangara water table aquifers are unconfined, multilayered, complex aquifers that lie west of the Darling Escarpment on the Swan Coastal Plain. The sediments of the aquifers range from mostly clay in the east to sand in the centre and a sand and limestone base in the west along the coast.

The Leederville aquifer is a multilayered, confined aquifer that underlies the majority of the Swan Coastal Plain within the Perth region. The only areas that are unconfined are where this aquifer immediately underlies the water table aquifer.

The aquifer ranges in thickness from 50 metres deep to more than 600 metres deep in the north of the region below the Gnangara water table aquifer, and from 50 to 300 metres deep in the middle part of the region below the Jandakot water table aquifer. It consists of around 50% sandstone and 50% siltstone and shale. The aquifer is a major source of water for agricultural, commercial and residential use.

The Yarragadee aquifer is a deep, multilayered, confined aquifer that underlies the majority of the Swan Coastal Plain within the Perth region. The base of the aquifer is more than 2,000 metres deep, underlying the Leederville aquifer. It consists of around 50% sandstone and 50% siltstone and shale. The aquifer is a major source of water for the urban water system.

The Perth region includes 16 groundwater management areas that all lie on the coastal plain (between the coast and the Darling Escarpment). These are proclaimed in the Rights in Water and Irrigation Act 1914. The proclaimed management areas are managed by the Department of Water and shown in Figure P8.

Figure P8. Map of groundwater management areas within the Perth region

The urban water system within the Perth region is operated by the Water Corporation. The system primarily supplies water to the Perth metropolitan area and some towns in the southwest area (including Mandurah and Harvey) (see Figure P3 in General description). Water into the system is sourced from surface water storages and bore fields within the region as well as the Perth Seawater Desalination Plant.

For more information on the urban water system in the Perth region, refer to the Water Corporation website.

Two irrigation districts – Waroona and Harvey – are located in the southern area of the Perth region within the Harvey Water Irrigation Area (see Figure P3 in General description). Harvey Water delivers water to irrigators in these districts via a network of pipes and channels from several storages in the region (see Table P2 in Surface water). 

For more information on the irrigation scheme, refer to the Harvey Water website.

Desalinated water comes from the Perth Seawater Desalination Plant, located near Kwinana. The desalination plant was commissioned by the Water Corporation in 2006 and is operated by Degrémont in alliance with the Water Corporation. The desalination plant supplies potable water to the Perth region for public water use.

A second plant, the Southern Seawater Desalination Plant, commenced operation in September 2011. This plant is located near Binningup in the southern part of the Perth region and also supplies water to the Perth region for public water use.

For more detail on desalinated water in the Perth region, see the Water Corporation website.

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.