Perth
Physical information

General description

Area: 21,156 km2
Population: 1.83 million (Australian Bureau of Statistics 2012)

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):

  • Swan Coastal
  • Murray River
  • Harvey River.

The Perth region boundary was extended beyond the Swan Coastal and Harvey River surface water catchments to capture 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 P1  Location map of the Perth region within Australia


Figure P2  Contextual map of the Perth region
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. 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, 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; and
  • the Perth Seawater Desalination Plant near Kwinana and the Southern Seawater Desalination Plant near Binningup that supply potable water to the Perth metropolitan area.

The Integrated Water Supply Scheme and the Harvey Water irrigation districts are shown in Figure P3.


Figure P3  Map of the Integrated Water Supply Scheme and the Harvey Water Irrigation Area within the Perth region
Figure P3  Map of the Integrated Water Supply Scheme and the Harvey Water Irrigation Area within the Perth region


Description of the 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; and
  • 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; and
  • water held in 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:

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
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 km2 and 15 km2 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 km2 and 55 km2 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 and natural environments
  • dryland agriculture
  • grazing.

Conservation and natural environments 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 Estuary 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).


Table P1  Major land uses within the Perth region

Land use

Area (km2)

Area (% of total)

Conservation and natural environments

10,080

48

Dryland agriculture

6,740

32

Forestry

587

3

Grazing

1,178

5

Irrigated agriculture

235

1

Mining

3

<1

Other intensive uses

454

2

Urban

1,607

8

Water

272

1

Total

21,156

100


Significant aquatic ecosystems

There are two significant aquatic ecosystems within the Perth region:

  • Forrestdale and Thomsons lakes
  • 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–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.

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.


Water resources

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.

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; and
  • Leederville and Yarragadee confined aquifers.

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

The above 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 (Perth–Peel Regional Water Plan 2009). 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

Rivers

There are three primary river systems within the Perth region:

  • Swan–Canning
  • Murray
  • Harvey.

These rivers generally flow throughout the year; however, most of the flow within these catchments usually occurs during a 3-month period between July and 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 P5).

Figure P6 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 P5.


Figure P5  Graph of mean monthly flows along the Swan, Murray and Harvey rivers and mean monthly rainfall for the Perth region
Figure P5  Graph of mean monthly flows along the Swan, Murray and Harvey rivers and mean monthly rainfall for the Perth region


Figure P6  Location map of key flow gauging stations along the main rivers within the Perth region
Figure P6  Location map of 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 both urban water and irrigation scheme supply. The storages, which are managed by the Water Corporation, are shown in Figure P7. The capacity of each storage and its main purpose are 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 P7  Location map of the surface water storages within the Perth region
Figure P7  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.


Table P2  Surface water storages within the Perth region

Storage

Capacity (ML)

Dead storage (ML)

Purpose

Canning

90,300

60

Urban supply

Churchman Brook

2,200

40

Urban supply

Drakes Brook1

2,300

20

Irrigation supply

Harvey2

55,700

780

Irrigation supply

Logue Brook3

24,200

380

Irrigation supply

Mundaring

43,000

20,560

Urban supply

North Dandalup

73,800

1,020

Urban supply

Samson Brook4

7,900

90

Urban and irrigation supply

Serpentine

136,700

1,010

Urban supply

Serpentine Pipehead

2,200

460

Urban supply

South Dandalup

125,100

12,940

Urban supply

Stirling5

54,300

1,800

Urban and irrigation supply

Victoria

9,400

50

Urban supply

Waroona6

14,800

170

Irrigation supply

Wungong

56,400

3,430

Urban supply

Total

698,300

42,810

 

1–3, 6: Also available for recreation purposes.
4–5: 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.

Groundwater

Water table aquifer

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, 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 in the east to sand in the centre and a sand and limestone base in the west along the coast.

Leederville aquifer

The Leederville aquifer is a multi-layered, 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 50–300 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.

Yarragadee aquifer

The Yarragadee aquifer is a deep, multi-layered, 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.

Groundwater management areas

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
Figure P8  Map of groundwater management areas within the Perth region


Other water resources and systems

Urban water system

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 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

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

Desalinated water for the Perth region comes from two desalination plants:

  • Perth Seawater Desalination Plant, located near Kwinana; and
  • Southern Seawater Desalination Plant, located near Binningup in the southern part of the region.

The Perth Seawater Desalination Plant was commissioned by the Water Corporation in 2006 and is operated by Degrémont in alliance with the Water Corporation. The first stage of the Southern Seawater Desalination Plant was commissioned in September 2011. The second stage of the plant was commissioned in January 2013 and will double the plant's capacity to provide desalinated water to the region.

The desalination plants supply potable water to the Perth metropolitan area for public water use.

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; and
  • managed aquifer recharge.

The managed aquifer recharge has been part of a groundwater replenishment trial conducted in the Perth region since November 2010. Treated wastewater from the Beenyup wastewater treatment plant is further treated to drinking water standards and recharged back into the groundwater store for future use. For more information on the groundwater replenishment trial, see the Water Corporation website.