The Swan Coastal Plain 

Of Western Australia

Around 2,900 million years ago when the shape of Australia was different and we were still attached to a greater land mass called Gondwana, a large fault formed along what we now call the Darling Scarp.  

Over time with the water levels going higher inland and lower out to sea a huge sedimentary basin was formed, now called the Perth Basin.  This filled up with 15 km of marine and river sediments such as crustaceans. 

The last ice age in this area saw the sea level drop 130 metres below its present level and the shoreline was west of Rottnest Island.  Since then the sea has risen to its present level flooding the coast and forming sand dunes along the coast. 

Now, over some of this basin area is a thin layer of soil, sand and a variety of different landforms forming what is now known as the Swan Coastal Plain. This area is a low lying area and is situated between the Indian ocean to the west and the Darling Scarp to the East, and as far North as Geraldton and to Dunsborough in the South.

This map is hand drawn and is not to scale.  The yellow represents the Swan coastal plain.

In this basin there are sand dunes, Tamala limestone, plains and rivers. This is limestone magnified 60x

The Bassendean sands near the Darling Scarp are the oldest sands in this area.  They are infertile and leeched out by rainwater.

There are rivers such as the Moore River in the north and  the Swan and Avon River in Perth.  In the South there is the Murray River and Collie River which drain water from the Darling Plateau and across the plain. 

Most of the Swan Coastal Plain consists of quartz and lime sand formed by wind blown dunes.  Tamala limestone is the main rock type on the Swan Coastal Plain and forms coastal cliffs and larger hills such as Kings Park.

Kings Park

 What's the weather got to do with it? 

Climate is the most important component in the ecosystems of the South-West.
It has direct control on all life forms and can change landforms.
The soil that develops on top is determined by the wind, rainfall and temperature.  The soils are essential for plants which in turn native animals are reliant on for food, shelter, cover from predators etc.

This area has a Mediterranean climate.

It is the wind and rivers that fill the basin with sediments, and it is the wind that blows the loose sand to form sand dunes along the coastline.

In the south are the coastal dunes in Spearwood which has been weathered to form a limestone cave landscape.  Caves developed by rainwater filtering down through the limestone dissolving the calcium carbonate, which in turn weakens it.

 Soil of the Swan Coastal Plain 

The coast sandy soils are different to the Darling Plateau soils.  They have been developed by sediments washed down from the Darling Plateau (alluvial) and by the material weathered by the coastal areas and transported by the waves (aeolian). 
The Guilford, Beermullah, Swan, Yanga, Dardanup and Serpentine Rivers are areas where soils washed down from the Darling Plateau or Scarp.  Other areas like Bassendean, Karrakatta, Cottesloe, Quindalup and Herdsman are soils formed from the deposits of the ocean.
Within the coastal plain are different soils, the soil nearest the Darling Plateau has more gravel, the soil that is much further away from the Scarp has more lime and is more poorly structured.  
The sand dunes are mostly infertile.
The Swan soils are the most fertile.
Clay and loamy soils of Pinjarra were formed by rivers and streams transporting the minerals down from the Darling Scarp.

 Plants and wildlife of the Swan Coastal Plain 

It  is said that the Swan coastal plain contains 2,000 species of plants.  There are banksia and eucalypt woodlands, but most of the area has already been cleared and is used as the city and suburbs (nearly 80%).

On the sandy plains scrub heath grows, where the Christmas trees prefer the dryer soils and the Dryandra, Grevillea's and Banksia's prefer the wetter soils. Also the Marri and Grass Trees have their woodlands in this area and Tuart trees grow on the southern end of the Swan Coastal Plain.  Some of the plants in this area are listed as endangered such as the Kingia (Kingia) and a Marri tree (Eucalyptus calophylla).

About 15% of the wildflowers found in this region are pollinated only by vertebrate animals ie; animals with a spine, such as the honey possums and western pygmy possums and bats.   The Tamar wallabies were wide spread in this region before settlement of people.  Black cockatoo's - both short beaked and long beaked - can still be seen in this region.  And the Swan coastal plain is home to the endangered western swamp turtle.  It is also home to kangaroo's, possums, lizards, snakes and frogs, insects and fungi.  Please go to our WILDLIFE HOTSPOTS pages to see the wildlife of this region.

Western Swamp Tortoise 

Tamar Wallaby 

Moaning frog coming up out of the ground at night

Tiger Snake

Other links you may like to look at to get a greater understanding of this region and how it formed; 

  This is for upper primary school students and gives a more detailed description of what we have discussed here. Check out the rest of this site too.
 Go here to find out some of the events taking place in this region.
A site useful to teachers and upper primary school with lots of interesting articles on Western Australian limestone and caves.
  This site is good for mid to upper primary students.  It describes the Swan Coastal Plain

Text;
 "The Geology and Landforms of the South West" by lain Copp
Leaf and Branch Trees and Tall Shrubs of Perth by Robert Powell

Assignments: 

1)  The best way to learn is to get outside and look.  If you live in this region, ask your parents to take a drive along the coast and see if you can see any limestone along the beaches. Or  visit  the Darling Range and see if you can tell where the Perth Basin ends and the Darling Range starts.

2)  Find out what nutrients are in the sandy soil of the Swan Coastal Plains.  What grows here that doesn't do well in richer more fertile forest soils?  Do all plants thrive if you give them a lot of fresh water regularly?  You could talk to nursery's.

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 All photos Copyright © Rachel Martinovich 2003 unless otherwise mentioned. Contact us Wildlife Education Services 
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